Chemical characterization of wintertime aerosols over the Arabian Sea: Impact of marine sources and long-range transport
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We examined here the compositional characteristics of total suspended particulate (TSP) samples collected along the east coast of the Arabian Sea during a winter cruise (SS379: 6-24 December 2018) to understand the extent of influence of air pollutants from terrestrial sources. The TSP samples (N = 17) were analyzed for water-soluble inorganic species (WSIS), elemental carbon (EC), organic carbon (OC) and water-soluble organic carbon (WSOC). Backward air mass trajectories and satellite-based fire counts revealed an influence of long-range transport of biomass burning emissions in the Indo-Gangetic Plain and southern India. Anthropogenic (82-97%) SO4 2- is the most abundant WSIS followed by Na+ and/or NH4+. Ambient EC loadings (0.5-2.4 mu g m-3) and OC/EC ratios (2.5-10.5) are higher than usually expected for fossil-fuel combustion sources. Low mass ratios of NO3-/non-sea-salt SO4 2- (0.08-0.49), as well as high ratios of nss-K+/EC (0.14-1.18) and WSOC/OC (0.30-0.74), highlight the significance of coal combustion and biomass burning emissions in the regional influx of air pollutants to the Arabian Sea. The multiple linear regression analysis has indicated strong correlations among sea salt components (Na+, Cl- and Mg2+), carbonaceous components (OC, EC and WSOC), and anthropogenic WSIS (NH4+ and SO4 2-). Furthermore, we used minimum R-squared technique based primary OC/EC ratio in the EC-tracer method to estimate the contribution of secondary organic carbon (SOC) to OC (7-61%) and TSP mass (0.7-11%). Overall, the composition of TSP is characterized by 21 ±10% of particulate organic matter, 2.3 ± 1.1% of EC, 21 ± 9% of anthropogenic WSIS and 43 ± 15% of unidentified fraction including dust. This study has implications for understanding the evolving nature of secondary inorganic and organic aerosols in the continental outflows.
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