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Acidity of rain in Europe
Armosphcvtr
Enrironmrnr
Vol.
17. No.
I. pp. 127-137.
CKlO4-6981:83~010127-II SO3.00.0 c’ 1983 Pergamon Press Ltd.
1983
Prmted I” Great Brnam.
ACIDITY OF RAIN IN EUROPE A. S. KALLEND, A. R. W. MARSH, J. H. PICKLFB~~~ M. V. PROCTOR Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey KT22 7SE, U.K. (First
received 18 February 1982 and received@ publicarion 6 April 1982)
Abstract-A detailed statistical evaluation has been made of the precipitation acidity data from the European Atmospheric Chemistry Network for the time period 19561976 in an attempt to establish what trends are apparent. Out of 120 sites with 5 or more years data, 29 show a sign&ant trend of increasing annual average precipitation acidity during the period and five a decrease. For these sites substantially the same result arises for the hydrogen ion concentration calculated from ionic balance based on detailed chemical analysis of the precipitation samples. The data showed that the k-eased annual kvels of H+ arose from an incmased number of intermittent high monthly values after about 1964 rather than a sustained high level of acidity, with some months continuing to show low values similar to those seen prc+l964. This gives rise to an apparent stepincrease in annual average precipitation acidity for several of the sites at this time. Comparison of data from four adjacent Swedish sites showed that they were not well correlated suggesting that the major part of the variance was explained by local rather than regional influences.
I. INTRODUCTION
2. BASICDATA ANALYSIS:TIME TRENDS
more than 20 years precipitation has been routinely collected and analysed in several countries of Western Europe at a netwcyk of about 160 sites forming the European Atmospheric Chemistry Network (E.A.C.N.). This represents a period of continuous monitoring long enough to detect trends in the concentration and deposition of the major components of precipitation and such an analysis forms the basis of several publications by Granat (1972, 1978). Particular attention has been focused on sulphate in precipitation and indeed it was on the basis of data from the E.A.C.N. that it was first suggested that pollutants such as sulphur dioxide could be transported over long distances, and that increased emissions had led to increased deposition of sulphate in precipitation (Oden, 1968). However, in spite of the current interest in acid rain, no complete analysis has been presented of precipitation acidity in the E.A.C.N., although data for individual stations has been published from time to time (Oden, 1968, 1976; Likens er al., 1979) and Granat presented data on deposition of net acid for the period up to 1970 (Granat, 1972). Precipitation acidity is clearly a parameter of primary interest. In particular it has been claimed that in both Europe and North America there are expanding areas receiving acidic precipitation (Cogbill and Likens, 1974; Likens er al., 1979). We therefore, present here a statistical evaluation of the E.A.C.N. data on precipitation acidity and we examine, site-by-site, the trends that are apparent for the period 19554975. For comparison we also present a similar evaluation for sulphate and nitrate concentration.
The E.A.C.N. precipitation consists of monthly measurements of precipitation amount in mm, its pH, the deposition of ions SO, (as sulphur), Cl, NO, and NH4 (as nitrogen), Na, K, Mg and Ca in mg m-‘, the concentration of HCO, in m /- ’ and the conductivity in pscm- ‘. The collectors were continuously open and so collected both wet and dry deposited material. In previous analyses of the data, concentrations were presented as volume weighted annual averages and, accordingly, the initial analysis in the present study was carried out in this way. On this basis, annual average concentrations were evaluated for each chemical species. In this initial analysis, no data points were rejected but a large number of stations had data missing for one or two months in a given year, or data missing for two or three months for just a few of the ions, notably NH: and NO;. In those instances the values for the missing months were assumed to correspond to the yearly mean values. Where less than six months’ data were available yearly means were not evaluated. Five or more years’ data were available to CERL at 120 stations, giving a basis for an examination of trends in the network. In each case a linear regression analysis was performed and the correlation coefficient between H+ concentration and time calculated for each station over the period for which data were available. The results are listed in Table 1. Twenty-nine stations out of the 120 show a statistically significant increase in H+ concentration, and five a significant decrease although the underlying trends are obscured
For
127
Le Mans
zA=Ha=ux
Bruges St. Andre UCCk Botrange Duubces
z: 703
De Bilt
651 652 653 654
witteren
Lkn Helder
Romericke FiWjlf
H&UIl&
Gotebirg Stskhdm B&s-M&non Ry&-Kungsprd Uppsata Nas Kludkyttan Fama Bmk BjOrStllld TaiXi As L&a Trysil Kise Toreboda AW Granan KonosSe
Erken Forahult Kvamtorp 7 Fiahult Plonninge
Station name
:: 603
z 124 126 128 129 165 166
12 13 I5 16 21 23 25 32 38 39 40 42 43 44 46 47 48 51 53 59
Station No.
0.2597 - 0.9150 0.7324
0.133 0.387
-0.060
1.0100 1.524 0.9121 0.6274
0.5625 - 1.167 2.6234
0.501 0.136 1.765 0.402 0.785 1.401 1.301 1.269 1.397 - l.oBl 2021 1.664 - 3.071 - 0.324 -0.169 -0.912 0.269 2.323 1.954 3.533 2.431 2.877 5.174 4.863 1.269 6.196 - 1.469 - 2.900
Slope peql-‘ye’
0.269 0.453 0.380 0.246
0.297 0.03 1 0.468* 0.232 0.201 0.505; 0.473f 0.188 0.228 -0.293* 0.6% 0.328 - 0.777$ -0.124 - 0.642* -0.363 0.111 0.765$ 0683f 0.857t 0.787i 0.633. 0.633 0.837’ 0.292 0.568 - 0.288 -0.847 0.126 -0.149 0.355
55-62,67-70 55-m 55-71 55-75 55-66.69-75 55-74 55-71 57-68, m-73 57-77 58-77 58-77 65-77 65-76 66-76 66-75 66-76 66-76 55-75 55-75 57-73 57-75 67-77 70-77 72-77 72-77 72-77 69-73 69-73 57-68, 74 57-68, 74 56-68, 74 56-68.74 55-68.74 56-68,14 56-68,74 58-68,74 sad% 74 58-68.14
Correlation coefficient
Years with Calculated means
H+ ion
0.216 - 0.020 0.171
0.155 -0.126 0.515; 0.388
0.281 0.311 0.075
