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Estimation of atmospheric inorganic water-soluble aerosols in the western region of Bahrain by ion chromatography
Chemosphere: Global Change Science 2 (2000) 85±94
Estimation of atmospheric inorganic water-soluble aerosols in the western region of Bahrain by ion chromatography Ahmed Y. Ali-Mohamed*, Ali Hassan Jaar Department of Chemistry, College of Science, University of Bahrain, P.O. Box 32038, Isa Town, Bahrain Received 2 March 1998; accepted 14 January 1999
Importance of this paper: Deposition of aerosols may induce a response on soil and water ecosystems, in addition to deterioration in visibility caused by suspended particulates. The presence of increased concentration of water-soluble ions was reported globally to in¯uence natural processes of nucleation. Such particulate pollutants were found to contain a great diversity of both water-soluble and insoluble components. In this research work the dry deposition collection of aerosols in the troposphere and their composition in the western region of Bahrain have been chosen, where little interference from industrial sources is anticipated. The use of ion chromatography instead of conventional wet chemical methods is an attractive method because of its simultaneous detection and sensitivity. Abstract Dry fall aerosol particulate matter was collected in the western rural area of Bahrain. The collection was carried out using an open beaker trap of deionized water placed on the roof of an 8 m high building in seven villages representing the area under study. The water-soluble matter was analyzed for its chemical components by ion chromatography. The data obtained were in good correlation with the meteorological and surface features of Bahrain. The sizes of 108 randomly chosen particles, measured with a photomicrographic microscope, ranged between 6 and 230 lm. The latter value gives an indication that most of these particles were soil-derived. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: Aerosol particulate matter; Water-soluble matter; Ion chromatography; Rural area; Bahrain; Anions and cations
1. Introduction The identi®cation of natural and man-made sources of air particulates in rural atmosphere and estimation of relative strengths of particulate pollution sources in urban areas has received further attention by the application of improved analytical and statistical techniques (Cawse, 1982). Ion chromatography has become an indispensable tool for the analytical chemist in the area of anion analysis. In many cases this method has superseded * Corresponding author. Tel.: +973-782343/782351; fax: +973-682-582.
conventional wet chemical methods such as titration, photometry, gravimetry, turbidimetry, and colorimetry, all of which are labor-intensive, time-consuming, and occasionally susceptible to interferences. In the ®eld of cation analysis, ion chromatography is attractive because of its simultaneous detection and sensitivity (Weiss, 1995). The amount of dry-deposited material depends on the pollutant and surface properties as well as on the meteorological situation and the extent of pollution. The latter depends on the emission rate and is again in¯uenced by the uptake of the pollutant at the surface and by atmospheric transport (Schl unzen and Pahl, 1992). Gaseous pollutants make up about 90% of the total mass emitted to the atmosphere with particulates and
1465-9972/99/$ - see front matter Ó 1999 Elsevier Science Ltd. All rights reserved. PII: S 1 4 6 5 - 9 9 7 2 ( 9 9 ) 0 0 0 5 8 - 6
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aerosols accounting for the remaining 10%. Particulates are emitted into the atmosphere by a diverse group of sources and vary over a wide range of sizes, shapes, densities, and chemical composition. Small particulates are of particular importance because they may be in the respirable size range. These small particles may contain biologically active elements and compounds (Morgan et al., 1970). The present study is aimed at estimating the atmospheric dry fall deposition of the suspended particulate matter in a rural area of the state of Bahrain. The chemical components of the water-soluble matter were determined using the technique of ion chromatography. Correlations have been made between the data obtained and the meteorological and surface characteristics of Bahrain.
1.1. Area under study The group of islands of Bahrain lie in an arm of the Arabian Gulf, known as the Gulf of Salwa, which separates the Qatar peninsula and Saudi Arabia (Fig. 1). Geographically, they are located in the core of an extensive zone of aridity. The main island, called Bahrain, has dierent features. Population density is high in the northern and northeastern parts where the major industries are located. On the other hand, there is a rural, fertile area in the western and northwestern part of the island. Our sites for this study are located in the western rural area of Bahrain, an area that comprises about 15% of the total land of Bahrain. Nearly 22,000 people live in this area compared to the total population of Bahrain which was 500,000 in 1991. Seven small villages were chosen to represent this region. From the north, these are Al-Hamalah [HM], Dumistan [DM], Karzakk an [KZ], Al-M alikiyah [ML], Sadad [SD], Shahrakk an [SK], and D ar Kulayb [DK]. These villages are separated from the western shores by a large strip of agricultural land that stretches more than 12 km from the north to the south. The villages from Dumistan to Shahrakk an are joined by an 8 km low trac highway. There are ancient burial mounds to the north of D ar Kulayb covering an area of about 0.26 km2 . Northeast of Dumistan is located a very saline lake called ``Al-Lawzi Lake''.
2. Experimental 2.1. Sampling Seven 1 l beakers ®lled with deionized water were placed in seven villages representing the area under
Fig. 1. Map of the state of Bahrain showing the location of the studied sites: [HM] Al-Hamalah; [DM] Dumistan; [KZ] Karzakk an; [ML] Al-M alikiyah; [SD] Sadad; [SK] Shahrakk an; [DK] D ar kulayb.
study. Each beaker was placed on the roof of an 8 m high building for 1 week. 2.2. Suspended matter determination The water sample was ®ltered on a previously dried and weighed 0.45 lm ®lter paper. The ®lter paper was then dried in an oven at 70°C and ®nally reweighed. The total suspended solid was obtained by subtracting the weight of the ®lter paper before ®ltration from that after ®ltration. The ®ltrate was diluted to 500 cm3 (sometimes to 1 l) using deionized water. The following steps were then carried out. 2.2.1. Anions and cations analysis 2ÿ ÿ ÿ The anions Clÿ ; NOÿ 2 ; Br ; NO3 ; and SO4 and 2 2 the cations (Li ; Na ; NH4 ; K ; Mg ; Ca ; Sr2 ; and Ba2 were determined by a Metrohm ion chromatograph (IC-690). Injection of 100 ll of the sample into a PRP-X100 anion column (Manufactured by
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
87
Fig. 2. Separation of inorganic anions. Separator column : PRP-X100; Eluent: 0.002 mol lÿ1 phthalic acid, 10% acetone, pH 5.0; ¯ow. Rate: 2 ml minÿ1 ; detection: conductivity detector, injection volume: 100 ll, (A) Standard solution of anions. Solute concentrations: 5 ppm chloride, 5 ppm nitrite, 10 ppm bromide, 10 ppm nitrate, and 10 ppm sulphate. (B) Water-soluble components in Shahrakk an sample. Solute concentrations: 9.74 ppm chloride, 2.06 ppm nitrate, and 16.84 ppm sulphate.
