Impacts of anthropogenic aerosols on the Formation and Development of Fog in North China Plain

North China Plain (NCP) is one of the most populated and polluted regions in China. A long-term record of fog duration and visibility in the past 46 yrs (from 1960 to 2005) in Beijing is analyzed in this study. The results show that the average duration of fog has increased from 3.9 hrs before 1990 to 6.2 hrs after 1990 and the frequency of occurrence of low visibility fog (VIS<1 km) is much higher than relative clean period which before 1980. In order to better understand the impact of aerosols on the formation and development of fog in NCP, the WRF/Chem Model coupled with local anthropogenic atmospheric pollution emissions were used. Different aerosol scenarios are considered in WRF/Chem model experiment, including ‘Low' and ‘Typical' aerosol conditions. The simulated temporal evolution of boundary profile and PM2.5 concentration in the ‘Typical' experiment are in agreement with the measurements. The results of simulation suggest that increasing concentration of aerosols can lead to an enhancement of fog in region, intensity and duration. The polluted atmosphere is found to create a favorable condition for fog formation, increasing the fog area up to 20%, the intensity up to 40% in maximum, and the duration of nearly 1h in average. Comparing with low aerosol condition, the number concentration of fog condensation nuclei (FCN) is much higher in heavy aerosol loading, which causes higher fog droplet number concentration and smaller droplet radius, influences the processes of droplet condensation, long wave radiation, turbulent motion, and provides the favorable dynamic and thermal boundary conditions in fog development period.