Research On Distribution And Source Characteristics Of Atmospheric Organic Aerosols Based On ME-2 Model

In recent years,fine particulate matter(PM_2.5)pollution in urban air in China has been significantly improved,but it is still the primary atmospheric pollutant in northern cities.As the main component of PM_2.5,organic aerosol（OA）is of great significance to explore its source and formation process for continuous improvement of PM_2.5 pollution.In this study,a high time resolution time-of-flight aerosol chemical composition monitor（TOF-ACSM）was used to conduct the online measurement of non-refractory PM_2.5(NR-PM_2.5)chemical components(OA,SO₄^2-,NO₃^-,NH₄⁺and Cl^-)in a place in Taiyuan Basin in January,April,August and October 2020.The seasonal variation characteristics of NR-PM_2.5 chemical components,the sources of OA were analyzed,and the influencing factors of the formation process of secondary organic aerosol（SOA）were discussed,with a view to providing basic data for PM_2.5 indicator control.The main conclusions are as follows:（1）The average concentrations of OA in spring,summer,autumn and winter are 11.34±5.37μg/m³,11.26±8.75μg/m³,10.28±7.53μg/m³ and 60.17±41.41μg/m³,respectively.They contributed 40.93%,30.47%,29.26%and 33.56%of NR-PM_2.5,respectively.In winter,due to the influence of coal burning for heating,the primary emissions are enhanced,and the concentration of OA is much higher than other seasons.（2）Based on the results of ME-2 receptor model,in addition to HOA（vehicle exhaust）,COA（cooking OA）,LO-OOA（less oxidized OOA）and MO-OOA（more oxidized OOA）,the influence of CCOA（coal combustion OA,19.6%）and BBOA（biomass burning OA,16.8%）increased in winter.In spring,autumn and winter,MO-OOA accounted for the largest proportion of OA,78.6%,58.4%and43.4%respectively,in summer,LO-OOA accounted for the largest proportion of OA（70.6%）.SOA（LO-OOA+MO-OOA）is the main source of OA and contributed 85.6%,85.3%,89.1%and 55.9%of OA in the four seasons,respectively.（3）The influence of RH and Ox on SOA shows that,in spring,both aqueous phase reaction and photochemical reaction are the formation mechanism of MO-OOA,and photochemical reaction is conducive to the formation of LO-OOA.In summer,the photochemical reaction is beneficial to the formation of LO-OOA and MO-OOA.In Autumn,the aqueous phase reaction is the main formation mechanism of LO-OOA,and photochemical reaction is the main formation mechanism of MO-OOA.In winter,photochemical reaction and aqueous phase reaction are favorable for the formation of MO-OOA,and aqueous phase reaction is favorable for the formation of LO-OOA.（4）The influence of wind speed and direction on OA sources is shown,in spring,the wind direction is northeast and the wind speed is lower than 4m/s,and the MO-OOA is higher（11.94μg/m³）.In summer,the wind direction is northeast and northwest and the wind speed is lower than 1m/s,and the LO-OOA is higher（11.87μg/m³ and 10.43μg/m³）.When the wind direction in autumn is northeast wind and the wind speed is lower than 3 m/s,LO-OOA and MO-OOA are higher（5.94μg/m³ and 6.58μg/m³）.In winter,the wind direction is northeast wind and northwest wind,and the wind speed is lower than 2m/s,LO-OOA and MO-OOA are higher（10.72μg/m³,39.46μg/m³ and 13.76μg/m³,27.48μg/m³）.The control of coking enterprises in the northeast direction should be strengthened in spring and autumn,and the control of coking enterprises in the northeast and northwest direction should be strengthened in summer and winter.