Wind-dependence of sea-salt and non-sea-salt aerosols over the oceanic environment

Aerosols in the oceanic environment essentially consist of a sea-salt component generated from the ocean surface by the action of wind and a non-sea-salt component advected from adjacent continents and these aerosols together constitute a continuum of sizes. Though it is fairly well accepted that the concentration of in situ produced sea-salt aerosols increases with increasing wind speed the behavior of the advected continental component in the oceanic environment is less understood. A study was carried out on the wind speed dependence of sea-salt and non-sea-salt components of aerosols based on the chemical composition of the total suspended particulates (TSP) in the marine environment. It is observed that while the mass concentration of sea-salt aerosols increases with increasing wind speed the mass concentration of non-sea-salt aerosols decreases with increasing wind speed. This feature could be observed in the mass concentration of sea-salt and non-sea-salt components of the total aerosol mass concentration as well as in the mass concentration of individual chemical species. Ions like NO3, Fe, Cu, Pb, etc., which are of continental origin showed negative correlation with wind speed and in general, components like Na, K, Mg, and Cl, which are mostly of oceanic origin showed positive correlation with wind speed. In the case of those ionic constituents like SO4, K, Mg and Ca which will have both sea-salt and non-sea-salt components (as they can originate from ocean waters as well as from the continental land mass), while the sea-salt component of the mass concentration of each of these ions (estimated by taking Na as reference) showed a positive correlation with wind speed, the remaining non-sea-salt component showed a negative correlation with wind speed. This study showed that in all the cases the concentration of non-sea-salt aerosols in the oceanic environments decreases with increasing wind speed, which is partly attributed to an increase in the dry deposition rate of aerosols at increasing wind speeds.