基于在线观测的北京冬季一次PM2.5重污染过程特征分析

选取2017年1月初北京一次典型PM_(2.5)重污染过程为研究对象,应用污染物在线监测仪器并结合气象要素对地面PM_(2.5)及化学组分质量浓度污染特征进行了分析,采用微脉冲激光雷达对垂直方向进行观测,分析边界层及消光系数的变化特征。结果表明,从PM_(2.5)质量浓度的演变过程来看,本次污染可大致分为爬升、重污染、清除3个阶段。重污染时期的气象特征为高湿、低压、低风速;南部琉璃河((336.8±118.6)μg/m~3)、永乐店((323.1±86.2)μg/m~3)PM_(2.5)污染水平相近,均高于城区车公庄((278.7±138.7)μg/m~3);碳组分和二次水溶性离子是PM_(2.5)的主要组分,占到PM_(2.5)质量浓度的58.09%(车公庄)、71.43%(琉璃河)、76.57%(永乐店);SO2-4质量浓度上升显著,在总组分中比例由非重污染时期的16.73%升高到重污染时期的22.29%;3处监测点SOR和NOR均值分别为0.57和0.24,表明重污染期间二次转化明显。垂直方向观测结果表明,重污染时期边界层高度明显降低;气溶胶近地面消光系数高,表明污染物主要集中在近地面层。

Characteristic analysis for the thick winter air pollution accidents in Beijing based on the online observations

The present paper intends to choose a typical PM2.5 pollution status-in-situ that took place one day in Jan.,2017,in Beijing as a research sample,with the specific features of PM2.5 and its constituent components analyzed via the online-monitoring device at the 3 sites,known as Chegongzhuang (CGZ) site,Liulihe (LLH) site and and that of Yongledian (YLD).The results of the final analysis show that what we have gained can be divided into 3 stages according to PM2.5 content components,that is,those in rising stage,contamination stage and clear-away or extinction stage.It turns out that there occurs significant difference with the meteorological factors between the clear and clean days and heavily polluted days.For example,as compared to clear and clean days,the meteorological condition seems to function more obviously,such as higher relative humidity,lower atmospheric pressure and movement during the heavy pollution stages.Particularly speaking,the PM2.5 content concentration rates of the suburban areas (LLH and YLD) would become much high-er than those in the downtown or near suburban site (CGZ) with the concentration rates of (336.8 ± 118.6) μg/m3,(323.1 ± 86.2) μg/m3 and (278.7 ± 138.7) μg/m3,respectively.However,in the heavy polluted stages,main constituent components of PM2.5 prove to be made up of carbon and other secondary inorganic water-soluble ions,which may account correspondingly for 58.09％,71.43％,76.57％ in the PM2.5,whose chief components are of CGZ,LLH and YLD.Further analysis helps us to find that the SO42-content concentration is responsible for the thicker pollution stages at about 22.29％,whereas there is merely 16.73％ in the cleaner periods.The mean pollution data of SOR and NOR has been worked out at about 0.57 and 0.24 in the aforementioned 3 monitoring sites,which reveals that the secondary recreation or restoration of the pollution should also be noticeable during this pollution juncture.What is more,it also occurs that obvious extinction coefficient can also be noticed by the radar receiver on the ground surface in the thick pollution stage.This may imply that the air pollutants may turn out in an accumulated way near the surface ground.Besides,the radar monitoring results also suggest that the height of the boundary layer proves lower in the thick pollution periods than in other less polluted periods.