Atmospheric transport of mineral dust from the Indo‐Gangetic Plain: Temporal variability, acid processing, and iron solubility

Abstract

AbstractAtmospheric transport of chemical constituents from the Indo‐Gangetic Plain (IGP) to the Bay of Bengal is a conspicuous seasonal feature that occurs during the late NE‐monsoon (December–March). With this perspective, aerosol composition and abundance of mineral dust have been studied during November 2009 to March 2010 from a sampling site (Kharagpur: 22.3°N, 87.3°E) in the IGP, representing the atmospheric outflow to the Bay of Bengal. The chemical composition of PM2.5 suggests the dominance of nss‐ (6.9–24.3 µg m−3); whereas the abundance of mineral dust varied from 3 to 18 µg m−3. The concentration of aerosol iron (FeTot) and its fractional solubility (Fews % = Fews/FeTot *100, where Fews is the water‐soluble fraction of FeTot) varied from 60 to 1144 ng m−3 and from 6.7 to 26.5%, respectively. A striking similarity in the temporal variability of total inorganic acidity (TIA = + nss‐ ) and Fews (%) provides evidence for acid processing of mineral dust (alluvium) during atmospheric transport from the IGP. The contribution of TIA to water‐soluble inorganic species [(nss‐ + )/ΣWSIS], mass ratios of Ca/Al and Fe/Al, and abundance of dust (%) and Fews (%) in the IGP‐outflow are similar to the aerosol composition over the Bay of Bengal. With the rapid increase in anthropogenic activities over south and south‐east Asia, the enhanced fractional solubility of aerosol iron (attributed to acid processing of mineral dust) has implications to further increase in the air‐sea deposition of Fe to the Ocean surface.