Hamilton, Reno, NV, USA) using 0.002 mol dmÿ3 phthalic acid eluent (10% acetone, pH 5, conductivity approximately 180 lS cmÿ1 ) will separate the above anions in less than 20 min. Several peaks, each representing a certain anion, were obtained from the chart recorder. (Fig. 2). Length analysis of these peaks using standard peaks obtained from a standard solution of the anions will give an indication of the concentration of the stated anions in the sample. Separation of the above cations was attained in less than 15 min by injection of 10 ll of the sample into a SUPER-SEP cation column (manufactured by Hamilton PRP-X100) using 0.75 mg/l tartaric acid eluent (conductivity approximately 500 lS cmÿ1 ) and [5 mmol/l citric acid]/[0.5 mmol/l dipicolinic acid] eluent (conductivity approximately 500 lS cmÿ1 ). The concentration of the cations in the sample were determined by area analysis of the peaks representing these cations using standard peaks obtained from a
standard solution of the cations (Fig. 3). The anions and cations in both the sample and the standard were analyzed three times following the above procedure. 2.2.2. Conductivity and pH determination The pH and conductivity measurements of the water trap samples at 22.5°C were measured using a Crison 525 conductimeter (cell constant 1.38) and Crison 507 pH meter. 2.2.3. Particle size determination The particles collected on micromembrane were magni®ed 10 times their actual size using an Olympus Microscope-model BHS-photomicrographic-system (PM-10AD)-re¯ected light-¯uorescence attachmentBH2-RFL. The length of a total of 108 randomly chosen particles was determined using the appropriate scale attached to the microscope.
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Fig. 3. Separation of inorganic cations. Separator column: SUPER-SEP; eluent: 0.75 mg lÿ1 tarataric acid, pH 4.5; ¯ow rate: 1 ml minÿ1 ; detection: conductivity detector; injection volume: 10 ll. (A) Standard solution of cations. Solute concentrations: 1 ppm lithium, 5 ppm sodium, 5 ppm ammonium, 10 ppm potassium, 10 ppm magnesium, 10 ppm calcium, 20 ppm strontium, and 20 ppm barium. (B) Water-soluble components in Shahrakk an sample. Solute concentrations 5.67 ppm sodium, 0.21 ppm potassium, 1.01 ppm magnesium, and 22.03 ppm calcium.
3. Results and discussion The climate of Bahrain features high temperatures, high relative humidities, low but seasonal rainfall, and a predominantly northwesterly wind direction which has associated with it the strongest winds. The `Shamal' is the predominant dust-raising wind, sometimes bringing airborne silts from Arabia or even from Iraq, some 250 miles to the northwest (Doornkamp et al., 1980). Weekly and mean monthly values of meteorological data over the studied period 1 are summarized in Table 1. These climatic features of Bahrain have a considerable eect on the dry fall deposition and its chemical composition. High concentrations of anions, especially Clÿ and 2ÿ SO4 and cations, especially Na and Ca2 , were reported in Dumistan village during the months of Octo-
1
Interested people can get the data from the authors.
ber±December 1994 and February 1995.2 About 750 m to the northeast of this village is located Al-Lawzi Lake which is characterized by its high salinity. Salt particles from this lake accompanied by the Northerly, Easterly or the Northeasterly winds seems to have brought about the high anionic and cationic constituents in the village of Dumistan. Worth noticing is the high conductivity values of the water-soluble components associated with this phenomenon. Values as high as 1447 and 1600 lS cmÿ1 were reported in the third week of December and the ®rst week of November 1994, respectively. The corresponding Clÿ concentrations were 418.18 and 537.6 ppm, and the corresponding SO2ÿ 4 concentrations were 269.44 and 307.58 ppm (Fig. 4), the latter value in each case being the highest during the period studied. A dust storm was reported on 18 October 1994 caused by southeasterly winds. As a result, a high
2
Interested people can get the data from the authors.
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
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Table 1 Mean weekly climatological summary over the studied perioda Month
Week no.
Period
Press (hpa)
Rh (%)
Sun (h)
Temp (°C)
Rain (mm)
Vis (km)
Wind Dir
Oct 94
1 2 3 4 Mean
2±8,10,94 8±16,10,94 16±22,10,94 22±29,10,94
1010.6 1013.2 1014.3 1014.5 1013.2
62.6 66.3 69.1 65 65.5
10 9.5 7.3 10.3 9.3
30.8 29.8 29.4 27.8 29.4
0.00 0.00 0.00 0.00 0.00
17.9 15.4 14 14.9 15.7
N E/SE SE/N N N
7.1 5.6 8.9 6.7 7
Nov 94
1 2 3 4 Mean
29,10±15,11,94 5±12,11,94 12±19,11,94 19±26,11,94
1015.9 1016.6 1015.1 1016.5 1016
68.5 64.56 65.5 65.87 66.3
10 9.1 8.4 7.7 8.8
28.1 26.9 25.3 25.1 26.4
0.00 0.00 0.00 0.00 0.00
14.7 18.06 15.95 13.87 15.5
N/E S/N N SE N
5.9 12.19 10.36 8.69 9.3
Dec 94
1 2 3 4 5 Mean
26,11±3,12,94 3±10,12,94 10±17,12,94 17±24,12,94 24±31,12,94
1015.1 1021.8 1021.3 1020.8 1021.7 1020.3
67.23 57.57 74.09 69.67 66.61 66.48
8.3 8 6.8 8.4 8.4 8
23.2 16.3 18.1 19.5 16.4 18.7
0.00 0.00 0.00 0.00 0.00 0.00
15.35 15.1 14.52 14.52 14.3 15.36
S/N NW NW N/NW NW NW/N
8.46 15.43 7.26 11.18 8.18 10.42
Jan 95
1 2 3 4 Mean
31,12±7,1,95 7±14,1,95 14±21,1,95 21±28,1,95
1020.6 1018 1020.8 1021.5 1020.2
75.69 72.34 72.88 64.96 71.68
8.7 8.2 8.2 8.3 8.6
17.2 18.4 18.4 16.1 17.5
0.00 0.00 0.00 0.04 TR
11.69 12.02 12.97 19.08 13.84
NW W/S N NW NW
10.26 8.08 10.23 13.19 10.11
Feb 95
1 2 3 4 Mean
28,1±4,2,95 4±11,2,95 11±18,2,95 18±25,2,95
1019.1 1015.8 1017.6 1016.5 1017.3
73.31 70.98 69.3 66.48 70.36
8.9 4.9 8.7 8.9 7.9
18.2 19 17.6 18.2 18.2
0.00 3.11 0.08 0.00 0.88
15.18 14.94 16.52 17.22 15.87
NW N NW/N N/NW N/NW
6.03 11.99 10.98 10.5 9.64
1017.4
68.06
8.5
22
0.18
15.25
N/NW
9.29
Mean
Wind Spd (knots)
a
Press ± station pressure; Rh ± relative humidity; Sun ± total of bright sunshine; Temp ± dry-bulb temperature; Vis ± visibility; Wind Dir ± prevailing wind direction; Wind Spd ± wind speed.
