Analysis of Meteorological Transport Conditions and Daily Variation Characteristics of PM 2.5 Heavy Pollution Process in Hubei Province during the Winter of 2015
PM2.5 pollution remains the primary type of winter air pollution in Hubei Province, with obvious regional transmission characteristics. The meteorological conditions for air pollution during heavy pollution processes are different from those in North China, and are worth paying attention to. Using simulation results under different emission scenarios of WRF/Chem and combined with observation analysis, the meteorological transport conditions and daily variation characteristics of the PM2.5 heavy pollution process in Hubei Province from December 2015 to January 2016 were studied. The processes of horizontal transport, suspended aggregation, and downward transport of foreign pollutants were analyzed from the perspective of large-scale transport conditions and local boundary layer dynamics, and the meteorological causes of the observed afternoon PM2.5 concentration special peak in the region were explained. The results show that the outbreak of heavy pollution in Hubei is mainly caused by regional transmission. The ground observation PM2.5 extreme value corresponds to a wind speed of 8-10 m/s at 10 meters, and the boundary layer 0-1 km is a strong northerly wind transport. The extreme value of pollution transfer flux is located near a height of 400 meters, which is an important transmission channel. There is no obvious inversion in low altitude, and the heavy pollution process has "non-stationary" boundary layer meteorological characteristics. The large-scale transportation conditions for the formation of heavy pollution are as follows: abnormally strong northerly winds in the middle and lower reaches of the Yangtze River and the northern region, slow wind speeds in the southern region, causing pollutants to accumulate in the middle reaches of the plain. The higher the wind speed at the northern boundary of Hubei, the more favorable the growth of pollution transportation. Transmission pollution mainly comes from the transportation of pollution sources in the north and northeast directions, with potential source areas contributing mainly to the Yuzhong and Nanyang basins and Guanzhong regions passing through the north passage, as well as some areas such as Shandong, Anhui, and Jiangsu passing through the northeast passage. The weather causes of the bimodal structure of daily variation of PM2.5 concentration are different. The peak at 21-24 hours (Beijing time) is static pollution, and the peak at 11-14 hours is transport pollution. The transport of pollution is influenced by the height of the atmospheric boundary layer. Before sunrise, the height of the atmospheric boundary layer is relatively low, and the stratification is stable and accompanied by upward movement, causing low-level external transport to suspend and gather near a height of 400 meters; After sunrise, as the height of the atmospheric boundary layer increases, the static stable stratification is disrupted, and under the action of dry deposition, high concentration PM2.5 begins to transport downwards, forming a peak on the ground in the afternoon.
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