Impacts of land use and land cover change on regional meteorology and air quality over the Beijing-Tianjin-Hebei region, China

The land use and land cover (LULC) change can modulate regional meteorology and consequently influence the air quality. This study incorporates two types of LULC data (representing early 1990s and most recent years respectively) into the Weather Research and Forecasting Model-Community Multiscale Air Quality (WRF-CMAQ) model to investigate the impacts of LULC change on the meteorology and air quality. The LULC change and associated parameters including land cover proportion, land surface albedo, roughness length result in some variations of surface energy balance, surface temperature, planetary boundary layer height (PBLH), surface wind speed and direction, which lead to domain-wide increases of 2-m temperature (T-2) (0.53-0.96 degrees C, 3.6-14.9%), PBLH (3.3-130 m, 3.5-38.3%) and decrease of 10-m wind speed (WS10) (0.12-0.47 m/s, 5.2-15.7%) in the urban. As a result, the concentrations of air pollutants are also affected by LULC change. It leads to a domain- wide decrease of PM2.5 in the urban. The reductions are more obvious during the rush hour in the morning and evening. The impacts of LULC change on O-3 vary in different seasons and cities. In Beijing, O-3 increases by 0.5-4.3 ppb during daytime in July. While in Tianjin, O-3 decreases by up to 3.4 ppb at noon. In summer, the change of O-3 is inversely corresponding to NOx change, which may be associated with the VOC-limited O(3 )chemistry in daytime and NOx titration at night in the urban. In winter, the change of O-3 is mainly related to the reduced radiation which is unfavorable for O-3 formation. Meanwhile, these changes of PM2.5 and O-3 are different under variable levels of air pollution. The largest reduction ratio of PM2.5 occurs at slightly-heavily polluted levels instead of severely polluted level, while the extent of O-3 increase becomes greater along with the aggravation of O-3 pollution.