Composition Of Rainwater Research Articles

Geochemical and hydrological processes controlling groundwater salinity of a large inland wetland of northwest Australia

Understanding mechanisms of hydrochemical evolution of groundwater under saline and brine wetlands in arid and semiarid regions is necessary to assess how groundwater extraction or injection in large-scale basins may affect the natural interface between saline–fresh aquifers in those systems. We investigated the evolution of groundwater of the Fortescue Marsh, a large inland wetland of northwest Australia that is mainly supplied by floodwater from the upper Fortescue River catchment. The marsh is located in the Pilbara region, one of the world's major iron ore provinces, where mining activities often occur below water tables. Here, we quantified the stable isotope and chemical composition of groundwater, surface water and rainfall in and around the marsh to better understand how saline marshes and playa lakes function geochemically, hydrologically and ecologically. The deep groundwater (>50m depth) of the Fortescue Marsh is highly saline (>100gL−1), whilst shallow groundwater (~0–20m depth) and surface water are mainly fresh or brackish. Currently, the marsh is mainly recharged by occasional floodwater. Consequently, salt in the marsh is concentrated by evaporation of rainfall. We expected that the hydrochemical composition of surface and groundwater would therefore reflect the chemical composition of rainwater. We analysed 206 water samples for stable isotope composition (δ2H, δ18O) and water chemistry, including: pH, dissolved oxygen, electrical conductivity (EC), and total dissolved solids (TDS), as well as Na, Ca, Mg, K, Si, Fe, HCO3, SO4, Cl, Sr and Br. We then developed geochemical models and a salt inventory to estimate the geological time of salt accumulation and to decouple geochemical characteristics of salt from modern groundwater. We found that groundwater associated with the marsh can be divided into two distinct groups that are characterised by their stable isotope compositions; i) fresh and brackish groundwater (TDS <10gL−1; δ18O −8.0±0.9‰) and ii) saline and brine groundwater (TDS >10gL−1, δ18O varies from +2.5 to −7.2‰). Fresh groundwater was evaporated by <20% compared to rainwater. Brackish water mainly reflects modern recharge whilst saline and brine groundwater reflects mixing between modern rainfall, brackish water and relatively old groundwater. The Cl load in the groundwater originates from rainfall and accumulates over time as it is recycled due to precipitation of evaporates and re-dissolution on the marsh during subsequent flooding events. The stable isotope composition of the deeper brine groundwater also suggests a complex evolution, which cannot be explained by evaporation under current conditions from modern rainfall. We thus conclude that the deeper brine groundwater under the Fortescue Marsh developed under a different climatic regime and that the current salt in the marsh has accumulated over at least 40,000years, but could have been as long as 700,000years.

A regional study of the seasonal variation in the molecular composition of rainwater

Rainwater is not only a critical source of drinking and agricultural water but it plays a key role in the fate and transport of contaminants through their removal by wet deposition. Rainwater is a complex mixture of organic compounds yet despite its importance its spatial and temporal variability are not well understood and less than 50% of the organic matter has been characterized. In-depth analytical approaches were used in this study to characterize the seasonal variation in rainwater composition. Rainwater samples were collected over a one-year period in Scarborough, Ontario, Canada. The seasonal variation of atmospheric organic carbon (AOC) in rainwater was analyzed by excitation-emission matrix spectroscopy (EEMs), 1D and 2D NMR with compound identification by spectral database matching, GC–MS, FT-ICR-MS, and GC × GC-TOFMS. This combination of techniques provided four complementary datasets, with less than 10% overlap, of anthropogenic and biogenic AOC. NMR with database matching identified over 100 compounds, primarily carboxylic acids, carbohydrates, and nitrogen-containing compounds. GC × GC-TOFMS analysis identified 344 compounds in two rain events with 33% of the compounds common to both events. FT-ICR-MS generated a seasonally dependent profile of 1226–1575 molecular ions of CHO, CHOS, and CHON elemental composition. FT-ICR-MS and GC × GC-TOFMS datasets were compared using van Krevelen diagrams (H/C vs. O/C), the H/C ratio vs. mass/charge (m/z), and the carbon oxidation state/carbon number matrix. Fluorescence patterns were correlated with NMR results resulting in the identification one seasonally-dependent component of chromophoric dissolved organic matter (CDOM). This study demonstrated the importance of using of an integrated analytical approach to monitor the compositional variation of AOC.

