Chemical composition of wet and dry atmospheric depositions in an urban environment: local,regional and long-range influences

The results of a 8 year survey of wet and dry depositions collected in Bologna (Northern Italy) are presented and discussed: monthly fluxes of the main ions (hydrogen, sodium, potassium, calcium, magnesium, ammoniacal and nitrate nitrogen, sulphate and chloride) have been registered and statistically discussed. The trend of hydrogen ion, whose largest correlation in the global deposition was found with sulphate, is clearly downwards, with peaks mainly in winter months. By means of a data factor analysis, three main sources to explain the variability of the deposition chemistry were recognized: an anthropogenic contribution (particularly represented by NO₃ ⁻, SO₄ ²⁻, H⁺), the sea spray (Na⁺, Cl⁻ and, to a lesser extent, K⁺ and Mg²⁺) and a terrigenous fraction, particularly characterized by higher Ca²⁺ concentration; however, some concentration peaks of this ion have been found in association with some episodes of Saharan dust transportation.     

A study on the precipitation in Izmir,Turkey: chemical composition and source apportionment by receptor models

The chemistry of rainwater was studied in three sites of a metropolitan city of Turkey to determine the spatial variation, sources affecting composition and the extent of their influence. The acidity of rainwater, Ca, Co, Cr, Zn, Ba, V and Ni showed significant spatial variations. The most of measured species were moderately to extremely enriched compared to the local soil, which is likely arisen from the anthropogenic activities. SO₄ ^2?, K and Ca were found to be predominantly non-sea origin. Two receptor models, Positive Matrix Factorization (PMF) and Chemical Mass Balance (CMB), agreed well on the source contribution estimations of Al, K, Zn, V, Pb and Cr. The PMF and CMB resolved very similar source contribution profiles to the elemental concentrations of Ca, Zn, V, Pb, K and Na, which the majority of those resulted from mineral industries, bell casting+steel industries, fossil fuel burning, biomass burning+sea salt and sea salt, respectively. The PMF resolved the source contributions of long-transported emissions, particularly for Ba, Sr and Mn, which could not be estimated by the CMB.     

Chemical composition and source apportionment of rainwater at Guiyang, SW China

This study systematically analyzed the concentrations of cations and anions and determined the pH in the rainwater at Guiyang from Oct. 2008 to Sep. 2009. The pH in the rainwater varied between 3.35 and 9.99 with a volume-weighted mean value of 4.23. The volume-weighted mean concentrations of anions followed the order SO₄ ^2->Cl^->F^->NO₃ ^-, whereas the volume-weighted mean concentrations of cations followed the order Ca²⁺>NH₄ ⁺>Na⁺>Mg²⁺>K⁺. This finding indicates that SO₄ ^2- was the main anion and that Ca²⁺ and NH₄ ⁺ were the main cations. Significant correlations between each pair of ions (SO₄ ^2-, NO₃ ^-, NH₄ ⁺, Ca²⁺, and Mg²⁺) were observed, suggesting that CaSO₄, Ca(NO₃)₂, MgSO₄, Mg(NO₃)₂, NH₄NO₃, (NH₄)₂SO₄, and/or NH₄HSO₄ exist in the atmosphere at Guiyang. The soil-derived species (such as Ca²⁺) played an important role in the neutralization of the acidity in rainwater. The SO₄ ^2- and NO₃ ^- in the rainwater were mainly from anthropogenic sources, and their contributions accounted for 98.1 % and 94.7 %, respectively. NH₄ ⁺ was also most likely derived from anthropogenic sources, such as domestic and commercial sewage, and played an important role in the neutralization of the rainwater at Guiyang.     

Precipitation Chemistry and Wet Deposition in Kruger National Park, South Africa

The chemical composition, as well as the sources contributing to rainwater chemistry have been determined at Skukuza, in the Kruger National Park, South Africa. Major inorganic and organic ions were determined in 93 rainwater samples collected using an automated wet-only sampler from July 1999 to June 2002. The results indicate that the rain is acidic and the averaged precipitation pH was 4.72. This acidity results from a mixture of mineral acids (82%, of which 50% is H₂SO₄) and organic acids (18%). Most of the H₂SO₄ component can be attributed to the emissions of sulphur dioxide from the industrial region on the Highveld. The wet deposition of S and N is 5.9 kgS⋅ha⁻¹⋅yr⁻¹ and 2.8 kgN⋅ha⁻¹⋅yr⁻¹, respectively. The N deposition was mainly in the form of NH₄ ⁺. Terrigenous, sea salt component, nitrogenous and anthropogenic pollutants have been identified as potential sources of chemical components in rainwater. The results are compared to observations from other African regions.     