0.68 1l 0.287 0.344 0.180 0.467* 0.678t 0.578t 0.703t 0.43 I 0.081 0.311 -0.135 0.594’ 0.599 0.260 -0.129 0.426 0.661t 0.403 0.509* 0.435 -0.108 - 0.323 - 0.084 -0.721 0.269 - 0.055 -0.112
Correlation coefficient
1.6994 -0.7331 3.1304 2.3551 1.4961 -0.1413 1.2373
3.9684 0.298 1 0.4456
3.305 2.890 0.970 0.6% 1.519 4.533 2.458 4.228 2.709 1.058 2.033 - 0.645 4.787 2.599 0.531 - 1.370 1.647 2.281 2.463 10.504 1.711 - 0.322 -2.483 - 0.768 -3.141 4.125 - 0.481 - 0.792
0.756-J 0.817$ 0.919$
0.643* 0.737t 0.881$ 0.7491
0.909$ 0.872$ 0.846.j
0.850$ 0.324 0.777$ 0.923$ 0.901$ 0.886$ 0.846$ 0.8w 0.875$ 0.663$ 0.7493 0.428 0.595* 0.086 0.426 0.025 0.586 0.901$ 0.W 0.624t 0.8214 0.549 0.254 0.062 0.597 0.306 - 0.420 -0.161
__. _.____~ Slope Correlation PeqP-‘y-l coefficient
Excess SO1
Table 1. Correlations with time for excess sulphate and nitrate concentrations NO,
2.7928 2.7375 4.1244 2.9855 4.7337 4.7209 4.3301
6.5853 4.2233 6.4355
1.178 0.38 1 0.512 1.195 0.885 1.526 1.419 1.884 1.652 3.343 2.140 0.764 3.185 0.345 0.582 0.082 0.800 1.267 1.371 2.164 1.058 0.900 - 1.821 - 0.229 1.057 1.229 -l.lXlO - 0.477
Slope peq/-‘y-l
;
mb ?1
2 56 57 58 61 62 63 64 65 66 67 68 177 178 179 183 2 3 4 5 6
52
69 70 71
E 509 590 511 114 99 100 101 102
Z
Rjupnahed Vegatung
49 50 501
Kauhavia Kuopio Jyvaskyia Tvarminne Sodankyla Punkanarja Kuoliioki Puda$arvi Hailuoto Heisingfors Kiruna Arjcplog Ojet;ynRobacksdalen Offer
Odum Askov Tystofte Vagamo Tana Ytteroj Gjermudnes Fortun Fanaraken Stend Dalen
Klagcnfurt
Westerland Sehlcswig Braunsehweig Vokcnrode Bonn Augustenberg Ringshcim ~~cnw~erhof Feldbers Hohen&issenberg Retz ZJ; (Vienna)
Luxeuil Bourges Ambcricu
704 705 706
55-76 55-59 55-60 55-72 55-60
55-62 57-75 55-62 57-69 57-62 57-69 57-62 57-62 55-70 55-70 55-70 55-70 57-70 57-70 65-70 65-70 65-70 65-70 0.24% 0.514 0.481 -0.208 0.93ot 0.587 - 0.808 0.744$ 0.73% 0.97% 0.50Sf 0.648
0.404
0.727$ - 0.295
0.219 0.001 -0.102 0.250 0.47 0.734% 0.734$ 0.564 0.284 - 0.927t 0.619. - 0.824’ 0.245 -0.754 - 0.673
57-77 57-77 57-77 57-73 55-70 55-70 5560, 64-70
0.884* 0.792 0.87 1t 0.793 0.8283 0.901$ 0.462
0.703 0.938$
0.406 0.07 1
0.199 0.507 -0.104
57-63 5661 M-64 5761 5664 55-64 57-77
5863 5663
58-68, 74 58-68, 74 5868 61-77 61-72
1.686 - 0.274 1 a5987 0.6549 0.6856 0.8559 - 0.8339 4.0139 2.0676 - 3.323 0.709 0.8727 1.5932 2.881 0.8505
0.0855 0.5741 -0.177 0.3179 -0.1996 0.1146 - 1.8278 -0.7475
2.933 3.0075 2.8971
0.6292 0.0003 - 0.2328 - 0.3602
33.272 5.186 6.1949 0.2537 11.477 12.1726 1.2668
7.6649 21.304
0.2511 0.1294
0.3567 0.7383 -0.137
0.642% - 0.589* -0.156 0.833$ - 0.642
0.294 0.264 0.488 0.73ot 0.839$ - 0.237 0.782 0.736 - 0.266 0.478
0.648 - 0.005 0.799 0.230 0.524 -0.544 -0.031 0.595
0.241 0.466 0.547
0.785$ 0.612t 0.325 0.760$
0.224
0.398
0.559
- 0.698
- 0.045 - 0.472 0.183
0.564 0.315
-0.0197 -0.129
0.567 0.258 - 0.280
2.0427 1.8290 -0.7147 5.8452 - 1.5143
1.7425 1.7209 1.7789 3.5626 5.5641 -1.4604 7.9814 4.0524 - 1.2958 IO.9534
5.3340
0.3697
3.4879 0.00322 6.3781 1.2806 1.3404 1.3114
1.1406 2.3222 4.3952
6.7758 8.9322 1SO268 7.6086
-0.8315 -15.1134 2.5414 -8.7114 9.3876 3.9520 0.6174
- 23.4692 5.1575
-0.0819 - 0.3472
2.1503 1.3744 - 1.5416
0.7653 0.153 0.841. 0.x39* 0.633
0.329
0.579* 0.653+ 0.171 0.765$ 0.505 0.525 0.404 - 0.050 -0.184
- 0.026 0.689t - 0.043 0.137 -0.507 -0.719 - 0.829 - 0.296
0.676*
OS4S 0.63Ot
0.606I
0.938t 0.861t 0.927f
0.573 0.841* 0.797s 0.738 0.751* 0.730’ 0.646t
0.760 0.656
0.397 0.44
0.817$ 0.716t 0.699*
0.6912 1.1103 0.1794 2.8548 0.7121 1.0418 1.2286 -0.1143 - 0.6856 3.2000 0.3088 0.0714 0.9714 I .0537 0.6572
-0.0357 I.1390 - 0.0752 0.3846 0.5143 0.5165 0.5429 -0.3714
2.8971 1.1173 1.6025
2.3234 3.3999 4.7104 1.1372
5.6286 12.7428 3.7833 8.4999 2.8167 1.3212 1.1844
2.8571 1.3690
1.6912 0.0140
4.1102 2.3033 3.4091
,,, ,,,, ,,
* Denotessip
No.
Station
Tabk 1. umtd
/, ,,
Years with
al-70,72,74
s-70,72,74 58-70.72,74 5a-70,72,74 5%70.72 14 5&67,69, 70, 12, 14 58-70.72,74 s-q 72,74
izi 67-74
;izi
iiz 55-66 58-74 Ml. 64-66
s-74
n”-6”: 66-72 71-77 69-77 -77 70-77 12-77 73-n
~~ 5ss9
5566
E-z 55-59
:zi
55-60
cdctilatcd means
Slope
zzi a2410 0.0375
0.2977 -a&26 0.1NJ3 0.1136
-zil
-$Z
-JwJ3 --am4 -0AJ73 - 29J7S
-tmpl s
#cq/-'y-t
,,
.,
,, ,,
,,
,,,,,
,,
,,
- 0.025
-0.398 -a051 -0.m ail67 -0.767 -a494 -a459
s
l
s* O&w
izi as7*
:gg
~~ am3
-@ii
-s
~~ mw iiN1
$iK
-4217 a550 -b%iJ -atts -tM1t -QJ6J
,,
eocakicllrt
- 3.0549 -a2135 - 1.3576 Q.4451 - 1.9209 - 3.4396 -2.7965 -0.1206
“i$c 33924
:%f 8iJut Q4rn
- 27233 - 5.18JS 2Jw cm!6
--i!k -a7273 - I.UJ3 -1w
pqr*y-
Slope
ExcessSOA
co’.;;
P c 0.05, t P < 0.01, $ P < 0.001. Statiot~ 251-258, So, not corra%d for settsalt.
Station name
H+ ion
0.5715 0.1837 0.8915 1.7528 ii4% -0Io53 0.5638 03116 -o&38 a382
1.2843 1.9mo 1.43% 4.m 1.1838 cstfo 5.8217 1.03JS 8.2657 2.1333 l‘s691
ii%7 -au?14 -0.3214 0314 -0.1999
!!!i
-mm0
-&gig
-z71 a2#7
0.0571 a5357
fJlope
m/ -‘y-’
O.Mt* 0.188 ascnS 0.480
a226
z a4J2
z
iii!? a&w
z*
a!w
-ii%
a233 a29t -atm -a219
z
--iii:
as77 -aJ34
-iii!
0.131 a497 a493
c?oeacht
Chmlation
NO,
ii
131
Acidity of rain in Europe by the scatter in the data and because many of the stations operated for different periods. Most of the stations with the longer runs of data are in Scandinavia, where 12 sites with at least 18 years data for the 20 year period 19561975 showed increases in hydrogen ion concentration averaging 7”/, per year, compared with a year to year scatter of 50-100 “/, of the mean values. Table 2 shows these 12 sites with their H + mean value, standard deviation and the regression slope. For comparison, Table 1 also lists correlations with time for both excess sulphate ahd nitrate concentrations. Excess sulphate is defined as the residual sulphate after the observed sulphate has been corrected for the contribution from sea salt assuming that all the magnesium concentration derives from sea salt. In the case of sulphate 23 sites show a positive significant trend and one shows a negative trend. The average increase at the Scandinavian sites of Table 2 is 2.5 “/, per year. Many more stations (55) show a significant increase in weighted annual nitrate concentration, including all of the sites in Table 2, where the average rate of increase was about 67; a year. No station showed a significant decrease in nitrate concentration.
