重庆市O3污染日的大气环流分型与传输特征

Characterization of atmospheric circulation and transmission in Chongqing City during ozone polluted days

通过分析重庆市主城区2015~2019年O3浓度和气象要素观测数据,发现主城区O3超标日数、超标日O3中位值和90百分位浓度值均呈现逐年升高趋势,O3与温度成正相关、与相对湿度成负相关,高O3浓度对应每日最高温度区间为35℃以上以及相对湿度区间70%以下.采用T-mode主成分分析法(PCT)对2015~2019年的4~9月850hPa低层位势高度场和风场进行分型,总结出重庆市O3污染期间主要有8种天气类型,其中有利于出现高浓度O3现象的天气类型分别是低压西北侧型(T1)、低压后部型(T4)和高压西侧(T3),对应O3平均超标率分别为34.6%、17.0%和14.2%.利用HYSPLIT4模型后向轨迹聚类方法和潜在源贡献算法(PSCF),计算得到O3污染日的气团主要以中短距离输送为主,主要传输轨迹来自北、东北、南以及西南四个方向,从2015~2019年,主要污染来源有一个明显的从北转南的趋势,O3污染的潜在源贡献分析结果与全市工业源NOx、VOCs排放量空间分布的一致性较高.

The pollution of tropospheric ozone has become an emerging issue in the urban areas of Chongqing.From 2015 to 2019,the near-surface ozone concentrations have elevated with increasing days of exceeding the national air quality standard(NAQS).The comprehensive analysis using meteorological data showed that high ozone concentration frequently appeared when the daily maximum temperature over 35℃ as well as relative humidity below 70%.T-mode principal component analysis(PCT)was applied to synoptic classification.The result demonstrated that the occurrence of ozone pollution in Chongqing was mostly related correlated to three typical weather patterns,such as patterns of the northwest to low(T1),low low-pressure rear type(T4)and west to high(T3),and the corresponding ratio of days of ozone exceeding the NAQS were 34.6%,17.0%,and 14.2% respectively.The result of HYSPLIT4 indicated air masses during days of ozone exceeding NAQS were mainly short and moderate distance from the north,northeast,south,and west directions.It is worth mentioning that the south areas of urban Chongqing have become more and more important potential source regions of ozone from 2015 to 2019,according to the Potential Source Contribution Function(PSCF)distribution.In addition,PSCF results were highly consistent with the spatial distribution of NOx and VOCs emissions in Chongqing.