Impact of continental outflow on chemistry of atmospheric aerosols over tropical Bay of Bengal

Abstract. The continental outflow from Indo-Gangetic Plain and south-east Asia dominates the widespread dispersal of pollutants over tropical Bay of Bengal (BoB) during the late NE-monsoon (January–March). It is thus pertinent to assess the impact on marine atmospheric boundary layer of BoB. The chemical data, based on analyses of size-segregated (PM_2.5 and PM₁₀) aerosols, suggest the dominance of nss-SO₄²⁻ (range: 1.3 to 28 μg m⁻³) in PM_2.5. Almost all SO₄²⁻ is of anthropogenic origin and accounts for as much as 65 % of the water-soluble inorganic constituents. The impact of anthropogenic sources is further evident from the widespread depletion of chloride (range: 40 to 100 %) compared to sea-salt composition. The carbonaceous species (EC and OC) contribute nearly 25 % to PM_2.5; and significant linear relationship with K⁺ suggests biomass burning as their dominant source (biofuels and agricultural waste). The enhancement in the fractional solubility of aerosol Fe, as assessed in PM_2.5, re-emphasizes the impact of combustion sources (biomass and fossil-fuel) and chemical processing (of dust) during the long-range transport. The high enrichment factors of heavy metals (Pb and Cd) further demonstrate the influence of pollution sources on the chemistry of MABL. The downwind transport of pollutants and exchange across air-sea interface can, thus, have profound impact on the ocean surface biogeochemistry.