Impact assessment of continental and marine air-mass on size-resolved aerosol chemical composition over coastal atmosphere: Significant organic contribution in coarse mode fraction

Size-segregated aerosols (five stages from 7 μm in diameter) collected from a coastal location in south-west peninsular India were analysed for water-soluble ionic species, carbonaceous aerosols and metallic species on a seasonal basis for two years (2017–19). The annual mean concentration of the components Na+, Ca2+, Mg2+, Cl−, NO3−, Al, Fe exhibited coarse mode (> 2 μm) enhancement; while NH4+, K+, SO42−, MSA−, oxalate, Organic carbon (OC), Elemental carbon (EC) peaked in fine mode (< 2 μm). The contribution of fine mode aerosols dominated under the influence of continental air-mass and a relative shift towards coarse mode size regime with respect to marine air-mass was observed. The relative contribution of analysed species showed the dominance of sea-salt fraction in coarse mode during monsoon, anthropogenic ions in fine mode during post-monsoon, crustal species in coarse mode during pre-monsoon and carbonaceous species in fine mode during winter. While nss-SO42− was found to be a major component of fine mode aerosol fraction, OC contributed significantly for both coarse and fine mode. Distinct seasonal variation in OC size-distribution was observed. Fine mode OC dominated during post-monsoon and winter while coarse mode OC peaked during pre-monsoon and monsoon, indicating its multiple sources and formation pathways. The water-soluble fraction of OC predominantly existed in fine mode and was modulated by changing synoptic air-masses. The water insoluble OC fraction was found to be modified by sea-land breeze activities and exhibited coarse mode nature. The significant contribution of OC in coarse mode size regime over this coastal atmosphere has been attributed to; the condensation of gaseous precursors on pre-existing coarse particles leading to the formation of coarse mode WSOC and the primary emission from natural terrestrial and marine organic matter resulting in the emission of coarse mode WIOC. •Size-segregated chemical composition of aerosols for different air-mass is a first of its kind from tropical atmosphere.•Seasonal dependence of organics gives new insights into their role in many atmospheric processes and climatic impacts.•Present study finds its importance in aerosol life cycle processes and its climatic implications on a regional scale.