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Ionic composition of wet precipitation in the Petra Region, Jordan
Atmospheric Research 78 (2005) 1 – 12 www.elsevier.com/locate/atmos
Ionic composition of wet precipitation in the Petra Region, Jordan Omar A. Al-KhashmanT Water and Environment Study Center, Mutah University, Al-Karak 61710, Jordan Received 29 November 2004; accepted 20 February 2005
Abstract The results of chemical analysis of precipitation samples collected in Petra between October 2002 and May 2004 are presented. All samples were analyzed for major cations (NH4+, Na+, K+, Ca2+ and Mg2+ ), major anions (Cl , NO3 , HCO3 and SO42 ), conductivity and pH. The daily sample pH values ranged from 5.71 to 8.15 with an average value of 6.85 F 0.5. Rainwater quality is characterized by low salinity and neutralized pH. Generally, the pH is high due to dust in the atmosphere, which contains a large fraction of calcite. Factor analysis was used to identify the factors that affect the presence of ions in wet precipitation; these factors permitted the identification of three source groups, namely crustal dust, sea-salt spray and combustion products. In general, the results of the present study suggest that the atmospheric composition in the Petra region is strongly influenced by natural sources rather than anthropogenic sources. D 2005 Elsevier B.V. All rights reserved. Keywords: Chemical element; Factor analysis; Jordan; Major ions; Precipitation chemistry
1. Introduction The chemical composition of rainfall is strongly affected by the chemical composition of the atmosphere. The study of the chemical composition of atmospheric eolian dust and T Tel.: +962 32372380; fax: +962 32375540. E-mail address: [email protected]. 0169-8095/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2005.02.003
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aerosols is especially important and significant, because of the immediate influence on human health and the ecosystem. The composition of metals emitted into the atmosphere in the form of eolian dust or aerosols is mainly from anthropogenic activities, these are taken away by dry or wet deposition and cause damage to the surface water and organisms. The chemical composition of eolian dust and precipitation in the Mediterranean region and the factors affecting these compositions are fairly well established through many studies performed since the 1990s. The analysis of ionic and heavy metals in atmosphere particles and precipitation is very important because certain species are emitted from particular source types and they can be used as tracers for these sources (Rahn and Lowenthal, 1985). There are two main sources that strongly affect the composition of atmospheric aerosols and precipitation in the Mediterranean area. One of these is the eolian dust transported from North Africa (Kubilay and Saydam, 1995) and the other is the pollution aerosol transported from Europe (Bergametti et al., 1989; Gullu et al., 1998). The chemistry of wet and dry precipitation in both rural-continental and urban areas has been the subject of intense research and study in the in the last two decades, especially in developing and industrial countries. Jordan is situated 80 km to the east of the Mediterranean Sea, the climate of Jordan is predominantly of the Mediterranean type. Petra, (rose-red city), now a UNESCO World Heritage Site (population 60,000) is one of the great archaeological treasures in the world. It is the most important famous attraction of Jordan. This city is located in the southern part of Jordan and is located to the eastern side of the Mediterranean weather regime. The investigated area is in general considered as a very arid to semiarid area, it is marked by sharp seasonal variation in both temperature and precipitation. It is about 80 km from the sea and the annual rainfall is about 298 mm/year (Department of Meteorology, 2003). The winter season in Jordan is the principle season of rainfall, the water year starts in early October–May. The prevailing wind direction is from westerly to northwesterly, this wind bringing cold wet air during winter and spring from Europe and the Mediterranean Sea and from the east and south bringing hot dry air during summer and autumn from Saudi Arabia, Africa and India (Department of Meteorology, 2003). Water resources in Jordan mainly depend on rainfall, which is subject to great variability. Meanwhile, there is an observed population growth, so there is high demand for water. This paper presents 2-year study of precipitation contents carried out on a daily basis in Petra city. The objective of this study is to find out the ionic composition of precipitation in this city, to study the variation in the chemical composition of rainwater samples and to explain the reason of the concentration of major ions for the period between October 2002 and May 2004.
2. Materials and methods Precipitation samples were collected from the Petra area approximately 250 km to the south of the capital of Jordan, Amman. The station was located inside the region, which is about 1115 m above sea level (Fig. 1). Twenty-eight rainwater samples were collected in the investigated area between the period October 2002 and May 2004. Two samplers were used in this study; both consist of a polyethylene funnel with a 25-cm diameter opening
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
0
LEBANON
0
Mediterranean Sea
Golan Heights (Israeli occupied)
50
3
100 km 50
100 mi
SY R I A IRAQ
Irbid West Bank Gaza Strip*
Az Zarqa' AMMAN
Dead Sea
ISRAEL
Al Karak
SAUDI ARABIA
Ma‘an
EGYPT
Study Area
Al ‘Aqabah Gulf of Aqaba Fig. 1. Location of the studied area.
connected to a neck-screwed polyethylene-receiving bottle, with a filter holder between the funnel and the receiving bottle. Rain collected by the funnel was gravity filtered through a 0.45-Am pore size membrane filter to remove the insoluble fraction, then collected in the collection bottle. Each sample was divided into two bottles, one for major anion analysis using Ion Chromatography, and the other was acidified by adding 1 ml of 5% ultra-pure HNO3. Precipitation from this sampler was used for the determination of major cations (Al-Momani, 2003; Jaradat et al., 1999). The pH and conductivity were determined instantaneously at the end of the rain events. Major cations (Na+, K+, Ca2+, and Mg2+) were measured by Flame Atomic Absorption Spectroscopy using a Varian 800 instrument; major anions (Cl , NO3 and SO42 ) were analyzed by Ion Chromatography using a Dionex-100 instrument. Concentration of NH4+ was determined spectrophotometrically using the Nessler method. The mineralogy of dust material of four samples collected during dust storms was identified by X-ray diffraction using a Philips model PW 1729 goniometer and CuKa. radiation.
