Effects of acidic processing, transport history, and dust and sea salt loadings on the dissolution of iron from Asian dust

Abstract

Aerosol particles collected over the East China Sea (ECS) were analyzed for water-soluble Fe (FeS), total Fe (FeT), and other chemical species. Eight samples were classified as high Asian dust (HAD) on the basis of total Al concentrations ≥1500 ng/m3. Comparisons with low Asian dust (LAD) samples showed that unlike FeT or most other substances, the percentage of FeT soluble in deionized water (%FeS) was lower in the HAD samples. The %FeS in the HAD samples varied with transport pattern and air mass history. As the difference in FeS concentrations between HAD and LAD is relatively small and HAD occurs several days each year, the supply of FeS through dry deposition to the surface ocean may be less sporadic than previously thought. Soluble Fe correlated with non-sea-salt sulfate, water-soluble organic carbon, and nitrate, possibly because of an anthropogenic, relatively soluble, form of Fe or enhanced dissolution caused by reactions with anthropogenic acids. Sea salt loadings evidently have a negative effect on %FeS, presumably due to buffering effects of the salts. Dust concentrations and %FeS followed an inverse power law relationship with a moderate correlation, suggesting that the %FeS may be increased by acid processing during transport as dust loadings gradually decrease.