2018年汾渭平原及其周边地区大气颗粒物的传输特征

Transport characteristics of atmospheric particulates in Fenwei Plain and its surrounding regions in 2018

煤炭产业的集中使汾渭平原及其周边地区成为中国大气污染新高地.本研究基于FLEXPART-WRF模式,数值模拟了2018年三门峡、西安和郑州粒子逐日72 h后向轨迹,并利用停留时间分析方法(RTA)分析了在不同城市、不同季节和不同污染程度的情况下大气颗粒物在水平和垂直方向的传输特征.结果表明,秋冬季汾渭平原及其周边地区存在偏西和偏东北两条主要的传输路径,偏西路径是源自关中平原西部的粒子沿秦岭向东的传输,偏东北路径为来源于京津冀及其周边地区的粒子沿太行山向西南的传输.由于地形等因素的影响,到达西安的粒子水平传输距离最短,其次是三门峡,到达郑州的粒子传输距离最长,重污染期间三门峡的垂直传输高度最高,其次是西安,郑州最低.秋冬季重污染期间汾渭平原及其周边地区水平传输距离r≤100 km,垂直传输高度在300 m<h≤900 m的粒子占主导,春季重污染期间传输距离r≤200 km,垂直传输高度在300 m<h≤900 m的粒子占主导.2017年和2018年重污染期间,粒子穿越边界层的概率偏低.

The concentration of coal industry makes Fenwei Plain and its surrounding regions become a new high-value area of air pollutant concentration in China.Based on the FLEXPART-WRF model,this study simulated the 72 hour backward trajectory of air particulates in Sanmenxia,Xi′an and Zhengzhou in 2018,and the transport characteristics of atmospheric particulates in horizontal and vertical directions in different cities,different seasons and different pollution degrees were analyzed by using residence time analysis(RTA).The results showed that,there were two main transport paths in Fenwei Plain and its surrounding regions in autumn and winter,the westward path was the transport of particulates from the west of Guanzhong Plain to the east along the Qinling Mountains,and the northeast path was the transport of particulates from Beijing-Tianjin-Hebei and its surrounding regions along the Taihang Mountain to the southwest.Due to the influence of topography and other factors,the horizontal transport distance of particulates arriving in Xi′an was the shortest,followed by Sanmenxia,and the longest was Zhengzhou.The vertical transport height of Sanmenxia was the highest during heavy pollution,followed by Xi′an and Zhengzhou.During the period of heavy pollution in autumn and winter,particulates with horizontal transport distance r≤100 km,and vertical transport height of 300 m<h≤900 m were predominated,and particulates with horizontal transport distance r≤200 km,and vertical transport height of 300 m<h≤900 m were dominant during heavy pollution in spring.In 2017 and 2018,the probability of particulates crossing the boundary layer during heavy pollution was low.