Composition Of Rainwater Research Articles

Chemical composition of rainwater collected at a southwest site of Mexico City, Mexico

Measurements of the trace metals Cd, Cr, Mn, Ni, Pb, V and Al in soluble and insoluble rain fractions and SO 4 − 2 , NO 3 −, Cl −, HCO 3 −, Ca 2+, Mg 2+, Na +, K +, NH 4 + and H + in soluble fractions were performed in rainwater collected at a southwest site of Mexico City during the rainy seasons of 2001 and 2002. Aluminum presented the highest volume-weighted mean concentration (VWMC) in both insoluble and soluble fractions. In the insoluble fractions, the VWM of the other trace metals decreased in the order Mn, Pb, Ni, V, Cr and Cd, and in the soluble fractions in the order Mn, V, Ni, Pb, Cd and Cr. Ammonium presented the higher VWMC, followed by SO 4 2−, NO 3 −, HCO 3 −, Ca 2+, Cl −, H +, Na +, Mg 2+ and K +. Air mass back trajectories were associated to the concentrations of trace metals and of SO 4 2−, Ca 2+, Mg 2+, NH 4 + and H + observed during each rainy day. Trace metal concentrations were not clearly related to wind direction. Enrichment factors related to the relative abundance of elements in crustal material were calculated using Mg as reference. The high enrichment factors (EF c) suggested that, in general, trace metals and major ions had an anthropogenic origin. Aluminum, K +, and Ca 2+ were the only elements that had a significant crustal source. Factor analysis (Principal Component Analysis) with Varimax normalized rotation grouping the elements analyzed into three factors. Factor 1 indicated a crustal contribution for Ca 2+, K +, Mg 2+ and anthropogenic sources for SO 4 2−, NH 4 + and V. Factor 2 indicated a high loading for Al, Ni and Mn, that indicate possible contribution of anthropogenic sources but with a significant crustal contribution for Al. Factor 3 indicated an anthropogenic origin for H + and NO 3 −. Pearson's correlations show that Al correlated with all the metals, including Ca 2+ and Mg 2+. The solubility of trace metals did not depend on rainwater pH. As it was expected, Al presented the highest wet deposition flux.

Relationship between the origin of precipitation in the Jordan Rift valley and their geochemical composition

Rainwater was sampled during seven winters at eight sites along the Jordan Rift valley in Israel. The study area is divided into two regions: the northern part located between the Sea of Galilee and the Dead Sea and the southern part between the Dead Sea and the Dead Sea–Red Sea water divide line in the Arava valley. The Dead Sea region is considered as a desert, the northern part of the study area is semidesert whereas the southern region is considered as extreme desert. Good agreement was found between the chemical and isotopic composition of rainwater its sources and air mass trajectories. In the arid areas, the contribution of salts was mainly from local sources (of up to 500 Km in diameter). Significant chemical divergence was found between rainwater deriving from marine air masses characterized by NaCl enrichment and rainwater deriving from continental air masses which are mainly characterized by Ca‐carbonate enrichment. Six main marine and continental air mass trajectories were defined, i.e., northern, northwestern, western, southwestern, eastern and local. The northern air mass trajectories contribute more salts than the southwestern air mass trajectories which exhibit the lowest rainwater salinities. The western trajectory is exclusively marine originating from the Mediterranean, while the eastern trajectory is exclusively continental and originates in the Arabian Desert. Rainwater isotopes revealed three chemically differing systems. The western marine trajectories reflect chemical setting associated with East Mediterranean Meteoric Water Line system; the continental air masses are mainly associated with the Mean Meteoric Water Line system; and whenever the eastern component is significant, a Local Meteoric Water Line prevails.