Rainwater chemistry and bulk atmospheric deposition in a tropical semiarid ecosystem: the Brazilian Caatinga

We assessed the rainwater chemistry, the potential sources of its main inorganic components and bulk atmospheric deposition in a rural tropical semiarid region in the Brazilian Caatinga. Rainfall samples were collected during two wet seasons, one during an extremely dry year (2012) and one during a year with normal rainfall (2013). According to measurements of the main inorganic ions in the rainwater (H⁺, Na⁺, NH₄ ⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, NO₃ ^?, and SO₄ ^2?), no differences were observed in the total ionic charge between the two investigated wet seasons. However, Ca²⁺, K⁺, NH₄ ⁺ and NO₃ ^? were significant higher in the wetter year (p < 0.05) which was attributed to anthropogenic activities, such as organic fertilizer applications. The total ionic contents of the rainwater suggested a dominant marine contribution, accounting for 76 % and 58 % of the rainwater in 2012 and 2013, respectively. The sum of the non-sea-salt fractions of Cl^?, SO₄ ^2?, Mg²⁺, Ca²⁺ and K⁺ were 19 % and 33 % in 2012 and 2013, and the nitrogenous compounds accounted for 2.8 % and 6.0 % of the total ionic contents in 2012 and 2013, respectively. The ionic ratios suggested that Mg²⁺ was probably the main neutralizing constituent of rainwater acidity, followed by Ca²⁺. We observed a low bulk atmospheric deposition of all major rainwater ions during both wet seasons. Regarding nitrogen deposition, we estimated slightly lower annual inputs than previous global estimates. Our findings contribute to the understanding of rainfall chemistry in northeastern Brazil by providing baseline information for a previously unstudied tropical semiarid ecosystem.     

Chemical compositions of wet precipitation and anthropogenic influences at a developing urban site in southeastern China

A comprehensive study on the chemical compositions of wet precipitation was carried out from January 2004 to December 2004 in Jinhua, southeastern China's Zhejiang Province. All samples were analyzed for pH, electrical conductivity and major ions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻, K⁺, Na⁺, Ca²⁺, Mg²⁺ and NH₄⁺). The rainwater was typically acidic with a volume-weighted mean pH of 4.54, which ranged from 3.64 to 6.76. SO₄²⁻ and NO₃⁻ were the main anions, while NH₄⁺ and Ca²⁺ were the main cations. The concentrations of these major ions were generally higher compared to those reported in other parts of the world, but much lower than those in northern China.Wet deposition fluxes of major ions showed pronounced seasonal variations with maximum in spring and minimum in autumn. Significant correlations were found in soil-derived species among Ca²⁺, Mg²⁺ and K⁺ and sea-salt species between Na⁺ and Cl⁻. Other relatively good correlations were also observed between Ca²⁺ and SO₄^2-, Mg²⁺ and SO₄^2-, Mg²⁺ and NO₃⁻, Mg²⁺ and Cl⁻. Principal component analysis was also performed on individual precipitation to find possible sources of the major ionic species. Varimax rotated four components accounting for 85.9% of the total variance, and were interpreted as acid and alkaline pollutants, sea spray and mixed source, soil and acid/neutralization. Calculation of enrichment factors for rainwater components relative to soil and seawater indicated that Ca²⁺ and K⁺ mainly originated from the terrestrial source, and SO₄^2- and NO₃⁻ were mostly attributed for the anthropogenic activities in the study area. In general, the results suggested that precipitation chemistry is strongly influenced by anthropogenic sources rather than natural and marine sources. The pollutants in rainwater were mainly derived from long distance transport, local industry and traffic sources.     

Influence of local sources on rainwater chemistry over Pune region,India

Rainwater samples were collected at five locations in the Pune region, an urban area in the south-west part of India, during 2006–2009. These locations; viz., Swargate (Traffic), Bhosari (Industrial), Pashan, Sangvi (Urban) and Sinhagad (Rural and High Altitude), represent different environments in this region. The study based on chemical analyses of these samples reveals that, on average, rainwater was alkaline at all the locations with pH values of 6.7, 6.16, 5.94, 6.04 and 5.92, respectively. Higher pH value of rainwater at the traffic location than those at the other locations is due mainly to the abundance of Ca²⁺ caused by vehicle-driven road-side dust. The maximum SO₄^2? and NO₃^? concentrations were found at Bhosari and Swargate respectively caused by local industrial and vehicular emissions. The average Fractional acidity over Pune area is 0.024, indicating about 98% acidity is neutralized by alkaline constituents. Factor analysis of the results indicated the influence of various sources, such as anthropogenic, soil dust, sea salt and biomass burning.     

