Identifying the dominant driver of elevated surface ozone concentration in North China plain during summertime 2012–2017

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.