Interactions between inorganic trace gases and supermicrometer particles at a coastal site

Interactions between inorganic trace gases and supermicrometer aerosol particles were studied at a coastal site of Finland. The measurements revealed two supermicron mass modes for both nitrate and non-sea-salt sulfate. The lower-size modes were likely formed when sulfate and nitrate, or their precursor vapors, reacted with sea-salt particles. The upper-size modes were primarily due to accumulation of sulfate and nitrate into particles of continental origin. Chloride displayed only one supermicron mode centered at somewhat larger size than the sea-salt particle mode due to the more efficient evaporation of hydrochloric acid from smaller sea-salt particles. The average chloride losses were calculated to vary from over 95% for 1 mu m particles to about 30% for particles greater than 10 mu m in diameter. Supermicrometer particles were a net source of gaseous hydrochloric acid at our site, even though some indications of the reactions between HCl(g) and continental particles could be identified. The estimated chloride loss from sea-salt particles was balanced quite accurately by the additional sulfate and nitrate formed on these particles. It was hypothesized that sea-salt particles collected mostly sulfate in marine air masses, with nitrate collection becoming more important as the particles interact with polluted air. The dry deposition of supermicron particulate nitrate accounted for a significant fraction of total nitrate flux (NO3-+HNO3(g)) into the ground, and dominated the overall particulate nitrate flux. Both sea-salt and continental particles were important contributors to this flux. The role of supermicron particles in overall nitrogen and sulfur budgets was of less importance when one considers the relatively large deposition fluxes of NO2 and SO2 at the site. (C) 1997 Elsevier Science Ltd.