The propagation of fog and its related pollutants in the Central and Eastern China in winter

A widespread dense fog event associated with heavy air pollution occurred in the central and eastern regions of China from 30 December 2016 to 5 January 2017. The fog event was characterized by three distinct propagation processes on different spatial scales. This study investigated the propagation of fog and variations of pollutants during the fog event in order to better understand the mechanisms of fog. The cold high-pressure system moved southward, and the southerly wind on the western flank of the high-pressure system enhanced the temperature inversion, both of which were favorable for fog propagation. In addition, the invasion of the weak cold air and radiative cooling, and the different land-sea thermodynamic properties also contributed to the formation and propagation of the fog. Heavy pollution related to this severe fog was also investigated. The field experiment indicates that amounts of aerosol particles accounted for the enhancement of fog droplets through its role of being the condensation nuclei. As a result, the PM(2.5 & nbsp;& nbsp;)concentration decreased when the fog became strong. The strong temperature inversion and gas to particle phase conversion led to an increase of the PM2.5 concentration and a decrease of pollution gases (SO2, NO2) concentration during the mature stage.