Chemical Composition Of Rainwater Research Articles

Chemical characteristics of rainwater collected at a western site of Jordan

A comprehensive study on the chemical composition of rainwater was carried out from October 2006 to May 2007 in Ghore El-Safi area western side of Jordan nearby the Dead Sea. Rainwater samples were analyzed for major ions (Ca 2+, Mg 2+, K +, Na +, NH 4 +, HCO 3 −, Cl −, NO 3 − and SO 4 2−) and trace metals (Fe, Al, Zn, Pb, Cu, and Cd). The highest concentration of elements is observed at the beginning of the rainfall season when large amounts of dust accumulated in the atmosphere scavenged by rain. The majority of rainwater had a neutral or alkaline character as a result of neutralization caused by the alkaline local dusts which contain large amount of CaCO 3. The pH ranged from 4.8 to 8.2 with a mean value of 6.9 ± 0.65 which was in alkaline range considering 5.6 as the neutral pH of cloud water with atmospheric CO 2 equilibrium. In the total 35 rain events, only three events were observed in acidic range (< 5.6) which occurred after continuous rains. The equivalent concentration of components followed the order: Ca 2+ > HCO 3 − > Cl − > Mg 2+ > NO 3 − > SO 4 2− > NH 4 + > Na + > K +. Rainwater chemistry was analyzed using Factor Component Analysis to find the possible sources of the measured species. Three components that accounted for 84% of the total variance were extracted sea salts spray (Na+, Cl − and Mg 2+), and soil particles (natural origin), (Mg 2+, Ca 2+ and HCO 3 −) and biomass burning (NH 4 +). The results obtained in this study are compared with those other studies conducted at different sites in the world. In general, the results of this study suggested that rainwater chemistry is strongly influenced by local anthropogenic sources (potash factory and agricultural activities in Ghore El-Safi area) rather than natural and marine sources. The pollutants in rainwater samples were mainly derived from long distance transport, local industry and traffic sources.

Comparison of wet-only and bulk deposition at Chiang Mai (Thailand) based on rainwater chemical composition

The chemical composition of 122 rainwater samples collected daily from bulk and wet-only collectors in a sub-urban area of Chiang Mai (Thailand) during August 2005–July 2006 has been analyzed and compared to assess usability of a cheaper and less complex bulk collector over a sophisticated wet-only collector. Statistical analysis was performed on log-transformed daily rain amount and depositions of major ions for each collector type. The analysis of variance (ANOVA) test revealed that the amount of rainfall collected from a rain gauge, bulk collector and wet-only collector showed no significant difference ( ∝=0.05). The volume weight mean electro-conductivity (EC) values of bulk and wet-only samples were 0.69 and 0.65 mS/m, respectively. The average pH of the samples from both types of collectors was 5.5. Scatter plots between log-transformed depositions of specific ions obtained from bulk and wet-only samples showed high correlation ( r>0.91). Means of log-transformed bulk deposition were 14% (Na + and K +), 13% (Mg 2+), 7% (Ca 2+), 4% (NO 3 −), 3% (SO 4 2− and Cl −) and 2% (NH 4 +) higher than that of wet-only deposition. However, multivariate analysis of variance (MANOVA) revealed that ion depositions obtained from bulk and wet-only collectors were not significantly different ( ∝=0.05). Therefore, it was concluded that a bulk collector can be used instead of a wet-only collector in a sub-urban area.

A four-year investigation on wet deposition in western Thailand

The investigation of pH variation and the chemical composition of rainwater have been studied from April 2003 to October 2006 at a rural area of Nakorn Pathom Province, western Thailand. The pH value ranged from 4.0 to 7.8 with an average of 6.1. Out of 319 rain events, 72 events were observed in acidic range (pH < 5.6). The pH of rainwater gradually increased over the sampling period. The volume-weighted mean concentrations (microeq/L) of ion species followed the order: Ca2+ > NH4+ > SO4(2-) > HCO3- > NO3- > Na+ > Cl- > CH3COO- > Mg2+ > K+ > H+ > HCOO- > PO4(3-). Neutralization factor calculations reveal that Ca2+ plays a major role in neutralization processes in this area. Enrichment factor calculations indicate that SO4(2-), K+, Ca2+ and Mg2+ were originated from non-marine sources. The statistical measure principle component analysis indicates influence of various local emission sources e.g., soil, limestone mines, biomass burning and agricultural emissions, on the chemical composition of rainwater.