Characterisation of the input signal to aquifers in the French Basque Country: Emphasis on parameters influencing the chemical and isotopic composition of recharge waters

Summary A hydrochemical and isotopic survey of rainwater and groundwater has been carried out during almost two years on the Ursuya Mount in the northern Basque Country (southwestern France) with the aim of enhancing the understanding of the behaviour of this aquifer and more peculiarly the recharge mode of groundwater. The input signal of this aquifer is defined thanks to 112 rainwater samples. The computed meteoric water line (δD = 7.3 δ 18 O + 5.1; r = 0.96) is consistent with that defined in the European IAEA/WMO network stations. The weighted mean deuterium excess about 9.7‰ is really close to the value obtained for Atlantic precipitations and clearly demonstrates an oceanic major origin. The computations conducted on the chemical dataset show that the rainwater composition is controlled by four major factors: (1) a mixed source of anthropogenic pollution and crustal material; (2) a marine source; (3) an urban source; (4) an acid source. Further, the quantification of neutralizing potentials clearly revealed below cloud processes in which crustal and anthropogenic components are responsible for the neutralization of anions. Besides the major Atlantic origin of the recharge water, the chemical and isotopic content of the samples coupled with the corresponding air mass back trajectories revealed four major geographical origins of the components: (1) northwestern part of Atlantic Ocean and (2) Southwestern part of Atlantic Ocean. The oceanic influence in airmasses from these origins is highlighted by the stable isotopic content (weighted mean close to the Atlantic Ocean signature) and by the chemical concentrations dominated by sea salt elements. (3) Northern Europe with a continental influence shown by a light depletion on isotopic signal besides purely oceanic origin and a higher concentration of crustal and anthropogenic components. 4) Southeastern area (Southeastern Europe, Northern Africa and Mediterranean Sea) with an isotopic signature consistent with the Mediterranean one and a chemical composition clearly influenced by the industrial activities of this region. The dataset is confronted with the chemical and isotopic characteristics of groundwater in order to assess the recharge water signature of the aquifer of the Ursuya Mount. The groundwater isotopic signal is close to the defined LMWL, showing actual and local recharge. Nevertheless, a slightly difference is observed between the mean value of stable isotopic content in groundwater and in rainwater. The slightly depleted values of groundwater besides rainwater can be attributed to a preferential winter/autumn recharge. An altitudinal gradient about −0.11‰ δ 18 O/100 m is defined and both water–rock interactions and physicochemical processes fingerprint on the groundwater composition are characterised.

Insights into dissolved organic matter complexity in rainwater from continental and coastal storms by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry

Abstract. A series of seven rainwater samples were collected in Wilmington, North Carolina USA originating from both continental and coastal storms and analyzed by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). This data set is unique in that it represents a detailed comparison of the molecular level composition of DOM in rainwater collected from distinctly different air mass back trajectories by FT-ICR MS. Approximately 25% of the roughly 2000 assigned CHO molecular formulas are unique to a single storm classification indicating the importance of air mass back trajectory on the composition of rainwater dissolved organic matter (DOM). Analysis of the unique molecular formula assignments highlighted distinct groupings of various bio- and geo-molecule classes with coastal storms containing unique formulas representative of lignin and cellulose-like formulas while continental storms had lipid-like formulas. A series of 18 distinct methylene oligomers were identified in coastal storms and 13 unique methylene oligomers in continental storms, suggesting oligomer formation is ubiquitous in rainwater albeit different for each storm classification. Oligomers of small acids and C3H4O2 were detected in both storm types indicating their processing may be similar in both back trajectories. Condensed aromatic hydrocarbons were detected in continental storms with phenol moieties that are not as oxidized as similar compounds detected in aquatic DOM.

