Research On Density And Diffusion Trajectory Of NO₂ During Heavy Pollution Period In Urumqi

In the implementation of various regulatory policies and pollution control measures,the air pollution in Urumqi has been alleviated throughout the year,but the pollution in the heavy pollution period（November to March）is still increasing.To master the emission and diffusion laws of pollutants during heavy pollution and to solve the problem of air pollution during the heavy pollution period is the key to Urumqi the next step of atmospheric environmental management.In this paper,the temporal and spatial variation of the vertical column densities（NO₂ VCD_S）of Urumqi troposphere NO₂ in the heavy polluted period is retrieved by using the fixed point and mobile technique of the foundation multiaxial Differential Absorption spectrometer（MAX-DOAS）,and the meteorological conditions,topography,flow volume,OMI satellite product and diffusion model are analyzed,The following conclusions were obtained:（1）2014-2017 years of heavy pollution in Urumqi 3 monitoring stations（normal University station referred to as SD,Zhongtai chemical monitoring station referred to as ZTHG,three dam monitoring station for short SDB）NO₂ VCD_S performance for SD(13.76×10¹⁵ molec·cm^-2)>ZTHG(12.75×10¹⁵ molec·cm^-2)>SDB(8.47×10¹⁵ molec·cm^-2),that is,urban station>Industrial station>Farmland station.The NO₂ VCDs of SD and SDB station in 3 times of heavy pollution,the ZTHG 2015-2016-year heavy pollution showed an increase,and 2016-2017 years was reduced.During the 2014-2015-year heavy pollution period,the average monthly values of the troposphere NO₂ VCD_S 3 stations in Urumqi show continuous"n-type"change law and amplitude ZTHG>SDB>SD.3 station NO₂ VCD_S highest value all appear in January or February,the SD station NO₂ VCD_S lowest value all appears in November,but ZTHG and SDB station 2016-2017 year heavy pollution period lowest value appears in November,other lowest value all appears in March.（2）The 3 diurnal variation of tropospheric NO₂ VCD_S in heavy pollution period of monitoring stations,are present in the evening high,midday low change characteristics,ZTHG and SDB monitoring Station also presents the morning and evening high,midday Low"U-type"trend of change,in which the ZTHG trend is more obvious,the SD showed a gradual increase from morning to evening changes.The diurnal variation of NO₂ VCD_S is closely related to the diurnal variation of solar radiation and vehicular flow.The early peak of traffic flow has a higher value at 11:30,and there is a"hysteresis"in the 10:30,NO₂ VCD_S.（3）Urumqi outer ring road above the NO₂ VCD_S show the wind direction,the wind,the NO₂ VCD_S above the flood road performance is"North and south low,Middle High",the lowest value appears near the Nanshan parking lot,high values appear in the outer ring road,and they all show the road node is easy to appear high value.SD monitoring station NO₂ VCD_S and OMNO2d product data have a general trend of change,the correlation between the two is good,R=0.71.The NO₂ VCD_S of Mobile DOAS and OMI’s products also have good consistency in space.Under the influence of aerosol shielding effect,there is a systematic underestimation of OMI tropospheric NO₂ column concentration during heavy pollution period in Urumqi.（4）The Gaussian plume（GPM）model obtains from the Suzhou Road overpass which is near to the city center in Urumqi Road to the north to the Upper Shahe overpass,the NO₂concentration gradient shows the downward trend,moreover Henan East Road overpass to the Upper Shahe overpass falls the tendency to be big,this and the DOAS movement monitoring conclusion is consistent.The posterior trajectory（HYSPLIT）model shows that the air pollutants in Urumqi during heavy pollution have less proportion to the air flow from the field,the local source is the main,and the air flow is affected by the degree of the local pollution in the way of handling and dilution.