In order to evaluate the effects of pollution control measures executed during the G20 Summit in Hangzhou, data from the numerical simulation of the WRF-Chem model and observations of AQI, PM2. 5 , SO2 and others were analyzed. The results indicated:( 1) The data of numerical simulation indicated that the pollution control measures induced obvious emissions reductions. The greatest proportion of pollutant reductions was in the core area, the second was in the strict control area and the last was in the normal control area. The levels of pollutant reductions were in the order ( biggest to smallest ): SO2 , PM2. 5 , NOx and VOCs. ( 2 ) According to the observational data, the air quality in Zhejiang Province was improved obviously, but with different levels in different control areas, during the G20 Summit in Hangzhou. Compared to the AQI in September 2015 and August 2016, the AQI in September 2016 in the core area was decreased by about 35 and 25, respectively, while the decreases in the strict control area were about 20 and 15, and the decreases in the normal control area were about 8 and 5. The distributions of PM2. 5 concentration showed the same change characteristics as AQI, and thus the actual observations were in agreement with the simulation results. ( 3) During the G20 Summit in Hangzhou, the daily AQI and pollutant concentrations decreased and reached the lowest values on September 5th in Hangzhou City and Zhejiang Province. From September 4th to 5th , the daily AQIs in Hangzhou City and Zhejiang Province were 90, 62 and 77, 51, reaching the national secondary standard, and the daily average PM2. 5 concentrations were 37, 35 μg∕m3 and 20, 21 μg∕m3 , respectively, which were superior to the national secondary standard. (4) Pollution control measures changed the characteristics of primary pollutants. In Hangzhou, there were no daily proportions of primary pollutants for PM2. 5 from June to August 2016. The daily proportions of primary pollutants for NO2 declined to zero from July to September 2016 and then greatly increased to 60% in October. The daily proportions of primary pollutants for O3 appeared to quickly rise beginning in April 2016, and then reached the maximum in July. Its change trend presented a unimodal type which was totally different from the bimodal type in the past years. Besides advantageous meteorological conditions, pollution control measures were the key factor for achieving good air quality during the G20 Summit in Hangzhou.%为了实现杭州G20峰会(二十国集团财长和央行行长会议)期间的环境空气质量目标,2016年初开始长江三角洲地区尤其是浙江省加快推进大气污染防治行动,分区分时间节点实施多种污染控制措施.为了评估这些措施实施成效,利用WRF-Chem(Weather Research and Forecasting Model Coupled to Chemistry)模式对2015—2016年浙江省AQI(air quality index)、PM2.5、SO2等污染物浓度观测资料进行了模拟计算及分析.结果表明:①模拟计算显示,G20峰会期间各污控措施减排效果明显,核心区减排比例最大,严控区次之,管控区最小,4种污染物浓度减排比例从大到小顺序依次是SO2、PM2.5、NOx和VOCs.②观测资料分析显示,G20峰会期间浙江省环境空气质量明显改善,但不同控制区改善状况不尽相同.与2015年9月、2016年8月相比,2016年9月核心区月均AQI的降幅约为35和25;严控区次之,AQI降幅约为20和15;管控区最弱,AQI降幅约为8和5.ρ(PM2.5)情况与AQI相似,观测结果与模拟计算一致.③G20峰会期间日均AQI及各种污染物浓度振荡下降,9月5日降至最低值.9月4—5日杭州市和浙江省日均AQI分别为90、62和77、51,均在GB 3095—2012《环境空气质量标准》的二级标准限值以下;日均ρ(PM2.5)分别为37、35μg∕m3和20、21μg∕m3,优于GB 3095—2012二级标准.④污控措施改变了大气中的首要污染物.以杭州市为例,2016年6—8月没有出现以PM2.5为首要污染物的污染天气情况;7—9月没有出现以NO2为首要污染物的污染天气情况,2015仅8月出现这种情况,10月出现跃升,日数占比高达60%左右;从4月开始以O3为首要污染物的日数占比较往年呈更快的增长状态,7月出现最大值,并呈现与往年双峰型不同的单峰型结构.研究显示,除有利气象条件外,对污染源所采取的严格控制措施是杭州G20峰会取得良好效果的主要原因.
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