南京北郊冬季典型灰霾天气气象成因及来源分析

2015年1月14~28日南京发生了入冬以来最为严重的持续性霾污染事件。利用地面气象资料、后向轨迹分析和污染物浓度数据,结合加强观测实验所获得的3 h高频次PM2.5中有机碳(OC)和元素碳(EC)的数据,分析了此次霾过程的成因和污染物来源。结果表明高压系统和静稳的均压场是观测期间霾过程形成的天气背景。后向轨迹和气态前体物的分析结果显示第一次霾过程的形成受到山西河北境内高污染气团区域传输的影响。第二次霾过程是一次短时局地污染事件,主要是由于低风速和极低的边界层高度等不利的扩散条件导致污染物在近地层的堆积。OC/EC计算结果(7.66)结合卫星火点资料和轨迹分析进一步说明第三次霾过程受到南方生物质燃烧的影响。高相对湿度有利于二次污染物的生成,因而加剧了第四次霾过程的污染程度。CO、SO_2、NO_2与颗粒物浓度显著相关,OC/EC比值范围2.54~11.61,表明化石燃料和生物质燃烧以及汽车尾气排放是此次观测期间霾形成的主要污染来源。

The Meteorological Causes and Source Analysis of Typical Haze Event During Wintertime in Nanjing Northern Suburb

Nanjing has suffered one of the most serious persistent haze episodes in winter from January 14 to 28, 2015. During a comprehensive observation-based campaign, ground meteorological data, backward trajectory analysis and major air pollutants, as well as organic carbon (OC) and elemental carbon (EC) concentrations in PM2.5 were used to investigate the causes of the haze and source of pollutants. The results have demonstrated that high-pressure system and stationary pressure field were the synoptic background for haze processes during the campaign. The analysis of the trajectories and gaseous precursors showed that the formation of the first haze process was significantly affected by the regional transport of highly polluted air masses in Shanxi and Hebei. The second haze process was a short-term local pollution event, mainly caused by the unfavorable diffusion conditions such as low wind speed and extremely low boundary layer which led to a rapid accumulation of pollutants in the surface layer. Referred to the satellite fire spot map, an average value 7.66 of the OC / EC ratio indicated that the third haze episode influenced by biomass burning from south China considerably. High relative humidity is favorable for the formation of the secondary pollutants, increasing the pollution degree of the fourth haze process. CO, SO2 and NO2 were significantly correlated with particulate matter, and the OC / EC ratio ranged from 2.54 to 11.61, indicating that coal fossil fuel, biomass burning and vehicle exhaust emissions were the major sources of pollutants in the haze formation during this campaign.