Sources, solubility, and dry deposition of aerosol trace elements over the East China Sea

Abstract

A total of 47 marine aerosols collected from the East China Sea between the spring of 2005 and the spring of 2007 were analyzed for both the water-soluble and the total concentrations of 25 trace elements and phosphorus and the water-soluble major ions, organic carbon, as well as silicon. During the sampling periods, eight samples were significantly influenced by Asian dust events. The total concentrations of both the chemical species of dust origin and of anthropogenic origin were higher during the Asian dust period, suggesting that the Asian outflow of air pollutants often accompanies the Asian dust advection. Overall, the average solubilities were ≤ 20% for Al, Fe, Ti, Cr, Y, Sn, Ba, Ni, Ga, and Mo; 20–40% for Co, Cs, Rb, Sb, and Pb; 40–60% for Mn, V, Cu, Ge, and P; and ≥ 60% for Tl, Sr, As, Zn, Cd, and Se. The solubilities for many elements are lower in the high dust period than during the polluted northeasterly monsoon and the background summer period. A variety of controlling factors of the solubilities of the elements were discussed in this study. The relative importance could be concluded as follows: acid processing > chemical speciation ≈ aerosol source > dust loading. Finally, we estimated the dry depositional fluxes of soluble elements by assuming certain dry deposition velocities for each element. The fluxes were 39 ± 50 µg/m2/d for soluble Fe and 41 ±74 µg/m2/d for the combination of some bioavailable elements (e.g., Zn, Cu, Mn, Ba, Co, V, Ni, and Cd) during the northeasterly monsoon. Atmospheric deposition is an additional source of nutrient elements that may be important not only in the coastal/marginal sea, but also particularly in the remote open ocean because aerosol trace elements are associated mostly with fine mode particles that can be brought farther from the source regions.