四川盆地冬季典型污染过程分析及应急减排效果评估

Analysis of Typical Pollution Process and Effect Evaluation of Emergency Emission Reduction in Sichuan Basin in Winter

为探讨成都冬季污染过程成因,评估应急减排效果,以2019年12月成都发生的一次长时间污染过程为例,分析污染成因和典型污染物变化特征等,并对四川省启动预警的管控效果进行评估。结果表明:污染期间四川省PM_(2.5)平均质量浓度为77.9μg/m^(3),高出冬季常态浓度1倍左右,成都峰值浓度高达176.0μg/m^(3);盆地独特的地形和静稳小风的气象条件,加之高压脊控制影响,污染前期出现连续晴好天气,夜间逆温增强,污染物累积迅速,湿度增大导致污染物二次转化增强,是该次污染过程的重要外因;PM_(2.5)中硝酸根离子贡献最大(26.7%),NO_(x)及其二次转化的硝酸根离子是造成该次污染的主要原因;启动黄色预警后,NO_(2)及其转化后的硝酸根离子浓度以及PM_(2.5)浓度仍呈上升趋势,各类源贡献显著;升级橙色预警后,NO_(2)峰值浓度明显下降,硝酸根离子占PM_(2.5)的比例下降3.7个百分点,PM_(2.5)浓度上升趋势得到明显遏制;该次区域协同减排效果明显,区域PM_(2.5)日平均质量浓度下降9.1%~13.1%,区域性污染推迟1d出现,预警城市的重度污染、中度污染、轻度污染天数分别减少13、13、7 d;PM_(2.5)浓度下降主要来自于工业源、扬尘源和移动源的减排贡献,平均减排贡献比例分别为60.0%、31.3%和8.7%。

In order to explore the causes of the pollution process in winter in Chengdu and evaluate the effect of emergency emission reduction,a long-term pollution process that occurred in Chengdu in December 2019 was taken as an example to analyze the causes of pollution and the characteristics of typical pollutant changes,and evaluate the management and control effects of starting early warnings in Sichuan Province.The results showed that the average PM_(2.5) concentration in Sichuan Province was 77.9 μg/m~3 during the pollution period,which was about twice as high as the normal concentration in winter,and the peak concentration in Chengdu was as high as 176.0 μg/m~3.The unique topography of the basin and the weather conditions of quiet and stable wind,coupled with the influence of high pressure ridge control,the continuous fine weather,the increase of night temperature inversion,the rapid accumulation of pollutants,and the increase of humidity that leaded to secondary conversion of pollutants,which were important external causes of the pollution process.Nitrate ions contributed the most in PM_(2.5)(26.7%).NO_(x) and its secondary converted nitrate ions were the main causes of this pollution process.After the yellow warning was activated,NO_(2) and its converted nitrate ions concentration and PM_(2.5) concentration still showed an upward trend,and various sources contributed significantly.After the orange warning was activated,the peak NO_(2) concentration dropped significantly,and nitrate ions accounted for PM_(2.5) dropped by 3.7 percentage points,and the upward trend of PM_(2.5) concentration was obviously curbed.The regional coordinated emission reduction effect was obvious.The daily average concentration of PM_(2.5) had dropped by 9.1%-13.1%.The occurrence of regional pollution had been delayed by one day.The number of heavy,moderate,and light pollution days had been reduced by 13,13,and 7,respectively.The decrease of PM_(2.5) concentration was mainly due to the emission reduction of industrial sources,dust sources,and mobile sources,which the contributions were 60.0%,31.3%,and 8.7% respectively.