Fig. 4. Weekly values of conductivity (n) (lS cmÿ1 ): concentrations of Clÿ (d); SO2ÿ 4 (n) (ppm) at [HM] station.
Fig. 5. Weekly concentration of total suspended solid (mg an. [h] Aldmÿ3 ). [d] Al-Hamalah. [s] Dumistan. [n] Karzakk M alikiyah. [n] Sadad. [m] Shahrakk an. [r] D ar Kulayb.
90
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
Fig. 6. Microscopic photographs of aerosol dust particles 10 times magni®cation of dust particles collected: (a) 0.20 mm (AlMalikiyah); (b) 0.050 mm (Sadad); (c) 0.039 mm (Shahrakk an); (d) 0.022 mm (Al-Hamalah).
deposition of aerosol suspended solid was recorded reaching 203.4 and 202.9 mg lÿ1 in D ar Kulayb and Karzakk an villages, respectively, in the third week of October 1994. The second week of December 1994 was characterized by prevailing and strong northwesterly winds reaching 21.08 knots on 7 December which had lowered the visibility to 6.46 km on the same day (Bahrain Civil Aviation Meteorological Data, 1994±1995). The lowest temperature and relative humidity of the period from October 1994 to May 1995 were reported in this week, being 11.9°C on 8 December 1994 and 44.33% on 6 December 1994. This wintry week caused a high dry fall deposition especially in Al-M alikiyah village which has had the highest ever reported total suspended solid of 276.0 mg lÿ1 (Fig. 5). The only appreciable rainfall during the studied period was reported in the second week of February 1995. A total of 24.9 mm of rain fell on 6±8 of this month causing a washout of the atmospheric particulate matter. Consequently, high concentrations of total suspended solid were reported in this week, noticeably in AlM alikiyah and D ar Kulayb villages which were 269.1 and 218.5 mg lÿ1 , respectively.
As in the coastal areas to the south, the excess of evaporation over precipitation in the western coast has led to enrichment to the surface sediments in salts, mainly gypsum and in many areas the surface sands are composed almost entirely of gypsum (Doornkamp et al., 1980). This is the reason why there is a relatively high ÿ concentration of SO2ÿ 4 compared to Cl concentration except for some weeks in Dumistan for the reason stated previously. This conclusion is supported by a higher concentration of Ca2 compared to Na . The presence of the agricultural strip which stretches more than 12 km along the western coast of Bahrain and separates the villages from the sea might have minimized, to a considerable extent, the eect of the sea as a major source of Clÿ and Na ions. The mean total suspended solid ranges between 63.4 mg lÿ1 in Al-Hamalah village and 8.1 mg lÿ1 in Shahrakk an village.3 The considerably low dry deposition in Shahrakk an is probably due to the type of the top soil north of this village which is mainly mud. The last three
3
Interested people can get the data from the authors.
a
95% CL
0.53 1.41 0.73 0.45 0.55 0.66 0.86
0.0323 0.1425 0.0494 0.075 0.0424 0.518 0.1503
1.044 20.32 2.44 5.629 1.796 2.683 22.57
var 10ÿ3 0.0802 0.3539 0.1226 0.1663 0.1052 0.1286 0.373
95% CL
0.02 0.02 0.01 0.01 0.01 0.02 0.02
20.28 51.01 11.22 7.34 20.44 5.57 10.3
x
Snÿ1 x
0.1898 0.649 0.1925 0.265 0.3677 0.127 0.1611
x
0.0058 0.117 0.006 0.0114 0.0219 0.0026 0.0042 SO2ÿ 4
0.0764 0.342 0.0775 0.107 0.146 0.0512 0.0649
NOÿ 3
6.13 74.53 4.94 3.85 1.18 2.33 7.03
x
var
x
Snÿ1 x
NOÿ 2
Clÿ
0.1476 0.4833 0.0923 0.1764 0.1425 0.0743 0.1573
Snÿ1 x
0.0144 0.01 0.0072 0.00 0.0072 0.0107 0.0031
Snÿ1 x
21.79 233.5 8.527 31.12 20.3 5.519 24.74
var 10ÿ3
207.6 99.662 51.74 0.00 51.59 114.85 9.378
var 10
ÿ6
0.3665 1.1997 0.2292 0.436 0.3537 0.1844 0.3905
95% CL
0.0356 0.0246 0.0179 0.00 0.0176 0.0266 0.0008
95% CL
x ± mean value of the anion (ppm); Snÿ1 x ± standard deviation; var ± variance; 95% CL ± 95% con®dence limit.
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Station
Table 2 Statistics of the anionic analysisa
0.31 0.94 1.11 0.7 0.88 0.95 0.29
x
Brÿ 0.0197 0.0999 0.0416 0.0265 0.0316 0.028 0.0402
Snÿ1 x
3.897 99.691 17.502 7.034 9.989 7.812 16.134
var 10ÿ4
0.049 0.2479 0.1039 0.0658 0.0785 0.0694 0.0997
95% CL
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94 91
a
95% CL
46.94 95.92 37.87 30.08 40.79 23.76 53.48
3.136 7.995 4.39 2.804 5.208 2.583 4.808
9.832 63.92 19.27 7.861 27.12 6.593 23.11
var 7.784 19.85 10.9 6.961 12.93 6.374 11.94
95% CL
0.63 0.37 0.48 0.6 0.46 0.72 0.54
0.05 0.04 0.03 0.02 0.03 0.01 0.04
x
Snÿ1 x
1.712 24.09 2.221 2.735 1.932 1.158 2.291
x
0.476 94.13 0.8 1.214 0.606 0.218 0.844 Sr2
0.89 9.702 0.834 1.102 0.778 0.466 0.919
Ca2
10.01 208.5 10.33 10.34 8.59 5.84 14.16
x
var
x
Snÿ1 x
NH 4
Na
0.13 0.084 0.167 0.167 0.00 0.081 0.00
Snÿ1 x
0.157 0.12 0.081 0.154 0.147 0.104 0.177
Snÿ1 x
0.017 0.007 0.028 0.028 0.00 0.007 0.00
var
0.025 0.014 0.007 0.024 0.022 0.011 0.031
var
0.328 0.208 0.416 0.416 0.00 0.201 0.00
95% CL
0.39 0.298 0.201 0.382 0.384 0.257 0.44
95% CL
0.05 0.15 0.19 0.08 0.11 0.17 0.05
x
Ba2
1.26 4.8 0.6 0.85 0.52 0.38 7.31
x
K
0.00 0.045 0.778 0.352 0.203 0.254 0.208
Snÿ1 x
0.169 80.341 0.099 0.403 0.107 0.07 0.585
Snÿ1 x
0.00 0.002 0.802 0.124 0.043 0.085 0.043
var
0.284 0.116 0.01 0.162 0.011 0.005 0.342
var
0.00 0.111 1.925 0.874 0.516 0.831 0.5186
95% CL
0.419 0.847 0.245 0.999 0.295 0.173 1.453
95% CL
x ± mean value of the concentration of the cation (ppm); Snÿ1 x ± standard deviation; var ± variance; 95% CL ± 95% con®dence limit.
