On the effectiveness of short-term intensive emission controls on ozone and particulate matter in a heavily polluted megacity in central China

Intensive temporary air pollution control measures were implemented in Zhengzhou (ZZ), a megacity in central China, and six neighboring cities during the 2019 National Games of Ethnic Minorities. The Community Multiscale Air Quality (CMAQ) model and a high-resolution local emission inventory were applied to evaluate the control measures. Reductions of similar to 35-60% of primary PM (PPM), 45-65% of VOCs, similar to 5% of NH3, 35-45% of NOx, and 30-70% of SO2 emissions in the central area (i.e., ZZ) and collaborative cities (i.e., the six neighboring cities) lead to significant reductions of daily PM2.5 by 25-45% in ZZ. Hourly concentrations of PM2.5 are reduced by as much as 100 mu g m(-3). Most of the reduction in PM2.5 is due to primary PM, and NO3-, SO42-, and NH4+ ion concentrations only decrease by 5-6%. Emission reductions in the collaborative cities contribute to 10-30% of the decrease in PM2.5 and PM10 in ZZ. Concentrations of daily maximum 8-hr (DM8H) O-3 increase by 2-5% on high O-3 days. Isopleth analysis suggests that the local molar reductions ratio of NOx to VOC needs to be < 0.5 to avoid the increases. More stable meteorology conditions make emission controls in ZZ more effective for PM2.5 and PM10 but lead to higher increases in DM8H O-3. These results suggest that control of PPM emissions in ZZ is the most effective in reducing PM2.5 and PM10. However, reductions of precursor gaseous in ZZ and the six neighboring cities alone are not effective in reducing the secondary PM components and most likely lead to increases in DM8H O-3.

Automated summary

Intensive temporary air pollution control measures in Zhengzhou and six neighboring cities during the 2019 National Games of Ethnic Minorities led to significant reductions in PM2.5, mainly due to reductions in primary PM emissions. The reductions in precursor gases were not as effective in reducing secondary PM components. Concentrations of daily maximum 8-hour Ozone increased on high O3 days, suggesting the need for a specific ratio of NOx to VOC reductions to avoid these increases.