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Spatial variation of long term annual precipitation volume weighted concentrations of major chemical constituents , NO 3 − , Cl − , NH 4 + , Ca +2 , Mg +2 , Na + and K + ) at all the ten Global Atmospheric Watch (GAW) stations in India for the period from 1981 to 2012 is studied in this paper. Ionic abundance and balance is studied as well. The range of long term annual mean pH at ten stations was 5.25 ± 0.82 to 6.91 ± 0.76, lowest at Mohanbari and highest at Jodhpur. The long term annual mean pH for the period 1981-2012 showed decreasing trend at all the stations (significant at 5 % level). Decadal mean pH among ten stations for 1981-1990, 1991-2000 and 2001-2012 ranged between 7.31 to 5.76, 7.45 to 4.92 and 6.16 to 4.77 respectively and showed decreasing trend at all the stations during 1981-1990 to 2001-12. The percentage occurrence of acidic pH (<5.65) at ten stations ranged from 3 to 72 %, lowest at Jodhpur and highest at Mohanbari and it increased from 1981-1990 to 2001-2012 almost at all the stations. Temporal variation of annual mean values of nssSO 4 −2 , NO 3 −, Ca +2 and pH for the study period were attempted. Variation of nss K (non sea salt Potassium) at all the stations was studied to assess the biomass burning contribution in different regions. Non-marine (terrestrial) contribution dominated for majority of ionic constituents at most of the stations. However marine contribution was found to be dominant for Mg at Port Blair and Minicoy. Also sea salt fraction of SO 4 was higher than terrestrial at Minicoy. Sources of measured ionic constituents in rain water are assessed through correlation analysis. The concentrations of all the ionic species were lowest at Kodaikanal, a high altitude hill top station and the total ionic mass was 136.0 μeq/l. Jodhpur, an arid station not only had highest concentrations of Ca +2 , SO 4 −2 and K + but also had highest total ionic content1051.8 μeq/l) among all the stations. At Srinagar, Jodhpur, Allahabad, Nagpur and Pune stations Ca +2 was the dominant cation while dominant anion was NO 3 − for Srinagar, Allahabad, and Nagpur and Cl − for Jodhpur and Pune; at Mohanbari NO 3 − and Ca +2 ; at Visakhapatnam, Port Blair and Minicoy Na + and Cl − were abundant. Temporal variation had shown an increasing trend for nssSO 4 −2 and NO 3 − and obviously decreasing trend for pH at all the stations. However, Ca +2 J Atmos Chem showed a decreasing trend at all the stations except at Port Blair. With the exception of Pune and Jodhpur stations, nssK showed a decreasing trend at all the stations revealing decreasing influence of soil/biomass burning over Indian GAW stations. Negative correlation of pH with SO 4 −2 was found to be weak compared to NO 3 -.

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Aerosols create great uncertainties in studying climate change under global warming and atmospheric dynamics. To understand the impacts of aerosols on cloud properties in Madurai, we have analyzed an extensive collection of aerosol and cloud properties, obtained from the Moderate resolution Imaging Spectroradiometer (MODIS) data, over the study site during 2012-2013. Monthly, seasonal and annual variations of aerosols and clouds studied along their interactions and impacts on climate. Considering annual averages for all these parameters, most often the year 2012 was dominated with a higher presence of AOD, COD, CER, CTT, CTP whereas rainfall and CF were found to be dominated in 2013. The presence of higher CF in 2013 may be a cause for the higher rainfall and the lower level of CF in 2012 may be a cause for less rainfall. High aerosol loading in this area is due to biomass burning and urban air pollution which may significantly suppress precipitation. Increased aerosols and the local aerosol emissions may reduce the precipitation efficiency, which is responsible for the precipitation reduction and vice-versa.

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