京津冀及周边民用散煤燃烧控制对北京市PM2.5的影响

为评估京津冀及周边“2+26”城市农村居民面源污染控制成效，揭示其对北京市秋冬季重污染天气PM_2.5污染的改善作用，及其对PM_2.5组分硫酸盐形成机制的影响，采用空气质量模型对北京市2018—2019年秋冬季5次重污染事件进行了模拟. 结果表明:①在“2+26”城市平原地区民用散煤削减90%的控制情景下，区域PM_2.5浓度最大值由324 μg/m3降至251 μg/m3，下降了23%. 北京市城区PM_2.5浓度由139 μg/m3降至124 μg/m3，下降了11%；同时，北京市城区SO₂、硫酸盐浓度分别降至6.2、14.9 μg/m3，分别下降了45%、24%. ②农村居民面源污染控制前北京市硫酸盐浓度的正贡献来源主要受水平平流输送过程影响，控制后水平平流输送过程仍起主导作用，但该过程在水平平流输送、垂直平流输送、水平扩散、垂直扩散这4个物理过程中的绝对重要性上升了2%；此外，农村居民面源污染控制后垂直扩散清除过程对硫酸盐浓度的贡献下降了33%，气溶胶二次转化过程的贡献下降了25%，但SO₂向硫酸盐转化的速率加快，其小时转化率上升了1.44%. ③ISAM源解析方法结果表明，控制情景下区域工业过程是影响北京市SO₂浓度的最主要行业源因素，平均贡献率为65%，硫酸盐工业过程源的平均贡献率为82%. 区域来源分析表明，北京市SO₂来源主要为外地源输送，硫酸盐主要来源与SO₂一致，其中河北省贡献较大，其对SO₂、硫酸盐的平均贡献率分别达43%、40%. 研究显示，控制情景下污染期间北京市PM_2.5污染改善，且污染物浓度、形成过程和来源贡献均发生明显变化. 

Impact of Residential Coal Combustion Control in Beijing-Tianjin-Hebei and Surrounding Region on PM2.5 in Beijing

In order to evaluate the effectiveness of non-point source pollution control of rural residents in the '2+26' cities in the Beijing-Tianjin-Hebei and surrounding areas, and to reveal the improvement of Beijing's PM_2.5 pollution in autumn and winter, as well as its impact on the formation mechanism of sulfate in PM_2.5, air quality model was used to simulate five heavy pollution incidents in the autumn and winter of 2018-2019 in Beijing. The results showed that: (1) Under the 90% emission reduction control scenario of civilian bulk coal in '2+26' plain area, the maximum PM_2.5 pollution concentration in this area decreased from 324 μg/m3 to 251 μg/m3, a decrease of 23%, and the PM_2.5 concentration in Beijing urban area dropped from 139 μg/m3 to 124 μg/m3, a decrease of 11%. Meanwhile, the concentration of SO₂ and sulfate in Beijing urban area dropped to 6.2 and 14.9 μg/m3, a decrease of 45% and 24%, respectively. (2) Process analysis showed that before the control, the positive contribution of sulfate concentration in Beijing was mainly affected by the horizontal advection transport process, and the horizontal advection process still dominated the positive contribution after control. However, the absolute importance of four physical processes of diffusion, namely horizontal and vertical advection transport, horizontal and vertical turbulent diffusion, increased by 2%. In addition, after control, the contribution of vertical diffusion process was reduced by 33%, while the contribution of the aerosol secondary conversion process was reduced by 25%, but the conversion rate of SO₂ to sulfate was accelerated, the conversion rate per hour could increase by 1.44%. (3) Source apportionment analysis showed that under the control scenario, the industrial process was the most important source sectors affecting SO₂ concentration in Beijing, with an average contribution rate of 65% and 82% for sulfate concentration. Regional source analysis showed that the main source of SO₂ was external sources, and the main source of sulfate was consistent with that of SO₂. Among them, the external source from Hebei Province made a prominent contribution, and its average contribution to SO₂ and sulfate was 43% and 40%, respectively. The research indicates that PM_2.5 pollution in Beijing has improved, and the concentration, formation processes and source apportionment of air pollutants in Beijing can change significantly during the heavy pollution events under controlled scenario.