Observational Analysis And Numerical Simulation Of A Pollution Transport Process In Beijing In Winter

In recent decades,with the rapid industrialization and urbanization,serious air pollution problems have appeared in many cities in China.In this paper,a serious pollution case of PM2.5in Beijing in 2016/2017,which is the most polluted winter since the"ten air regulations"was published,was selected as the research object.The hourly concentration observation data of PM2.5,SO₂ and other gas pollutants and meteorological elements data of 35 ground observation points in Beijing were used to analyze their characteristics,and the process was numerically simulated by WRF-Chem The characteristics of advection transport and the influence of Yanshan and Xishan mountains on PM2.5 were analyzed.Through the observation and analysis,we found that:（1）PM2.5 and CO exceeded the standard in this pollution process.PM2.5 of all observation points in Beijing has reached the level of severe pollution,and even reached the level of severe pollution in the southern border observation points.Only 5 stations had mild pollution of CO hourly concentration.（2）The PM2.5 hourly concentrations in southern Beijing,central Beijing and northern Beijing began to increase in turn,and the high concentration stage also began in this order.The duration of high concentration maintenance decreased in this order,and the time sequence of concentration decrease was opposite.（3）The PM2.5 concentration of the three regional points in the south of Beijing increased significantly when the south wind was prevailing,the PM2.5 concentration of the three regional points in the north of Beijing decreased significantly when the prevailing south wind turned to the north wind.There is no clear relationship between PM2.5concentration and wind direction in the main urban area.The numerical simulation of this case shows that:（1）the maximum transportation height of PM2.5 to Beijing through the south boundary of Beijing is about 600 m（ASL）.（2）The northward transportation of PM2.5 can be blocked by Yanshan mountain to increase the concentration on the windward side,and it can also increase the concentration on the leeward side after climbing the mountain.（3）There are two ways to be blocked by Yanshan mountain:one is that the PM2.5 is transported from the ground to the foot of the mountain is blocked;the other is that when there is downhill wind at night,some of the PM2.5 transported from the air to Yanshan will be transported to the foot of the mountain with the downhill wind,and then to the south of Yanshan in Beijing.The effect of Xishan is similar to Yanshan.（4）In the east boundary of Beijing,PM2.5 is transported into Beijing near the ground,while it is exported from the air below 2000m.When PM2.5 transported from the east boundary near the surface meets the west mountain climbing,it is found that the air rises vertically to reduce the pollutant concentration on the mountain slope.（5）The total amount of PM2.5 transported into Beijing from the east boundary of Beijing is far less than that from the south boundary.