Role of aerosols in deciding pH of rainwater

Nature of precipitation – alkaline or acidic – depends upon the concentration of major water soluble inorganic gaseous and soil derived particulates dissolved in it. If concentration of cations is higher than that of anions, the precipitation becomes alkaline and vise-a-versa.&#x0D; pH is the main parameter indicating the nature of precipitation. If pH of the solution is &lt; 5.65, it is acidic and &gt; 5.65, alkaline, in the pH scale ranging between 0 &amp; 14.&#x0D; Difference in the chemical composition of rainwater having pH in the alkaline range and acidic range has been studied in this paper. For this purpose, precipitation chemistry data of Allahabad, Jodhpur, Mohanbari and Nagpur for the period 1988-97 have been considered. APWM &amp; S.D. have been worked out. Precipitation chemistry data considering APWM values in acidic range and in alkaline range have been separated and compared. Coefficients of correlation have been calculated in possible cation-anion combinations.&#x0D; It is seen that the lowest pH values (monthly mean) have been recorded during 1997 – MHB (3.77), NGP (4.12), both in acidic range. % Frequency of occurrences of pH values in acidic range was the highest at Mohanbari (66%) in the study period. Jodhpur recorded all pH values in alkaline range indicating influence of soil derived alkaline particulates. Among cations Ca+² has shown its dominance over all cations. Jodhpur has recorded the highest APWM value of Ca+² (9.27mg/lit) in 1997.&#x0D; Data have also been compared with WMO Laboratory simulated acid rain sample analysis data and other non-departmental data.&#x0D; Results are discussed in the paper.

Chemical composition of rainwater in the northeastern Romania, Iasi region (2003–2006)

Chemical composition of rainwater was studied in the northeastern Romania, Iasi region, and the concentrations of major inorganic and organic ions were measured in samples collected between April 2003 and December 2006. The pH of the rainwater is 5.92 (volume weighted mean average, VWM) suggesting a sufficient load of alkaline components neutralizing its acidity. On average, 97% of the acidity in the collected samples is neutralized by CaCO 3 and NH 3. Clear seasonal variations were observed for some of the identified ions (e.g., SO 4 2−, NO 3 −, Ca 2+, NH 4 +). The data obtained during this work revealed that both concentrations and fluxes of anthropogenic source-related ions (e.g., SO 4 2−, NO 3 − and NH 4 +) are among the highest reported for European sites. It is shown that meteorology and long-range transport processes may concur to their high levels.

Spatial and temporal patterns of throughfall quantity and quality in a tropical montane forest in Ecuador

Summary In forests, complex canopy processes control the change in volume and chemical composition of rain water. We hypothesize that (i) spatial patterns, (ii) the temporal stability of spatial patterns, and (iii) the temporal course of solute concentrations can be used to explore these processes. The study area at 1950 m above sea level in the south Ecuadorian Andes is far away from anthropogenic emission sources and marine influences. It received ca. 2200 mm of rain annually. We collected rain and throughfall on an event and within-event basis for five precipitation periods between August and October 2005 at up to 25 sites and analyzed the samples for pH and concentrations of K, Na, Ca, Mg, NH 4 + , Cl−, NO 3 - , PO 4 3 - , and total N (TN), P (TP), and organic C (TOC). Cumulative throughfall amounted to 79% of rainfall. Compared with other tropical forests, rainfall solute concentrations were low and throughfall solute concentrations similar. Volumes and solute concentrations of rainfall were spatially and temporally little variable. The spatial coefficient of variation for throughfall volumes was 53%, for solute concentrations 28–292%, and for deposition 33–252%. Temporal persistence of spatial patterns was high for throughfall volumes and varied among solutes. Spatial patterns of K, Mg and TOC concentrations in throughfall were highly persistent. The spatial patterns of throughfall fluxes were less stable than those of concentrations. During a monitoring time of 72 h, solute concentrations in throughfall of selected rain events remained at a similar level indicating that the leachable element pool in the canopy was not exhausted. Our results demonstrate that the passage of rain through the canopy of a tropical montane forest in Ecuador results in a spatially heterogeneous throughfall pattern with a considerable stability during three months. There is a large leachable element pool in the canopy, which is not depleted by the typical light rain within 72 h.

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.