Identification of Ion sources in rainwater of a coastal site impacted by the gas and oil industry in the southeast of Mexico

The purpose of this research was to study the chemical composition of rainwater to assess the impact of marine aerosol and anthropogenic emissions by using back air-mass trajectories. Fieldwork was done from July to November 2004, in a coastal site probably impacted by gas and oil industry in Campeche, Mexico: San Antonio Cardenas. Na+, Cl-, and Mg2+, were the most abundant ions, being sea-salt aerosol their unique source. A significant portion of K+ and Ca2+ originated from non-sea-salt sources; and the sulphate excess exceeded the background level reported for remote marine sites, suggesting that besides of marine aerosol, there was a significant contribution of SO42- from anthropogenic sources. NO3- concentrations in San Antonio Cardenas exceeded the background level reported for coastal sites with minimal anthropogenic influence and showed a significant correlation with SO42-, suggesting a common source. Agricultural practices are null, for this reason NH4+ levels were low. Mean pH value was 4.64, this acidity showed a good correlation with SO42- and NO3- levels, and with the local meteorology. A sour gas recompression plant located 10 km at NE from San Antonio Cardenas was identified as the main source of this strong acidity.

Determination of soluble ultra-trace metals and metalloids in rainwater and atmospheric deposition fluxes: A 2-year survey and assessment

The present work investigates the relationships between composition of rainwater and dry deposition fluxes by trace metals and metalloids. A modification in automatic “wet-only” and “dry-only” samplers was applied, which allowed the collection and conservation of samples separately. ICP-MS technique was used for the determination of analytes in samples. Concentrations of soluble elements in rainwater were measured directly in filtered samples. A sequential acid treatment with nitric, hydrofluoric and finally perchloric acids was used to measure the total contents of metals and metalloids in coarse particles. Variation between periods of heavy and light rains was assessed. Almost all of the metals and metalloids – B, Tl, Th, U, Al, Cs, Be, Ti and others – studied in dry deposition showed important decreases in concentrations (40–92%) during periods of heavy rainfall. Most of these metals and metalloids – As, Cr, Co, Ni – presented their highest levels (53–90%) in heavy rainfall periods in rainwater samples. Sources were identified in both types of samples collected using a new chemometric tool (SPCA). Urban traffic, surrounding contaminated soils and local anthropogenic sources were identified for rainwater samples. Natural and contaminated soils and general anthropogenic emissions were the sources identified for dry deposition fluxes.

Dynamics of the chemical composition of rainwater throughout Hurricane Irene

Abstract. Sequential sampling of rainwater from Hurricane Irene was carried out in Wilmington, NC, USA on 26 and 27 August 2011. Eleven samples were analyzed for pH, major ions (Cl−, NO3−, SO42−, Na+, K+, Mg2+, Ca2+, NH4+), dissolved organic carbon (DOC) and hydrogen peroxide (H2O2). Hurricane Irene contributed 16% of the total rainwater and 18% of the total chloride wet deposition received in Wilmington NC during all of 2011. This work highlights the main physical factors influencing the chemical composition of tropical storm rainwater: wind speed, wind direction, back trajectory and vertical mixing, time of day and total rain volume. Samples collected early in the storm, when winds blew out of the east, contained dissolved components indicative of marine sources (salts from sea spray and low DOC). The sea-salt components in the samples had two maxima in concentration during the storm the first of which occurred before the volume of rain had sufficiently washed out sea salt from the atmosphere and the second when back trajectories showed large volumes of marine surface air were lifted. As the storm progressed and winds shifted to a westerly direction, the chemical composition of the rainwater became characteristic of terrestrial storms (high DOC and NH4+ and low sea salt). This work demonstrates that tropical storms are not only responsible for significant wet deposition of marine components to land, but terrestrial components can also become entrained in rainwater, which can then be delivered to coastal waters via wet deposition. This study also underscores why analysis of one composite sample can lead to an incomplete interpretation of the factors that influence the chemically divergent analytes in rainwater during extreme weather events.

