基于综合观测的中国中东部地区一次严重污染过程分析

Analysis of a severe fog⁃haze process in central and eastern China based on comprehensive observations

利用寿县国家气候观象台GRIMM80颗粒物监测仪、Aurora3000浊度计等探测的气溶胶浓度、大气散射系数分析了2018年1月中国中东部地区发生的一次严重污染过程.利用Airda微波辐射计探测的近地层温湿廓线数据,结合地面常规气象观测资料及EC再分析资料,探讨了此次污染过程形成、短时消散及清除的气象原因.结果表明:与历史同期相比,500 hPa极涡较浅、经向环流减弱;850 hPa西南气流强盛,中低层水汽充足加剧污染.污染发生于冷空气间歇期.在此污染过程中,地面平均风速为1.5 m·s^-1,日均日照时数为0.1 h,相对湿度为91.2%,高湿、小风、多云寡照不利于污染水平扩散.1月18-22日边界层持续存在多层逆温,第一逆温层基本多为贴地逆温,逆温高度低于200 m,近地层大气比湿超过5 g·kg^-1,最大值高于7 g·kg^-1.在此期间出现两次空气质量短时段好转,这主要源于对流层中低层转为西北风,900 hPa以下聚集相当位温(Qe)低于288 K的浅薄冷空气堆,导致贴地逆温层消失地面污染被稀释.但两次弱冷空气没有打破边界层内有利于污染聚集的逆温、高湿结构,地面气团温度露点差无明显变化.23日较强冷空气使高空干洁大气入侵近地层,850 hPa以下Qe<284 K,表明地面污染气团被置换,污染过程结束.

A severe,prolonged and regional fog⁃haze episode occurred in the central and eastern China on January 13⁃23,2018.The aerosol concentration by GRIMM80 Particulate Monitor,atmospheric scattering coefficient by Aurora⁃3000 Turbidimeter of Shouxian National Climate Observatory were used to analyze the evolution of the event.Based on the near⁃surface temperature and humidity profiles by Airda Microwave Radiometer,combined with hourly data of ground level meteorological parameters and EC reanalysis data,the meteorological reasons for the formation,short⁃term dissipation and elimination of this pollution event were investigated.Results show that:Compared with the same period of history,the 500 hPa polar vortex was shallower and the meridional circulation was weaker;The southwest air flow was stronger at 850 hPa,and the water vapor in the middle and lower troposphere was sufficient to aggravate the pollution.The pollution event occurred during the intermission of cold air activity.During the pollution event,the ground level meteorology were characterized as high humidity,light wind and cloudy,with the average wind speed of 1.5 m·s^-1,daily sunshine hours of 0.1 h and relative humidity of 91.2%,which were not conducive to the horizontal diffusion of pollution.From January 18 to 22,temperature inversion occurred frequently around the ground and the inversion height was less than 200 m.What′s more,the specific humidity of the atmosphere near surface was more than 5 g·kg^-1,with the maximum value over 7 g·kg^-1.The two air quality short⁃term improvement process during the maintenance of pollution was due to the transition to the northwest wind in the lower to middle troposphere,and the accumulation of shallow cold air stacks with the equivalent potential temperature(Qe)lower than 288 K below 900 hPa,resulting in the disappearance of the ground inversion layer and the dilution of ground pollutants.However,the two cold⁃air did not break the inversion and high humidity structure within the boundary layer,which resulted in pollution rebound in a short time.On January 23,dry cold air at high altitude invaded with Qe<284 K below 850 hPa,indicating ground⁃level polluted air mass was replaced and the pollution process was over.