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

Abstract

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 ^-, SO₄ ^2-, and HCO₃ ^-). The mean aerosol optical depth (AOD) (0.5 µ m) 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 (µ g/m³), out of which coarse mode dominated by 45%. While Cl^-, Na⁺, K⁺, and Mg²⁺ (sea salts) contributed nearly 56%, SO₄ ^2- 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 (σ¹), 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.