The Transport Of Pollutants Over Complex Terrain:a Numerical Simulation Research

A field experiment was conducted about the atmospheric aerosol and the microscopic properties of cloud/fog in order to establish the relationship between aerosol and CCN at Guangmingding of Huang Mountain from April to September2008. The diurnal variation of the top of mountain of aerosol number concentration is different from the plains. In this study, trace gas is added in WRF-Chem to explain the variation of aerosol. The main conclusion is:In sunny day, the pollution is brought to the upper of boundary layer by valley wind in the daytime leading to elevated pollution layer. Some pollutants is carried down to the surface by mountain wind at night and accumulates in the boundary layer. The mountain and valley breeze is weak at cloudy days so that the diurnal variation of boundary layer plays a major role in the vertical transport of pollution. The mountain and valley wind carries large quantities of precursors up to the top of mountain in sunny day. A large number of new particles is formed while there is enough illumination which leads to increase of aerosol number concentration at midday. The strength of vertical component of the mountain and valley wind is greater than the diffusion of boundary layer. The concentration of NO at Guangmingding grow faster and be higher in sunny day.Abnormal high mass concentration of aerosol exists in some period which may be influenced by the long-distance transport. In this study the real emission source is used to analyze the impact of long-distance transport on concentration of pollutant at Huang Mountain. The main conclusion is:There was an evident event of long-distance transport at April22-23,2008. The pollution from North China is transported to the south. When airflow moves over the mountain, the pollutions is delivered into two parts, with the first carried to Fujian and Taiwan and the second carried to Hubei and Hunan provinces. The pollutions is also blocked by mountain. The pollutant is always confined below3km because of the boundary layer. When the pollutant is blocked by mountain, it climbs the terrain and enters into the free atmosphere. This part of pollution enters into the free atmosphere and affects other region by long-distance transport. EC, NO3-and NH4+have good correlativity with PM2.5. SO42-is mainly from new particle formation and the long-distance transport has little influence. Cities have different contribution to the PM2.5of Huang Mountain in the different meteorological field:in this simulation, although the emission of Shijiazhuang is less than the other cities, it has the biggest influence on the the PM2.5at Huang Mountain; The local source of Huang Mountain has a small effect.