基于多源综合观测的徐州冬季重污染过程分析

Analysis of heavy pollution process in Xuzhou in winter based on multi-source comprehensive observation

经过多年的大气污染治理,我国的多种大气污染物浓度已呈现显著下降趋势,然而在不利气象条件下仍会导致重污染事件的发生.掌握此类影响较大的偶发重污染事件产生与发展的原因和机制,有助于进行下一步的大气污染预警和防控.本研究以徐州2020年12月中旬的一次重污染过程为例,通过地面站点观测、激光雷达、模式模拟、颗粒物组分观测与源解析、后向轨迹溯源等手段进行了全方位的观测与分析.结果表明,此次污染过程中颗粒物主要来源为二次离子、燃煤、生物质燃烧、机动车、扬尘等,其中,二次离子占比最高,为37.9%;污染期硫氧化率(SOR)和氮氧化率(NOR)明显高于污染前,增幅分别为176%和82%;污染期主要来自燃煤源的SO_(4)^(2-)较污染前升高幅度明显,由5.51μg·m^(-3)升高至16.3μg·m^(-3),升幅为196%;生物质燃烧的示踪物K^(+)由0.37μg·m^(-3)升高至0.83μg·m^(-3),升幅为123%;污染前期,局地高湿、静稳等主要外在不利气象因素促进了本地污染物的生成;污染中期受山东和安徽等地污染物传输增加的影响,外来源占主导,外源贡献增加至74.4%.研究表明,因气象和排放等因素的不确定性,致使冬季重污染过程具有复杂性.本研究可为了解大气污染机理及提高区域联防联控提供依据.

After years of air pollution control,the ambient concentration of many air pollutants in China has shown a significant downward trend.However,heavy pollution events under unfavorable meteorological conditions can still occur.Understanding the causes and mechanisms of such highimpact occasional heavy pollution events will be helpful for the prevention and control of air pollution in the next term.In this study,a heavy pollution process in Xuzhou in mid-December 2020 was investigated as a case study.Comprehensive observations and analysis were carried out by means of ground station observation,Lidar,model simulation,particle component observation and source apportionment,and backward trajectory tracing.The results showed that the main sources of particulate matter in this pollution process were secondary ions,coal burning,biomass combustion,motor vehicles,and dust.Secondary ions accounted most and up to 37.9%.Sulfur oxidation rate and nitrogen oxidation rate increased by 176%and 82%,respectively,during the pollution period.Similarly,SO_(4)^(2-),mainly from coal burning sources,increased significantly from 5.51μg·m^(-3) to 16.3μg·m^(-3),with an increase of 196%.The tracer of biomass combustion,K^(+),increased from 0.37μg·m^(-3) to 0.83μg·m^(-3) with an increase of 123%.In the early stage of pollution,unfavorable meteorological factors such as local high humidity and static stability weather,promoted the generation of local-source pollutants.In the middle stage of pollution,the transport of pollutants from Shandong and Anhui Province was more obvious and became the major source,the regional transport contributed up to 74.4%.The study shows that the heavy pollution process in winter is complex due to the instability of meteorological and emission factors.The findings provide part of basis for understanding the pollution mechanism and improving regional joint prevention and control.