Study On The Driving Factors Influencing The Change Of Atmospheric Fine Particle Concentration In Changchun City

As one of the main pollutants in the air,PM_2.5 is not only affected by emission sources,but also closely related to meteorological conditions,complex underlying surfaces,and various physical and chemical processes.In recent years,the implementation of a series of air pollution control measures has effectively controlled PM_2.5.However,the overall urban ambient air quality has not yet emerged from the"meteorological impact type",with 29.8%of the urban average concentration of PM_2.5exceeding the standard.In order to further improve ambient air quality,it is particularly important to formulate scientific and accurate pollution control policies and quantify the impact of meteorological conditions and underlying surface changes on PM_2.5concentration changes.Firstly,this paper constructs a localized third-generation air quality model system WRF-CMAQ in Changchun City,which uses Arc GIS and ISAT inventory allocation tools to allocate MEIC inventory,simulates and evaluates the meteorological conditions and PM_2.5 in Changchun City in January and July 2017;Then,the impacts of meteorological conditions and emission changes were separated using Kolmogorov-Zurbenko filtering method and WRF-CMAQ scenario analysis method,and the relative contribution of meteorological conditions to long-term changes in PM_2.5concentration in Changchun City from 2015 to 2020 were quantitatively calculated;By updating WRF default underlying surface data,a controlled experiment was conducted to explore the impact of land use type changes on regional meteorological conditions and PM_2.5 in Changchun City.The main conclusions are:（1）The model validation results show that the WRF-ISAT-CMAQ model system can reasonably reproduce the daily variation rules of meteorological elements and PM_2.5concentrations in Changchun City in January and July 2017,with a Pearson correlation coefficient（R）of 0.86 between the simulated and observed values,passing the significance test,and the mean fractional bias（MFB）and mean fractional error（MFE）were both within an acceptable range.Therefore,the model results can be used for subsequent discussions.（2）According to the results of KZ filtering,during the period 2015-2020,the relative impact of changes in meteorological conditions and emission control on the decline of PM_2.5 concentration in Changchun City was 11.36%and 88.64%,respectively;According to the simulation results of WRF-CMAQ,the relative impacts of meteorological conditions and emission control on the decline of PM_2.5 concentration in Changchun City were 14.79%and 85.21%,respectively.Overall,long-term meteorological conditions are conducive to the improvement of PM_2.5 pollution in Changchun City.（3）Changchun City experienced rapid urban expansion from 2001 to 2017.Compared with the underlying surface scenario in 2001,the meteorological elements of the urban expansion area（UEA）under the underlying surface scenario in 2017 have significantly changed.The temperature at 2 meters increased significantly at night,rising by 4℃and 3℃in January and July,respectively;The wind speed increased by1.05 m/s and 1.60 m/s respectively;The height of the planetary boundary layer has increased by 100 m and 117 m respectively;The sensible heat flux increased by a maximum of 154 W/m² and 162 W/m²,respectively;The latent heat flux decreased by a maximum of 22.84 W/m² and 180.75 W/m² during the daytime,respectively.（4）Changes in underlying surfaces led to a general downward trend in PM_2.5concentrations in the UEA region in Changchun,with a maximum decrease of 34μg/m³and 20μg/m³ in January and July,respectively.The change trend of the total concentration of SO₄^2-and PM_2.5 is similar,with a significant decrease at night,while the change of NO₃^-and NH₄⁺is not significant.SOA formed from anthropogenic VOC precursors（ASOA）slightly increased,while SOA formed from biogenic VOC precursors（BSOA）and elemental carbon（EC）slightly decreased.（5）The process analysis results of the PA module in the CMAQ mode indicate that the main reason for the decrease of PM_2.5 concentration in Changchun due to changes in the underlying surface is the enhancement of transmission and diffusion in the horizontal and vertical directions.In January,the contribution of vertical advection（ZADV）to the negative PM_2.5 increased by 25μg/m³,vertical diffusion（VDIF）increased the decrease in PM_2.5 concentration by 40μg/m³ and 16μg/m³ during the day and night,respectively,and the contribution of horizontal advection（HADV）to the negative PM_2.5 increased by 40μg/m³.In July,vertical diffusion（VDIF）caused a maximum increase of 40μg/m³ in PM_2.5 concentration reduction at night,while horizontal advection（HADV）caused a maximum increase of 32μg/m³ in PM_2.5concentration reduction at night.