The synergetic control of NO2 and O3 concentrations in a manufacturing city of southern China

This study explored effective methods to control NO2 and O-3 concentrations in a manufacturing city, Foshan, in the Pearl River Delta (PRD) region. A "double high" pollution episode (i.e., both NO2 and O-3 concentrations exceeding the ambient air quality standards of China) was selected as a typical case to identify a collaborative control method for NO2 and O-3 by using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and the Empirical Kinetic Modeling Approach (EKMA). Considering the nonlinear relationship between O-3 and its precursors; we scaled down the volatile organic carbons (VOC) and NO2 emission inventories to investigate O-3 responses. The results showed that Foshan is VOC-sensitive and that the VOC-NOx reduction ratio more than 1:1 not only helped to steadily reduce O-3 concentrations but also to avoid an increase in NO2 concentrations. On-road and Non-road mobile sources and ports were found to be the dominant sources of NO2, while O-3 was mostly affected by organic solvents in Foshan. Controls on ports and the organic solvents are key to achieving a synergetic control of NO2 and O-3 pollution in Foshan. About 2.5% and 2.0% reduction in NO2 and O-3 concentrations, respectively, were found to require only a 3.6% reduction in NOx emissions from ports and a 10.6% reduction in VOC emission from organic solvents. In addition to the "double high" episode, this control scheme has been extended to verify the effects of NO2 and O-3 pollution controls under various synoptic weather conditions.