西安市"阶梯型"持续污染过程演变及PM_2.5区域输送分析

In order to explore the dynamic evolution of the step-type continuous pollution process in Xi'an during November 2016, the NCEP reanalysis data was used to analyze the evolution of the weather situation from November 7th to 22nd, 2016. The regional transport and the changes of the chemical composition of atmospheric particles during the evolution of the "stepped" are analyzed by combining the CAMx-PSAT model and the online monitoring data of chemical composition. The results suggest that: ①Due to the special basin topographical factors and unique weather situation changes in Xi'an, the characteristic of the "stepped" pollution process has been "valley-peak-peak-peak-valley" time-series changes. The three rising stages thereof with the evolution of the weather situation is mainly "high-pressure ridge-Inner Mongolia low-pressure moved eastward-saddle field". ②In the process of " stepped " evolution, there are three main transportation channels of PM_2.5: northeast transport, north transport, and east transport. The northeast transport comes from Weinan, Yuncheng, Luoyang, Linfen, Luliang, and Jinzhong accounting for about 45%. The northerly transport is mainly local accumulation and Xianyang transport, accounting for about 90% of PM_2.5. To the east transport, the main cities are Weinan, Yuncheng, Luoyang and other regions, peaking at around 70%. ③ During the period of peak pollutant concentration in the three rising stages, the secondary inorganic salt SNA accounted for 50%, 41%, and 52% of PM_2.5, respectively, wherein the second conversion of pollutants was the most intense in the third rising stage. Studies have shown that the evolution of the " stepped " pollution in Xi'an is caused by both the unique topography and changes in weather conditions. There are different variation rules for regional transport and chemical composition of the "stepped" pollution process as well.