On the modification of sea-salt particles in the coastal atmosphere

Individual aerosol particles of 0.3–4 μm 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 impactors and examined with an electron microscope equipped with an energy-dispersive X-ray (EDX) analyser. Sea-salt particles were present in number proportions of 30–90% of the analysed particles for the different pollution levels and meteorological situations. In most of the cases modified sea-salt particles were observed in the fine (r<1 μm) and the coarse (r 1 μm) size ranges. In one sample taken in relatively clean air unmodified sea-salt particles were found in the coarse size range. The deficiency of Cl in the fine particles 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 modified sea-salt particles was proven by a nitrate test. In a polluted sample 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 particles in the modification of sea-salt particles along with heterogeneous reactions.