3. DATA QUALITY In deriving yearly means from measurements made month-by-month there is a necessary assumption that the monthly data are valid. One method of testing the consistency of the monthly data is to examine the balance between positive and negative ions. Any difference or imbalance (either positive or negative) can be expressed as a percentage of the total number of ions present. This can then be used to filter the data at different levels of consistency. Table 3 shows the ion balance month by month for a typical station, Kise (60), in Norway. Months where the ion balance cannot be calculated because ion measurements are missing are given the score 4. Score 1 indicates an ion imbalance of less than lo%, score 2 between 10 and
20 T,, and score 3, an imbalance of more than 20 7;. Monthly samples for Kise were analysed at the Meteorological institute in Stockholm. Other stations analyzed at Stockholm give similar ion balance matrices sometimes with less than 50% of the monthly data sets showing a satisfactory (score 1) ion balance. Poor quality data may, in part, be responsible for the apparent discrepancies in year to year variation of H+ for some Scandinavian stations. For example Figs l-3 show the plots of anrtual mean H + for Forshult (15), Plonninge (23) and Smedby (25). It can be seen that the H+ value jumps to a peak in 1965. In each case, data for 1965 had the worst level of consistency for the whole time period with respectively only 2, 2 and 3 months passing the 10% test for ion balance. Errors in pH determinations, and therefore, in the corresponding H+ concentration, are one potential source of discrepancy in the ion balance equation. To this extent the ion balance test provides a partial check on the accuracy of the H + value. Alternatively, Cogbill and Likens (1974) suggested that it should be possible to evaluate pH even when direct measurements are not available, from a complete analysis of the other ions present. Lillstrand and Morgan (1979) showed that for an analytical accuracy of f 10% the maximum error in pH calculated from ion balance is likely to occur at around pH = 5.6 (and is equal to 0.5), while the calculated standard deviation is likely to be less than 0.1 pH units at pH = 4. To check the reliability of the trendscalculated using yearly mean H+ the regression calculations for the 34 stations with significant trends in the yearly mean data for H + were repeated using the monthly data, first as it stands and then with data for “suspect” months omitted. At the same time monthly values for H+ were calculated from the other ionic concentrations for the same 34 stations and the regressions repeated with these calculated values. Table 4 shows the results of such an analysis for the station at Kise (60) in Norway. This station was operating from 1957 to 1975, i.e. 228 months. From this number 21 months had tobe discarded because of
Table 2. Mean H’ values for 12 Scandinavian siteswith at least 18 years data in the 20-year period 1956-1975
Station 2 15 16 21 23 25 38 40 54 51 53 60
Kiruna Forshult Kvarntorp 7 Flahuh Plonninge Smedby Goteburg Bohus-Malmon Tana
As Lista Kise
Mean H’ peq/-’
Standard deviation
6.5 29.1 19.4 27.3 37.3 23.4 60.0 29.9 4.3 27.6 32.9 21.8
6.8 25.6 10.2 25.4 16.4 18.7 38.1 17.1 11.5 18.8 17.7 17.4
Slope fieq /:-I y-t 0.71 1.77 0.40 0.79 1.40 1.30 1.40 2.02 0.57 2.32 1.95 2.43
132
A. S. KALLEND et al.
IX)--
3 i
I 90-
op am--
+x
1963
t 1975
Fig. 1. Forshult 15 yearly variation of H* showing actual l-I+ values and the resulting regression line.
Fig. 2. Plonninge 23 yearly variation of H” showing actual H+ values and the resulting regression line.
f
J
Fig. 3. Smedby 25 yaarly variation of H+ showing actual H+ vaIucs and the resulting regression line.
missing measurements la&g 207 months. Using all these it can be seen tbet there is a positive and statistically, sign&ant trend with time far the mcasurtd monthly H*. The regression was repeated omitting months where the percentage ion imbsiance was greater than f 20% (leaving 163 months) and then again omitting months w&e it was greater than f 10% (leaving 118 month& Of the 29 stations wIki& showed a positive significant trend for the yearly means, 24 also showed a similar trend for the monthly data for measured H’ passing the f 10% filter. Of the exceptions
133
Acidity of rain in Europe Table 4. Comparison of time trends using obset’vcximantbiy HC values and c&dated monthly H‘ values for Kise (60) Calculated H’
H+ Type of regression and no, of data points
Correlation coefTkient
Monthly (228 possibk) 207 Monthly ( f 209; limit) 163 Monthly (f 10% G&t) 118 Yearly 19
0.807$
Slope pegI-‘y-’
Correlation coefficient
0.632t
2.337
SiOpe
jIq(-‘y-’
2.189
co~~t~on coe&zient H+ to calculated
H+
0.565
H+ mean for & 10% limit = 29.8; standard deviation = 27.1. Cakuiated H+ mean for 2 10% lit = 32.Q standard deviation = 28.1. Symbols as in Table 1. _
Lana (17) and Granan (126) had only just achieved significance (P < 0.05) for yearly means and Pudasjarvi (178), while achkving signi&ance ( P < 0.01) for yearly means, had montbly data of which only 27 months out of a possibk 67 ptlwd tl%e!f 10% filter. Results for the two Irish stations Malin (251)and Rosslare (256) cannot be directly compared with the original H” regression over years 1958-1974 since measurement of the complete set of ions was not started until 1964.In the event.,Malin shows no trend and Rosslare shows a signiikant increase. The ~rr~~n~g picture of trends in the e&ulaced H+ for these stations is more confused although 21 of them show a significant positive trend where the 10% ion balance filter is imposed on the data. In most instances, the calculated H+ points are more scattered than the measured vahksSpartkularly for stations near the se%e.g. Lista, for which the very high levels of Na ’ and Cl- contribute to a krgc value for total ionic strengths. In these cases, discrepancies in ion baknce do not show up to the same extent as a proportion of the total and are not fIltered by the 4 10% limit, Roth Lista (53)and Rohus-Mahnon {40),which are exposed coastal sites, have low correlations between the measured H” and the adcukted H+ of 0.146 and O.lgl, respectively while Rise, which is inland, has a correlation coefficient of 0.904. Of the five stations which showed a negative trend in the original analysis for the yearly average measured vahtes of H +f four gave a silt negative trend for the monthly data QWred by the f 10% limit), while the calcukted H’ vales gave non-significant negative trends.
and o&y months with the ion balawx: within the f 10% lit were included. The results given in Tabk 5 which shows that the winter months have generally larger mean valuer and standard deviations. For the measured II+ coneentrationakast squares fit to a sine curve shows an annual cycle, peaking in February, with an amplitude of 11.2 peq C t, or about 35 % of a mean level of 30.9beq I- *.The amplitude of the eorrespondmg cycle in pH is 0.15. exe&e
More detaikd ~tio~ of the data for individual stations shows that, for about l/3 of the stations with significant correktions in Table 1,a more-or-less sudden change in precipitation acidity seems to have ~~int~~l~~~~a~~ change in pH over the whok time period. Figure 4 showsjust three examplesfor the stations Lista (53XAs (51) and Rise (60). Regressions of monthly data were run for two separate time periods (1) up to the end of 1964and (2) from I&mary 1965onwards (Tabk 6) for each of the eight stations in Tabk 2 which showed a sign&ant positive trend over the whole period. The cakukted ratea of imuease in measured II + concentration in the. post 1965 regressions average 2 % per year and do not attain statistical signitkance (P < 0.05) for any individual station. The behaviour shown mirrors simikr observations with resper;t to sulphate reported by Granat (1978)and could, therefore, he rekted to a sudden but maintained increase in annual deposition of sulphate. I&amination of the monthly data showed that the inc~~~l~ofH~~f~~~~ number of intermittent high monthly values (Fig. 5X 4. SEASONAL VARIA‘MONS with some months contimring to show low values In orcicr to 8cc tile effdct of seasonaI variations, data similar to those seen pm-lM, that is to say the post for both measured and cakukted H+ were examined 1%5 data show a much greater scatter. The increasusing madinge for each month separately. Ki (60), ing scatter in H+ data can be attributed to a constant being a fairly typical station, was chosen for this scatter in levels of pH over the whok period amplified
134
A. g.
KALLEND’ei
ai.
Fig. 4. Annual mean H’ c~n~~trati~~s vs year for Lista 53. As 51 and Kise 60.
by the exponential relationship between H + and pH. The larger residual standard deviations in the post1965 data sets are broadly ~ro~~ional to the increased mean values as would be expected on this basis.
