Chemical Composition Of Rainwater Research Articles

Confirming anthropogenic influences on the major organic and inorganic constituents of rainwater in an urban area

Abstract. Recently, rainwater composition affected by atmospheric pollutants has been the topic of intense study in East Asia because of its adverse environmental and human health effects. In the present study, the chemical composition and organic compounds of rainwater were investigated from June to December 2012 at Gwangju in Korea. The aim of this study is to determine the seasonal variation of rainwater chemical composition and to identify possible sources of inorganic and organic compounds. The volume-weighted mean of pH ranged from 3.83 to 8.90 with an average of 5.78. Of rainwater samples, 50 % had pH values below 5.6. The volume-weighted mean concentration (VWMC) of major ions followed the order Cl− > SO42− > NH4+ > Na+ > NO3− > Ca2+ > Mg2+ > K+. The VWMC of trace metals decreased in the order Zn > Al > Fe > Mn > Pb > Cu > Ni > Cd > Cr. The VWMCs of major ions and trace metals were higher in winter than in summer. The high enrichment factors indicate that Zn, Pb, Cu, and Cd originated predominantly from anthropogenic sources. Factor analysis (principal component analysis) indicates the influence of anthropogenic pollutants, sea salt, and crustal materials on the chemical compositions of rainwater. Benzoic acids, 1H-isoindole-1,3(2H)-dione, phthalic anhydride, benzene, acetic acids, 1,2-benzenedicarboxylic acids, benzonitrile, acetaldehyde, and acetamide were the most prominent pyrolysis fragments for rainwater organic compounds identified by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The results indicate that anthropogenic sources are the most important factors affecting the organic composition of rainwater in an urban area.

Multilayer modelling of ozone fluxes on winter wheat reveals large deposition on wet senescing leaves

Understanding how ozone is deposited on vegetation canopies is needed to perform tropospheric greenhouse gas budgets and evaluate the associated damage on vegetation. In this study, we propose a new multilayer scheme of ozone deposition on vegetation canopies that predicts stomatal, cuticular and soil deposition pathways separately. This mechanistic ozone deposition scheme is based on the multi-layer, multi-leaf mass and energy transfer model MuSICA. This model was chosen because it explicitly simulates the processes of rain interception, through fall and evaporation at different depths within the vegetation canopy, so that ozone deposition on wet leaf cuticles can be explicitly modelled with ozone dissolution, diffusion and chemical reaction inside the water films. The model was evaluated against a 3-year dataset of ozone, CO2 and evapotranspiration flux measurements over a winter wheat field near Paris, France (ICOS Fr-GRI). Only periods with fully developed canopies (including senescence) were considered to minimise the contribution of soil deposition to the total ozone flux. Before senescence, the model could reproduce the measured ozone deposition rates as well as the CO2 and water vapour fluxes. During senescence, large ozone deposition rates were observed under wet canopy conditions that could only be explained by first-order reaction rates in the water film of around 105s−1. Such reaction rates are not compatible with the chemical composition of rainwater. We therefore hypothesise that, during senescence, the cell content leaks out of the leaves when they become wet, exposing anti-oxidants to ozone. These results provide for the first time a mechanistic explanation of the commonly observed increase in ozone deposition rates during rain or dew formation.

Chemical composition of rainwater and the acid neutralizing effect at Beijing and Chizhou city, China

The chemical compositions were measured in rainwater samples collected during 2011–2012 from two representative cities, Beijing in north China and Chizhou city in south China. The rainwater was highly acidic with a volume-weighted mean (VWM) pH of 4.56, ranging from 3.77 to 5.67, and about 94% of the samples had pH below 5.0 in Chizhou. The pH values of rainwater in Beijing ranged from 3.78 to 6.62, with a VWM value of 4.85. The predominant ions in the precipitation were SO42−, Ca2+ and NH4+ at both sites. The VWM concentrations of ions in rainwater were higher in Beijing, and the SO42− concentration of rainwater in Beijing was about twice that in Chizhou. However, due to the weaker neutralization of acidity, the rainwater from Chizhou had relatively low pH values. According to the results of linear regression analysis, the percentage of the potential acidity counteracted by Ca2+ and NH4+ was higher in rainwater in Beijing (90.7%) than that in Chizhou (70.8%). Using Na as an indicator of marine origin, and Al for the terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. More than 98% of SO42− and Ca2+ in rainwater samples are non-sea-salt origin at both sites. Coal combustion may be the main source of SO42−, and local and remote soil dust may be an important source of Ca2+ in Beijing rainwater. The high concentrations of alkaline ions (Ca2+ and NH4+) have played an important role to neutralize the acidity of rainwater in Beijing.

