A Long Term Study on Chemical Composition of Rainwater

Journal of Atmospheric Chemistry41:265–279,2002.265©2002Kluwer Academic Publishers.Printed in the Netherlands.A Long Term Study on Chemical Compositionof Rainwater at Dayalbagh,a Suburban Site of Semiarid RegionRANJIT KUMAR,ABHA RANI,S.P.SINGH,K.MAHARAJ KUMARI and S.S.SRIV ASTA V ADepartment of Chemistry,Faculty of Science,Dayalbagh Educational Institute,Dayalbagh,Agra–282005,India,e-mail:sssdei@(Received:7December2000;infinal form:18July2001)Abstract.Rainwater samples were collected for the monsoon period of1988and1991–1996at Dayalbagh(Agra),a suburban site situated in semiarid region.The mean pH was7.01±1.03well above5.6,which is the reference pH.Concentration of Ca2+was observed to be highest followed by Mg2+,NH+4,SO2−4,Cl−,NO−3,Na+,F−and K+.The ratios of SO2−4+NO−3and Ca2++Mg2+ (TA/TC)have been considered as indicator for acidity.In the Agra region ratio of TA/TC is quite below1.0indicating alkaline nature of rainwater.The lowest value of0.24was observed in1991 likely due to the lowest rain depth of the decade.The highest value of0.54was observed in1996, a year with a large rain depth and increase in line(vehicular traffic)and area sources(population growth).Good correlation between Ca2+and NO−3,Ca2+and SO2−4and SO2−4and NO−3,indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.Key words:long term,rainwater,chemical composition,acidity,neutralization,soil.1.IntroductionDeveloping regions,mainly in tropics have faster population growth than industri-alized nations and can expect substantial increases in sulphur and nitrogen oxide emissions(Galloway,1989).Emissions of SO2in Asia are rapidly increasing due to high economic growth from about34Mt in1990to about110Mt by2020when no control measures are taken.Acidity is mainly due to the emissions of sulphur and nitrogen oxide,which undergo dispersion,transport and chemical reactions in the atmosphere before they are wet or dry deposited as suphuric and nitric acids or their partially or totally neutralized ammonium salts.These acids result from atmospheric oxidation of the SO2released into the atmosphere during the smelting of ores and from burning of fuels with high S content and oxidation of N produced by all forms of combustion. Precipitation is a very efficient pathway for removing these compounds from the atmosphere.266RANJIT KUMAR ET AL.Acid precipitation is also of concern in developing countries as in India where the rainwater is not yet acidic(Mukherjee,1957,1964;Handa,1969;Handa et al., 1982;Subramaniam and Saxena,1980;Satsangi et al.,1998)but the pollution lev-els are rapidly increasing(NEERI,1980)in metropolitan cities like,Calcutta,Delhi and Bombay(Khemani et al.,1987).Acid rain in India has been reported at isolated pockets in Bombay,Delhi and recently at Korba(Mahadevan et al.,1984;Khemani et al.,1989,1994;Krishna Nand,1984;Ravichandran and Padmanabhamurty, 1994;Chandrawanshi et al.,1997).During the last two decades,a large number of studies have been carried out on the chemical composition of precipitation in India(Khemani et al.,1989;Handa et al.,1982;Naik et al.,1994;Mahadevan et al.,1989;Saxena et al.,1991,1996; Kumar et al.,1993a;Khare et al.,1996,1997a;Kulshrestha et al.,1995;Varma, 1989).Mukherjee(1957)made thefirst systematic pH observation in India at Calcutta and he observed pH values of rainwater close to7.0,which was more than reference pH5.6of rainwater.Atmospheric CO2(because of its ubiquity in global atmosphere)at a concentration of335ppm leads to an equilibrium pH of 5.6at15◦C in natural precipitation,which was chosen as a reference pH(Charlson and Rodhe,1982).Data was collected from ten BAPMoN sites in India,which had been established to identify levels of pollution and for identifying long-term trends in concentration of significant atmospheric constituents,which may effect the environment.The above studies showed that pH ranges from5.0–9.0but it was close to7.0in the monsoon rainwater over India.To account for this high pH value,rainwater was thoroughly studied with respect to major cations and anions. The