Chemical and strontium isotope characterization of rainwater at an urban site in Loess Plateau, Northwest China

Major ion concentrations and strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr) were measured in rainwater samples collected at the urban site of Lanzhou, a city located on the Loess Plateau in the arid and semi-arid areas of northwest China. The rainwater samples possessed alkaline pH, at a reference level of 5.6, with a range of 6.82 to 8.28 and a volume-weighted mean (VWM) pH value of 7.70. The alkaline character of rainwater in Lanzhou is due to the result of neutralization caused by the alkaline soil dusts which contain large amount of CaCO₃. It was observed that Ca²⁺ was the most abundant cation with a VWM value of 886 µeq l^− 1 (115–2184 µeq l^− 1), accounting for 87.8% of the total cations. Without considering HCO₃⁻, SO₄²⁻ and NO₃⁻ were dominant among the anions, accounting for 64.2% and 23.0%, respectively, of the total measured anions. Using Na as an indicator of marine origin and Al for terrestrial inputs, the proportions of sea salt and non-sea-salt elements were estimated from elemental ratios. The precipitation in this region has typical continental characteristics. The Sr concentrations varied from 0.004 to 0.885 µmol l^− 1, and strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr) lay in the range of 0.71025–0.71302, with an average of 0.71143. The ⁸⁷Sr/⁸⁶Sr ratios of Lanzhou rainwater are higher than that of seawater, which reflects contributions from the radiogenic Sr sources of the aerosols. The most suitable candidate for the source would be the soil dust originating from local and distant loess and desert areas. The ⁸⁷Sr/⁸⁶Sr ratios were used to characterize different sources of base cations in rainwater, suggesting that the samples could be interpreted in terms of combinations of at least three components: soil dust derived from the Loess Plateau and desert areas in northwest China (with ⁸⁷Sr/⁸⁶Sr ~ 0.7130), seawater (with ⁸⁷Sr/⁸⁶Sr ~ 0.70917), and anthropogenic inputs (with ⁸⁷Sr/⁸⁶Sr ~ 0.7103). The high ⁸⁷Sr/⁸⁶Sr ratio and Ca and Sr content in the rainwater from Lanzhou can be attributed to the dissolution of calcium carbonate in soil dust.     

Trend in chemical composition of precipitation during 2005–2009 at a rural station of Bhubaneswar, eastern India

Precipitation samples collected during 2005–2009 from a rural forest station of Bhubaneswar were analyzed for their chemical composition. The samples were collected through a wet-only (WO) collector and two bulk (B1 and B2) collectors. The ions were evenly balanced indicating good data quality. The overall pH of rainwater was slightly acidic and ~47% of all rain events during the period were acidic (pH?<?5.6). Multilinear regression analysis showed relation between the free acidity (H⁺) and other components in rainwater. Enrichment factors (EF) of the major components with respect to their sources such as marine and crustal were calculated. Maximum EF was observed for NO ₃ ^? for both marine and crustal sources for all the three collectors. Source apportionments were also carried for the ions. Trend analysis showed continuous increase in most of the ions over years during the study period driven by anthropogenic emissions. Statistical/factorial analysis established correlation among different ions.     

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.     

Particulate morphology and elemental characteristics: variability at middle Indo-Gangetic Plain

