“大气十条”实施期间南京市PM2.5化学组成与来源的演变特征

为深入认识“大气污染防治行动计划”(“大气十条”)对大气细颗粒物(PM_2.5)污染的影响，基于“大气十条”实施期间南京市主城区(草场门)PM_2.5的化学组分监测资料，研究了PM_2.5主要组分的浓度和占比、富集因子和酸度等变化特征，并采用正定矩阵因子分解法(PMF)进行了PM_2.5的来源解析.结果发现，“大气十条”实施期间，南京市PM_2.5中硫酸根(SO₄^2-)的占比总体下降，但硝酸根(NO^-₃)和铵根(NH⁺₄)的占比均明显上升，两者的占比从2014年的25.58%上升到2017年的37.15%;碳组分(OC和EC)的浓度在“大气十条”早期出现大幅下降，但后期的下降趋势明显变缓，其中，有机碳(OC),特别是二次有机碳(SOC)的占比不降反升；PM_2.5酸性显著减弱，阴阳离子的摩尔当量比值(CE/AE)从2014年的0.83上升...

Evolution of PM2.5 Chemical Composition and Sources in Nanjing During the Implementation of the APPCAP

To acquire a deeper understanding about the impact of the Air Pollution Prevention and Control Action Plan (APPCAP) on ambient fine particulate matter (PM_2.5), measurements of PM_2.5 chemical components were conducted in the urban area of Nanjing during the implementation of the APPCAP. Evolution characteristics of several properties of the PM_2.5 were studied, including the concentrations, proportions, and enrichment factors of major PM_2.5 components and the acidity of the PM_2.5. In addition, the source apportion of the PM_2.5 was analyzed using the positive matrix factorization (PMF) model. The results showed that during the implementation of the APPCAP, the proportion of sulfate (SO₄^2-) in PM_2.5 decreased, whereas the proportions of nitrate (NO^-₃) and ammonium (NH⁺₄) increased significantly together, from 25.58% in 2014 to 37.15% in 2017. The concentrations of carbon components (OC and EC) decreased in the early stage of the APPCAP; however, the decreasing trend slowed down in the later stage. In particular, the proportion of organic carbon (OC) increased, especially for the secondary organic carbon (SOC). The acidity of the PM_2.5 decreased significantly, with the molar equivalent ratio of cations and anions increasing from 0.83 in 2014 to 1.13 in 2017. The contributions of coal combustion and the metallurgical and petrochemical industry to the PM_2.5 generally showed a downward trend, whereas the contribution of vehicle emissions increased rapidly, from 8.78% in 2014 to 13.92% in 2017. The contribution of general fugitive dust fluctuated greatly, but that of soil fugitive dust showed an upward trend. This study suggested that the direct PM_2.5 emissions, such as those from coal combustion and industries, were effectively controlled during the implementation of the APPCAP; however, the contribution of secondary aerosols became increasingly prominent, which indicates that future policies of PM_2.5 pollution control should focus on emission reduction of the precursors such as NO_x, NH₃, and VOCs. In addition, the effects of increasing alkalization of the PM_2.5 and enhanced oxidizability of the atmosphere on the PM_2.5 pollution also require further attention.