composition of precipitations showed high value of Ca2+in rainwater samples irrespective of the location of sampling site.Ca2+,which is component of dust and soil,can act as a good neutralizing agent.Wind blown dust and soil thus play an important role in precipitation chemistry of North Central India.Up to now long term measurements of the chemical composition of precipita-tion in south Asia have been quite limited and none in India.The present study reports a long-term systematic study on rainwater of Agra.Our research group has been monitoring quality of air in Agra in terms of vapor phase,aerosol,precipitation and dry deposition for the last decade,particularly characterization of precipitation(Sharma et al.,1990;Saxena et al.,1991,1992, 1996,1997;Kumar et al.,1993a,b;Khare et al.,1996,1997a,b;Satsangi et al., 1998;Parmar et al.,1999,2000;Khare,1997;Kulshrestha et al.,1998).Agra lies in a semi-arid tract of India,two thirds of its peripheral boundaries are bounded by Thar desert of Rajasthan(Figure1).The main industrial activities,which are in operation in Agra city and its outskirts,are foundry and forging industry.Foundry emissions have a high concen-tration of particulate matter including some of the metals known to catalytically oxidize SO2and others gaseous pollutants.The foundries use cupolas as the melting units that use common fuels like hard coke,steam coal,wood and oil. The cupola emissions include both gases and particulates.Gaseous emissionsA LONG TERM STUDY ON CHEMICAL COMPOSITION OF RAINWATER267Figure1.Map showing the location of sampling site and industries in Agra.include CO,CO2,SO2and NO x etc.SO2concentrations vary between68and 108mg m−3while NO2has been reported to vary between0.2and0.6mg m−3 (PCRI,1988).The other industrial activities in Agra are rubber processing,lime oxidation and pulverization,chemicals,engineering and brick refractory kilns. Table I shows percentage contribution of SO2by each category of industry.The foundry activities account for62%of the total contribution by industrial activities (CUPS/7/1981–1982).In1979,the Government of India(GOI)constituted a High Power Committee (HPC)to oversee the implementation of necessary air pollution control measures at Agra to protect the Taj Mahal monument from chemical corrosion and degradation. Accordingly since1981no polluting industry has been allowed to start and expan-sion on existing ones have not been permitted in Agra.Out of265,173industries have installed air pollution control unit by1994and by1996either they have air pollution control unit or they have been closed out.Table II shows line sources (vehicular traffic)and area sources(population)from1988to1996.Line sources mean automobiles,which emit many pollutants,although SO2is not a pollutant significantly contributed by automobile in contrast to CO,HCs,and oxides of nitrogen.Line sources have increased by about12%every year since1988to1991; thereafter the increase is about7%every year from1991–1996.Area sources on the other hand show an increase of about2%every year.Table II also shows ambient268RANJIT KUMAR ET AL.Table I.Percentage contribution of SO2by each category ofindustry in AgraIndustry category Percentage contribution of SO2by each category of industryFoundry62.74Ferro-alloy10.14Rubber processing 3.29Lime processing0.27Engineering 4.66Chemical12.88Brick refractory 6.02Total100.00Source:CUPS/7/1981–1982.level of SO2and NO x for1988,1991and1996,since data is not available for other years.Annual mean concentration(inµg m−3)of SO2,NO x,O3,NH3,HNO3, HCOOH,CH3COOH and SPM was found to be6.7±2.6,39.8±31.2,39.39±9.6, 23.6±18.4,0.64±0.56,2.82±2.06,4.17±3.43and190±75(Parmar et al., 1999,2000;Khare et al.,1997b,Khare,1997;Kulshrestha et al.,1998).Aerosol was analyzed for major anions and cations and found to be basic in nature(Kul-shrestha et al.,1998)as it is dominated by the soil derived components.A study on precipitation showed pH variation between6.1and7.3with volume weighted mean pH6.9all indicating alkaline nature(Saxena et al.,1996)as compared to reference level of5.6(Charlson and Rodhe,1982).On the basis