Distribution of PM 2.5, acidic and basic gases near highway in central Taiwan

Abstract

Particulate PM 2.5 and acidic gas samples were collected during two successive sampling periods at two different sampling sites namely, Nantou (near highway site) and Erlin (far highway site) of central Taiwan region. The distribution of PM 2.5, acidic and basic gases was assessed simultaneously in both the sampling sites using annual denuder system. Chemical species of PM 2.5 analyzed included NO 3 −, SO 4 2−, NH 4 +, Cl −, Ca 2+, K + and Na + and gaseous HNO 2, HNO 3, HCl, SO 2 and NH 3. Data on NO, NO 2, CO and meteorological parameters were obtained from air quality monitoring station, Environmental Protection Agency (EPA), Taiwan. Time-weighted mean concentration model was used to investigate the pollutant sources. In addition, formation of nitrate aerosols from NO 2 was discussed. The PM 2.5 concentrations were 41.1 and 32.9 μg m − 3 at near and far highway sites respectively. The average concentration of three main ionic species SO 4 2−, NO 3 − and NH 4 + accounted to 44% for PM 2.5 indicating that the formation was mainly via secondary process. The PM 2.5, HNO 3, NO 3 −, NO, NO 2 and CO were highest at near highway site compared to far highway site. Based on the results of this study we conclude that, higher traffic emissions coupled with poor ventilation due to topography of the area caused increased HNO 3, NO 3 −, NO, NO 2 and CO concentrations in near highway site.