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Aerosol-radiation feedback deteriorates the wintertime haze in North China Plain

Abstract. Atmospheric aerosols or fine particulate matters (PM2.5) scatter or absorb a fraction of the incoming solar radiation to cool or warm the atmosphere, decreasing surface temperature and altering atmospheric stability to further affect the dispersion of air pollutants in the planetary boundary layer (PBL). In the present study, simulations during a persistent and heavy haze pollution episode from 05 December 2015 to 04 January 2016 in the North China Plain (NCP) were performed using the WRF-CHEM model to comprehensively quantify contributions of the aerosol shortwave radiative feedback (ARF) to near-surface PM2.5 mass concentrations. The WRF-CHEM model generally performs well in simulating the temporal variations and spatial distributions of air pollutants concentrations compared to observations at ambient monitoring sites in NCP, and the simulated diurnal variations of aerosol species are also consistent with the measurements in Beijing. Additionally, the model simulates well the aerosol radiative properties, the downward shortwave flux, and the PBL height against observations in NCP during the episode. During the episode, the ARF deteriorates the haze pollution, increasing the near-surface PM2.5 concentration in NCP by 10.2 μg m−3 or with a contribution of 7.8 %. Sensitivity studies have revealed that high loadings of PM2.5 during the episode attenuate the incoming solar radiation down to the surface, cooling the temperature of the low-level atmosphere to suppress development of PBL and decrease the surface wind speed, further enhancing the relative humidity and hindering the PM2.5 dispersion and consequently exacerbating the haze pollution in NCP. The ensemble analysis indicates that when the near-surface PM2.5 mass concentration increases from around 50 to several hundred μg m−3, the ARF contributes to the near-surface PM2.5 by more than 20 % during daytime in NCP, substantially aggravating the heavy haze formation. However, when the near-surface PM2.5 concentration is less than around 50 μg m−3, the ARF generally reduces the near-surface PM2.5 concentration due to the consequent perturbation of atmospheric dynamic fields.
