Abstract:
Atmospheric fine particulate matter (PM
2.5) and ozone (O
3) pollution are influenced by meteorological conditions and emissions from pollution sources. Based on the data from China’s national air quality monitoring stations and fifth-generation reanalysis data from the European Centre for Medium-Range Weather Forecasts, the relationships of atmospheric PM
2.5 and O
3 with major meteorological factors in typical cities in the Beijing–Tianjin–Hebei region, including Beijing, Tianjin, Baoding, and Shijiazhuang, during 2015–2021 were investigated in this study. Moreover, the contribution of emission reduction to the annual trend of PM
2.5 and O
3 was quantitatively evaluated using the random forest algorithm. Excluding summer, daily PM
2.5 was positively and negatively correlated with relative humidity and boundary layer height, respectively. Meanwhile, daily PM
2.5 was positively correlated with O
3 and temperature in summer. Combined with the analysis of the variation characteristics of meteorological conditions associated with different concentration levels of PM
2.5 and O
3, it was found that adverse atmospheric diffusion conditions primarily affected the individual pollution days in terms of PM
2.5 in winter and summer. On PM
2.5 and O
3 pollution days, strong atmospheric oxidation and high relative humidity conditions critically aggravated PM
2.5 pollution in winter, while high temperature and strong solar radiation were important meteorological conditions responsible for increased PM
2.5 and O
3 co-pollution in summer. Quantitative trend analysis revealed that emission reduction was the driving factor leading to the annual change in PM
2.5 and O
3, and the contribution to the annual decrease in PM
2.5 was 84%–95%. O
3 showed an increasing trend from 2015 to 2018 but decreased after 2018 (−3.4 to −6.4 µg m
−3 a
−1). Furthermore, the trend of O
3 was overall consistent with the difference between the observed value and the prediction value obtained from the random forest algorithm. The contribution of emissions in Tianjin, Baoding, and Shijiazhuang to the trends was 18%–34%, indicating that the recent emission reduction measures may have had a certain effect on controlling O
3 pollution.