6. AD.lACENTSITES
Granat ( 1972) concluded that, in general, statues in the same geographical area seem to belong to the same trend pattern. This conclusion was based on data for yearly means in excess suiphate and Granat consequently grouped data for several sites, in order to derive regression lines and determine trends. We, therefore, sought a group of neigh~uring sites to look for correlations between their analytical data, In fact, very few areas have stations with data for a sufficiently long period but we fin&y seieeted a cluster of four stations round Uppsala (43) all within 25 km of each other. These were: Lat (Nf Uppsala (43) Bjorsund (47) Ryda-Kungsgard (42) Tama (48)
59 59 59 59
48 28 45 5t’
Long (RI 17 37 16’49‘ 17 08’ 16’38
All these sites operated between 1956 and 1976, The first observation of note is that UppssLa and Bjorsund both show sjgni~ant negative trends of hydrogen ion with time while Tarna and RydaKungsgard show non-sign~~~ant positive trends. Figure 6 shows a scatter pint of PI-I for the former pair of sites using all the avaiiable monthly data (r=0.3i7, PcO.01). Far the latter pair, the correlation coeficient was r = 0.223 (PC 0.05). For each pair of stations the r values indicate that there is a detectable common regional component in the variation in data which accounts for 20-30”,, of the variance. The greater part of the variance. however. is
Symbols as in Table 1.
Kiruna2
KiX60
Lista 53
As 51
Bohus-Mahnon 40
Smedby 25
Plonninge 23
Forshult 15
Station
1955-1964 (53) 1965-1977 (112) 1958-1964 (46) (1964-1977 ww 1955-1964 (65) 1964-197s (1OO) 1955-64 (81) l%W975 (1%) 1957-64 091 1964-74 (89) 1955-64 (41) 1965-78 (51)
1955-1964 (57) 1%~1977 (1%) 1952-1964 (69) 1965-1977
Time spas and No. of points
36.02
49.30
2.10
26.7
7.35
19.95 18.56
2.31
37.6
5*93
52.42 36.59
22.85 21.37
9.92
11.35
0.257
-Ql47
Q152
Ql98
o.037
-a046
d.035
0.07 1
0.020
43.16
30.77
0.232
a348
34.09 29.93 11.48 lo.32
-0.002
14.96 14.07
0.652$ - o.o42
0.054
38.04 21.42 29.14 24.15 43.80 22.91
0.480#
1.411
-0.116
1.376
a604
o.431
-a315
- 0.424
0.244
0.167
1.234
3.062
- 0.m
5.443 -0.3ao
0.338
2.812
Slope Meq/-‘y-’
H+ ion Correlation coeliicient
13.94 17.10
(H+) mean and std. dev. E u
0.448$
0.126
o.loo
0.406’
-O.O20
0.223.
- ao3s
0.212
-WI!i
-0.044
0.392
o.117
0.010
0.60%
0.018
0.529$
Correialion coefficient
- 0.028 0.889 2.891
0.886 0.947 0.259
0.737
- o.oo5 -0.589 2.177
o.o91
0.882 - 0.423 4.8%
oh83
0.043 0.933
a191
0.032
0.807 3.830 -0.894
0.828
0.903
0.679 0.414
0.903
0.113 5.304 0.116
0.913
Correlation of(H (cak. H’)
3.979
Slope peqeq/-‘y-’
Calculated H” ion
Table 6. Comparison of time trends for the periods up to the end of 1964 and from January I%5 onwards
136
A. S. KALLEND 130
00
1957
1976
Fig. 5. Kise 60 values of H * for months passing the IO’% filter.
uppsato pt4
Fig. 6. Scatter plot of monthly pH values for Bjorsund
vs those for Uppsala.
accounted for by measurement factors particular to each individual station which cannot be allowed for without detailed local knowledge. Benarie and Detrie ( 1978) found similar evidence for the “patchy pattern” of precipitation acidity in Europe and Norway in an examination of the data from the O.E.C.D. study. 7. DISCUsslON
This paper has been concerned to examine the E.A.C.N. data which has been reported as demonstmting a trend of increasing rainfall acidity with time @den. 1968, 1976; Likens et al., 1970; Granat, 1972). Patterson and Scorer (1973, 1975) have previously investigated the consistency of these data, applying a series of practical checks, and noted a variety of on-site recording errors and in~~~s~~~ between different analytical laboratories. Such sho~comings are wellappreciated by the co-ordinators of the E.A.C.N. network who have progressively improved siting and analysis over the years. For these reasons, data for more recent years should be given more weight than those from earlier. The ion balance checks reported here tackle the consistency problem from a more mathematical point
PI al.
of view, suitable for the computer analysis of the very large quantities of data involved, In many cases, the data show large discrepancies in ion balance or poor correlation between hydrogen ion concentrations determined from pH measurements and calculated from ion balance considerations. A simple regression analysis on weighted annual average precipitation acidity shows that only 29 of 120 sampling sites show a statistically significant trend of increasing acidity. For these the data filtering process followed does not substantially alter the main feature of the hydrogen ion data, namely that the concentrations measured in the 1970s are higher (typically by a factor of 3 or 4) than the concentrations measured in the 1950s. More substantial increases are seen for nitrate and a less marked increase for sulphate. The nature and cause of the increase in H + concentration at these sites remains unclear. A detailed analysis does not bear out the expectation of a steady increase in acidity over the whole period 1950-1975 paralleling, for example. the increase in sulphur emissions. Rather, the monthly data show that the increased average levels of H +. where they do occur, arise from an increased frequency of intermittent high monthly values occurring from about 1965 onwards. In several stations this appears to have occurred quite suddenly. around 1965, leading to an apparent step change in annual average acidity, while other stations showed single high values. However, it has not been possible to isolate any clear anomaly in the data which might be associated with changes in sampling or analytical technique. One possible explanation could he a sustained change in the regional meteorology starting at that time. Munn and Rodhe (1971) used the E.A.C.N. data for sulphate and chloride to examine the influence of meteorological factors on deposition. They concluded that differences in sulphur deposition at Flahult and Plonninge could be accounted for by changes in the flow pattern from the SE-SSW -NW sector together with the changes in sulphur emission in roughly equal proportions. However, not ail stations show this type of behaviour and this detracts from such claims for regional effects. In view of these uncertainties, interpretation of the changes in precipitation chemistry should proceed with care. In particular, isopleth maps (Likens rf al., t979) showing acidity and changes in acidity may be misleading in several respects, failing adequately to show the pattern of time variation over the years, the large degree of uncertainty attaching to individual contours and assuming a geographical homogeneity which is not borne out by detailed calculations with data taken from adjacent sites.
Acknowledyemenrs-The work described here was carried the Central Electricity Research laboratories. and is published by permission of the Central Electricity Generating Board. The authors are grateful to Dr. V. M. Morton of CERL for the use of his data analysis program.
out at
Acidity of rain in Europe REFERENCES
Benarie M. and Detrie P. (1978) Assessment of an O.E.C.D. Study on long-range transport of pollutants (LRTAP) involving some aspects of air chemistry. In Atmospheric Environment, 1978. Elsevier, Amsterdam. Cogbill C. V. and Likens G. E. (1974) Acid precipitation in the northeastern United States. War. Resources, 10,11331137. Granat L. (1972) On the relation between pH and the chemical composition in atmosphere pollution. Tel/us 24, 550-560.
Granat L. (1978) Sulphate in precipitation as observed by the European Atmospheric Chemistry Network. Atmospheric Environment 12,413-424.
Likens G. E., Wright R. F., Galloway J. N. and Butler T. J. (1979) Acid rain. Scient. Am. 241, 39-47.
137
Lillstrand H. M. and Morgan J. J. (1979) Error analysis applied to indirect methods for precipitation acidity. Tellus 31, 421-31. Munn R. E. and Rodhe H. (1971) On the meteorological interpretation of the chemical composition on monthly precipitation samples. Tellus 23, l-13. Oden S. (1968) The acidification of air and precipitation and its consequences on the natural environment. Swedish Nat. Sci. Res. Council, Ecology Committee, Bul. 1. p. 68, l-86. Oden S. (I 976) Acidity problem: an outline ofconcepts. Wur. Air Soil Pollur. 6, 137-166. Paterson M. P. and Scorer R. S. (1973) Data quality and the European Air Chemistry Network. Atmospheric Enoironment 7, 1163-l 171. Paterson M. P. and Scorer R. S. (1975) The chemistry of seasalt aerosol and its measurement. Nature 254. 491495.
