偏东风输送导致的关中地区冬季PM_(2.5)重污染个例研究

A Case Study of PM_(2.5) Heavy Pollution Caused by Easterly Wind Transport in Guanzhong Area in Winter

关中地区是我国大气污染的重点监测区域,为探究偏东风输送对关中地区冬季PM_(2.5)重污染的影响,重点分析了2018年1月12—18日在偏东风输送影响下关中地区ρ(PM_(2.5))日均值的变化过程;利用WRF和CAMx模式对PM_(2.5)重污染过程进行模拟并讨论其消长原因.结果表明:①冬季关中地区在高压脊和西南槽的控制下,偏东风将污染物输送至关中地区,加之关中地区地形阻滞,致使关中地区的ρ(PM_(2.5))上升.②研究期间,关中地区ρ(PM_(2.5))日均值范围为103~240μg m 3,偏东风输送是导致此次重污染过程的重要原因.重污染的发生还与气象要素的变化有关,其中ρ(PM_(2.5))日均值与气温、相对湿度均呈滞后相关性.在ρ(PM_(2.5))日均值相等的情况下,相对湿度越大,能见度越低;随着ρ(PM_(2.5))日均值和相对湿度的升高,能见度下降的速率逐渐变慢.③根据WRF-CAMx的模拟结果,此次重污染过程中关中地区PM_(2.5)污染输送关系不均衡,宝鸡市和咸阳市均以本地贡献为主,其本地贡献率超过45.00%,而渭南市接收关中地区其他城市及关中地区以外区域污染输送占比为69.82%;位于盆地中东部的咸阳市、西安市和渭南市的ρ(PM_(2.5))月均值均大于关中地区ρ(PM_(2.5))平均值;渭南市、西安市、运城市以及关中地区以外城市是此次关中地区跨市PM_(2.5)污染输送的主要来源.研究显示,偏东风输送是关中地区此次大气重污染过程的重要原因.

Guanzhong Area is the key monitoring area of air pollution in China.In order to explore the impact of easterly wind transport on PM_(2.5)heavy pollution in Guanzhong Area in winter,this study focuses on the analysis of the variation ofρ(PM_(2.5))in Guanzhong Area from January 12 th to 18 th,2018 under the control of easterly wind transport.The Weather Research and Forecasting Model(WRF)and Comprehensive Air quality Model with extensions(CAMx)are used to simulate PM_(2.5)pollution and determine the reasons for its growth and decline.The results show that:(1)In winter,under the control of the high-pressure ridge and the low-pressure trough,the pollutants are transported to Guanzhong Area by the easterly wind.Meanwhile,there is also the reason of terrain block,and finally the pollution concentration is increased in Guanzhong Area.(2)During the heavy pollution period,the daily meanρ(PM_(2.5))in the five cities of Guanzhong Area is between 103-240μg m 3,and the easterly wind transport plays an important role in the heavy pollution in winter.The occurrence of heavy pollution is also related to the change of meteorological elements,among whichρ(PM_(2.5))is related with temperature and relative humidity.In the case of the same concentration of PM_(2.5),the higher the relative humidity,the lower the visibility.With the increase ofρ(PM_(2.5))and relative humidity,the decline rate of visibility gradually slows down.(3)According to the simulation results of WRF-CAMx,the PM_(2.5)pollution transportation relationship is unbalanced among five cities in Guanzhong Area.The pollution of Baoji City and Xianyang City is mainly caused by local contributions,with the local contribution rate of more than 45.00%.Weinan City receives 69.82%of the pollution from other cities in Guanzhong Area and out of Guanzhong Area.The monthly averageρ(PM_(2.5))in Xianyang City,Xi′an City,and Weinan City,which are located in the middle and east of Guanzhong Area,is greater than the average value of Guanzhong Area.Weinan City,cities outside Guanzhong Area,Xi′an City,and Xianyang City are the main sources of cross-city PM_(2.5)pollution in Guanzhong Area.In conclusion,the easterly wind transport is the main cause of this heavy atmospheric pollution process in Guanzhong Area.