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3. Results and discussion A total of 28 precipitation samples were obtained during the measurement period. Nine ionic species, pH and conductivity were measured for each sample. The ratio of total anions to that of total cations (Aanions/Acations) is an indicator of completeness of the measured major constituents. The average equivalent sum of cations to that of anions (Aanions/Acations) was 0.85 F 0.25. The less than unity ratio suggests that a major anion was not measured. The soil in the area is calcareous, indicating that the observed anion deficiency is more likely due to the exclusion of HCO3 from the measurements (AlMomani et al., 1995; Loye-Pilot et al., 1986; Hontoria et al., 2003; Al-Momani, 2003). By computing the concentration of HCO3 (Granat, 1972), and using this equation, q[HCO3 ] = ln([HCO3 ]) = 11.24 pH. Assuming that the concentration of CO2 in the atmosphere is 350 ppm, the average (Aanions/Acations) ratio was raised to 0.93 F 0.14. The average volume weighted concentrations of ions in Petra precipitation are shown in Table 1 together with those found by others in areas around the world. The average volume weighted concentrations of ions in Petra rainwater are presented in (Table 1) together with those found by others in urban areas around the world. Concentrations of Ca2+ and K+ measured in this area are high relative to other rural sites. High concentrations of crustal elements in our samples are due to sporadic, intense incursions of Saharan dust and the long dry summer season in the investigated area which increases the atmospheric loading of soil particles which gets washed out by precipitation. The concentrations of Ca2+ are higher than those reported for Turkey, Singapore, Israel and France (Topcu et al., 2002; Balasubramanian et al., 2001; Herut et al., 2000; Losno et al., 1991) and it are lower than those reported for Thessaloniki, Greece (Samara et al., 1992). The high concentration is due to the large contribution of the Saharan soil dust, Table 1 Concentration of major ions in precipitation at selected sites worldwide (Concentrations are in Aeq/l except EC is in AS/cm and pH is in pH units) Variable
This study
Singaporea
Ankara (Turkey)b
Thessaloniki (Greece)c
Galilee, Israeld
Francee
pH H+ NH+4 EC HCO3 Cl NO3 SO24 Ca2+ Mg2+ K+ Na+
6.85 – 26.30 160.60 152.50 80.60 35.70 53.20 163.10 62.30 18.40 75.60
4.50 45.92 17.27 31.02 – 22.11 16.79 58.71 21.73 7.46 3.96 31.08
6.30 1.60 86.40 28.10 – 20.40 29.20 48.00 71.40 9.30 9.80 15.60
– 4.08 73.20 – – 50.10 49.70 194.00 254.00 22.90 12.20 34.00
– 18.30 24.30 – – 176.30 28.00 150.30 44.70 28.00 3.70 166.00
5.39 19.75 24.70 – – 357.00 28.00 42.20 32.70 35.50 8.50 261.20
a b c d e
Balasubramanian et al. (2001). Topcu et al. (2002). Samara et al. (1992). Herut et al. (2000). Losno et al. (1991).
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SO4-2 8% NO35%
NH4+ 4%
HCO3 CL-
HCO3 23%
K+ 3%
Ca+2 Mg+2 Na+
Na+ 11%
CL12%
Mg+2 9%
Ca+2 25%
K+ NO3SO4-2 NH4+
Fig. 2. Contribution of ions to total ion mass.
which contains large fractions of CaCO3 (Al-Momani, 2003; Al-Momani et al., 2000; Singer et al., 1993; Ganor et al., 1991). The concentration of marine elements (Cl , Na+, and Mg2+) were much higher in the Israel and France precipitation than ours. This is understandable and was attributed to the close proximity of their sampling site to the sea. The relatively low values of NH4+ may be due to the low levels of fertilizers uses in the investigated area. In Europe, NH4+ dominate all other ions due to the high level of fertilization use in agricultural activities in addition to the contribution of other anthropogenic activities (Al-Momani, 2003). The concentration of each ion to the cation/anion ratio and to the total ion mass in precipitation is shown in Figs. 2–4. The ionic abundance in precipitation (Aeq/l) show the general trend HCO3 N Cl N SO42 N NO3 for anions and Ca2+ N Na+ N Mg2+ N NH4+ N K+ for cations. The Ca2+ ion makes the highest contribution to the total mass of the ions, it accounts for 25% of the total ion mass and approximately 47% of the total mass of measured cations. The contribution of HCO3 was 23% of the total ion mass and approximately 47% of the total mass of measured anions. The contributions of Mg2+ and Cl were 9% and 12%, respectively, the high contribution of Ca2+ is due to the influence of Saharan dust soil in this region. The NO3 and SO42 ions make a relatively moderate contribution compared to Cl and HCO3 to both the total ion and the total anions mass, and the Na+, K+ ions make a relatively moderate contribution compared to Ca2+, Mg2+ to both the total ion and the total cation masses. The chemical composition of precipitation -2
SO4 17% NO311%
HCO3 47%
HCO3 CLNO3SO4-2
CL25% Fig. 3. Contribution of anions to total anion mass.