Enrironmrnr
Vol.
17. No.
I. pp. 127-137.
CKlO4-6981:83~010127-II SO3.00.0 c’ 1983 Pergamon Press Ltd.
1983
Prmted I” Great Brnam.
ACIDITY OF RAIN IN EUROPE A. S. KALLEND, A. R. W. MARSH, J. H. PICKLFB~~~ M. V. PROCTOR Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey KT22 7SE, U.K. (First
received 18 February 1982 and received@ publicarion 6 April 1982)
Abstract-A detailed statistical evaluation has been made of the precipitation acidity data from the European Atmospheric Chemistry Network for the time period 19561976 in an attempt to establish what trends are apparent. Out of 120 sites with 5 or more years data, 29 show a sign&ant trend of increasing annual average precipitation acidity during the period and five a decrease. For these sites substantially the same result arises for the hydrogen ion concentration calculated from ionic balance based on detailed chemical analysis of the precipitation samples. The data showed that the k-eased annual kvels of H+ arose from an incmased number of intermittent high monthly values after about 1964 rather than a sustained high level of acidity, with some months continuing to show low values similar to those seen prc+l964. This gives rise to an apparent stepincrease in annual average precipitation acidity for several of the sites at this time. Comparison of data from four adjacent Swedish sites showed that they were not well correlated suggesting that the major part of the variance was explained by local rather than regional influences.
I. INTRODUCTION
2. BASICDATA ANALYSIS:TIME TRENDS
more than 20 years precipitation has been routinely collected and analysed in several countries of Western Europe at a netwcyk of about 160 sites forming the European Atmospheric Chemistry Network (E.A.C.N.). This represents a period of continuous monitoring long enough to detect trends in the concentration and deposition of the major components of precipitation and such an analysis forms the basis of several publications by Granat (1972, 1978). Particular attention has been focused on sulphate in precipitation and indeed it was on the basis of data from the E.A.C.N. that it was first suggested that pollutants such as sulphur dioxide could be transported over long distances, and that increased emissions had led to increased deposition of sulphate in precipitation (Oden, 1968). However, in spite of the current interest in acid rain, no complete analysis has been presented of precipitation acidity in the E.A.C.N., although data for individual stations has been published from time to time (Oden, 1968, 1976; Likens er al., 1979) and Granat presented data on deposition of net acid for the period up to 1970 (Granat, 1972). Precipitation acidity is clearly a parameter of primary interest. In particular it has been claimed that in both Europe and North America there are expanding areas receiving acidic precipitation (Cogbill and Likens, 1974; Likens er al., 1979). We therefore, present here a statistical evaluation of the E.A.C.N. data on precipitation acidity and we examine, site-by-site, the trends that are apparent for the period 19554975. For comparison we also present a similar evaluation for sulphate and nitrate concentration.
The E.A.C.N. precipitation consists of monthly measurements of precipitation amount in mm, its pH, the deposition of ions SO, (as sulphur), Cl, NO, and NH4 (as nitrogen), Na, K, Mg and Ca in mg m-‘, the concentration of HCO, in m /- ’ and the conductivity in pscm- ‘. The collectors were continuously open and so collected both wet and dry deposited material. In previous analyses of the data, concentrations were presented as volume weighted annual averages and, accordingly, the initial analysis in the present study was carried out in this way. On this basis, annual average concentrations were evaluated for each chemical species. In this initial analysis, no data points were rejected but a large number of stations had data missing for one or two months in a given year, or data missing for two or three months for just a few of the ions, notably NH: and NO;. In those instances the values for the missing months were assumed to correspond to the yearly mean values. Where less than six months’ data were available yearly means were not evaluated. Five or more years’ data were available to CERL at 120 stations, giving a basis for an examination of trends in the network. In each case a linear regression analysis was performed and the correlation coefficient between H+ concentration and time calculated for each station over the period for which data were available. The results are listed in Table 1. Twenty-nine stations out of the 120 show a statistically significant increase in H+ concentration, and five a significant decrease although the underlying trends are obscured
For
127
Le Mans
zA=Ha=ux
Bruges St. Andre UCCk Botrange Duubces
z: 703
De Bilt
651 652 653 654
witteren
Lkn Helder
Romericke FiWjlf
H&UIl&
Gotebirg Stskhdm B&s-M&non Ry&-Kungsprd Uppsata Nas Kludkyttan Fama Bmk BjOrStllld TaiXi As L&a Trysil Kise Toreboda AW Granan KonosSe
Erken Forahult Kvamtorp 7 Fiahult Plonninge
Station name
:: 603
z 124 126 128 129 165 166
12 13 I5 16 21 23 25 32 38 39 40 42 43 44 46 47 48 51 53 59
Station No.
0.2597 - 0.9150 0.7324
0.133 0.387
-0.060
1.0100 1.524 0.9121 0.6274
0.5625 - 1.167 2.6234
0.501 0.136 1.765 0.402 0.785 1.401 1.301 1.269 1.397 - l.oBl 2021 1.664 - 3.071 - 0.324 -0.169 -0.912 0.269 2.323 1.954 3.533 2.431 2.877 5.174 4.863 1.269 6.196 - 1.469 - 2.900
Slope peql-‘ye’
0.269 0.453 0.380 0.246
0.297 0.03 1 0.468* 0.232 0.201 0.505; 0.473f 0.188 0.228 -0.293* 0.6% 0.328 - 0.777$ -0.124 - 0.642* -0.363 0.111 0.765$ 0683f 0.857t 0.787i 0.633. 0.633 0.837’ 0.292 0.568 - 0.288 -0.847 0.126 -0.149 0.355
55-62,67-70 55-m 55-71 55-75 55-66.69-75 55-74 55-71 57-68, m-73 57-77 58-77 58-77 65-77 65-76 66-76 66-75 66-76 66-76 55-75 55-75 57-73 57-75 67-77 70-77 72-77 72-77 72-77 69-73 69-73 57-68, 74 57-68, 74 56-68, 74 56-68.74 55-68.74 56-68,14 56-68,74 58-68,74 sad% 74 58-68.14
Correlation coefficient
Years with Calculated means
H+ ion
0.216 - 0.020 0.171
0.155 -0.126 0.515; 0.388
0.281 0.311 0.075
