Gaoyuan qixiang (Jun 2022)
Numerical Study on Transport Characteristics of PM2.5 under Different Pollution Conditions in Beijing during Wintertime
Abstract
The air quality in Beijing has been improved in recent years， but still fails to meet the national secondary standard.The heavy pollutions associated with the fine particle matters occurred in the winter of 2019 even though the effective emission reductions were carried out.Thus， it needs to do some researches targeted at the current sources of PM2.5 in Beijing.In this study， the regional air quality modeling system RAMS-CMAQ （the Regional Atmospheric Modeling System-Community Multiscale Air Quality） coupled with a source apportionment tool named ISAM （the Integrated Source Apportionment Method） was applied to investigate the variations in the chemical components of PM2.5 in Beijing and their sources during three different pollution （nonpolluted， light， moderate and heavy polluted） episodes in December 2019， including the regional transport characters of PM2.5 and its components as well as the corresponding precursors.Analysis of the model results shows that the regional transport was a major contributor to PM2.5 over Beijing during the winter time， and its contribution increased from 69.7% in the nonpolluted days to 75.7% in the moderate and heavy polluted days， and the major source regions were Hebei and Inner Mongolia.During the nonpolluted days， the westerly winds prevailed， and the pollution might happen and deteriorate in Beijing when the continuous air-mass came from the south appeared at the same time.In winter， the secondary inorganic aerosols played a dominated role in PM2.5 over Beijing， and their contributions increased with the aggravation of pollution.The contribution of secondary inorganic aerosols to PM2.5 was 6.7% higher in the moderate and heavy polluted days than that in the nonpolluted days.The contribution of sulfate aerosols to PM2.5 decreased from the nonpolluted days to the moderate and heavy polluted days， while the contribution of nitrate aerosols increased， which led to the worsening air pollution.Except nitrate aerosols， the regional transport was also a major contributor to sulfate， ammonium， organic carbon， primary dust and black carbon， and its contribution increased with the deterioration of pollution.The corresponding contribution increased by 3.8%， 15.7%， 9.8%， 6.9% and 7.4% in the moderate and heavy polluted days than that in the nonpolluted days， respectively.Furthermore， the regional transport contributed significantly to SO2， NH3 and NO2， and the contribution to SO2 and NH3 continuously increased by 5.4% and 6.2% in the moderate and heavy polluted days higher than that in the nonpolluted days， but did not show the same feature to NO2.
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