Study of formation of coarse particle nitrate aerosol

The results of analyses of six atmospheric aerosol samples collected in Helsinki, Finland, using a Berner low-pressure impactor, are reported. Formation of coarse particle nitrate was studied by evaluating various ion balances of the measured water-soluble ions (NH4+, Na+, K+, Mg2+, Ca2+, Cl-, NO3- and SO42-) and mass size distributions of Na+, Ca2+, Cl- and NO3-. Atmospheric coarse particle NO3- was found to be formed in the reaction of nitric acid with sea- and soil-derived coarse particles. The fraction of nitrate found on sea and soil particles followed the measured concentrations and size distributions of these two particle types: the concentration ratio of soil to sea particles increased with increasing particle size as did the fraction of nitrate on soil particles. The reaction with sea-salt particles resulted in the evaporation of Cl- as HCl. The presence of non-sea-salt SO42- indicates that also H2SO4 and/or SO2 reacted with sea salt and contributed to the Cl- loss. Overall, the percentage of evaporated Cl- decreased with increasing particle size, which suggests a surface reaction mechanism. Cl- evaporation was almost complete for the 1-2 mu m diameter size fraction indicating that all major sea-derived chlorides, NaCl, MgCl2, CaCl2 and KCl, may react with acidic species in the atmosphere. The results showed further some indications of possible reaction of HCl with soil particles. Copyright (C) 1996 Elsevier Science Ltd