This study involved sampling over 1 year of data on exposure to acid aerosols in the geothermal area of metropolitan Taipei. The temporal and spatial variations of the concentrations of acid aerosols were assessed by sampling at three sites: A, B, and C. Results indicate that the SO2 concentrations lead the concentrations of other acid aerosols at site C because two active fumaroles surround this site. The mean SO2 concentrations at sites A, B, and C were 2.4, 2.4, and 6.2 ppb. Previous studies have found that H2S levels were highest at site C. However, the SO4(-2) and H+ concentrations among the three sites were similar. The mean aerosol SO4(-2) concentrations were 7.0, 5.7, and 5.7 microg m(-3) at sites A, B, and C, respectively; their H+ concentrations were 5.5, 4.2, and 5.4 nmol m(-3). No seasonal variations are observed for most of the acid aerosols in the geothermal area except that the types of hot spring affect the SO4(-2) concentration nearby. The different seasonal fluctuation among the sites reflect the determinant of SO4(-2) emission from different geothermal sources. Sulfur-rich aerosols and some SO2 emitted from geothermal sources are obvious. The predominance of nitrogen-containing gases (sum of NO2 + HNO2 + HNO3) over SO2 indicates the importance of the anthropogenic origin of emissions. The effect of multiple exposures to sulfur-rich aerosol (including H2S, SO2, and SO4(-2)), H+, and nitrogen-containing aerosols on the health of nearby residents warrants concern.