Aerosol iron solubility in a semi-arid region: temporal trend and impact of anthropogenic sources

Abstract

A systematic 1-yr chemical data for the fine mode (PM_2.5) air-borne particulate matter, collected from a high-altitude site (Mt. Abu, 22.7°N, 74.6°E, 1680 m asl) in a semi-arid region of western India, reveal characteristic temporal variability in the abundance of mineral dust and fractional solubility of aerosol Fe (referred as water-soluble Fe). A notable feature of the data is seen from an inverse relationship between aerosol Fe (range: 50-915 ng m^-3) and fractional Fe solubility (range: 0.06-16.1%). A significant increase in the solubility of iron, during wintertime, is also marked by a uniform decrease in the mass fraction of mineral dust. These observations suggest that the advective transport of pollutants and Fe derived from combustion sources is one of the possible causes for the enhanced solubility of iron over a semi-arid region in western India. The relative dominance of anthropogenic sources, during wintertime, is also supported by a two to threefold increase in NH₄⁺ and SO₄^2- as well as enrichment of heavy metals in PM_2.5 (ascertained from Pb/Al and Cd/Al ratios).