New insight into pedogenic processes in extremely arid environments and their paleoclimatic implications—the Negev Desert, Israel

Stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern Arava Valley, Dead Sea Rift, indicate the existence of a calcic ‘soil’ developed 50–100 cm beneath the channel surfaces. This anomalous calcic ‘soil’ does not fall within the categories of any standard soil or paleosol definition and thus has been termed “Fluvial Pedogenic Unit” (FPU). The FPU occurs at the lower limit of the contemporary scour-and-fill processes in the aerated zone and it defines the maximum scour-and-fill during floods. The FPU is also found in late Pleistocene and Holocene terraces, termed paleo-FPU, indicating that the hydrological regime of past floods was similar to the present one. The formation of a calcic FPU in this unique environmental setting is associated with the cumulative influence of persistent differences in water availability to various parts of the channel before and during flood events. The carbonate accumulation results from low recurrence of flood events, relatively limited moisture amounts and almost no involvement of vegetation in its formation. The isotopic analyses of calcic crusts in the FPU and in the paleo-FPU indicate that arid climatic conditions prevailed during their formation. This indicates that the flood regime under arid climatic conditions characterized most of the Negev Desert during the late Pleistocene and the Holocene. However, a clear difference in the δ 18O and the δ 13C values was detected between the active channels and the terraces. This difference suggests a change in the rainwater composition, rather than changes of temperature or amounts of rainfall.

Chemical composition and its origin in spring rainwater over Taihu Lake

Chemical compositions of rainwater collected in three stations in Taihu Lake in Jiangsu Province, China between March and May 2003 were analyzed through numerical simulations and field observation data. In terms of average ion deposition rate in spring at the air/water interface, of all anions, that of SO42− was the largest followed by NO3−, whereas among all cations, Ca2+ concentration and the rate was the largest, and then NH4+ was the next. The correlation of ion concentration indicated that the catchment of the lake has been artificially polluted considerably. Using backward trajectory analysis, the raining water in the stations in Taihu Lake was classified. In spring, marine-originated rain is the main contribution to this area, counting for 92.7% of the total precipitation, in which SO42−, NO3− and NH4− contributed 89.2%, 88.1%, and 88.3% respectively to the total spring-rain chemicals, whereas land-originated rains contributed in a small amount. However, the ion concentration in the land-originated rain was higher and acidic, causing considerable harm to local ecosystem. The analysis of backward trajectory analysis shows that three types of air masses influenced the chemical composition of the lake water, namely, air mass from NE direction, air mass from SW direction, and local air mass. Although the local air masses often produced small rainfall amount, but the nature of high ion concentration and high acidity impacted the local ecosystem rmmarkably. The ion concentration and rainfall from long-distance boreal air mass are clearly greater than those in austral air.

The Influence of a Coal-Fired Power Plant in Turkey on the Chemical Composition of Rain Water in a Certain Region

In this study, the chemical composition of the rainwater in Yatağan, which is a region surrounding a coal power plant was investigated from February to April 2002. Rainwater samples were obtained from Yatağan, located northwest of Muğla City in Turkey. pH values and concentrations of major ions (Ca(2+), Na(+), K(+), SO(2-)(4), NO(-)(3), NH(+)(4)) in the rainwater samples were analyzed. The pH varied from 5.1 to 7.9 with an average of 6.7 which was in alkaline range considering 5.6 as the neutral pH of cloud water in equilibrium with atmospheric CO(2). In the total of 30 rain events, only three events were observed with water in the acidic range (<5.6), which occurred after continuous rains. The equivalent concentration of components followed the order: Ca(2+) > SO(2-)(4) > Na(+) > NH(+)(4) > NO(-)(3) > K(+) > H(+). The anion and cation concentrations in the rainwater samples showed a high sulphate concentration (131 microEq/l), as well as high sodium (40 microEq/l) and calcium (298 microEq/l) concentrations. These values indicate that one probable source of the high sodium concentration is fly ash, after the coal burning process and the power plant can be effective on level SO(2-)(4) concentrations in rainwater. In addition, the dust-rich local and surrounding limestone environment might have caused the high concentration of Ca(2+) in rainwater of the Yatağan Basin. Due to a large contribution of these cations to the sulphate neutralization action, the rainwater of this region displays only a moderate acidity, which does not cause significant environmental impact.

