- Email: [email protected]
Statistical analysis and inter-comparison of erythemal solar radiation for Athalassa and Larnaca, Cyprus
Accepted Manuscript Statistical analysis and inter-comparison of erythemal solar radiation for Athalassa and Larnaca, Cyprus
S.A. Kalogirou, S. Pashiardis, A. Pashiardi PII:
S0960-1481(17)30350-6
DOI:
10.1016/j.renene.2017.04.043
Reference:
RENE 8738
To appear in:
Renewable Energy
Received Date:
27 January 2017
Revised Date:
19 March 2017
Accepted Date:
22 April 2017
Please cite this article as: S.A. Kalogirou, S. Pashiardis, A. Pashiardi, Statistical analysis and intercomparison of erythemal solar radiation for Athalassa and Larnaca, Cyprus, Renewable Energy (2017), doi: 10.1016/j.renene.2017.04.043
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Highlights
Statistical analysis of ultraviolet erythemal radiation.
Monthly and diurnal variation of ultraviolet erythemal radiation.
Statistical relationships between ultraviolet erythemal and other radiation components, total ozone column, relative air mass, clearness index and solar zenith angle.
Calculation of UV Index.
Estimation of the cumulative doses during an average year for the four skin phototypes.
Comparison of ultraviolet erythemal radiation between two sites.
It is the first time that an analysis of this type is performed in Cyprus.
ACCEPTED MANUSCRIPT 1
Statistical analysis and inter-comparison of erythemal solar radiation for
2
Athalassa and Larnaca, Cyprus.
3 4
S.A. KALOGIROU*, S. PASHIARDIS*, * and A. PASHIARDI**
5
* Department of Mechanical Engineering and Materials Science and Engineering
6
Cyprus University of Technology, P. O. Box 50329, 3603, Limassol, Cyprus
7
Tel: +357-2500-2621, Fax: +357-2500-2637, Email: [email protected]
8
** Cyprus Statistical Services Ministry of Finance, Michael Karaoli,
9
1444 Nicosia, Cyprus
10
Abstract
11 12
A statistical analysis and inter-comparison of the erythemal ultraviolet radiation
13
(UVER) at two sites in Cyprus representing two different climate regimes of the
14
island (Athalassa-inland plain vs Larnaca-coastal location) covering the period
15
January 2013-December 2015 is presented. Mean annual and mean monthly daily
16
totals of the UVER irradiation and their frequency distribution at both sites are
17
computed and discussed. UVER irradiance fluctuates between 0.054 W m-2 in
18
December to 0.227 W m-2 in July at solar noon at Athalassa. The values at Larnaca
19
are lower than in Athalassa and they fluctuate between 0.043 W m-2 in December
20
and 0.172 W m-2 in July at solar noon. The total accumulated UVER irradiation along
21
a mean year reaches 1142 kJ m-2 at Athalassa and 909 kJ m-2. Large fluctuations of
22
the daily UVER irradiation are observed in the spring months and November, which
23
are mainly due to unstable meteorological conditions during the transition from cold
24
to warm weather and vice versa. During summer the daily UVER radiation exceeds
25
the value of 6 kJ m-2 at Athalassa and 4.8 kJ m-2 at Larnaca, while during the winter
26
season the lowest is about 0.2 kJ m-2 at both sites. Statistical relationships between
27
UVER and other radiation components (UVA, global radiation, clearness index and
28
relative optical air mass) are established. The UV Index reaches high (6-7) or very
29
high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca these
30
values are reached in 38.8%. It is observed that the cumulative doses of UVER
31
during an average year range from 9087 Standard Erythemal Dose (SEDs) in
32
Larnaca to 11418 SEDs in Athalassa. The most common skin type in Cyprus,
33
phototype III (about 70% of the population), could receive an annual cumulative dose
1
ACCEPTED MANUSCRIPT 34
between 2596 Minimum Erythemal Doses (MEDs) in Larnaca to 3262 MEDs in
35
Athalassa.
36 37
Keywords: Ultraviolet erythemal irradiance, statistical analysis, clearness index,
38
frequency distribution, transparency, statistical relationships, UV Index, cumulative
39
doses, skin phototypes, Cyprus
40 41
1. Introduction
42 43
Ultraviolet (UV) radiation covers wavelengths of the electromagnetic spectrum
44
between 100 and 400 nm and it constitutes 8.73% of the total extraterrestrial solar
45
spectrum irradiance [1]. Within the UV radiation spectrum three zones are
46
distinguished in relation to the effects that the radiation produces on living
47
organisms: UVC (100-280 nm), UVB (280-315 nm) and UVA (315-400 nm) [2]. UVC
48
does not reach the Earth’s surface since it is absorbed completely by the ozone layer
49
in the stratosphere. In the upper atmosphere, the UVB irradiance amounts to 1.3% of
50
the solar constant [1]. UVB is mostly absorbed by the ozone layer. On the other
51
hand, UVA undergoes minimal absorption by the ozone layer and it is associated
52
with photo ageing of the skin, immuno-suppression of the skin immune system and
53
potential enhancement of the negative effects of UVB exposure. UV radiation on the
54
Earth’s surface varies widely and depends mainly on latitude, solar elevation, ozone
55
column and local atmospheric conditions. The emission of certain gases due to
56
human activities is known to alter the composition of the atmosphere. Some of the
57
most serious damage caused is the reduction of the ozone layer in the stratosphere,
58
causing a corresponding increase in UV [3]. Measurements in Italy and England
59
indicate that UVB incidence increased with decreasing ozone amount at fixed solar
60
zenith angles [4-5].
61 62
Solar UV radiation, and particularly UVB, has an important influence on terrestrial
63
and marine ecosystems, being in many cases an indicator of their development due
64
to its impact over the physical and chemical conditions that allow ecosystems to
65
evolve [6-8]. The effects of UV solar radiation on human beings are mostly observed
66
on skin, the eyes (cataracts), the photo-ageing and the immune system. The effects
67
over the skin depend on the duration of the exposure to sunlight. Chronic skin 2
ACCEPTED MANUSCRIPT 68
exposure
produces
morphological
changes:
the
epidermis
turns
thicker,
69
disorganized, parakeratoric, and acanthotic [9]. Severe skin overexposure produces
70
severe sunburn that causes heat, erythema and other symptoms approximately 16
71
hours after exposure to natural sunlight [10]. Epidemiological evidence also exists of
72
the direct influence of sunlight over skin cancer in human beings [11-12]. On the
73
other hand, the benefits of human exposure to UV radiation are few. The primary
74
benefit is the need of UV for synthesizing vitamin D in the skin. This synthesis is
75
achieved with very low doses of UV radiation, such that a daily exposure of 10-15
76
min for the face, arms and hands at an intensity of the radiation received in Northern
77
Europe is sufficient [13].
78 79
The CIE (Commission Internationale de l’ Éclairage) adopted in 1987 a standard
80
erythema action spectrum [14], marginally modified in 1998 [15], which is currently
81
recommended for determining the UV erythemal radiation (UVER). UVER is
82
calculated by weighting the spectral curve of the incident solar radiation at ground
83
level with the spectral action curve proposed by CIE. The CIE spectrum of human
84
erythemal describes the energy efficiency at different wavelengths to produce the
85
particular biological effect and shows an absolute maximum at 297 nm; the UVER
86
irradiance consists of 17% UVA and 83% UVB, at the Earth’s surface [16].
87
Therefore, small changes in UVB may produce strong biological effects.
88 89
The MED (Minimum Erythemal Dose) is the minimum dose of UVER that produces a
90
noticeable reddening of a specific skin type (phototype) not exposed previously to
91
solar radiation [17]. Most countries have adopted a skin classification, which
92
considers four phototypes. Table 1 shows the main characteristics of these four
93
phototypes as well as the dose needed to produce one MED. The CIE has also
94
defined a Standard Erythemal Dose (SED) that corresponds to 100 J m-2 and does
95
not depend on the skin type.
96 97
Table 1. Skin types defined by ISO 17166 CIE S 007/E [15] Skin
Tanning
Phototype ability I
None
Sunburn
Hair color Eye color
MED (J m-2)
susceptibility High
Blond/red
3
Blue
200
ACCEPTED MANUSCRIPT II
Poor
Moderate
Blond
Blue/green
250
III
Good
Low
Brown
Grey/brown
350
IV
Very good
Very Low
Black
Brown
450
98 99
The effects of UV on skin can be quantified by the UV Index (UVI). UVI is an
100
estimation of the effectiveness of solar radiation to produce harmful effects on
101
human skin, where one unit is equal to 25 mW m-2, i.e., the UVI is quantitavely
102
obtained by multiplying the UVER value (expressed in W m-2) by 40 [18].
103 104
In spite of the important role of UVER, few radiometric stations measure it
105
systematically in the Mediterranean region. A network of UVER stations was
106
established in Greece [19-20], Spain [21-23], Israel [24-25] and Egypt [26]. In
107
Cyprus, UV (A&B) radiation is measured at Athalassa (inland) and recently at
108
Larnaca (coastal place) [27]. UVER is measured at the above two sites since 2013.
109 110
Various authors have analyzed the relation between solar UVER and global radiation
111
[22-24, 28]. Moreno et al. [29] studied the effect of the relative optical air mass and
112
the clearness index on UVER values in Valencia in the period 2003-2012. Kudish
113
and Evseev [30] analyzed UVB radiation as a function of solar global radiation,
114
ozone layer thickness and aerosol optical density in Beer Sheva (Israel). De Miguel
115
et al. [31] have studied the evolution of erythemal and total shortwave solar radiation
116
as a function of atmospheric factors in Valladolid (Central Spain). Esteve et al. [32]
117
have studied the influence of cloudiness over the values of UVER in Valencia
118
(Spain).
119 120
In recent decades, radiative transfer and theoretical models have been developed
121
that can be used to predict UVER radiation or UVI [e.g., 33-34]. Neural networks are
122
also applied for the estimation of UV erythemal irradiance [35]. Some authors use
123
empirical models, which are simpler and more manageable and understandable [36-
124
37]. The European Cooperation in Science and Technology (COST)-Action 713 has
125
tested a number of models for UVB forecasting using multiple scattering models
126
rather than radiative transfer models [38]. The results of these simulations were also
127
published in the final report of that COST Action [39]. More recently, the CEAM 4
ACCEPTED MANUSCRIPT 128
Foundation in Valencia (Spain) has developed an operational UVI forecasting
129
system based on the Santa Barbara DISORT Atmospheric Radiative Transfer
130
(SBDART) model [40].
131 132
An assessment of the solar radiation climate of the Cyprus environment was
133
presented by Jacovides et al. in 1993 [41]. Petrakis et al. [42] presented the ‘Typical
134
Meteorological Year’ for Nicosia. More recently, Kalogirou et al. [43] presented a
135
statistical analysis and inter-comparison of the solar global radiation at the same
136
sites as in this study, using measurements of 21 months at both sites. The common
137
feature of all the above studies is that they rely mostly on measurements of solar
138
radiation carried out at the actinometric stations of Athalassa and Larnaca.
139 140
The interest of this paper is that similar data series (UVER) have not been recorded
141
before and no similar work has previously been done in Cyprus. This work
142
constitutes the first UVER analysis in the island of Cyprus, which is also essential
143
because of the fact that the atmospheric conditions in the area favor dry summers
144
and cold winters, high air temperatures and low vapor pressure values at midday in
145
summer time, which affect the transmission of UVER through the atmosphere. In this
146
work we analyze hourly UVER and global irradiance data on a horizontal plane and
147
perform an inter-comparison study between the two locations in Cyprus as well as
148
between other sites in the Mediterranean region. Additionally, UVER measurements
149
have been used to estimate UVI and the cumulative doses for the four skin
150
phototypes are also considered here.
151 152
2. Materials and methods
153 154
The radiation data on which this study is based are being monitored at two
155
meteorological stations: one located at Athalassa, an inland plain location and the
156
other one at Larnaca Airport near the coast. The site parameters of the two stations
157
are listed in Table 2.
158 159 160 161 5
ACCEPTED MANUSCRIPT 162
Table 2. Site parameters for the two meteorological stations Site
Location
Latitude
Longitude
Altitude (m, m.s.l)
Athalassa
inland
35.1410 N
33.3960 E
165
Larnaca
coastal
34.8730 N
33.6310 E
1
163 164
The two sites are characterized by relatively high global horizontal and beam
165
horizontal radiation intensities. The average annual sunshine duration is 3332 hours
166
for Athalassa and slightly higher at Larnaca (3368 h). The annual average daily
167
global radiation exceeds 18.5 MJ m-2 at the two sites, whereas the average beam
168
horizontal radiation is 13.1 MJ m-2 for Athalassa and 14.2 MJ m-2 for Larnaca,
169
respectively. Consequently, the fraction of the beam component of the global
170
radiation is relatively high at both sites, viz., the annual average daily fraction is
171
>0.600 at the two sites. Comparing the two sites it seems that Larnaca has slightly
172
higher rates of global radiation than Athalassa, since the average yearly cumulative
173
global irradiation is 6835 MJ m-2 for Athalassa and 7183 MJ m-2 for Larnaca. The
174
monthly average frequency of days according to the classification of the magnitude
175
of the daily clearness index KT (daily global to daily extraterrestrial radiation), shows
176
that both clear and partially cloudy days exceed 90% annually (KT >0.35) [43].
177 178
The period for presenting the data at both stations is January 2013 to December
179
2015 (i.e., 3 years), when both stations operated simultaneously, so as to allow for
180
comparison of the different variables of solar and terrestrial radiation. Measurements
181
of total solar irradiance on a horizontal surface were taken with Kipp & Zonen CM11
182
pyranometers whose spectral range is from 285 to 2800 nm. Both stations are
183
equipped with Kipp & Zonen UVS-E-T broadband radiometers with a spectral range
184
of 280 to 315 nm (UVB) and 315 to 400 nm (UVA). The radiometers have directional
185
response up to 70° solar zenith angle (θz) less than 2.5%. All the sensors are factory
186
calibrated, in accordance with the World Radiometric Reference (WRR). Global
187
radiation instruments were calibrated outdoor against standard references at
188
irregular time intervals during the study period. The errors involved in the radiation
189
measurements were found to be no less than ±2% for the normal incidence beam
190
irradiance and ±3% for the global irradiance.
191 6
ACCEPTED MANUSCRIPT 192
A Campbell Scientific Instruments data-logger, located at each site (Model CR10),
193
monitors and stores the data at 10-min intervals (the radiometers are scanned every
194
10 seconds and average, maximum, minimum and instantaneous values at 10-min
195
intervals are calculated and stored). The stored data are downloaded to a desktop
196
computer periodically. The data refer to the Local Standard Time (LST=GMT+2).
197
About 5% of the data values are missing because of some problems with the
198
instruments and some defects and maintenance in the data acquisition systems. The
199
validity of the individual measurements was checked in accordance with the WMO
200
recommendations [44] and other tests proposed by various authors [45-47]. Details
201
about the quality control procedures used in this study are given by Pashiardis and
202
Kalogirou [48]. All data that do not meet the conditions specified by the suggested
203
tests were not used in the study.
204 205
Regarding the UVER irradiance the following upper limit was applied as suggested
206
by de Miguel et al. [49] in a similar way as the UVB quality control process:
207 208
UVER 1.2*UVER0
(1)
209 210
where, UVER is the measured value and UVER0 is the horizontal extraterrestrial
211
solar UVER irradiance ( GscUVER 9.89 W m-2 ), which was obtained from Tena et al.
212
[22]. The measurements of both stations were less than the horizontal extraterrestrial
213
solar UVER0 irradiance during the whole period of measurements. Occasionally,
214
night values were detected, which were excluded from the database. No other errors
215
were found. Long periods of missing data were detected during the period 1st
216
January – 18th February 2013 at Larnaca due to instability of the recording system.
217
However, only 10 missing days were recorded at Athalassa.
218 219
Regarding the quality control of the daily UVER radiation data, daily values were
220
rejected in case of incomplete data during the day. The time series plots of the daily
221
values of UVER irradiation for both stations are shown in Figure 1. The figure
222
indicates that the ascent during the first months of each year is very irregular with
223
fluctuations, while the descent is smoother. During summer the daily UVER radiation
224
exceeds the value of 6 kJ m-2 at Athalassa and 4.8 kJ m-2 at Larnaca, while during 7
ACCEPTED MANUSCRIPT 225
the winter season the lowest is about 0.2 kJ m-2 at both stations. Slightly lower
226
values were recorded in the year 2015 at both stations, which may be attributed to
227
higher amounts of aerosols in the atmosphere. The year 2015 is characterized as an
228
extremely dry year with more frequent dust episodes over the island (dust from the
229
deserts of Middle East and Sahara), increasing, therefore, the aerosols in the
230
atmosphere, which affect the absorption of the UVER radiation. It should be noted
231
that UV is mostly influenced by Rayleigh scattering than Mie one.
232
233 234
Fig. 1. Time series plot of daily UVER solar irradiation during the period 2013-2015
235
at Athalassa and Larnaca. Days start counting from January 1, 2013.
236 237
3. Results and discussion
238 239
3.1 Daily values
240 241
Global solar radiation and total UVER radiation have been analyzed and compared
242
in this study. Figure 2a shows the temporal evolution of daily UVER and global solar
243
irradiation at Athalassa. A similar graph with slightly lower values was obtained at
244
Larnaca (Fig.2b). Data reveal a common evolution shape with maxima in summer 8
ACCEPTED MANUSCRIPT 245
and minima in winter, mainly due to the daily minimum solar zenith angle and day-
246
length (astronomical factors) variation during the year. Large fluctuations in the
247
spring months and November are mainly due to unstable meteorological conditions
248
during the transition from cold to warm weather and vice versa. The maximum of
249
daily global solar horizontal irradiation is reached in June or July and it is around 31
250
MJ m-2 at Athalassa and around 32 MJ m-2 at Larnaca.
251 252
Fig. 2. Co-variability of daily measured UVER values (UVERd) and daily global
253
horizontal solar irradiation (Gd) during the period 2013-2015 at a) Athalassa and b) at
254
Larnaca. Days start counting from January 1, 2013.
255 256
The mean value of UVER for each day and the mean daily value of UVER over a
257
month have been calculated; Figure 3a shows the results for both stations. The
258
mean value of UVER was obtained by simply calculating the mean value for each
259
day of the year. Fourth order polynomial regression equations are fitted to describe
260
the relationship between the mean value of UVER for each day and Julian days (jd)
261
(1..365) for Athalassa and Larnaca (Eqs. 2-3):
262 263 264 265
UVERd 1.44946 0.02694 jd 0.00083 jd 2 4.0967*106 jd 3 5.561*109 jd 4 (2) UVERd 1.10756 0.01745 jd 0.00062 jd 2 3.1396*106 jd 3 4.312*109 jd 4 (3) 9
ACCEPTED MANUSCRIPT 266 267
The daily values present a greater fluctuation in spring. It can be seen that the
268
variation in the monthly mean values (continuous smooth line) is quite regular, with
269
the maximum values taking place in June/July and the minimum in December. Daily
270
UVER increases in spring to summer at a lower rate than that of the decrease in
271
autumn. The different slopes can be explained by the total ozone effects. During the
272
summer months, when solar zenith angle (SZA) leads to high UVER irradiance, the
273
total ozone column (TOC) is declining; this effect causes UVER to get maximum
274
levels from June to July (Fig. 3b). The time series of the mean daily values of TOC
275
during the study period were obtained from the satellite instrument MODIS
276
(http://giovanni.sci.gsfc.nasa.gov/giovanni/#service=ArAvTs). The peak TOC value is
277
recorded in April and its minimum in November, while the maximum of the midday
278
hour of cos(SZA) is observed in June and its minimum in December.
279
280 281
Fig. 3a. Annual evolution of daily and monthly UVER irradiation values (kJ m-2) at
282
Athalassa and Larnaca, during the period 2013-2015.
283 284
10
ACCEPTED MANUSCRIPT
285 286
Fig. 3b. Annual cycle of monthly mean TOC in Dobson Units (DU) and the mean of
287
the cosine of the midday SZA.
288 289
Table 3 shows the statistical characteristics of daily UVER data for all-sky conditions.
290
The Table shows the following statistical parameters: number of observations (N),
291
arithmetic mean (Mean), standard deviation (StDev), coefficient of variation in
292
percent (CoefVar), minimum (Min), the first and third quartiles (Q1 and Q3), median,
293
maximum (Max), inter quartile range (IQR), percentiles (P5 and P95), skewness and
294
kurtosis coefficients (As and K) and the type of distribution obtained from the last two
295
coefficients (Table 4) [25]. The median values are mainly slightly higher than the
296
average ones; the maximum of the standard deviation occurs in May, while the
297
coefficient of variation shows the lowest values in the summer months, which means
298
that higher stability is observed in these months. The differences between the Min
299
and P5 values are quite high, and therefore, the minimum values correspond to
300
unusually extreme values. On the other hand, the differences between the Max and
301
P95 values are small. The observed daily maximum occurs in June at both stations
302
(6.164 kJ m-2 at Athalassa and 4.863 kJ m-2 at Larnaca). The mean daily UVER for
303
the whole year is 3.126 kJ m-2 for Athalassa and 2.552 kJ m-2 for Larnaca. The
304
variability of the daily UVER irradiation is also demonstrated with the graph of 11
ACCEPTED MANUSCRIPT 305
boxplots for each month of the year. The boxplot presents the Median and the IQR
306
as well as the outliers of the daily values of UVER irradiation for both stations (Fig.
307
4). The smooth line represents the mean daily values of each month. As indicated in
308
the graphs, the spring season shows the greatest variability. The presence of the
309
minimum values as outliers in most of the months of the year confirms the statement
310
that the minimum values correspond to unusually extreme ones.
311 312
Type I frequency distributions curves, i.e., normal distribution, characterize the daily
313
erythemal radiation intensities for the months of February, April, August and
314
November at Athalassa. The most frequent distribution at Athalassa is Type IV,
315
which is almost normal with negative tail (January, March, June, September, October
316
and December). May and July are of Type V, which is a distribution with narrow peak
317
and negative tail. Almost similar distributions are observed at Larnaca. Type I is
318
recorded in February, August and November and the most frequent distribution is
319
again Type IV (January, March, April, July and October). May, September and
320
December are of Type V, while June is Type VI (bimodal, symmetrical with flat
321
peak).
322 323
The monthly mean daily values of the two stations are compared to the respective
324
values of other Mediterranean sites (Fig. 5) [23-25, 50]. It is observed that the curves
325
of the monthly mean daily values follow a sinusoidal evolution, with a minimum in
326
December and a maximum in June or July. As indicated in the graph the highest
327
values are recorded in Beer Sheva (Israel) with the second ones at Athalassa, as
328
expected, since these stations are at lower latitude and have higher sunshine
329
duration comparing to other stations. The coastal sites (Larnaca, Kos, Athens,
330
Thesaloniki, Neve Zohar and Valencia) have almost similar levels of erythemal
331
irradiation, in contrast to the inland locations (Athalassa and Beer Sheva), which
332
have higher levels of UVER. The differences between the inland and coastal
333
locations are more pronounced during the summer period.
