卫星观测不仅能反映区域宏观大气污染状况，也能从城市尺度上监测大气污染物的变化。基于以上优势，本文利用MODIS气溶胶光学厚度（AOD）和OMI对流层NO₂垂直柱浓度数据，比较2015年与2012年—2014年以及2015年3个时期（减排前、减排中、减排后）AOD和NO₂柱浓度的变化，定性分析了阅兵期间华北平原地区污染物减排效果，重点定量评估北京市联控减排措施的效果。研究发现2015年减排中华北平原重污染地区AOD和NO₂柱浓度相比于前3年同期有明显降低。定量分析北京市的减排效果得到：2015年减排中较前3年同期而言，AOD降低59%，NO₂柱浓度降低41%；较2015年减排前而言，AOD降低73%，NO₂柱浓度降低30%，去除气象条件影响后，AOD下降43%，NO₂柱浓度下降21%，说明严格的联控减排措施有效地改善了空气质量，气象条件也起到积极的作用。减排措施结束后，AOD和NO₂柱浓度比减排中分别增加159%和71%。研究结果表明，卫星遥感与地基监测评估效果相当，能反映北京地面污染物排放能力；它既能观测区域尺度大气污染变化，又可评估城市尺度大气污染减排。随着卫星技术水平的提高，期望未来卫星遥感可作为一种独立手段来定量评估区域及城市尺度空气质量减排措施的效果。

To ensure good air quality in Beijing, China, during the 2015 China Victory Day Parade (V-day Parade), Beijing and its neighboring six provinces and the associated cities implemented strict cooperative emission reduction measures. So the "Parade Blue" happened on September 3. To evaluate impact of emission control measures during the military parade 2015, we use the remote sensing technique in this study.
Remote sensing can not only monitor the regional atmospheric pollutants, but also can catch the change of pollutants in urban scale. This paper aims to emphatically verify the ability of remote sensing in urban scale by comparing with the ground results.
We use the OMI NO₂ data and MODIS AOD data to evaluate the effect of emission control measures. The study period includes three parts:before the military parade (2015-08-07-2015-08-19), during the military parade (2015.8.20-2015.9.3) and after the military parade (2015.9.4-2015.9.20). We make qualitative analysis of the change of atmospheric pollutants on North China Plain (34.6°-43°N, 110°-123°E) with spatial distribution maps and focus on the quantitative evaluation of Beijing with the time series maps.
First of all, through correlation analysis, we found that NO₂ columns have a good correlation with NO₂ mass concentration in the suburbs. Because the ground-based observations represent the regional atmospheric background in the suburbs, they have good consistency with satellite observations. The urban sites selected in this study distribute uniformly in satellite pixels and their average values can reflect the extent of corresponding pixels. However, NO₂ mass concentrations of sites near road are affected greatly by the local emissions, so in these sites there are some poor correlations between NO₂ columns with NO₂ mass concentration. Secondly, through qualitative analysis of the change of atmospheric pollutants on North China Plain, we found that AOD and NO₂ concentration of heavy polluted area in the North China Plain during the military parade were significantly lower than those with the same period in the first three years, and far less than those before the military parade in 2015. AOD and NO₂ returned to their previous values even higher after the lifting of emission control measures. And lastly, through quantitative evaluation of Beijing, we found that compared to the previous three years AOD reduced 59% and NO₂ reduced 41% during the military parade, while before the military parade AOD reduced 73% and NO₂ reduced 30%. The result was similar with ground-based observations. By excluding the effects of meteorological parameters, AOD and NO₂ reduced 43% and 21% respectively because of the emission controls. AOD and NO₂ increased 159% and 71% after the lifting of emission control measures. So strict control measures improve the air quality and meteorological conditions also play a positive role in this mega-event.
Based on the above results the following conclusions are reached. First, the NO₂ column density retrieved by satellite can effectively reflect the ground pollutant emissions. Next, satellite can observe the pollutants in regional scale such as the North China Plain. Finally, satellite observations can acquire the change of pollutant emissions in the urban scale such as Beijing. We will gradually expand the research area and increase the research object to comprehensively display the ability of remote sensing. We hope satellite observation can be used as an independent method to assess air quality from regional and urban scales in the future.