Chemical composition of rainwater in a tropical urban area of northern India

Rainwater samples during the monsoon of 2001 and 2002 were collected from Roorkee urban area, a medium sized “town group” situated on the right bank of Solani River, a tributary of the Ganga River, near the Himalayan foothills and analyzed for EC, pH, TSS, TDS and major ions. The median value of pH was 7.05, well above 5.6, which is the reference pH. The ratios of SO 4 2−+NO 3 − and Ca 2++Mg 2+ (TA/TC) have been considered for acidity. In this study, ratio of TA/TC is quite below 1.0, indicating alkaline nature of rainwater. The concentration of ions in rain water have been observed to follow the pattern Ca 2+>HCO 3 −>Cl −>NO 3 −>Na +>Mg 2+>SO 4 2−>K +. In order to estimate the marine and non-marine contribution, sea salt fraction has been calculated taking Na + as reference. All ionic ratios have been found to be higher than the recommended sea water ratios in all three types of land use, viz. residential, commercial and industrial, suggesting a significant contribution of non-marine origin for these components. A comparison with the data of the other Indian sites validates the inverse relation of Cl − and Na + with distance from the sea and highlights higher Ca 2+ concentration and lower SO 4 2− concentration.

Experimental evaluation of rainwater quality for non-potable applications in the city of São Paulo, Brazil

This study summarizes the evaluation of rainwater quality and its potential for non-potable applications in the city of São Paulo, Brazil. An experimental system was installed at the Centro de Técnicas de Construção Civil (Civil Construction Techniques Centre, Escola Politécnica, University of São Paulo) such that analysis of the physical, chemical and bacteriological composition of rainwater—total and faecal coliforms, Clostridium Sulphite-reducer, Enterococcus and Pseudomonas aeruginosa—could be conducted. The need for water treatment was also evaluated in order to match quality to specific uses. Rainwater samples were collected from the roof by an automatic sample collector. Samples were also collected from a rainwater storage tank. In the operation of the system, analysis of rainwater's potential use in non-potable applications, such as flushing toilet bowls, was also conducted. The results obtained did not meet recognised quality standards, leading to the conclusion that water disinfection prior to use is required.

Estimation of evaporation rate from soil surface using stable isotopic composition of throughfall and stream water in a tropical seasonal rain forest of Xishuangbanna, Southwest China

Xishuangbanna is located at the northern edge of the distribution of tropical forests in Southeast Asia, and it has a very high frequency of radiation fog, especially during the dry season (November-April). In this study, rainwater, throughfall, intercepted fog water (fog drip) by forest canopy, and stream water were collected in January 2002 and December 2003 for stable isotopic analysis at a tropical seasonal rain forest site in Xishuangbanna, Southwest China. The objective of the study is to estimate the evaporation rate from the forest floor. The stable hydrogen (δD) and oxygen isotope composition (δ 18O) of rainwater, throughfall, fog drip, and stream water was determined using an isotope ratio mass spectrometer. Stream water during the non-storm runoff period was considered to reflect the effect of evaporation from the forest floor. The evaporation rates from the forest floor were estimated using isotope composition values in stream water and the total throughfall was estimated using the Rayleigh distillation equation under equilibrium conditions. The results indicated that the annual weighted means of δD and δ 18O in fog drip were consistently more enriched than those of rainwater and stream water, and the fog drip was thought to contain water that had evaporated and recycled. The weighted means of δD and δ 18O in stream water during the non-storm runoff period were 5.69% and 0.39% more enriched than those of the total throughfall (rain throughfall + fog drip) in 2002, while in 2003 these were 5.05% and 0.28%, respectively. Evapotranspiration in the humid year 2002 and the dry year 2003, computed from the water balance, was 1186 mm and 987 mm, respectively, which was quite low when compared with the values reported in some humid tropical forests. Consequently, the evaporation rate from the forest floor was 5.1% of the evapotranspiration in 2002, and 3.1% in 2003. The lower evaporation rate was thought to be mainly a result of the influence of the high frequency of heavy radiation fog on the rain forest during the night in the dry season (November-April).