334 335
12
ACCEPTED MANUSCRIPT
336 337
338 339
Fig. 4. Boxplots of the daily UVER irradiation (kJ m-2) for each month of the year at
340
a) Athalassa and b) Larnaca. The boxplot shows the IQR and the Median values;
341
the asterisks denote the outliers. The smooth line represents the mean daily values
342
of each month. 13
ACCEPTED MANUSCRIPT 343 344
Table 3. Statistical estimators of the daily UVER (kJ m-2) for the period 2013-2015 at
345
a) Athalassa and b) Larnaca
346
a) Athalassa
Month
N
Mean
StDev
CoefVar(%)
Min
Q1
1
93
1.186
0.360
30.33
0.224
0.891
2
84
1.806
0.494
27.38
0.788
3
93
2.641
0.692
26.20
4
90
3.542
0.836
23.60
5
90
4.252
0.976
6
89
5.254
7
92
8
93
9
Median
Q3
Max
IQR
P5
P95
As
K
Distr. Type
1.242
1.486
1.743
0.596
0.499
1.692
-0.46
-0.59
IV
1.532
1.765
2.152
2.894
0.620
0.890
2.613
-0.02
-0.36
I
0.353
2.144
2.677
3.169
3.969
1.026
1.375
3.748
-0.47
0.39
IV
1.613
2.987
3.628
4.118
5.103
1.131
1.885
4.808
-0.38
-0.40
I
22.95
0.848
3.777
4.512
4.886
5.712
1.109
2.203
5.359
-1.36
2.10
V
0.664
12.63
3.478
4.824
5.444
5.796
6.164
0.972
3.774
6.024
-0.86
0.03
IV
5.495
0.361
6.58
4.083
5.314
5.562
5.756
6.144
0.442
4.748
6.003
-1.04
1.88
V
4.805
0.419
8.71
3.731
4.515
4.871
5.043
5.669
0.528
3.966
5.552
-0.29
-0.03
I
90
3.523
0.575
16.32
1.666
3.186
3.597
3.980
4.646
0.793
2.403
4.312
-0.70
0.44
IV
10
93
2.441
0.537
21.99
1.003
2.058
2.559
2.842
3.322
0.783
1.431
3.192
-0.57
-0.21
IV
11
89
1.472
0.298
20.26
0.479
1.300
1.480
1.664
2.071
0.363
0.934
1.985
-0.34
0.67
I
12
91
1.036
0.282
27.25
0.221
0.935
1.112
1.240
1.438
0.304
0.427
1.350
-1.16
0.63
IV
Year
1087
3.126
1.631
52.18
0.221
1.574
2.968
4.632
6.164
3.057
0.890
5.706
0.16
-1.30
VI
Q3
Max
IQR
P5
P95
As
K
Distr. Type
347 348
b) Larnaca
Month
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
1
62
0.956
0.244
25.56
0.316
0.836
0.993
1.137
1.371
0.301
0.417
1.289
-0.80
0.28
2
66
1.517
0.385
25.39
0.601
1.267
1.493
1.864
2.315
0.597
0.836
2.152
-0.05
-0.41
I
3
93
2.136
0.532
24.90
0.418
1.820
2.165
2.477
3.313
0.657
1.104
3.060
-0.47
0.66
IV
4
90
2.902
0.625
21.53
1.242
2.620
2.972
3.377
4.070
0.757
1.516
3.777
-0.77
0.44
IV
5
93
3.507
0.639
18.23
0.773
3.296
3.650
3.898
4.489
0.603
2.403
4.216
-1.97
5.79
V
6
90
4.187
0.432
10.33
3.335
3.898
4.201
4.581
4.825
0.683
3.371
4.773
-0.34
-0.94
VI
7
93
4.240
0.309
7.29
3.149
4.006
4.253
4.444
4.863
0.438
3.732
4.753
-0.47
0.64
IV
8
93
3.705
0.297
8.03
3.069
3.492
3.703
3.909
4.336
0.417
3.248
4.253
0.14
-0.58
I
9
90
2.855
0.542
18.97
0.364
2.605
2.820
3.266
3.743
0.661
1.830
3.594
-1.33
4.27
V
10
93
1.892
0.417
22.03
0.868
1.619
1.921
2.216
2.650
0.596
1.122
2.439
-0.44
-0.36
IV
11
90
1.093
0.221
20.20
0.462
0.932
1.083
1.266
1.499
0.335
0.720
1.449
-0.27
-0.12
I
12
93
0.826
0.183
22.11
0.224
0.754
0.872
0.940
1.089
0.186
0.391
1.045
-1.29
1.45
V
Year
1046
2.552
1.269
49.72
0.224
1.289
2.574
3.691
4.863
2.402
0.793
4.476
0.02
-1.35
VI
349 350
Table 4. Definition of the frequency distribution type as a function of the range of the
351
skewness and kurtosis values obtained from [25]. Distribution Distribution Curve
Skewness (As)
Kurtosis (K)
Type No. I
Normal
-0.4 < As < 0.4
-0.8 < K < 0.8
II
Almost normal with positive tail
As ≥ 0.4
-0.8 < K < 0.8
14
IV
ACCEPTED MANUSCRIPT III
Narrow peak with positive tail
As ≥ 0.4
K ≤ -0.8 K ≥ 0.8
IV
Almost normal with negative tail
As ≤ -0.4
-0.8 < K < 0.8
V
Narrow peak with negative tail
As ≤ -0.4
K ≥ 0.8
VI
Bimodal, symmetrical with flat -0.4 < As < 0.4
K ≤ -0.8
peak 352 353
354 355
Fig. 5. Monthly mean daily UVER (kJ m-2) at various sites in the Mediterranean area.
356 357
It is also interesting to know the statistics of the daily UVER radiation obtained from
358
different daily global radiation thresholds, since most of the actinometric stations
359
measure global radiation. Table 5 presents the results of the above classifications. At
360
Athalassa, the most frequent cases occurred in the bins of 10-12 MJ m-2 of daily
361
global irradiation followed by the bins of 26-28 and 28-30 MJ m-2. At Larnaca, the
362
most frequent cases occurred in the bins of the range 24-30 MJ m-2 of daily global
363
irradiation. The mean and the median values of UVER irradiation are almost similar
364
at both stations. It is estimated that the UVER irradiation is about 0.016% of the
15
ACCEPTED MANUSCRIPT 365
global one at Athalassa (inland location) and about 0.012% at Larnaca (coastal
366
location).
367 368
Table 5. Statistics of daily UVER irradiation (kJ m-2) based on various thresholds of
369
daily global radiation (MJ m-2) for the period of measurements for a) Athalassa and
370
b) Larnaca.
371
a) Athalassa Ath_Daily Global Radiation Bin End (MJ m-2) Lower Upper 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18 18 20 20 22 22 24 24 26 26 28 28 30 30 32
UVER (kJ m-2) Occurrences 4 14 25 41 59 119 90 72 81 64 76 79 91 110 106 18
Mean Median 0.258 0.503 0.770 0.964 1.187 1.445 1.730 2.161 2.623 3.031 3.520 4.036 4.511 5.018 5.523 5.866
0.234 0.479 0.788 0.951 1.159 1.383 1.684 2.081 2.595 3.030 3.586 4.063 4.632 5.103 5.631 5.904
Min
Max
Std. Dev.
0.221 0.395 0.568 0.677 0.935 1.000 1.320 1.605 2.119 2.021 2.637 3.010 3.226 3.629 4.011 5.330
0.353 0.848 1.156 1.236 1.693 2.251 2.847 2.944 3.625 3.906 4.487 4.996 5.206 5.672 6.023 6.164
0.064 0.119 0.137 0.124 0.161 0.256 0.287 0.345 0.300 0.320 0.416 0.470 0.471 0.441 0.399 0.239
Min
Max
Std. Dev.
0.224 0.362 0.470 0.620 0.364 0.798 0.871 1.191 1.417 1.589 2.069
0.316 0.566 0.892 1.200 1.242 1.660 2.013 2.134 2.650 2.980 3.274
0.051 0.062 0.155 0.109 0.128 0.169 0.217 0.226 0.268 0.278 0.251
372 373
b) Larnaca Lca_Daily Global Radiation Bin End (MJ m-2) Lower Upper 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18 18 20 20 22
UVER (kJ m-2) Occurrences 3 12 11 37 52 88 94 60 58 64 77
Mean Median 0.282 0.440 0.631 0.786 0.886 1.044 1.245 1.581 1.910 2.226 2.527
16
0.307 0.429 0.601 0.772 0.875 1.006 1.211 1.541 1.921 2.175 2.532
ACCEPTED MANUSCRIPT 22 24 26 28 30 32
24 26 28 30 32 34
62 91 114 137 85 1
2.934 3.331 3.661 4.027 4.362 4.436
2.912 3.361 3.685 3.987 4.361 4.436
2.306 2.455 2.654 3.087 3.466 4.436
3.650 3.895 4.418 4.808 4.863 4.436
0.329 0.285 0.357 0.364 0.313 0.000
374 375
3.2. Analysis of accumulated UVER irradiation
376 377
In studies on the biological effects of UVER, we require the accumulated UVER solar
378
irradiation (kJ m-2) through a period of time. The accumulated values of UVER
379
irradiation are also important for vitamin-D synthesis production. Figure 6 shows the
380
accumulated hourly UVER irradiation values for an average day of each month; the
381
last value is the daily total.
382 383
It can be seen that the highest value for UVER irradiation was produced in July, with
384
a daily average of 5.5 kJ m-2 for Athalassa, and 4.24 kJ m-2 for Larnaca. On the other
385
hand, in December the average irradiation received was minimal (1.04 kJ m-2 at
386
Athalassa and 0.85 kJ m-2 at Larnaca). The accumulated irradiation received in an
387
average year is 1142 kJ m-2 for Athalassa and 909 kJ m-2 for Larnaca (Fig. 7). The
388
seasonal distribution of UVER radiant exposure is shown in Table 6. The highest
389
values are recorded in summer with the second higher one in spring.
390
17
ACCEPTED MANUSCRIPT
391 392 393
394 395
Fig.6. Accumulated UVER irradiation (kJ m-2) for an average day for the period 2013-
396
2015 at a) Athalassa and b) Larnaca.
397 18
ACCEPTED MANUSCRIPT 398
Table 6. Seasonal totals of UVER radiant exposure (kJ m-2) for Athalassa and
399
Larnaca. Season
Athalassa
Larnaca
Spring
320.0
262.0
Summer
477.0
371.9
Autumn
225.5
177.1
Winter
119.4
97.7
Annual
1141.9
908.7
400 401
402 403
Fig.7. UVER radiant exposure accumulated during an average year (kJ m-2) at
404
Athalassa and Larnaca.
405 406
3.3 Frequency of daily UVER irradiation
407 408
The type of the frequency distribution of the daily UVER radiation was presented in
409
section 3.1. The cumulative density functions (CDF) of the daily UVER irradiation for
410
both stations are shown in Fig. 8. The figure indicates that in about 65% of the year,
411
the daily sums of UVER irradiation at Athalassa are below 4 kJ m-2, while at Larnaca 19
ACCEPTED MANUSCRIPT 412
for the same value the probability is about 85%. It can also be estimated that about
413
30% of the days of the year have values of daily sum within the range of 3 to 5 kJ m-
414
2
at Athalassa and between 2 and 4 kJ m-2 at Larnaca.
415
416 417
Fig. 8. Annual cumulative frequency distribution of daily UVER irradiation at a)
418
Athalassa and b) Larnaca.
419 420
3.4. Statistical analysis of hourly UVER irradiance
421 422
A statistical study of the most representative UVER indices for each month of the
423
year has been carried out and the UVER accumulated values have been evaluated
424
because they are very useful in studies of effects on human beings.
425 426
Tables 7a and 7b show the hourly statistical estimators of mean hourly UVER
427
irradiance, for July for both stations, while Table 7c presents only the statistics of
428
December at local solar noon for both stations. These months usually present the
429
highest and lowest values of UVER, following the annual evolution of TOC, which
430
shows a maximum in the spring months (April-May) and a minimum in November
431
[51]. The peak at solar noon represents the maximum daily value and, therefore,
432
only the time of the solar noon is selected for the statistics of December (Table 7c)
433
(see section 3.9 on UVI). The statistical parameters presented in the Table are the
434
same as those used for daily statistics (Table 3). In order to understand the 20
ACCEPTED MANUSCRIPT 435
behaviour of the maximum values of UVER, which will be used later to estimate UVI,
436
the most representative statistics of UVER, which were obtained mainly at local
437
noon, will be discussed. It can be observed that the median values are almost similar
438
to the average ones, which suggest that the average hourly UVER distribution is
439
approaching the normal curve.
440 441
In July, the absolute maxima of the UVER measured at local noon vary from 195.3
442
mW m-2 in Larnaca to 248.8 mW m-2 in Athalassa, whereas the absolute minima
443
range between 140.8 mW m-2 and 188.0 mW m-2, respectively. The difference (in
444
percentage) between the absolute maxima and the P95 percentiles is around 2% at
445
both locations. These values are systematically lower than the difference observed
446
between the absolute minima and the P5 percentiles, which varies between 7%
447
(Athalassa) and 8% (Larnaca). The absolute extreme values have also been
448
compared with their corresponding quartile values to verify if they are representative
449
of the UVER records for the measuring sites. The difference between the Q1
450
quartiles and the absolute minima is around 14% at both sites, whereas the
451
difference between the Q3 quartiles and the absolute maxima varies between 6%
452
(Athalassa) and 7% (Larnaca). Therefore, although the maximum values can be
453
considered representative of the UVER at local noon in July, the minimum values
454
represent unusual extreme values for this month. The maximum values of UVER
455
recorded in Cyprus are comparable with those in Israel [25], in Valladolid (Spain) [31]
456
and in Greece [50].
457 458
In December, the values of the absolute maximum measured at local noon range
459
from 57.0 mW m-2 in Larnaca to 77.3 mW m-2 in Athalassa, whereas the values of
460
the absolute minimum are almost similar at both stations (around 8 mW m-2) (Table
461
7c). As it happened for July, the difference between the absolute maxima and the P95
462
percentiles is systematically lower than that observed between the absolute minima
463
and the P5 percentiles. These differences vary between 4.2% (Larnaca) and 7.2%
464
(Athalassa) for the absolute maxima and P95 percentiles, and between 46%
465
(Athalassa) and 55% (Larnaca) for the absolute minima and the P5 percentiles. The
466
comparison of the extreme values with their corresponding quartiles shows a
467
variation between 81% (Larnaca) and 84% (Athalassa) for the difference between
468
the Q1 quartiles and the absolute minima, whereas the difference between the Q3 21
ACCEPTED MANUSCRIPT 469
quartiles and the absolute maxima ranges from 13.7% (Larnaca) to 15.3%
470
(Athalassa). Thus, as it happened for July, the maximum values can be considered
471
representative of the UVER at local noon in December, while the minimum values
472
may be considered as unusual extreme values.
473 474
The UVER variability has been studied by means of the coefficient of variation
475
(CoefVar). As it can be seen in Table 7, the CVs in July are low during midday (5-
476
10%) at both stations, indicating a high stability along these hours in summer.
477
Furthermore, CoefVars fluctuate between 5 and 16% at Athalassa, while at Larnaca
478
they are slightly higher (5-27%). The standard deviation is higher along midday
479
hours and symmetrically distributed around solar noon during the summer months.
480
This could be explained by a minor presence of clouds in the summer months that
481
lead to a high stability of the atmosphere.
482 483
Table 7. Statistical estimators of the mean hourly UVER irradiance (mW m-2), in July,
484
under all-sky conditions for the period 2013-2015, at a) Athalassa and b) Larnaca.
485
a) Athalassa
Hour
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
Q3
Max
IQR
As
K
P5
P95
Dly UVER (%)
6
93
9.46
1.31
13.80
5.33
8.67
9.33
10.33
12.25
1.67
-0.23
0.31
7.3
11.80
1
7
93
25.08
3.43
13.66
13.83
23.08
25.17
27.17
32.50
4.08
-0.26
0.42
19.7
31.30
2
8
92
59.49
5.97
10.03
42.50
55.67
59.92
63.67
71.50
8.00
-0.27
-0.08
49.1
69.80
4
9
92
107.87
7.86
7.29
84.67
102.87
108.25
113.46
124.17
10.58
-0.26
0.12
94.5
121.20
7
10
92
160.14
10.07
6.29
118.67
154.42
160.58
166.46
180.33
12.04
-0.72
2.12
143.5
176.10
10
11
92
203.55
10.68
5.25
166.00
196.87
203.92
210.92
226.17
14.04
-0.47
0.96
184.9
220.80
13
12
92
226.60
11.22
4.95
188.00
219.13
227.08
234.33
248.83
15.21
-0.63
0.91
202.9
243.70
15
13
92
222.37
15.40
6.93
155.17
217.17
226.08
232.00
247.50
14.83
-1.94
4.82
182.1
238.20
15
14
92
191.26
19.89
10.40
113.50
188.04
198.00
203.21
215.83
15.17
-2.09
4.43
146.5
209.40
13
15
92
142.50
23.72
16.65
55.00
140.88
150.83
156.42
164.00
15.54
-2.31
4.99
78.1
161.10
9
16
92
95.19
12.96
13.62
19.83
91.67
99.08
101.96
108.50
10.29
-3.10
13.18
67.2
106.20
6
17
92
52.32
4.75
9.08
29.17
50.54
53.33
55.00
58.83
4.46
-2.02
6.28
43
58.10
3
18
92
21.39
1.89
8.84
13.17
20.33
21.50
22.79
25.00
2.46
-1.04
2.81
18.3
24.00
1
19
92
9.23
0.98
10.64
6.00
8.63
9.00
10.00
11.00
1.38
-0.82
1.32
7.7
10.50
1
486 487
b) Larnaca
Hour
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
Q3
Max
IQR
As
K
P5
P95
Dly UVER (%)
6
93
6.21
1.40
22.56
3.50
5.17
6.00
7.25
9.40
2.08
0.62
-0.45
4.5
9.2
1
7
93
16.88
4.64
27.46
10.50
13.17
15.17
21.58
27.67
8.42
0.72
-0.82
11.5
25.7
1
8
93
41.94
8.72
20.79
26.50
35.33
39.83
50.92
60.83
15.58
0.50
-0.94
31.1
57.4
4
9
93
77.81
12.08
15.52
49.67
68.92
74.50
89.67
102.00
20.75
0.32
-0.89
62.2
98.9
7
22
ACCEPTED MANUSCRIPT 10
93
117.93
13.85
11.74
82.17
107.50
116.00
130.92
143.67
23.42
0.10
-0.83
98.2
141.2
10
11
93
152.13
13.87
9.12
113.33
140.83
151.17
164.08
177.83
23.25
-0.07
-0.67
131.5
174.5
13
12
93
172.02
12.08
7.02
140.83
162.17
172.33
181.33
195.33
19.17
-0.14
-0.69
153.2
191.5
15
13
93
172.47
9.10
5.28
151.33
165.83
174.00
178.67
190.83
12.83
-0.23
-0.65
156.3
186.3
15
14
93
153.50
7.22
4.70
134.17
149.00
153.83
159.00
169.50
10.00
-0.27
0.03
139.7
165.9
13
15
93
119.59
9.15
7.65
54.17
116.17
119.67
124.42
135.33
8.25
-3.98
27.82
108.8
129.5
10
16
93
79.42
7.74
9.74
40.00
76.00
80.00
84.58
92.00
8.58
-1.90
7.26
66.2
89.7
7
17
93
41.45
4.85
11.71
28.00
37.92
41.00
44.83
50.67
6.92
-0.02
-0.48
33.6
50.0
4
18
93
18.80
2.77
14.73
7.83
16.67
19.00
21.17
23.00
4.50
-0.75
1.13
14.6
25.0
2
19
84
8.53
0.97
11.42
6.00
8.00
8.50
9.00
11.00
1.00
-0.29
0.21
7.0
10.0
1
488 489
Table 7c. Statistical estimators of the mean hourly UVER irradiance (mW m-2), in
490
December at solar noon for each location.
Station
N
Mean
StDev
CoefVar(%)
Min
Q1
Q3
Max
IQR
As
K
P5
P95
Athalassa
91
54.34
17.07
31.41
8.00
49.67
Median 59.50
65.50
77.33
15.83
-1.24
0.58
14.80
71.60
Larnaca
93
42.67
10.39
24.35
7.67
39.58
45.83
49.17
57.00
9.58
-1.56
2.32
17.10
54.60
491 492
The sun’s UVER rays are strongest in the six-hour period (10 to 15) around local
493
noon when 75% of a summer day UVER is received. Tables 7a and 7b summarize
494
the percentage of UVER radiation present at different times during a summer day.
495 496
3.5 Analysis of monthly average hourly UVER irradiance
497 498
The daily variation of the average hourly UVER irradiance is shown in Fig. 9. The
499
figure shows that the hourly average UVER irradiance fluctuates between 0.054 W
500
m-2 in December and 0.227 W m-2 in July at solar noon at Athalassa. The values at
501
Larnaca are lower than in Athalassa and they fluctuate between 0.043 W m-2 in
502
December and 0.172 W m-2 in July at solar noon. A high symmetry is also observed
503
around the months of June or July when the irradiance reaches its maximum, while it
504
decreases in spring and autumn and reaches its minimum in winter months. The
505
results can be explained taking into account the symmetry relation between the
506
summer and winter solstices.
507 508
According to measurements obtained from instruments of MODIS, the TOC reaches
509
its maximum value at Athalassa in April (Monthly Mean TOC=345 D.U.) and its
510
minimum value in November (Monthly Mean TOC=285 D.U.) Similar results were
511
obtained by Zerefos et al. [19] and by Bilbao et al. [52], with the maximum occurring 23
ACCEPTED MANUSCRIPT 512
in April in the Northern Hemisphere. Figure 9 shows that the results are quite in
513
accordance with ozone evolution; comparing March and September, when the solar
514
declination is about zero, it can be seen that the UVER hourly values, due to an
515
ozone decrease, are higher in September than in March.
516 517
Fig.9. Daily evolution of the monthly mean hourly UVER irradiance (W m-2) for the
518
period 2013-2015 at a) Athalassa and b) Larnaca.
519 520
3.6. Relationship between UVER and other radiation components
521 522
It can be useful to estimate UVER irradiance based on UVB, UVA and global
523
irradiances. The relationship between UVER and UVB is linear, since UVER consists
524
of 83% of UVB irradiance. The correlation between the data have been analysed by
525
assuming relations of the following empirical forms:
526 527 528
Y aX b
(4)
529
Y c dX eX 2
(5)
530 531
Table 8 shows the values of the fit parameters for Eqns. (4) and (5) as well as the
532
coefficient of determination, R 2 , for the hourly (W m-2) and daily values (kJ m-2) for 24
ACCEPTED MANUSCRIPT 533
both stations. The characteristic of these relationships is that R2 are close to 1. For
534
the model of Eq. (4) the fit of the result is given by the parameter S, which is the
535
standard error of the regression. S is measured in the units of the response variable
536
and represents the standard distance about the regression line where the data
537
values fall within, or the standard deviation of the residuals. For a given study, higher
538
S values indicate lower performance of the fitted curves. From Table 8a, it is
539
indicated that the results are more satisfactory for estimating UVER from UVB and
540
UVA, rather than from the global irradiance, although they continue to be acceptable
541
in the latter case. Similar results were obtained for the estimation of the daily values
542
of UVER (Table 8b). Generally, the constants of the equations of the two stations are
543
comparable.
544 545
Table 8a. Relationships between hourly UVER irradiance (W m-2) and UVB, UVA
546
and global (G) irradiance (W m-2) at both stations. Variable y UVER_Ath
Variable x UVA_Ath
UVER_Lca
UVA_Lca
UVER_Ath UVER_Lca UVER_Ath
UVA_Ath UVA_Lca G_Ath
UVER_Lca
G_Lca
UVER_Ath
G_Ath
UVER_Lca
G_Lca
UVER_Ath UVER_Lca
UVB_Ath UVB_Lca
Equation
y 6.07*104 x1.448 y 3.02*104 x1.492 y 6.73*104 0.0015 x 3.9*105 x 2 y 3.026*10 7.52*10 x 2.4*10 x 3
4
5
2
y 2.752*106 x1.639 y 2.02*106 x1.637 y 0.0106 1.6*105 x 1.0*106 x 2 y 6.83*103 1.7*106 x 1*107 x 2 y 0.0027 0.107 x y 0.0032 0.067 x
R2 / S S=0.008 S=0.007 0.98 0.98 S=0.014 S=0.111 0.95 0.96 0.99 0.99
547 548
Table 8b. Relationships between daily UVERd irradiation (kJ m-2) and UVBd, UVAd
549
(kJ m-2) and Global (Gd) (MJ m-2) radiation at both stations. Variable y UVERd Ath
Variable x UVAd_Ath
UVERd_Lca
UVAd_Lca
UVERd_Ath
UVAd_Ath
UVERd_Lca
UVAd_Lca
UVERd Ath
Gd_Ath
UVERd Lca
Gd_Lca
UVERd Ath
Gd_Ath
Equation
y 3.85*104 x1.288 y 1.38*104 x1.361 y 0.133 0.0023x 1*106 x 2 y 0.026 0.0011x 1*106 x 2 y 0.053x1.382 y 0.0377 x1.388 y 0.1382 0.0831x 0.0036 x 2 25
R2 /S S=0.219 S=0.196 0.98 0.98 S=0.332 S=0.268 0.96
ACCEPTED MANUSCRIPT UVERd Lca
Gd_Lca
UVERd Ath UVERd_Lca
UVBd_Ath UVBd_Lca
y 0.1303 0.0587 x 0.00264 x 2 y 0.1379 0.1066 x y 0.1015 0.254 x
0.96 0.99 0.99
550 551
The relationships of the UVER variables between the two stations are shown below.
552
R2 is high for both equations as expected because of the co-variability of UVER at
553
both stations (Fig. 3a).
554 555
Hourly data (W m-2):
556 557 558 559 560 561 562 563
UVER _ Ath 0.00176 1.23*UVER _ Lca
R 2 0.93
(6)
R 2 0.95
(7)
Daily data (kJ m-2):
UVERd _ Ath 0.01136 1.253*UVERd _ Lca
3.7. Attenuation of the UVER radiation-Daily UVER ratios
564 565
In order to assess the attenuation of UVER solar radiation we have estimated the
566
potential UVER irradiation (UVERc), which is defined as the irradiation when the
567
clearness index (KT) is above 0.65, i.e., a clear day. KT is defined as the ratio of the
568
measured daily global solar radiation at the Earth’s surface to the extraterrestrial
569
radiation at the top of the atmosphere both measured on a horizontal surface. The
570
days are classified as cloudy when KT < 0.35, as partly cloudy when 0.35< KT <0.65
571
and clear days when KT > 0.65. The statistics of UVERd for different KT values are
572
presented in Table 9. The most frequent cases occur in the bins above 0.55 in both
573
stations, i.e. towards the clear-day classification. The averages in most cases are
574
higher than the median values. The numbers of clear days on a monthly basis, which
575
are based on the above criteria for the whole period of measurements (3 years), are
576
presented in Table 10. The total number of clear days is 541 for Athalassa and 708
577
for Larnaca. As it is indicated in Table 10, during the summer season most days are
578
defined as clear.
579 580
Figure 10 shows the monthly average daily values of extraterrestrial (UVER0),
581
UVERc and measured UVER irradiation at both stations. The graph shows that both 26
ACCEPTED MANUSCRIPT 582
UVER and UVERc at Athalassa are higher than the respective values at Larnaca.
583
The difference between the UVERc and UVER measured values is greater in the
584
spring and winter time, while during the summer the difference is small. This is
585
attributed to the fact that during the summer almost all days are clear.
586 587
The UVER0 irradiation is estimated from the following equation:
588 589
UVER0 (24 / ) GscUVER [sin sin ((s ) /180) cos cos sin s ]
590 591
where ε is the eccentricity of the ecliptic path of the Earth around the Sun, φ is the
592
latitude, δ is the solar declination, ωs is the sunset hour angle and GscUVER=9.89 W
593
m-2, which it was obtained from Tena et al. [22].