Chemical Composition and Sources of Rainwater Collected at a Semi-Rural Site in Ya’an, Southwestern China

Rain and snow water samples were collected from Sep. 2010 to Jun. 2011 at a semi-rural site in Ya’an, a city located in the rain-belt along the Tibetan Plateau, to characterize the chemical composition and the sources of precipitation. The collected samples were severely acidified with an annual volume-weighted mean (VWM) pH of 4.03 and an annual acid rain frequency of 79%. SO42- and NH4+ were the most abundant ions, followed by Ca2+, H+, NO3-, Cl-, K+, Na+, F- and Mg2+. The acidity of samples was predominantly generated by H2SO4 and HNO3, which were neutralized by NH4+ and Ca2+ as much as 65%. NH3 played a major role in neutralizing the acid rain. The average ambient concentration of NH3 was 174.2 μg/m3 during sampling periods. Different source apportionment methods, including principle component analysis (PCA), enrichment factor (EF), correlation and back-trajectory analysis were used to track the sources of rainwater. The methods suggested that the pollutants in rainwater were from both local and long-distance transport (1:2.2), or they were from anthropogenic actions (86.4%), sea salts (8.1%) and crustal (5.5%) respectively.

Impact of volcanic emissions on rainwater chemistry: The case of Mt. Nyiragongo in the Virunga volcanic region (DRC)

Chemical composition of rainwater is strictly related to atmosphere scavenging. Active degassing volcanoes release acid gases and solid particulate in the surrounding environment. Nyiragongo Volcano (DRC) is characterized by a high degassing activity from an active lava lake hosted within the crater. Chemistry of rainwater in the area is clearly dependent on the influence of the volcanic plume, especially at the rim of the Nyiragongo summit crater. Rainwater collected from this zone has pH values as low as 2, high salinity (EC 28–1800μS/cm), and high contents of F− and Cl− (up to 193 and 270ppm, respectively), NH4+ (up to 146ppm) and SO42− ions (up to 340ppm) relative to worldwide rainwater. The chemical composition of rainwater after interaction with the volcanic plume tends to shift towards the condensable fraction of fumarolic fluids discharged from the summit crater. Rainwater acidified by the volcanic plume also removes metals from particulate suspended in the atmosphere, thus undergoing metal enrichment. Displacement of the Nyiragongo volcanic plume by predominantly westward-directed wind causes “natural” contamination of rainwater collected for drinking purposes in villages located on the western flank of the volcano. Rainwater falling in urban centers located S–SE of the Nyiragongo Volcano is not usually affected by the rain–plume interactions which strictly depends on wind directions. However, areas of possible contamination by the volcanic plume might create a further emergency and critical situations on top of an already existing severe humanitarian crisis. Rainwater is the principal drinking water supply in the Nyiragongo area, thus the geochemical monitoring of rainwater quality is of great importance to mitigate the hazard of natural contamination of this fundamental resource for the local communities.

87Sr/86Sr and major ion composition of rainwater of Ahmedabad, India: Sources of base cations