The hydrochemistry properties of precipitation in karst tourism city (Guilin), Southwest China

A comprehensive study on the chemical compositions of rainwater was carried out from January 2008 to November 2011 in Guilin, China. The 396 samples were analyzed for pH and electrical conductivity, and 44 among of 396 samples were analyzed for major ions. The result shows that pH value ranges from 3.44 to 7.16, and the occurrences of acid rain may increase with natural factors and human activities. The order of the main ion concentration in precipitation is SO4 2− > Ca2+ > NH4 + > NO3 − > Cl− > Na+ > F− > Mg2+ > K+ (weighted average). The correlation of the main cations, neutralization factors (NF), enrichment factor, and ionic ratio shows that acid rain can be mitigated slightly by the neutralization effect of a large amount of alkali ions. The SO4 2−, NO3 −, NH4 +, and a fraction of Ca2+ may originate from emissions of human activities, and the K+, Mg2+, and a majority of Ca2+ may originate from weathering of soil and rock. Mg2+ may transport long distance from large cities in the surrounding area. Among them, hyper-accumulation of NO3 − is produced by lots of vehicle and festival emissions. The hydrochloride may increase rainfall acidity, which refers to the temporary acidity. In addition to the input of pH value and acid ions, the input of alkali ions should be considered in the future evaluation of acid deposition in cites.

Assessing the Impact of Locally Produced Aerosol on the Rainwater Composition at the Gosan Background Site in East Asia

It is often assumed that atmospheric observations at remote sites represent long-range transport of airborne material, and local influences are overlooked. We evaluated the impact of local input on the rainwater composition at Gosan Station, a strategic site for monitoring the continental outflow from Asia. We analyzed a 14-year record of rainwater chemical composition archived by the Korea Meteorological Administration and detected local terrestrial contribution for nitrate, sulfate and ammonium. We also measured the chemical composition of rainwater sampled simultaneously at multiple locations within the premises of the Gosan Station, from which local influence with meter-scale spatial heterogeneity could be discerned. We estimate that the local input accounted for at least ~10% of the wet deposition of nitrogen and ~12% of the wet deposition of sulfur during the 14 years. This highlights the significance of the local influence, which should be carefully assessed when interpreting atmospheric observations at this site.

Chemical composition of rainwater at Lijiang on the Southeast Tibetan Plateau: influences from various air mass sources

Daily rainwater samples collected at Lijiang in 2009 were analyzed for pH, electrical conductivity, major ion (SO4 2−, Cl−, NO3 −, Na+, Ca2+, Mg2+, and NH4 +) concentrations, and δ18O. The rainwater was alkaline with the volume-weighted mean pH of 6.34 (range: 5.71 to 7.11). Ion concentrations and δ18O during the pre-monsoon period were higher than in the monsoon. Air mass trajectories indicated that water vapor from South Asia was polluted with biomass burning emissions during the pre-monsoon. Precipitation during the monsoon was mainly transported by flow from the Bay of Bengal, and it showed high sea salt ion concentrations. Some precipitation brought by southwest monsoon originated from Burma; it was characterized by low δ18O and low sea salt, indicating that the water vapor from the region was mainly recycled monsoon precipitation. Water vapor from South China contained large quantities of SO4 2−, NO3 −, and NH4 +. Throughout the study, Ca2+ was the main neutralizing agent. Positive matrix factorization analysis indicated that crustal dust sources contributed the following percentages of the ions Ca2+ 85 %, Mg2+ 75 %, K+ 61 %, NO3 − 32 % and SO4 2− 21 %. Anthropogenic sources accounted for 79 %, 68 %, and 76 % of the SO4 2−, NO3 − and NH4 +, respectively; and approximately 93 %, 99 %, and 37 % of the Cl−, Na+, and K+ were from a sea salt source.

