Chemistry of rainwater and aerosols over Bay of Bengal during CTCZ program

Abstract

For the first time, simultaneous study on physical and chemical characteristics of PM₁₀, PM_2.5, and rainwater chemistry was attempted over the Bay of Bengal in monsoon season of 2009. The aerosols and rainwater samples were collected onboard ship ‘SK-261, ORV Sagar Kanya’ during Oceanographic Observations in the Northern Bay of Bengal under the Continental Tropical Convergence Zone (CTCZ) program conducted during 16 July to 19 Aug 2009. Aerosol samples collected by PM₁₀ and PM_2.5 were analyzed for various water soluble (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH ⁺₄ , Cl⁻, SO ²⁻₄ and NO ⁻₃ and acid soluble (Fe²⁺, Al³⁺, Zn²⁺, Mn³⁺ and Ni²⁺) ionic constituents. The pH of rainwater varied from 5.10 to 7.04. Chloride ions contributed most to the total ion concentration in aerosol and rainwater, followed by Na⁺. Significant contributions of SO ²⁻₄ , NO ⁻₃ and NH ⁺₄ found in PM_2.5, PM₁₀ and high concentrations of TSP and non sea-salt SO ²⁻₄ over the mid-ocean is attributed to the long range transport of anthropogenic pollution from the Indian continent. The scavenging ratio was maximum for coarse particles such as Ca²⁺ and minimum for fine particles like NH ⁺_{4 .}