Wind, rain and bacteria: The effect of weather on the microbial composition of roof-harvested rainwater

The microbiological and chemical quality of tank-stored rainwater is impacted directly by roof catchment and subsequent run-off contamination, via direct depositions by birds and small mammals, decay of accumulated organic debris, and atmospheric deposition of airborne micro-organisms and chemical pollutants. Previous literature reports on roof water quality have given little consideration to the relative significance of airborne micro-organisms. This study involved analyses of direct roof run-off at an urban housing development in Newcastle, on the east coast of Australia. A total of 77 samples were collected during 11 separate rainfall events, and microbial counts and mean concentrations of several ionic contaminants were matched to climatic data corresponding to each of the monitored events. Conditions both antecedent to, and those prevailing during each event, were examined to investigate the influence of certain meteorological parameters on the bacterial composition of the roof water and indirectly assess the relative contribution of airborne micro-organisms to the total bacterial load. Results indicated that airborne micro-organisms represented a significant contribution to the bacterial load of roof water at this site, and that the overall contaminant load was influenced by wind velocities, while the profile (composition) of the load varied with wind direction. The implications of these findings to the issues of tank water quality and health risk analysis, appropriate usage and system design are discussed.

The chemical composition of throughfall beneath oak, birch and pine canopies in Northwest Germany

The chemical composition of rainwater is altered upon its passage through tree canopies. In order to investigate how rainwater chemistry is affected by canopy-dependent processes in characteristic forest types of Northwest German sandy lowland regions – oak–birch-forests, Betula pubescens Ehrh. swamp forests, and stands of Pinus sylvestris L. – comparative studies on the chemical composition of throughfall were carried out at seven forest sites, situated in close proximity within a nature reserve. Additionally, rainwater was sampled at three heathland sites for analysis of open-field precipitation and at three sites along an oak–birch-forest edge. Throughfall concentrations of most of the parameters analysed were significantly higher than open-field concentrations, especially with regard to electric conductivity, NH4-N, K+, and KMnO4-index. Ion concentrations in throughfall were the lowest in a 10-year-old stand of Betula pendula Roth. and Pinus sylvestris and in a Betula pubescens swamp forest and were highest beneath a stand of Pinus sylvestris. Except for Na+, Cl−, and NO 3 − , ion concentrations in both throughfall and open-field precipitation increased during the growing season (May–October). In throughfall, Ca2+, Mg2+, K+, and Mn2+ were strongly correlated. Enrichment ratios between throughfall and open-field deposition varied among sites and elements and were the highest for K‰+, Mg2‰+, and Mn2‰+. Estimates of canopy leaching indicated high leaching rates of K‰+ and Mn2‰+ and moderate leaching of Mg2‰+. The contribution of foliar leaching to throughfall deposition was higher at the deciduous than at the coniferous stands.

Long-term changes in hydrological pathways in an upland peat catchment—recovery from severe drought?

This study analyses long-term water quality data from an upland peat catchment in order to understand long-term changes in hydrological flowpaths and how they relate to recovery from severe drought and control the release of DOC. The study examined comparative records from rainfall, soil and stream samples over a 9-year period, which included an approximately 1 in 30-year drought 2 years into the period. The study examined single tracers and utilised multivariate statistics to examine changing sources and routes of runoff. The study shows that the severe drought is part of dry period not restricted to a single summer and this extended dry period may give rise to the extent of the chemical changes observed in the stream chemistry. During this period of drought there is no evidence for substantive new flowpaths being generated during the drought, instead the residence time of the water in the upper peat horizon (<10 cm depth) increases and that this increase is reflected in the chemistry of runoff. The soil waters deeper in the peat profile (approx. 50 cm) show increased influence of rainwater compositions and that during drought the residence times at depth increase. There is an offset between the severe drought and maximums in concentrations of Fe, DOC and Al are related to the hydrophobic nature of the peat matrix. The effects of a 30-year drought persisted for no more than 3 years ending with the end of the dry period, and at least the effects of severe drought lasted only a year. The study suggests that in peat catchments summer's are hydrologically independent of the winters and this fact limits the consequences of severe drought.

