春季沙尘过程北京市不同粒径大气气溶胶污染特征及来源分析

To understand the evolution of the physical and chemical properties of dust aerosols in the atmosphere, the concentrations and chemical compositions of differently sized particles were continuously observed and analyzed using an ion chromatograph and carbonaceous analyzer during the outbreak of dust in May 2017 in Beijing. The concentrations of total suspended particulate (TSP), water-soluble organic carbon (WSOC), elemental carbon (EC), OC, and water-soluble inorganic ions were (2237.59±681.49), (29.90±18.05), (1.46±3.05), (67.35±29.07), and (136.75±46.38) μg•m ^-3 during the dust period, respectively, and significantly exceeded that of the non-dust period, except for EC. The Na ⁺ , NH ₄ ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Cl ^- , NO ₃ ^- , SO ₄ ^2- , and WSOC concentrations during the dust storm period were 11.55, 3.00, 14.88, 14.89, 9.40, 4.60, 2.40, 3.91, and 1.83 times higher than that during the non-dust period. The growth of crustal ions, such as Ca ²⁺ and K ⁺ , was notably the largest and NH ₄ ⁺ and NO ₃ ^- were minimal. The size distribution indicates that crustal ions primarily occur in the coarse mode during the whole sampling campaign. The SO ₄ ^2- and NO ₃ ^- ions are slightly bimodal during the dust storm, with a dominant peak in the coarse mode at 4.7-5.8 μm and a very minor peak in the fine mode with a size range of 0.43-0.65 μm. During the non-dust period, SO ₄ ^2- is the dominant mode in the fine mode, while NO ₃ ^- changes little compared with that during the dust period, which indicates that heterogeneous reaction with crustal ions is the main formation mechanism of NO ₃ ^- in the coarse mode. A significant positive correlation was observed between SO ₄ ^2- and the sum of crustal ions during the dust period, indicating that the source of SO ₄ ^2- during the dust period is remote transmission of the dust storm. During the non-dust period, the positive correlation of SO ₄ ^2- with NH ₄ ⁺ indicates that secondary formation is the main source of SO ₄ ^2- . Based on correlation analysis of NO ₃ ^- with crustal ions and NH ₄ ⁺ , both remote transmission and secondary formation are the sources of NO ₃ ^- during the dust storm and heterogeneous reactions are predominant during the non-dust period.