Airborne particulates were monitored at an urban location of middle Indo-Gangetic Plain (IGP) and subsequently analyzed for particulate diversity and mixing states. Exceptionally high particulate loadings were found both in case of coarser (PM₁₀: 157.5 ± 102.9 μgm^?3, n = 46) and finer particulates (PM_2.5: 92.5 ± 49.8 μgm^?3). Based on particulate morphology and elemental composition, five different clusters of particulates namely tarball, soot, sulphur-rich, aluminosilicate and mineral species were found to dominate. Soot particles (0.1–5 μm) were found to be partly coated, having voids filled by coating material without being completely engulfed. A specific type of amorphous, carbonaceous spherules was evident in wintertime fine particulates signifying emissions from biomass burning and wild fire. Traces of S, Na and Ca were found associated with carbonaceous agglomerates suggesting its metal scavenging behavior. Particle laden filters were further processed for metallic and water soluble ionic species to constitute aerosol composition. Coarser particulates were characterized with higher metallic species (9.2–17.8 %), mostly of crustal origin (Ca: 5.5 %; Fe: 1.6 %; Zn: 1.3 % and Na: 3.8 %) while PM_2.5 also revealed their association with metallic components (6.0–14.9 %) having Ca (4.6 %), Fe (0.9 %) and K (0.8 %) as principle constituents. Ca, Na and NH₄ ⁺ found to generate chloride and sulphate salts thus affecting particulate hygroscopicity. Elevated fractions of NO₃ ^? and K⁺ in PM_2.5 signified contribution of biomass burning while presence of Cl^? with carbonaceous aerosols having traces of Si and K denoted contribution of farming and burning practices. Black carbon aerosol exhibited significant seasonal variability (6.9?21.9 μgm^?3) which support larger association of carbonaceous aerosols in particle micrograph.     

Determination of inorganic ions and trace elements in total suspended particles at three urban zones in the Mexico City Metropolitan Area and one rural site

Inorganic ions and trace metals in total suspended particles were measured during the period 2006–2007 at four sites; three urban sites in the Mexico City Metropolitan Area (MCMA) and one nearby rural site in the state of Morelos. SO₄²⁻, NO₃⁻, Cl⁻ and NH₄⁺ ions were analyzed by ion chromatography; Na⁺, K⁺, Ca²⁺ and Mg²⁺ by flame atomic absorption spectroscopy, and Al, Cd, Cr, Mn, Pb and V by an atomic absorption spectrometer with a graphite furnace attachment. The results indicated that SO₄²⁻ was the most abundant ion. All trace elements except Mn and V showed statistically significant differences between sampling sites. Pearson's correlation applied to all data showed a high correlation among SO₄²⁻, NO₃⁻ and NH₄⁺, indicating a common anthropogenic origin. In addition, the correlation observed between Ca²⁺ and Al indicated a crustal origin, as supported by the enrichment factors. Over the total sampling period, significant differences in particles and trace metals were found between sites and meteorological seasons. To gain a better insight into the origin of trace metals and major inorganic ions, a Principal Component Analysis was applied to the results for six trace metal and eight inorganic ions.     

Chemical characterization and multivariate analysis of atmospheric PM<Subscript>2.5</Subscript> particles

The new European Council Directive (PE-CONS 3696/07) frames the inhalable (PM₁₀) and fine particles (PM_2.5) on priority to chemically characterize these fractions in order to understand their possible relation with health effects. Considering this, PM_2.5 was collected during four different seasons to evaluate the relative abundance of bulk elements (Cl, S, Si, Al, Br, Cu, Fe, Ti, Ca, K, Pb, Zn, Ni, Mn, Cr and V) and water soluble ions (F⁻, Cl⁻, NO₂ ⁻, NO₃ ⁻, SO₄ ²⁻, Na⁺, NH₄ ⁺, Ca²⁺ and Mg²⁺) over Menen, a Belgian city near the French border. The air quality over Menen is influenced by industrialized regions on both sides of the border. The most abundant ionic species were NO₃ ⁻, SO₄ ²⁻ and NH₄ ⁺, and they showed distinct seasonal variation. The elevated levels of NO₃ ⁻ during spring and summer were found to be related to the larger availability of the NO_x precursor. The various elemental species analyzed were distinguished into crustal and anthropogenic source categories. The dominating elements were S and Cl in the PM_2.5 particles. The anthropogenic fraction (e.g. Zn, Pb, and Cu) shows a more scattered abundance. Furthermore, the ions and elemental data were also processed using principal component analysis and cluster analysis to identify their sources and chemistry. These approach identifies anthropogenic (traffic and industrial) emissions as a major source for fine particles. The variations in the natural/anthropogenic fractions of PM_2.5 were also found to be a function of meteorological conditions as well as of long-range transport of air masses from the industrialized regions of the continent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Studies on Intercorrelation between Ions Co-Occurring in Precipitation in the Gdańsk-Sopot-Gdynia Tricity (Poland)