594 595
Table 9. Statistics of daily UVER irradiation (kJ m-2) based on various daily values KT
596
in the period of measurements for a) Athalassa and b) Larnaca.
597
a) Athalassa Ath_ KT Bin End Lower 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75
Daily UVER (kJ m-2) Occurrences Mean Median Min Upper 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80
5 4 6 10 20 18 35 38 53 71 103 145 328 210 3
0.376 0.542 0.463 0.838 1.000 1.147 1.456 1.841 1.911 2.071 2.567 3.023 3.731 4.280 5.341
0.234 0.500 0.464 0.933 0.816 0.901 1.293 1.820 1.788 1.487 2.422 3.063 4.165 4.582 5.904
0.221 0.395 0.426 0.428 0.568 0.581 0.677 0.826 0.859 0.935 1.026 1.095 1.000 1.273 4.011
Max
Std. Dev.
0.848 0.865 0.529 1.233 1.979 2.710 2.902 3.626 3.731 4.576 4.996 5.348 5.972 6.164 6.107
0.270 0.220 0.037 0.300 0.454 0.558 0.649 0.789 0.750 1.089 1.107 1.282 1.529 1.426 1.156
598 599
b) Larnaca Lca_ KT Bin End Lower Upper 0.05 0.10
Occurrences 3
Daily UVER (kJ m-2) Mean Median Min Max 0.319
27
0.316
0.224 0.418
Std. Dev. 0.097
(8)
ACCEPTED MANUSCRIPT 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80
0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85
6 8 7 7 14 17 26 34 52 70 94 222 419 66 1
0.515 0.488 0.856 0.802 0.969 1.030 1.075 1.337 1.540 1.692 1.976 2.523 3.283 3.396 1.054
0.395 0.492 0.887 0.868 0.841 0.795 0.879 1.174 1.510 1.355 1.762 2.643 3.564 3.461 1.054
0.307 0.403 0.429 0.364 0.530 0.620 0.668 0.632 0.730 0.774 0.798 0.802 0.871 1.436 1.054
0.892 0.601 1.242 1.524 2.013 1.727 2.650 2.903 2.962 3.895 4.236 4.531 4.808 4.863 1.054
0.250 0.071 0.312 0.405 0.441 0.393 0.473 0.645 0.619 0.868 0.907 1.127 1.060 0.884 0.000
600 601 602
Table 10. Number of clear days defined by KT>0.65 with UVER measurements in
603
Athalassa and Larnaca in the period 2013-2015. Station Athalassa Larnaca
Jan 24 22
Feb 32 36
Mar 40 51
Apr 46 62
May 42 69
Jun 61 79
Jul 80 91
Aug 74 91
Sep 39 72
Oct 45 64
Nov 26 29
Dec 32 42
Year 541 708
604 605
From the monthly mean values of UVERc, UVER0 and measured UVER radiation,
606
the ratios between these variables were estimated. The ratio UVER/UVERc
607
represents information about the percentage of radiation which, on the average, is
608
transmitted through the atmosphere and may be considered as the atmospheric
609
transparency under average conditions, i.e. including hydrometeors and aerosols.
610
The ratio UVERc/UVER0 gives information about the atmospheric transparency on
611
clear days, i.e, without clouds but with aerosols, though in low proportion. Figure 11
612
shows the monthly mean daily values of the above ratios for each station. The
613
greatest variability is shown in the ratio of UVER/UVERc. The other ratios show
614
similar variation, but the values are very low. The evolution of these ratios increases
615
from spring to summer and decreases from summer to winter.
616
28
ACCEPTED MANUSCRIPT
617 618
Fig. 10. Annual variation of monthly mean values of UVER0, UVERc and measured
619
UVER irradiation at Athalassa and Larnaca.
620
621 622
Fig. 11. Monthly mean values of the ratios UVER/UVERc, UVERc/UVER0, and
623
UVER/UVER0 at Athalassa and Larnaca. 29
ACCEPTED MANUSCRIPT 624 625
3.8. Relationship between hourly hemispherical transmittances ( ktUVER ) and
626
clearness index ( kt )
627 628
In this section the relationship between the clearness index (global hemispherical
629
transmittance) ( kt ) and the UVER hemispherical transmittance ( ktUVER ) is examined.
630
The clearness index is defined as: kt G / G0 , G being the measured global
631
irradiance and G0 the extraterrestrial solar irradiance, both measured on horizontal
632
surface and in the same time interval. In the same way the UVER hemispherical
633
transmittance ( ktUVER ) is defined as: ktUVER UVER / UVER0 , where UVER is the
634
measured variable and UVER0 is the extraterrestrial UVER irradiance, both
635
measured on a horizontal surface during the same time interval. The small ‘k’ refers
636
to hourly values, while the capital letter ‘K’ denotes daily values. The monthly mean
637
values of the daily UVER hemispherical transmittance ( KTUVER ) were given in the
638
previous section (Fig. 11).
639 640
Figure 12 shows the histograms with the hourly values of kt. Most of the data are
641
concentrated in the 0.7-0.8 range at both stations. The clearness index is mostly
642
affected by the presence of clouds. Figure 13 shows the histograms with the hourly
643
values of ktUVER. Most of the data are concentrated in the 0.7-1.5 (*102) range at both
644
stations. The above results suggest that is difficult to establish relationships of the
645
form of Eqs. (4) and (5) between the indexes kt and ktUVER . Tena et al. [22] have
646
established linear regressions between ktUVER and kt for the four central hours of the
647
day during the summer months.
648
30
ACCEPTED MANUSCRIPT
649
650 651
Fig. 12. Frequency distribution of kt at a) Athalassa and b) Larnaca, in the period
652
2013-2015.
653 654
31
ACCEPTED MANUSCRIPT
655 656
657 658
Fig. 13. Frequency distribution of hourly UVER hemispherical transmittance (ktUVER)
659
at a) Athalassa and b) Larnaca, in the period 2013-2015.
660 661 32
ACCEPTED MANUSCRIPT 662
Moreno et al. [29] have proposed two models having the following forms:
663 664 665
ktUVER exp(a b *ln(kt ))
666
In Eq. (10), UVERx is the maximum value of UVER irradiance at a given hour.
667
Furthermore, they propose relationships of UVER irradiance and ktUVER with relative
668
optical air mass (m) of the form:
(9)
ktUVER c d *(kt *UVERx )
(10)
669 670
ktUVER a * mb
(11)
UVER a * mb
(12)
671 672
m depends on the solar altitude angle (γs) (in rad), and the site pressure and is
673
calculated using Eq. (13) (Kasten and Young [53]). The relative optical air mass was
674
estimated for the middle of each hour for solar altitude αs>7 deg.:
675 676 677
m ( P / P0 ) / (sin( s ) 0.50572*(57.29578* s 6.07995)1.6364 )
678
where P and P0 are the site and standard atmospheric pressure (P0 = 1013.25 hPa),
679
respectively; the ratio P / P0 is estimated using Eq. (14) from the elevation (z) (in m)
680
of the site:
(13)
681
P / P0 exp( z / 8435.2)
682 683 684 685
(14)
The above forms of relationships (Eqs. 9-12) were tested with the data of the two
686
stations in Cyprus and the results of fitting with the relevant regressions are shown in
687
Table 11. As indicated in this Table, the coefficients of the fitted equations show
688
similarities between the two stations. Additionally, the coefficients of the regressions
689
show similarities with those obtained by Moreno et al. [29] in Valencia (Spain).
690 691
Mateos et al. [54] have proposed an empirical model for the estimation of total UV
692
irradiance based on the UV extraterrestrial irradiance (UV0), the clearness index (kt)
693
and relative optical air mass (m) using the following form:
694 695 696
UV a *UV0 * ktb * mc
(15) 33
ACCEPTED MANUSCRIPT 697
If we extend the above equation by analogy for the estimation of UVER irradiance
698
we can estimate the coefficients of the equation as shown in Table 11. The
699
coefficients of the two stations are almost similar.
700 701
Table 11. Relationships between hourly UVER irradiance (W m-2) and ktUVER with kt ,
702
m and UVERx at both stations. Variable y ktUVER _Ath
Variable x kt_Ath
ktUVER _Lca ktUVER _Ath ktUVER _Lca ktUVER _Ath ktUVER _Lca
kt_Lca
UVER_Ath
kt_Ath
UVER_Lca
kt_Lca
UVER_Ath
kt&UVERx_Ath
UVER_Lca
kt&UVERx_Lca
UVER_Ath
m_Ath
UVER_Lca
m_Lca
UVER_Ath
kt, UVER0, m
UVER_Lca
kt, UVER0, m
kt&UVERx_Ath kt&UVERx_Lca m_Ath m_Lca
Equation
y exp(3.51 0.981*ln(kt )) y exp(3.71 1.239*ln(kt )) y 0.0066 0.147* kt *UVERx y 0.0079 0.155* kt *UVERx
S 0.0062 0.0049 0.0019 0.0020
y 0.0299* m0.939 y 0.0239* m0.949
0.0048
y exp(1.634 1.892*ln(kt )) y exp(1.807 2.396*ln(kt )) y 0.0014 1.206* kt *UVERx y 0.00055 1.194* kt *UVERx
0.0508
y 0.2079* m2.084 y 0.1669* m2.118
0.0229
y 0.043*UVER0 * kt0.826 m0.955 y 0.032*UVER0 * kt0.809 m0.933
0.0095
0.0036 0.0408 0.1029 0.0069 0.0151 0.0087
703 704
Extending the analysis of the relationships for different types of hours i.e., clear: kt
705
>0.65 and partly cloudy (0.35< kt <0.65), we have estimated the regression
706
coefficients of Eqs. (11) and (12). Table 12 presents these coefficients for the two
707
types of hours, while Fig. 14 shows the relationship of UVER and m for both stations.
708 709
Table 12. Regression coefficients of the functions of Eqs (11) and (12) on clear ( kt
710
>0.65) and partly cloudy hours (0.35< kt <0.65) at both stations. Station
Athalassa
kt kt >0.65
ktUVER /UVER ktUVER
34
Regression coefficients a
b
0.0334
0.967
ACCEPTED MANUSCRIPT Larnaca
kt >0.65
ktUVER
0.0255
0.957
Athalassa
0.35< kt <0.65
ktUVER
0.0224
0.605
Larnaca
0.35< kt <0.65
ktUVER
0.0244
0.480
Athalassa
kt >0.65
UVER
0.2227
1.931
Larnaca
kt >0.65
UVER
0.1714
1.983
Athalassa
0.35< kt <0.65
UVER
0.1576
1.764
Larnaca
0.35< kt <0.65
UVER
0.1134
1.657
711 712
713 714
35
ACCEPTED MANUSCRIPT
715 716
Fig. 14. Relationship of UVER irradiance (W m-2) and m for a) Athalassa and b)
717
Larnaca, in the period 2013-2015.
718 719
Different authors have established relationships between UVER irradiance and a
720
number of other variables such as TOC, SZA, UV and global irradiance with high
721
coefficients of determination [23]. Equations 16 and 17 show the relationships
722
between UVER irradiance under cloud-free conditions at midday and the cosine of
723
SZA angle as well as the TOC at both stations:
724 725 726 727 728
Ath _ UVERc 0.243*cos( SZA)2.008 *(TOC / 300)0.851
(16)
Lca _ UVERc 0.188*cos( SZA)2.013 *(TOC / 300)0.704
(17)
729
The relationships between the UVER irradiance under cloud-free conditions for each
730
hour of the day and the cosine SZA are shown below:
731 732 733 734 735
Ath _ UVERc 0.231*cos( SZA)1.923
(18)
Lca _ UVERc 0.179*cos( SZA)2.018
(19)
36
ACCEPTED MANUSCRIPT 736
Almost similar coefficients were obtained by Bilbao et al. [55] at Marsaxlokk in Malta.
737
The fitted line of Eq. (18) is shown in Fig. 15. Similar graph is obtained for Larnaca
738
(not shown).
739
740 741
Fig. 15. Relationship between UVERc and cos(SZA) at Athalassa in the period 2013-
742
2015.
743 744
3.9. UV Index
745 746
The UVI is estimated from the measured hourly UVER (in W m-2) by multiplying it by
747
40. The monthly average hourly UVI values throughout the day are reported in Fig.
748
16 for both stations. The UVI values on the ordinates have been separated into five
749
zones according to the WHO recommendations [17], viz., extreme ≥11; very high 8-
750
10; high 6-7; moderate 3-5 and low ≤2. In terms of Sun exposure time to achieve
751
incipient redness of skin type II, these five ranges of UVI values translate into 15, 20,
752
25, 35 min and more than 1 h, respectively [39]. The time taken ( tE in minutes) to
753
induce skin damage is calculated from the following formula [56]:
754 755 756
tE (4000 / 60)*( MEDF * SPF ) / UVI
(20) 37
ACCEPTED MANUSCRIPT 757
where the factor 4000/60 accounts for the conversion from UVER irradiance to UVI,
758
and seconds to minutes; MEDF is a factor to account for the different skin types and
759
it is expressed as a number of Standard Erythemal Dose
760
UVER) required to induce erythema; SPF is the Sun protection factor of any Sun
761
block applied. For unprotected skin SPF=1. For UVI=10 at midday in summer and
762
unprotected skin, the time taken to induce erythema for the four skin phototypes,
763
calculated from the above formula, would be 13.3, 16.7, 23.3 and 30 minutes,
764
respectively. For UVI=10 with a Sun block of SPF=10 the time required to induce
765
erythema for the four skin phototypes is about 10 times the estimated values given
766
above (i.e., ̴2.2, 2.8, 3.9 and 5.0 hours, respectively).
(1 SED=100 J m-2 of
767 768
The highest mean hourly UVI is 9 and is recorded at Athalassa, whereas the highest
769
at Larnaca is 7. If we use the hourly maximum values instead of the mean ones, then
770
the UV Indices higher than 10 are recorded at Athalassa and about 8 at Larnaca.
771
During the summer months the UVI is higher than 7 (very high) from about 10 to 15
772
LST, while at Larnaca the UVI is higher than 5 (high) for the same time interval. If we
773
use the maximum hourly values then the time interval is extended by one hour.
774
775 776 38
ACCEPTED MANUSCRIPT
777 778
Fig. 16. Monthly average hourly UVI values at a) Athalassa and b) Larnaca in the
779
period 2013-2015.
780 781
The UV Index was also determined from the UVER measurements using two
782
different criteria: a) The value at solar noon and b) the maximum daily value [21].
783
Therefore, for the two stations the percentages were found for which the differences
784
in the results given by the differences of the above two criteria were 0, 1, 2 and 3 or
785
more units of UVI. The results of the deviations of the values of the UVI at solar noon
786
compared with the maximum daily UVI values are summarised in Table 13. It has to
787
be noted that at Larnaca 39 days are missing while at Athalassa only 10 days are
788
missing. The percentage coincidence (zero difference between the two criteria in
789
UVI) varied between 52% (Larnaca) and 66% (Athalassa). If we consider the cases
790
for which the difference was 0 or 1 unit, the coincidence is around 94% for both
791
stations. Therefore, it is reasonable to consider that estimating the UVI value at solar
792
noon is acceptable method. Similar results were obtained for 16 stations in Spain for
793
which the difference between the two criteria was zero or one UVI unit varying
794
between 89% and 95% with an average value of 92% [21].
795
39
ACCEPTED MANUSCRIPT 796
Table 13. Deviations of the UVI values at solar noon compared with the maximum
797
daily UVI values for the two stations. The results are given as a percent of the
798
available daily values given in parenthesis for each station. Percentages Station
0
1
2
≥3
Athalassa (1085)
66
27
5
2
Larnaca
52
42
2
1
(1056)
799 800
Table 14 shows the percentage of the daily maximum values of the UVI for the two
801
sites classified according to the exposition categories recommended by WHO [18].
802
The UVI was rounded to the nearest integer value. The UVI reaches high (6-7) or
803
very high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca
804
these values are reached in 38.8%. Using the maximum hourly values of UVER, the
805
percentages of the high and very high cases of UVI are slightly higher in both
806
stations (Table 14 b cases), than using the maximum of the mean hourly values
807
(Table 14 a cases). It has to be noted that no extreme values are recorded. The
808
average annual number of hours with UVI>5 at Athalassa is 935 and 604 at Larnaca,
809
while the average annual number of hours with UVI>7 at Athalassa is 431 and only
810
61 at Larnaca. It has to be reminded that long missing records were detected in
811
Larnaca.
812 813
Table 14. Days (in % during the three years considered) in which the indicated
814
maximum value of the UV Index is reached at the two measuring sites. a) Value at
815
solar noon, b) maximum daily value. UV Index (%) Station
≤2
3-5
6-7
8-10
≥11
(low)
(moderate)
(high)
(very high)
(extreme)
Athalassa (a)
9.1
37.1
21.0
31.9
Athalassa (b)
4.1
36.0
20.6
38.6
Larnaca
(a)
20.9
35.8
36.9
1.9
Larnaca
(b)
16.6
36.2
38.8
4.0
816 817 40
ACCEPTED MANUSCRIPT 818
3.10. Cumulative doses
819 820
Figure 17 shows the annual cumulative dose for each phototype and for Standard
821
Erythemal Dose obtained by dividing the daily UVER values by the corresponding
822
MED and SED values (Table 1) over an average year at the two measuring sites.
823
These values correspond to a continuous and uninterrupted exposure to the Sun, on
824
a horizontal position, throughout the year. It is observed that the cumulative doses
825
during an average year range from 9087 SEDs in Larnaca to 11418 SEDs in
826
Athalassa. The most common skin type in Cyprus is phototype III (about 70% of the
827
population, southern European type [56]), which could receive an annual cumulative
828
dose between 2596 MEDs in Larnaca to 3262 MEDs in Athalassa. The second
829
common skin type in Cyprus is phototype II (about 20% of the population, central
830
European type) that could receive an annual cumulative dose between 3635 MEDs
831
in Larnaca to 4568 MEDs in Athalassa. The third common skin type in Cyprus is
832
phototype IV (about 10% of the population, north African type) that could receive an
833
annual cumulative dose between 2019 MEDs in Larnaca to 2537 MEDs in
834
Athalassa. Regarding the phototype I (Scandinavian type), it could receive an annual
835
cumulative dose between 4544 MEDs in Larnaca to 5709 MEDs in Athalassa. The
836
annual cumulative doses are comparable with the respective values in 16
837
radiometric stations in Spain [21]. The curves of Fig. 17 show a clear change of
838
slope during the summer. The cumulative doses for the phototype III for summer is
839
41%, for spring 28%, for autumn 20% and for winter 11% of the annual cumulative
840
dose, for both stations.
841 842
It is estimated that schoolchildren received about 5% of the total daily solar UV
843
radiation, while outdoor workers received about 20-26% of the total daily solar UV
844
radiation levels [57-59].
845
41
ACCEPTED MANUSCRIPT
846 847
848 849
Fig. 17. Annual cumulative dose for the skin types defined in Table1 and the
850
Standard Erythemal Dose (SED) at a) Athalassa and b) Larnaca.
851 852 42
ACCEPTED MANUSCRIPT 853
4. Inter-comparison of the two sites
854 855
The inter-comparison of the broad-band solar radiation intensity measurements at
856
both sites are reported in Table 15 for the global and UVER radiation. The solar
857
radiation intensities are reported as monthly average daily values, the number of
858
days of each variable for the period of measurements and the relative attenuation
859
reported for each one, which is defined as:
860
Re lativeAttenuation(%) (( X Lca X Ath ) / X Ath ))*100
861 862 863
(21)
where X refers to the type of solar radiation, i.e., either global or UVER. The
864
subscripts refer to the particular site.
865 866
As indicated in Table 15, the magnitudes of the monthly average daily values of the
867
solar global radiation are higher at Larnaca than at Athalassa. Generally, the
868
percentages of relative attenuation are lower during the summer period. The
869
magnitudes of the monthly average daily solar global radiation intensity at the two
870
sites are very similar.
871
difference in altitude between the two stations is not significant and, therefore, the
872
daily values are almost similar. However, the UVER radiation at Larnaca is lower
873
than that at Athalassa; therefore, the relative attenuation of UVER is negative
874
(approximately about -20% throughout the year). The percent relative attenuation is
875
also presented graphically for the two solar radiation components in Figure 18. The
876
summary of the inter-comparison of the two sites is presented in Table 16.
The % relative attenuation is < 10% for all months. The
877 878
Table 15. Monthly average daily solar global and UVER at Athalassa and Larnaca in
879
the period 2013-2015 and their relative differences. Ath(Gd) Lca(Gd) Ath(UVERd) Month N Mean N Mean % Relative N Mean MJ/m2 MJ/m2 attenuation kJ/m2 1 93 9.36 92 10.01 6.99 93 1.19 2 84 13.27 66 14.35 8.13 84 1.81 3 93 17.54 93 18.57 5.92 93 2.64 4 90 22.27 90 23.92 7.40 90 3.54 5 77 24.05 93 26.38 9.69 90 4.25 6 82 27.78 90 29.53 6.29 89 5.25 7 92 27.96 93 29.26 4.65 92 5.50
43
Lca(UVERd) N Mean % Relative kJ/m2 attenuation 62 0.96 -19.38 66 1.52 -15.97 93 2.14 -19.12 90 2.90 -18.08 93 3.51 -17.53 90 4.19 -20.32 93 4.24 -22.84
ACCEPTED MANUSCRIPT 8 9 10 11 12 Year
93 84 93 78 91 1050
24.91 20.09 15.51 11.37 8.78 18.53
93 90 93 90 93 1076
26.30 21.68 16.72 11.45 9.44 19.93
5.57 7.92 7.81 0.72 7.46 7.54
93 90 93 89 91 1087
4.81 3.52 2.44 1.47 1.04 3.13
93 90 93 90 93 1046
3.70 2.85 1.89 1.09 0.83 2.55
-22.90 -18.97 -22.48 -25.74 -20.27 -18.36
880
881 882
Fig. 18. Relative attenuation of solar global and UVER radiation for Athalassa and
883
Larnaca in the period 2013-2015.
884 885
The main factors which affect the levels of UVER and shortwave (SW) irradiances
886
are the solar zenith angle, clouds, ozone, water vapour and aerosols. UVER
887
irradiance on clear days depends on SZA cosine by a power law (Fig. 15) (Eqs. 18-
888
19), while SW irradiances on clear days show a linear trend with a high R2 for both
889
stations:
890 891 892 893 894 895
Measurements in Malta and Spain quantified the effects of the above factors on
896
UVER and SW irradiances on clear days [60-62]. According to these measurements,
Ath _ Gc 11.43 964*cos( SZA)
R 2 0.97
(22)
Lca _ Gc 7.102 1018*cos( SZA)
R 2 0.98
(23)
44
ACCEPTED MANUSCRIPT 897
UVER is mostly affected by ozone which reduces UVER levels by around -0.31
898
%DU-1. However, the ozone effect on SW irradiance is negligible. The water vapour
899
effect on UVER is negligible, but SW depends on water vapour (̴ -3.36% cm-1). The
900
effect of aerosols is stronger on UVER irradiance than the SW one. The trends show
901
an average value of -37% for aerosol optical depth at 440 nm (AOD440), and for SW
902
irradiance this percentage falls up to -28.4% for AOD440 unity. Furthermore, Robaa
903
[26] found that the mean relative reduction of global and UV solar radiation in Cairo
904
(Egypt) were 17.4% and 27.4%, respectively. In dusty days, the reduction in the
905
received global and UV radiation due to dust particles effects ranged between 26%
906
and 45% for global and between 33% and 59% for UV. Jacovides et al. [27] have
907
demonstrated that high aerosol loads produce significant relative attenuations of
908
UVB to global solar radiation ratio in comparison to that for low aerosol loadings.
909 910
The global solar radiation at Larnaca exceeds that in Athalassa throughout the year.
911
This can be explained by the fact that there is much more number of clear days at
912
Larnaca than at Athalassa (Table 10). The attenuation of solar radiation within the
913
global spectral range due to the difference of altitude between the two sites by
914
scattering phenomena is negligible. The higher attenuation of UVER radiation can be
915
attributed to its shorter wavelengths, since the scattering process is inversely
916
proportional to the fourth power of its wavelength (λ-4). The scattering of solar
917
radiation by water molecules is a function of the amount of precipitable water above
918
the observation site. An empirical scattering coefficient for water vapour that varies
919
according to λ-2 has been proposed, while for aerosols, an empirical coefficient of
920
λ-0.75 was used [24]. In all cases, the degree of attenuation by scattering is an inverse
921
function of the wavelength, i.e., attenuation decreases with increasing wavelength.
922
The variation in the monthly percent of relative attenuation values for UVER is also
923
influenced by the local climatic conditions.
924 925
On the other hand, the aerosol load and the type of aerosols may also affect the
926
levels of UVER irradiance at the two locations. According to measurements of the
927
Department of Air Quality Control of the Ministry of Labour in Cyprus, in 2004, the
928
pollution load at Larnaca is much higher than that at Athalassa which is due to a
929
much larger vehicular and aeroplane traffic and the location of a number of industrial
930
plants in the vicinity of the station. The station at Athalassa is surrounded by a forest, 45
ACCEPTED MANUSCRIPT 931
while the station at Larnaca is within the area of the Airport. The mean annual
932
particulate matter concentrations of PM10 at Larnaca station, is slightly higher than
933
60 μg m-3, while at the station of General Hospital in Nicosia, which is close to
934
Athalassa station, is around 48 μg m-3 [63]. Furthermore, there are more days with
935
hazy conditions at Larnaca due to dust episodes, which affect mostly the southern
936
parts of the island.
