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The chemical composition of aerosols in the Marine Atmospheric Boundary Layer (MABL) of Bay of Bengal (BoB) and Arabian Sea (AS) has been studied during the spring and inter-monsoon (March-May, 2006) based on the analysis of water soluble constituents (Na1+, NH+, K-+,K- Mg2+ 4 Ca2+, Cl- NO3- and SO42-) crustal elements (Al, Fe, and Ca) and carbonaceous species (EC, OC).The total suspended particulates (TSP) ranged from 5.2 to 46.6 mu g m(-3) and 8.2 to 46.9 mu g m(-3) during the sampling transects in the BoB and AS respectively. The water-soluble species, Oil average., accounted for 44% and 33% of TSP over BoB and AS respectively, with dominant contribution 2 of SO42- over both the oceanic regions. However, distinct differences with respect to elevated abundances of NH+ in the MABL of BOB and that of Na+ and Ca2+ in AS are clearlv evident. The 4 non-sea-salt component Of SO42 ranging from 82 to 98% over BoB and 35 to 98% over AS: together 4 with nss-Ca2+/nss-SO42- equivalent ratios 0.12 to 0.5 and 0.2 to 1.16, respectively provide evidence for the predominance of anthropogenic constituents and chemical transformation processes occurring within MABL. The concentrations of OC and EC average around 1.9 and 0.4 mu g m(-3) in BOB and exhibit a decreasing trend from north to south; however, abundance of these carbonaceous species are not, significantly pronounced over AS. The abundance of At, used as a, proxy for mineral aerosols, varied from 0.2 to 1.9 mu g m(-3) over BoB and AS, with a distinctly different spatial pattern - decreasing north to south in BoB in contrast to an increasing pattern in the Arabian Sea.