Ionic Composition of Rainwater at Selected Sites of Kuantan, Pahang, Malaysia: A Preliminary Study

A short-term investigation on the chemical composition of rainwater was carried out at five selected sampling stations in Kuantan district, Pahang, Malaysia. Sampling of rainwater was conducted by event basis between September and November 2011. Rainwater samples were collected using polyethylene containers and the parameters measured were cations (sodium, potassium, ammonium, calcium and magnesium) and anions (chlorides, nitrates and sulphates). The average pH value for rainwater samples was 6.0 ± 0.57 in which most of the sampling sites exhibited pH values >5.6. Calcium and sulphate were the most abundant cation and anion, respectively, whilst the concentrations of other major ions varied according to sampling location.

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.

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 < 2.5 μm) and coarse mode (2.5 μm < d < 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.

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.

Chemical composition of rainwater at a coastal town on the southwest of Europe: What changes in 20 years?

Rainwater was collected at the Portuguese west coast between September 2008 and September 2009, and analysed for pH, conductivity, and Cl−, NO3−, SO42−, and NH4+ concentrations. Results of rainwater chemical composition were compared with those obtained at the same site between 1986 and 1989. In both collection periods rainwater was predominantly (≈ 80%) associated to oceanic air masses. The rainwater concentration of H+ was in the same range as twenty years ago. A clear decrease of non sea salt sulphate (NSS-SO42−) was observed in 2008–2009 relatively to 1986–1989, not only in samples with origin in central and northern Europe, but also in samples from Atlantic Ocean and Mediterranean. This decrease indicates that SO2 emissions were reduced, which may be due to a lower content of sulphur in oil by-products. A decrease was also observed in NH4+ concentration in 2008–2009. On the contrary an increase of NO3− concentration was observed for samples of all origins in 2008–2009 relatively to 1986–1989, which was particularly high (more than 3 fold) for samples with origin in Atlantic Ocean, suggesting the incorporation of this ion by rainout at the sampling site. The contribution of local sources is indeed suggested by the moderate negative correlation of NH4+, NO3− and NSS-SO42− with rainwater volume. The high increase of NO3− concentration can be attributed to the increase of local vehicular and industrial emissions in the sampling area.

Acid rain and alkalization in southwestern China: chemical and strontium isotope evidence in rainwater from Guiyang

A comprehensive study on the chemical compositions of rainwater was carried out from June 2007 to December 2008 in Guiyang, a city located on the acid rain control zone of southwest China. All samples were analyzed for pH, major anions (F−, Cl−, NO3−, SO42−), major cations (K+, Na+, Ca2+, Mg2+, NH4+), Sr2+ and Sr isotope. The pH increase is due to the result of neutralization caused by the alkaline dust which contain large amount of CaCO3. It was observed that Ca2+ was the most abundant cation with a volume-weighted mean (VWM) value of 217.6 μeq/L (52.7–1928 μeq/L), accounting for 66% (39%–88%) of the total cations. SO42− was the most abundant anion with VWM value of 237.8 μeq/L (49.6-1643 μeq/L). SO42− and NO3− were dominant among the anions, accounting for 66%–97% of the total measured anions. The Sr concentrations vary from 0.01 to 0.92 μmol/L, and strontium isotopic ratios vary in the range of 0.707684–0.710094, with an average of 0.708092. The elements ratios and the 87Sr/86Sr ratios showed that the solutes of rainwater mainly come from weathering of carbonate and secondary dust input. Moreover, urbanization results in the calcium-rich dust increased and the high concentrations of alkaline ions (mainly Ca2+) have played an important role to neutralize the acidity of rainwater, leading to the increase of arithmetic pH mean value by 0.5 units since 2002. It is worth noting that the emission of SO2 and NOx from the automobile exhaust is increasing and is becoming another important precursor of acid rain now.

