成都市夏季臭氧污染的环流分型与来源分析

Circulation Classification and Source Analysis of Summer Ozone Pollution in Chengdu

为探究大尺度环流对成都市O_(3)污染的影响,基于四川盆地700 hPa位势高度场,采用T-PCA方法,将2015—2019年夏季(6—8月)各日的大气环流归纳为5类环流型,并对不同环流型下的成都市O_(3)污染特征与污染来源进行分析。5类环流型中,东北高压型(NEH)和高压底部型(UNF)条件下,四川盆地气温较高,湿度和云量相对较低;对比过去24小时的变温,UNF下四川盆地增温显著,NEH下变化不明显,另外三类环流型(即东南高压型、西北低压型和西北高压型)下则出现不同程度的降温。NEH和UNF下的气象条件更有利于四川盆地O_(3)的光化学生成。研究时段内,NEH和UNF下成都市O_(3)浓度水平和O_(3)超标日比例明显高于另外三类环流型,是夏季发生O_(3)污染的主要环流型。成都市O_(3)污染较重的月份具有较高的NEH和UNF环流型占比。通过对成都市夏季O_(3)来源的模拟分析,发现O_(3)污染主要来自四川盆地内的污染源排放(占55.0%),以成都本地贡献为主(31.6%),其他重要贡献城市包括德阳(5.4%)、重庆(4.0%)、资阳(3.9%)和眉山(2.2%)。然而,不同环流型下成都市的O_(3)来源具有不同特点,NEH下成都平原内部污染传输影响较强,德阳市O_(3)贡献显著增加(占14.9%);UNF下成都市O_(3)污染呈现很强的局地性污染特征,成都市排放的O_(3)贡献占比接近一半(46.8%)。

In order to explore the impact of large-scale circulations on O_(3) pollution in Chengdu,based on the 700 hPa geopotential height field in the Sichuan Basin(SCB)and using the T-PCA method,the atmospheric circulations in the summer of 2015–2019(June–August)were classified into five circulation patterns,and the characteristics of O_(3) pollution and O_(3) sources in Chengdu under different circulation patterns were identified.Among the five types of circulation patterns,the northeast-high pressure(NEH)pattern and the under-high pressure field(UNF)pattern generally led to higher air temperature,and lower humidity and cloud cover in the SCB.Air temperature change compared to the previous days showed an obvious increasing trend in the SCB under the UNF pattern,kept stable under the NEH pattern,and indicated cooling effects with varying intensities under the other three circulation patterns(the southeast-high pressure pattern,the northwest-low pressure pattern and the northwest-high pressure pattern).The meteorological conditions under NEH and UNF were more conducive to the photochemical production of O_(3) in the SCB.During the study period,O_(3) concentrations and the percentages of over-standard days of O_(3) in Chengdu under NEH and UNF were significantly higher than those under the other three circulation patterns,and thus NEH and UNF were the main circulation patterns that were related to O_(3) pollution in summer.Months with more severe O_(3) pollution in Chengdu tended to have higher proportion of days under the NEH and UNF patterns.The simulation studies of O_(3) sources in Chengdu in summer suggested that O_(3) was mainly derived from the SCB(55.0%),with local contribution of Chengdu(31.6%),and other important contributing cities including Deyang(5.4%),Chongqing(4.0%),Ziyang(3.9%)and Meishan(2.2%).However,O_(3) sources in Chengdu under different circulation patterns showed different characteristics.Under the NEH pattern,O_(3) transport within the Chengdu Plain had notable impact on O_(3) pollution in Chengdu,with a significant increasing contribution from Deyang(14.9%).By contrast,under the UNF pattern,O_(3) pollution in Chengdu became more localized,with nearly half(46.8%)of O_(3) contributed by local emissions.