Heavy aerosol pollution episodes in winter Beijing enhanced by radiative cooling effects of aerosols

Heavy aerosol pollution episodes (HPEs) often occurred in winter Beijing, but precise causes of pollution-intensifying mechanisms are uncertain, particularly the feedback between aerosols and weather. Building on the surface and vertical observations in January 2013, February 2014, December 2015, and December 2016 to 10th January 2017, here we show aerosol's radiative cooling effects exert remarkable impacts on the local synoptic weather which further aggravates aerosol pollution. From clean stages to transport stages (TS) to cumulative stages (CS) in HPEs, surface direct and global radiation sharply diminish, with daily the cumulative sum of radiant exposure reduced by 89% and 56% respectively from clean stages to CSs. Due to the appreciably drop in surface radiation and favorable weak winds, from TSs to the earlier period in CSs to the later period, the temperature profile changes from nearly no inversion to a weak inversion to an anomalous inversion with the temperature difference over 4 °C from 200 to 600 m, which leads to PM2.5 and moisture accumulated in a very shallow BL with height ~200 m. Such a positive feedback is reinforced by high near-ground RH through accelerating liquid-phase and heterogeneous reactions and enhancing aerosol hygroscopic growth.