Aerosol characterization during the summer monsoon period over a tropical coastal Indian station, Visakhapatnam



[1] Columnar optical depth and near-surface mass concentration of aerosols over Visakhapatnam, an urban location along the east coast of India during the summer monsoon period (May–August 2005), were measured simultaneously along with chemical sampling for water-soluble ionic species (NH4+, Na+, K+, Mg2+, Ca2+, Cl, NO3, SO42−, and HCO3). The mean aerosol optical depth (AOD) (0.5 μm) and Angstrom parameters (α, β) during this period were obtained as 0.72 ± 0.39 and 0.88 ± 0.39, 0.48 ± 0.36, respectively. The total surface aerosol mass concentration varied from 95 to 128 (μg/m3), out of which coarse mode dominated by 45%. While Cl, Na+, K+, and Mg2+ (sea salts) contributed nearly 56%, SO42− and NO3 (anthropogenic constituents) contributed 33% in surface aerosol constituents. During this period, high spectral variability in AOD, negative curvature of second-order Angstrom coefficient (α1), abundance of columnar submicron aerosols, role of air mass trajectories as tracers of long-range transport, cation deficiency, and sea-salt dependence on wind speed are some of the observations over Visakhapatnam. The synergy of the results from these complementary measurements can be reflected while computing the aerosol radiative forcing.