of neutralizing factors and correlations,it was shown that neutralization is mainly brought about by Ca2+and Mg2+rather than NH3(Saxena et al.,1996).However,sequential sampling of rainwater revealed that in earlier part of an event washout process dominated where Ca2+appears to be dominant acid neutralizer while other majorions(Mg2+,NH+4,Na+,K+)in addition to Ca2+play a role in neutralization ofacidity of rain water in latter part of the event(Khare et al.,1996).2.Methods and Materials2.1.SITE DESCRIPTIONSampling of rainwater was carried out at Dayalbagh.The sampling site was located in Agra(North Central India,27◦10 N,78◦05 E),which is about200km southeast of Delhi(Figure1).It is situated in a semi arid zone.Apart from the local sources, Mathura refinery and Ferozabad glass industries are both situated at a distance of 40km from Agra.Meteorology of Agra is so that prevailing winds are mostly fromA LONG TERM STUDY ON CHEMICAL COMPOSITION OF RAINWATER269T a b l e I I .S t a t i s t i c s o f n u m b e r o f v e h i c l e s (l i n e s o u r c e )a n d p o p u l a t i o n (a r e a s o u r c e )a n d c o n c e n t r a t i o n o f S O 2a n d N O x (i n µg /m 3)f r o m 1988t o 1996S p e c i e s19881990199119921993199419951996S O 28.6N A 6.7N A N A N A N A16.0N O x 4.2N A 11.3N A N AN A N A21.2N o .o f v e h i c l e s 1,16,7501,46,7501,64,251,77,2301,90,0702,02,4902,16,3502,46,823P o p u l a t i o n10,37,75810,86,64611,11,09011,35,53311,59,97711,84,42112,08,8652,33,309270RANJIT KUMAR ET AL. the northwest so that Mathura lies upwind while Ferozabad downwind.However, on the basis of Gaussian dispersion model it has been shown that Mathura refinery contributes insignificant amount of SO2(Goyal and Singh,1990).Rain water samples were collected in the monsoon season of1988and1991to 1996at Dayalbagh,a suburban site which is located in the north of the city.The site is surrounded by areas almost exclusively devoted to agriculture and has low residential density.A national high way lies about2km from the sampling site. Although there are no industries in the immediate vicinity of the sampling site, during the monsoon,site becomes downwind with respect to the city’s pollution sources.The prominent wind directions during the monsoon are SW,S,SE and E, which correspond to the industrial sectors of the city.2.2.SAMPLE COLLECTIONRainwater samples were collected on the roof of the faculty building of this In-stitute about8m from ground level and1m from thefloor of the roof using polyethylene funnel(diameter,14.5cm)and bottle.The collectors(bottles and funnels)were deployed as soon as the rain began and were retrieved immediately after the rain stopped.Sampling was done manually on an event basis where an event may be defined as the span of rain between two dry periods of duration greater than1h.A total of176samples have been collected.After retrieval,pH was measured within2h of the end of the rain event andfiltered through PTFE filter(0.45µm pore size).Afterfiltration samples were divided into two parts, one fraction was preserved with chloroform in a previously washed polyethylene bottle for anions and ammonium analysis and another fraction was preserved with 1%nitric acid(v/v)for the analysis of cations.All the samples were stored in the refrigerator.2.3.CHEMICAL ANALYSISAnions(F−,Cl−,NO−3,SO2−4)were analyzed by Ion Chromatograph(Dionex2000i/SP)using a CO2−3/HCO−3buffer as eluent(1.7mM Na2CO3/1.8mMNaHCO3)and25mN H2SO4as regenerant.All concentrations were calculated based upon peak area of standards that were prepared daily from100ppm stock solutions of sodium salts of each of the ions and were found to be stable for many months.Typical standard concentrations were in the range of0.025to10ppm. Standards were run in triplicates after everyfive samples to check peak response. If deviation was more than2%,recalibration was done.Field blanks were handled in exactly the same way as other samples and analyzed.Level of all ions in thefield blanks and in rinses of the platicwares were below detection limits.The concentration of cations(Na+,K+,Ca2+and Mg2+)were determined