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Station
Table 3 Statistics of the cationic analysisa
2.38 12.6 2.07 1.83 1.48 1.66 4.48
x
Mg2
0.389 1.055 0.239 0.221 0.224 0.228 0.687
Snÿ1 x
0.151 1.113 0.057 0.045 0.05 0.052 0.472
var
0.988 2.619 0.534 0.549 0.556 0.565 1.705
95% CL
92 A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
results con®rm the early conclusion that most of the transported material is of regional origin (Ali-Mohamed, 1991; Ali-Mohamed et al., 1995). As no other sources could be identi®ed, the major sources of the bromide ions are cars, fuelled with leaded petrol, and the sea. Although the Pb is added to motor fuel in organic form as tetraethyl- or tetramethyl-lead, the particulate emissions are composed of inorganic oxides, sulphates, halides, and carbonates (Cawse, 1982). At good correlations of Pb and Br, it was concluded that the occurrence of both elements in Cairo street dust was mainly due to trac emissions (Ruscheinski and Scheer, 1989). A study on the chemical composition of settling particles from 23 heavy dust storms in Israel presumed that Br enrichment was due to contamination from the use of leaded petrol in motor cars or from the sea (Ganor et al., 1991). The sulphate particulates are mainly coming from the soil. The sulphate may be long distance transport from industrial area to the north and west. Since the area has low trac, oxidation of SO2 emitted by cars to SO2ÿ 4 may be considered as a minor source. The soil represents the only source of the nitrite ions, as no other sources could be identi®ed. The major source of NOÿ 3 is the atmospheric oxidation of NOx to HNO3 and its total or partial neutralization by natural atmospheric ammonia. The latter process is considered to be the main source of the ammonium ions. Sodium, magnesium and chloride ions are largely coming from sea-salt particles. The main source of calcium and potassium ions is the soil. The soluble constituents of the solid particulate matter show no contribution of lithium, small contribution of strontium and barium ions which are generally present in the soil as trace elements2 . The particle sizes of 108 randomly chosen particles ranged from 6 to 230 lm with an average value of 35 lm (Fig. 6). A study in Italy reported a particle size range of 10±100 lm in with an average value of approximately 25 lm (Paoletti et al., 1989). The relationship between particle size and depth of penetration into the respiratory system has been reviewed by Fergusson (1982). From this review, it can be concluded that particles with sizes <9 lm can easily penetrate into the respiratory system. It was found that mortality was more strongly associated with the levels of ®ne, inhalable, and sulphate particles than with the levels of total particulate pollution, aerosol acidity, sulphur dioxide, or nitrogen dioxide (Dockery et al., 1993). Fine particles are chie¯y coming from the combustion of fossil fuels, whereas larger particles are mainly derived from the soil. Our results which show an average particle size of 35 lm indicate that the majority of the particles are soil-derived. This is expected since the area is one of low trac.
93
Statistical data of the anionic and cationic analysis are shown in Tables 2 and 3, respectively.
4. Conclusion All in all, it seems that there is a correlation between the dry fall deposition of suspended particulate matter together with its soluble components and the meteorological and surface features of Bahrain. The highest values of Clÿ and SO2ÿ 4 concentrations and conductivity were 537.64 and 307.58 ppm and 1600 lS cmÿ1 , respectively. These values were reported in Dumistan, the village northeast of which Al-Lawzi Lake is located. The highest total suspended solid was 276.0 mg dmÿ3 reported in Al-M alikiyah village and was probably caused by prevailing and strong northwesterly winds. The major sources of the ionic components were most probably natural. The presence of gypsum in the surface sands of the western region of Bahrain seems to have been resulted in the higher concentrations of Ca2 ÿ and SO2ÿ 4 compared to Na and Cl .
Acknowledgements The authors would like to express their thanks to Mr. Bill Shaw, Head of the Meteorological section at the Directorate of Civil Aviation in Bahrain for the meteorological data he has provided.
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amp, Brunsden, Jones (Eds.), Bahrain Surface Material Resources Survey. Geo Abstracts UEA, Norwich NR4 7 TJ, UK, pp. 95 and 321. Fergusson, J.E., 1982. The Inorganic Chemistry and The Earth. Chemical Resources, their Extraction, Use and Environmental Impact, vol. 6. Pergamon Series on Environmental Science. Pergamon Press, Oxford, pp. 244±247. Ganor, E., Foner, H.A., Brenner, S., Neeman, E., Lavi, N., 1991. The chemical compositon of aerosols settling in Israel following dust storms. Atmospheric Environment 25A, 2665±2670. Morgan, G.B., Ozolins, G., Tabor, E.C., 1970. Air pollution surveillance systems. Science 170, 289±296. Paoletti, L., Falchi, M., Viviano, G., Ziemacki, G., Batisti, D., Pisani, D., 1989. Features of airborne breathable particulate in a remote rural and in an urban area. Water, Air, and Soil Pollution 43, 85±94. Ruscheinski, I.M., Scheer, J., 1989. On Br and Pb in Cairo street dust. J. Environ. Sci. Health 24, 695±710.
Schl unzen, K.H., Pahl, S., 1992. Modi®cation of dry deposition in a developing sea-breeze circulation ± a numerical case study. Atmospheric Environment 26, 51±61. Weiss, J., 1995. Ion Chromatography, 2nd edition. VCH, Weinheim, p. 347.
Dr. Ahmed Y. Ali-Mohamed (B.Sc., Kuwait, 1974; Ph.D., Wales, UK, 1982): Associate Professor of Inorganic Chemistry (1990 to present); Vice-President, University of Bahrain for Academic Programmes and Research (1995 to present). His research interest is in atmospheric chemistry, especially the study of the dry deposition or the dry fall of aerosol particulate matters, and the application of transition metal complexes as antimicrobial agents. Mr.Ali H. Jaar (B.Sc., 1995±96) is a science teacher at an intermediate school. At present he is studying for an M.S. in Atmospheric Chemistry in the School of Environmental Studies at the University of East Anglia, UK.
