Multi-scale analysis of the impacts of meteorology and emissions on PM2.5 and O3 trends at various regions in China from 2013 to 2020 3. Mechanism assessment of O3 trends by a model

A multiscale analysis of meteorological trends was carried out to investigate the impacts of the large-scale circulation types as well as the local-scale key weather elements on the complex air pollutants, i.e., PM2.5 and O-3 in China. Following accompanying papers on synoptic circulation impact and key weather elements and emission contributions (Gong et al., 2022a; Gong et al., 2022b), an emission-driven Observation-based Box Model (e-OBM) was developed to study the impact mechanisms on O-3 trend and quantitatively assess the effects of variation in the emissions control over 2013-2020 for Beijing, Chengdu, Guangzhou and Shanghai. Compared with the original OBM, the e-OBM not only improves the performance to simulate the hourly O-3 peak concentration in daytime, but also reasonably reproduces the maximum daily 8-hour average (MDA8) O-3 concentrations in the four cities. Based upon the sensitivity experiments, it is found that the meteorology is the dominant driver for the MDA8 O-3 trend, contributing from about 32% to 139% to the variations. From the mechanistic point of view, the variations of meteorology lead to the enhancement of atmospheric oxidation capacity and the acceleration of O-3 production. Further evaluation to the emission changes in four cities shows that the O-3-precursors relationships of the four cities have been changed from the VOC-limited regime in 2013 to the transition regime or near-transition regime in 2020. Though the NOx/VOCs ratios have been obviously decreased, the emission reductions up to 2020 were still not enough to mitigate O-3 pollution in these cities. It is emphasized in this study that the strengthened control measures with maintaining a certain ratio of NOx and VOCs should be implemented to further curb the increasing trend of O-3 in urban areas.

Automated summary

A multiscale analysis was conducted to investigate the impacts of large-scale circulation types and local-scale key weather elements on complex air pollutants in China. An emission-driven Observation-based Box Model (e-OBM) was developed to study the impact mechanisms and assess the effects of emission control in four cities. The results showed that meteorology was the dominant driver for the trend of ozone (O-3) and the current emission reductions were not enough to mitigate O-3 pollution.