0.68 1l 0.287 0.344 0.180 0.467* 0.678t 0.578t 0.703t 0.43 I 0.081 0.311 -0.135 0.594’ 0.599 0.260 -0.129 0.426 0.661t 0.403 0.509* 0.435 -0.108 - 0.323 - 0.084 -0.721 0.269 - 0.055 -0.112
Correlation coefficient
1.6994 -0.7331 3.1304 2.3551 1.4961 -0.1413 1.2373
3.9684 0.298 1 0.4456
3.305 2.890 0.970 0.6% 1.519 4.533 2.458 4.228 2.709 1.058 2.033 - 0.645 4.787 2.599 0.531 - 1.370 1.647 2.281 2.463 10.504 1.711 - 0.322 -2.483 - 0.768 -3.141 4.125 - 0.481 - 0.792
0.756-J 0.817$ 0.919$
0.643* 0.737t 0.881$ 0.7491
0.909$ 0.872$ 0.846.j
0.850$ 0.324 0.777$ 0.923$ 0.901$ 0.886$ 0.846$ 0.8w 0.875$ 0.663$ 0.7493 0.428 0.595* 0.086 0.426 0.025 0.586 0.901$ 0.W 0.624t 0.8214 0.549 0.254 0.062 0.597 0.306 - 0.420 -0.161
__. _.____~ Slope Correlation PeqP-‘y-l coefficient
Excess SO1
Table 1. Correlations with time for excess sulphate and nitrate concentrations NO,
2.7928 2.7375 4.1244 2.9855 4.7337 4.7209 4.3301
6.5853 4.2233 6.4355
1.178 0.38 1 0.512 1.195 0.885 1.526 1.419 1.884 1.652 3.343 2.140 0.764 3.185 0.345 0.582 0.082 0.800 1.267 1.371 2.164 1.058 0.900 - 1.821 - 0.229 1.057 1.229 -l.lXlO - 0.477
Slope peq/-‘y-l
;
mb ?1
2 56 57 58 61 62 63 64 65 66 67 68 177 178 179 183 2 3 4 5 6
52
69 70 71
E 509 590 511 114 99 100 101 102
Z
Rjupnahed Vegatung
49 50 501
Kauhavia Kuopio Jyvaskyia Tvarminne Sodankyla Punkanarja Kuoliioki Puda$arvi Hailuoto Heisingfors Kiruna Arjcplog Ojet;ynRobacksdalen Offer
Odum Askov Tystofte Vagamo Tana Ytteroj Gjermudnes Fortun Fanaraken Stend Dalen
Klagcnfurt
Westerland Sehlcswig Braunsehweig Vokcnrode Bonn Augustenberg Ringshcim ~~cnw~erhof Feldbers Hohen&issenberg Retz ZJ; (Vienna)
Luxeuil Bourges Ambcricu
704 705 706
55-76 55-59 55-60 55-72 55-60
55-62 57-75 55-62 57-69 57-62 57-69 57-62 57-62 55-70 55-70 55-70 55-70 57-70 57-70 65-70 65-70 65-70 65-70 0.24% 0.514 0.481 -0.208 0.93ot 0.587 - 0.808 0.744$ 0.73% 0.97% 0.50Sf 0.648
0.404
0.727$ - 0.295
0.219 0.001 -0.102 0.250 0.47 0.734% 0.734$ 0.564 0.284 - 0.927t 0.619. - 0.824’ 0.245 -0.754 - 0.673
57-77 57-77 57-77 57-73 55-70 55-70 5560, 64-70
0.884* 0.792 0.87 1t 0.793 0.8283 0.901$ 0.462
0.703 0.938$
0.406 0.07 1
0.199 0.507 -0.104
57-63 5661 M-64 5761 5664 55-64 57-77
5863 5663
58-68, 74 58-68, 74 5868 61-77 61-72
1.686 - 0.274 1 a5987 0.6549 0.6856 0.8559 - 0.8339 4.0139 2.0676 - 3.323 0.709 0.8727 1.5932 2.881 0.8505
0.0855 0.5741 -0.177 0.3179 -0.1996 0.1146 - 1.8278 -0.7475
2.933 3.0075 2.8971
0.6292 0.0003 - 0.2328 - 0.3602
33.272 5.186 6.1949 0.2537 11.477 12.1726 1.2668
7.6649 21.304
0.2511 0.1294
0.3567 0.7383 -0.137
0.642% - 0.589* -0.156 0.833$ - 0.642
0.294 0.264 0.488 0.73ot 0.839$ - 0.237 0.782 0.736 - 0.266 0.478
0.648 - 0.005 0.799 0.230 0.524 -0.544 -0.031 0.595
0.241 0.466 0.547
0.785$ 0.612t 0.325 0.760$
0.224
0.398
0.559
- 0.698
- 0.045 - 0.472 0.183
0.564 0.315
-0.0197 -0.129
0.567 0.258 - 0.280
2.0427 1.8290 -0.7147 5.8452 - 1.5143
1.7425 1.7209 1.7789 3.5626 5.5641 -1.4604 7.9814 4.0524 - 1.2958 IO.9534
5.3340
0.3697
3.4879 0.00322 6.3781 1.2806 1.3404 1.3114
1.1406 2.3222 4.3952
6.7758 8.9322 1SO268 7.6086
-0.8315 -15.1134 2.5414 -8.7114 9.3876 3.9520 0.6174
- 23.4692 5.1575
-0.0819 - 0.3472
2.1503 1.3744 - 1.5416
0.7653 0.153 0.841. 0.x39* 0.633
0.329
0.579* 0.653+ 0.171 0.765$ 0.505 0.525 0.404 - 0.050 -0.184
- 0.026 0.689t - 0.043 0.137 -0.507 -0.719 - 0.829 - 0.296
0.676*
OS4S 0.63Ot
0.606I
0.938t 0.861t 0.927f
0.573 0.841* 0.797s 0.738 0.751* 0.730’ 0.646t
0.760 0.656
0.397 0.44
0.817$ 0.716t 0.699*
0.6912 1.1103 0.1794 2.8548 0.7121 1.0418 1.2286 -0.1143 - 0.6856 3.2000 0.3088 0.0714 0.9714 I .0537 0.6572
-0.0357 I.1390 - 0.0752 0.3846 0.5143 0.5165 0.5429 -0.3714
2.8971 1.1173 1.6025
2.3234 3.3999 4.7104 1.1372
5.6286 12.7428 3.7833 8.4999 2.8167 1.3212 1.1844
2.8571 1.3690
1.6912 0.0140
4.1102 2.3033 3.4091
,,, ,,,, ,,
* Denotessip
No.
Station
Tabk 1. umtd
/, ,,
Years with
al-70,72,74
s-70,72,74 58-70.72,74 5a-70,72,74 5%70.72 14 5&67,69, 70, 12, 14 58-70.72,74 s-q 72,74
izi 67-74
;izi
iiz 55-66 58-74 Ml. 64-66
s-74
n”-6”: 66-72 71-77 69-77 -77 70-77 12-77 73-n
~~ 5ss9
5566
E-z 55-59
:zi
55-60
cdctilatcd means
Slope
zzi a2410 0.0375
0.2977 -a&26 0.1NJ3 0.1136
-zil
-$Z
-JwJ3 --am4 -0AJ73 - 29J7S
-tmpl s
#cq/-'y-t
,,
.,
,, ,,
,,
,,,,,
,,
,,
- 0.025
-0.398 -a051 -0.m ail67 -0.767 -a494 -a459
s
l
s* O&w
izi as7*
:gg
~~ am3
-@ii
-s
~~ mw iiN1
$iK
-4217 a550 -b%iJ -atts -tM1t -QJ6J
,,
eocakicllrt
- 3.0549 -a2135 - 1.3576 Q.4451 - 1.9209 - 3.4396 -2.7965 -0.1206
“i$c 33924
:%f 8iJut Q4rn
- 27233 - 5.18JS 2Jw cm!6
--i!k -a7273 - I.UJ3 -1w
pqr*y-
Slope
ExcessSOA
co’.;;
P c 0.05, t P < 0.01, $ P < 0.001. Statiot~ 251-258, So, not corra%d for settsalt.
Station name
H+ ion
0.5715 0.1837 0.8915 1.7528 ii4% -0Io53 0.5638 03116 -o&38 a382
1.2843 1.9mo 1.43% 4.m 1.1838 cstfo 5.8217 1.03JS 8.2657 2.1333 l‘s691
ii%7 -au?14 -0.3214 0314 -0.1999
!!!i
-mm0
-&gig
-z71 a2#7
0.0571 a5357
fJlope
m/ -‘y-’
O.Mt* 0.188 ascnS 0.480
a226
z a4J2
z
iii!? a&w
z*
a!w
-ii%
a233 a29t -atm -a219
z
--iii:
as77 -aJ34
-iii!
0.131 a497 a493
c?oeacht
Chmlation
NO,
ii
131
Acidity of rain in Europe by the scatter in the data and because many of the stations operated for different periods. Most of the stations with the longer runs of data are in Scandinavia, where 12 sites with at least 18 years data for the 20 year period 19561975 showed increases in hydrogen ion concentration averaging 7”/, per year, compared with a year to year scatter of 50-100 “/, of the mean values. Table 2 shows these 12 sites with their H + mean value, standard deviation and the regression slope. For comparison, Table 1 also lists correlations with time for both excess sulphate ahd nitrate concentrations. Excess sulphate is defined as the residual sulphate after the observed sulphate has been corrected for the contribution from sea salt assuming that all the magnesium concentration derives from sea salt. In the case of sulphate 23 sites show a positive significant trend and one shows a negative trend. The average increase at the Scandinavian sites of Table 2 is 2.5 “/, per year. Many more stations (55) show a significant increase in weighted annual nitrate concentration, including all of the sites in Table 2, where the average rate of increase was about 67; a year. No station showed a significant decrease in nitrate concentration.