Rainwater samples from Ahmedabad, an urban site in India are analysed for their chemical composition and Sr isotopic ratio. Dominance of Ca in the cation budget indicates its importance in the acid neutralization whereas SO4 and NO3 dominate the anion budget. The major ion concentrations measured in this study are on the lower side of the range reported in the previous study (Rastogi and Sarin, 2007) from the same site. Na and Cl show very good correlation with ratio similar to the seawater ratio, implying their marine origin. Na concentration in these samples has been used as a proxy to calculate the non sea salt fraction of other major ions. Non sea salt Ca and Mg vary from 99.0% to 99.6% and 24.6% to 89.1% of the measured Ca and Mg respectively whereas non sea salt component of SO4 and HCO3 contribute 84.3% to 98.9% and 99.1% to 99.9% respectively. Sr concentrations in these rainwaters vary from 32 to 191 nM and 87Sr/86Sr ranges from 0.70878 to 0.71027. Sr concentration shows a very good correlation (coefficient 0.93) with the non-sea salt component of Ca and Mg indicating their continental sources and having similar provenances. Carbonates and basalts seem to contribute significantly to dissolved base cations of the rainwaters. The basalts from Deccan region, which is isotopically indistinguishable from the African basalts and the silicate and carbonates from African region along with the sediments from the Ganga plain (which is originated from the Himalayan lithologies) could be potential dust sources for this particular site. The sources of dissolved base cations deduced from Sr isotope composition of the rainwaters are consistent with wind back trajectory data obtained from NOAA HYSPLIT model.

Acid rain and particulate matter dynamics in a mid-sized Andean city: The effect of rain intensity on ion scavenging

Acid rain phenomenon (average WVM pH = 4.9) and a strong association of sulfate scavenging and rain intensity (R2 = 0.8118) were observed over a seven-month period (October 2010–April 2011) at a densely populated mid-sized Andean city (pop 380,000) that occupies mountain ridge topography (2150 m.a.s.l.). Rain chemistry and PM10 were fairly consistent over four sampling sites representing various scenarios of urban density and topography. All stations exhibited differences in the sulfate content in PM10 between dry and wet periods, further illustrating the sulfate scavenging dynamic. Concentration of major ions evaluated in rain were in order of sulfates (35.2–53.5 μeq L−1) > calcium (14.6–17.3 μeq L−1) > chlorides (3.5–5.1 μeq L−1) > nitrates (2.1–3.1 μeq L−1). Major chemical constituents of PM10 were related with ionic composition of rainwater through scavenging ratios (SRs). High sulfate SRs associated with increased rain intensity reflected higher sulfate ion solubility. Significant contribution of sulfates to total ionic content, higher than 50% at all monitoring stations, suggests important contributions of SO2 emissions, which could come from three principal sources: vehicular emissions due to Colombian fuels with elevated sulfur content, industrial emissions at southeast of the city, and sulfur gas emissions from a nearby active volcano, Nevado del Ruiz, located 27 km southeast of the city.

Aerosol and precipitation chemistry measurements in a remote site in Central Amazonia: the role of biogenic contribution

Abstract. In this analysis a 3.5 years data set of aerosol and precipitation chemistry, obtained in a remote site in Central Amazonia (Balbina, (1°55' S, 59°29' W, 174 m a.s.l.), about 200 km north of Manaus) is discussed. Aerosols were sampled using stacked filter units (SFU), which separate fine (d &lt; 2.5 μm) and coarse mode (2.5 μm &lt; d &lt; 10.0 μm) aerosol particles. Filters were analyzed for particulate mass (PM), Equivalent Black Carbon (BCE) and elemental composition by Particle Induced X-Ray Emission (PIXE). Rainwater samples were collected using a wet-only sampler and samples were analyzed for pH and ionic composition, which was determined using ionic chromatography (IC). Natural sources dominated the aerosol mass during the wet season, when it was predominantly of natural biogenic origin mostly in the coarse mode, which comprised up to 81% of PM10. Biogenic aerosol from both primary emissions and secondary organic aerosol dominates the fine mode in the wet season, with very low concentrations (average 2.2 μg m-3). Soil dust was responsible for a minor fraction of the aerosol mass (less than 17%). Sudden increases in the concentration of elements as Al, Ti and Fe were also observed, both in fine and coarse mode (mostly during the April-may months), which we attribute to episodes of Saharan dust transport. During the dry periods, a significant contribution to the fine aerosols loading was observed, due to the large-scale transport of smoke from biomass burning in other portions of the Amazon basin. This contribution is associated with the enhancement of the concentration of S, K, Zn and BCE. Chlorine, which is commonly associated to sea salt and also to biomass burning emissions, presented higher concentration not only during the dry season but also for the April–June months, due to the establishment of more favorable meteorological conditions to the transport of Atlantic air masses to Central Amazonia. The chemical composition of rainwater was similar to those ones observed in other remote sites in tropical forests. The volume-weighted mean (VWM) pH was 4.90. The most important contribution to acidity was from weak organic acids. The organic acidity was predominantly associated with the presence of acetic acid instead of formic acid, which is more often observed in pristine tropical areas. Wet deposition rates for major species did not differ significantly between dry and wet season, except for NH4+, citrate and acetate, which had smaller deposition rates during dry season. While biomass burning emissions were clearly identified in the aerosol component, it did not present a clear signature in rainwater. The biogenic component and the long-range transport of sea salt were observed both in aerosols and rainwater composition. The results shown here indicate that in Central Amazonia it is still possible to observe quite pristine atmospheric conditions, relatively free of anthropogenic influences.