Estimation of atmospheric inorganic water-soluble aerosols in the western region of Bahrain by ion chromatography Ahmed Y. Ali-Mohamed*, Ali Hassan Jaar Department of Chemistry, College of Science, University of Bahrain, P.O. Box 32038, Isa Town, Bahrain Received 2 March 1998; accepted 14 January 1999
Importance of this paper: Deposition of aerosols may induce a response on soil and water ecosystems, in addition to deterioration in visibility caused by suspended particulates. The presence of increased concentration of water-soluble ions was reported globally to in¯uence natural processes of nucleation. Such particulate pollutants were found to contain a great diversity of both water-soluble and insoluble components. In this research work the dry deposition collection of aerosols in the troposphere and their composition in the western region of Bahrain have been chosen, where little interference from industrial sources is anticipated. The use of ion chromatography instead of conventional wet chemical methods is an attractive method because of its simultaneous detection and sensitivity. Abstract Dry fall aerosol particulate matter was collected in the western rural area of Bahrain. The collection was carried out using an open beaker trap of deionized water placed on the roof of an 8 m high building in seven villages representing the area under study. The water-soluble matter was analyzed for its chemical components by ion chromatography. The data obtained were in good correlation with the meteorological and surface features of Bahrain. The sizes of 108 randomly chosen particles, measured with a photomicrographic microscope, ranged between 6 and 230 lm. The latter value gives an indication that most of these particles were soil-derived. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: Aerosol particulate matter; Water-soluble matter; Ion chromatography; Rural area; Bahrain; Anions and cations
1. Introduction The identi®cation of natural and man-made sources of air particulates in rural atmosphere and estimation of relative strengths of particulate pollution sources in urban areas has received further attention by the application of improved analytical and statistical techniques (Cawse, 1982). Ion chromatography has become an indispensable tool for the analytical chemist in the area of anion analysis. In many cases this method has superseded * Corresponding author. Tel.: +973-782343/782351; fax: +973-682-582.
conventional wet chemical methods such as titration, photometry, gravimetry, turbidimetry, and colorimetry, all of which are labor-intensive, time-consuming, and occasionally susceptible to interferences. In the ®eld of cation analysis, ion chromatography is attractive because of its simultaneous detection and sensitivity (Weiss, 1995). The amount of dry-deposited material depends on the pollutant and surface properties as well as on the meteorological situation and the extent of pollution. The latter depends on the emission rate and is again in¯uenced by the uptake of the pollutant at the surface and by atmospheric transport (Schl unzen and Pahl, 1992). Gaseous pollutants make up about 90% of the total mass emitted to the atmosphere with particulates and
1465-9972/99/$ - see front matter Ó 1999 Elsevier Science Ltd. All rights reserved. PII: S 1 4 6 5 - 9 9 7 2 ( 9 9 ) 0 0 0 5 8 - 6
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A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
aerosols accounting for the remaining 10%. Particulates are emitted into the atmosphere by a diverse group of sources and vary over a wide range of sizes, shapes, densities, and chemical composition. Small particulates are of particular importance because they may be in the respirable size range. These small particles may contain biologically active elements and compounds (Morgan et al., 1970). The present study is aimed at estimating the atmospheric dry fall deposition of the suspended particulate matter in a rural area of the state of Bahrain. The chemical components of the water-soluble matter were determined using the technique of ion chromatography. Correlations have been made between the data obtained and the meteorological and surface characteristics of Bahrain.
1.1. Area under study The group of islands of Bahrain lie in an arm of the Arabian Gulf, known as the Gulf of Salwa, which separates the Qatar peninsula and Saudi Arabia (Fig. 1). Geographically, they are located in the core of an extensive zone of aridity. The main island, called Bahrain, has dierent features. Population density is high in the northern and northeastern parts where the major industries are located. On the other hand, there is a rural, fertile area in the western and northwestern part of the island. Our sites for this study are located in the western rural area of Bahrain, an area that comprises about 15% of the total land of Bahrain. Nearly 22,000 people live in this area compared to the total population of Bahrain which was 500,000 in 1991. Seven small villages were chosen to represent this region. From the north, these are Al-Hamalah [HM], Dumistan [DM], Karzakk an [KZ], Al-M alikiyah [ML], Sadad [SD], Shahrakk an [SK], and D ar Kulayb [DK]. These villages are separated from the western shores by a large strip of agricultural land that stretches more than 12 km from the north to the south. The villages from Dumistan to Shahrakk an are joined by an 8 km low trac highway. There are ancient burial mounds to the north of D ar Kulayb covering an area of about 0.26 km2 . Northeast of Dumistan is located a very saline lake called ``Al-Lawzi Lake''.
2. Experimental 2.1. Sampling Seven 1 l beakers ®lled with deionized water were placed in seven villages representing the area under
Fig. 1. Map of the state of Bahrain showing the location of the studied sites: [HM] Al-Hamalah; [DM] Dumistan; [KZ] Karzakk an; [ML] Al-M alikiyah; [SD] Sadad; [SK] Shahrakk an; [DK] D ar kulayb.
study. Each beaker was placed on the roof of an 8 m high building for 1 week. 2.2. Suspended matter determination The water sample was ®ltered on a previously dried and weighed 0.45 lm ®lter paper. The ®lter paper was then dried in an oven at 70°C and ®nally reweighed. The total suspended solid was obtained by subtracting the weight of the ®lter paper before ®ltration from that after ®ltration. The ®ltrate was diluted to 500 cm3 (sometimes to 1 l) using deionized water. The following steps were then carried out. 2.2.1. Anions and cations analysis 2ÿ ÿ ÿ The anions Clÿ ; NOÿ 2 ; Br ; NO3 ; and SO4 and 2 2 the cations (Li ; Na ; NH4 ; K ; Mg ; Ca ; Sr2 ; and Ba2 were determined by a Metrohm ion chromatograph (IC-690). Injection of 100 ll of the sample into a PRP-X100 anion column (Manufactured by
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
87
Fig. 2. Separation of inorganic anions. Separator column : PRP-X100; Eluent: 0.002 mol lÿ1 phthalic acid, 10% acetone, pH 5.0; ¯ow. Rate: 2 ml minÿ1 ; detection: conductivity detector, injection volume: 100 ll, (A) Standard solution of anions. Solute concentrations: 5 ppm chloride, 5 ppm nitrite, 10 ppm bromide, 10 ppm nitrate, and 10 ppm sulphate. (B) Water-soluble components in Shahrakk an sample. Solute concentrations: 9.74 ppm chloride, 2.06 ppm nitrate, and 16.84 ppm sulphate.
