北京市颗粒物污染特征及其大气环流成因分析

Analysis on the Characteristics of Atmospheric Particulate Matter and Its Causes of Atmospheric Circulation in Beijing

本文利用北京市大气污染物逐时观测数据、气象观测资料、NCEP/NCAR再分析资料,系统分析了2015年~2017年北京市大气污染概况,总结了不同时间尺度颗粒物浓度变化特征,结果表明北京市空气污染综合指数下降,空气污染状况好转,颗粒物和氮氧化物日均浓度超标天数逐年减少,但PM2.5超标倍数最高达6.7倍,年均超标率达32%,颗粒物污染问题仍然值得重视。选择伴随冬季冷空气过程发生的7例细颗粒物污染事件分析其大气环流成因,发现污染天气过程中,稳定的大气环境、高湿天气条件、较差的水平垂直扩散条件和外部污染物输送共同作用导致了北京市污染天气的发生;之后,高空阻塞形势崩溃,横槽转竖,引导冷空气南下,西北清洁气流与地面蒙古高压系统相互配合,易在北京地区造成剧烈大风天气,打破逆温层,增强颗粒物扩散能力,同时冷空气南下形成的降水天气会进一步清除颗粒物,污染天气消退。

In this paper, hourly observation data of air pollutants in Beijing, meteorological observation data and NCEP/NCAR reanalysis data were used to systematically analyze the air pollution situation, to summarize the variation characteristics of particulate matter concentration in different time scales in Beijing from 2015 to 2017. It was found that air pollution index of Beijing dropped, the air pollution situation improved, and the average daily concentrations of particulate matter and nitrogen oxide decreased year by year. However, the highest daily concentration of PM2.5 was 6.7 times higher than that of the grade II limits by China. The aver-age number of days for the daily concentration of PM2.5 exceeding the grade II limits by China reached 32% of the total in the whole year. The problem of particulate matter pollution still deserved attention. 7 cases of fine particle pollution in winter during the whole cold surge process were selected to analyze its causes of atmospheric circulation. It was found that the combination of stable atmospheric environment, high humidity, poor horizontal and vertical dispersion conditions and external pollutant transport resulted in the occurrence of polluted weather in Beijing. After that, the upper-air blocking situation collapsed, the horizontal trough turned vertical, leading the cold air southward. The northwest clean air flow cooperated with the surface Mongolian high pressure system, which easily caused severe gale weather in the Beijing area, broke the inversion layer, and enhanced the particle diffusion ability. At the same time, the cold air southward will form precipitation weather and further remove the particles. The pollution weather ended.