Chemical composition of rainwater at Maldives Climate Observatory at Hanimaadhoo (MCOH)

Abstract. Water-soluble inorganic components in rain deposited at the Maldives Climate Observatory Hanimaadhoo (MCOH) were examined to determine seasonality and possible source regions. The study, which is part of the Atmospheric Brown Cloud (ABC) project, covers the period June 2005 to December 2007. Air mass trajectories were used to separate the data into situations with transport of air from India and adjacent parts of the Asian continent during the months December and January (Indian group) and those with southerly flow from the Indian Ocean during the summer monsoon season June to September (Marine group). A third trajectory group was identified with transport from the northern parts of the Arabian Sea and adjacent land areas during the months March, April and October (Arabian Sea group). The concentrations of nss-SO42−, NH4+ and NO3− were more than a factor of 4 higher in the Indian group than in the Marine group. The average rainwater pH was significantly lower in the Indian group (4.7) than in the Marine group (6.0). This shows a pronounced influence of continental pollutants during December and January. The origin of the very high concentration of nss-Ca2+ found in the Marine group – a factor of 7 higher than in the Indian group – is unclear. We discuss various possibilities including long-range transport from the African or Australian continents, local dust from nearby islands and calcareous plankton debris and exopolymer gels emitted from the ocean surface. The occurrence of NO3− and NH4+ in the Marine group suggests emissions from the ocean surface. Part of the NO3− could also be associated with lightning over the ocean. Despite the fact that the concentrations of nss-SO42−, NO3−, and NH4+ were highest in the Indian group the wet deposition was at least as big in the Marine group reflecting the larger amount of rainfall during the monsoon season. The annual wet deposition of NO3−, NH4+ and nss-SO42− at MCOH is about a factor of three lower than observed at rural sites in India.

Potential for Tufa Precipitation from Crushed Concrete Containing Coarse Basaltic and Fine Coralline Sand Aggregates

Crushed recycled concrete aggregate (RCA) has been widely utilized as base and sub-base course and as backfill. Despite the advantages of RCA, one of the potential concerns in some states is that its use can lead to the precipitation of calcium carbonate, or tufa, which can impair drainage and clog filter fabrics, which in turn can lead to premature failure of roads and other infrastructure systems. Tufa precipitation of RCA has been studied in various states, but no studies have been conducted on RCA containing a coarse basaltic and a fine coralline sand aggregate. By passing carbon dioxide gas through RCA soaked in rainwater for over 3 months to simulate an accelerated exposure of RCA to the elements of nature, the potential for tufa precipitation was studied by examining the pH and chemical composition of rainwater over time, the make-up of the RCA aggregate before and after testing, and by visual observation of the aggregate itself. From these observations, there is no evidence indicating that RCA containing a coarse basaltic and fine coralline sand aggregate has a serious tufa precipitation potential.

Chemical composition of rainwater and anthropogenic influences in Chengdu, Southwest China

A comprehensive study on the chemical compositions of rainwater was carried out from Jan. to Dec. in 2008 in Chengdu, a city located on the acid rain control zone of southwest China. All samples were analyzed for pH and major ions (F –, Cl −, NO 3 −, SO 4 2−, K +, Na +, Ca 2+, Mg 2+, and NH 4 +). The pH increased due to the result of neutralization caused by the base ions. It was observed that Ca 2+ was the most abundant cation with a VWM value of 196.6 μeq/L (17.3–1568.7 μeq/L), accounting for 49.7% (9.4%–79.2%) of the total cations. SO 4 2− was the most abundant anion with VWM value of 212.8 μeq/L (41.8–1227.6 μeq/L). SO 4 2− and NO 3 − were dominant among the anions, accounting for 90.4%–99.1% of the total measured anions. The concentrations of NO 3 − were higher than the most polluted cities abroad, which indicated Chengdu has been a severe polluted city over the world. The high fuel consumption from urbanization and the rapid increase of vehicles resulted in the high emission of SO 2 and NO x, which were the precursor of the high concentration of acidic ions NO 3 − and SO 4 2−. It was the main reason of the severe acid rain in Chengdu. The high concentrations of alkaline ions (mainly Ca 2+, NH 4 +) in Chengdu city atmosphere have played an important role to neutralize the acidity of rainwater and the pH value has increased by 0.7 units since 1989. It is worth noting that the emission of NO x from the automobile exhaust is increased and is becoming the important precursor of acid rain now.

