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Absorption of atmospheric CO 2 is lowering the pH of surface-ocean at the rate of 0.0015 ± 0.0005 units per year (Bates et al., 2014;Sutton et al., 2017) in the global ocean. The rate of acidification is reported as higher in the coastal than offshore region due to the proximal multiple human activities that modify the carbonate equilibria (e.g., Cai et al., 2011). Deposition of sulfate and nitrate aerosols, formed from fossil fuel and biomass burning, may further decrease pH of surface ocean (Doney et al., 2007;Mackenzie, 1995;Schlesinger, 1997).The Bay of Bengal (BoB or northeastern Indian Ocean) is the best suited region to study impact of atmospheric aerosols deposition on surface ocean acidification due to its proximity to populated areas, this region is under the influence of multitude human activities of the world's most populated region (Boblme, 2014). Zhang and Reid (2010) reported higher levels of aerosol optical depth (AOD) over the BoB and the rate of increase is the highest compared to elsewhere in the world. Recently Yadav et al. (2021) estimated higher rate of increase in anthropogenic aerosols over the northwestern and western coastal BoB (0.006-0.01/yr respectively) between 2001 and 2019 than earlier report (Zhang & Reid, 2010). Based on atmosphere-ocean couple model, Doney et al. (2007) found that atmospheric deposition of pollutants in the open sea region of BoB is decreased pH of surface-ocean by 0. 003 between 1990003 between and 2000003 between . Sarma et al. (2015 reported rapid increase in acidification in the western coastal BoB, based on data collected during 1991 and 2011, due to deposition of atmospheric pollutants. Since this study is based on two snapshot measurements, it is unclear the longterm variability in pH and potential reasons responsible for its variability. In order to examine the influence of atmosphere-ocean interactions on long-term variability in ocean acidification, time-series observations were conducted between 2007 and 2018 in the BoB. Based on this data, we would like to evaluate the (a) rate of acidification in the coastal BoB, (b) long-term variability in composition of atmospheric aerosols, and (c) impact of deposition of atmospheric pollutants on coastal water pH through laboratory experiments.

Abstract. Rivers are strong source of dissolved inorganic carbon (DIC) to the adjacent coastal 10 waters. In order to identify the major sources of DIC in the Indian monsoonal estuaries and their 11 export flux to the north Indian Ocean, 27 major and medium estuaries along the Indian coast 12 were sampled during discharge period.

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