The paper presents monitoring results and environmental pollution assessment for the Gdask-Sopot-Gdynia Tricity (Poland), based onanalysis of precipitation. Precipitation samples were collected over a period of 12 months (January–December 1998) at ten locations in the Tricity. The following selected ions were determined in the samples:SO₄ ^2–, F^–, Cl^–, NO₃ ^–,PO₄ ^3–, NH₄ ⁺, Na⁺,Mg²⁺, Ca²⁺, K⁺. The results were subjected to full statistical evaluation. Values of the parameters determined were correlated with each other. An attempt was made to explain co-occurrences of certain ions and the significance of their mutual effects. Pollutant concentrations and loads in precipitation were also correlated with data on wind direction and temperature in the region.Deposition of pollutants was very high in spring due to the prevailing air circulation patterns and low temperatures. Analysis of the correlations between co-occurring ions confirmed the significant impact of the location (sea coast) on the composition of rain water. Ionic ratios in rainwater were similar to those observed for sea salt samples. In addition, heavy traffic was most probably responsible for high concentrations of various forms of nitrogen and sulphates in the vicinity of major highways.     

Chemical components of lower tropospheric aerosols in the high arctic: Six years of observations

Six years of observations (1980 to 1986) of the composition of lower tropospheric aerosols at Alert on northern Ellesmere Island in the Canadian high Arctic yield insight into the seasonal variation of Arctic air pollutants as well as of substances of natural origin. A principal component analysis of 138 observations of 21 aerosol constituents (major ions, metals, nonmetallic trace elements) for the most polluted period of December to April identified not only a soil, sea salt and anthropogenic aerosol component, but also one associated with photochemical reactions in the atmosphere that occur at polar sunrise. Depending on the source of their gaseous precursors, elements in the photochemical component can be natural or anthropogenic in origin. For instance, SO₄ ^2-, existing mostly as H₂SO₄, originates probably from both anthropogenic and natural sources while Br^– is likely of marine origin. In contrast, SO₄ ^2- in the anthropogenic component has the stoichiometry of NH₄HSO₄. In the winter months, over 90% of Arctic SO₄ ^2- is in the anthropogenic and photochemical components.In winter, a substantial portion (11 to 35%) of Na⁺ is associated with the anthropogenic aerosol component suggesting either that marine aerosols have been physically or chemically modified by interactions with air pollution or that there are anthropogenic sources of Na⁺.The aerosol soil component is controlled by both local and distant dust sources. During a year, it has two peaks at Alert, one in April/May coinciding with the Asian dust storm season and one in September.There is a marked difference in the seasonal variation of particulate Br^– and iodine concentrations in the air. Both have a peak in April/May associated with polar sunrise and, hence, photochemical reactions in the atmosphere. However, iodine also peaks in early fall. This may be a product of biogenic iodine emissions to the atmosphere during secondary blooms in northern oceans in late summer.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988     

MEASUREMENT OF pH AND CHEMICAL ANALYSIS OF RAIN WATER IN RURAL AREA OF INDIA

Large number of rain water samples, at 7 rural locations in the semi-arid region of the DeccanPlateau were collected during 4 consecutive monsoon seasons (1979-1982).pH, conductivityand the major ionic components (C1~-, SO_4~= , NO_3~- , NH_4~+ , Na~+, K~+, Ca~(++), Mg~(++) of the abovesamples were determined. The pH of rain water was found to be highly alkaline and the valuesvaried from 6.4 to 7.8. Soil-oriented elements showed good correltioan (r~0.6) with pH valuesof rain water. The high concentration of soil-oriented elements, specially Ca~(++), is found to play animportant role in neutralizing the acidity of rain water and maintaining high alkaline pH. The studysuggested that the contribution of atmospheric aerosol of natural sources (sea and soil) to thechemical composition of rain water is more than that of anthropogenic origin.     

Anthropogenic sulphate aerosols and large Cl-deficit in marine atmospheric boundary layer of tropical Bay of Bengal

Our long-term study provides an unequivocal evidence for near-quantitative (80–100%) depletion of chloride from sea-salts in the marine atmospheric boundary layer (MABL) of tropical Bay of Bengal. During the late NE-monsoon (Jan-Mar), continental outflow from south and south-east Asia dominate the wide-spread dispersal of pollutants over the Bay of Bengal. Among anthropogenic constituents, SO ₄ ^2? (range: 0.6–35 μg m^?3) is the most dominant. The non-sea-salt SO ₄ ^2? (nss-SO ₄ ^2? ) constitutes a major fraction (55–65%) of the aerosol water-soluble ionic composition (WSIC), whereas contribution of NO ₃ ^? is relatively minor. The magnitude of Cl-deficit (with respect to its sea-salt proportion) exhibits linear increase with the excess-nss-SO ₄ ^2? (excess over NH ₄ ⁺ ). We propose that displacement of HCl from sea-salt aerosols by H₂SO₄ is a dominant reaction mechanism for the chloride-depletion. These results also suggest that sea-salts could serve as a potential sink for anthropogenic SO₂ in the downwind polluted marine environment. Furthermore, loss of hydrogen chloride, representing a large source of reactive chlorine, has implications to the oxidant chemistry in the MABL (oxidation of hydrocarbons and dimethyl sulphide).     

