Monika J. Kulshrestha

Chemical characteristics of rainwater at an urban site of south-central India

Abstract The pH variation and the chemical characteristics of rainwater have been studied during monsoons from 1999 to 2001 at Hyderabad, a city in south-central India. The pH varied from 5.5 to 7.2 with an average of 6.4 which is in alkaline range considering 5.6 as the neutral pH of cloud water with atmospheric CO 2 equilibrium. Out of 28 rain events, only two events were observed in acidic range ( 2+ >Cl − >SO 4 2+ >NH 4 + >Na + >HCO 3 − >NO 3 − >K + >Mg 2+ . The ratios of different components with respect to seawater ratios were observed to be higher, indicating the significant influence of non-marine sources at this site.

Estimation of SO4 contribution by dry deposition of SO2 onto the dust particles in India

Dustfall deposition fluxes of major water-soluble components Cl, NO3, SO4, NH4, Na, K, Ca and Mg were estimated at five different sites of Delhi. The pH of water extracts of samples has been observed minimum at NPL ranging from 5.8 to 7.1 and maximum at Iqbalpur ranging from 7.9 to 8.7. The high values of pH of dustfall deposition suggest the dominance of crustal components that add higher alkalinity due to presence of components like Ca, Mg, etc. Dustfall fluxes were observed highest for Ca. considering the importance of alkaline nature of dust particles; the fraction of SO4 contributed by dry deposition of SO2 on the dust particles was estimated. Using these estimates, further the ambient concentrations of SO2 were calculated which were in a very good positive agreement with experimental concentration of SO2.

Temporal Variation and Concentration Weighted Trajectory Analysis of Lead in PM 10 Aerosols at a Site in Central Delhi, India

Ambient levels of lead (Pb) in PM10 were studied at a site in Central Delhi for the period of one year during day and night. The annual mean concentration of lead has been observed as 625 and 1051 ng/m3 during day and night time, respectively. The seasonal averaged concentrations of Pb have followed the order winter > postmonsoon > summer > monsoon. Highest levels of lead have been observed in winter with 31% samples exceeding the CPCB-NAAQS value as 1000 ng/m3. Lead levels during winter have been found to be 5.7 times higher than in monsoon, which might be attributed to prevailing meteorological conditions and more biomass burning. The low levels of Pb during summer might be attributed to its higher dispersion in the atmosphere. A sharp rise of Pb during postmonsoon might be linked to the local nonpoint sources, more biomass burning, and shifting of boundary layer. However, the higher concentrations of lead were observed during night time in all the seasons of the year as compared to those of the day time. To identify the potential source regions of Pb, Concentration Weighted Trajectories (CWT) have been plotted which showed higher influence of local sources during winter and postmonsoon while showing distant sources during summer.

Investigation of Alkaline Nature of Rain Water in India

Increased industrialization and urbanization lead to the atmospheric acidity which causes acid rain. However, in India, the nature of rain water has been observed to be alkaline. The reason for alkaline nature of rain water is found to be the buffering of acidity by soil-derived aerosols which are rich in Ca. Over the Indian Ocean where concentrations of soil dust are negligible, the acid rain has been observed to be a common phenomenon during INDOEX campaigns. In the Indian subcontinent, observations have indicated that rain becomes acidic when the buffering potential of rain water is weak. The weak buffering potential may be due to less interference of soil dust, acidic nature of soil or very high influence of industrial source.

