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 nit rate, or their precursor vapors, reacted with sea-salt particles. The upper-size modes were primarily due to accumulation of sulfate and nit rate into particles of continental origin. Chloride displayed only one supermicron mode centered at somewhat larger size than the sea-salt p article mode due to the more efficient evaporation of hydrochloric aci d from smaller sea-salt particles. The average chloride losses were ca lculated to vary from over 95% for 1 mu m particles to about 30% for p articles greater than 10 mu m in diameter. Supermicrometer particles w ere a net source of gaseous hydrochloric acid at our site, even though some indications of the reactions between HCl(g) and continental part icles could be identified. The estimated chloride loss from sea-salt p articles was balanced quite accurately by the additional sulfate and n itrate formed on these particles. It was hypothesized that sea-salt pa rticles collected mostly sulfate in marine air masses, with nitrate co llection becoming more important as the particles interact with pollut ed air. The dry deposition of supermicron particulate nitrate accounte d 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 sulfu r budgets was of less importance when one considers the relatively lar ge deposition fluxes of NO2 and SO2 at the site. (C) 1997 Elsevier Sci ence Ltd.