Chemistry of rainwaters in the south Pacific area of Russia

On the south-eastern edge of Russia, the chemical composition of rainwater is controlled by sea salts, terrestrial material, as well as volcanic (Kuril islands volcanic area) and anthropogenic emissions, mostly in the southern part of the area. The predominant major ions of the Primorye, Sakhalin and the Kuril Islands rainwaters were respectively HCO 3 −–SO 4 2−, Ca–Na, and of Cl–Na. Concentration of trace elements changes within 1–2 orders of magnitude but some difference in the distribution of the elements between continental and island rainwater is found. The concentration of the chemical elements in the particulate fraction varies from < 10% to 90% of the total concentration (dissolved + particulate) with the following distribution: Tl, Na, Ca, Sr, Zn, Cd (< 10%)–Be, Th, Bi, Rb, U, K, Sc (10–20%)–Cu, Mn, Mg, Mo, Se, Ba, Ni, As, Ag, Cs, Co, Y, Ga, V (20–50%)–Sb, Pb, Ge, Cr, Fe, Al (50–90%). The concentration of elements of the particulate fraction of the rainwater usually is significantly different from concentrations in the crust, including both higher and lower concentrations. The terrestrial contribution to dissolved elements was evaluated and follows the decreasing order: Fe > K, Mg, Ca > Ba, Sr > Na (65–1%). Close order was found for total (dissolved and solid) concentrations. Sea salt contribution to dissolved element concentration in the rainwater decrease in the following order: Cl, Mg > K, SO 4 > Ca > HCO 3 −, Ba, Fe (78–0.1%). Calculation of anthropogenic and volcanic inputs for two ions (Cl − and SO 4 2−) shows that anthropogenic inputs for the Vladivostok and Yuzno-Sakhalinsk cities can be evaluated as 15–20% of Cl − and up to 80–90% of SO 4 2−. Volcanic components in the Kuril Islands, where anthropogenic inputs are absent, can reach up to 76% of SO 4 2− and 36% of Cl −.

Variations of U and Sr isotope ratios in Alsace and Luxembourg rain waters: origin and hydrogeochemical implications

Abstract Major and trace element concentrations, as well as Sr and U isotope ratios, were measured in rainwater samples collected in three different locations in Alsace (East of France) and Luxembourg: a mid-altitude mountain site (Aubure Environment HydroGeochemical Observatory), an urban site (Strasbourg) and a peri-urban site located in an area of well developed industrial activity (Esch-sur-Alzette in Luxembourg). Results highlight the quite high spatial and temporal variability of the chemical and isotopic characteristics of rainwater at the regional scale. They also suggest a quite systematic contribution of a local component in the chemical composition of rainwater. In urban and peri-urban sites, the local component is certainly linked to human activities, as it is well illustrated in this study with the Esch-sur-Alzette samples. On the other hand, for the Aubure site, i.e. a small forested watershed of mid-altitude mountain, data presented in this study demonstrate the influence of the vegetation on the chemical composition of rainwater for alkali and calc-alkali elements, as well as for the Sr isotope ratios. Such a result questions the reliability of the method classically used to estimate the rainwater contribution on the river chemical budget. In addition, data of the present study confirm the very low content of uranium in rainwater and demonstrate, especially through the U isotope analysis of Aubure rainwater, the negligible effect of rainwater on U budget of river waters. This work thus outlines the property of U to be a geochemical tracer specific of weathering fluxes carried by rivers. To cite this article: F. Chabaux et al., C. R. Geoscience 337 (2005).

Chemical composition of rainwater and dustfall at Bhubaneswar in the east coast of India

Chemical composition of rainwater and dustfall was studied in two different stations of Bhubaneswar, located in the east coast of India. A wet-only and a bulk collector were placed at Regional Research Laboratory (RRL), a suburban area, during 1995–1997 and in the State Botanical Garden (SBG), a rural forest area, during 1997–1998. Of the rain events, 93% recorded alkaline pH (>5.6) at RRL while at SBG, 57% of the rain events were alkaline and the rest were acidic. Non-sea salt (nss) Ca 2+ and NH 3 were the primary neutralizing agents of rainwater acidity at both the locations. Low concentrations of alkaline constituents in the dustfall are an important finding in this study under Indian conditions. The Cl − /Na + ratio in rainwater at RRL was same as the seawater ratio (1.167) which indicates that sea salt contribution is local to RRL. It may be of indirect marine origin and resuspended locally. Rainwater samples were enriched with nss SO 4 2− , nss Ca 2+ and nss Mg 2+ at both the sites. Most of the nss SO 4 2− and NO 3 − were of anthropogenic origin, while a part of those might be soil derived.