on a Perkin-Elmer(2380model)double beam atomic absorption spectrophotometerA LONG TERM STUDY ON CHEMICAL COMPOSITION OF RAINWATER271 Table III.Analytical protocolParameter Technique Instrument Precision Accuracy Analytical(µg ml−1)(µg ml−1)detectionlimit(µg ml−1)Na+Atomic emission,AAS,Perkin Elmer0.050.020.15 Air/C2H2589.0nm Model2380K+Atomic emission,AAS,Perkin Elmer0.020.010.06 Air/C2H2589.0nm Model2380Ca2+Atomic absorption,AAS,Perkin Elmer0.130.070.4Air/C2H2422.7nm Model2380Mg2+Atomic absorption,AAS,Perkin Elmer0.150.050.45 Air/C2H2422.7nm Model2380NH+4Colorimetric as Hitachi2000UV-Vis0.10.050.25 Indophenols blue620nm SpectrophotometerSuppressed ionF−Chromatography Eluant Dionex2000i/SP Ion0.160.070.2=1.8mM,Na2CO3/1.7ChromatographmM NaHCO3,2ml min−1Regenerant=25mMH2SO4,3–5ml min−1Cl−-do-Dionex2000i/SP Ion0.170.890.5ChromatographNO−3-do-Dionex2000i/SP Ion0.060.030.12ChromatographSO2−4-do-Dionex2000i/SP Ion0.040.020.12Chromatographwith an air-acetyleneflame while NH+4was determined colorimetrically at620nmusing indophenol-blue method(Weatherburn,1967).2.4.UNCERTAINTYThe term precision is used to describe the reproducibility of results.In order to calculate the precision a standard of1ppm was run nine times and the precision reported as deviation from the mean in terms of percentage.The term accuracy denotes the nearness of a measurement to its accepted value and is expressed in terms of error(%).In all the cases the concentration of thefield blank was below the detection limit.The analytical precision,accuracy and detection limits are given in Table III.272RANJIT KUMAR ET AL. Table IV.Average mean concentration(µeq l−1)of rainwater components for present site and some acid rain occurring sites of IndiaSites Present site Chembur a Kalyan a Delhi b Korba c components Mean±S.D.Range Mean Mean Mean MeanMin.Max.pH7.01±1.03 5.98.0 4.8 5.7 5.4 4.8F−17.6±19.8 1.381.6–––12.2Cl−31.8±24.77.1102.5140.8111.8140.131.8NO−322.8±18.8 6.388.5–30.966.825.1SO2−436.4±30.5 2.1183.7420.8108.389.7213.0Na+18.4±14.5 1.875.295.65102.681.720.7K+7.6±9.9 1.158.228.1326.144.3 3.7Ca2+56.1±40.7 2.1183.7175.093.0133.7182.9Mg2+45.6±29.2 5.0194.056.739.169.642.8NH+440.1±37.910.566.1116.621.125.815.3a Khemani et al.,1989.b Ravichandran and Padmanabhamurty,1994.c Chandawanshi et al.,1997.3.Results and DiscussionAverage mean concentrations and standard deviations of ions in rainwater of Agra with minimum and maximum values are presented in Table IV along with some acid rain occurring area of India.Table V presents the variations in chemical con-stituents of rain water samples collected during monsoon periods of1988and1991 to1996.POSITION OF RAIN WATERThe concentration of ions follows a general pattern Ca2+>Mg2+>NH+4>SO2−4>Cl−>NO−3>Na2+>F−>K+.The acidity of rainwater dependson the concentration of anionic as well as cationic species.Acidic pH reveals the presence of strong acids in rainwater while neutral or alkaline pH indicates neutralization of acids by soil dust and ammonia.The pH of precipitation ranged between5.9and8indicating an alkaline nature as compared to the reference level of5.6(Charlson and Rodhe,1982)while mean pH was7.01±1.03.In India,pH between6and7.5has been reported in urban areas(Khemani et al.,1989)and5.2–7.6in forested areas(Rao et al.,1995).In contrast,in temperate countries much lower pH values have been reported,5.1at Amsterdam Island(remote marine site) (Moody et al.,1991),4.96at Chile,pacific ocean(Galloway et al.,1996),4.73 at continental regions such as Katherine,Australia(Likens et al.,1987),4.0to 5.6at Venezuelan Savannah(Sanhueza et al.,1989).The percentage contributionA LONG TERM STUDY ON CHEMICAL COMPOSITION OF RAINWATER273Table V.Variations in chemical constituents(geometric mean)of rainwater forDayalbagh along with rain depth and number of eventsYear198819911992199419951996pH7.05 6.9 6.8 6.77.037.07H+0.0890.120.150.190.0930.085F−7.6 1.37.4 4.018.252.5Cl−24.620.832.333.119.028.8NO−3 5.714.99.519.914.527.5SO2−446.923.917.317.724.530.2Na+21.748.015.323.922.317.8K+12.3 5.1 3.7 4.314.8 4.6Ca2+121.3136.947.966.366.156.2Mg2+7.924.126.5422.964.548.9NH+437.642.3–22.947.2114.8Rain