Characteristics of acid aerosols in the geothermal area of metropolitan Taipei, Taiwan

To our knowledge, the characteristics of acid aerosols from sulfur-rich geothermal emissions and human activity have not been reported. This study determines the ambient air concentrations of such chemical components as H₂S, SO₂, HONO, HNO₃, NO₂^-, NO₃^-, SO₄^2- and H⁺ in the geothermal area of metropolitan Taipei. Acid aerosols were sampled using a honeycomb denuder/filter pack sampling system (HDS). The highest H₂S concentration was 680.7ppb and the mean was 185.7ppb at the geothermal sampling site. Very high sulfate concentrations (mean concentration higher than 10μgm^-3) were also observed. The spatial variations are typical of sulfur-containing compounds and H⁺ aerosols; both have concentrations higher closer to the source of geothermal emissions. The daytime means of acid aerosols are generally higher than the corresponding nighttime values. Geothermal emissions, automobile combustion sources and photochemical reactions are concluded to dominate the characteristics of acid aerosols in the studied area. Direct emissions of SO₄^2- and H⁺ with geothermal steam must be further clarified.