Rapid change in nitrate and sulfate concentrations observed in early stage of precipitation and their deposition processes

The concentrations of H⁺, nitrate (NO₃ ^-), and sulfate (SO₄ ^2-) in rainwater and their temporal changes were analyzed on the basis of continuous observation from 1 July 1991 to 30 June 1992 at a suburb of Nagoya, Japan. The yearly average for pH was 4.4. In general, an increasing pH with increase in precipitation amount was observed for rain events. Relatively high pH rainwater was sometimes observed at the beginning of rainfall, even though high concentrations of NO₃ ^- and SO₄ ^2- were involved. The high pH values were considered to be caused by the neutralization process with particulate matter containing cations. The yearly averaged ratio of equivalent concentration of nitrate to sulfate (N/S) in rainwater was 0.58. In the early stage of rain, the N/S value was usually more than 1.0 due to the difference of scavenging process between NO₃ ^- and SO₄ ^2-. High values of N/S ranging from 5 to 10 were found under the atmospheric conditions of calm winds and low humidity, during which it is possible that atmospheric particles float for a long time in the air before a rain event. The adsorption of NO₃ ^- in the early stage of rainfall by particulate matter was suggested from the difference in scavenging processes of NO₃ ^- and SO₄ ^2-. A possible scavenging process, called limb cloud scavenging, is presented to explain the interaction of particles and nitrate ions at the early stage of rain. In limb cloud scavenging, the repeated migration of cloud particles or raindrops between the inside and outside of clouds increases the absorption of ions to a highly condensed level, thus increasing the N/S value of rainwater. The influence of global scale seasonal phenomena with large amounts of particulates, such as typhoons or Asian dust storms, was also studied.     

Chemical Composition and Association of Size-Differentiated Aerosols at a Suburban Site in a Semi-Arid Tract of India

Size-differentiated concentrations of SPM, F, Cl, NO₃, SO₄, Na, K, Ca, Mg and NH₄ in atmospheric aerosols were measured in a suburban area of Agra city during December 1992 to March 1993. Except for NH₄, Cl and Na, all components were found to have a bimodal distribution. The fine fraction was dominated by NH₄, K, NO₃ and SO₄, while Na, Ca, Mg, F and Cl contributed to the coarse fraction. Fifty-eight percent of SO₄ and 67% of NO₃ were found in the fine mode and the coarse mode comprised 42 and 33% of SO₄ and NO₃, respectively. SO₄ was found to have a peak above the submicron range at 1.1 µm which has been attributed to secondary sulphate formation by heterogeneous oxidation of SO₂ on alkaline particles of Ca and Mg. The total aerosol was basic in nature and dominated by the soil-derived acid neutralising components (Ca, Mg and Na).     

Chemistry of rainwater and aerosols over Bay of Bengal during CTCZ program

For the first time, simultaneous study on physical and chemical characteristics of PM₁₀, PM_2.5, and rainwater chemistry was attempted over the Bay of Bengal in monsoon season of 2009. The aerosols and rainwater samples were collected onboard ship ‘SK-261, ORV Sagar Kanya’ during Oceanographic Observations in the Northern Bay of Bengal under the Continental Tropical Convergence Zone (CTCZ) program conducted during 16 July to 19 Aug 2009. Aerosol samples collected by PM₁₀ and PM_2.5 were analyzed for various water soluble (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH ₄ ⁺ , Cl^?, SO ₄ ^2? and NO ₃ ^? and acid soluble (Fe²⁺, Al³⁺, Zn²⁺, Mn³⁺ and Ni²⁺) ionic constituents. The pH of rainwater varied from 5.10 to 7.04. Chloride ions contributed most to the total ion concentration in aerosol and rainwater, followed by Na⁺. Significant contributions of SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ found in PM_2.5, PM₁₀ and high concentrations of TSP and non sea-salt SO ₄ ^2? over the mid-ocean is attributed to the long range transport of anthropogenic pollution from the Indian continent. The scavenging ratio was maximum for coarse particles such as Ca²⁺ and minimum for fine particles like NH ₄ ⁺ _.