Concentrations of H2O2 and HNO3 and O3–VOC–NOx sensitivity in ambient air in southern Taiwan

The gaseous concentrations of hydrogen peroxide (H2O2) and nitric acid (HNO3) 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 H2O2 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 HNO3 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 NOx sensitivity of ozone (O3) formation. The threshold values of either H2O2/HNO3=0.3–0.6 or O3/HNO3=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 NOx-sensitive chemistry was dominant in spring. The VOC-sensitive and NOx-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.