浙江北部一次爆发式发展重度大气污染的气象特点和成因

基于全国空气质量指数和PM_(2.5)监测、常规气象观测、浙江省6种主要大气污染物和自动气象监测、宁波镇海激光雷达、美国国家环境预报中心GDAS和欧洲中期天气预报中心ERA-interim再分析等多种资料,对2017年12月30日―2018年1月1日浙江北部一次爆发式发展大气污染事件气象特点及成因进行分析,应用HYSPLIT4模式进行粒子后向轨迹分析.结果表明:PM_(10)和PM_(2.5)质量浓度在浙江省表现出明显的爆发性增长和自西北向东南传输的特征,污染程度自浙北向浙中、浙南逐渐减轻,重度污染时浙北大范围出现2000 m以下的重度霾,污染粒子主要来自上游的安徽和江苏省.大气污染爆发式发展与冷空气有关,1000 m以下边界层内冷空气偏弱,但足以将盛行风改变为西北风,是污染物粒子输送的动力条件,污染粒子集中在该层内,层内没有下沉运动,因此水平风场对污染事件爆发有决定性作用;1000 m以上层次冷平流表现明显,且伴有下沉运动,抑制了边界层粒子的垂直扩散,对污染事件的发展和维持有间接影响.激光雷达的消光系数变化不仅与污染物粒子浓度变化有关,还与气象条件密切相关.污染物粒子质量浓度通量散度的变化对预报粒子浓度的增减有较好的参考作用.

Meteorological characteristics and outbreak causes of a heavy air pollution episode in northern Zhejiang Province

We analyzed the weather characteristics of an explosive outbreak pollution event in Zhejiang Province from December 30, 2017 to January 1, 2018, using the national Air Quality Index and PM_2.5 mass concentrations, routine meteorological observations, the major pollutant concentration observations in Zhejiang, measurements from Zhejiang''s Automatic Weather Stations and the Zhenhai lidar at Ningbo, the GDAS from the National Centers for Environmental Prediction and the ERA-interim reanalysis data from the European Centers for Medium-Range Weather Forecasts. The causes of the explosive outbreak were analyzed as well. HYSPLIT4 model was used to investigate the characteristics of pollutant backward trajectories. The results showed that the PM₁₀ and PM_2.5 mass concentration in Zhejiang Province increased explosively and tended to be transported from northwest to southeast. The degree of pollution gradually reduced from the north, to the middle, and then to the south of Zhejiang Province. Heavy haze with visibility less than 2000 m was commonly observed in northern Zhejiang Province during the pollution episode, and the haze particles were mainly originated from Anhui and Jiangsu Provinces. The explosive development of the pollution outbreak was closely related to the cold air. Although cold advections were weak below 1000 m, it was enough to change the prevailing wind directions to northwest in the boundary layer, which was the dynamic condition for pollutant transportation. Pollutants were mainly confined within the boundary layer below 1000 m, where no downward movements were found. Therefore, horizontal winds played a decisive role on explosive pollutant outbreaks. In the levels above 1000 m, there were obvious cold advections with descending motions, which suppressed the vertical diffusion of boundary layer particles. It had an indirect impact on the rapid development and maintenance of the pollution. Extinction coefficient of the lidar were not only related to pollutant concentrations, but also closely related to weather conditions. Pollutant mass concentration flux divergence could be used as a reference for particle concentration forecasts.