摘要
基于大气污染六要素(PM_(2.5)、PM10、SO_(2)、NO_(2)、CO和O_(3))、PM_(2.5)化学组分数据、地面气象观测数据、微波辐射计数据和大气再分析数据,采用物质平衡和硫/氮氧化速率(SOR/NOR)等方法对2019年1月西安市一次重污染事件过程和成因机制进行综合分析.将该次污染过程划分为累积阶段(P1)、维持阶段(P2)和消散阶段(P3),本次重污染过程主要是由于不利天气形势叠加反馈效应造成的,P1和P2阶段西安在500hPa都受平直西风气流影响,海平面气压为均压场,等压线稀疏,天气形势稳定,且925hPa以偏东风为主,不利于大气污染扩散.地基微波辐射计可辅助反映气象条件与重污染间的反馈机制,其反演的水汽密度和逆温均与PM_(2.5)存在显著线性相关关系,相关系数分别为0.86和0.38.反馈机制主要表现为:当污染达到一定程度时产生辐射冷却效应使地面降温,进而导致或加强逆温,混合层高度降低,水汽积聚,高湿条件通过加速二次转化和促进气溶胶吸湿增长使污染进一步维持,因此P2阶段二次无机离子(SO_(4)^(2-)+NO_(3)^(-)+NH_(4)^(+),SNA)和"其他"组分对PM_(2.5)的贡献率较大,分别为43.2%和23.1%,且SOR、NOR和消光系数均在P2阶段达到峰值.NH4NO_(3)、有机物(OM)、(NH4)2SO4和元素碳(EC)对消光系数的总贡献率超过85%,但各组分占比排序在每个阶段略有不同.
Air pollution continues to be a serious problem in Xi'an.A heavy pollution process and formation mechanism were investigated in Xi'an in January 2019 using multi-source methods(such as material balance and sulfur/nitrogen oxidation rate(SOR/NOR)).The multi-source data included the concentrations of PM_(2.5),PM10,SO_(2),NO_(2),CO,and O_(3);the chemical components of PM_(2.5);the meteorological records of ground and vertical observations;the atmospheric reanalysis data.Three phases were obtained including the accumulation phase(P1),maintenance phase(P2),and dispersion phase(P3)during the pollution period.The pollution event was primarily attributed to the superposition of adverse weather conditions and feedback effects.During the periods of P1 and P2,the area of Xi'an was affected by blocking and zonal westerly airflow at 500 hPa(with flat westerly airflow)and uniform-distribution pressure at sea level with a limited pressure gradient and stable weather conditions,and the easterly wind was dominant at 925 hPa;not all of these factors were conducive to the pollutant diffusion.An interaction feedback mechanism between meteorological conditions and heavy pollution could be studied using the ground-based microwave radiometer.The correlations between PM_(2.5)and inversions of water vapor density,relative humidity,air temperature,and temperature inversion were significant with coefficients of 0.86,0.62,0.53,and 0.38,respectively.The feedback mechanism was primarily manifested as follows:with the pollutant accumulation,the radiative cooling effect could lead to or strengthen the occurrence and intensity of temperature inversion,decrease the mixed layer height,and cause moisture accumulation.High humidity could further maintain the pollution by accelerating the secondary formation and promoting the hygroscopic growth of aerosol particles.Therefore,the dominant chemical components to PM_(2.5)were secondary inorganic ions(SO_(4)^(2-)+NO_(3)^(-)+NH_(4)^(+),SNA)and"other"components during the period of P2,with contributions of 43.2%and 23.1%,respectively.In addition,the peak values of PM_(2.5),SOR,NOR,and the light extinction coefficients all occurred on the same days(January 3 and 6),indicating that the effect of secondary formation was important for both heavy pollution events and visibility.The total contribution of NH4NO_(3),organic matter(OM),(NH4)2SO4,and EC to the light extinction coefficient was more than 85%.Limited variations in the proportion for components were observed in three phases.During the period of P3,the strong cold air in the mid-lower atmosphere was conducive to the dry and clean air sinking and the pressure gradient at sea level increasing.These were beneficial to the diffusion of air pollutants and water vapor.
作者
王楠
高宇星
屈垚
曲静
师菊莲
时迎强
周岳
朱崇抒
WANG Nan;GAO Yu-xing;QU Yao;QU Jing;SHI Ju-lian;SHI Ying-qiang;ZHOU Yue;ZHU Chong-shu(Xi'an Institute for Innovative Earth Environment Research,Xi'an 710061,China;Key Laboratory of Aerosol Chemistry and Physics,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,China;National Observation and Research Station of Regional Ecological Environment Change and Comprehensive Management in the Guanzhong Plain,Xi'an 710061,China;Xi'an Meteorological Bureau,Xi'an 710016,China)
出处
《环境科学》
EI
CAS
CSCD
北大核心
2023年第10期5382-5391,共10页
Environmental Science
基金
国家重点研发计划项目(2017YFC0212200)。
关键词
重污染
PM_(2.5)
化学组分
天气形势
大气垂直特性
形成机制
heavy pollution
PM_(2.5)
chemical components
weather conditions
atmospheric vertical properties
formation mechanism
