Impacts of land use and land cover changes on local meteorology and PM2.5 concentrations in Changchun, Northeast China

Land use and land cover (LULC) changes have a considerable influence on the surface energy balance, altering regional meteorology and air quality. However, this impact is not quantified in Changchun, an important city in the old industrial base of Northeast China. In this study, based on the Weather Research and ForecastingCommunity Multiscale Air Quality (WRF-CMAQ) model, the LULC2017 (LULC data in 2017) and LULC2001 (LULC data in 2001) scenarios were simulated for January and July 2017, respectively, to assess the impact of LULC changes on meteorology and fine particulate matter (PM2.5) concentrations in Changchun. The results show that the sensible heat flux in the urban expansion area (UEA) increased during the daytime, reaching a maximum value of 154 W/m(2) and 162 W/m(2), respectively, while the latent heat flux decreased during the daytime, reaching a maximum value of 22.84 W/m(2) and 180.75 W/m(2), respectively. Consequently, 2 m temperature (T2) increased by 4 degrees C and 3 degrees C, respectively; 10 m wind speed (WS10) increased by 1.05 m/s and 1.60 m/s, respectively; and planetary boundary layer height (PBLH) increased by 100 m and 117 m, respectively. These variations in meteorological factors can substantially impact the spatial distribution of air pollutants. In the UEA, PM2.5 concentrations decreased by 34 mu g/m(3) and 20 mu g/m(3) in January and July, respectively. The change in SO42- accounted for approximately 25% of the total concentration change of PM2.5, with a decrease of approximately 5-6 mu g/m(3) during the nighttime in January. Secondary organic aerosol (SOA) formed from biogenic volatile organic compounds (BVOC) precursors (BSOA) slightly decreased owing to the reduction in croplands dominated by green vegetation. Meanwhile, PM2.5 concentrations in the surrounding areas of the UEA increased significantly in January. The results of the process analysis based on the CMAQ model indicate that the main reason for the spatial variation of PM2.5 concentrations is the enhancement of transport and diffusion in the horizontal and vertical directions in the UEA. In January, the negative contribution of vertical advection (ZADV) and horizontal advection (HADV) processes to PM2.5 in the UEA increased by 25 mu g/m(3) and 40 mu g/m(3), respectively. Vertical diffusion (VDIF) process caused an increase in PM2.5 diffusion by 40 mu g/m(3) and 16 mu g/m(3) during the daytime and nighttime in the UEA, respectively. In July, the negative contribution of VDIF and HADV processes to PM2.5 increased by 40 mu g/m(3) and 32 mu g/m(3) during the nighttime in the UEA, respectively.