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NH4+ 8%
+
K 5%
Ca+2 47%
+
Na 22%
Ca+2 Mg+2 Na+ K+ NH4+
+2
Mg 18% Fig. 4. Contribution of cations to total cation mass.
samples in this region contains different concentrations of chemical constituents depending on the amount of rainfall, direction of rain front and the period between the precipitation events (Granat, 1972). The measured pH values range from 5.71 to 8.15 with an average value of 6.85 (Table 1; Fig 5). Usually the pH of the rainwater is around 5.6, owing to carbonate buffer as a result of CO2 dissolved in rain droplets (Charlson and Rodhe, 1982). The relatively high average pH values measured in the area (6.85) are not due to lack of acidity in precipitation, but rather due to the neutralization of acidity in precipitation. In Jordan and the surrounding area, carbonate is the most dominant neutralizing agent. The neutralization by CaCO3 is usually reported in the region, where the composition of rainwater is strongly affected by the high CaCO3 content of Saharan dust (Al-Momani et al., 2000). The highest value of salinity was measured in this region (360 AS/cm), because the weather system contained a high quantity of dust and was affected by Red Sea storms or eastern depressions, but the lowest value (25 AS/cm) was measured, where intense rain was precipitated with no dust when the atmosphere was washed (Fig. 6). HCO3 represents 47% of the total anion mass, which is the highest anion contribution. The lowest value of HCO3 was recorded during the coldest month of the rainy season, high intensity of precipitation and low dust in the atmosphere. The pH 9 8 7 6
pH
5 4
pH
3 2 1 0 1
3
5
7
9 11 13 15 17 19 21 23 25 27
Samples Fig. 5. pH values for the different wet precipitation samples.
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
7
EC 400 350 300 250
EC 200 EC
150 100 50 0 1
3
5
7
9 11 13 15 17 19 21 23 25 27
Samples Fig. 6. Conductivity values for the different wet precipitation samples.
temperature, duration and intensity of precipitation as well as its dust content played the main role in the concentration of HCO3 . The highest value of HCO3 was measured during warmer dusty storms. The Cl- ions account for approximately 25% of the anions, which is the highest mass contribution after HCO3 . The highest values of Cl in rainwater samples were due to the Khamasini wind, which affected the investigated area during the spring season. Ca2+ represents 47% of the total cation mass, the surrounding area is free of any construction activities and other works involving the use of concrete and other source of calcium. Therefore, the origin of Ca2+ was considered to be mainly from natural sources
Fig. 7. X-ray diffraction of dust sample collected from a rain event.
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O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
due to calcareous soil in the area and the eastern and Red Sea depression rainfall that affected Jordan. These depressions contain dust materials of different mineral composition such as: calcite, quartz, clays and traces of gypsum (Fig. 7). The Mg2+ ion makes 18% of the cation mass which is the highest contribution after Ca2+, the Na+ ions account for approximately 22% of the cation mass, but the K+ ion makes up 5% of the cation mass. The origin of Na+ and K+ was mainly derived from the dust sea salts, and the aerosols of the Dead Sea, Mediterranean Sea and polar depressions that affected Jordan. NO3 accounts for 11% of the total mass of anions. Thunderstorms and agricultural activities in the Ghore area to the west of the investigated area are the most responsible factors for the high concentration of NO3 in some rainwater samples. The SO42 ion accounts for approximately 17% of the anion mass. The source of SO42 can be Saharan soil dust, which contains a large fraction of calcite, dolomite, halite, gypsum and clay minerals (Foner and Ganor, 1992). The possible source of SO42 in the atmosphere can be derived from SO2 in the air as well as dry deposition of particles over the area, as a large amount is produced through fuel combustion during the rainy cold season. The mineralogy of dust materials as determined by XRD (Fig. 7) confirms the presence of calcite, quartz and dolomite. 3.1. Determination of chemical sources The most usual method of evaluating the contribution of sea salts to ion contents in precipitation is to compare the Cl /Na+ ratio in rainwater to that of seawater. Sea is considered to be the major source of both ions, although they may also be emitted from other natural and industrial sources (Raynor and Hayes, 1982a,b; Samara et al., 1992). The arithmetic mean of the Na+/Cl molar ratio was found to be 0.94 F 0.50. This value is higher than the corresponding value for seawater, which is 0.86 (Brewer, 1975). Chlorine ions show low correlation with Na+ (r = 0.31) while they are better correlated with Mg2+, Ca2+, SO42 and NO3 (r = 0.87, 0.78, 0.73 and 0.71), respectively. This suggested that the origin of Cl might be Saharan dust, which affected the area. The arithmetic mean of the NO3 /SO42 molar ratio was found to be 0.67 F 0.45. This value indicates that there are more NO3 ions per each SO42 ion in the samples. Takahashi and Fujita (2000) explained the relative contribution of H2SO4 and HNO3 to the acidity of precipitation using the ratio of NO3 concentration to SO42 concentration. Relationships between ionic species were determined by correlation analysis. Table 2 gives the linear correlation coefficients computed from 28 samples. As shown from the inspection of these values, there is no association between free acidity and SO42 and NO3 . This suggests that SO42 and NO3 salts in precipitation originate from ionization of sulfate and nitrate salts, which are produced from neutralizing processes. Strong correlation of HCO3 with Na+ and Mg2+ (r HCO3 /Na+ = 0.75; r HCO3 /Mg2+ = 0.63), this correlation supports the assumption of neutralization with soil dust and sea spray soil dust from the Red Sea and eastern depressions. There is a strong correlation of Cl with Mg2+, Ca2+, SO42 and NO3 (r Cl /Mg2+ = 0.87; r Cl /Ca2+ = 0.79; r Cl /SO42 = 0.73; r Cl /NO3 = 0.71). The calcium ion is well correlated with Mg2+, SO42 and NO3 (r Ca2+/Mg2+ = 0.78; r Ca2+/SO42 = 0.68; r Ca2+/NO3 = 0.64) suggesting the presence of a natural contribution to the observed values of these ions. The Mg2+ concentration is strongly correlated with
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
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Table 2 Spearman’s rank correlation matrix for rainwater samples (n = 28), all values in (Aeq/l), conductivity (AS/cm) Var. pH EC HCO3 Cl Ca2+ Mg2+ Na+ K+ NO3 SO24 NH+4
pH 1.00 0.45 0.05 0.20 0.36 0.15 0.20 0.12 0.17 0.07 0.23
EC
HCO3
1.00 0.37 0.26 0.18 0.29 0.42 0.28 0.22 0.35 0.34
1.00 0.52 0.46 0.63 0.75 0.14 0.13 0.35 0.16
Cl
1.00 0.79 0.87 0.31 0.17 0.71 0.73 0.30
Ca2+
1.00 0.78 0.14 0.26 0.64 0.68 0.12
Mg2+
1.00 0.54 0.14 0.70 0.79 0.19
Na+
1.00 0.19 0.18 0.40 0.17
K+
NO3
SO24
NH+4
1.00 0.08 0.20 0.10
1.00 0.86 0.21
1.00 0.21
1.00
Bold text shows strong correlations. 0.60–1.00 = strong correlation; 0.50–0.59 = moderate; 0.40–0.49 = weak; 0.00–0.39 = little or no association.