The source of calcium in wet atmospheric deposits: Ca-Sr isotope evidence

Tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient. Here we present the first calcium isotope ratio measurements for rain and snow. Samples from northeastern and southern locations (France, Switzerland, Luxembourg, California and Japan) suggest a carbonate origin. Only at a local scale in a forested watershed (Vosges mountains, France) the Ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution, which is a mixing product of Ca from dissolved atmospheric dust particles and leave excretions. If this proves to be widely true, the contribution of Ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds. In such cases Ca and Sr cycles are decoupled in the lower atmosphere. In contrast to Sr isotopes, Ca isotopes can be applied to tracing processes occurring in the biosphere.

Influence of small‐ and large‐scale variables on the chemical and isotopic compositions of urban rainwater, as illustrated by a case study in Ashdod, Israel

The source of air pollution must be identified to select the appropriate monitoring activities and remedial measures. The present case study illustrates how analyses of (1) regional‐scale synoptics and air mass trajectories, (2) local‐scale atmospheric measurements (wind direction and speed, air temperature, dust load, sulfur and nitrogen oxide concentrations in the air, rain amount, and intensity) and (3) chemical and isotopic compositions of rainwater from 46 rain events, collected in the coastal city of Ashdod, Israel, were used to identify the various sources contributing to rainwater salts and contaminants and their timing. Rainwater affected by the Mediterranean Sea was characterized by a large marine fraction of salts, high chloride concentrations, and low values of δ18O and δD. These rain events were associated with the Cyprus Low system, which typically prevails in midwinter. Rainwater affected by continental sources had a small contribution of marine salts, high bicarbonate and calcium concentrations, and high values of δ18O and δD. These rains were related to continental trajectories from the Red Sea and north African coast prevailing during the fall and spring. Rainwater affected by anthropogenic sources was characterized by low marine fraction, high sulfate concentrations, and low values of δ34S. Whereas remote anthropogenic source was associated with the Red Sea trough system and were characterized by high nitrate concentrations (representing desert dust), the local anthropogenic source was characterized by high air concentrations of sulfur oxides at the local monitoring stations and high potassium and low nitrate concentrations. The identification of local anthropogenic source suggests that measures taken to reduce emissions from local oil refineries and power stations are likely to reduce the overall air pollution in the study area.

Temporal variation in the surface‐water chemistry of a blanket bog on Dartmoor, southwest England: analysis of 5 years' data

SummaryBlanket‐bog peats, mapped as the Winter Hill and Crowdy associations by the Soil Survey of England and Wales, are an oceanic manifestation of the ombrotrophic ‘raised‐bog’ (Hochmoor) peats that cover large tracts in the boreal zone of the northern hemisphere. This paper examines monthly analyses from 1992 to 1997 of major ions and other variables from an upland blanket bog in southwest England in relation to seasonality, rainfall, and the chemical composition of rainwater. Average ionic composition of surface water (and peat) integrates variable atmospheric solute inputs over the years. The dominant ions in the surface water, Na+ and Cl–, showed only weak seasonality, but divalent cations a stronger seasonal pattern with a summer maximum. Mean pH ranged from c. 4.4 in February to c. 4.2 in August. Changes in concentration of different cations were closely interlinked by cation exchange. The anion deficit, accounted for by anionic groups on the dissolved organic matter, was strongly seasonal with a summer maximum, as was optical absorbance at 320 nm. Nitrate and NH4+ were both at much smaller concentrations than in rain. Nitrate exceeded 1 μmol l−1 only during cold periods in winter, mainly following drought in the summer of 1995; NH4+ reached a few μmol l−1 only in summer. There was evidence of net retention of S by the peat in wet sites and during wet periods, and of net release of SO42– (and acidity) under dry conditions. The 1995 summer drought and ensuing dry year in 1996 had marked and persistent effects on pH, apparent ion deficit (DEF), SO42–, the divalent cations and Fe.