937 938
Table 16. Inter-comparison of the two sites with respect to global and UVER
939
radiation. Variable Location Annual daily average global irradiation (Gd) (MJ/m2) Annual total global irradiation (MJ/m2) Annual daily average UVER irradiation (UVERd) (kJ/m2) Daily average UVER irradiation in July (kJ/m2) Daily average UVER irradiation in December (kJ/m2) Accumulated daily UVER irradiation in Spring (kJ/m2) Accumulated daily UVER irradiation in Summer (kJ/m2) Accumulated daily UVER irradiation in Autumn (kJ/m2) Accumulated daily UVER irradiation in Winter (kJ/m2) Annual total UVER irradiation (kJ/m2) Maximum Hourly Average UVER irradiance in July (W/m2) Maximum Hourly Average UVER irradiance in December (W/m2) Maximum Mean Hourly UV Index Absolute Maximum UV Index Mean Annual Cumulative doses Phototype I (MEDs) Mean Annual Cumulative doses Phototype II (MEDs) Mean Annual Cumulative doses Phototype III (MEDs) Mean Annual Cumulative doses Phototype IV (MEDs) Mean Annual Cumulative doses (SEDs)
Athalassa inland 18.53 6835 3.126 5.50 1.04 320.0 477.0 225.5 119.4 1141.9 0.249 0.077 9 10 5709 4567 3262 2537 11418
Larnaca coastal 19.93 7183 2.552 4.24 0.83 262.0 371.9 177.1 97.7 908.7 0.195 0.057 7 8 4543 3635 2596 2019 9087
940 941
5. Conclusions
942 943
Measured data at 10 min intervals, obtained by UV Kipp & Zonen radiometers
944
installed at two locations in Cyprus, one at Athalassa (inland location) and the other
945
at Larnaca (coastal location) during the period January 2013 to December 2015
946
have been used to define the statistical characteristics of both hourly and daily
947
UVER radiation values. These measurements have also been used to estimate UVI
948
and the cumulative doses for the different skin types. The interest of this work
949
resides in the fact that it is the first thorough analysis of this type performed in the 46
ACCEPTED MANUSCRIPT 950
island of Cyprus. Furthermore, the levels of UVER irradiation were compared with
951
other sites in the Mediterranean region. The highest values are recorded in Beer
952
Sheva (Israel) with the second ones at Athalassa, as expected, since these stations
953
are at lower latitude and have higher sunshine duration comparing to other stations.
954
The coastal sites (Larnaca, Kos, Athens, Thesaloniki, Neve Zohar and Valencia)
955
have almost similar levels of erythemal irradiation, in contrast to the inland locations
956
(Athalassa and Beer Sheva), which have higher levels of UVER. The differences
957
between the inland and coastal locations are more pronounced during the summer
958
period.
959 960
Large fluctuations in the spring months and November are mainly due to unstable
961
meteorological conditions during the transition from cold to warm weather and vice
962
versa. During summer the daily UVER radiation exceeds the value of 6 kJ m-2 at
963
Athalassa and 4.8 kJ m-2 at Larnaca, while during the winter season the lowest is
964
about 0.2 kJ m-2 at both sites. Slightly lower values were recorded in 2015 at both
965
stations, which can be attributed to higher amounts of aerosols in the atmosphere.
966
The year 2015 is characterized as an extremely dry year with more frequent dust
967
episodes over the island (dust from the deserts of Middle East and Sahara),
968
increasing, therefore, aerosols in the atmosphere that can affect the absorption of
969
UVER radiation. The accumulated UVER irradiation received in an average year is
970
1142 kJ m-2 for Athalassa and 909 kJ m-2 for Larnaca.
971 972
By analysing the daily evolution of the monthly average values of the UVER
973
irradiances a high degree of symmetry could be observed in the annual and
974
seasonal distributions of this radiation component. The UVER variability has been
975
studied by means of the coefficient of variation (CV). It was demonstrated that the
976
CVs in July are low during midday (5-10%) at both stations, indicating a high stability
977
along these hours in summer.
978 979
In July, the absolute maxima of the UVER irradiance measured at local noon varied
980
from 0.195 W m-2 in Larnaca to 0.248 W m-2 in Athalassa, whereas the absolute
981
minima ranges between 0.141 W m-2 and 0.188 W m-2, respectively. Since the
982
difference between the Q1 quartiles and the absolute minima was high, and the
983
difference between the Q3 quartiles and the absolute maxima was small, the 47
ACCEPTED MANUSCRIPT 984
maximum values can be considered representative of UVER at local noon, but the
985
minimum values represent unusual extreme values.
986 987
With respect to the estimation of UVER irradiance, it is indicated that the results from
988
the expression that estimates UVER from UVA were more satisfactory than those
989
from the global irradiance, although they continued to be acceptable in the latter
990
case. Similar results were obtained for the estimation of the daily UVER values of.
991
Generally, the constants of the equations of the two sites are comparable.
992 993
The difference between the potential UVER (UVERp) and the measured UVER
994
values is greater in the spring and winter time due to the presence of clouds, while
995
during the summer the difference is small. This is attributed to the fact that during the
996
summer almost all days are cloud free. The clearness index kt at Larnaca is slightly
997
higher than that at Athalassa. On the other hand, kTUVER of Athalassa is higher than
998
that at Larnaca.
999 1000
Regarding the UV Index, this shows minimum differences between the value at solar
1001
noon and the maximum daily value, with more than 90% of the cases showing
1002
differences of one or less UVI units for both sites. The UVI reaches high (6-7) or very
1003
high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca these
1004
values are reached in 38.8%. During the summer months the UV Index is higher
1005
than 7 (very high) from about 10 to 15 LST, while at Larnaca it is higher than 5
1006
(high) for the same time interval. If we use the maximum hourly values then the time
1007
interval of high values is extended by one hour.
1008 1009
Finally, the cumulative doses for each phototype and for the StED over an average
1010
year have also been studied for the two sites. It is observed that the cumulative
1011
doses during an average year range from 9087 SEDs in Larnaca to 11418 SEDs in
1012
Athalassa. The most common skin type in Cyprus, phototype III (about 70% of the
1013
population, southern European type) could receive an annual cumulative dose
1014
between 2596 MEDs in Larnaca to 3262 MEDs in Athalassa.
1015
48
ACCEPTED MANUSCRIPT 1016
Based upon the above analysis, we conclude that the two sites in Cyprus are
1017
characterised by relatively high average-daily irradiation rates and a relatively high
1018
frequency of clear days. Comparing the two sites we may observe that Larnaca has
1019
slightly higher rates of global radiation than Athalassa. Regarding UVER irradiation
1020
and UV Index, Athalassa shows higher values than Larnaca.
1021 1022
In future studies, the radiation climate of the two sites will be further examined for the
1023
other UV solar radiation components (UVB, UVA and UV total radiation) as well as
1024
the long-wave radiation. Then, the net radiation balance will be estimated and the
1025
climate characteristics will be assessed at a given site based on the levels of each
1026
radiation component.
1027 1028
Nomenclature
1029 1030
As
Skewness coefficient
1031
CDF
Cumulative probability density function
1032
CV
Coefficient of variation (%) (CoefVar)
1033
D.U.
Dobson unit (thickness of ozone in units of 10 μm)
1034
G
Global solar irradiance [W m-2]
1035
G0
Extraterrestrial irradiance [W m-2]
1036
G0d
Daily extraterrestrial irradiation (ETR) [MJ m-2]
1037
Gd
Daily global irradiation [MJ m-2]
1038
Gsc
Solar constant [1367 W m-2]
1039
GscUVER
Solar constant of UVER irradiance [9.89 W m-2]
1040
IQR
Interquartile range
1041
jd
Julian day number (1..365)
1042
K
Kurtosis
1043
kt
Hourly clearness index ( kt G / G0 )
1044
ktUVER
Hourly UVER transmittance ( ktUVER UVER / UVER0 )
1045
KT
Daily clearness index ( KT Gd / G0 d )
1046
m
Relative air mass
1047
MED
Minimum Erythemal Dose
1048
Max
Maximum 49
ACCEPTED MANUSCRIPT 1049
Min
Minimum
1050
N
Nonmissing observations
1051
N*
Missing observations
1052
P
Atmospheric pressure at the site [hPa]
1053
P0
Standard atmospheric pressure (1013.25 hPa)
1054
P5
Percentile 5%
1055
P95
Percentile 95%
1056
PDF
Probability density function
1057
PM10
Particulate matter concentration (μg m-3)
1058
Q1
First Quartile
1059
Q3
Third Quartile
1060
R2
Coefficient of determination
1061
S
Standard error of the regression or standard deviation of the residuals
1062
SED
Standard Erythemal Dose (1 SED=100 J m-2)
1063
StDev
Standard deviation
1064 1065
tE TOC
Time to induce erythema [minutes] Total Ozone column
1066
UV
UV irradiance [W m-2] / UV irradiation [kJ m-2] (UV(A+B))
1067
UVA
UVA irradiance [W m-2] / UVA irradiation [kJ m-2]
1068
UVAd
Daily UVA irradiation [kJ m-2]
1069
UVB
UVB irradiance [W m-2] / UVB irradiation [kJ m-2]
1070
UVBd
Daily UVB irradiation [kJ m-2]
1071
UVC
Ultraviolet radiation in the range of 100 to 280 nm
1072
UVER
UV erythema irradiance [W m-2] / UV erythema irradiation [kJ m-2]
1073
UVERd
Daily UVER irradiation [kJ m-2]
1074
UVER0
Extraterrestrial UVER irradiance [W m-2]
1075
UVERp
Potential UVER irradiance [W m-2]
1076
UVERx
Maximum hourly UVER irradiance [W m-2]
1077
UVI
UV Index
1078
z
Elevation [m]
1079 1080
Greek:
1081
αs
Solar altitude (degrees)
1082
δ
Solar declination [degrees] 50
tE
ACCEPTED MANUSCRIPT 1083
ε
eccentricity correction
1084
z
Solar zenith angle (SZA) [degrees]
1085
λ
Wavelength (nm)
1086
φ
Latitude [degrees]
1087
s
Sunset hour angle [degrees]
1088 1089
References
1090 1091
[1] Iqbal M., 1983. An Introduction to Solar radiation. Academic Press, New York.
1092 1093
[2] CIE, 1999. Standardization of the terms UV-A1, UV-A2 and UV-B. Vienna: CIE,
1094
Report CIE-134/1.
1095 1096
[3] WMO and UNEP, 2006. Executive Summary: WMO/UNEP Scientific Assessment
1097
of Ozone Depletion. Prepared by the Scientific Assessment Panel of the Montreal
1098
Protocol on Substances That Deplete the Ozone Layer.
1099 1100
[4] Casale G.R., Meloni D., Miano S., Palmieri S., Siani A.M., 2000. Solar UV-B
1101
irradiance and total ozone in Italy: fluctuations and trends. J. Geophys. Res. 105,
1102
4895-4901.
1103 1104
[5] Bartlett L.M., Webb A.R., 2000. Changes in ultraviolet radiation in the 1990s:
1105
spectral measurements from Reading, England. J. Geophys. Res. 105, 4889-4893.
1106 1107
[6] EUR 19098 - 2000. Biological UV dosimetry, a tool for assessing the impact of
1108
UV radiation on health and ecosystems. Edited by Rettberg p., Horneck G.,
1109
Baumstark-Khan C., Amanatidis G., Air Pollution Research Report 71. European
1110
Commission. Conference proceedings, ISBN 92-828-7820-1, 262 pp.
1111 1112
[7] Ghetti F., Checcucci G. and Bornman J.,2001. Series IV: Earth and
1113
Environmental Sciences – Vol. 57. Proceedings of the NATO Advanced Study
1114
Institute on Environmental UV Radiation: Impact on Ecosystems and Human Health
1115
and Predictive models. Pisa, Italy, 287 pp. ISBN 1-4020-3696-5. Springer. 51
ACCEPTED MANUSCRIPT 1116 1117
[8] Gao W., Schmoldt D. and Slusser J., 2009. UV Radiation in Global Climate
1118
Change. Measurements, Modeling and Effects on Ecosystems. 544 pp. ISBN 978-7-
1119
302-20360., Springer.
1120 1121
[9] Coldiron B., 1998. The UV Index: A weather report for skin. Clin. Dermatol. 16,
1122
441-446.
1123 1124
[10] Diffey B., 1982. The consistency of studies of ultraviolet erythema in normal
1125
human skin. Phys. Med. Biol. 27, 715-720.
1126 1127
[11] Diffey B., 1991 Solar ultraviolet effects on biological systems. Physics in
1128
Medicine and Biology 36, 299-328.
1129 1130
[12] MacKie R., 2006. Long-term health risk to the skin of ultraviolet radiation. Prog.
1131
Biophys. Mol. Bio. 92, 92-96.
1132 1133
[13] Fioletov E., McArthur E., Mathews T., Marrett L., 2009. On the relationship
1134
between erythemal and vitamin D action spectrum weighted ultraviolet radiation.
1135
Journal of Photochemistry and Photobiology B: Biology 95, 9-16.
1136 1137
[14] McKinlay A., Diffey B., 1987. A reference spectrum for ultraviolet induced
1138
erythema in human skin. CIE J. 6, 17-22.
1139 1140
[15] ISO 17166:1999E/CIE S 007/E-1998, Joint ISO/CIE standard: erythema
1141
reference action spectrum and standard erythema dose.
1142 1143
[16] de Miguel A., Bilbao J., Román R. and Mateos D., 2012. Measurements and
1144
attenuation of erythemal radiation in Central Spain. International Journal of
1145
Climatology 32, 929-940.
1146 1147
[17] Diffey B., 1990. Human Exposure to Ultraviolet Radiation. Semin. Dermatol. 9,
1148
2-10.
1149 52
ACCEPTED MANUSCRIPT 1150
[18] World Health Organization (WHO), World Meteorological Organization (WMO),
1151
United Nations Environment Programme (UNEP), International Commission on Non-
1152
Ionizing Radiation Protection (ICNIRP), 2002. Global Solar UV Index: Apractical
1153
guide, Watch No. 95, WMO/TD No. 625, Geneva, Switzerland, p 32.
1154 1155
[19] Zerefos C., Meleti C., Lambros A., 1995. The recent UV variability over south-
1156
eastern Europe. Journal of Photochemistry and Photobiology 20, 15-19.
1157 1158
[20] Mantis H., Repapis C., Philandras C., Pañiatsos A., Zerefos C., Bais A., Meleti
1159
C., Balis D., 2000. A 5-year climatology of solar erythemal ultraviolet in Athens,
1160
Greece. International Journal of Climatology 20, 1237-1247.
1161 1162
[21] Utrillas M., Marín M., Esteve A., Estellés V., Gandía S., Núnez J., Martinez-
1163
Lozano J., 2013. Ten years of measured UV Index from the Spanish UVB
1164
Radiometric Network. Journal of Photoch. and Photob. B: Biology 125, 1-7.
1165 1166
[22] Tena F., Martínez-Lozano J., Utrillas M., Marín M., Esteve A. and Cañada J.,
1167
2009. The erythemal clearness index for Valencia, Spain. International Journal of
1168
Climatology 29, 147-155.
1169 1170
[23] Cañada J., Esteve A., Marín M., Utrillas M, Tena F. and Martínez-Lozano J.,
1171
2008. Study of erythemal, UV (A+B) and global solar radiation in Valencia (Spain).
1172
International Journal of Climatology 28, 693-702.
1173 1174
[24] Kudish A., Lyubanksky V., Evseev E., Ianetz A., 2005. Statistical analysis and
1175
inter-comparison of the solar UVB, UVA and global radiation for Beer Sheva and
1176
Neve Zohar (Dead Sea), Israel. Ther. Appl. Climatol. 80, 1-15.
1177 1178
[25] Kudish A., Evseev E., 2014. Analysis of erythemal UVB and UVA irradiance at
1179
Beer Sheva, Israel from 1994 through 2012. Renewable Energy 63, 84-89.
1180 1181
[26] Robaa, S.M., 2004. A study of ultraviolet solar radiation at Cairo urban area,
1182
Egypt. Solar Energy
1183 53
ACCEPTED MANUSCRIPT 1184
[27] Jacovides C., Tymvios F., Assimakopoulos D., Kaltsunides N., Theocharatos G.
1185
Tsitouri M., 2009. Solar global UVB (280-315 nm) and UVA (315-380 nm) radiant
1186
fluxes and their relationships with broadband global radiant flux at an eastern
1187
Mediterranean site. Agricultural and Forest Meteorology, 149, 1188-1200.
1188 1189
[28] Ghoneim A.A., Kadad I.M., Altouq M.S., 2013. Statistical analysis of solar UVB
1190
and global radiation in Kuwait. Energy 60, 23-34.
1191 1192
[29] Moreno J.,Serrano M., Cañada J., Gurrea G., Utrillas M., Solar radiation Group.,
1193
2014. Effect of the relative optical air mass and the clearness index on solar
1194
erythemal UV irradiance. Journal of Photochemistry and Photobiology B:Biology 138,
1195
92-98.
1196 1197
[30] Kudish A. and Evseev E., 2011. The analysis of solar UVB radiation as a
1198
function of solar global radiation, ozone layer thickness and aerosol optical density.
1199
Renewable Energy 36, 1854-1860.
1200 1201
[31] de Miguel A., Román R., Mateos D., 2011. Evolution of erythemal and total
1202
shortwave solar radiation in Valladolid, Spain: Effects of atmospheric factors. Journal
1203
of Atmospheric and Solar-Terrestrial Physics 73, 578-586.
1204 1205
[32] Esteve A., Marín M., Tena F., Utrillas M. and Martínez-Lozano J., 2010.
1206
Influence of cloudiness over the values of erythemal radiation in Valencia, Spain.
1207
International Journal of Climatology 30, 127-136.
1208 1209
[33] Antón M., Serrano A., Cancillo M., García J., Madronich S., 2011. Empirical
1210
Evaluation of Simple Analytical Formula for the Ultraviolet Index. Photochemistry and
1211
Photobiology 87, 478-482.
1212 1213
[34] Kudish A. and Evseev E., 2012. UVB irradiance and atmospheric optical depth
1214
at the Dead Sea basin, Israel: Measurements and modeling. Renewable Energy 48,
1215
344-349.
1216
54
ACCEPTED MANUSCRIPT 1217
[35] Alados I., Gomera M., Foyo-Moreno I. and Alados-Arboledas L., 2007. Neural
1218
network of the estimation of UV erythemal irradiance using solar broadband
1219
irradiance. International Journal of Climatology 27: 1791-1799.
1220 1221
[36] Moreno J., Serrano M., Lorente M., Cañada J. and Utrillas M., 2013. An
1222
empirical model of erythemal ultraviolet radiation in the city of Valencia, Spain.
1223
Photochemical & Photobiological Sciences. 12, 1707-1716.
1224 1225
[37] Sabziparvar A., 2009. Estimation of clear-sky effective erythema radiation from
1226
broadband solar radiation (300-3000 nm) data in arid climate. International Journal of
1227
Climatology 29, 2027-2032.
1228 1229
[38] Koepke P. Bais A., Balis D., Buchwitz M., de Backer H. de Cabo X., Eckert P.,
1230
Eriksen P., Gillotay D., Heikkila A., Koskela T., Lapeta B., Litynska Z., Lorente J.,
1231
Mayer B., Renaud A., Ruggaber A., Schauberger G., Seckmeyer G., Seifert P.,
1232
Schmalweiser A., Schwander H., Vanicek K., Wever M., 1998. Comparison of
1233
models used for UV index calculations. Photochem. Photobiol. 67, 657-662.
1234 1235
[39] EUR 20611. 2003. UV-B forecasting. Final Report of COST Action 713.
1236 1237
[40] Gómez I., Marín M., Pastor F., Estrela M., 2012. Improvement of the Valencia
1238
region Ultraviolet index (UVI) forecasting system. Computers & Geosciences 41, 72-
1239
82.
1240 1241
[41] Jacovides C., Kaltsunides N., Hachioannou L. & Stefanou L., 1993. An
1242
assessment of the solar radiation climate of the Cyprus environment. Renewable
1243
Energy Vol. 3, 913-918.
1244 1245
[42] Petrakis M., Kambezidis C., Lycoudis S., Adamopoulos A., Kassomenos P.,
1246
Michaelides I., Kalogirou S., Rotitis G., Chrysis L., Hadjigianni A. 1998. Generation
1247
of a ‘typical meteorological year’ for Nicosia, Cyprus. Renewable Energy 13 (3), 381-
1248
388.
1249
55
ACCEPTED MANUSCRIPT 1250
[43] Kalogirou S., Pashiardis S. and Pashiardi A., 2017. Statistical analysis and
1251
inter-comparison of the global solar radiation at two sites in Cyprus. Renewable
1252
Energy 101, 1102-1123.
1253 1254
[44] World Meteorological Organization. WMO, 1987. Guidelines on the quality
1255
control of data from the World Radiometric Network. WCDP-3, WMO/TD-No. 258, p
1256
30, WMO, Geneva, Swittzerland.
1257 1258
[45] Long C.N. and Dutton E.G. 2002. Global Network recommended QC tests, V2.0,
1259
BSRN Technical Report (http://ezksun3.ethz.ch/bsrn/admin/dokus/qualitycheck.pdf).
1260 1261
[46] Long C.N. and Shi Y. (2008). An automated quality assessment and control
1262
algorithm for surface radiation measurements. The Open Atmospheric Science
1263
Journal 2008, 2, 23-37.
1264 1265
[47] Muneer T. 2004. Solar Radiation and Daylight models.2nd Edition. Oxford:
1266
Elsevier.
1267 1268
[48] Pashiardis S and Kalogirou S. 2016. Quality control of solar shortwave and
1269
terrestrial longwave radiation for surface radiation measurements at two sites in
1270
Cyprus. Renewable Energy 96 (2016) 1015-1033.
1271 1272
[49] de Miguel A., Bilbao J., Aguilar R., Kambezidis H., Negro E., 2001. Diffuse solar
1273
irradiation model evaluation in the North Mediterranean belt area. Solar Energy 70-2,
1274
143-153.
1275 1276
[50] Meleti H., 1999. The influence of meteorological parameters and total ozone on
1277
the measurements of ultraviolet solar radiation on the earth surface. Phd Thesis at
1278
Aristoteles University of Thesaloniki (in Greek).
1279 1280
[51] Zembila M., 2013. Climatological study of Ultraviolet Radiation in the Eastern
1281
Mediterranean. PhD Thesis at University of Thessaloniki (in Greek).
1282
56
ACCEPTED MANUSCRIPT 1283
[52] Bilbao J., Miguel A., Salvador P., 2006. UV-B solar irradiance and the influence
1284
of total ozone and aerosols at central Spain. In Conference on Visibility, Aerosols
1285
and Atmospheric Optics, Viena, September, 2006.
1286 1287
[53] Kasten F., Young AT., 1989. Revised optical air mass tables and approximation
1288
formula. Appl. Opt. 28, 4735-4738.
1289 1290
[54] Mateos D., de Miguel A., Bilbao J., 2010. Empirical models of UV total radiation
1291
and cloud effect study. International Journal of Climatology, 30, 1407-1415.
1292 1293
[55] Bilbao J., Mateos D., Yousif C., Román R., De Miguel A., 2016. Influence of
1294
cloudiness on erythemal solar irradiance in Marsaxlokk, Malta: Two case studies.
1295
Solar Energy 136, 475-486.
1296 1297
[56] Fellas A., Frederick Research Center, 2003. Skin cancer and Ultraviolet Solar
1298
Radiation: The case of Cyprus. Final Report (in Greek).
1299 1300
[57] McKenzie R. L., Liley J.B. and Björn L.O., 2009. UV Radiation: Balancing Risks
1301
and Benefits. Photochemistry and Photobiology 85, 88-98.
1302 1303
[58] Diffey L., Gibson J., Haylock R., McKinlay F., 1996. Outdoor ultraviolet exposure
1304
of children and adolescents. Br. J. Dermatol. 134, 1030-1034.
1305 1306
[59] Gies P., Roy C., MacLennan R., Watson M., 1995. UVR exposures of three
1307
groups of outdoor workers on the Sunshine Coast, Queensland. Photochem.
1308
Photobiol. 62, 1015-1021.
1309 1310
[60] Román R., Mateos D., de Miguel A., Bilbao J., Pérez-Burgos A., Rodrigo R.,
1311
Cachorro V., 2012. Atmospheric effects on the ultraviolet erythemal and total
1312
shortwave solar radiation in Vallaolid, Spain. Opt. Pura Apl. 45 (1), 17-21.
1313 1314
[61] Bilbao J., Román R., Yousif C., Mateos D., de Miguel A., 2014. Total ozone
1315
column, water vapour and aerosol effects on erythemal and global solar irradiance in
1316
Marsaxlokk, Malta. Atmos. Environ. 99, 508-518. 57
ACCEPTED MANUSCRIPT 1317 1318
[62] Bilbao J., Román R., Yousif C., Pérez-Burgos A., Mateos D., de Miguel A.,
1319
2015. Global, diffuse, beam and ultraviolet solar irradiance recorded in Malta and
1320
atmospheric component influences under cloudless skies. Solar Energy 121, 131-
1321
138.
1322 1323
[63] Cyprus Government report, taken from www.airquality.dli.mlsi.gov.cy/Reports/5
1324
Partculate Matter.pdf. 2004.