Hamilton, Reno, NV, USA) using 0.002 mol dmÿ3 phthalic acid eluent (10% acetone, pH 5, conductivity approximately 180 lS cmÿ1 ) will separate the above anions in less than 20 min. Several peaks, each representing a certain anion, were obtained from the chart recorder. (Fig. 2). Length analysis of these peaks using standard peaks obtained from a standard solution of the anions will give an indication of the concentration of the stated anions in the sample. Separation of the above cations was attained in less than 15 min by injection of 10 ll of the sample into a SUPER-SEP cation column (manufactured by Hamilton PRP-X100) using 0.75 mg/l tartaric acid eluent (conductivity approximately 500 lS cmÿ1 ) and [5 mmol/l citric acid]/[0.5 mmol/l dipicolinic acid] eluent (conductivity approximately 500 lS cmÿ1 ). The concentration of the cations in the sample were determined by area analysis of the peaks representing these cations using standard peaks obtained from a
standard solution of the cations (Fig. 3). The anions and cations in both the sample and the standard were analyzed three times following the above procedure. 2.2.2. Conductivity and pH determination The pH and conductivity measurements of the water trap samples at 22.5°C were measured using a Crison 525 conductimeter (cell constant 1.38) and Crison 507 pH meter. 2.2.3. Particle size determination The particles collected on micromembrane were magni®ed 10 times their actual size using an Olympus Microscope-model BHS-photomicrographic-system (PM-10AD)-re¯ected light-¯uorescence attachmentBH2-RFL. The length of a total of 108 randomly chosen particles was determined using the appropriate scale attached to the microscope.
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Fig. 3. Separation of inorganic cations. Separator column: SUPER-SEP; eluent: 0.75 mg lÿ1 tarataric acid, pH 4.5; ¯ow rate: 1 ml minÿ1 ; detection: conductivity detector; injection volume: 10 ll. (A) Standard solution of cations. Solute concentrations: 1 ppm lithium, 5 ppm sodium, 5 ppm ammonium, 10 ppm potassium, 10 ppm magnesium, 10 ppm calcium, 20 ppm strontium, and 20 ppm barium. (B) Water-soluble components in Shahrakk an sample. Solute concentrations 5.67 ppm sodium, 0.21 ppm potassium, 1.01 ppm magnesium, and 22.03 ppm calcium.
3. Results and discussion The climate of Bahrain features high temperatures, high relative humidities, low but seasonal rainfall, and a predominantly northwesterly wind direction which has associated with it the strongest winds. The `Shamal' is the predominant dust-raising wind, sometimes bringing airborne silts from Arabia or even from Iraq, some 250 miles to the northwest (Doornkamp et al., 1980). Weekly and mean monthly values of meteorological data over the studied period 1 are summarized in Table 1. These climatic features of Bahrain have a considerable eect on the dry fall deposition and its chemical composition. High concentrations of anions, especially Clÿ and 2ÿ SO4 and cations, especially Na and Ca2 , were reported in Dumistan village during the months of Octo-
1
Interested people can get the data from the authors.
ber±December 1994 and February 1995.2 About 750 m to the northeast of this village is located Al-Lawzi Lake which is characterized by its high salinity. Salt particles from this lake accompanied by the Northerly, Easterly or the Northeasterly winds seems to have brought about the high anionic and cationic constituents in the village of Dumistan. Worth noticing is the high conductivity values of the water-soluble components associated with this phenomenon. Values as high as 1447 and 1600 lS cmÿ1 were reported in the third week of December and the ®rst week of November 1994, respectively. The corresponding Clÿ concentrations were 418.18 and 537.6 ppm, and the corresponding SO2ÿ 4 concentrations were 269.44 and 307.58 ppm (Fig. 4), the latter value in each case being the highest during the period studied. A dust storm was reported on 18 October 1994 caused by southeasterly winds. As a result, a high
2
Interested people can get the data from the authors.
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
89
Table 1 Mean weekly climatological summary over the studied perioda Month
Week no.
Period
Press (hpa)
Rh (%)
Sun (h)
Temp (°C)
Rain (mm)
Vis (km)
Wind Dir
Oct 94
1 2 3 4 Mean
2±8,10,94 8±16,10,94 16±22,10,94 22±29,10,94
1010.6 1013.2 1014.3 1014.5 1013.2
62.6 66.3 69.1 65 65.5
10 9.5 7.3 10.3 9.3
30.8 29.8 29.4 27.8 29.4
0.00 0.00 0.00 0.00 0.00
17.9 15.4 14 14.9 15.7
N E/SE SE/N N N
7.1 5.6 8.9 6.7 7
Nov 94
1 2 3 4 Mean
29,10±15,11,94 5±12,11,94 12±19,11,94 19±26,11,94
1015.9 1016.6 1015.1 1016.5 1016
68.5 64.56 65.5 65.87 66.3
10 9.1 8.4 7.7 8.8
28.1 26.9 25.3 25.1 26.4
0.00 0.00 0.00 0.00 0.00
14.7 18.06 15.95 13.87 15.5
N/E S/N N SE N
5.9 12.19 10.36 8.69 9.3
Dec 94
1 2 3 4 5 Mean
26,11±3,12,94 3±10,12,94 10±17,12,94 17±24,12,94 24±31,12,94
1015.1 1021.8 1021.3 1020.8 1021.7 1020.3
67.23 57.57 74.09 69.67 66.61 66.48
8.3 8 6.8 8.4 8.4 8
23.2 16.3 18.1 19.5 16.4 18.7
0.00 0.00 0.00 0.00 0.00 0.00
15.35 15.1 14.52 14.52 14.3 15.36
S/N NW NW N/NW NW NW/N
8.46 15.43 7.26 11.18 8.18 10.42
Jan 95
1 2 3 4 Mean
31,12±7,1,95 7±14,1,95 14±21,1,95 21±28,1,95
1020.6 1018 1020.8 1021.5 1020.2
75.69 72.34 72.88 64.96 71.68
8.7 8.2 8.2 8.3 8.6
17.2 18.4 18.4 16.1 17.5
0.00 0.00 0.00 0.04 TR
11.69 12.02 12.97 19.08 13.84
NW W/S N NW NW
10.26 8.08 10.23 13.19 10.11
Feb 95
1 2 3 4 Mean
28,1±4,2,95 4±11,2,95 11±18,2,95 18±25,2,95
1019.1 1015.8 1017.6 1016.5 1017.3
73.31 70.98 69.3 66.48 70.36
8.9 4.9 8.7 8.9 7.9
18.2 19 17.6 18.2 18.2
0.00 3.11 0.08 0.00 0.88
15.18 14.94 16.52 17.22 15.87
NW N NW/N N/NW N/NW
6.03 11.99 10.98 10.5 9.64
1017.4
68.06
8.5
22
0.18
15.25
N/NW
9.29
Mean
Wind Spd (knots)
a
Press ± station pressure; Rh ± relative humidity; Sun ± total of bright sunshine; Temp ± dry-bulb temperature; Vis ± visibility; Wind Dir ± prevailing wind direction; Wind Spd ± wind speed.
