Role of photoexcited nitrogen dioxide chemistry on ozone formation and emission control strategy over the Pearl River Delta, China

A new hydroxyl radical formation pathway via photo-excited nitrogen dioxide chemistry is incorporated into a chemistry-only box model as well as a 3D air quality model to examine its potential role on ozone formation and emission control strategy over the Pearl River Delta region in China. While the box model results suggest that the photo-excited nitrogen dioxide chemistry can substantially enhance ozone at high NOx and VOC concentrations, results of 3D air quality model show only a moderate increase in ozone. Though the photo-excited nitrogen dioxide chemistry enhances ozone by a maximum of 10 ppbV over the urban area in the vicinity of abundant NOx and VOC concentrations, its typical enhancements range between 2 and 3 ppbV. It enhances ozone within the entire planetary boundary layer under conditions featured in weak synoptic wind, abundant water vapor and strong land-sea breeze circulation. No significant improvement in model performance statistics for ozone is found with the photo-excited nitrogen dioxide chemistry. The photo-excited nitrogen dioxide chemistry marginally changes ozone responses to NOx and VOC emission controls.