NO3 and SO42 (r Mg2+/SO42 = 0.79; r Mg2+/NO3 = 0.70). There is a strong correlation between NO3 and SO42 (r NO3 /SO42 = 0.86). The reason for nitrate and sulfate might be due to accumulation of these ions in the upper atmosphere being washed down with rains during the rainy season. Besides, anthropogenic sources and agricultural activities west of the area may contribute a lot more to NO3 and SO42 generation during summer and autumn. 3.2. Statistical analysis In this study, relationship between concentrations of ions was examined with factor analysis. Factor analysis allows the identification of a small number of factors that could explain the variability of most of the original data. Factor analysis was used to determine the various sources of the measured ions in rainwater. The method used was Principle Component Analysis (PCA). The factor loadings obtained by PCA normalized with varimax for various ions are presented in Table 3. The loadings having a value greater than 0.70 are marked in bold in the table. Table 3 Results of factor analysis for the major ion concentrations in rainwater samples Variables
Factor 1
Factor 2
Factor 3
pH HCO3 Cl Ca2+ Mg2+ Na+ K+ NO3 SO24 NH+4 Total variance, %
0.12 0.20 0.73 0.55 0.61 0.17 0.31 0.91 0.92 0.22 34.0
0.17 0.90 0.40 0.50 0.70 0.86 0.55 0.15 0.15 0.23 30.6
0.90 0.28 0.42 0.60 0.26 0.25 0.21 0.16 0.19 0.26 17
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Table 4 Mean mass contribution from identified sources for rainwater Source
Mean contribution
Percentage of total predicted mass
Soil dust (natural) Anthropogenic Sea spray (marine) Total predicted mass
440.1 F 45.5 135.7 F 23.3 120.7 F 19.9 696.5 F 50.4
63.2 19.5 17.3 –
Factor 1 accounts for 34% of the total variance. This factor has a high loading for Cl , SO42 , NO3 , Ca2+, Na+ and Mg2+ in decreasing order; strong positive correlations among the ions are found in the correlation analysis. The correlation coefficient between Cl and Ca2+ is 0.70, between Cl and Mg2+ 0.87, between Cl with NO3 and SO42 0.71 and 0.73, respectively. This factor is associated with soil and sea-salt sources. The association Na+ and Cl in factor 1 indicates the presence of sea salts arriving in masses of polar sea air (Lee et al., 2000; Mello, 2001; Lara et al., 2001). Ca2+ and Mg2+ are frequently found in soil and dust (or particulate matter) as well as fallout of Saharan dust. Also factor 1 shows high loadings for SO42 , Cl and NO3 and this may be related to long-range transport of anthropogenic origin, i.e., deriving from human activities from industrial countries. On the other hand, Factor 2 shows that about 30.6% of the total variance has high loadings for HCO3 , Mg2+, Na+, K+ and Ca2+ in decreasing order. This factor is associated with soil source crustal contribution for these ions. There are strong positive correlations among the ions, which belong to factor 2, the correlation coefficient between HCO3 and Mg2+ is 0.63, between HCO3 and Na+ 0.75, a weak correlation between HCO3 and Ca2+ is 0.46. The high concentrations of these ions in rainwater samples are due to the large contribution of the Saharan soil dust, which contains large fractions of CaCO3, MgCO3 and MgSO4. This results of the analysis of dust materials collected during Saharan dust storms in Israel (Foner and Ganor, 1992) indicated that the dust is composed predominantly of quartz with considerable amounts of carbonates, halite, gypsum and illite. Factor 3 accounts for 17% of the total variance, the loading of this factor in the study area was not significant. Factor 1 represents the contribution of ions from local anthropogenic activities, but the factor 2 represent the contribution of ions from a natural source (Saharan dust). In Table 4, the data from the PC analysis with respect to mean mass contribution from identified by PCA sources is presented. It could be seen that for rainwater samples, the marine source delivers the dominant quantity of chloride, sodium and potassium; the anthropogenic source emits mostly nitrate and ammonium with additional of chlorides and sulfates. Soil dust (Saharan soil) source contributes bicarbonate, calcium, and magnesium with additional contribution of chloride and sulfate.
4. Conclusion The chemical composition of precipitation in the Petra region of south Jordan has been investigated. The chemistry of precipitation in the study area is similar to that of other areas of the Mediterranean basin. Even though concentrations of HCO3 , Ca2+ and SO42
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
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were high, precipitation was neutral. The observed pH values of precipitation range between 5.71 and 8.15 with an average value of 6.85 F 0.5. The acidity of the rainwater was significantly neutralized using the alkaline soil dust, principally calcium, and the role of ammonium in the neutralization process is very limited. The chemical composition of precipitation in the investigated area is influenced by either local conditions such as: the Dead Sea, agricultural activities in the Ghore area or remote sites associated with depressions rich in calcite, dolomite and gypsum, and polar and Mediterranean depressions rich in sulfate and nitrate ions. The use of factor analysis facilitates the interpretation of the precipitation characterization, highlighting the influence of the anthropogenic sources in the studied area. The results are related to various sources such as; soil dust, sea-salt spray, agriculture activities and finally combustion products.
Acknowledgements The author would like to acknowledge Dr. Eng. Reyad. A. Shawabakh (Chairman of Chemical Engineering Department at Mutah University) for his help and critical reviewing of the text.