Chemical composition of rainwater in a karstic agricultural area, Southwest China: The impact of urbanization

The chemical composition of rainwater has been studied in a karstic agricultural area, Southwest China. Rainwater pH and major ions were measured in samples collected from the town of Puding, Guizhou province, during the rainy season, between March and October 2008. The pH of samples varied between 4.6 and 7.1, with a volume-weighted mean (VWM) of 5.4. These relatively high-pH values do not signify a lack of acid components in the precipitation; instead, they demonstrate neutralization of acidity. Ca2+ and NH4+ were the dominant cations in the rainwater, with VWM concentrations of 156 and 33μeq/L, respectively. SO42− was the predominant anion, with a VWM concentration of 152μeq/L, followed by NO3− (17μeq/L). Our results show that most of the acidity in the collected samples was neutralized by Ca2+-rich alkaline soil dusts. We compared our findings with other areas of China that experience acid rain. The concentration of ions in Puding rainwater generally exceeded that reported in southern China but was lower than in northern China. This is probably due to karst rock desertification, which could provide the atmosphere with a source of alkaline dust. From back-trajectory analysis, correlation studies, and a comparison of major ion composition with other selected sites worldwide, we conclude that the rainwater ion composition of Puding is more significantly influenced by terrestrial and anthropogenic sources (mainly due to industrial and traffic emissions in surrounding large cities), rather than by marine sources.

Immigration to Tikal, Guatemala: Evidence from stable strontium and oxygen isotopes

This paper presents strontium and oxygen isotopic measurements on archaeological human teeth from the ancient Maya city of Tikal, Guatemala, that illuminate the role that migration played in the history of the state. Stable strontium isotope ratios of human teeth parallel the bedrock geology of the location where foods were grown, while stable oxygen isotope ratios reflect the sources of water imbibed, and track geographic variation in the isotopic composition of rain water. Because tooth enamel forms during childhood and is not remodeled during life, we can identify foreign-born individuals at Tikal by their outlying strontium and oxygen isotope ratios. These data indicate that approximately 11–16% of the sampled Tikal skeletons spent their childhood at distant sites. Most of the migrant burials date from the Early Classic period and are high status contexts. Several royal burials demonstrate long distance movement of both males and females, and shed light on the identification of epigraphically-known individuals. Yet, both Early and Late Classic migrants are found in lower status domestic burials. Interaction with distant peers was important in the rise of the Tikal polity, however, immigration from all social tiers contributed to the city’s rapid population growth.