Atmospheric Deposition of Reactive Nitrogen in India

The increasing demand of food and energy of the global population is contributing excess reactive nitrogen (Nr) in the atmosphere primarily in the form of ammonium and nitrate compounds. Subsequently, through wet and dry deposition processes, these compounds are deposited onto the ground, vegetation, soils, water bodies etc. enriching these systems with excess nitrogen (N). Knowledge about N deposition in North America and Europe is quite advanced because of systematic studies. But the present knowledge about N deposition in India and the south Asian region is very limited due to a lack of systematic measurements dedicated to nitrogenous compounds. Though a number of wet deposition studies have been reported by various groups for different sites and years in India, only a few of these are considered as having good quality data. This chapter reports quality controlled wet deposition fluxes of Nr at rural (2006–2008) and urban (2005–2008) sites in south India as part of the RAPIDC-CAD programme. The rural site Hudegadde is located in the reserve forest area of Western Ghats by the south-west coast of India while the urban site Hyderabad, the capital of Andhra Pradesh State is located in south-central India. In general, at both the sites, wet deposition of N through NH4 + was observed to be higher than NO3 −. Fluxes of NH4 + showed an increasing pattern at Hudegadde, while those of NO3 − showed an increasing pattern at Hyderabad. The possible reason for increasing NH4 + at Hudegadde may be an increase in biomass burning and vegetation decay in the forest areas, which contribute higher ammonia to the atmosphere, together with transboundary pollution due to air-masses from nearby continental areas. The increasing pattern of NO3 − fluxes at Hyderabad might be due to an increase in population, vehicular density and other urban activities. Projections using the MATCH model coupled with rain chemistry measurements showed that the Indo-Gangetic region experiences very high wet deposition of NH4 + which might be due to a prevailing higher density of ammonia sources in the region. This chapter also highlights the importance of dry deposition of Nr species for the Indian region.

Influence of crustal aerosols on wet deposition at a rural site of North-East India

A total of 42 rain water samples were collected for a period of one year, March 2005 to February 2006, at Jorhat, a rural site of North-East India. The pH of the samples varied from 4.1 to 7.1 with a mean 5.5 showing the acidic nature of rainwater with reference to 5.6 (natural pH of rain water due to CO2 equilibrium in the atmosphere). More than 50% of the rain events have been found to be acidic. Mean concentrations of major ions in the rain water followed the order SO > Ca2+ > NH > NO > PO > H+ > HCO > Na+ > Mg2+ > Cl– > K+ > F–. Ca2+, NH and Mg2+ have shown a neutralization factor less than 1, indicating partial neutralization of anions. EFSoil indicated that soil plays a major role in rain water composition. Maximum concentration for most of the ionic species has been observed during winter followed by summer, post-monsoon and monsoon periods, respectively. Occurrence of acid rain events has been observed throughout the year suggesting that the soil is acidic.

Deposition fluxes of chemical components of fog water at a rural site in north-east India

The north-eastern part of India has not been investigated for atmospheric deposition studies so far. In this study, deposition fluxes on an artificial surface of chemical components due to fog have been calculated during winter from December 2002 to January 2003 at Jorhat, a rural site in north-east India. As the land in this area is covered with vegetation, the site is representative of rural characteristics in this region. The average pH of fog water is 5.6. Among chemical components, NH+4 was observed to be dominating ion. Soil pH in this region is acidic (4.9). Unlike other parts of the country, chemical analysis of soil in this region revealed that influence of suspended soil dust on fog deposition was insignificant. A comparison of fluxes of fog with rain water during December—January months showed that deposition fluxes due to rain water were higher by almost one order of magnitude on an artificial surface but on natural surfaces, the fluxes may be comparable.

Chemical characteristics of trace metals in PM10 and their concentrated weighted trajectory analysis at Central Delhi, India

Trace metals associated with PM10 aerosols and their variation during day and nighttime as well as during different seasons have been studied for the year 2012. PCA analysis suggested 5 PCs, which accounted for 86.8% cumulative variance. PC1 accounted for 30% with a significant loading of metals of anthropogenic origin, while PC2 showed 28% variance with the loading of metals of crustal origin. These trace metals showed seasonal distinct day and night time characteristics. The concentrations of Cu, Pb, and Cd were found to be higher during nighttime in all the seasons. Only Fe was observed with significantly higher mean concentrations during daytime of all seasons except monsoon. The highest mean values of Cu, Cd, Zn, and Pb during post-monsoon might be attributed to winds advection over the regions of waste/biomass burning and industrial activities in Punjab and Haryana regions. Furthermore, concentration weighted trajectory analysis suggested that metals of crustal origin were contributed by long-range transport while metals of anthropogenic and industrial activities were contributed by regional/local source regions.