Significant land cover change in China during 2001-2019: Implications for direct and indirect effects on surface ozone concentration.

China has become one of the most prominent areas of global land cover change during the past few decades. These changes can directly influence meteorological parameters thus further regulating tropospheric ozone (O) formation. Moreover, changes in biogenic emissions due to land cover variation can also have an indirect effect on O concentration. This study applied the Community Multiscale Air Quality model to comprehensively evaluate the impacts of significant land cover change on O levels in China during summertime between 2001 and 2019. The results showed that the daily maximum 8-h average O concentration (MDA8 O) increased by 3.6-8.9 μg/m, 2.8-8.0 μg/m, 3.8-9.6 μg/m, -1.5-6.2 μg/m, and -0.6-2.5 μg/m in Beijing-Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta, Sichuan Basin, and Fenwei Plain, respectively, in response to land cover variation. The research identified that the direct effect was the primary factor in raising O levels which mainly altered O concentration by changing vertical import and dry deposition velocity. Moreover, land cover variation tended to decrease biogenic nitric oxide emission and increase biogenic volatile organic compounds emission on the whole, and cause an obvious increase of MDA8 O by 1.8-4.9 μg/m in Pearl River Delta due to the indirect effect. This study offered valuable insights into the impacts of land cover change on O levels, highlighting the need for policymakers to consider land cover variation on air pollutants concentration for devising comprehensive multi-pollutant control strategies.