Identifying the dominant driver of elevated surface ozone concentration in North China plain during summertime...

The increasingly serious surface ozone (O₃) pollution in North China Plain (NCP) has received wide attention. However, the contribution of the changes for each emission source to the elevated O₃ concentration, as well as the direct and indirect effect of meteorological condition variation on increased O₃ level have not been comprehensively analyzed. This study applied the Community Multiscale Air Quality (CMAQ) model coupled with the integrated source apportionment method (ISAM) to quantify changes in daily maximum 8-h average O₃ concentration (MDA8 O₃) under different air pollutants emissions and meteorological conditions during summertime 2012-2017. The results showed that incoordinate NOx/VOC emission control sustainably increased MDA8 O₃ by 2.2-36.2 μg/m³ in the NCP, of which emission changes from industrial and transportation sectors were the predominant contributors (-0.6-19.5 μg/m³ for industrial sector and 1.2-18.1 μg/m³ for transportation, respectively). In contrast, MDA8 O₃ decreased by 2.5-9.2 μg/m³ for the power plants. The effect of changes in meteorological condition on MDA8 O₃ exhibited significantly spatial and temporal variation and unfavorable meteorological fields were shown in 2014, 2016, and 2017, which enhanced MDA8 O₃ by -2.5-23.1, -5.3-20.7, and -7.2-25.8 μg/m³, respectively. In addition, the changed meteorological factors indirectly affected the biogenic emission thus prompting the increases of MDA8 O₃ by -3.9-4.9 μg/m³ in the NCP during 2012-2017. The sensitive simulations suggested that more aggressive control measures about VOC reduction in industrial and transportation sectors should be implemented to further mitigate the O₃ pollution under unfavorable meteorological condition.