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Ionic composition of wet precipitation in the Petra Region, Jordan Omar A. Al-KhashmanT Water and Environment Study Center, Mutah University, Al-Karak 61710, Jordan Received 29 November 2004; accepted 20 February 2005
Abstract The results of chemical analysis of precipitation samples collected in Petra between October 2002 and May 2004 are presented. All samples were analyzed for major cations (NH4+, Na+, K+, Ca2+ and Mg2+ ), major anions (Cl , NO3 , HCO3 and SO42 ), conductivity and pH. The daily sample pH values ranged from 5.71 to 8.15 with an average value of 6.85 F 0.5. Rainwater quality is characterized by low salinity and neutralized pH. Generally, the pH is high due to dust in the atmosphere, which contains a large fraction of calcite. Factor analysis was used to identify the factors that affect the presence of ions in wet precipitation; these factors permitted the identification of three source groups, namely crustal dust, sea-salt spray and combustion products. In general, the results of the present study suggest that the atmospheric composition in the Petra region is strongly influenced by natural sources rather than anthropogenic sources. D 2005 Elsevier B.V. All rights reserved. Keywords: Chemical element; Factor analysis; Jordan; Major ions; Precipitation chemistry
1. Introduction The chemical composition of rainfall is strongly affected by the chemical composition of the atmosphere. The study of the chemical composition of atmospheric eolian dust and T Tel.: +962 32372380; fax: +962 32375540. E-mail address: [email protected]. 0169-8095/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2005.02.003
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aerosols is especially important and significant, because of the immediate influence on human health and the ecosystem. The composition of metals emitted into the atmosphere in the form of eolian dust or aerosols is mainly from anthropogenic activities, these are taken away by dry or wet deposition and cause damage to the surface water and organisms. The chemical composition of eolian dust and precipitation in the Mediterranean region and the factors affecting these compositions are fairly well established through many studies performed since the 1990s. The analysis of ionic and heavy metals in atmosphere particles and precipitation is very important because certain species are emitted from particular source types and they can be used as tracers for these sources (Rahn and Lowenthal, 1985). There are two main sources that strongly affect the composition of atmospheric aerosols and precipitation in the Mediterranean area. One of these is the eolian dust transported from North Africa (Kubilay and Saydam, 1995) and the other is the pollution aerosol transported from Europe (Bergametti et al., 1989; Gullu et al., 1998). The chemistry of wet and dry precipitation in both rural-continental and urban areas has been the subject of intense research and study in the in the last two decades, especially in developing and industrial countries. Jordan is situated 80 km to the east of the Mediterranean Sea, the climate of Jordan is predominantly of the Mediterranean type. Petra, (rose-red city), now a UNESCO World Heritage Site (population 60,000) is one of the great archaeological treasures in the world. It is the most important famous attraction of Jordan. This city is located in the southern part of Jordan and is located to the eastern side of the Mediterranean weather regime. The investigated area is in general considered as a very arid to semiarid area, it is marked by sharp seasonal variation in both temperature and precipitation. It is about 80 km from the sea and the annual rainfall is about 298 mm/year (Department of Meteorology, 2003). The winter season in Jordan is the principle season of rainfall, the water year starts in early October–May. The prevailing wind direction is from westerly to northwesterly, this wind bringing cold wet air during winter and spring from Europe and the Mediterranean Sea and from the east and south bringing hot dry air during summer and autumn from Saudi Arabia, Africa and India (Department of Meteorology, 2003). Water resources in Jordan mainly depend on rainfall, which is subject to great variability. Meanwhile, there is an observed population growth, so there is high demand for water. This paper presents 2-year study of precipitation contents carried out on a daily basis in Petra city. The objective of this study is to find out the ionic composition of precipitation in this city, to study the variation in the chemical composition of rainwater samples and to explain the reason of the concentration of major ions for the period between October 2002 and May 2004.
2. Materials and methods Precipitation samples were collected from the Petra area approximately 250 km to the south of the capital of Jordan, Amman. The station was located inside the region, which is about 1115 m above sea level (Fig. 1). Twenty-eight rainwater samples were collected in the investigated area between the period October 2002 and May 2004. Two samplers were used in this study; both consist of a polyethylene funnel with a 25-cm diameter opening
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
0
LEBANON
0
Mediterranean Sea
Golan Heights (Israeli occupied)
50
3
100 km 50
100 mi
SY R I A IRAQ
Irbid West Bank Gaza Strip*
Az Zarqa' AMMAN
Dead Sea
ISRAEL
Al Karak
SAUDI ARABIA
Ma‘an
EGYPT
Study Area
Al ‘Aqabah Gulf of Aqaba Fig. 1. Location of the studied area.
connected to a neck-screwed polyethylene-receiving bottle, with a filter holder between the funnel and the receiving bottle. Rain collected by the funnel was gravity filtered through a 0.45-Am pore size membrane filter to remove the insoluble fraction, then collected in the collection bottle. Each sample was divided into two bottles, one for major anion analysis using Ion Chromatography, and the other was acidified by adding 1 ml of 5% ultra-pure HNO3. Precipitation from this sampler was used for the determination of major cations (Al-Momani, 2003; Jaradat et al., 1999). The pH and conductivity were determined instantaneously at the end of the rain events. Major cations (Na+, K+, Ca2+, and Mg2+) were measured by Flame Atomic Absorption Spectroscopy using a Varian 800 instrument; major anions (Cl , NO3 and SO42 ) were analyzed by Ion Chromatography using a Dionex-100 instrument. Concentration of NH4+ was determined spectrophotometrically using the Nessler method. The mineralogy of dust material of four samples collected during dust storms was identified by X-ray diffraction using a Philips model PW 1729 goniometer and CuKa. radiation.