depth(in mm)1090.4644.5880.7753.1781.01097.3No.of events292732243034of cationic components(Na+,K+,Ca2+and Mg2+)is46.2%,NH+414.5%andacidifying components was39.3%towards total deposition.The slight cationic excess is probably due to some unaccounted anions.It has been seen in Table IV that the highest concentration of Cl−is at Chembur (coastal site)and the lowest at present site,an Inland site.As the distance increases from the sea the contribution of chloride decreases.The concentration of SO2−4 is highest at Chembur a highly industrialized location in the Bombay region and lowest at Dayalbagh an agricultural suburban site.The highest concentration of Ca2+has been reported at Korba,a site with huge deposits of fossil fuel that is coalcovering an area of over∼4×104km2.The high concentration of NO−3has beenseen at Delhi and lowest at present site.The high level at Delhi may be probably due to heavy vehicular traffic about22,39,000(Lal,1996).3.2.VARIATION IN p H,CHEMICAL COMPOSITIONThrough the years mean pHfluctuated between7.07and6.7and these values fall within the standard deviation indicating there is no change in pH of rainwater from 1988–1996.However,the slightfluctuation could be attributed to meteorological parameters like rain depth,rain intensity,wind direction and wind velocity etc.It is well known that SO2−4and NO−3are acid contributors and Ca2+acts as acidneutralizer in this region(Khemani et al.,1989;Saxena et al.,1996).Mean value ofSO2−4for the entire data(1988,1991–1996)was36.4±30.5µeq l−1.The levels ofSO2−4through the years varied between17.3and46.9µeq l−1,maximum is twice274RANJIT KUMAR ET AL. that of minimum and all values were falling within standard deviation showing no statistical variation in the levels.No specific pattern was observed in variation ofSO2−4level from year to year.Aqueous phase oxidation is the main process forformation of SO2−4in cloud water and rainwater and aqueous phase scavenging ofSO2is limited by pH of aqueous droplets.At high pH(greater than4.5)aqueous phase oxidation occurs mainly by O3and O2in presence of Iron and Manganese. Oxidation by these depends on pH,temperature,and relative humidity.Mean valueof NO−3was found to be22.8±18.8µeq l−1while the yearly mean values variedbetween5.7and27.5µeq l−1,maximum isfive times more than minimum andthere was regular increase in the level of NO−3in rainwater.The increase in NO−3concentration could be due to increase in line sources.The main source of NO x,precursor of NO−3,is automobile exhaust;motor vehicles are increasing at veryfast rate in Agra(Table II).NO−3is either contributed by soil or by incorporation ofgas phase HNO3into aqueous aerosols and rain drops.Level of NO x is more than AQS and vapor phase HNO3is0.64µg m−3,which is higher than those values reported from urban sites in the temperate countries(Solomon et al.,1992).Gas phase oxidation of NO2into HNO3by OH free radical is at least twenty times more than gas phase oxidation of SO2.Mean value of Ca2+was found to be56.1±40.7µeq l−1and yearly mean value varied between47.9and136.9µeq l−1.The value of Ca2+decreased continuously most likely due to rapid urbanization and decrease in barren land.Assuming that precipitation acidity originates primarily from sulfuric acidand nitric acid and neutralization by Ca2+and Mg2+,so the ratios of SO2−4+NO−3/Ca2++Mg2+(TA/TC)can be considered as indicator for acidity,if TA/TCis less than one it indicates alkaline nature of rainwater and the ratios(TA/TC) greater than unity indicates the presence of free anions which is responsible forprecipitation acidity.Table VI shows the ratio of sum of SO2−4and NO−3and sumof Ca2+and Mg2+(TA/TC).It has been seen from the table that TA/TC ratios were higher for acid rain occurring sites.This value was2.99for Delhi where the acid rain occurs in25%of events(Kulshrestha et al.,1995)and1.06for Korba (Chandrawanshi et al.,1997)where acid rain occurs generally.In Agra region this (TA/TC)ratio has been observed to be much less than one indicating basic nature of rainwater.The value varied from0.24to0.54.The lowest value