Fig. 4. Weekly values of conductivity (n) (lS cmÿ1 ): concentrations of Clÿ (d); SO2ÿ 4 (n) (ppm) at [HM] station.
Fig. 5. Weekly concentration of total suspended solid (mg an. [h] Aldmÿ3 ). [d] Al-Hamalah. [s] Dumistan. [n] Karzakk M alikiyah. [n] Sadad. [m] Shahrakk an. [r] D ar Kulayb.
90
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
Fig. 6. Microscopic photographs of aerosol dust particles 10 times magni®cation of dust particles collected: (a) 0.20 mm (AlMalikiyah); (b) 0.050 mm (Sadad); (c) 0.039 mm (Shahrakk an); (d) 0.022 mm (Al-Hamalah).
deposition of aerosol suspended solid was recorded reaching 203.4 and 202.9 mg lÿ1 in D ar Kulayb and Karzakk an villages, respectively, in the third week of October 1994. The second week of December 1994 was characterized by prevailing and strong northwesterly winds reaching 21.08 knots on 7 December which had lowered the visibility to 6.46 km on the same day (Bahrain Civil Aviation Meteorological Data, 1994±1995). The lowest temperature and relative humidity of the period from October 1994 to May 1995 were reported in this week, being 11.9°C on 8 December 1994 and 44.33% on 6 December 1994. This wintry week caused a high dry fall deposition especially in Al-M alikiyah village which has had the highest ever reported total suspended solid of 276.0 mg lÿ1 (Fig. 5). The only appreciable rainfall during the studied period was reported in the second week of February 1995. A total of 24.9 mm of rain fell on 6±8 of this month causing a washout of the atmospheric particulate matter. Consequently, high concentrations of total suspended solid were reported in this week, noticeably in AlM alikiyah and D ar Kulayb villages which were 269.1 and 218.5 mg lÿ1 , respectively.
As in the coastal areas to the south, the excess of evaporation over precipitation in the western coast has led to enrichment to the surface sediments in salts, mainly gypsum and in many areas the surface sands are composed almost entirely of gypsum (Doornkamp et al., 1980). This is the reason why there is a relatively high ÿ concentration of SO2ÿ 4 compared to Cl concentration except for some weeks in Dumistan for the reason stated previously. This conclusion is supported by a higher concentration of Ca2 compared to Na . The presence of the agricultural strip which stretches more than 12 km along the western coast of Bahrain and separates the villages from the sea might have minimized, to a considerable extent, the eect of the sea as a major source of Clÿ and Na ions. The mean total suspended solid ranges between 63.4 mg lÿ1 in Al-Hamalah village and 8.1 mg lÿ1 in Shahrakk an village.3 The considerably low dry deposition in Shahrakk an is probably due to the type of the top soil north of this village which is mainly mud. The last three
3
Interested people can get the data from the authors.
a
95% CL
0.53 1.41 0.73 0.45 0.55 0.66 0.86
0.0323 0.1425 0.0494 0.075 0.0424 0.518 0.1503
1.044 20.32 2.44 5.629 1.796 2.683 22.57
var 10ÿ3 0.0802 0.3539 0.1226 0.1663 0.1052 0.1286 0.373
95% CL
0.02 0.02 0.01 0.01 0.01 0.02 0.02
20.28 51.01 11.22 7.34 20.44 5.57 10.3
x
Snÿ1 x
0.1898 0.649 0.1925 0.265 0.3677 0.127 0.1611
x
0.0058 0.117 0.006 0.0114 0.0219 0.0026 0.0042 SO2ÿ 4
0.0764 0.342 0.0775 0.107 0.146 0.0512 0.0649
NOÿ 3
6.13 74.53 4.94 3.85 1.18 2.33 7.03
x
var
x
Snÿ1 x
NOÿ 2
Clÿ
0.1476 0.4833 0.0923 0.1764 0.1425 0.0743 0.1573
Snÿ1 x
0.0144 0.01 0.0072 0.00 0.0072 0.0107 0.0031
Snÿ1 x
21.79 233.5 8.527 31.12 20.3 5.519 24.74
var 10ÿ3
207.6 99.662 51.74 0.00 51.59 114.85 9.378
var 10
ÿ6
0.3665 1.1997 0.2292 0.436 0.3537 0.1844 0.3905
95% CL
0.0356 0.0246 0.0179 0.00 0.0176 0.0266 0.0008
95% CL
x ± mean value of the anion (ppm); Snÿ1 x ± standard deviation; var ± variance; 95% CL ± 95% con®dence limit.
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Station
Table 2 Statistics of the anionic analysisa
0.31 0.94 1.11 0.7 0.88 0.95 0.29
x
Brÿ 0.0197 0.0999 0.0416 0.0265 0.0316 0.028 0.0402
Snÿ1 x
3.897 99.691 17.502 7.034 9.989 7.812 16.134
var 10ÿ4
0.049 0.2479 0.1039 0.0658 0.0785 0.0694 0.0997
95% CL
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94 91
a
95% CL
46.94 95.92 37.87 30.08 40.79 23.76 53.48
3.136 7.995 4.39 2.804 5.208 2.583 4.808
9.832 63.92 19.27 7.861 27.12 6.593 23.11
var 7.784 19.85 10.9 6.961 12.93 6.374 11.94
95% CL
0.63 0.37 0.48 0.6 0.46 0.72 0.54
0.05 0.04 0.03 0.02 0.03 0.01 0.04
x
Snÿ1 x
1.712 24.09 2.221 2.735 1.932 1.158 2.291
x
0.476 94.13 0.8 1.214 0.606 0.218 0.844 Sr2
0.89 9.702 0.834 1.102 0.778 0.466 0.919
Ca2
10.01 208.5 10.33 10.34 8.59 5.84 14.16
x
var
x
Snÿ1 x
NH 4
Na
0.13 0.084 0.167 0.167 0.00 0.081 0.00
Snÿ1 x
0.157 0.12 0.081 0.154 0.147 0.104 0.177
Snÿ1 x
0.017 0.007 0.028 0.028 0.00 0.007 0.00
var
0.025 0.014 0.007 0.024 0.022 0.011 0.031
var
0.328 0.208 0.416 0.416 0.00 0.201 0.00
95% CL
0.39 0.298 0.201 0.382 0.384 0.257 0.44
95% CL
0.05 0.15 0.19 0.08 0.11 0.17 0.05
x
Ba2
1.26 4.8 0.6 0.85 0.52 0.38 7.31
x
K
0.00 0.045 0.778 0.352 0.203 0.254 0.208
Snÿ1 x
0.169 80.341 0.099 0.403 0.107 0.07 0.585
Snÿ1 x
0.00 0.002 0.802 0.124 0.043 0.085 0.043
var
0.284 0.116 0.01 0.162 0.011 0.005 0.342
var
0.00 0.111 1.925 0.874 0.516 0.831 0.5186
95% CL
0.419 0.847 0.245 0.999 0.295 0.173 1.453
95% CL
x ± mean value of the concentration of the cation (ppm); Snÿ1 x ± standard deviation; var ± variance; 95% CL ± 95% con®dence limit.
