Atmospheric dry-deposition of mineral dust and anthropogenic trace metals to the Bay of Bengal

Abstract

This manuscript presents a comprehensive data set on concentrations of crustal elements (Al, Ca, Fe and Mg) and trace metals (Pb, Cd, Cu, Mn, Cr, Co and Ni) in ambient aerosols studied from the marine atmospheric boundary layer (MABL) of the Bay of Bengal during the period of continental outflow (January–April). Based on cruises conducted during January'09 (winter) and March–April'06 (spring inter-monsoon), mass concentrations (ngm−3) of Pb (9–57), Cd (0.01–2.8), Cr (1–17) and Mn (4–103) in the outflow from the Indo-Gangetic Plain were higher during the winter compared to those in the spring inter-monsoon (Pb: 3.2–13.5; Cd: 0.1–1.6; Cr: 0.2–7.2 and Mn: 4.6–42.7). In contrast, Cu concentration was relatively high during the spring inter-monsoon (3.2–27.9ngm−3); whereas concentrations of Co and Ni were not significantly different (p-value>0.05) during the two seasons. In general, enrichment factors of Pb and Cd are higher (EFPb: ~225; EFCd: ~1165) over the southern Bay (south of 15°N) associated with south-east Asian outflow. A significant (p-value<0.05) linear relation of Pb, Cd and Cu with nss-SO42− reaffirms their anthropogenic origin. Another notable feature of temporal data relates to significantly higher ratios of crustal elements (Ca/Al and Fe/Al) associated with the long-range transport of mineral dust from the Thar Desert during the spring inter-monsoon. The deposition of mineral dust (0.3–6gm−2yr−1) to the Bay of Bengal is consistent with model results reported in the literature. However, the dominance of anthropogenic trace metals and their air–sea deposition must be considered in any assessment of factors that influence the marine ecosystem in the Bay of Bengal.