珠三角西部一次冬季臭氧污染过程分析

Analysis of a winter ozone pollution process in the western Pearl River Delta

利用地面气象和空气质量观测资料、高空气象观测资料以及再分析数据,对2021年12月8~12日位于珠三角西部的中山市的O_(3)污染过程的特点及成因进行分析.结果表明,该次过程为近年来罕见的冬季O_(3)连续污染过程,期间O_(3)平均峰值浓度是当月非污染日的2.3倍.污染期间受副热带高压和地面大陆高压脊控制,中山市气温、日照和相对湿度偏高,风速偏小,日间风向以北风为主,近地面的下沉气流、逆温层和日间相对湿度下降对O_(3)污染起到增幅作用.污染过程存在明显的外来污染物输送现象,污染潜在源区主要位于中山市东北方向.在前体物积累阶段,大量的NO_(2)从上游地区流入中山市,为O_(3)污染的出现提供了充足的前体物.污染期间NO_(2)在有利的太阳辐射条件下,光解速率比当月非污染日平均偏高23%,导致日间O_(3)浓度快速上升,并在较差的扩散条件下形成污染.

Using surface meteorological and air quality observational data,the vertical sounding meteorological data and the reanalysis data,the characteristics and cause of an ozone pollution process in Zhongshan City,located in the western part of Pearl River Delta from December 8 to 12,2021 were analyzed.The results showed that this process was a rare winter continuous O_(3) pollution process in recent years,during which the average O_(3) peak concentration in pollution days was 2.3 times higher than that of non-pollution days of the month.Under the control of subtropical high and the surface cold high ridge during the pollution days,the temperature,sunshine hour and humidity in Zhongshan were relatively high,while the wind speed was relatively low,and the daytime wind direction was dominated by north wind.The downdraft,the inversion layer and the descending relative humidity in the daytime near surface enhanced the ozone pollution.There was a clear phenomenon of external pollutant transport during the pollution process,and the potential sources areas of pollution were mainly located in the northeast direction of Zhongshan.A large amount of NO_(2) flowed into Zhongshan from upstream areas during the accumulation stage of precursors,providing sufficient precursors for the occurrence of O_(3) pollution.During the pollution days,under favorable solar radiation conditions,the average photolysis rate of NO_(2) was 23%higher than that of non-pollution days of that month,leading to a rapid increase in daytime O_(3) concentration and the formation of pollution under poor diffusion conditions.