The Behavior of Sea Salt Particle, Nitrate, and Sulfate in the Marine Atmosphere on the Two Remote Islands, Hachijo-jima and Chichi-jima

The marine aerosol was collected by Andersen sampler and two-stage filter sampler during January 13~20 and December 14~20, 1981 on the two remote islands, Hachijo-jima and Chichi-jima in order to investigate its size distribution and atmospheric concentration. The concentrations of Na+, Cl-, NO3-, and SO42-, in the marine aerosol were determined by ion chromatography. Sulfur dioxide in the marine atmosphere was collected with an alkali filter and also measured by ion chromatography. The size distributions of Na+ and Cl- in the marine aerosol had coarse mode and their modal diameter were 3~5 ¼m (Fig. 1). More than 85% of total Na+ and Cl- existed in coarse particles (>2 ¼m), which presumably originated from sea spray. The nitrate particle in the marine atmosphere was almost coarse and was different from the submieron nitrate usually observed in the urban air (Fig. 2), indicating that the reaction between sea salt particles and HNO3 vapor occured in the marine atmosphere. The size distribution of sulfate was bimodal, suggesting that coarse sulfate particles (>2 ¼m) were derived from sea spray and fine sulfate particle (<2 ¼m) were transported from polluted area (Fig. 2). The concentrations of nitrate, fine sulfate, and sulfur dioxide in marine atmosphere in Chichi-jima islands., 1000 km remote from Japan, were 0.14, 0. 36, and 0.20 ¼g/m3, respectively. These concentrations were concluded to be background levels in the marine atmosphere since they were 1/10~1/100 times lower than those in polluted Yokohama area. However these pollutant concentrations in the winter when the north-west seasonal wind blew were 2~4 times higher than the above background levels, and the migration of pollutants from the Japan islands to Chichi-jima was observed.