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Al-Hamalah Dumistan Karzakk an Al-M aikiyah Sadad Shahrakk an D ar Kulayb
Station
Table 3 Statistics of the cationic analysisa
2.38 12.6 2.07 1.83 1.48 1.66 4.48
x
Mg2
0.389 1.055 0.239 0.221 0.224 0.228 0.687
Snÿ1 x
0.151 1.113 0.057 0.045 0.05 0.052 0.472
var
0.988 2.619 0.534 0.549 0.556 0.565 1.705
95% CL
92 A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
A.Y. Ali-Mohamed, A.H. Jaar / Chemosphere: Global Change Science 2 (2000) 85±94
results con®rm the early conclusion that most of the transported material is of regional origin (Ali-Mohamed, 1991; Ali-Mohamed et al., 1995). As no other sources could be identi®ed, the major sources of the bromide ions are cars, fuelled with leaded petrol, and the sea. Although the Pb is added to motor fuel in organic form as tetraethyl- or tetramethyl-lead, the particulate emissions are composed of inorganic oxides, sulphates, halides, and carbonates (Cawse, 1982). At good correlations of Pb and Br, it was concluded that the occurrence of both elements in Cairo street dust was mainly due to trac emissions (Ruscheinski and Scheer, 1989). A study on the chemical composition of settling particles from 23 heavy dust storms in Israel presumed that Br enrichment was due to contamination from the use of leaded petrol in motor cars or from the sea (Ganor et al., 1991). The sulphate particulates are mainly coming from the soil. The sulphate may be long distance transport from industrial area to the north and west. Since the area has low trac, oxidation of SO2 emitted by cars to SO2ÿ 4 may be considered as a minor source. The soil represents the only source of the nitrite ions, as no other sources could be identi®ed. The major source of NOÿ 3 is the atmospheric oxidation of NOx to HNO3 and its total or partial neutralization by natural atmospheric ammonia. The latter process is considered to be the main source of the ammonium ions. Sodium, magnesium and chloride ions are largely coming from sea-salt particles. The main source of calcium and potassium ions is the soil. The soluble constituents of the solid particulate matter show no contribution of lithium, small contribution of strontium and barium ions which are generally present in the soil as trace elements2 . The particle sizes of 108 randomly chosen particles ranged from 6 to 230 lm with an average value of 35 lm (Fig. 6). A study in Italy reported a particle size range of 10±100 lm in with an average value of approximately 25 lm (Paoletti et al., 1989). The relationship between particle size and depth of penetration into the respiratory system has been reviewed by Fergusson (1982). From this review, it can be concluded that particles with sizes <9 lm can easily penetrate into the respiratory system. It was found that mortality was more strongly associated with the levels of ®ne, inhalable, and sulphate particles than with the levels of total particulate pollution, aerosol acidity, sulphur dioxide, or nitrogen dioxide (Dockery et al., 1993). Fine particles are chie¯y coming from the combustion of fossil fuels, whereas larger particles are mainly derived from the soil. Our results which show an average particle size of 35 lm indicate that the majority of the particles are soil-derived. This is expected since the area is one of low trac.
93
Statistical data of the anionic and cationic analysis are shown in Tables 2 and 3, respectively.
4. Conclusion All in all, it seems that there is a correlation between the dry fall deposition of suspended particulate matter together with its soluble components and the meteorological and surface features of Bahrain. The highest values of Clÿ and SO2ÿ 4 concentrations and conductivity were 537.64 and 307.58 ppm and 1600 lS cmÿ1 , respectively. These values were reported in Dumistan, the village northeast of which Al-Lawzi Lake is located. The highest total suspended solid was 276.0 mg dmÿ3 reported in Al-M alikiyah village and was probably caused by prevailing and strong northwesterly winds. The major sources of the ionic components were most probably natural. The presence of gypsum in the surface sands of the western region of Bahrain seems to have been resulted in the higher concentrations of Ca2 ÿ and SO2ÿ 4 compared to Na and Cl .
Acknowledgements The authors would like to express their thanks to Mr. Bill Shaw, Head of the Meteorological section at the Directorate of Civil Aviation in Bahrain for the meteorological data he has provided.
References Ali-Mohamed, A.Y., 1991. Estimation of inorganic particulate matter in the atmosphere of Isa town, Bahrain, by dry deposition. Atmospheric Environment 25B, 397±405. Ali-Mohamed, A.Y., Maki, K.E., Saeed, A.A.A., Abdulla, A.M., Abdulla, M.I., 1995. Estimation of inorganic particulate matter in atmospheres of villages in Bahrain by dryfall. Atmospheric Environment 29A, 1519±1529. Bahrain Civil Aviation Aairs ± Meteorological Service, 1994. Monthly climatic summary. Bahrain Civil Aviation Aairs ± Meteorological Service, 1995. Monthly climatic summary. Cawse, P.A., 1982. Inorganic particulate matter in the atmosphere. Environmental chemistry ± Specialist Periodical Reports, vol. 2, Senior reporter, Bowen, H.J.M. The Royal Society of Chemistry, pp. 39,40. Dockery, D.W., Pope III, C.A., Xu, X., Spengler, J.D., Ware, J.H., Fay, M.E., Ferris, B.G., Speizer, F.E., 1993. An association between air pollution and mortality in six US cities. The New England Journal of Medicine 329, 1753± 1759. Doornkamp, J.C., Brunsden, D., Jones, D.K.C., 1980. Geology, geomorphology and pedology of Bahrain. In: Doornk-
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Dr. Ahmed Y. Ali-Mohamed (B.Sc., Kuwait, 1974; Ph.D., Wales, UK, 1982): Associate Professor of Inorganic Chemistry (1990 to present); Vice-President, University of Bahrain for Academic Programmes and Research (1995 to present). His research interest is in atmospheric chemistry, especially the study of the dry deposition or the dry fall of aerosol particulate matters, and the application of transition metal complexes as antimicrobial agents. Mr.Ali H. Jaar (B.Sc., 1995±96) is a science teacher at an intermediate school. At present he is studying for an M.S. in Atmospheric Chemistry in the School of Environmental Studies at the University of East Anglia, UK.