3. DATA QUALITY In deriving yearly means from measurements made month-by-month there is a necessary assumption that the monthly data are valid. One method of testing the consistency of the monthly data is to examine the balance between positive and negative ions. Any difference or imbalance (either positive or negative) can be expressed as a percentage of the total number of ions present. This can then be used to filter the data at different levels of consistency. Table 3 shows the ion balance month by month for a typical station, Kise (60), in Norway. Months where the ion balance cannot be calculated because ion measurements are missing are given the score 4. Score 1 indicates an ion imbalance of less than lo%, score 2 between 10 and
20 T,, and score 3, an imbalance of more than 20 7;. Monthly samples for Kise were analysed at the Meteorological institute in Stockholm. Other stations analyzed at Stockholm give similar ion balance matrices sometimes with less than 50% of the monthly data sets showing a satisfactory (score 1) ion balance. Poor quality data may, in part, be responsible for the apparent discrepancies in year to year variation of H+ for some Scandinavian stations. For example Figs l-3 show the plots of anrtual mean H + for Forshult (15), Plonninge (23) and Smedby (25). It can be seen that the H+ value jumps to a peak in 1965. In each case, data for 1965 had the worst level of consistency for the whole time period with respectively only 2, 2 and 3 months passing the 10% test for ion balance. Errors in pH determinations, and therefore, in the corresponding H+ concentration, are one potential source of discrepancy in the ion balance equation. To this extent the ion balance test provides a partial check on the accuracy of the H + value. Alternatively, Cogbill and Likens (1974) suggested that it should be possible to evaluate pH even when direct measurements are not available, from a complete analysis of the other ions present. Lillstrand and Morgan (1979) showed that for an analytical accuracy of f 10% the maximum error in pH calculated from ion balance is likely to occur at around pH = 5.6 (and is equal to 0.5), while the calculated standard deviation is likely to be less than 0.1 pH units at pH = 4. To check the reliability of the trendscalculated using yearly mean H+ the regression calculations for the 34 stations with significant trends in the yearly mean data for H + were repeated using the monthly data, first as it stands and then with data for “suspect” months omitted. At the same time monthly values for H+ were calculated from the other ionic concentrations for the same 34 stations and the regressions repeated with these calculated values. Table 4 shows the results of such an analysis for the station at Kise (60) in Norway. This station was operating from 1957 to 1975, i.e. 228 months. From this number 21 months had tobe discarded because of
Table 2. Mean H’ values for 12 Scandinavian siteswith at least 18 years data in the 20-year period 1956-1975
Station 2 15 16 21 23 25 38 40 54 51 53 60
Kiruna Forshult Kvarntorp 7 Flahuh Plonninge Smedby Goteburg Bohus-Malmon Tana
As Lista Kise
Mean H’ peq/-’
Standard deviation
6.5 29.1 19.4 27.3 37.3 23.4 60.0 29.9 4.3 27.6 32.9 21.8
6.8 25.6 10.2 25.4 16.4 18.7 38.1 17.1 11.5 18.8 17.7 17.4
Slope fieq /:-I y-t 0.71 1.77 0.40 0.79 1.40 1.30 1.40 2.02 0.57 2.32 1.95 2.43
132
A. S. KALLEND et al.
IX)--
3 i
I 90-
op am--
+x
1963
t 1975
Fig. 1. Forshult 15 yearly variation of H* showing actual l-I+ values and the resulting regression line.
Fig. 2. Plonninge 23 yearly variation of H” showing actual H+ values and the resulting regression line.
f
J
Fig. 3. Smedby 25 yaarly variation of H+ showing actual H+ vaIucs and the resulting regression line.
missing measurements la&g 207 months. Using all these it can be seen tbet there is a positive and statistically, sign&ant trend with time far the mcasurtd monthly H*. The regression was repeated omitting months where the percentage ion imbsiance was greater than f 20% (leaving 163 months) and then again omitting months w&e it was greater than f 10% (leaving 118 month& Of the 29 stations wIki& showed a positive significant trend for the yearly means, 24 also showed a similar trend for the monthly data for measured H’ passing the f 10% filter. Of the exceptions
133
Acidity of rain in Europe Table 4. Comparison of time trends using obset’vcximantbiy HC values and c&dated monthly H‘ values for Kise (60) Calculated H’
H+ Type of regression and no, of data points
Correlation coefTkient
Monthly (228 possibk) 207 Monthly ( f 209; limit) 163 Monthly (f 10% G&t) 118 Yearly 19
0.807$
Slope pegI-‘y-’
Correlation coefficient
0.632t
2.337
SiOpe
jIq(-‘y-’
2.189
co~~t~on coe&zient H+ to calculated
H+
0.565
H+ mean for & 10% limit = 29.8; standard deviation = 27.1. Cakuiated H+ mean for 2 10% lit = 32.Q standard deviation = 28.1. Symbols as in Table 1. _
Lana (17) and Granan (126) had only just achieved significance (P < 0.05) for yearly means and Pudasjarvi (178), while achkving signi&ance ( P < 0.01) for yearly means, had montbly data of which only 27 months out of a possibk 67 ptlwd tl%e!f 10% filter. Results for the two Irish stations Malin (251)and Rosslare (256) cannot be directly compared with the original H” regression over years 1958-1974 since measurement of the complete set of ions was not started until 1964.In the event.,Malin shows no trend and Rosslare shows a signiikant increase. The ~rr~~n~g picture of trends in the e&ulaced H+ for these stations is more confused although 21 of them show a significant positive trend where the 10% ion balance filter is imposed on the data. In most instances, the calculated H+ points are more scattered than the measured vahksSpartkularly for stations near the se%e.g. Lista, for which the very high levels of Na ’ and Cl- contribute to a krgc value for total ionic strengths. In these cases, discrepancies in ion baknce do not show up to the same extent as a proportion of the total and are not fIltered by the 4 10% limit, Roth Lista (53)and Rohus-Mahnon {40),which are exposed coastal sites, have low correlations between the measured H” and the adcukted H+ of 0.146 and O.lgl, respectively while Rise, which is inland, has a correlation coefficient of 0.904. Of the five stations which showed a negative trend in the original analysis for the yearly average measured vahtes of H +f four gave a silt negative trend for the monthly data QWred by the f 10% limit), while the calcukted H’ vales gave non-significant negative trends.
and o&y months with the ion balawx: within the f 10% lit were included. The results given in Tabk 5 which shows that the winter months have generally larger mean valuer and standard deviations. For the measured II+ coneentrationakast squares fit to a sine curve shows an annual cycle, peaking in February, with an amplitude of 11.2 peq C t, or about 35 % of a mean level of 30.9beq I- *.The amplitude of the eorrespondmg cycle in pH is 0.15. exe&e
More detaikd ~tio~ of the data for individual stations shows that, for about l/3 of the stations with significant correktions in Table 1,a more-or-less sudden change in precipitation acidity seems to have ~~int~~l~~~~a~~ change in pH over the whok time period. Figure 4 showsjust three examplesfor the stations Lista (53XAs (51) and Rise (60). Regressions of monthly data were run for two separate time periods (1) up to the end of 1964and (2) from I&mary 1965onwards (Tabk 6) for each of the eight stations in Tabk 2 which showed a sign&ant positive trend over the whole period. The cakukted ratea of imuease in measured II + concentration in the. post 1965 regressions average 2 % per year and do not attain statistical signitkance (P < 0.05) for any individual station. The behaviour shown mirrors simikr observations with resper;t to sulphate reported by Granat (1978)and could, therefore, he rekted to a sudden but maintained increase in annual deposition of sulphate. I&amination of the monthly data showed that the inc~~~l~ofH~~f~~~~ number of intermittent high monthly values (Fig. 5X 4. SEASONAL VARIA‘MONS with some months contimring to show low values In orcicr to 8cc tile effdct of seasonaI variations, data similar to those seen pm-lM, that is to say the post for both measured and cakukted H+ were examined 1%5 data show a much greater scatter. The increasusing madinge for each month separately. Ki (60), ing scatter in H+ data can be attributed to a constant being a fairly typical station, was chosen for this scatter in levels of pH over the whok period amplified
134
A. g.
KALLEND’ei
ai.
Fig. 4. Annual mean H’ c~n~~trati~~s vs year for Lista 53. As 51 and Kise 60.
by the exponential relationship between H + and pH. The larger residual standard deviations in the post1965 data sets are broadly ~ro~~ional to the increased mean values as would be expected on this basis.