Rainwater chemical composition at two sites in Central Mexico

Chemical analyses were performed on rainwater samples collected at the National Autonomous University of Mexico (UNAM) in Mexico City and at a wooded site, Rancho Viejo (RV) in the State of Mexico, for the periods 1994–2000 and 1994–1999, respectively. At UNAM, rainwater was collected for the entire rainy season period each year, while at RV, technical considerations limited collection to weekends only. The results showed large variations in rainwater chemical composition in most years, mainly because of the variability of meteorological conditions and also because of changes in source emissions. Sulfates and NH 4 + showed higher annual volume-weighted mean concentrations (VWMC) in both sites. At UNAM, the maximum annual VWMC for SO 4 2− occurred in March and the minimum in July and August. Lower concentrations of almost all ions were found at RV; however, the H + concentration was higher at this site. The pH in Mexico City, calculated from the annual VWMC of H +, was 4.95, which is a little higher than pH values reported in some other countries. Despite the fact that sulfate and NO 3 − concentrations were lower at RV, the pH was lower. Air-mass back trajectories were calculated for individual concentrations of SO 4 2−, H +, NH 4 +, Ca 2+, and Mg 2+, observed at each sampling site for weekend data. At RV, sulfate concentrations were higher when air-mass back trajectories indicated a wind flow from Mexico City and Toluca at 1000 MAGL (meters above ground level) and 3000 MAGL. The hydrogen ion exhibited the same behavior. Calcium and Mg 2+ concentrations were also higher when the wind blew from urban areas at 1000 and 3000 MAGL. At UNAM, H + concentration was lower and Ca 2+ and Mg 2+ were higher when wind blew from the northern sector of the city at 1000 and 3000 MAGL. In UNAM, the NO 3 −/SO 4 2− and NH 4 +/SO 4 2− ratios were 0.5 and 1.09 in 1994 and 0.86 and 1.64 in 2000, respectively, indicating a decrease in SO 2 emissions resulting from the change of fuel oil to gas fuel. The SO 4 2−/Ca 2+ ratio was significantly lower at the UNAM site (1.82) compared to RV (5.36), and the SO 4 2−/H + ratio was significantly higher at the UNAM site (6.77) compared to RV (2.01). The Spearman's rho correlation between ionic concentrations indicated a positive correlation in most cases ( p < 0.05) for data from UNAM and RV. The multiple regression correlation analysis to predict H + concentration in Mexico City showed that NO 3 −, NH 4 +, SO 4 2−, and Ca 2+ contributed 23.2%, 20.9%, 8.0%, and 6.1%, respectively, to the H + prediction, while Cl − plus Na + plus K + only contributed 2.2%, and Mg 2+ did not contribute. Sea-salt contribution to rainwater chemical composition was negligible with any wind direction at both levels. Excess sulfate (non-sea-salt sulfate) represented 98.7% of the total sulfate in rainwater collected during weekends at RV and 98.6% for weekend and annual rain samples at UNAM.

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.

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 −.

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.

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.

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−.

The chemical composition of rainwater over Büyükçekmece Lake, Istanbul

In the present study, the precipitation near Büyükçekmece Lake, which is one of the important drinking water sources of Istanbul city, was studied during October 2001–July 2002. Seventy-nine bulk precipitation samples were collected at two sampling stations near the Lake (41°2′35″N, 28°35′25″E and 41°5′30″N, 28°37′7″E). The study comprised the determination of H +, Cl −, NO 3 −, SO 4 2−, NH 4 +, Na, K, Mg, Ca, Al, Ba, Fe, Cu and Mn concentrations in bulk deposition rain event samples. The average volume-weighted pH value was found to be 4.81, which points out that the rain is slightly acidic. High sulfate concentrations were observed together with high H + ion values. Sulfur emissions were the major cause for the observed high hydrogen ion levels. On the basis of factor analysis and correlation matrix analysis, it has been found that in this region, acid neutralization is brought about by calcium rather than the ammonium ion. The varimax rotated factor analysis grouped the variables into four factors, which are crustal, marine and two anthropogenic sources.

Chemical composition of rainwater around an industrial region in Mumbai : Naik, M. et al. Current Science, 2002, 82, (9), 1131–1137

Chemical analysis of rainwater samples collected at Kalyan, a downwind location of a large industrial belt, and at Alibag and Colaba, the upwind locations, during the southwest monsoon seasons of 1994 and 1995 and comparison with similar data of 1973-74 reveal that pH of rainwater at Kalyan which was alkaline 20 years ago became acidic due to long-term effect of pollutants. A decreasing trend in excess SO4 was observed at Colaba and Kalyan, which is attributed to the pollution control measures adopted by industries and switching over from coal to natural gas which contains low sulphur. Whereas the increasing trend in NOx observed at Kalyan and Colaba, is attributable to increased automobile emission.

