Characteristics of atmospheric aerosol and acidic gases from urban and forest sites in central taiwan.

Measurements of atmospheric fine aerosols, acidic gases and ammonia were made at National Chung Hsing University (Urban) and Huisun forest area (Forest) sites in central Taiwan region during October (highest ozone month). Annular Denuder System (ADS) was used for sampling gaseous (nitrous acid, nitric acid, sulfur dioxide and ammonia) and fine aerosol species (ammonium, nitrate and sulfate). The results showed a significant diurnal variation in nitrous acid and nitric acid concentrations. Nitric acid was produced primarily during daytime in both sites. In the urban site, the average concentration of nitric acid during daytime was 5.8 times higher compared to nighttime while the average nitrous acid concentration during daytime was lower compared to nighttime, due to the photo-dissociation of nitrous acid. Sulfate, nitrate and ammonium were the major constituents of PM(2.5). Higher concentrations of nitrous acid, nitric acid, particulate nitrate and ammonium were recorded at urban site.