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The formation of nitrate and sulfate on coarse particles and its relationships with meteorological conditions and relative abundance of sea-salt and soil particles were studied. Size distributions of particulate SO ²⁻₄, NO ⁻₃, NH ⁺₄, Cl⁻, Na⁺, K⁺, Mg²⁺ and Ca²⁺ were measured using a MOUDI cascade impactor for 11 days in July to December 1997 at a coastal site in Hong Kong. Most of the nitrate and a small fraction of sulfate were distributed in the coarse mode. Since Hong Kong is influenced by both marine and continental aerosols, the distribution of coarse mode nitrate and sulfate depends on the weather conditions. Evidence of nitrate formation on both sea-salt and soil compounds was found in this study. Chloride depletion of sea-salt by both nitrate and sulfate formation was also observed. When Hong Kong was under prevailing easterly wind accompanied with high relative humidity, Na⁺ was the dominant …