1325 1326
58
S.A. Kalogirou, S. Pashiardis, A. Pashiardi PII:
S0960-1481(17)30350-6
DOI:
10.1016/j.renene.2017.04.043
Reference:
RENE 8738
To appear in:
Renewable Energy
Received Date:
27 January 2017
Revised Date:
19 March 2017
Accepted Date:
22 April 2017
Please cite this article as: S.A. Kalogirou, S. Pashiardis, A. Pashiardi, Statistical analysis and intercomparison of erythemal solar radiation for Athalassa and Larnaca, Cyprus, Renewable Energy (2017), doi: 10.1016/j.renene.2017.04.043
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Highlights
Statistical analysis of ultraviolet erythemal radiation.
Monthly and diurnal variation of ultraviolet erythemal radiation.
Statistical relationships between ultraviolet erythemal and other radiation components, total ozone column, relative air mass, clearness index and solar zenith angle.
Calculation of UV Index.
Estimation of the cumulative doses during an average year for the four skin phototypes.
Comparison of ultraviolet erythemal radiation between two sites.
It is the first time that an analysis of this type is performed in Cyprus.
ACCEPTED MANUSCRIPT 1
Statistical analysis and inter-comparison of erythemal solar radiation for
2
Athalassa and Larnaca, Cyprus.
3 4
S.A. KALOGIROU*, S. PASHIARDIS*, * and A. PASHIARDI**
5
* Department of Mechanical Engineering and Materials Science and Engineering
6
Cyprus University of Technology, P. O. Box 50329, 3603, Limassol, Cyprus
7
Tel: +357-2500-2621, Fax: +357-2500-2637, Email: [email protected]
8
** Cyprus Statistical Services Ministry of Finance, Michael Karaoli,
9
1444 Nicosia, Cyprus
10
Abstract
11 12
A statistical analysis and inter-comparison of the erythemal ultraviolet radiation
13
(UVER) at two sites in Cyprus representing two different climate regimes of the
14
island (Athalassa-inland plain vs Larnaca-coastal location) covering the period
15
January 2013-December 2015 is presented. Mean annual and mean monthly daily
16
totals of the UVER irradiation and their frequency distribution at both sites are
17
computed and discussed. UVER irradiance fluctuates between 0.054 W m-2 in
18
December to 0.227 W m-2 in July at solar noon at Athalassa. The values at Larnaca
19
are lower than in Athalassa and they fluctuate between 0.043 W m-2 in December
20
and 0.172 W m-2 in July at solar noon. The total accumulated UVER irradiation along
21
a mean year reaches 1142 kJ m-2 at Athalassa and 909 kJ m-2. Large fluctuations of
22
the daily UVER irradiation are observed in the spring months and November, which
23
are mainly due to unstable meteorological conditions during the transition from cold
24
to warm weather and vice versa. During summer the daily UVER radiation exceeds
25
the value of 6 kJ m-2 at Athalassa and 4.8 kJ m-2 at Larnaca, while during the winter
26
season the lowest is about 0.2 kJ m-2 at both sites. Statistical relationships between
27
UVER and other radiation components (UVA, global radiation, clearness index and
28
relative optical air mass) are established. The UV Index reaches high (6-7) or very
29
high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca these
30
values are reached in 38.8%. It is observed that the cumulative doses of UVER
31
during an average year range from 9087 Standard Erythemal Dose (SEDs) in
32
Larnaca to 11418 SEDs in Athalassa. The most common skin type in Cyprus,
33
phototype III (about 70% of the population), could receive an annual cumulative dose
1
ACCEPTED MANUSCRIPT 34
between 2596 Minimum Erythemal Doses (MEDs) in Larnaca to 3262 MEDs in
35
Athalassa.
36 37
Keywords: Ultraviolet erythemal irradiance, statistical analysis, clearness index,
38
frequency distribution, transparency, statistical relationships, UV Index, cumulative
39
doses, skin phototypes, Cyprus
40 41
1. Introduction
42 43
Ultraviolet (UV) radiation covers wavelengths of the electromagnetic spectrum
44
between 100 and 400 nm and it constitutes 8.73% of the total extraterrestrial solar
45
spectrum irradiance [1]. Within the UV radiation spectrum three zones are
46
distinguished in relation to the effects that the radiation produces on living
47
organisms: UVC (100-280 nm), UVB (280-315 nm) and UVA (315-400 nm) [2]. UVC
48
does not reach the Earth’s surface since it is absorbed completely by the ozone layer
49
in the stratosphere. In the upper atmosphere, the UVB irradiance amounts to 1.3% of
50
the solar constant [1]. UVB is mostly absorbed by the ozone layer. On the other
51
hand, UVA undergoes minimal absorption by the ozone layer and it is associated
52
with photo ageing of the skin, immuno-suppression of the skin immune system and
53
potential enhancement of the negative effects of UVB exposure. UV radiation on the
54
Earth’s surface varies widely and depends mainly on latitude, solar elevation, ozone
55
column and local atmospheric conditions. The emission of certain gases due to
56
human activities is known to alter the composition of the atmosphere. Some of the
57
most serious damage caused is the reduction of the ozone layer in the stratosphere,
58
causing a corresponding increase in UV [3]. Measurements in Italy and England
59
indicate that UVB incidence increased with decreasing ozone amount at fixed solar
60
zenith angles [4-5].
61 62
Solar UV radiation, and particularly UVB, has an important influence on terrestrial
63
and marine ecosystems, being in many cases an indicator of their development due
64
to its impact over the physical and chemical conditions that allow ecosystems to
65
evolve [6-8]. The effects of UV solar radiation on human beings are mostly observed
66
on skin, the eyes (cataracts), the photo-ageing and the immune system. The effects
67
over the skin depend on the duration of the exposure to sunlight. Chronic skin 2
ACCEPTED MANUSCRIPT 68
exposure
produces
morphological
changes:
the
epidermis
turns
thicker,
69
disorganized, parakeratoric, and acanthotic [9]. Severe skin overexposure produces
70
severe sunburn that causes heat, erythema and other symptoms approximately 16
71
hours after exposure to natural sunlight [10]. Epidemiological evidence also exists of
72
the direct influence of sunlight over skin cancer in human beings [11-12]. On the
73
other hand, the benefits of human exposure to UV radiation are few. The primary
74
benefit is the need of UV for synthesizing vitamin D in the skin. This synthesis is
75
achieved with very low doses of UV radiation, such that a daily exposure of 10-15
76
min for the face, arms and hands at an intensity of the radiation received in Northern
77
Europe is sufficient [13].
78 79
The CIE (Commission Internationale de l’ Éclairage) adopted in 1987 a standard
80
erythema action spectrum [14], marginally modified in 1998 [15], which is currently
81
recommended for determining the UV erythemal radiation (UVER). UVER is
82
calculated by weighting the spectral curve of the incident solar radiation at ground
83
level with the spectral action curve proposed by CIE. The CIE spectrum of human
84
erythemal describes the energy efficiency at different wavelengths to produce the
85
particular biological effect and shows an absolute maximum at 297 nm; the UVER
86
irradiance consists of 17% UVA and 83% UVB, at the Earth’s surface [16].
87
Therefore, small changes in UVB may produce strong biological effects.
88 89
The MED (Minimum Erythemal Dose) is the minimum dose of UVER that produces a
90
noticeable reddening of a specific skin type (phototype) not exposed previously to
91
solar radiation [17]. Most countries have adopted a skin classification, which
92
considers four phototypes. Table 1 shows the main characteristics of these four
93
phototypes as well as the dose needed to produce one MED. The CIE has also
94
defined a Standard Erythemal Dose (SED) that corresponds to 100 J m-2 and does
95
not depend on the skin type.
96 97
Table 1. Skin types defined by ISO 17166 CIE S 007/E [15] Skin
Tanning
Phototype ability I
None
Sunburn
Hair color Eye color
MED (J m-2)
susceptibility High
Blond/red
3
Blue
200
ACCEPTED MANUSCRIPT II
Poor
Moderate
Blond
Blue/green
250
III
Good
Low
Brown
Grey/brown
350
IV
Very good
Very Low
Black
Brown
450
98 99
The effects of UV on skin can be quantified by the UV Index (UVI). UVI is an
100
estimation of the effectiveness of solar radiation to produce harmful effects on
101
human skin, where one unit is equal to 25 mW m-2, i.e., the UVI is quantitavely
102
obtained by multiplying the UVER value (expressed in W m-2) by 40 [18].
103 104
In spite of the important role of UVER, few radiometric stations measure it
105
systematically in the Mediterranean region. A network of UVER stations was
106
established in Greece [19-20], Spain [21-23], Israel [24-25] and Egypt [26]. In
107
Cyprus, UV (A&B) radiation is measured at Athalassa (inland) and recently at
108
Larnaca (coastal place) [27]. UVER is measured at the above two sites since 2013.
109 110
Various authors have analyzed the relation between solar UVER and global radiation
111
[22-24, 28]. Moreno et al. [29] studied the effect of the relative optical air mass and
112
the clearness index on UVER values in Valencia in the period 2003-2012. Kudish
113
and Evseev [30] analyzed UVB radiation as a function of solar global radiation,
114
ozone layer thickness and aerosol optical density in Beer Sheva (Israel). De Miguel
115
et al. [31] have studied the evolution of erythemal and total shortwave solar radiation
116
as a function of atmospheric factors in Valladolid (Central Spain). Esteve et al. [32]
117
have studied the influence of cloudiness over the values of UVER in Valencia
118
(Spain).
119 120
In recent decades, radiative transfer and theoretical models have been developed
121
that can be used to predict UVER radiation or UVI [e.g., 33-34]. Neural networks are
122
also applied for the estimation of UV erythemal irradiance [35]. Some authors use
123
empirical models, which are simpler and more manageable and understandable [36-
124
37]. The European Cooperation in Science and Technology (COST)-Action 713 has
125
tested a number of models for UVB forecasting using multiple scattering models
126
rather than radiative transfer models [38]. The results of these simulations were also
127
published in the final report of that COST Action [39]. More recently, the CEAM 4
ACCEPTED MANUSCRIPT 128
Foundation in Valencia (Spain) has developed an operational UVI forecasting
129
system based on the Santa Barbara DISORT Atmospheric Radiative Transfer
130
(SBDART) model [40].
131 132
An assessment of the solar radiation climate of the Cyprus environment was
133
presented by Jacovides et al. in 1993 [41]. Petrakis et al. [42] presented the ‘Typical
134
Meteorological Year’ for Nicosia. More recently, Kalogirou et al. [43] presented a
135
statistical analysis and inter-comparison of the solar global radiation at the same
136
sites as in this study, using measurements of 21 months at both sites. The common
137
feature of all the above studies is that they rely mostly on measurements of solar
138
radiation carried out at the actinometric stations of Athalassa and Larnaca.
139 140
The interest of this paper is that similar data series (UVER) have not been recorded
141
before and no similar work has previously been done in Cyprus. This work
142
constitutes the first UVER analysis in the island of Cyprus, which is also essential
143
because of the fact that the atmospheric conditions in the area favor dry summers
144
and cold winters, high air temperatures and low vapor pressure values at midday in
145
summer time, which affect the transmission of UVER through the atmosphere. In this
146
work we analyze hourly UVER and global irradiance data on a horizontal plane and
147
perform an inter-comparison study between the two locations in Cyprus as well as
148
between other sites in the Mediterranean region. Additionally, UVER measurements
149
have been used to estimate UVI and the cumulative doses for the four skin
150
phototypes are also considered here.
151 152
2. Materials and methods
153 154
The radiation data on which this study is based are being monitored at two
155
meteorological stations: one located at Athalassa, an inland plain location and the
156
other one at Larnaca Airport near the coast. The site parameters of the two stations
157
are listed in Table 2.
158 159 160 161 5
ACCEPTED MANUSCRIPT 162
Table 2. Site parameters for the two meteorological stations Site
Location
Latitude
Longitude
Altitude (m, m.s.l)
Athalassa
inland
35.1410 N
33.3960 E
165
Larnaca
coastal
34.8730 N
33.6310 E
1
163 164
The two sites are characterized by relatively high global horizontal and beam
165
horizontal radiation intensities. The average annual sunshine duration is 3332 hours
166
for Athalassa and slightly higher at Larnaca (3368 h). The annual average daily
167
global radiation exceeds 18.5 MJ m-2 at the two sites, whereas the average beam
168
horizontal radiation is 13.1 MJ m-2 for Athalassa and 14.2 MJ m-2 for Larnaca,
169
respectively. Consequently, the fraction of the beam component of the global
170
radiation is relatively high at both sites, viz., the annual average daily fraction is
171
>0.600 at the two sites. Comparing the two sites it seems that Larnaca has slightly
172
higher rates of global radiation than Athalassa, since the average yearly cumulative
173
global irradiation is 6835 MJ m-2 for Athalassa and 7183 MJ m-2 for Larnaca. The
174
monthly average frequency of days according to the classification of the magnitude
175
of the daily clearness index KT (daily global to daily extraterrestrial radiation), shows
176
that both clear and partially cloudy days exceed 90% annually (KT >0.35) [43].
177 178
The period for presenting the data at both stations is January 2013 to December
179
2015 (i.e., 3 years), when both stations operated simultaneously, so as to allow for
180
comparison of the different variables of solar and terrestrial radiation. Measurements
181
of total solar irradiance on a horizontal surface were taken with Kipp & Zonen CM11
182
pyranometers whose spectral range is from 285 to 2800 nm. Both stations are
183
equipped with Kipp & Zonen UVS-E-T broadband radiometers with a spectral range
184
of 280 to 315 nm (UVB) and 315 to 400 nm (UVA). The radiometers have directional
185
response up to 70° solar zenith angle (θz) less than 2.5%. All the sensors are factory
186
calibrated, in accordance with the World Radiometric Reference (WRR). Global
187
radiation instruments were calibrated outdoor against standard references at
188
irregular time intervals during the study period. The errors involved in the radiation
189
measurements were found to be no less than ±2% for the normal incidence beam
190
irradiance and ±3% for the global irradiance.
191 6
ACCEPTED MANUSCRIPT 192
A Campbell Scientific Instruments data-logger, located at each site (Model CR10),
193
monitors and stores the data at 10-min intervals (the radiometers are scanned every
194
10 seconds and average, maximum, minimum and instantaneous values at 10-min
195
intervals are calculated and stored). The stored data are downloaded to a desktop
196
computer periodically. The data refer to the Local Standard Time (LST=GMT+2).
197
About 5% of the data values are missing because of some problems with the
198
instruments and some defects and maintenance in the data acquisition systems. The
199
validity of the individual measurements was checked in accordance with the WMO
200
recommendations [44] and other tests proposed by various authors [45-47]. Details
201
about the quality control procedures used in this study are given by Pashiardis and
202
Kalogirou [48]. All data that do not meet the conditions specified by the suggested
203
tests were not used in the study.
204 205
Regarding the UVER irradiance the following upper limit was applied as suggested
206
by de Miguel et al. [49] in a similar way as the UVB quality control process:
207 208
UVER 1.2*UVER0
(1)
209 210
where, UVER is the measured value and UVER0 is the horizontal extraterrestrial
211
solar UVER irradiance ( GscUVER 9.89 W m-2 ), which was obtained from Tena et al.
212
[22]. The measurements of both stations were less than the horizontal extraterrestrial
213
solar UVER0 irradiance during the whole period of measurements. Occasionally,
214
night values were detected, which were excluded from the database. No other errors
215
were found. Long periods of missing data were detected during the period 1st
216
January – 18th February 2013 at Larnaca due to instability of the recording system.
217
However, only 10 missing days were recorded at Athalassa.
218 219
Regarding the quality control of the daily UVER radiation data, daily values were
220
rejected in case of incomplete data during the day. The time series plots of the daily
221
values of UVER irradiation for both stations are shown in Figure 1. The figure
222
indicates that the ascent during the first months of each year is very irregular with
223
fluctuations, while the descent is smoother. During summer the daily UVER radiation
224
exceeds the value of 6 kJ m-2 at Athalassa and 4.8 kJ m-2 at Larnaca, while during 7
ACCEPTED MANUSCRIPT 225
the winter season the lowest is about 0.2 kJ m-2 at both stations. Slightly lower
226
values were recorded in the year 2015 at both stations, which may be attributed to
227
higher amounts of aerosols in the atmosphere. The year 2015 is characterized as an
228
extremely dry year with more frequent dust episodes over the island (dust from the
229
deserts of Middle East and Sahara), increasing, therefore, the aerosols in the
230
atmosphere, which affect the absorption of the UVER radiation. It should be noted
231
that UV is mostly influenced by Rayleigh scattering than Mie one.
232
233 234
Fig. 1. Time series plot of daily UVER solar irradiation during the period 2013-2015
235
at Athalassa and Larnaca. Days start counting from January 1, 2013.
236 237
3. Results and discussion
238 239
3.1 Daily values
240 241
Global solar radiation and total UVER radiation have been analyzed and compared
242
in this study. Figure 2a shows the temporal evolution of daily UVER and global solar
243
irradiation at Athalassa. A similar graph with slightly lower values was obtained at
244
Larnaca (Fig.2b). Data reveal a common evolution shape with maxima in summer 8
ACCEPTED MANUSCRIPT 245
and minima in winter, mainly due to the daily minimum solar zenith angle and day-
246
length (astronomical factors) variation during the year. Large fluctuations in the
247
spring months and November are mainly due to unstable meteorological conditions
248
during the transition from cold to warm weather and vice versa. The maximum of
249
daily global solar horizontal irradiation is reached in June or July and it is around 31
250
MJ m-2 at Athalassa and around 32 MJ m-2 at Larnaca.
251 252
Fig. 2. Co-variability of daily measured UVER values (UVERd) and daily global
253
horizontal solar irradiation (Gd) during the period 2013-2015 at a) Athalassa and b) at
254
Larnaca. Days start counting from January 1, 2013.
255 256
The mean value of UVER for each day and the mean daily value of UVER over a
257
month have been calculated; Figure 3a shows the results for both stations. The
258
mean value of UVER was obtained by simply calculating the mean value for each
259
day of the year. Fourth order polynomial regression equations are fitted to describe
260
the relationship between the mean value of UVER for each day and Julian days (jd)
261
(1..365) for Athalassa and Larnaca (Eqs. 2-3):
262 263 264 265
UVERd 1.44946 0.02694 jd 0.00083 jd 2 4.0967*106 jd 3 5.561*109 jd 4 (2) UVERd 1.10756 0.01745 jd 0.00062 jd 2 3.1396*106 jd 3 4.312*109 jd 4 (3) 9
ACCEPTED MANUSCRIPT 266 267
The daily values present a greater fluctuation in spring. It can be seen that the
268
variation in the monthly mean values (continuous smooth line) is quite regular, with
269
the maximum values taking place in June/July and the minimum in December. Daily
270
UVER increases in spring to summer at a lower rate than that of the decrease in
271
autumn. The different slopes can be explained by the total ozone effects. During the
272
summer months, when solar zenith angle (SZA) leads to high UVER irradiance, the
273
total ozone column (TOC) is declining; this effect causes UVER to get maximum
274
levels from June to July (Fig. 3b). The time series of the mean daily values of TOC
275
during the study period were obtained from the satellite instrument MODIS
276
(http://giovanni.sci.gsfc.nasa.gov/giovanni/#service=ArAvTs). The peak TOC value is
277
recorded in April and its minimum in November, while the maximum of the midday
278
hour of cos(SZA) is observed in June and its minimum in December.
279
280 281
Fig. 3a. Annual evolution of daily and monthly UVER irradiation values (kJ m-2) at
282
Athalassa and Larnaca, during the period 2013-2015.
283 284
10
ACCEPTED MANUSCRIPT
285 286
Fig. 3b. Annual cycle of monthly mean TOC in Dobson Units (DU) and the mean of
287
the cosine of the midday SZA.
288 289
Table 3 shows the statistical characteristics of daily UVER data for all-sky conditions.
290
The Table shows the following statistical parameters: number of observations (N),
291
arithmetic mean (Mean), standard deviation (StDev), coefficient of variation in
292
percent (CoefVar), minimum (Min), the first and third quartiles (Q1 and Q3), median,
293
maximum (Max), inter quartile range (IQR), percentiles (P5 and P95), skewness and
294
kurtosis coefficients (As and K) and the type of distribution obtained from the last two
295
coefficients (Table 4) [25]. The median values are mainly slightly higher than the
296
average ones; the maximum of the standard deviation occurs in May, while the
297
coefficient of variation shows the lowest values in the summer months, which means
298
that higher stability is observed in these months. The differences between the Min
299
and P5 values are quite high, and therefore, the minimum values correspond to
300
unusually extreme values. On the other hand, the differences between the Max and
301
P95 values are small. The observed daily maximum occurs in June at both stations
302
(6.164 kJ m-2 at Athalassa and 4.863 kJ m-2 at Larnaca). The mean daily UVER for
303
the whole year is 3.126 kJ m-2 for Athalassa and 2.552 kJ m-2 for Larnaca. The
304
variability of the daily UVER irradiation is also demonstrated with the graph of 11
ACCEPTED MANUSCRIPT 305
boxplots for each month of the year. The boxplot presents the Median and the IQR
306
as well as the outliers of the daily values of UVER irradiation for both stations (Fig.
307
4). The smooth line represents the mean daily values of each month. As indicated in
308
the graphs, the spring season shows the greatest variability. The presence of the
309
minimum values as outliers in most of the months of the year confirms the statement
310
that the minimum values correspond to unusually extreme ones.
311 312
Type I frequency distributions curves, i.e., normal distribution, characterize the daily
313
erythemal radiation intensities for the months of February, April, August and
314
November at Athalassa. The most frequent distribution at Athalassa is Type IV,
315
which is almost normal with negative tail (January, March, June, September, October
316
and December). May and July are of Type V, which is a distribution with narrow peak
317
and negative tail. Almost similar distributions are observed at Larnaca. Type I is
318
recorded in February, August and November and the most frequent distribution is
319
again Type IV (January, March, April, July and October). May, September and
320
December are of Type V, while June is Type VI (bimodal, symmetrical with flat
321
peak).
322 323
The monthly mean daily values of the two stations are compared to the respective
324
values of other Mediterranean sites (Fig. 5) [23-25, 50]. It is observed that the curves
325
of the monthly mean daily values follow a sinusoidal evolution, with a minimum in
326
December and a maximum in June or July. As indicated in the graph the highest
327
values are recorded in Beer Sheva (Israel) with the second ones at Athalassa, as
328
expected, since these stations are at lower latitude and have higher sunshine
329
duration comparing to other stations. The coastal sites (Larnaca, Kos, Athens,
330
Thesaloniki, Neve Zohar and Valencia) have almost similar levels of erythemal
331
irradiation, in contrast to the inland locations (Athalassa and Beer Sheva), which
332
have higher levels of UVER. The differences between the inland and coastal
333
locations are more pronounced during the summer period.
