Aerosol-radiation interaction and its variation in North China within 2015–2019 period under continuous PM2.5 improvements

Abstract

A study was conducted on aerosol-radiation interactions over six cities in this region within the 2015–2019 period. WRF-Chem simulations on 2017 showed that based on the six-city average, the aerosol load (PM2.5 concentrations) of 121.9, 49.6, 43.3, and 66.3 µg/m3 in January, April, July, and October, mainly lowered the level of downward shortwave radiation by 38.9, 24.0, 59.1, and 24.4 W/m2 and reduced the boundary layer height by 79.9, 40.8, 87.4, and 31.0 m, via scattering and absorbing solar radiation. The sensitivity of meteorological changes to identical aerosol loads varied in the order July > January > October and April. Then, the cooling and stabilizing effects of aerosols further led to increases in PM2.5, by 23.0, 3.4, 4.6, and 7.3 µg/m3 respectively in the four months. The sensitivity of the effect of aerosols on PM2.5 was greatest in January rather than in July, contrary to the effect on meteorology. Moreover, a negative linear relation was observed between daily BLH reductions and aerosol loads in fall and winter, and between PM2.5 increases and aerosol loads in all seasons. With the PM2.5 pollution improvements in this region, the aerosol radiative forcing was effectively reduced. This should result in daily BLH increases of 10–24 m in fall and winter, and the estimates in Beijing agreed well with the corresponding results based on AMDAR data. Additionally, the reduction in aerosol radiation effects brought about daily PM2.5 decreases of 1.6-2.8 µg/m3, accounting for 7.0%–17.7% in PM2.5 improvements.