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3. Results and discussion A total of 28 precipitation samples were obtained during the measurement period. Nine ionic species, pH and conductivity were measured for each sample. The ratio of total anions to that of total cations (Aanions/Acations) is an indicator of completeness of the measured major constituents. The average equivalent sum of cations to that of anions (Aanions/Acations) was 0.85 F 0.25. The less than unity ratio suggests that a major anion was not measured. The soil in the area is calcareous, indicating that the observed anion deficiency is more likely due to the exclusion of HCO3 from the measurements (AlMomani et al., 1995; Loye-Pilot et al., 1986; Hontoria et al., 2003; Al-Momani, 2003). By computing the concentration of HCO3 (Granat, 1972), and using this equation, q[HCO3 ] = ln([HCO3 ]) = 11.24 pH. Assuming that the concentration of CO2 in the atmosphere is 350 ppm, the average (Aanions/Acations) ratio was raised to 0.93 F 0.14. The average volume weighted concentrations of ions in Petra precipitation are shown in Table 1 together with those found by others in areas around the world. The average volume weighted concentrations of ions in Petra rainwater are presented in (Table 1) together with those found by others in urban areas around the world. Concentrations of Ca2+ and K+ measured in this area are high relative to other rural sites. High concentrations of crustal elements in our samples are due to sporadic, intense incursions of Saharan dust and the long dry summer season in the investigated area which increases the atmospheric loading of soil particles which gets washed out by precipitation. The concentrations of Ca2+ are higher than those reported for Turkey, Singapore, Israel and France (Topcu et al., 2002; Balasubramanian et al., 2001; Herut et al., 2000; Losno et al., 1991) and it are lower than those reported for Thessaloniki, Greece (Samara et al., 1992). The high concentration is due to the large contribution of the Saharan soil dust, Table 1 Concentration of major ions in precipitation at selected sites worldwide (Concentrations are in Aeq/l except EC is in AS/cm and pH is in pH units) Variable
This study
Singaporea
Ankara (Turkey)b
Thessaloniki (Greece)c
Galilee, Israeld
Francee
pH H+ NH+4 EC HCO3 Cl NO3 SO24 Ca2+ Mg2+ K+ Na+
6.85 – 26.30 160.60 152.50 80.60 35.70 53.20 163.10 62.30 18.40 75.60
4.50 45.92 17.27 31.02 – 22.11 16.79 58.71 21.73 7.46 3.96 31.08
6.30 1.60 86.40 28.10 – 20.40 29.20 48.00 71.40 9.30 9.80 15.60
– 4.08 73.20 – – 50.10 49.70 194.00 254.00 22.90 12.20 34.00
– 18.30 24.30 – – 176.30 28.00 150.30 44.70 28.00 3.70 166.00
5.39 19.75 24.70 – – 357.00 28.00 42.20 32.70 35.50 8.50 261.20
a b c d e
Balasubramanian et al. (2001). Topcu et al. (2002). Samara et al. (1992). Herut et al. (2000). Losno et al. (1991).
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SO4-2 8% NO35%
NH4+ 4%
HCO3 CL-
HCO3 23%
K+ 3%
Ca+2 Mg+2 Na+
Na+ 11%
CL12%
Mg+2 9%
Ca+2 25%
K+ NO3SO4-2 NH4+
Fig. 2. Contribution of ions to total ion mass.
which contains large fractions of CaCO3 (Al-Momani, 2003; Al-Momani et al., 2000; Singer et al., 1993; Ganor et al., 1991). The concentration of marine elements (Cl , Na+, and Mg2+) were much higher in the Israel and France precipitation than ours. This is understandable and was attributed to the close proximity of their sampling site to the sea. The relatively low values of NH4+ may be due to the low levels of fertilizers uses in the investigated area. In Europe, NH4+ dominate all other ions due to the high level of fertilization use in agricultural activities in addition to the contribution of other anthropogenic activities (Al-Momani, 2003). The concentration of each ion to the cation/anion ratio and to the total ion mass in precipitation is shown in Figs. 2–4. The ionic abundance in precipitation (Aeq/l) show the general trend HCO3 N Cl N SO42 N NO3 for anions and Ca2+ N Na+ N Mg2+ N NH4+ N K+ for cations. The Ca2+ ion makes the highest contribution to the total mass of the ions, it accounts for 25% of the total ion mass and approximately 47% of the total mass of measured cations. The contribution of HCO3 was 23% of the total ion mass and approximately 47% of the total mass of measured anions. The contributions of Mg2+ and Cl were 9% and 12%, respectively, the high contribution of Ca2+ is due to the influence of Saharan dust soil in this region. The NO3 and SO42 ions make a relatively moderate contribution compared to Cl and HCO3 to both the total ion and the total anions mass, and the Na+, K+ ions make a relatively moderate contribution compared to Ca2+, Mg2+ to both the total ion and the total cation masses. The chemical composition of precipitation -2
SO4 17% NO311%
HCO3 47%
HCO3 CLNO3SO4-2
CL25% Fig. 3. Contribution of anions to total anion mass.
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NH4+ 8%
+
K 5%
Ca+2 47%
+
Na 22%
Ca+2 Mg+2 Na+ K+ NH4+
+2
Mg 18% Fig. 4. Contribution of cations to total cation mass.
samples in this region contains different concentrations of chemical constituents depending on the amount of rainfall, direction of rain front and the period between the precipitation events (Granat, 1972). The measured pH values range from 5.71 to 8.15 with an average value of 6.85 (Table 1; Fig 5). Usually the pH of the rainwater is around 5.6, owing to carbonate buffer as a result of CO2 dissolved in rain droplets (Charlson and Rodhe, 1982). The relatively high average pH values measured in the area (6.85) are not due to lack of acidity in precipitation, but rather due to the neutralization of acidity in precipitation. In Jordan and the surrounding area, carbonate is the most dominant neutralizing agent. The neutralization by CaCO3 is usually reported in the region, where the composition of rainwater is strongly affected by the high CaCO3 content of Saharan dust (Al-Momani et al., 2000). The highest value of salinity was measured in this region (360 AS/cm), because the weather system contained a high quantity of dust and was affected by Red Sea storms or eastern depressions, but the lowest value (25 AS/cm) was measured, where intense rain was precipitated with no dust when the atmosphere was washed (Fig. 6). HCO3 represents 47% of the total anion mass, which is the highest anion contribution. The lowest value of HCO3 was recorded during the coldest month of the rainy season, high intensity of precipitation and low dust in the atmosphere. The pH 9 8 7 6
pH
5 4
pH
3 2 1 0 1
3
5
7
9 11 13 15 17 19 21 23 25 27
Samples Fig. 5. pH values for the different wet precipitation samples.
