2016~2020年北京城区和郊区PM_(2.5)爆发性增长特征对比研究

The contrast study of the characteristics of PM_(2.5)explosive growth at urban and rural stations in Beijing from 2016 to 2020

利用PM_(2.5)浓度、气象要素、NCEP以及ECMWF再分析资料等,对比分析2016~2020年北京城区和郊区的污染特征,根据多种阈值指标定义爆发性增长过程,并着重分析爆发性增长过程中的环流形势以及污染物的不同来源.结果显示,北京城郊全年污染日数呈逐年下降趋势,但秋冬季的污染日数占比2016~2017年逐年下降,2018~2020年逐年升高,城区污染改善速度慢于郊区.2016~2020年城郊污染持续时长一般≤3d,城区≥2d的污染日次数均多于郊区,且均呈逐年下降趋势.城区和郊区细颗粒物污染存在明显的相互影响特征,城区对郊区的影响更为显著.城郊爆发性增长次数和爆发性污染占比整体先下降再升高.城区发生的爆发性增长过程次数多于郊区,但爆发性污染占比城区低于郊区.爆发性增长过程出现概率≥10%的地面天气形势为均压场型和高压前部型,高空形势为纬向环流和槽后型.城区传输型爆发性增长过程出现概率最高的天气形势为高空槽后配合地面高压前部型,占比可达37.0%,郊区传输型爆发性增长过程出现概率最高的天气形势为高空纬向环流配合地面高压前部型,占比可达31.6%,城区和郊区本地型爆发性增长过程出现概率最高的天气形势均为高空纬向环流配合地面均压场型,占比分别可达34.5%和56.5%.

The difference of pollution characteristics between urban and rural stations in Beijing from 2016 to 2020 was analysed using PM_(2.5)concentration,meteorological observational data,NCEP and ECMWF reanalysis dataset.Explosive growth processes were defined based on multiple threshold metrics,focusing on the analysis of atmospheric circulation and different sources of pollutants in the process of explosive growth.The results showed that the number of air pollution days had decreased year by year,while the proportion of pollution days in autumn and winter decreased from 2016 to 2017.In addition,the proportion of pollution days increased from 2018 to 2020.The pollution improvement at urban stations was slower than that at rural stations.The duration of pollution were generally less than or equal to 3d from 2016 to 2020.The number of air pollution days at urban stations were more than that at rural stations when the duration of pollution were more or equal to 2d,and the frequency of air pollution days had decreased year by year.There were obvious mutual influence characteristics of fine particulate pollution at urban stations and rural stations,and the impact of urban stations on rural stations was more significant.The number of explosive growth and the proportion of explosive pollution at urban stations and rural stations first decreased and then increased.The number of explosive growth process at urban stations was more than that at rural stations,however,the proportion of explosive pollution in urban areas was lower than that in suburbs.Most of the explosive growth processes occurred under types of uniform pressure field,such as the front of high pressure,zonal circulation and behind trough(the frequency of explosive growth were≥10%).The transmission during explosive growth processes at urban station occurred most frequently under the weather type of behind trough and the front of high pressure,with an occurrence frequency of 37.0%.The transmission during explosive growth processes at rural station occurred most frequently under the weather type of zonal circulation and the front of high pressure,with an occurrence frequency of 31.6%.The local explosive growth at urban and rural stations occured most frequently under the weather type of zonal circulation and uniform pressure field,with the exceeding ratio of 34.5%and 56.5%respectively.