Concentrations of H 2O 2 and HNO 3 and O 3–VOC–NO x sensitivity in ambient air in southern Taiwan

The gaseous concentrations of hydrogen peroxide (H 2O 2) and nitric acid (HNO 3) were measured at two sites in Kaohsiung City and two sites in Pingtung County, on three days in autumn, winter and spring during 2002–2003. The mean H 2O 2 concentrations were 1.76–1.79 ppbv at Nan-Chie and Hsiung-Kong in Kaohsiung City and 1.40–1.76 ppbv at Pingtung and Chao-Chou in Pingtung County. Meanwhile, the mean concentrations of HNO 3 were 6.11–7.79 ppbv in Kaohsiung City and 3.78–4.92 ppbv in Pingtung County. The hourly data were then used to evaluate VOC and NO x sensitivity of ozone (O 3) formation. The threshold values of either H 2O 2/HNO 3=0.3–0.6 or O 3/HNO 3=12–16 indicate that VOC-sensitive chemistry were dominant at Nan-Chie, Hsiung-Kong, and Pingtung in all three seasons; while VOC-sensitive chemistry was dominant at Chao-Chou only in winter, but NO x -sensitive chemistry was dominant in spring. The VOC-sensitive and NO x -sensitive regimes determined using the indicator ratios agree well with those obtained from the SPM (smog production model) using threshold value E (extent of reaction)=0.6–0.8.