2015年北京“阅兵蓝”特征及成因探讨

Characteristics and cause of the “parade blue” in Beijing 2015

利用大气成分和气象要素观测数据,对2015年8~9月北京田径世锦赛和抗战胜利70周年纪念活动期间的北京PM_(2.5)浓度变化特征及其相关的大气污染气象条件进行了研究,并采用大气化学数值模式模拟了气象条件、减排措施和区域减排联合行动对北京PM_(2.5)浓度下降的作用和贡献.结果表明:纪念活动期间北京地区空气质量显著改善,PM_(2.5)平均浓度仅为18.7μg/m^3,比前期8月1~19日下降70%,比2014年同期降低74.0%;东北冷涡长时间稳定少动为空气质量改善提供了良好的大气环流条件,北京地区混合层高度相比前期升高20%,相对湿度降低17%,风速增大7%,气象要素变化为庆祝活动期间PM_(2.5)浓度下降提供了良好的气象条件,尤其是地面主导风向转为偏北风后,阻止了北京城南及华北中南部地区的污染物输入北京城区;CAMx模式的模拟结果表明,与2014年同期相比,气象条件变化在北京PM_(2.5)浓度降幅中的贡献率达73%;纪念活动期间有无减排的模拟分析显示,在相同的气象条件下,减排措施使北京PM_(2.5)浓度下降约33%;期间北京PM_(2.5)来源以本地排放为主,本地的减排措施对改善空气质量的贡献率约为72%,周边地区减排的贡献率约为28%.

By using atmospheric composition and meteorological observation data, PM2.5 concentration variationcharacteristics and relevant meteorological conditions during the period from August to September 2015 in Beijing werestudied. With the application of the Comprehensive Air quality Model with extensions (CMAx), the contributions of themeteorological conditions, emission control policies and regional collaborations on emission control to the air quality inBeijing were analyzed. The results show that, the air quality of Beijing was significantly improved during the memorialactivity period (20 August to 03 September). The average PM2.5 concentration was 18.7μg/m3, reduced by 70% comparedwith the previous period (August 1st to August 19 th) and reduced by 74% compared with the same period last year. Longperiod maintain of northeast cold vortex provided the favorable circulation background for the air quality improvement.During the period of memorial activity, the meteorological factors such as mixed layer height, relative humidity and windspeed presented favorable conditions in improving the air quality. In particular, the shifting of dominant wind direction onthe ground level prevented the pollutant invading from the southern part of Beijing and from middle and southern areas ofNorth China. CMAx model well simulated the variations of PM2.5 concentrations in Beijing. The simulation results showthat, comparing with the same period last year, the meteorological conditions contributed 73% to the total change of PM2.5.33% of the PM2.5 reduction was attributed to the emission control polices. The contribution of PM2.5 in Beijing wasprimarily come from local emissions. The local emission reduction took account for 72% for the PM2.5 concentrationdecrease, while the surrounding areas of emission reduction contributed about 28%.