Effects of rainfall on soil moisture and water movement in a subalpine dark coniferous forest in southwestern China

AbstractWater content and movement in soil profile and hydrogen isotope composition (δD) of soil water, rainwater, and groundwater were examined in a subalpine dark coniferous forest in the Wolong National Nature Reserve in Sichuan, China, following rainfall events in 2003–2004. Light rainfall increased water content in the litter and at soil depth of 0–80 cm, but the increased soil water was lost in several days. Heavy rainfall increased soil water content up to 85% at depths of 0–40 cm. Following the light rainfall in early spring, the δD of water from the litter, humus, illuvial, and material layers decreased first and then gradually reached the pre‐rainfall level. In summer, light rainfall reached the litter humus, and illuvial layer, but did not hit the material layer. Heavy rainfall affected δD of water in all layers. The δD of soil interflow slightly fluctuated with rainfall events. The δD of shallow groundwater did not differ significantly among all rainfall events. Light rainfall altered the shape of δD profile curve of water in the upper layer of soil, whereas heavy rainfall greatly affected the shape of δD profile curve of water in all soil layers. Following the heavy rainfall, preferential flow initially occurred through macropores, decayed plant roots, and rocks at different depths of soil profile. With continuing rainfall, the litter and surface soil were nearly saturated or fully saturated, and infiltration became homogeneous and plug‐like. Forest soil water, particularly in deeper soil profile, was slightly affected by rainfall and, thus, can be a source of water supply for regional needs, particularly during dry seasons. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Air Masses and Weather Types: A Useful Tool for Characterizing Precipitation Chemistry and Wet Deposition

This study is an analysis of 344 days with rainfall recorded during five years in a remote regional background EMEP (Cooperative Programme for the Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe) station in Spain. The chemical composition of the rainwater associated with air masses (nine categories) and weather types (26 categories) was characterized. The chemical composition of rainwater was dominated by calcium (Ca2+) and sulphate (SO42−-S), with VWM (Volume Weighted Mean) during the period studied (2002–2006), with 55 μeq/L and 34 μeqS/L, respectively. Calcium, sodium (Na+), ammonium (NH4+-N) and magnesium (Mg2+) seem to be dominant components in the neutralization of the rainwater. By applying Pearson correlations, principal component analysis and enrichment factors, it is possible to identify source types for the precipitation constituents. Interannual and intra-annual variability was also been studied. High calcium levels are associated with the frequent intrusions of Saharan dust that occur during the summer, and the maximums of chlorine and sodium in the winter may be due to the greater amount of maritime air recorded during this season. Wet deposition was determined by focusing on nitrogen deposition, registering mean annual values of 155 mgN/m2/year (from the NO3−-N) and 165 mgN/m2/year (from the NH4+-N).

ELEMENTAL ANALYSIS OF RAINWATER BY PIXE TECHNIQUE

Analysis of trace and toxic metals in untreated rainwater has been carried out using nondestructive proton induced X-ray emission (PIXE) in combination with pre-concentration technique. The pre-concentration technique used for this purpose was carried out by evaporation of the rainwater samples at 50°C under atmospheric pressure. Untreated rainwater samples were collected from 10 different locations across Baghdad city, Iraq. The mean concentration values of the elements ( Al, Ca, Co, Ti, V, Cr, Mn, Fe, Zn, Br, Rb and Sr ) in rainwater samples were determined simultaneously at the parts per billion (ppb) levels. The rainwater samples and certified reference materials (CRMs) were irradiated with 2.0 MeV proton beam from Van de Graaff accelerator. The accuracy of the results was proved by using certified reference materials (GSP-2). The results were compared with the published data, Iraqi standards (IRQ), European standards (EU), and World Health Organization (WHO) guidelines for drinking water quality. The purpose of this work was to obtain the total elemental compositions of rainwater in Iraq.