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
7
EC 400 350 300 250
EC 200 EC
150 100 50 0 1
3
5
7
9 11 13 15 17 19 21 23 25 27
Samples Fig. 6. Conductivity values for the different wet precipitation samples.
temperature, duration and intensity of precipitation as well as its dust content played the main role in the concentration of HCO3 . The highest value of HCO3 was measured during warmer dusty storms. The Cl- ions account for approximately 25% of the anions, which is the highest mass contribution after HCO3 . The highest values of Cl in rainwater samples were due to the Khamasini wind, which affected the investigated area during the spring season. Ca2+ represents 47% of the total cation mass, the surrounding area is free of any construction activities and other works involving the use of concrete and other source of calcium. Therefore, the origin of Ca2+ was considered to be mainly from natural sources
Fig. 7. X-ray diffraction of dust sample collected from a rain event.
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due to calcareous soil in the area and the eastern and Red Sea depression rainfall that affected Jordan. These depressions contain dust materials of different mineral composition such as: calcite, quartz, clays and traces of gypsum (Fig. 7). The Mg2+ ion makes 18% of the cation mass which is the highest contribution after Ca2+, the Na+ ions account for approximately 22% of the cation mass, but the K+ ion makes up 5% of the cation mass. The origin of Na+ and K+ was mainly derived from the dust sea salts, and the aerosols of the Dead Sea, Mediterranean Sea and polar depressions that affected Jordan. NO3 accounts for 11% of the total mass of anions. Thunderstorms and agricultural activities in the Ghore area to the west of the investigated area are the most responsible factors for the high concentration of NO3 in some rainwater samples. The SO42 ion accounts for approximately 17% of the anion mass. The source of SO42 can be Saharan soil dust, which contains a large fraction of calcite, dolomite, halite, gypsum and clay minerals (Foner and Ganor, 1992). The possible source of SO42 in the atmosphere can be derived from SO2 in the air as well as dry deposition of particles over the area, as a large amount is produced through fuel combustion during the rainy cold season. The mineralogy of dust materials as determined by XRD (Fig. 7) confirms the presence of calcite, quartz and dolomite. 3.1. Determination of chemical sources The most usual method of evaluating the contribution of sea salts to ion contents in precipitation is to compare the Cl /Na+ ratio in rainwater to that of seawater. Sea is considered to be the major source of both ions, although they may also be emitted from other natural and industrial sources (Raynor and Hayes, 1982a,b; Samara et al., 1992). The arithmetic mean of the Na+/Cl molar ratio was found to be 0.94 F 0.50. This value is higher than the corresponding value for seawater, which is 0.86 (Brewer, 1975). Chlorine ions show low correlation with Na+ (r = 0.31) while they are better correlated with Mg2+, Ca2+, SO42 and NO3 (r = 0.87, 0.78, 0.73 and 0.71), respectively. This suggested that the origin of Cl might be Saharan dust, which affected the area. The arithmetic mean of the NO3 /SO42 molar ratio was found to be 0.67 F 0.45. This value indicates that there are more NO3 ions per each SO42 ion in the samples. Takahashi and Fujita (2000) explained the relative contribution of H2SO4 and HNO3 to the acidity of precipitation using the ratio of NO3 concentration to SO42 concentration. Relationships between ionic species were determined by correlation analysis. Table 2 gives the linear correlation coefficients computed from 28 samples. As shown from the inspection of these values, there is no association between free acidity and SO42 and NO3 . This suggests that SO42 and NO3 salts in precipitation originate from ionization of sulfate and nitrate salts, which are produced from neutralizing processes. Strong correlation of HCO3 with Na+ and Mg2+ (r HCO3 /Na+ = 0.75; r HCO3 /Mg2+ = 0.63), this correlation supports the assumption of neutralization with soil dust and sea spray soil dust from the Red Sea and eastern depressions. There is a strong correlation of Cl with Mg2+, Ca2+, SO42 and NO3 (r Cl /Mg2+ = 0.87; r Cl /Ca2+ = 0.79; r Cl /SO42 = 0.73; r Cl /NO3 = 0.71). The calcium ion is well correlated with Mg2+, SO42 and NO3 (r Ca2+/Mg2+ = 0.78; r Ca2+/SO42 = 0.68; r Ca2+/NO3 = 0.64) suggesting the presence of a natural contribution to the observed values of these ions. The Mg2+ concentration is strongly correlated with
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Table 2 Spearman’s rank correlation matrix for rainwater samples (n = 28), all values in (Aeq/l), conductivity (AS/cm) Var. pH EC HCO3 Cl Ca2+ Mg2+ Na+ K+ NO3 SO24 NH+4
pH 1.00 0.45 0.05 0.20 0.36 0.15 0.20 0.12 0.17 0.07 0.23
EC
HCO3
1.00 0.37 0.26 0.18 0.29 0.42 0.28 0.22 0.35 0.34
1.00 0.52 0.46 0.63 0.75 0.14 0.13 0.35 0.16
Cl
1.00 0.79 0.87 0.31 0.17 0.71 0.73 0.30
Ca2+
1.00 0.78 0.14 0.26 0.64 0.68 0.12
Mg2+
1.00 0.54 0.14 0.70 0.79 0.19
Na+
1.00 0.19 0.18 0.40 0.17
K+
NO3
SO24
NH+4
1.00 0.08 0.20 0.10
1.00 0.86 0.21
1.00 0.21
1.00
Bold text shows strong correlations. 0.60–1.00 = strong correlation; 0.50–0.59 = moderate; 0.40–0.49 = weak; 0.00–0.39 = little or no association.
