Observational Insight into the Heterogeneous Sulfate Formation on Dust Surface- Importance of the Mineralogy and Adsorbed Water

摘要

This study focuses on providing direct insight into the formation process of sulfate on mineral dust surface in the actual atmosphere. Collection of tropospheric dust over various parts of East Asia, along the mainstream of westerly wind was made by the means of balloon and aircraft-borne measurements. Mineralogy of individual dust particles, and the associated S content was investigated by SEM-EDX analysis. It was suggested that mineral dust is a common and major fraction of the coarse particles in the region, even during the periods unaffected by the severe dust storms. An exceeding amount of S was detected in the dust downwind of the source region. The heterogeneous uptake of gaseous SO_2, and the subsequent oxidation on dust was suggested as the main pathway that actually takes place in the ambient environment. Calcite showed significantly higher reactivity than the Clay particles, which together account for the majority of the dust. A positive correlation was found with the number of S containing particles and the relative humidity. Observed dependence of S uptake on the mineralogy and relative humidity is fairly consistent with the laboratory-based experiments.