Chemical composition of rain water and influence of airmass trajectories at a rural site in an ecological sensitive area of Western Ghats (India)

Samples of rain water were collected during monsoon season (June to September) of 2006 and 2007 at Hudegadde, a rural site located in an ecological sensitive area of Western Ghats. The collected samples were analyzed for pH, conductivity and major ions. At this site, rainwater pH varied from 4.20 to 7.39 with 5.65 as volume weighed mean. The observed mean was slightly lower than the average pH reported at most of the Indian continental sites. Monthly variation showed that average pH of rain water was the lowest during September (end of monsoon) and the highest during July (peak of monsoon). Overall, marine sources had dominating influence at this site. However, significant influence of anthropogenic and crustal sources from local as well as inter-continental regions was also noticed. As compared to NO 3 − , higher concentration of SO 4 2− was noticed which might be due to contribution from industrial activities responsible for SO2 emission. At this site, influence of five types of airmass trajectories was noticed i.e. i) C.I.O. (Central part of Indian Ocean)-when air masses blown from Maldives and nearby region of central Indian ocean. These airmasses had higher concentrations of nss Ca2+ which did not show any adverse impact on the pH; ii) N.W.I.O.(North-West Indian Ocean)-when airmasses travelled from oceanic region close to north-east Africa. These airmassses had higher concentrations of nss sulphate and nitrate and gave rise to acid rain; iii) S.W.I.O. (South -West Indian Ocean)- when airmasses came from southern part of Indian ocean (close to Mauritius). During these airmasses, rain water samples had almost equal ratio of nss SO 4 2− and nss Ca2+ similar to N.W.I.O but very low NO 3 − ; iv) Gulf-when airmasses were observed coming from Gulf region. Although these airmasses contributed only 2% of the total number of samples but carried high amount of nss SO 4 2− which gave rise to acid rain. The second lowest pH was observed during these airmasses which might be due to very high nssSO 4 2− /nssCa2+ ratios; v) N.W.I.O. + S.W.I.C. (North-West Indian Ocean+South-West Indian Continental)- when airmasses originated from north-west Indian Ocean travelling towards south continental part of India and then arriving to the site. During these airmasses, samples showed typical influence of urban activities having high concentrations of nss SO 4 2− and NO 3 − leading to the lowest pH of rain water.

Seasonal variation in long-range transported dust to a subtropical islet offshore northern Taiwan: Chemical composition and Sr isotopic evidence in rainwater

We investigated chemical and Sr isotopic composition of monthly rainwater collected on Peng-Chia-Yu (PCY) in northern Taiwan. Rainwater 87Sr/ 86Sr ratios, Na/Cl, Ca/Cl, Sr/Cl, Sr/Ca, NH 4/Cl, NO 3/Cl, SO 4/Cl and Na/Sr, showed clear seasonal cycles, reflecting mixture of loess carbonates (high Ca/Sr and more radiogenic 87Sr/ 86Sr) and seawater (low Ca/Sr and intermediate 87Sr/ 86Sr). Model results showed that the former source contributes up to 45% during the winter monsoon period, but seawater is the dominant Sr source in rainwater (>50%) at other times. Two anomalously low 87Sr/ 86Sr values occurred in July and August 1998, coinciding with the Merapi eruption in Indonesia. Air-mass backward trajectories and the geochemical and isotopic compositions in rainwater and Merapi lava (i.e. Ca/Sr = 100 and 87Sr/ 86Sr = 0.705400) suggested that the Merapi eruption delivered ash across the western equatorial Pacific to PCY. Aerosols leaching experiments were conducted to examine the impact of the 1998 eruption, demonstrating that only a minor terrestrial signature can be extracted by distilled water, implying rapid dispatch of volcanic gases or high-efficiency dissolution of ash related substance in acidic rains.