Study of chemical composition of rainwater at an urban (Pune) and a rural (Sinhagad) location in India

Data are presented on the chemical composition of rainwater collected at a rural site (Sinhagad) near Pune, India, between August 2002 and August 2003 and at an urban site in Pune between April 2002 and August 2003. Both bulk water samples and wet‐only samples were alkaline at both sites, with an average pH of 6.6 (both bulk and wet‐only) at Pune and 6.4 (bulk) and 6.2 (wet‐only) at Sinhagad. Only one case of acidic rain was recorded: at Sinhagad with pH of 5.2 (bulk) and 4.9 (wet‐only). The major cations were Ca2+ and Na+, and the major anions were Cl− and SO42−. Higher concentrations of both SO42− and Cl− at Pune compared to Sinhagad were balanced by higher concentration of Ca2+ such that the pH remained approximately similar and, on average, well on the alkaline side. The difference in ionic composition between the two sites, available so far only for the monsoon period, is quite small (especially in case of wet only samples) and interpreted as an influence of local sources at the Pune site. At both sites the concentrations in the bulk samples were only slightly larger than those in the wet‐only samples. Our analysis demonstrates that the Sinhagad site provides useful data representative of the regional situation. The data are also analyzed in terms of seasonal (monsoon versus postmonsoon) variations and air mass trajectories. Surprisingly high concentrations of SO42− at the rural site (Sinhagad) during the SW monsoon period may indicate transport from the African continent.

Chemical characteristics of individual rain events from a semi-arid region in India: Three-year study

Abstract A systematic study of individual precipitation (wet-only) events ( n = 91 ), collected for three years (2000–2002) during the period of SW-monsoon (June–September) from a semi-arid region (Ahmedabad, 23°03′N, 72°38′E) in India, reveals that rainwater is characteristically alkaline in nature (pH range: 5.2–8.2, Av.=6.7). The ionic ratio of Cl− and Na+ in each event closely follows that of sea-salt composition. The measured abundances of Ca2+ (5.5–1057 μeq l−1), Mg2+ (1.5–251 μeq l−1) and HCO3− (8–836 μeq l−1); non-sea-salt (nss) components of Ca2+ and Mg2+ varying as 94–99% and 0–84%; and linear regression parameters among (nss-Ca2++nss-Mg2+) and HCO3− (slope=0.71, r 2 = 0.96 ) all tend to suggest that crustal sources dominate the chemical composition of precipitation. The concentrations of acidic constituents SO2−4 and NO3− vary over a wide range, from 4.8 to 431 and 1.0 to 115 μeq l−1, respectively; and that of NH4+ varied from 1.7 to 220 μeq l−1 and K+ as 0.6–53 μeq l−1. A significant impact of anthropogenic sources on rainwater composition is evident based on the nss-fraction of SO2−4 (67–99%, VWM=86%) and equivalent ratio of nss-SO42−/NO3− (0.8–6.7, VWM=2.5). With the exception of NH4+, concentration of an individual species in a rain event is largely controlled by the precipitation amount. The inter-annual variations in the volume-weighted-mean composition are not significantly pronounced; making this a representative data set for the study region.

Effect of typhoon on chemical composition of rainwater in Okinawa Island, Japan

Abstract We have studied the effects of typhoons on the behavior of chemical components of rainwater. Samples were collected at Yona in the northern part of Okinawa Island and analyzed for major cations and anions. The chemical components in rainwater could be classified into three types. Components belonging to type I originated from sea salt (ss-) in which their concentrations in rainwater increased with an increase in maximum wind speed (MWS). Those belonging to type II were non-sea salt (nss-) components in which their concentrations in rainwater decreased with an increase in MWS. Ca2+ and SO42− belonging to type III in which their concentrations in rainwater had no relationship with MWS. To clarify the behaviors of type III components, they were separated into the two fractions: ss- and nss- by assuming that all Na+ ions were supplied from ocean. Each fraction of Ca2+ and SO42− except nss-Ca2+ showed a significant correlation with MWS. Moreover, When MWS was slower than 10–13 ms−1, the concentration of nss-SO42− was dominant in rainwater. But, the concentration of ss-SO42− in rainwater became dominant when MWS was faster than 13 ms−1. The chemical compositions in rainwater also changed drastically with MWS. Values of Σacid–Σbase (D value) in rainwater ranged from 1.11 to 62.4 μeq l−1 and correlated strongly with pH (5.92 to 4.17). Values of pH during typhoon were higher in contrast to those during non-typhoon weather, which is attributed to the higher decreasing rate of Σacid than Σbase. This result suggests that a typhoon has the ability to remove or dilute pollutants such as NO3− and nss-SO42−.