334 335
12
ACCEPTED MANUSCRIPT
336 337
338 339
Fig. 4. Boxplots of the daily UVER irradiation (kJ m-2) for each month of the year at
340
a) Athalassa and b) Larnaca. The boxplot shows the IQR and the Median values;
341
the asterisks denote the outliers. The smooth line represents the mean daily values
342
of each month. 13
ACCEPTED MANUSCRIPT 343 344
Table 3. Statistical estimators of the daily UVER (kJ m-2) for the period 2013-2015 at
345
a) Athalassa and b) Larnaca
346
a) Athalassa
Month
N
Mean
StDev
CoefVar(%)
Min
Q1
1
93
1.186
0.360
30.33
0.224
0.891
2
84
1.806
0.494
27.38
0.788
3
93
2.641
0.692
26.20
4
90
3.542
0.836
23.60
5
90
4.252
0.976
6
89
5.254
7
92
8
93
9
Median
Q3
Max
IQR
P5
P95
As
K
Distr. Type
1.242
1.486
1.743
0.596
0.499
1.692
-0.46
-0.59
IV
1.532
1.765
2.152
2.894
0.620
0.890
2.613
-0.02
-0.36
I
0.353
2.144
2.677
3.169
3.969
1.026
1.375
3.748
-0.47
0.39
IV
1.613
2.987
3.628
4.118
5.103
1.131
1.885
4.808
-0.38
-0.40
I
22.95
0.848
3.777
4.512
4.886
5.712
1.109
2.203
5.359
-1.36
2.10
V
0.664
12.63
3.478
4.824
5.444
5.796
6.164
0.972
3.774
6.024
-0.86
0.03
IV
5.495
0.361
6.58
4.083
5.314
5.562
5.756
6.144
0.442
4.748
6.003
-1.04
1.88
V
4.805
0.419
8.71
3.731
4.515
4.871
5.043
5.669
0.528
3.966
5.552
-0.29
-0.03
I
90
3.523
0.575
16.32
1.666
3.186
3.597
3.980
4.646
0.793
2.403
4.312
-0.70
0.44
IV
10
93
2.441
0.537
21.99
1.003
2.058
2.559
2.842
3.322
0.783
1.431
3.192
-0.57
-0.21
IV
11
89
1.472
0.298
20.26
0.479
1.300
1.480
1.664
2.071
0.363
0.934
1.985
-0.34
0.67
I
12
91
1.036
0.282
27.25
0.221
0.935
1.112
1.240
1.438
0.304
0.427
1.350
-1.16
0.63
IV
Year
1087
3.126
1.631
52.18
0.221
1.574
2.968
4.632
6.164
3.057
0.890
5.706
0.16
-1.30
VI
Q3
Max
IQR
P5
P95
As
K
Distr. Type
347 348
b) Larnaca
Month
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
1
62
0.956
0.244
25.56
0.316
0.836
0.993
1.137
1.371
0.301
0.417
1.289
-0.80
0.28
2
66
1.517
0.385
25.39
0.601
1.267
1.493
1.864
2.315
0.597
0.836
2.152
-0.05
-0.41
I
3
93
2.136
0.532
24.90
0.418
1.820
2.165
2.477
3.313
0.657
1.104
3.060
-0.47
0.66
IV
4
90
2.902
0.625
21.53
1.242
2.620
2.972
3.377
4.070
0.757
1.516
3.777
-0.77
0.44
IV
5
93
3.507
0.639
18.23
0.773
3.296
3.650
3.898
4.489
0.603
2.403
4.216
-1.97
5.79
V
6
90
4.187
0.432
10.33
3.335
3.898
4.201
4.581
4.825
0.683
3.371
4.773
-0.34
-0.94
VI
7
93
4.240
0.309
7.29
3.149
4.006
4.253
4.444
4.863
0.438
3.732
4.753
-0.47
0.64
IV
8
93
3.705
0.297
8.03
3.069
3.492
3.703
3.909
4.336
0.417
3.248
4.253
0.14
-0.58
I
9
90
2.855
0.542
18.97
0.364
2.605
2.820
3.266
3.743
0.661
1.830
3.594
-1.33
4.27
V
10
93
1.892
0.417
22.03
0.868
1.619
1.921
2.216
2.650
0.596
1.122
2.439
-0.44
-0.36
IV
11
90
1.093
0.221
20.20
0.462
0.932
1.083
1.266
1.499
0.335
0.720
1.449
-0.27
-0.12
I
12
93
0.826
0.183
22.11
0.224
0.754
0.872
0.940
1.089
0.186
0.391
1.045
-1.29
1.45
V
Year
1046
2.552
1.269
49.72
0.224
1.289
2.574
3.691
4.863
2.402
0.793
4.476
0.02
-1.35
VI
349 350
Table 4. Definition of the frequency distribution type as a function of the range of the
351
skewness and kurtosis values obtained from [25]. Distribution Distribution Curve
Skewness (As)
Kurtosis (K)
Type No. I
Normal
-0.4 < As < 0.4
-0.8 < K < 0.8
II
Almost normal with positive tail
As ≥ 0.4
-0.8 < K < 0.8
14
IV
ACCEPTED MANUSCRIPT III
Narrow peak with positive tail
As ≥ 0.4
K ≤ -0.8 K ≥ 0.8
IV
Almost normal with negative tail
As ≤ -0.4
-0.8 < K < 0.8
V
Narrow peak with negative tail
As ≤ -0.4
K ≥ 0.8
VI
Bimodal, symmetrical with flat -0.4 < As < 0.4
K ≤ -0.8
peak 352 353
354 355
Fig. 5. Monthly mean daily UVER (kJ m-2) at various sites in the Mediterranean area.
356 357
It is also interesting to know the statistics of the daily UVER radiation obtained from
358
different daily global radiation thresholds, since most of the actinometric stations
359
measure global radiation. Table 5 presents the results of the above classifications. At
360
Athalassa, the most frequent cases occurred in the bins of 10-12 MJ m-2 of daily
361
global irradiation followed by the bins of 26-28 and 28-30 MJ m-2. At Larnaca, the
362
most frequent cases occurred in the bins of the range 24-30 MJ m-2 of daily global
363
irradiation. The mean and the median values of UVER irradiation are almost similar
364
at both stations. It is estimated that the UVER irradiation is about 0.016% of the
15
ACCEPTED MANUSCRIPT 365
global one at Athalassa (inland location) and about 0.012% at Larnaca (coastal
366
location).
367 368
Table 5. Statistics of daily UVER irradiation (kJ m-2) based on various thresholds of
369
daily global radiation (MJ m-2) for the period of measurements for a) Athalassa and
370
b) Larnaca.
371
a) Athalassa Ath_Daily Global Radiation Bin End (MJ m-2) Lower Upper 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18 18 20 20 22 22 24 24 26 26 28 28 30 30 32
UVER (kJ m-2) Occurrences 4 14 25 41 59 119 90 72 81 64 76 79 91 110 106 18
Mean Median 0.258 0.503 0.770 0.964 1.187 1.445 1.730 2.161 2.623 3.031 3.520 4.036 4.511 5.018 5.523 5.866
0.234 0.479 0.788 0.951 1.159 1.383 1.684 2.081 2.595 3.030 3.586 4.063 4.632 5.103 5.631 5.904
Min
Max
Std. Dev.
0.221 0.395 0.568 0.677 0.935 1.000 1.320 1.605 2.119 2.021 2.637 3.010 3.226 3.629 4.011 5.330
0.353 0.848 1.156 1.236 1.693 2.251 2.847 2.944 3.625 3.906 4.487 4.996 5.206 5.672 6.023 6.164
0.064 0.119 0.137 0.124 0.161 0.256 0.287 0.345 0.300 0.320 0.416 0.470 0.471 0.441 0.399 0.239
Min
Max
Std. Dev.
0.224 0.362 0.470 0.620 0.364 0.798 0.871 1.191 1.417 1.589 2.069
0.316 0.566 0.892 1.200 1.242 1.660 2.013 2.134 2.650 2.980 3.274
0.051 0.062 0.155 0.109 0.128 0.169 0.217 0.226 0.268 0.278 0.251
372 373
b) Larnaca Lca_Daily Global Radiation Bin End (MJ m-2) Lower Upper 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18 18 20 20 22
UVER (kJ m-2) Occurrences 3 12 11 37 52 88 94 60 58 64 77
Mean Median 0.282 0.440 0.631 0.786 0.886 1.044 1.245 1.581 1.910 2.226 2.527
16
0.307 0.429 0.601 0.772 0.875 1.006 1.211 1.541 1.921 2.175 2.532
ACCEPTED MANUSCRIPT 22 24 26 28 30 32
24 26 28 30 32 34
62 91 114 137 85 1
2.934 3.331 3.661 4.027 4.362 4.436
2.912 3.361 3.685 3.987 4.361 4.436
2.306 2.455 2.654 3.087 3.466 4.436
3.650 3.895 4.418 4.808 4.863 4.436
0.329 0.285 0.357 0.364 0.313 0.000
374 375
3.2. Analysis of accumulated UVER irradiation
376 377
In studies on the biological effects of UVER, we require the accumulated UVER solar
378
irradiation (kJ m-2) through a period of time. The accumulated values of UVER
379
irradiation are also important for vitamin-D synthesis production. Figure 6 shows the
380
accumulated hourly UVER irradiation values for an average day of each month; the
381
last value is the daily total.
382 383
It can be seen that the highest value for UVER irradiation was produced in July, with
384
a daily average of 5.5 kJ m-2 for Athalassa, and 4.24 kJ m-2 for Larnaca. On the other
385
hand, in December the average irradiation received was minimal (1.04 kJ m-2 at
386
Athalassa and 0.85 kJ m-2 at Larnaca). The accumulated irradiation received in an
387
average year is 1142 kJ m-2 for Athalassa and 909 kJ m-2 for Larnaca (Fig. 7). The
388
seasonal distribution of UVER radiant exposure is shown in Table 6. The highest
389
values are recorded in summer with the second higher one in spring.
390
17
ACCEPTED MANUSCRIPT
391 392 393
394 395
Fig.6. Accumulated UVER irradiation (kJ m-2) for an average day for the period 2013-
396
2015 at a) Athalassa and b) Larnaca.
397 18
ACCEPTED MANUSCRIPT 398
Table 6. Seasonal totals of UVER radiant exposure (kJ m-2) for Athalassa and
399
Larnaca. Season
Athalassa
Larnaca
Spring
320.0
262.0
Summer
477.0
371.9
Autumn
225.5
177.1
Winter
119.4
97.7
Annual
1141.9
908.7
400 401
402 403
Fig.7. UVER radiant exposure accumulated during an average year (kJ m-2) at
404
Athalassa and Larnaca.
405 406
3.3 Frequency of daily UVER irradiation
407 408
The type of the frequency distribution of the daily UVER radiation was presented in
409
section 3.1. The cumulative density functions (CDF) of the daily UVER irradiation for
410
both stations are shown in Fig. 8. The figure indicates that in about 65% of the year,
411
the daily sums of UVER irradiation at Athalassa are below 4 kJ m-2, while at Larnaca 19
ACCEPTED MANUSCRIPT 412
for the same value the probability is about 85%. It can also be estimated that about
413
30% of the days of the year have values of daily sum within the range of 3 to 5 kJ m-
414
2
at Athalassa and between 2 and 4 kJ m-2 at Larnaca.
415
416 417
Fig. 8. Annual cumulative frequency distribution of daily UVER irradiation at a)
418
Athalassa and b) Larnaca.
419 420
3.4. Statistical analysis of hourly UVER irradiance
421 422
A statistical study of the most representative UVER indices for each month of the
423
year has been carried out and the UVER accumulated values have been evaluated
424
because they are very useful in studies of effects on human beings.
425 426
Tables 7a and 7b show the hourly statistical estimators of mean hourly UVER
427
irradiance, for July for both stations, while Table 7c presents only the statistics of
428
December at local solar noon for both stations. These months usually present the
429
highest and lowest values of UVER, following the annual evolution of TOC, which
430
shows a maximum in the spring months (April-May) and a minimum in November
431
[51]. The peak at solar noon represents the maximum daily value and, therefore,
432
only the time of the solar noon is selected for the statistics of December (Table 7c)
433
(see section 3.9 on UVI). The statistical parameters presented in the Table are the
434
same as those used for daily statistics (Table 3). In order to understand the 20
ACCEPTED MANUSCRIPT 435
behaviour of the maximum values of UVER, which will be used later to estimate UVI,
436
the most representative statistics of UVER, which were obtained mainly at local
437
noon, will be discussed. It can be observed that the median values are almost similar
438
to the average ones, which suggest that the average hourly UVER distribution is
439
approaching the normal curve.
440 441
In July, the absolute maxima of the UVER measured at local noon vary from 195.3
442
mW m-2 in Larnaca to 248.8 mW m-2 in Athalassa, whereas the absolute minima
443
range between 140.8 mW m-2 and 188.0 mW m-2, respectively. The difference (in
444
percentage) between the absolute maxima and the P95 percentiles is around 2% at
445
both locations. These values are systematically lower than the difference observed
446
between the absolute minima and the P5 percentiles, which varies between 7%
447
(Athalassa) and 8% (Larnaca). The absolute extreme values have also been
448
compared with their corresponding quartile values to verify if they are representative
449
of the UVER records for the measuring sites. The difference between the Q1
450
quartiles and the absolute minima is around 14% at both sites, whereas the
451
difference between the Q3 quartiles and the absolute maxima varies between 6%
452
(Athalassa) and 7% (Larnaca). Therefore, although the maximum values can be
453
considered representative of the UVER at local noon in July, the minimum values
454
represent unusual extreme values for this month. The maximum values of UVER
455
recorded in Cyprus are comparable with those in Israel [25], in Valladolid (Spain) [31]
456
and in Greece [50].
457 458
In December, the values of the absolute maximum measured at local noon range
459
from 57.0 mW m-2 in Larnaca to 77.3 mW m-2 in Athalassa, whereas the values of
460
the absolute minimum are almost similar at both stations (around 8 mW m-2) (Table
461
7c). As it happened for July, the difference between the absolute maxima and the P95
462
percentiles is systematically lower than that observed between the absolute minima
463
and the P5 percentiles. These differences vary between 4.2% (Larnaca) and 7.2%
464
(Athalassa) for the absolute maxima and P95 percentiles, and between 46%
465
(Athalassa) and 55% (Larnaca) for the absolute minima and the P5 percentiles. The
466
comparison of the extreme values with their corresponding quartiles shows a
467
variation between 81% (Larnaca) and 84% (Athalassa) for the difference between
468
the Q1 quartiles and the absolute minima, whereas the difference between the Q3 21
ACCEPTED MANUSCRIPT 469
quartiles and the absolute maxima ranges from 13.7% (Larnaca) to 15.3%
470
(Athalassa). Thus, as it happened for July, the maximum values can be considered
471
representative of the UVER at local noon in December, while the minimum values
472
may be considered as unusual extreme values.
473 474
The UVER variability has been studied by means of the coefficient of variation
475
(CoefVar). As it can be seen in Table 7, the CVs in July are low during midday (5-
476
10%) at both stations, indicating a high stability along these hours in summer.
477
Furthermore, CoefVars fluctuate between 5 and 16% at Athalassa, while at Larnaca
478
they are slightly higher (5-27%). The standard deviation is higher along midday
479
hours and symmetrically distributed around solar noon during the summer months.
480
This could be explained by a minor presence of clouds in the summer months that
481
lead to a high stability of the atmosphere.
482 483
Table 7. Statistical estimators of the mean hourly UVER irradiance (mW m-2), in July,
484
under all-sky conditions for the period 2013-2015, at a) Athalassa and b) Larnaca.
485
a) Athalassa
Hour
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
Q3
Max
IQR
As
K
P5
P95
Dly UVER (%)
6
93
9.46
1.31
13.80
5.33
8.67
9.33
10.33
12.25
1.67
-0.23
0.31
7.3
11.80
1
7
93
25.08
3.43
13.66
13.83
23.08
25.17
27.17
32.50
4.08
-0.26
0.42
19.7
31.30
2
8
92
59.49
5.97
10.03
42.50
55.67
59.92
63.67
71.50
8.00
-0.27
-0.08
49.1
69.80
4
9
92
107.87
7.86
7.29
84.67
102.87
108.25
113.46
124.17
10.58
-0.26
0.12
94.5
121.20
7
10
92
160.14
10.07
6.29
118.67
154.42
160.58
166.46
180.33
12.04
-0.72
2.12
143.5
176.10
10
11
92
203.55
10.68
5.25
166.00
196.87
203.92
210.92
226.17
14.04
-0.47
0.96
184.9
220.80
13
12
92
226.60
11.22
4.95
188.00
219.13
227.08
234.33
248.83
15.21
-0.63
0.91
202.9
243.70
15
13
92
222.37
15.40
6.93
155.17
217.17
226.08
232.00
247.50
14.83
-1.94
4.82
182.1
238.20
15
14
92
191.26
19.89
10.40
113.50
188.04
198.00
203.21
215.83
15.17
-2.09
4.43
146.5
209.40
13
15
92
142.50
23.72
16.65
55.00
140.88
150.83
156.42
164.00
15.54
-2.31
4.99
78.1
161.10
9
16
92
95.19
12.96
13.62
19.83
91.67
99.08
101.96
108.50
10.29
-3.10
13.18
67.2
106.20
6
17
92
52.32
4.75
9.08
29.17
50.54
53.33
55.00
58.83
4.46
-2.02
6.28
43
58.10
3
18
92
21.39
1.89
8.84
13.17
20.33
21.50
22.79
25.00
2.46
-1.04
2.81
18.3
24.00
1
19
92
9.23
0.98
10.64
6.00
8.63
9.00
10.00
11.00
1.38
-0.82
1.32
7.7
10.50
1
486 487
b) Larnaca
Hour
N
Mean
StDev
CoefVar(%)
Min
Q1
Median
Q3
Max
IQR
As
K
P5
P95
Dly UVER (%)
6
93
6.21
1.40
22.56
3.50
5.17
6.00
7.25
9.40
2.08
0.62
-0.45
4.5
9.2
1
7
93
16.88
4.64
27.46
10.50
13.17
15.17
21.58
27.67
8.42
0.72
-0.82
11.5
25.7
1
8
93
41.94
8.72
20.79
26.50
35.33
39.83
50.92
60.83
15.58
0.50
-0.94
31.1
57.4
4
9
93
77.81
12.08
15.52
49.67
68.92
74.50
89.67
102.00
20.75
0.32
-0.89
62.2
98.9
7
22
ACCEPTED MANUSCRIPT 10
93
117.93
13.85
11.74
82.17
107.50
116.00
130.92
143.67
23.42
0.10
-0.83
98.2
141.2
10
11
93
152.13
13.87
9.12
113.33
140.83
151.17
164.08
177.83
23.25
-0.07
-0.67
131.5
174.5
13
12
93
172.02
12.08
7.02
140.83
162.17
172.33
181.33
195.33
19.17
-0.14
-0.69
153.2
191.5
15
13
93
172.47
9.10
5.28
151.33
165.83
174.00
178.67
190.83
12.83
-0.23
-0.65
156.3
186.3
15
14
93
153.50
7.22
4.70
134.17
149.00
153.83
159.00
169.50
10.00
-0.27
0.03
139.7
165.9
13
15
93
119.59
9.15
7.65
54.17
116.17
119.67
124.42
135.33
8.25
-3.98
27.82
108.8
129.5
10
16
93
79.42
7.74
9.74
40.00
76.00
80.00
84.58
92.00
8.58
-1.90
7.26
66.2
89.7
7
17
93
41.45
4.85
11.71
28.00
37.92
41.00
44.83
50.67
6.92
-0.02
-0.48
33.6
50.0
4
18
93
18.80
2.77
14.73
7.83
16.67
19.00
21.17
23.00
4.50
-0.75
1.13
14.6
25.0
2
19
84
8.53
0.97
11.42
6.00
8.00
8.50
9.00
11.00
1.00
-0.29
0.21
7.0
10.0
1
488 489
Table 7c. Statistical estimators of the mean hourly UVER irradiance (mW m-2), in
490
December at solar noon for each location.
Station
N
Mean
StDev
CoefVar(%)
Min
Q1
Q3
Max
IQR
As
K
P5
P95
Athalassa
91
54.34
17.07
31.41
8.00
49.67
Median 59.50
65.50
77.33
15.83
-1.24
0.58
14.80
71.60
Larnaca
93
42.67
10.39
24.35
7.67
39.58
45.83
49.17
57.00
9.58
-1.56
2.32
17.10
54.60
491 492
The sun’s UVER rays are strongest in the six-hour period (10 to 15) around local
493
noon when 75% of a summer day UVER is received. Tables 7a and 7b summarize
494
the percentage of UVER radiation present at different times during a summer day.
495 496
3.5 Analysis of monthly average hourly UVER irradiance
497 498
The daily variation of the average hourly UVER irradiance is shown in Fig. 9. The
499
figure shows that the hourly average UVER irradiance fluctuates between 0.054 W
500
m-2 in December and 0.227 W m-2 in July at solar noon at Athalassa. The values at
501
Larnaca are lower than in Athalassa and they fluctuate between 0.043 W m-2 in
502
December and 0.172 W m-2 in July at solar noon. A high symmetry is also observed
503
around the months of June or July when the irradiance reaches its maximum, while it
504
decreases in spring and autumn and reaches its minimum in winter months. The
505
results can be explained taking into account the symmetry relation between the
506
summer and winter solstices.
507 508
According to measurements obtained from instruments of MODIS, the TOC reaches
509
its maximum value at Athalassa in April (Monthly Mean TOC=345 D.U.) and its
510
minimum value in November (Monthly Mean TOC=285 D.U.) Similar results were
511
obtained by Zerefos et al. [19] and by Bilbao et al. [52], with the maximum occurring 23
ACCEPTED MANUSCRIPT 512
in April in the Northern Hemisphere. Figure 9 shows that the results are quite in
513
accordance with ozone evolution; comparing March and September, when the solar
514
declination is about zero, it can be seen that the UVER hourly values, due to an
515
ozone decrease, are higher in September than in March.
516 517
Fig.9. Daily evolution of the monthly mean hourly UVER irradiance (W m-2) for the
518
period 2013-2015 at a) Athalassa and b) Larnaca.
519 520
3.6. Relationship between UVER and other radiation components
521 522
It can be useful to estimate UVER irradiance based on UVB, UVA and global
523
irradiances. The relationship between UVER and UVB is linear, since UVER consists
524
of 83% of UVB irradiance. The correlation between the data have been analysed by
525
assuming relations of the following empirical forms:
526 527 528
Y aX b
(4)
529
Y c dX eX 2
(5)
530 531
Table 8 shows the values of the fit parameters for Eqns. (4) and (5) as well as the
532
coefficient of determination, R 2 , for the hourly (W m-2) and daily values (kJ m-2) for 24
ACCEPTED MANUSCRIPT 533
both stations. The characteristic of these relationships is that R2 are close to 1. For
534
the model of Eq. (4) the fit of the result is given by the parameter S, which is the
535
standard error of the regression. S is measured in the units of the response variable
536
and represents the standard distance about the regression line where the data
537
values fall within, or the standard deviation of the residuals. For a given study, higher
538
S values indicate lower performance of the fitted curves. From Table 8a, it is
539
indicated that the results are more satisfactory for estimating UVER from UVB and
540
UVA, rather than from the global irradiance, although they continue to be acceptable
541
in the latter case. Similar results were obtained for the estimation of the daily values
542
of UVER (Table 8b). Generally, the constants of the equations of the two stations are
543
comparable.
544 545
Table 8a. Relationships between hourly UVER irradiance (W m-2) and UVB, UVA
546
and global (G) irradiance (W m-2) at both stations. Variable y UVER_Ath
Variable x UVA_Ath
UVER_Lca
UVA_Lca
UVER_Ath UVER_Lca UVER_Ath
UVA_Ath UVA_Lca G_Ath
UVER_Lca
G_Lca
UVER_Ath
G_Ath
UVER_Lca
G_Lca
UVER_Ath UVER_Lca
UVB_Ath UVB_Lca
Equation
y 6.07*104 x1.448 y 3.02*104 x1.492 y 6.73*104 0.0015 x 3.9*105 x 2 y 3.026*10 7.52*10 x 2.4*10 x 3
4
5
2
y 2.752*106 x1.639 y 2.02*106 x1.637 y 0.0106 1.6*105 x 1.0*106 x 2 y 6.83*103 1.7*106 x 1*107 x 2 y 0.0027 0.107 x y 0.0032 0.067 x
R2 / S S=0.008 S=0.007 0.98 0.98 S=0.014 S=0.111 0.95 0.96 0.99 0.99
547 548
Table 8b. Relationships between daily UVERd irradiation (kJ m-2) and UVBd, UVAd
549
(kJ m-2) and Global (Gd) (MJ m-2) radiation at both stations. Variable y UVERd Ath
Variable x UVAd_Ath
UVERd_Lca
UVAd_Lca
UVERd_Ath
UVAd_Ath
UVERd_Lca
UVAd_Lca
UVERd Ath
Gd_Ath
UVERd Lca
Gd_Lca
UVERd Ath
Gd_Ath
Equation
y 3.85*104 x1.288 y 1.38*104 x1.361 y 0.133 0.0023x 1*106 x 2 y 0.026 0.0011x 1*106 x 2 y 0.053x1.382 y 0.0377 x1.388 y 0.1382 0.0831x 0.0036 x 2 25
R2 /S S=0.219 S=0.196 0.98 0.98 S=0.332 S=0.268 0.96
ACCEPTED MANUSCRIPT UVERd Lca
Gd_Lca
UVERd Ath UVERd_Lca
UVBd_Ath UVBd_Lca
y 0.1303 0.0587 x 0.00264 x 2 y 0.1379 0.1066 x y 0.1015 0.254 x
0.96 0.99 0.99
550 551
The relationships of the UVER variables between the two stations are shown below.
552
R2 is high for both equations as expected because of the co-variability of UVER at
553
both stations (Fig. 3a).
554 555
Hourly data (W m-2):
556 557 558 559 560 561 562 563
UVER _ Ath 0.00176 1.23*UVER _ Lca
R 2 0.93
(6)
R 2 0.95
(7)
Daily data (kJ m-2):
UVERd _ Ath 0.01136 1.253*UVERd _ Lca
3.7. Attenuation of the UVER radiation-Daily UVER ratios
564 565
In order to assess the attenuation of UVER solar radiation we have estimated the
566
potential UVER irradiation (UVERc), which is defined as the irradiation when the
567
clearness index (KT) is above 0.65, i.e., a clear day. KT is defined as the ratio of the
568
measured daily global solar radiation at the Earth’s surface to the extraterrestrial
569
radiation at the top of the atmosphere both measured on a horizontal surface. The
570
days are classified as cloudy when KT < 0.35, as partly cloudy when 0.35< KT <0.65
571
and clear days when KT > 0.65. The statistics of UVERd for different KT values are
572
presented in Table 9. The most frequent cases occur in the bins above 0.55 in both
573
stations, i.e. towards the clear-day classification. The averages in most cases are
574
higher than the median values. The numbers of clear days on a monthly basis, which
575
are based on the above criteria for the whole period of measurements (3 years), are
576
presented in Table 10. The total number of clear days is 541 for Athalassa and 708
577
for Larnaca. As it is indicated in Table 10, during the summer season most days are
578
defined as clear.
579 580
Figure 10 shows the monthly average daily values of extraterrestrial (UVER0),
581
UVERc and measured UVER irradiation at both stations. The graph shows that both 26
ACCEPTED MANUSCRIPT 582
UVER and UVERc at Athalassa are higher than the respective values at Larnaca.
583
The difference between the UVERc and UVER measured values is greater in the
584
spring and winter time, while during the summer the difference is small. This is
585
attributed to the fact that during the summer almost all days are clear.
586 587
The UVER0 irradiation is estimated from the following equation:
588 589
UVER0 (24 / ) GscUVER [sin sin ((s ) /180) cos cos sin s ]
590 591
where ε is the eccentricity of the ecliptic path of the Earth around the Sun, φ is the
592
latitude, δ is the solar declination, ωs is the sunset hour angle and GscUVER=9.89 W
593
m-2, which it was obtained from Tena et al. [22].
