Abstract
Abstract. Atmospheric aerosols 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 5 December 2015 to 4 January 2016 in the North China Plain (NCP) were performed using the Weather Research and Forecasting model with Chemistry (WRF-Chem) to comprehensively quantify contributions of aerosol shortwave radiative feedback (ARF) to near-surface (around 15 m above the ground 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 the NCP, and the simulated diurnal variations of aerosol species are also consistent with the measurements in Beijing. Additionally, the model simulates the aerosol radiative properties, the downward shortwave flux, and the PBL height against observations in the NCP well. During the episode, ARF deteriorates the haze pollution, increasing the near-surface PM2.5 concentrations in the NCP by 10.2 µg m−3 or with a contribution of 7.8 % on average. Sensitivity studies have revealed that high loadings of PM2.5 attenuate the incoming solar radiation reaching the surface to cool the low-level atmosphere, suppressing the development of the PBL, decreasing the surface wind speed, further hindering the PM2.5 dispersion, and consequently exacerbating the haze pollution in the NCP. Furthermore, when the near-surface PM2.5 mass concentration increases from around 50 to several hundred µg m−3, ARF contributes to the near-surface PM2.5 by more than 20 % during daytime in the NCP, substantially aggravating the heavy haze formation. However, when the near-surface PM2.5 concentration is less than around 50 µg m−3, ARF generally reduces the near-surface PM2.5 concentration due to the consequent perturbation of atmospheric dynamic fields.
Highlights
Atmospheric aerosols, produced both naturally and anthropogenically, influence the radiative energy budget of the Earth’s atmospheric system in many ways
We first define the base simulation in which aerosol shortwave radiative feedback (ARF) is considered, and results from fbase are compared to observations in the North China Plain (NCP)
The calculated temporal variations of aerosol species are consistent with the Aerosol Chemical Speciation Monitor (ACSM) measurement in Beijing, with regard to the simulation of sulfate, nitrate, and ammonium
Summary
Atmospheric aerosols, produced both naturally and anthropogenically, influence the radiative energy budget of the Earth’s atmospheric system in many ways. Wu et al.: Aerosol–radiation feedback deteriorates the wintertime haze altering atmospheric stability (e.g., Ackerman, 1977; Jacobson, 1998, 2002) They serve as cloud condensation nuclei (CCN) and ice nuclei (IN), modifying cloud optical properties and lifetime (e.g., Zhang et al, 2007; Li et al, 2008a, b, 2009). Among those impacts, the scattering and absorption of solar radiation by aerosols and the associated feedbacks (hereafter referred to as aerosol–radiation feedback or ARF) constitute one of the main uncertainties in climate prediction (IPCC, 2007), and substantially affect the atmospheric chemistry by perturbing the temperature profile and moisture, winds, and planetary boundary layer (PBL) stability (Boucher et al, 2013).
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