NO3 and SO42 (r Mg2+/SO42 = 0.79; r Mg2+/NO3 = 0.70). There is a strong correlation between NO3 and SO42 (r NO3 /SO42 = 0.86). The reason for nitrate and sulfate might be due to accumulation of these ions in the upper atmosphere being washed down with rains during the rainy season. Besides, anthropogenic sources and agricultural activities west of the area may contribute a lot more to NO3 and SO42 generation during summer and autumn. 3.2. Statistical analysis In this study, relationship between concentrations of ions was examined with factor analysis. Factor analysis allows the identification of a small number of factors that could explain the variability of most of the original data. Factor analysis was used to determine the various sources of the measured ions in rainwater. The method used was Principle Component Analysis (PCA). The factor loadings obtained by PCA normalized with varimax for various ions are presented in Table 3. The loadings having a value greater than 0.70 are marked in bold in the table. Table 3 Results of factor analysis for the major ion concentrations in rainwater samples Variables
Factor 1
Factor 2
Factor 3
pH HCO3 Cl Ca2+ Mg2+ Na+ K+ NO3 SO24 NH+4 Total variance, %
0.12 0.20 0.73 0.55 0.61 0.17 0.31 0.91 0.92 0.22 34.0
0.17 0.90 0.40 0.50 0.70 0.86 0.55 0.15 0.15 0.23 30.6
0.90 0.28 0.42 0.60 0.26 0.25 0.21 0.16 0.19 0.26 17
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Table 4 Mean mass contribution from identified sources for rainwater Source
Mean contribution
Percentage of total predicted mass
Soil dust (natural) Anthropogenic Sea spray (marine) Total predicted mass
440.1 F 45.5 135.7 F 23.3 120.7 F 19.9 696.5 F 50.4
63.2 19.5 17.3 –
Factor 1 accounts for 34% of the total variance. This factor has a high loading for Cl , SO42 , NO3 , Ca2+, Na+ and Mg2+ in decreasing order; strong positive correlations among the ions are found in the correlation analysis. The correlation coefficient between Cl and Ca2+ is 0.70, between Cl and Mg2+ 0.87, between Cl with NO3 and SO42 0.71 and 0.73, respectively. This factor is associated with soil and sea-salt sources. The association Na+ and Cl in factor 1 indicates the presence of sea salts arriving in masses of polar sea air (Lee et al., 2000; Mello, 2001; Lara et al., 2001). Ca2+ and Mg2+ are frequently found in soil and dust (or particulate matter) as well as fallout of Saharan dust. Also factor 1 shows high loadings for SO42 , Cl and NO3 and this may be related to long-range transport of anthropogenic origin, i.e., deriving from human activities from industrial countries. On the other hand, Factor 2 shows that about 30.6% of the total variance has high loadings for HCO3 , Mg2+, Na+, K+ and Ca2+ in decreasing order. This factor is associated with soil source crustal contribution for these ions. There are strong positive correlations among the ions, which belong to factor 2, the correlation coefficient between HCO3 and Mg2+ is 0.63, between HCO3 and Na+ 0.75, a weak correlation between HCO3 and Ca2+ is 0.46. The high concentrations of these ions in rainwater samples are due to the large contribution of the Saharan soil dust, which contains large fractions of CaCO3, MgCO3 and MgSO4. This results of the analysis of dust materials collected during Saharan dust storms in Israel (Foner and Ganor, 1992) indicated that the dust is composed predominantly of quartz with considerable amounts of carbonates, halite, gypsum and illite. Factor 3 accounts for 17% of the total variance, the loading of this factor in the study area was not significant. Factor 1 represents the contribution of ions from local anthropogenic activities, but the factor 2 represent the contribution of ions from a natural source (Saharan dust). In Table 4, the data from the PC analysis with respect to mean mass contribution from identified by PCA sources is presented. It could be seen that for rainwater samples, the marine source delivers the dominant quantity of chloride, sodium and potassium; the anthropogenic source emits mostly nitrate and ammonium with additional of chlorides and sulfates. Soil dust (Saharan soil) source contributes bicarbonate, calcium, and magnesium with additional contribution of chloride and sulfate.
4. Conclusion The chemical composition of precipitation in the Petra region of south Jordan has been investigated. The chemistry of precipitation in the study area is similar to that of other areas of the Mediterranean basin. Even though concentrations of HCO3 , Ca2+ and SO42
O.A. Al-Khashman / Atmospheric Research 78 (2005) 1–12
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were high, precipitation was neutral. The observed pH values of precipitation range between 5.71 and 8.15 with an average value of 6.85 F 0.5. The acidity of the rainwater was significantly neutralized using the alkaline soil dust, principally calcium, and the role of ammonium in the neutralization process is very limited. The chemical composition of precipitation in the investigated area is influenced by either local conditions such as: the Dead Sea, agricultural activities in the Ghore area or remote sites associated with depressions rich in calcite, dolomite and gypsum, and polar and Mediterranean depressions rich in sulfate and nitrate ions. The use of factor analysis facilitates the interpretation of the precipitation characterization, highlighting the influence of the anthropogenic sources in the studied area. The results are related to various sources such as; soil dust, sea-salt spray, agriculture activities and finally combustion products.
Acknowledgements The author would like to acknowledge Dr. Eng. Reyad. A. Shawabakh (Chairman of Chemical Engineering Department at Mutah University) for his help and critical reviewing of the text.
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