Impacts of urban–rural disparities in the trends of PM2.5 and ozone levels in China during 2013–2019

Fine particulate matter (PM2.5) and ozone (O3) are two important pollutants in China. PM2.5 and O3 concentrations have changed significantly since 2013 because of the Clean Air Action in China. However, the trends in PM2.5 and O3 levels have potentially shown great urban–rural disparities. In this study, urban–rural disparities in PM2.5 and O3 concentration trends during 2013–2019 and their causes were analyzed based on observations from 1343 sites in China. For each site, we defined an urbanization-degree index (UD3) by calculating the urban-area pixel to total pixel ratio within a circular buffer area of 3 km. The PM2.5 decrease rates from 2013 to 2019 increased with increasing UD3 values, relating to greater emission declines in more urbanized areas compared with less urbanized areas. The daily maximum 8 h average O3 increase rates from 2013 to 2019 increased with the increasing UD3 values, relating to larger increases in volatile organic compound emissions and larger declines in NOx (NO + NO2) emissions over more urbanized areas than over less urbanized areas. The PM2.5 and O3 pollution levels were the worst over the Fenwei region, where the PM2.5 and O3 ranks both increased from 2015 to 2019. Our study indicates that urban–rural disparities in PM2.5 and O3 concentrations in China during 2013–2019 have decreased and increased, respectively. PM2.5 and O3 pollution in more urbanized areas were more severe than in less urbanized areas during 2013–2019. Therefore, the emission control strategy should continuously be made stricter for high urbanized areas.