Impacts of Anthropogenic Atmospheric Pollutant on Formation and Development of a Winter Heavy Fog Event

The WRF/Chem model coupled with local anthropogenic atmospheric pollution emissions and fog observational data were used to assess the effects of human-induced pollutants on a heavy fog event on 1 Dec 2009 in North China and East China. The experiments with and without anthropogenic emissions were designed and conducted. The results suggest that the simulated fog distribution and intensity with anthropogenic emission are closer to observed ones. The polluted atmospheric boundary condition is found to create a favorable condition for fog formation, increasing the fog area up to 50%, the intensity of 5 times in maximum, and the duration of 1.5 h on average. Compared with that under clean air condition, the number concentration of fog condensation nuclei (FCN) is much higher in polluted air, which causes a higher fog droplet number concentration, and influences the processes of droplet condensation, long wave radiation, turbulent motion, and provides the favorable dynamic and thermal boundary conditions for fog development. The secondary aerosols produced by trace gases SO₂, NO_x, and NH₃ make great influence on the formation and development of fog, and the averaged liquid water content has a decrease of 32%, without these trace gas emission.