污染源减排时刻和减排比例对北京市PM_(2.5)浓度的影响

利用Model-3/CMAQ及京津冀地区高分辨率排放源清单,选取文献19]中污染峰值当天启动50%污染源削减方案的同时,进一步设置了3种污染源控制方案(峰值当天启动75%源削减;峰值日前1d、2d开始启动25%源削减),比较了峰值日前启动适量减排与峰值日当天启动大幅度减排的效果差异.结果表明:污染峰值当天启动50%、75%减排时,北京市PM2.5浓度下降率分布不均匀,高值区集中于PM2.5浓度高值区,减排后PM2.5浓度分布较减排前均匀.提前1~2d启动25%源削减时,峰值日北京市PM2.5浓度整体下降.城、郊PM2.5下降率均表现为当天减排50%小于提前1d开始减排25%;当天启动减排提高到75%时,城区PM2.5下降率大于提前2d启动25%减排,郊区表现为峰值前2d启动25%削减优于当天减排75%.将峰值前1d、2d启动25%减排分别与当天启动50%、75%减排时北京市峰值日PM2.5浓度下降率相减,北京市绝大部分区域下降率差值为正;峰值前1d、2d启动25%减排分别比峰值日启动50%、75%减排时北京市平均PM2.5多下降4.7μg/m3(6%)、2.9μg/m3(4%).综上所述,在污染峰值来临之前采取适量减排较污染当天才启动大幅度减排更有利于北京市整体空气质量达标.

Effects of emission-sources reduction time and ratios on PM25 concentration over Beijing Municipality

Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with a high resolution inventory data over Beijing-Tianjin-Hebei region was implemented to investigate the different effects of ‘reducing a moderate amount of emission-sources ahead’ against ‘reducing a large amount of emission-sources on the peak day’ in the region, one of which is to cut emission-sources at a ratio of 50% on the peak day (Feb 13th, 2012) as described in reference 19]. Another 3 emission-sources reduction strategies: (1) cutting 75% emission-sources on the peak day; (2) cutting 25% 1day before the peak day (3) cutting 25% 2days before, were newly designed. The simulation results under these cutting strategies showed that when starting emission-sources reduction ratios of 50%, 75% on the peak day, the PM2.5 concentration decreasing ratios distribution over Beijing were uneven, with high decreasing ratios at the high PM2.5 concentration zone, resulting in more evenly distributed PM2.5 concentrations. When reducing 25% emission-sources 1~2days ahead of the peak day, Beijing encountered an overall PM2.5 concentration decrease. Both urban and rural Beijing showed a higher PM2.5 concentration decreasing ratio when reducing 25% emission-sources 1day ahead than reducing 50% emission-sources on the peak day. When the emission-sources reduction ratio on the peak day was increased to 75%, the PM2.5 decreasing ratio was higher than reducing 25% emission-sources 2days ahead over urban Beijing, which was not seen over the rural. When the PM2.5 concentration decreasing ratios of cutting 50%, 75% emission-source on the peak day were subtracted from cutting 25% emission-source 1day and 2days ahead of the peak day respectively, the difference of PM2.5 concentration decreasing ratios over Beijing were mainly positive. Over whole Beijing, reducing 25% emission-source 1day ahead would decrease more PM2.5 (4.7μg/m3, or 6%) than reducing 50% at the peak day; while reducing 25% emission-source 2days ahead would decrease more PM2.5 (2.9μg/m3or 4%) than reducing 75% at the peak day. In summary, it’s more effective for Beijing to reach the air quality standard by reducing a moderate amount of emission-sources ahead than reducing a large amount of emission-sources on the peak day.