594 595
Table 9. Statistics of daily UVER irradiation (kJ m-2) based on various daily values KT
596
in the period of measurements for a) Athalassa and b) Larnaca.
597
a) Athalassa Ath_ KT Bin End Lower 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75
Daily UVER (kJ m-2) Occurrences Mean Median Min Upper 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80
5 4 6 10 20 18 35 38 53 71 103 145 328 210 3
0.376 0.542 0.463 0.838 1.000 1.147 1.456 1.841 1.911 2.071 2.567 3.023 3.731 4.280 5.341
0.234 0.500 0.464 0.933 0.816 0.901 1.293 1.820 1.788 1.487 2.422 3.063 4.165 4.582 5.904
0.221 0.395 0.426 0.428 0.568 0.581 0.677 0.826 0.859 0.935 1.026 1.095 1.000 1.273 4.011
Max
Std. Dev.
0.848 0.865 0.529 1.233 1.979 2.710 2.902 3.626 3.731 4.576 4.996 5.348 5.972 6.164 6.107
0.270 0.220 0.037 0.300 0.454 0.558 0.649 0.789 0.750 1.089 1.107 1.282 1.529 1.426 1.156
598 599
b) Larnaca Lca_ KT Bin End Lower Upper 0.05 0.10
Occurrences 3
Daily UVER (kJ m-2) Mean Median Min Max 0.319
27
0.316
0.224 0.418
Std. Dev. 0.097
(8)
ACCEPTED MANUSCRIPT 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80
0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85
6 8 7 7 14 17 26 34 52 70 94 222 419 66 1
0.515 0.488 0.856 0.802 0.969 1.030 1.075 1.337 1.540 1.692 1.976 2.523 3.283 3.396 1.054
0.395 0.492 0.887 0.868 0.841 0.795 0.879 1.174 1.510 1.355 1.762 2.643 3.564 3.461 1.054
0.307 0.403 0.429 0.364 0.530 0.620 0.668 0.632 0.730 0.774 0.798 0.802 0.871 1.436 1.054
0.892 0.601 1.242 1.524 2.013 1.727 2.650 2.903 2.962 3.895 4.236 4.531 4.808 4.863 1.054
0.250 0.071 0.312 0.405 0.441 0.393 0.473 0.645 0.619 0.868 0.907 1.127 1.060 0.884 0.000
600 601 602
Table 10. Number of clear days defined by KT>0.65 with UVER measurements in
603
Athalassa and Larnaca in the period 2013-2015. Station Athalassa Larnaca
Jan 24 22
Feb 32 36
Mar 40 51
Apr 46 62
May 42 69
Jun 61 79
Jul 80 91
Aug 74 91
Sep 39 72
Oct 45 64
Nov 26 29
Dec 32 42
Year 541 708
604 605
From the monthly mean values of UVERc, UVER0 and measured UVER radiation,
606
the ratios between these variables were estimated. The ratio UVER/UVERc
607
represents information about the percentage of radiation which, on the average, is
608
transmitted through the atmosphere and may be considered as the atmospheric
609
transparency under average conditions, i.e. including hydrometeors and aerosols.
610
The ratio UVERc/UVER0 gives information about the atmospheric transparency on
611
clear days, i.e, without clouds but with aerosols, though in low proportion. Figure 11
612
shows the monthly mean daily values of the above ratios for each station. The
613
greatest variability is shown in the ratio of UVER/UVERc. The other ratios show
614
similar variation, but the values are very low. The evolution of these ratios increases
615
from spring to summer and decreases from summer to winter.
616
28
ACCEPTED MANUSCRIPT
617 618
Fig. 10. Annual variation of monthly mean values of UVER0, UVERc and measured
619
UVER irradiation at Athalassa and Larnaca.
620
621 622
Fig. 11. Monthly mean values of the ratios UVER/UVERc, UVERc/UVER0, and
623
UVER/UVER0 at Athalassa and Larnaca. 29
ACCEPTED MANUSCRIPT 624 625
3.8. Relationship between hourly hemispherical transmittances ( ktUVER ) and
626
clearness index ( kt )
627 628
In this section the relationship between the clearness index (global hemispherical
629
transmittance) ( kt ) and the UVER hemispherical transmittance ( ktUVER ) is examined.
630
The clearness index is defined as: kt G / G0 , G being the measured global
631
irradiance and G0 the extraterrestrial solar irradiance, both measured on horizontal
632
surface and in the same time interval. In the same way the UVER hemispherical
633
transmittance ( ktUVER ) is defined as: ktUVER UVER / UVER0 , where UVER is the
634
measured variable and UVER0 is the extraterrestrial UVER irradiance, both
635
measured on a horizontal surface during the same time interval. The small ‘k’ refers
636
to hourly values, while the capital letter ‘K’ denotes daily values. The monthly mean
637
values of the daily UVER hemispherical transmittance ( KTUVER ) were given in the
638
previous section (Fig. 11).
639 640
Figure 12 shows the histograms with the hourly values of kt. Most of the data are
641
concentrated in the 0.7-0.8 range at both stations. The clearness index is mostly
642
affected by the presence of clouds. Figure 13 shows the histograms with the hourly
643
values of ktUVER. Most of the data are concentrated in the 0.7-1.5 (*102) range at both
644
stations. The above results suggest that is difficult to establish relationships of the
645
form of Eqs. (4) and (5) between the indexes kt and ktUVER . Tena et al. [22] have
646
established linear regressions between ktUVER and kt for the four central hours of the
647
day during the summer months.
648
30
ACCEPTED MANUSCRIPT
649
650 651
Fig. 12. Frequency distribution of kt at a) Athalassa and b) Larnaca, in the period
652
2013-2015.
653 654
31
ACCEPTED MANUSCRIPT
655 656
657 658
Fig. 13. Frequency distribution of hourly UVER hemispherical transmittance (ktUVER)
659
at a) Athalassa and b) Larnaca, in the period 2013-2015.
660 661 32
ACCEPTED MANUSCRIPT 662
Moreno et al. [29] have proposed two models having the following forms:
663 664 665
ktUVER exp(a b *ln(kt ))
666
In Eq. (10), UVERx is the maximum value of UVER irradiance at a given hour.
667
Furthermore, they propose relationships of UVER irradiance and ktUVER with relative
668
optical air mass (m) of the form:
(9)
ktUVER c d *(kt *UVERx )
(10)
669 670
ktUVER a * mb
(11)
UVER a * mb
(12)
671 672
m depends on the solar altitude angle (γs) (in rad), and the site pressure and is
673
calculated using Eq. (13) (Kasten and Young [53]). The relative optical air mass was
674
estimated for the middle of each hour for solar altitude αs>7 deg.:
675 676 677
m ( P / P0 ) / (sin( s ) 0.50572*(57.29578* s 6.07995)1.6364 )
678
where P and P0 are the site and standard atmospheric pressure (P0 = 1013.25 hPa),
679
respectively; the ratio P / P0 is estimated using Eq. (14) from the elevation (z) (in m)
680
of the site:
(13)
681
P / P0 exp( z / 8435.2)
682 683 684 685
(14)
The above forms of relationships (Eqs. 9-12) were tested with the data of the two
686
stations in Cyprus and the results of fitting with the relevant regressions are shown in
687
Table 11. As indicated in this Table, the coefficients of the fitted equations show
688
similarities between the two stations. Additionally, the coefficients of the regressions
689
show similarities with those obtained by Moreno et al. [29] in Valencia (Spain).
690 691
Mateos et al. [54] have proposed an empirical model for the estimation of total UV
692
irradiance based on the UV extraterrestrial irradiance (UV0), the clearness index (kt)
693
and relative optical air mass (m) using the following form:
694 695 696
UV a *UV0 * ktb * mc
(15) 33
ACCEPTED MANUSCRIPT 697
If we extend the above equation by analogy for the estimation of UVER irradiance
698
we can estimate the coefficients of the equation as shown in Table 11. The
699
coefficients of the two stations are almost similar.
700 701
Table 11. Relationships between hourly UVER irradiance (W m-2) and ktUVER with kt ,
702
m and UVERx at both stations. Variable y ktUVER _Ath
Variable x kt_Ath
ktUVER _Lca ktUVER _Ath ktUVER _Lca ktUVER _Ath ktUVER _Lca
kt_Lca
UVER_Ath
kt_Ath
UVER_Lca
kt_Lca
UVER_Ath
kt&UVERx_Ath
UVER_Lca
kt&UVERx_Lca
UVER_Ath
m_Ath
UVER_Lca
m_Lca
UVER_Ath
kt, UVER0, m
UVER_Lca
kt, UVER0, m
kt&UVERx_Ath kt&UVERx_Lca m_Ath m_Lca
Equation
y exp(3.51 0.981*ln(kt )) y exp(3.71 1.239*ln(kt )) y 0.0066 0.147* kt *UVERx y 0.0079 0.155* kt *UVERx
S 0.0062 0.0049 0.0019 0.0020
y 0.0299* m0.939 y 0.0239* m0.949
0.0048
y exp(1.634 1.892*ln(kt )) y exp(1.807 2.396*ln(kt )) y 0.0014 1.206* kt *UVERx y 0.00055 1.194* kt *UVERx
0.0508
y 0.2079* m2.084 y 0.1669* m2.118
0.0229
y 0.043*UVER0 * kt0.826 m0.955 y 0.032*UVER0 * kt0.809 m0.933
0.0095
0.0036 0.0408 0.1029 0.0069 0.0151 0.0087
703 704
Extending the analysis of the relationships for different types of hours i.e., clear: kt
705
>0.65 and partly cloudy (0.35< kt <0.65), we have estimated the regression
706
coefficients of Eqs. (11) and (12). Table 12 presents these coefficients for the two
707
types of hours, while Fig. 14 shows the relationship of UVER and m for both stations.
708 709
Table 12. Regression coefficients of the functions of Eqs (11) and (12) on clear ( kt
710
>0.65) and partly cloudy hours (0.35< kt <0.65) at both stations. Station
Athalassa
kt kt >0.65
ktUVER /UVER ktUVER
34
Regression coefficients a
b
0.0334
0.967
ACCEPTED MANUSCRIPT Larnaca
kt >0.65
ktUVER
0.0255
0.957
Athalassa
0.35< kt <0.65
ktUVER
0.0224
0.605
Larnaca
0.35< kt <0.65
ktUVER
0.0244
0.480
Athalassa
kt >0.65
UVER
0.2227
1.931
Larnaca
kt >0.65
UVER
0.1714
1.983
Athalassa
0.35< kt <0.65
UVER
0.1576
1.764
Larnaca
0.35< kt <0.65
UVER
0.1134
1.657
711 712
713 714
35
ACCEPTED MANUSCRIPT
715 716
Fig. 14. Relationship of UVER irradiance (W m-2) and m for a) Athalassa and b)
717
Larnaca, in the period 2013-2015.
718 719
Different authors have established relationships between UVER irradiance and a
720
number of other variables such as TOC, SZA, UV and global irradiance with high
721
coefficients of determination [23]. Equations 16 and 17 show the relationships
722
between UVER irradiance under cloud-free conditions at midday and the cosine of
723
SZA angle as well as the TOC at both stations:
724 725 726 727 728
Ath _ UVERc 0.243*cos( SZA)2.008 *(TOC / 300)0.851
(16)
Lca _ UVERc 0.188*cos( SZA)2.013 *(TOC / 300)0.704
(17)
729
The relationships between the UVER irradiance under cloud-free conditions for each
730
hour of the day and the cosine SZA are shown below:
731 732 733 734 735
Ath _ UVERc 0.231*cos( SZA)1.923
(18)
Lca _ UVERc 0.179*cos( SZA)2.018
(19)
36
ACCEPTED MANUSCRIPT 736
Almost similar coefficients were obtained by Bilbao et al. [55] at Marsaxlokk in Malta.
737
The fitted line of Eq. (18) is shown in Fig. 15. Similar graph is obtained for Larnaca
738
(not shown).
739
740 741
Fig. 15. Relationship between UVERc and cos(SZA) at Athalassa in the period 2013-
742
2015.
743 744
3.9. UV Index
745 746
The UVI is estimated from the measured hourly UVER (in W m-2) by multiplying it by
747
40. The monthly average hourly UVI values throughout the day are reported in Fig.
748
16 for both stations. The UVI values on the ordinates have been separated into five
749
zones according to the WHO recommendations [17], viz., extreme ≥11; very high 8-
750
10; high 6-7; moderate 3-5 and low ≤2. In terms of Sun exposure time to achieve
751
incipient redness of skin type II, these five ranges of UVI values translate into 15, 20,
752
25, 35 min and more than 1 h, respectively [39]. The time taken ( tE in minutes) to
753
induce skin damage is calculated from the following formula [56]:
754 755 756
tE (4000 / 60)*( MEDF * SPF ) / UVI
(20) 37
ACCEPTED MANUSCRIPT 757
where the factor 4000/60 accounts for the conversion from UVER irradiance to UVI,
758
and seconds to minutes; MEDF is a factor to account for the different skin types and
759
it is expressed as a number of Standard Erythemal Dose
760
UVER) required to induce erythema; SPF is the Sun protection factor of any Sun
761
block applied. For unprotected skin SPF=1. For UVI=10 at midday in summer and
762
unprotected skin, the time taken to induce erythema for the four skin phototypes,
763
calculated from the above formula, would be 13.3, 16.7, 23.3 and 30 minutes,
764
respectively. For UVI=10 with a Sun block of SPF=10 the time required to induce
765
erythema for the four skin phototypes is about 10 times the estimated values given
766
above (i.e., ̴2.2, 2.8, 3.9 and 5.0 hours, respectively).
(1 SED=100 J m-2 of
767 768
The highest mean hourly UVI is 9 and is recorded at Athalassa, whereas the highest
769
at Larnaca is 7. If we use the hourly maximum values instead of the mean ones, then
770
the UV Indices higher than 10 are recorded at Athalassa and about 8 at Larnaca.
771
During the summer months the UVI is higher than 7 (very high) from about 10 to 15
772
LST, while at Larnaca the UVI is higher than 5 (high) for the same time interval. If we
773
use the maximum hourly values then the time interval is extended by one hour.
774
775 776 38
ACCEPTED MANUSCRIPT
777 778
Fig. 16. Monthly average hourly UVI values at a) Athalassa and b) Larnaca in the
779
period 2013-2015.
780 781
The UV Index was also determined from the UVER measurements using two
782
different criteria: a) The value at solar noon and b) the maximum daily value [21].
783
Therefore, for the two stations the percentages were found for which the differences
784
in the results given by the differences of the above two criteria were 0, 1, 2 and 3 or
785
more units of UVI. The results of the deviations of the values of the UVI at solar noon
786
compared with the maximum daily UVI values are summarised in Table 13. It has to
787
be noted that at Larnaca 39 days are missing while at Athalassa only 10 days are
788
missing. The percentage coincidence (zero difference between the two criteria in
789
UVI) varied between 52% (Larnaca) and 66% (Athalassa). If we consider the cases
790
for which the difference was 0 or 1 unit, the coincidence is around 94% for both
791
stations. Therefore, it is reasonable to consider that estimating the UVI value at solar
792
noon is acceptable method. Similar results were obtained for 16 stations in Spain for
793
which the difference between the two criteria was zero or one UVI unit varying
794
between 89% and 95% with an average value of 92% [21].
795
39
ACCEPTED MANUSCRIPT 796
Table 13. Deviations of the UVI values at solar noon compared with the maximum
797
daily UVI values for the two stations. The results are given as a percent of the
798
available daily values given in parenthesis for each station. Percentages Station
0
1
2
≥3
Athalassa (1085)
66
27
5
2
Larnaca
52
42
2
1
(1056)
799 800
Table 14 shows the percentage of the daily maximum values of the UVI for the two
801
sites classified according to the exposition categories recommended by WHO [18].
802
The UVI was rounded to the nearest integer value. The UVI reaches high (6-7) or
803
very high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca
804
these values are reached in 38.8%. Using the maximum hourly values of UVER, the
805
percentages of the high and very high cases of UVI are slightly higher in both
806
stations (Table 14 b cases), than using the maximum of the mean hourly values
807
(Table 14 a cases). It has to be noted that no extreme values are recorded. The
808
average annual number of hours with UVI>5 at Athalassa is 935 and 604 at Larnaca,
809
while the average annual number of hours with UVI>7 at Athalassa is 431 and only
810
61 at Larnaca. It has to be reminded that long missing records were detected in
811
Larnaca.
812 813
Table 14. Days (in % during the three years considered) in which the indicated
814
maximum value of the UV Index is reached at the two measuring sites. a) Value at
815
solar noon, b) maximum daily value. UV Index (%) Station
≤2
3-5
6-7
8-10
≥11
(low)
(moderate)
(high)
(very high)
(extreme)
Athalassa (a)
9.1
37.1
21.0
31.9
Athalassa (b)
4.1
36.0
20.6
38.6
Larnaca
(a)
20.9
35.8
36.9
1.9
Larnaca
(b)
16.6
36.2
38.8
4.0
816 817 40
ACCEPTED MANUSCRIPT 818
3.10. Cumulative doses
819 820
Figure 17 shows the annual cumulative dose for each phototype and for Standard
821
Erythemal Dose obtained by dividing the daily UVER values by the corresponding
822
MED and SED values (Table 1) over an average year at the two measuring sites.
823
These values correspond to a continuous and uninterrupted exposure to the Sun, on
824
a horizontal position, throughout the year. It is observed that the cumulative doses
825
during an average year range from 9087 SEDs in Larnaca to 11418 SEDs in
826
Athalassa. The most common skin type in Cyprus is phototype III (about 70% of the
827
population, southern European type [56]), which could receive an annual cumulative
828
dose between 2596 MEDs in Larnaca to 3262 MEDs in Athalassa. The second
829
common skin type in Cyprus is phototype II (about 20% of the population, central
830
European type) that could receive an annual cumulative dose between 3635 MEDs
831
in Larnaca to 4568 MEDs in Athalassa. The third common skin type in Cyprus is
832
phototype IV (about 10% of the population, north African type) that could receive an
833
annual cumulative dose between 2019 MEDs in Larnaca to 2537 MEDs in
834
Athalassa. Regarding the phototype I (Scandinavian type), it could receive an annual
835
cumulative dose between 4544 MEDs in Larnaca to 5709 MEDs in Athalassa. The
836
annual cumulative doses are comparable with the respective values in 16
837
radiometric stations in Spain [21]. The curves of Fig. 17 show a clear change of
838
slope during the summer. The cumulative doses for the phototype III for summer is
839
41%, for spring 28%, for autumn 20% and for winter 11% of the annual cumulative
840
dose, for both stations.
841 842
It is estimated that schoolchildren received about 5% of the total daily solar UV
843
radiation, while outdoor workers received about 20-26% of the total daily solar UV
844
radiation levels [57-59].
845
41
ACCEPTED MANUSCRIPT
846 847
848 849
Fig. 17. Annual cumulative dose for the skin types defined in Table1 and the
850
Standard Erythemal Dose (SED) at a) Athalassa and b) Larnaca.
851 852 42
ACCEPTED MANUSCRIPT 853
4. Inter-comparison of the two sites
854 855
The inter-comparison of the broad-band solar radiation intensity measurements at
856
both sites are reported in Table 15 for the global and UVER radiation. The solar
857
radiation intensities are reported as monthly average daily values, the number of
858
days of each variable for the period of measurements and the relative attenuation
859
reported for each one, which is defined as:
860
Re lativeAttenuation(%) (( X Lca X Ath ) / X Ath ))*100
861 862 863
(21)
where X refers to the type of solar radiation, i.e., either global or UVER. The
864
subscripts refer to the particular site.
865 866
As indicated in Table 15, the magnitudes of the monthly average daily values of the
867
solar global radiation are higher at Larnaca than at Athalassa. Generally, the
868
percentages of relative attenuation are lower during the summer period. The
869
magnitudes of the monthly average daily solar global radiation intensity at the two
870
sites are very similar.
871
difference in altitude between the two stations is not significant and, therefore, the
872
daily values are almost similar. However, the UVER radiation at Larnaca is lower
873
than that at Athalassa; therefore, the relative attenuation of UVER is negative
874
(approximately about -20% throughout the year). The percent relative attenuation is
875
also presented graphically for the two solar radiation components in Figure 18. The
876
summary of the inter-comparison of the two sites is presented in Table 16.
The % relative attenuation is < 10% for all months. The
877 878
Table 15. Monthly average daily solar global and UVER at Athalassa and Larnaca in
879
the period 2013-2015 and their relative differences. Ath(Gd) Lca(Gd) Ath(UVERd) Month N Mean N Mean % Relative N Mean MJ/m2 MJ/m2 attenuation kJ/m2 1 93 9.36 92 10.01 6.99 93 1.19 2 84 13.27 66 14.35 8.13 84 1.81 3 93 17.54 93 18.57 5.92 93 2.64 4 90 22.27 90 23.92 7.40 90 3.54 5 77 24.05 93 26.38 9.69 90 4.25 6 82 27.78 90 29.53 6.29 89 5.25 7 92 27.96 93 29.26 4.65 92 5.50
43
Lca(UVERd) N Mean % Relative kJ/m2 attenuation 62 0.96 -19.38 66 1.52 -15.97 93 2.14 -19.12 90 2.90 -18.08 93 3.51 -17.53 90 4.19 -20.32 93 4.24 -22.84
ACCEPTED MANUSCRIPT 8 9 10 11 12 Year
93 84 93 78 91 1050
24.91 20.09 15.51 11.37 8.78 18.53
93 90 93 90 93 1076
26.30 21.68 16.72 11.45 9.44 19.93
5.57 7.92 7.81 0.72 7.46 7.54
93 90 93 89 91 1087
4.81 3.52 2.44 1.47 1.04 3.13
93 90 93 90 93 1046
3.70 2.85 1.89 1.09 0.83 2.55
-22.90 -18.97 -22.48 -25.74 -20.27 -18.36
880
881 882
Fig. 18. Relative attenuation of solar global and UVER radiation for Athalassa and
883
Larnaca in the period 2013-2015.
884 885
The main factors which affect the levels of UVER and shortwave (SW) irradiances
886
are the solar zenith angle, clouds, ozone, water vapour and aerosols. UVER
887
irradiance on clear days depends on SZA cosine by a power law (Fig. 15) (Eqs. 18-
888
19), while SW irradiances on clear days show a linear trend with a high R2 for both
889
stations:
890 891 892 893 894 895
Measurements in Malta and Spain quantified the effects of the above factors on
896
UVER and SW irradiances on clear days [60-62]. According to these measurements,
Ath _ Gc 11.43 964*cos( SZA)
R 2 0.97
(22)
Lca _ Gc 7.102 1018*cos( SZA)
R 2 0.98
(23)
44
ACCEPTED MANUSCRIPT 897
UVER is mostly affected by ozone which reduces UVER levels by around -0.31
898
%DU-1. However, the ozone effect on SW irradiance is negligible. The water vapour
899
effect on UVER is negligible, but SW depends on water vapour (̴ -3.36% cm-1). The
900
effect of aerosols is stronger on UVER irradiance than the SW one. The trends show
901
an average value of -37% for aerosol optical depth at 440 nm (AOD440), and for SW
902
irradiance this percentage falls up to -28.4% for AOD440 unity. Furthermore, Robaa
903
[26] found that the mean relative reduction of global and UV solar radiation in Cairo
904
(Egypt) were 17.4% and 27.4%, respectively. In dusty days, the reduction in the
905
received global and UV radiation due to dust particles effects ranged between 26%
906
and 45% for global and between 33% and 59% for UV. Jacovides et al. [27] have
907
demonstrated that high aerosol loads produce significant relative attenuations of
908
UVB to global solar radiation ratio in comparison to that for low aerosol loadings.
909 910
The global solar radiation at Larnaca exceeds that in Athalassa throughout the year.
911
This can be explained by the fact that there is much more number of clear days at
912
Larnaca than at Athalassa (Table 10). The attenuation of solar radiation within the
913
global spectral range due to the difference of altitude between the two sites by
914
scattering phenomena is negligible. The higher attenuation of UVER radiation can be
915
attributed to its shorter wavelengths, since the scattering process is inversely
916
proportional to the fourth power of its wavelength (λ-4). The scattering of solar
917
radiation by water molecules is a function of the amount of precipitable water above
918
the observation site. An empirical scattering coefficient for water vapour that varies
919
according to λ-2 has been proposed, while for aerosols, an empirical coefficient of
920
λ-0.75 was used [24]. In all cases, the degree of attenuation by scattering is an inverse
921
function of the wavelength, i.e., attenuation decreases with increasing wavelength.
922
The variation in the monthly percent of relative attenuation values for UVER is also
923
influenced by the local climatic conditions.
924 925
On the other hand, the aerosol load and the type of aerosols may also affect the
926
levels of UVER irradiance at the two locations. According to measurements of the
927
Department of Air Quality Control of the Ministry of Labour in Cyprus, in 2004, the
928
pollution load at Larnaca is much higher than that at Athalassa which is due to a
929
much larger vehicular and aeroplane traffic and the location of a number of industrial
930
plants in the vicinity of the station. The station at Athalassa is surrounded by a forest, 45
ACCEPTED MANUSCRIPT 931
while the station at Larnaca is within the area of the Airport. The mean annual
932
particulate matter concentrations of PM10 at Larnaca station, is slightly higher than
933
60 μg m-3, while at the station of General Hospital in Nicosia, which is close to
934
Athalassa station, is around 48 μg m-3 [63]. Furthermore, there are more days with
935
hazy conditions at Larnaca due to dust episodes, which affect mostly the southern
936
parts of the island.