6. AD.lACENTSITES
Granat ( 1972) concluded that, in general, statues in the same geographical area seem to belong to the same trend pattern. This conclusion was based on data for yearly means in excess suiphate and Granat consequently grouped data for several sites, in order to derive regression lines and determine trends. We, therefore, sought a group of neigh~uring sites to look for correlations between their analytical data, In fact, very few areas have stations with data for a sufficiently long period but we fin&y seieeted a cluster of four stations round Uppsala (43) all within 25 km of each other. These were: Lat (Nf Uppsala (43) Bjorsund (47) Ryda-Kungsgard (42) Tama (48)
59 59 59 59
48 28 45 5t’
Long (RI 17 37 16’49‘ 17 08’ 16’38
All these sites operated between 1956 and 1976, The first observation of note is that UppssLa and Bjorsund both show sjgni~ant negative trends of hydrogen ion with time while Tarna and RydaKungsgard show non-sign~~~ant positive trends. Figure 6 shows a scatter pint of PI-I for the former pair of sites using all the avaiiable monthly data (r=0.3i7, PcO.01). Far the latter pair, the correlation coeficient was r = 0.223 (PC 0.05). For each pair of stations the r values indicate that there is a detectable common regional component in the variation in data which accounts for 20-30”,, of the variance. The greater part of the variance. however. is
Symbols as in Table 1.
Kiruna2
KiX60
Lista 53
As 51
Bohus-Mahnon 40
Smedby 25
Plonninge 23
Forshult 15
Station
1955-1964 (53) 1965-1977 (112) 1958-1964 (46) (1964-1977 ww 1955-1964 (65) 1964-197s (1OO) 1955-64 (81) l%W975 (1%) 1957-64 091 1964-74 (89) 1955-64 (41) 1965-78 (51)
1955-1964 (57) 1%~1977 (1%) 1952-1964 (69) 1965-1977
Time spas and No. of points
36.02
49.30
2.10
26.7
7.35
19.95 18.56
2.31
37.6
5*93
52.42 36.59
22.85 21.37
9.92
11.35
0.257
-Ql47
Q152
Ql98
o.037
-a046
d.035
0.07 1
0.020
43.16
30.77
0.232
a348
34.09 29.93 11.48 lo.32
-0.002
14.96 14.07
0.652$ - o.o42
0.054
38.04 21.42 29.14 24.15 43.80 22.91
0.480#
1.411
-0.116
1.376
a604
o.431
-a315
- 0.424
0.244
0.167
1.234
3.062
- 0.m
5.443 -0.3ao
0.338
2.812
Slope Meq/-‘y-’
H+ ion Correlation coeliicient
13.94 17.10
(H+) mean and std. dev. E u
0.448$
0.126
o.loo
0.406’
-O.O20
0.223.
- ao3s
0.212
-WI!i
-0.044
0.392
o.117
0.010
0.60%
0.018
0.529$
Correialion coefficient
- 0.028 0.889 2.891
0.886 0.947 0.259
0.737
- o.oo5 -0.589 2.177
o.o91
0.882 - 0.423 4.8%
oh83
0.043 0.933
a191
0.032
0.807 3.830 -0.894
0.828
0.903
0.679 0.414
0.903
0.113 5.304 0.116
0.913
Correlation of(H (cak. H’)
3.979
Slope peqeq/-‘y-’
Calculated H” ion
Table 6. Comparison of time trends for the periods up to the end of 1964 and from January I%5 onwards
136
A. S. KALLEND 130
00
1957
1976
Fig. 5. Kise 60 values of H * for months passing the IO’% filter.
uppsato pt4
Fig. 6. Scatter plot of monthly pH values for Bjorsund
vs those for Uppsala.
accounted for by measurement factors particular to each individual station which cannot be allowed for without detailed local knowledge. Benarie and Detrie ( 1978) found similar evidence for the “patchy pattern” of precipitation acidity in Europe and Norway in an examination of the data from the O.E.C.D. study. 7. DISCUsslON
This paper has been concerned to examine the E.A.C.N. data which has been reported as demonstmting a trend of increasing rainfall acidity with time @den. 1968, 1976; Likens et al., 1970; Granat, 1972). Patterson and Scorer (1973, 1975) have previously investigated the consistency of these data, applying a series of practical checks, and noted a variety of on-site recording errors and in~~~s~~~ between different analytical laboratories. Such sho~comings are wellappreciated by the co-ordinators of the E.A.C.N. network who have progressively improved siting and analysis over the years. For these reasons, data for more recent years should be given more weight than those from earlier. The ion balance checks reported here tackle the consistency problem from a more mathematical point
PI al.
of view, suitable for the computer analysis of the very large quantities of data involved, In many cases, the data show large discrepancies in ion balance or poor correlation between hydrogen ion concentrations determined from pH measurements and calculated from ion balance considerations. A simple regression analysis on weighted annual average precipitation acidity shows that only 29 of 120 sampling sites show a statistically significant trend of increasing acidity. For these the data filtering process followed does not substantially alter the main feature of the hydrogen ion data, namely that the concentrations measured in the 1970s are higher (typically by a factor of 3 or 4) than the concentrations measured in the 1950s. More substantial increases are seen for nitrate and a less marked increase for sulphate. The nature and cause of the increase in H + concentration at these sites remains unclear. A detailed analysis does not bear out the expectation of a steady increase in acidity over the whole period 1950-1975 paralleling, for example. the increase in sulphur emissions. Rather, the monthly data show that the increased average levels of H +. where they do occur, arise from an increased frequency of intermittent high monthly values occurring from about 1965 onwards. In several stations this appears to have occurred quite suddenly. around 1965, leading to an apparent step change in annual average acidity, while other stations showed single high values. However, it has not been possible to isolate any clear anomaly in the data which might be associated with changes in sampling or analytical technique. One possible explanation could he a sustained change in the regional meteorology starting at that time. Munn and Rodhe (1971) used the E.A.C.N. data for sulphate and chloride to examine the influence of meteorological factors on deposition. They concluded that differences in sulphur deposition at Flahult and Plonninge could be accounted for by changes in the flow pattern from the SE-SSW -NW sector together with the changes in sulphur emission in roughly equal proportions. However, not ail stations show this type of behaviour and this detracts from such claims for regional effects. In view of these uncertainties, interpretation of the changes in precipitation chemistry should proceed with care. In particular, isopleth maps (Likens rf al., t979) showing acidity and changes in acidity may be misleading in several respects, failing adequately to show the pattern of time variation over the years, the large degree of uncertainty attaching to individual contours and assuming a geographical homogeneity which is not borne out by detailed calculations with data taken from adjacent sites.
Acknowledyemenrs-The work described here was carried the Central Electricity Research laboratories. and is published by permission of the Central Electricity Generating Board. The authors are grateful to Dr. V. M. Morton of CERL for the use of his data analysis program.
out at
Acidity of rain in Europe REFERENCES
Benarie M. and Detrie P. (1978) Assessment of an O.E.C.D. Study on long-range transport of pollutants (LRTAP) involving some aspects of air chemistry. In Atmospheric Environment, 1978. Elsevier, Amsterdam. Cogbill C. V. and Likens G. E. (1974) Acid precipitation in the northeastern United States. War. Resources, 10,11331137. Granat L. (1972) On the relation between pH and the chemical composition in atmosphere pollution. Tel/us 24, 550-560.
Granat L. (1978) Sulphate in precipitation as observed by the European Atmospheric Chemistry Network. Atmospheric Environment 12,413-424.
Likens G. E., Wright R. F., Galloway J. N. and Butler T. J. (1979) Acid rain. Scient. Am. 241, 39-47.
137
Lillstrand H. M. and Morgan J. J. (1979) Error analysis applied to indirect methods for precipitation acidity. Tellus 31, 421-31. Munn R. E. and Rodhe H. (1971) On the meteorological interpretation of the chemical composition on monthly precipitation samples. Tellus 23, l-13. Oden S. (1968) The acidification of air and precipitation and its consequences on the natural environment. Swedish Nat. Sci. Res. Council, Ecology Committee, Bul. 1. p. 68, l-86. Oden S. (I 976) Acidity problem: an outline ofconcepts. Wur. Air Soil Pollur. 6, 137-166. Paterson M. P. and Scorer R. S. (1973) Data quality and the European Air Chemistry Network. Atmospheric Enoironment 7, 1163-l 171. Paterson M. P. and Scorer R. S. (1975) The chemistry of seasalt aerosol and its measurement. Nature 254. 491495.