of0.24observed in1991was probably due to the lowest rain depth of the decade.The highest value of0.54was observed in1996would be explained on the basis of large rain depth and continuous increase in SO2and NO x levels from1991–1996due to area and line sources(Table II).3.3.IONIC CORRELATIONCorrelation matrix is a common way of hypothesizing potential precursors of ions in rainwater samples.Correlation between ions suggests the likely sourcesTable VI.pH and ratio of sulphate and nitrate(TA)and calcium and magnesium(TC)foracid rain occurring sites and present siteSites pH TA/TCDelhi 4.42 2.99Korba 4.80 1.06Chembur 4.80 1.05Kalyan 5.700.76Indraprastha a 5.000.43Agra19887.060.421991 6.900.241992 6.800.361994 6.700.4219957.030.2919967.070.54a TA/TC(SO4/Ca++).Table VII.Ionic correlation of different ionsH+Na+K+Ca++Mg++NH+4F−Cl−NO−3SO2−4H+ 1.00Na+–0.15 1.00K+–0.170.04 1.00Ca2+–0.480.450.25 1.00Mg2+–0.220.400.490.78 1.00NH+40.85–0.570.03–0.120.78 1.00F−–0.060.070.130.320.320.33 1.00Cl−–0.05–0.030.190.010.250.310.29 1.00NO−3–0.220.320.220.590.830.620.380.07 1.00SO2−4–0.180.260.340.510.380.300.490.210.53 1.00of pollutants and also indicates the gaseous reaction occurring in the atmosphere. Logarithmatic correlation coefficients between ion pairs are shown in Table VII.NO−3and SO2−4showed good correlation(r=0.53)in samples indicating theirorigin from similar sources.It was possible that a fraction of NO−3and SO2−4maybe derived from soil as a primary pollutant or may be associated with Ca2+and Mg2+after neutralization process.This was corroborated by significant correlationbetween Ca++and SO2−4(r=0.51),Ca2+and NO−3(r=0.59),Mg2+and NO−3(r=0.83).Ca2+and Mg2+,which are essential components of soil,have good correlation with each other(r=0.78)implying a common origin.All these fea-tures indicated that wind carried dust and soil play a significant role in precipitation chemistry.Ammonia is one of the important alkaline compounds found in the atmosphere and plays a key role in limiting the pH of rainwater.Singh et al.(2001)have confirmed local sources of ammonia are stockyard by short-term study on gas phase concentration of ammonia at this site.In the atmosphere ammonia generallyoccurs as(NH4)2SO4(Seinfeld,1986),but at this site it appears that NH+4waslargely associated with NO−3.This was supported by the fact that NH+4has goodcorrelation with NO−3(r=0.62)than SO2−4(r=0.30).NH4NO3was possiblyformed by the reaction of HNO3with NH3on moist soil surfaces and partly because of formation of un-dissociated NH4NO3when RH is more than62%.This was consistent with an earlier study by Hildmann et al.(1984)who also explained thelinkage of NO−3with salt and alkaline earth components.Dominance of NH4NO3has been reported by Sequeira(1982)and Saxena et al.(1996)in India.Chemistry of NH4NO3formation at this site has been discussed in one of earlier papers Parmar et al.(2000).4.ConclusionRainwater samples were collected at Dayalbagh,a suburban site of Agra for year 1988,1991–1996,during the monsoon period(July–September).The mean pH of rain water was7.01±1.03well above5.6,which is the reference pH of rainwater while pH ranges between5.9and8.The study revealed that rainwater is alkaline;its acidity was being neutralized by Ca2+,Mg2+and NH+4.Through the yearspHfluctuated between6.7–7.07and these values fall within standard deviation indicating there was no change in pH of rainwater from1988–1996.In the Agra region ratio of TA/TC is quite below1.0indicating alkaline nature of rainwater.The lowest value of0.24was observed in1991likely due to the lowest rain depth of the decade.The highest value of0.54was observed in1996,a year with a large rain depth and increase in line(vehicular traffic)and area sources(population growth).Good correlation between Ca2+and NO−3,Ca2+and SO2−4and SO2−4and NO−3,indicated that wind carried dust and soil play a significant role in precipitation chemistry.On the basis of ionic correlation it can be concluded that wind carried dust and soil play a significant role in precipitation chemistry of Agra region. 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