Rainwater chemistry in the North Western Himalayan Region, India

Precipitation chemistry studies were conducted at Kothi (32.31°N, 77.20°E), a rural Indian location, in the North Western Himalayas during June to October of 2006 and 2007. The volume weighted mean pH values ranged from 5.16 to 6.36 with a mean of 5.68±0.26 indicating mostly alkaline precipitation events. However, 18% samples were found acidic due to dominance of acidic components. The alkaline to acidic ions ratio (1.05) confirms that acidic components are neutralized by alkali radicals in rainwater. Of the total ionic composition 159μeq/l, in rainwater samples, dominant were Ca2+ (19%) followed by Na+ (14%). Among the anions, Cl− (17%) was slightly higher than SO42− (16%) and NO3− (11%). The ratio (NO3−+Cl−)/SO42−) 1.05 indicates acidity in rainwater by the cumulative effects of HNO3, H2SO4 and HCl. The ratios NH4+/NO3− as 0.76 and NH4+/SO42− as 0.50 show the pre-dominance of atmospheric NH4NO3 and (NH4)2SO4. Significant correlation between Na+ and Cl− (r=0.97; p<0.0001) and between SO42− and NO3− (r=0.60; p<0.0001) indicates their origin from similar sources. Neutralization factor calculations show that Ca2+ plays a major role in the neutralizing processes. Enrichment factors indicate that Ca2+, SO42− K+ and Mg2+ were originated from non-marine sources. The principle component analysis indicates the influence of transportation of air-born primary and secondary particles on the chemical composition of rainwater.

Chemical Composition of Rainwater over a Mining Area in Ghana

A comprehensive study on the chemical composition of rainwater was carried out in Obuasi, a gold mining town in Ghana. Rainwater samples were analyzed for major ions (Ca 2+ ,Mg 2+ , K + , Na + , NH 4 + , Cl - , NO 3 - and SO 4 2- ) and trace metals (Fe, Al, Zn, Pb, Cr, and Cd). The rainwater was typically acidic with a mean pH of 4.76±0.47, which ranged from 4.0 to 5.6. The low pH found in the water suggests that the concentration of the alkaline particles in the rainwater were not high enough to neutralize acidic species present. SO 4 2" and Cl " were the main anions, while Ca 2+ and K + were the main cations. Concentrations of trace metals in this study were compared with those of other studies conducted at different sites in the world. The result of this study generally suggests that rainwater chemistry in the area is strongly influenced by local anthropogenic sources (mining). The pollutants in rainwater samples were mainly derived from mining activities. Concentrations of Pb in all the samples were above the WHO permissible limit of 0.01 mg/L for drinking water.

Source identification and variation in the chemical composition of rainwater at coastal and industrial areas of India

Studies on precipitation chemistry were carried out to understand the nature and sources of rainwater at Rameswaram and NTPC Dadri, India representing coastal and industrial region during 2010. The rainwater samples, collected at these locations, were analyzed for major ions and pH. The data were assessed for its quality. The pH of rainwater at two locations varied from 5.53 to 6.73 and 5.1–6.6, indicating alkaline nature except a few acidic events. The dominance of Cl− and Na+ were observed in coastal environment whereas dominance of Ca2+ was seen in industrial environment. The nss-SO42- (37.9%) at Rameswaram is less influenced by anthropogenic activities whereas nss-SO42- (72.5%) at NTPC Dadri is influenced by pollutants emitted by anthropogenic sources. The ratio of H+/(NO3- + SO42-) was observed as 0.04 and 0.008 for Rameswaram and NTPC Dadri which is close to zero, indicate 99.99% of acidity was neutralized in precipitation. Ca2+, NH4+ and Mg2+ play an important role in neutralization of acidic ions in rainwater. For source identification, correlation matrix analysis was established, which showed that in general, at both sites; correlation between the acidic ions SO42- and NO3- indicating their origin from similar sources, because of the similarity in their behavior in precipitation and the co-emissions of their precursors SO2 and NOX. The correlation coefficient of (SO42- + NO3-) vs (Ca2+) at Rameswaram and NTPC Dadri were 0.77 and 0.87 indicates that CaCO3 is the major neutralizing agent for both the region. Overall, the influence of marine, terrestrial and anthropogenic sources was observed in the rain events.