Dry Deposition of Trace Elements to the Western North Atlantic

The concentrations of selected elements, including Al, Fe, Na, Sb, Se V, and Zn, were determined for bulk aerosol samples collected at Bermuda between 1988 and 1993 as part of the Atmospheric/Ocean Chemistry Experiment (AEROCE). These data were combined with parameterized dry deposition velocities to investigate trace element recycling on atmospheric sea salt. During July and August, which are in the high dust season, > 10% of the monthly mean aerosol Na can be ascribed to crustal sources rather than sea salt, but in general the contribution of mineral dust to Na dry deposition is small (~ 1%) relative to that from sea salt. In fall and winter, ~ 10 to 20% of the aerosol Al, a commonly used indicator of mineral dust, is attributable to recycled sea salt, but the dust fluxes then are small, and longer-term averages show a recycling effect of only 1 to 5% on dry deposition. The percentage of recycled Fe appears to be even less than for Al, reaching a maximum of ~ 5% per month from December to February and averaging only a few percent per day when calculated over the duration of the study. Non-crustal/non-sea salt (NC/NSS) sources account for > 70% of the aerosol Sb, Se, V, and Zn, but differences in the dry deposition velocities for three particle types, which do still need to be verified, strongly affect their air/sea exchange rates. According to the simple model calculations, dust can account for more than half of the new dry deposition inputs of V and Zn, but the amounts of Sb and Se recycled on sea spray approach or exceed their new inputs from dust and the NSS/NC sources.