Year-round observation of atmospheric inorganic aerosols in urban Beijing: Size distribution, source analysis, and reduction mechanism

To investigate particle characteristics and find an effective measure to control severe particle pollution, year-round observation of size-segregated inorganic aerosols was conducted in Beijing from January to December, 2016. The sampled atmospheric particles all presented bimodal size distribution at four pollution levels(clear, slight pollution, moderate pollution and severe pollution), and peak values appeared at the size range of 0.7-2.1 μm and >9.0 μm,respectively. As dominant particle compositions, NO3~-, SO42-, and NH4~+ in four pollution levels all showed significant peaks in fine mode, especially at the size range of 1.1-2.1 μm.Secondary inorganic aerosols accounted for about 67.6%(36.3%(secondary sulfates) + 31.3%(secondary nitrates)) of the total sources of fine particles in urban Beijing. Severe pollution of fine particles was mainly caused by the air masses transported from nearby western and southern areas, which are industrial and densely populated region, respectively. Sensitivity tests further revealed that the control measures focusing on ammonium emission reduction was the most effective for particle pollution mitigation, and fine particles all showed nonlinear responses after reducing ammonium, nitrate, and sulfate concentrations, with the fitting curves of y =-120.8 x-306.1 x~2+ 290.2 x3, y =-43.5 x-67.8 x~2, and y =-25.8 x-110.4 x~2+ 7.6 x~3, respectively(y and x present fine particle mass variation(μg/m~3) and concentration reduction ratio(CRR)/100(dimensionless)). Overall, our study presents useful information for understanding the characteristics of atmospheric inorganic aerosols in urban Beijing, as well as offers policy makers with effective measure for mitigating particle pollution.