Distribution of PM2.5, acidic and basic gases near highway in central Taiwan

Particulate PM2.5 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 PM2.5, acidic and basic gases was assessed simultaneously in both the sampling sites using annual denuder system. Chemical species of PM2.5 analyzed included NO3−, SO42−, NH4+, Cl−, Ca2+, K+ and Na+ and gaseous HNO2, HNO3, HCl, SO2 and NH3. Data on NO, NO2, 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 NO2 was discussed. The PM2.5 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 SO42−, NO3− and NH4+ accounted to 44% for PM2.5 indicating that the formation was mainly via secondary process. The PM2.5, HNO3, NO3−, NO, NO2 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 HNO3, NO3−, NO, NO2 and CO concentrations in near highway site.