A universal bias in inorganic rainwater chemical composition data

In the late 1970s, it was recognised that organic acids contributed to the acidity and ionic content of rainwater, but that these acids had not been detected because they were consumed biologically in the period between rainwater collection and subsequent laboratory analysis. Discussion of consequences for measured rainwater composition has been limited to assessment of pH gain that attends organic acid loss. We show that biological effects on rainwater ionic composition are not restricted to pH alone. Ammonium, potassium, nitrate, sulfate, methanesulfonate, and phosphate ions are also removed biologically, but remain in the rainwater in biomass, implying that most previous rainwater composition studies based on ionic analyses will have systematically underestimated nutrient deposition.

Chemical composition of rainwater at EMEP station in Ankara, Turkey

The chemical characteristics of rainfall and its seasonal variation at the EMEP (The Cooperative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air Pollutants in Europe) station located in Cubuk, Ankara were studied for the period between September 1994 and December 1996. The station is located in a rural area about 50 km north of Ankara and is considered as a background station for air pollution. The rainwater samples collected were analyzed for pH, major ions concentrations and conductivity. Seasonal variations for some major ions are pronounced. Generally, maximum concentrations appeared in winter or autumn, and minimum concentrations in spring or summer seasons. The average pH of rainwater samples is around 6.3 due to neutralization. Only about 4% of the rain samples had a pH below 5.0 and about 15% of the total rainwater samples had a pH below 5.6. This reflects strong inputs of alkaline species to rainwater samples in this location. The average pH of the samples higher than 5.6 observed in rural area of Ankara is due to a high loading of calcium ions in the form of CaCO 3 because of the alkaline nature of the soil. There is a strong relationship between pHs and other ions in summer. However, in winter, a weak relationship is found between SO 4 2−, NO 3 −, Na + and Mg 2+. On the other hand, relationships between the conductivity and SO 4 2− concentration are stronger in summer than in winter. The low concentrations of H + found in rainwater samples from Cubuk suggests that an important portion of H 2SO 4 and HNO 3 have been neutralized by alkaline particles in the atmosphere. Weak correlations are found between the hydrogen ions and SO 4 2− or NO 3 − ions for all seasons because of neutralization of these ions with alkaline particles. The dust-rich local and surrounding limestone environment might have caused the high concentration of Ca 2+ in Cubuk area. The relatively high concentration of NH 4 + observed at Cubuk is suspected to be due to surrounding agricultural activity. This agricultural activity has been found to be effective not only in spring, but also in autumn and winter to cause neutralization of the rainwater.

Rainwater chemical composition at the end of the mid-summer drought in the Caribbean shore of the Yucatan Peninsula

Rainwater was sampled at Puerto Morelos in the Caribbean coast of the Yucatan Peninsula during two sampling periods: from 27 August to 6 September 2000 (at the end of the summer drought), and from 7 to 27 September 2000 (just after the summer drought). Rainwater chemical composition (except nitrate concentration) was similar to that observed in other regions in the Caribbean Sea. Sodium and magnesium presented the highest average concentrations, sea-salt aerosols being almost the unique source, of 91% and 95%, respectively. Excess potassium, calcium and sulfate originated from non-sea-salt sources. Excess sulfate concentration was 0.65 mg l −1, which agrees with the background concentration of 0.48 mg l −1, as it was expected. However, rainwater nitrate concentration was much higher than that observed in the rest of the Caribbean Sea region. Nitrate concentration was as high as nearly 20 times the background value of 0.155 mg l −1. According to wind data analysis, only nitrate concentration depended on wind direction. Nitrate concentration peaked when wind blew from the Yucatan Peninsula, and it was higher when forest fires were spotted, therefore forest fires must have been the main nitrate source during the dry period. Forest fires emit nitrogen oxides that are rapidly converted to HNO 3. This was strongly supported by the fact that the lowest pH value (3.48) was measured in the rainwater sample with the highest nitrate concentration (4.51 mg l −1), and that 80% of the rain samples presented pH values below 5.6. Also, there was a significant difference in nitrate concentrations between the dry and humid periods, whereas the rest of the ionic species did not present significant differences. However, nitrate concentration was still higher than in other Caribbean regions during the humid period, suggesting that other sources are important too. These sources could not be identified.