ON THE MODIFICATION OF SEA-SALT PARTICLES IN THE COASTAL ATMOSPHERE

Individual aerosol particles of 0.3-4 mu m radius were collected on 5 days with slightly different meteorological conditions (wind direction ) and at different SO2 and NO2 concentrations in August, September and October of 1996 in Tsukuba, Japan, which is located approximately 50 km from the coast of the Pacific Ocean. The samples were taken using i mpactors and examined with an electron microscope equipped with an ene rgy-dispersive X-ray (EDX) analyser. Sea-salt particles were present i n number proportions of 30-90% of the analysed particles for the diffe rent pollution levels and meteorological situations. In most of the ca ses modified sea-salt particles were observed in the fine (r < 1 mu m) and the coarse (r greater than or equal to 1 mu m) size ranges. In on e sample taken in relatively clean air unmodified sea-salt particles w ere found in the coarse size range. The deficiency of Cl in the fine p articles of this sample was found to be due to a reaction of sea-salt particles with nitric acid. The presence of nitrate ions in the modifi ed sea-salt particles was proven by a nitrate test. In a polluted samp le a large number of sea-salt particles showed a complete loss of Cl. Also, sea-salt particles which contained Zn were present in the sample . This suggests the importance of the attachment of anthropogenic part icles in the modification of sea-salt particles along with heterogeneo us reactions. (C) 1998 Elsevier Science Ltd. All rights reserved.