937 938
Table 16. Inter-comparison of the two sites with respect to global and UVER
939
radiation. Variable Location Annual daily average global irradiation (Gd) (MJ/m2) Annual total global irradiation (MJ/m2) Annual daily average UVER irradiation (UVERd) (kJ/m2) Daily average UVER irradiation in July (kJ/m2) Daily average UVER irradiation in December (kJ/m2) Accumulated daily UVER irradiation in Spring (kJ/m2) Accumulated daily UVER irradiation in Summer (kJ/m2) Accumulated daily UVER irradiation in Autumn (kJ/m2) Accumulated daily UVER irradiation in Winter (kJ/m2) Annual total UVER irradiation (kJ/m2) Maximum Hourly Average UVER irradiance in July (W/m2) Maximum Hourly Average UVER irradiance in December (W/m2) Maximum Mean Hourly UV Index Absolute Maximum UV Index Mean Annual Cumulative doses Phototype I (MEDs) Mean Annual Cumulative doses Phototype II (MEDs) Mean Annual Cumulative doses Phototype III (MEDs) Mean Annual Cumulative doses Phototype IV (MEDs) Mean Annual Cumulative doses (SEDs)
Athalassa inland 18.53 6835 3.126 5.50 1.04 320.0 477.0 225.5 119.4 1141.9 0.249 0.077 9 10 5709 4567 3262 2537 11418
Larnaca coastal 19.93 7183 2.552 4.24 0.83 262.0 371.9 177.1 97.7 908.7 0.195 0.057 7 8 4543 3635 2596 2019 9087
940 941
5. Conclusions
942 943
Measured data at 10 min intervals, obtained by UV Kipp & Zonen radiometers
944
installed at two locations in Cyprus, one at Athalassa (inland location) and the other
945
at Larnaca (coastal location) during the period January 2013 to December 2015
946
have been used to define the statistical characteristics of both hourly and daily
947
UVER radiation values. These measurements have also been used to estimate UVI
948
and the cumulative doses for the different skin types. The interest of this work
949
resides in the fact that it is the first thorough analysis of this type performed in the 46
ACCEPTED MANUSCRIPT 950
island of Cyprus. Furthermore, the levels of UVER irradiation were compared with
951
other sites in the Mediterranean region. The highest values are recorded in Beer
952
Sheva (Israel) with the second ones at Athalassa, as expected, since these stations
953
are at lower latitude and have higher sunshine duration comparing to other stations.
954
The coastal sites (Larnaca, Kos, Athens, Thesaloniki, Neve Zohar and Valencia)
955
have almost similar levels of erythemal irradiation, in contrast to the inland locations
956
(Athalassa and Beer Sheva), which have higher levels of UVER. The differences
957
between the inland and coastal locations are more pronounced during the summer
958
period.
959 960
Large fluctuations in the spring months and November are mainly due to unstable
961
meteorological conditions during the transition from cold to warm weather and vice
962
versa. During summer the daily UVER radiation exceeds the value of 6 kJ m-2 at
963
Athalassa and 4.8 kJ m-2 at Larnaca, while during the winter season the lowest is
964
about 0.2 kJ m-2 at both sites. Slightly lower values were recorded in 2015 at both
965
stations, which can be attributed to higher amounts of aerosols in the atmosphere.
966
The year 2015 is characterized as an extremely dry year with more frequent dust
967
episodes over the island (dust from the deserts of Middle East and Sahara),
968
increasing, therefore, aerosols in the atmosphere that can affect the absorption of
969
UVER radiation. The accumulated UVER irradiation received in an average year is
970
1142 kJ m-2 for Athalassa and 909 kJ m-2 for Larnaca.
971 972
By analysing the daily evolution of the monthly average values of the UVER
973
irradiances a high degree of symmetry could be observed in the annual and
974
seasonal distributions of this radiation component. The UVER variability has been
975
studied by means of the coefficient of variation (CV). It was demonstrated that the
976
CVs in July are low during midday (5-10%) at both stations, indicating a high stability
977
along these hours in summer.
978 979
In July, the absolute maxima of the UVER irradiance measured at local noon varied
980
from 0.195 W m-2 in Larnaca to 0.248 W m-2 in Athalassa, whereas the absolute
981
minima ranges between 0.141 W m-2 and 0.188 W m-2, respectively. Since the
982
difference between the Q1 quartiles and the absolute minima was high, and the
983
difference between the Q3 quartiles and the absolute maxima was small, the 47
ACCEPTED MANUSCRIPT 984
maximum values can be considered representative of UVER at local noon, but the
985
minimum values represent unusual extreme values.
986 987
With respect to the estimation of UVER irradiance, it is indicated that the results from
988
the expression that estimates UVER from UVA were more satisfactory than those
989
from the global irradiance, although they continued to be acceptable in the latter
990
case. Similar results were obtained for the estimation of the daily UVER values of.
991
Generally, the constants of the equations of the two sites are comparable.
992 993
The difference between the potential UVER (UVERp) and the measured UVER
994
values is greater in the spring and winter time due to the presence of clouds, while
995
during the summer the difference is small. This is attributed to the fact that during the
996
summer almost all days are cloud free. The clearness index kt at Larnaca is slightly
997
higher than that at Athalassa. On the other hand, kTUVER of Athalassa is higher than
998
that at Larnaca.
999 1000
Regarding the UV Index, this shows minimum differences between the value at solar
1001
noon and the maximum daily value, with more than 90% of the cases showing
1002
differences of one or less UVI units for both sites. The UVI reaches high (6-7) or very
1003
high (8-10) values in 58.1% of the cases in Athalassa, whereas in Larnaca these
1004
values are reached in 38.8%. During the summer months the UV Index is higher
1005
than 7 (very high) from about 10 to 15 LST, while at Larnaca it is higher than 5
1006
(high) for the same time interval. If we use the maximum hourly values then the time
1007
interval of high values is extended by one hour.
1008 1009
Finally, the cumulative doses for each phototype and for the StED over an average
1010
year have also been studied for the two sites. It is observed that the cumulative
1011
doses during an average year range from 9087 SEDs in Larnaca to 11418 SEDs in
1012
Athalassa. The most common skin type in Cyprus, phototype III (about 70% of the
1013
population, southern European type) could receive an annual cumulative dose
1014
between 2596 MEDs in Larnaca to 3262 MEDs in Athalassa.
1015
48
ACCEPTED MANUSCRIPT 1016
Based upon the above analysis, we conclude that the two sites in Cyprus are
1017
characterised by relatively high average-daily irradiation rates and a relatively high
1018
frequency of clear days. Comparing the two sites we may observe that Larnaca has
1019
slightly higher rates of global radiation than Athalassa. Regarding UVER irradiation
1020
and UV Index, Athalassa shows higher values than Larnaca.
1021 1022
In future studies, the radiation climate of the two sites will be further examined for the
1023
other UV solar radiation components (UVB, UVA and UV total radiation) as well as
1024
the long-wave radiation. Then, the net radiation balance will be estimated and the
1025
climate characteristics will be assessed at a given site based on the levels of each
1026
radiation component.
1027 1028
Nomenclature
1029 1030
As
Skewness coefficient
1031
CDF
Cumulative probability density function
1032
CV
Coefficient of variation (%) (CoefVar)
1033
D.U.
Dobson unit (thickness of ozone in units of 10 μm)
1034
G
Global solar irradiance [W m-2]
1035
G0
Extraterrestrial irradiance [W m-2]
1036
G0d
Daily extraterrestrial irradiation (ETR) [MJ m-2]
1037
Gd
Daily global irradiation [MJ m-2]
1038
Gsc
Solar constant [1367 W m-2]
1039
GscUVER
Solar constant of UVER irradiance [9.89 W m-2]
1040
IQR
Interquartile range
1041
jd
Julian day number (1..365)
1042
K
Kurtosis
1043
kt
Hourly clearness index ( kt G / G0 )
1044
ktUVER
Hourly UVER transmittance ( ktUVER UVER / UVER0 )
1045
KT
Daily clearness index ( KT Gd / G0 d )
1046
m
Relative air mass
1047
MED
Minimum Erythemal Dose
1048
Max
Maximum 49
ACCEPTED MANUSCRIPT 1049
Min
Minimum
1050
N
Nonmissing observations
1051
N*
Missing observations
1052
P
Atmospheric pressure at the site [hPa]
1053
P0
Standard atmospheric pressure (1013.25 hPa)
1054
P5
Percentile 5%
1055
P95
Percentile 95%
1056
Probability density function
1057
PM10
Particulate matter concentration (μg m-3)
1058
Q1
First Quartile
1059
Q3
Third Quartile
1060
R2
Coefficient of determination
1061
S
Standard error of the regression or standard deviation of the residuals
1062
SED
Standard Erythemal Dose (1 SED=100 J m-2)
1063
StDev
Standard deviation
1064 1065
tE TOC
Time to induce erythema [minutes] Total Ozone column
1066
UV
UV irradiance [W m-2] / UV irradiation [kJ m-2] (UV(A+B))
1067
UVA
UVA irradiance [W m-2] / UVA irradiation [kJ m-2]
1068
UVAd
Daily UVA irradiation [kJ m-2]
1069
UVB
UVB irradiance [W m-2] / UVB irradiation [kJ m-2]
1070
UVBd
Daily UVB irradiation [kJ m-2]
1071
UVC
Ultraviolet radiation in the range of 100 to 280 nm
1072
UVER
UV erythema irradiance [W m-2] / UV erythema irradiation [kJ m-2]
1073
UVERd
Daily UVER irradiation [kJ m-2]
1074
UVER0
Extraterrestrial UVER irradiance [W m-2]
1075
UVERp
Potential UVER irradiance [W m-2]
1076
UVERx
Maximum hourly UVER irradiance [W m-2]
1077
UVI
UV Index
1078
z
Elevation [m]
1079 1080
Greek:
1081
αs
Solar altitude (degrees)
1082
δ
Solar declination [degrees] 50
tE
ACCEPTED MANUSCRIPT 1083
ε
eccentricity correction
1084
z
Solar zenith angle (SZA) [degrees]
1085
λ
Wavelength (nm)
1086
φ
Latitude [degrees]
1087
s
Sunset hour angle [degrees]
1088 1089
References
1090 1091
[1] Iqbal M., 1983. An Introduction to Solar radiation. Academic Press, New York.
1092 1093
[2] CIE, 1999. Standardization of the terms UV-A1, UV-A2 and UV-B. Vienna: CIE,
1094
Report CIE-134/1.
1095 1096
[3] WMO and UNEP, 2006. Executive Summary: WMO/UNEP Scientific Assessment
1097
of Ozone Depletion. Prepared by the Scientific Assessment Panel of the Montreal
1098
Protocol on Substances That Deplete the Ozone Layer.
1099 1100
[4] Casale G.R., Meloni D., Miano S., Palmieri S., Siani A.M., 2000. Solar UV-B
1101
irradiance and total ozone in Italy: fluctuations and trends. J. Geophys. Res. 105,
1102
4895-4901.
1103 1104
[5] Bartlett L.M., Webb A.R., 2000. Changes in ultraviolet radiation in the 1990s:
1105
spectral measurements from Reading, England. J. Geophys. Res. 105, 4889-4893.
1106 1107
[6] EUR 19098 - 2000. Biological UV dosimetry, a tool for assessing the impact of
1108
UV radiation on health and ecosystems. Edited by Rettberg p., Horneck G.,
1109
Baumstark-Khan C., Amanatidis G., Air Pollution Research Report 71. European
1110
Commission. Conference proceedings, ISBN 92-828-7820-1, 262 pp.
1111 1112
[7] Ghetti F., Checcucci G. and Bornman J.,2001. Series IV: Earth and
1113
Environmental Sciences – Vol. 57. Proceedings of the NATO Advanced Study
1114
Institute on Environmental UV Radiation: Impact on Ecosystems and Human Health
1115
and Predictive models. Pisa, Italy, 287 pp. ISBN 1-4020-3696-5. Springer. 51
ACCEPTED MANUSCRIPT 1116 1117
[8] Gao W., Schmoldt D. and Slusser J., 2009. UV Radiation in Global Climate
1118
Change. Measurements, Modeling and Effects on Ecosystems. 544 pp. ISBN 978-7-
1119
302-20360., Springer.
1120 1121
[9] Coldiron B., 1998. The UV Index: A weather report for skin. Clin. Dermatol. 16,
1122
441-446.
1123 1124
[10] Diffey B., 1982. The consistency of studies of ultraviolet erythema in normal
1125
human skin. Phys. Med. Biol. 27, 715-720.
1126 1127
[11] Diffey B., 1991 Solar ultraviolet effects on biological systems. Physics in
1128
Medicine and Biology 36, 299-328.
1129 1130
[12] MacKie R., 2006. Long-term health risk to the skin of ultraviolet radiation. Prog.
1131
Biophys. Mol. Bio. 92, 92-96.
1132 1133
[13] Fioletov E., McArthur E., Mathews T., Marrett L., 2009. On the relationship
1134
between erythemal and vitamin D action spectrum weighted ultraviolet radiation.
1135
Journal of Photochemistry and Photobiology B: Biology 95, 9-16.
1136 1137
[14] McKinlay A., Diffey B., 1987. A reference spectrum for ultraviolet induced
1138
erythema in human skin. CIE J. 6, 17-22.
1139 1140
[15] ISO 17166:1999E/CIE S 007/E-1998, Joint ISO/CIE standard: erythema
1141
reference action spectrum and standard erythema dose.
1142 1143
[16] de Miguel A., Bilbao J., Román R. and Mateos D., 2012. Measurements and
1144
attenuation of erythemal radiation in Central Spain. International Journal of
1145
Climatology 32, 929-940.
1146 1147
[17] Diffey B., 1990. Human Exposure to Ultraviolet Radiation. Semin. Dermatol. 9,
1148
2-10.
1149 52
ACCEPTED MANUSCRIPT 1150
[18] World Health Organization (WHO), World Meteorological Organization (WMO),
1151
United Nations Environment Programme (UNEP), International Commission on Non-
1152
Ionizing Radiation Protection (ICNIRP), 2002. Global Solar UV Index: Apractical
1153
guide, Watch No. 95, WMO/TD No. 625, Geneva, Switzerland, p 32.
1154 1155
[19] Zerefos C., Meleti C., Lambros A., 1995. The recent UV variability over south-
1156
eastern Europe. Journal of Photochemistry and Photobiology 20, 15-19.
1157 1158
[20] Mantis H., Repapis C., Philandras C., Pañiatsos A., Zerefos C., Bais A., Meleti
1159
C., Balis D., 2000. A 5-year climatology of solar erythemal ultraviolet in Athens,
1160
Greece. International Journal of Climatology 20, 1237-1247.
1161 1162
[21] Utrillas M., Marín M., Esteve A., Estellés V., Gandía S., Núnez J., Martinez-
1163
Lozano J., 2013. Ten years of measured UV Index from the Spanish UVB
1164
Radiometric Network. Journal of Photoch. and Photob. B: Biology 125, 1-7.
1165 1166
[22] Tena F., Martínez-Lozano J., Utrillas M., Marín M., Esteve A. and Cañada J.,
1167
2009. The erythemal clearness index for Valencia, Spain. International Journal of
1168
Climatology 29, 147-155.
1169 1170
[23] Cañada J., Esteve A., Marín M., Utrillas M, Tena F. and Martínez-Lozano J.,
1171
2008. Study of erythemal, UV (A+B) and global solar radiation in Valencia (Spain).
1172
International Journal of Climatology 28, 693-702.
1173 1174
[24] Kudish A., Lyubanksky V., Evseev E., Ianetz A., 2005. Statistical analysis and
1175
inter-comparison of the solar UVB, UVA and global radiation for Beer Sheva and
1176
Neve Zohar (Dead Sea), Israel. Ther. Appl. Climatol. 80, 1-15.
1177 1178
[25] Kudish A., Evseev E., 2014. Analysis of erythemal UVB and UVA irradiance at
1179
Beer Sheva, Israel from 1994 through 2012. Renewable Energy 63, 84-89.
1180 1181
[26] Robaa, S.M., 2004. A study of ultraviolet solar radiation at Cairo urban area,
1182
Egypt. Solar Energy
1183 53
ACCEPTED MANUSCRIPT 1184
[27] Jacovides C., Tymvios F., Assimakopoulos D., Kaltsunides N., Theocharatos G.
1185
Tsitouri M., 2009. Solar global UVB (280-315 nm) and UVA (315-380 nm) radiant
1186
fluxes and their relationships with broadband global radiant flux at an eastern
1187
Mediterranean site. Agricultural and Forest Meteorology, 149, 1188-1200.
1188 1189
[28] Ghoneim A.A., Kadad I.M., Altouq M.S., 2013. Statistical analysis of solar UVB
1190
and global radiation in Kuwait. Energy 60, 23-34.
1191 1192
[29] Moreno J.,Serrano M., Cañada J., Gurrea G., Utrillas M., Solar radiation Group.,
1193
2014. Effect of the relative optical air mass and the clearness index on solar
1194
erythemal UV irradiance. Journal of Photochemistry and Photobiology B:Biology 138,
1195
92-98.
1196 1197
[30] Kudish A. and Evseev E., 2011. The analysis of solar UVB radiation as a
1198
function of solar global radiation, ozone layer thickness and aerosol optical density.
1199
Renewable Energy 36, 1854-1860.
1200 1201
[31] de Miguel A., Román R., Mateos D., 2011. Evolution of erythemal and total
1202
shortwave solar radiation in Valladolid, Spain: Effects of atmospheric factors. Journal
1203
of Atmospheric and Solar-Terrestrial Physics 73, 578-586.
1204 1205
[32] Esteve A., Marín M., Tena F., Utrillas M. and Martínez-Lozano J., 2010.
1206
Influence of cloudiness over the values of erythemal radiation in Valencia, Spain.
1207
International Journal of Climatology 30, 127-136.
1208 1209
[33] Antón M., Serrano A., Cancillo M., García J., Madronich S., 2011. Empirical
1210
Evaluation of Simple Analytical Formula for the Ultraviolet Index. Photochemistry and
1211
Photobiology 87, 478-482.
1212 1213
[34] Kudish A. and Evseev E., 2012. UVB irradiance and atmospheric optical depth
1214
at the Dead Sea basin, Israel: Measurements and modeling. Renewable Energy 48,
1215
344-349.
1216
54
ACCEPTED MANUSCRIPT 1217
[35] Alados I., Gomera M., Foyo-Moreno I. and Alados-Arboledas L., 2007. Neural
1218
network of the estimation of UV erythemal irradiance using solar broadband
1219
irradiance. International Journal of Climatology 27: 1791-1799.
1220 1221
[36] Moreno J., Serrano M., Lorente M., Cañada J. and Utrillas M., 2013. An
1222
empirical model of erythemal ultraviolet radiation in the city of Valencia, Spain.
1223
Photochemical & Photobiological Sciences. 12, 1707-1716.
1224 1225
[37] Sabziparvar A., 2009. Estimation of clear-sky effective erythema radiation from
1226
broadband solar radiation (300-3000 nm) data in arid climate. International Journal of
1227
Climatology 29, 2027-2032.
1228 1229
[38] Koepke P. Bais A., Balis D., Buchwitz M., de Backer H. de Cabo X., Eckert P.,
1230
Eriksen P., Gillotay D., Heikkila A., Koskela T., Lapeta B., Litynska Z., Lorente J.,
1231
Mayer B., Renaud A., Ruggaber A., Schauberger G., Seckmeyer G., Seifert P.,
1232
Schmalweiser A., Schwander H., Vanicek K., Wever M., 1998. Comparison of
1233
models used for UV index calculations. Photochem. Photobiol. 67, 657-662.
1234 1235
[39] EUR 20611. 2003. UV-B forecasting. Final Report of COST Action 713.
1236 1237
[40] Gómez I., Marín M., Pastor F., Estrela M., 2012. Improvement of the Valencia
1238
region Ultraviolet index (UVI) forecasting system. Computers & Geosciences 41, 72-
1239
82.
1240 1241
[41] Jacovides C., Kaltsunides N., Hachioannou L. & Stefanou L., 1993. An
1242
assessment of the solar radiation climate of the Cyprus environment. Renewable
1243
Energy Vol. 3, 913-918.
1244 1245
[42] Petrakis M., Kambezidis C., Lycoudis S., Adamopoulos A., Kassomenos P.,
1246
Michaelides I., Kalogirou S., Rotitis G., Chrysis L., Hadjigianni A. 1998. Generation
1247
of a ‘typical meteorological year’ for Nicosia, Cyprus. Renewable Energy 13 (3), 381-
1248
388.
1249
55
ACCEPTED MANUSCRIPT 1250
[43] Kalogirou S., Pashiardis S. and Pashiardi A., 2017. Statistical analysis and
1251
inter-comparison of the global solar radiation at two sites in Cyprus. Renewable
1252
Energy 101, 1102-1123.
1253 1254
[44] World Meteorological Organization. WMO, 1987. Guidelines on the quality
1255
control of data from the World Radiometric Network. WCDP-3, WMO/TD-No. 258, p
1256
30, WMO, Geneva, Swittzerland.
1257 1258
[45] Long C.N. and Dutton E.G. 2002. Global Network recommended QC tests, V2.0,
1259
BSRN Technical Report (http://ezksun3.ethz.ch/bsrn/admin/dokus/qualitycheck.pdf).
1260 1261
[46] Long C.N. and Shi Y. (2008). An automated quality assessment and control
1262
algorithm for surface radiation measurements. The Open Atmospheric Science
1263
Journal 2008, 2, 23-37.
1264 1265
[47] Muneer T. 2004. Solar Radiation and Daylight models.2nd Edition. Oxford:
1266
Elsevier.
1267 1268
[48] Pashiardis S and Kalogirou S. 2016. Quality control of solar shortwave and
1269
terrestrial longwave radiation for surface radiation measurements at two sites in
1270
Cyprus. Renewable Energy 96 (2016) 1015-1033.
1271 1272
[49] de Miguel A., Bilbao J., Aguilar R., Kambezidis H., Negro E., 2001. Diffuse solar
1273
irradiation model evaluation in the North Mediterranean belt area. Solar Energy 70-2,
1274
143-153.
1275 1276
[50] Meleti H., 1999. The influence of meteorological parameters and total ozone on
1277
the measurements of ultraviolet solar radiation on the earth surface. Phd Thesis at
1278
Aristoteles University of Thesaloniki (in Greek).
1279 1280
[51] Zembila M., 2013. Climatological study of Ultraviolet Radiation in the Eastern
1281
Mediterranean. PhD Thesis at University of Thessaloniki (in Greek).
1282
56
ACCEPTED MANUSCRIPT 1283
[52] Bilbao J., Miguel A., Salvador P., 2006. UV-B solar irradiance and the influence
1284
of total ozone and aerosols at central Spain. In Conference on Visibility, Aerosols
1285
and Atmospheric Optics, Viena, September, 2006.
1286 1287
[53] Kasten F., Young AT., 1989. Revised optical air mass tables and approximation
1288
formula. Appl. Opt. 28, 4735-4738.
1289 1290
[54] Mateos D., de Miguel A., Bilbao J., 2010. Empirical models of UV total radiation
1291
and cloud effect study. International Journal of Climatology, 30, 1407-1415.
1292 1293
[55] Bilbao J., Mateos D., Yousif C., Román R., De Miguel A., 2016. Influence of
1294
cloudiness on erythemal solar irradiance in Marsaxlokk, Malta: Two case studies.
1295
Solar Energy 136, 475-486.
1296 1297
[56] Fellas A., Frederick Research Center, 2003. Skin cancer and Ultraviolet Solar
1298
Radiation: The case of Cyprus. Final Report (in Greek).
1299 1300
[57] McKenzie R. L., Liley J.B. and Björn L.O., 2009. UV Radiation: Balancing Risks
1301
and Benefits. Photochemistry and Photobiology 85, 88-98.
1302 1303
[58] Diffey L., Gibson J., Haylock R., McKinlay F., 1996. Outdoor ultraviolet exposure
1304
of children and adolescents. Br. J. Dermatol. 134, 1030-1034.
1305 1306
[59] Gies P., Roy C., MacLennan R., Watson M., 1995. UVR exposures of three
1307
groups of outdoor workers on the Sunshine Coast, Queensland. Photochem.
1308
Photobiol. 62, 1015-1021.
1309 1310
[60] Román R., Mateos D., de Miguel A., Bilbao J., Pérez-Burgos A., Rodrigo R.,
1311
Cachorro V., 2012. Atmospheric effects on the ultraviolet erythemal and total
1312
shortwave solar radiation in Vallaolid, Spain. Opt. Pura Apl. 45 (1), 17-21.
1313 1314
[61] Bilbao J., Román R., Yousif C., Mateos D., de Miguel A., 2014. Total ozone
1315
column, water vapour and aerosol effects on erythemal and global solar irradiance in
1316
Marsaxlokk, Malta. Atmos. Environ. 99, 508-518. 57
ACCEPTED MANUSCRIPT 1317 1318
[62] Bilbao J., Román R., Yousif C., Pérez-Burgos A., Mateos D., de Miguel A.,
1319
2015. Global, diffuse, beam and ultraviolet solar irradiance recorded in Malta and
1320
atmospheric component influences under cloudless skies. Solar Energy 121, 131-
1321
138.
1322 1323
[63] Cyprus Government report, taken from www.airquality.dli.mlsi.gov.cy/Reports/5
1324
Partculate Matter.pdf. 2004.
1325 1326
58