沈阳市一次PM2.5污染天气过程成因分析

利用气象与环境监测数据,对沈阳市2015—2018年PM_2.5的污染事件、浓度变化特征和污染物相关性进行分析;并利用WRF-Chem模式、HYSPLIT模型,从气象要素、高空环流形势和污染传输特征等方面对沈阳市2018年一次污染天气过程进行分析。结果表明:PM_2.5月浓度变化呈冬季>春季>秋季>夏季的“V”形特征,日浓度变化呈“双峰”特征。相关性分析显示,气温(-0.3666)和相对湿度(-0.1158)是影响PM_2.5浓度主要的气象因子,PM₁₀(0.9964)和NO₂(0.7242)是影响PM_2.5浓度的主要污染物。2018年1月26—28日沈阳地区出现了一次持续重污染过程,在重污染开始过程中,高空环流平直,浅槽前暖平流占主导地位,地面为弱高压均压场控制,地面风速以静小风为主,风场辐合,气象条件有利于污染物积聚。在重污染发展的过程中,地面相对湿度增大有利于颗粒物吸湿增长,贴地和高空逆温层厚度较大,污染加剧。在重污染减弱的过程中,逆温层消失,大气层结稳定,垂直扩散条件变好。“静稳”气象条件下本地污染物以及外部传输的积累是导致沈阳市此次重污染过程的主要原因。

CAUSE ANALYSIS OF A HEAVY PM2.5 POLLUTION PROCESS OCCURED IN SHENYANG

Using meteorological and environmental monitoring data, the pollution events, concentration variation characteristics and pollutant correlation of PM_2.5 in Shenyang from 2015 to 2018 were analyzed. Using WRF-Chem and HYSPLIT model, a pollution process in Shenyang in 2018 was analyzed from the aspects of meteorological elements, high-altitude circulation situation and pollution transmission characteristics. The results indicated that the monthly concentration showed the characteristics of V-shaped, with a sequence of winter>spring>autumn>summer, and the daily concentration showed the characteristics of double peak. Correlation analysis showed that temperature(-0.3666) and relative humidity(-0.1158) were the main meteorological factors affecting PM_2.5 concentration, while PM₁₀(0.9964) and NO₂(0.7242) were the main pollutants. From January 26th to 28th in 2018, a heavy pollution process occurred in Shenyang. At the beginning of the pollution, the high-altitude circulation was flat, the warm advection in front of the shallow trough was dominant, the ground was controlled by a weak high-pressure pressure equalizing field, the ground wind speed was dominated by the static and light wind, and the wind field convergence was conducive to the accumulation of pollutants. In the development process of pollution, the increase of ground relative humidity was conducive to the growth of particle moisture absorption; the thickness of ground and high-altitude inversion layer were large, and then the pollution was intensified. In the weakening process of pollution, the inversion layer disappeared, the stratification was stable, and the vertical diffusion conditions turned better. The accumulation of local pollutants and external transmission under static and stable meteorological conditions were the main reason of the heavy pollution.