Impacts of Changes in Land Use and Land Cover Between 2001 and 2018 on Summertime O3 Formation in North China Plain and Surrounding Areas–A Case Study

Changes in land use and land cover (LULC) influence meteorological fields and biogenic emissions, further affecting the atmospheric chemistry and air quality. Combining the satellite measurements and WRF-Chem model simulations, we evaluate the impacts of the LULC change between 2001 and 2018 on the summertime ozone (O-3) formation in North China Plain and surrounding areas (NCPs). Satellite measurements have revealed that from Taihang to Yanshan Mountain, the fraction of broadleaf and needle forest coverage has increased by 5%-20% and the urban area has increased by up to 25% in the NCP. Additionally, the vegetation density has increased significantly in the NCPs except for urban areas. The LULC change generally enhances biogenic volatile compounds emissions in the NCPs, particularly over Taihang and Yanshan mountain, but the O-3 variation is divergent. The maximum daily 8-ihr average (MDA8) O-3 concentrations are reduced by 1%-7% over Taihang and Yanshan Mountain because the raised vegetation density increases O-3 dry deposition velocity to accelerate the O-3 loss. The raised vegetation density enhances the evapotranspiration to decrease the near-surface temperature by 0.1 degrees C-1.5 degrees C, which also generates a divergence in the low-level atmosphere in the NCPs, causing secondary northerly or easterly winds in the NCP. The O-3 enhancement along the coastal areas of the NCP is attributed to the perturbation of wind fields and photolysis induced by the LULC change. The divergent variation of the MDA8 O-3 concentrations in the NCP is generally caused by the variations of biogenic emissions and photolysis.