中国PM2 .5与AOD的关系：时空变化的前后
The relationships between PM2.5 and AOD in China: About and behind spatiotemporal variations
摘要：
卫星气溶胶产品因其覆盖范围广、空间发布连续等特点，被广泛应用于地面PM2. 5浓度的反演。虽然越来越多的研究集中在反演算法上，但我们发现，在中国，PM2.5浓度与卫星气溶胶光学厚度之间的关系尚未得到充分讨论。卫星气溶胶光学厚度在不同地区是否都是PM2.5的良好指示器，以及随着这些年来污染条件的变化，气溶胶光学厚度是否仍能用于PM2.5的反演尚不清楚。本研究从2013年2月至2017年12月连续调查了中国368个城市不同时间和区域尺度的PM2.5与气溶胶光学厚度的关系。Pearson相关系数和PM2.5/AOD比值作为指标。首先，我们总结了PM2.5和气溶胶光学厚度的时空变化关系。并讨论了气象因子、气溶胶粒径和地形等因素的影响。最后，通过一个GWR反演实验，研究了PM2. 5-AOD关系的变化对反演精度的影响。研究发现，在空间上，京津冀和成渝地区的相关性较高，长三角和珠三角等沿海地区的相关性较弱。PM2.5/AOD比值存在明显的南北差异，华北地区较高，华南地区较低。从时间上看，PM2.5/AOD比值冬季较高，夏季较低，相关系数在5月和9月趋于较高。从2013 - 2017年的年际变化来看，PM2.5/AOD比值呈下降趋势。GWR反演的准确性也在下降，这可能意味着AOD可能不是未来PM2.5的良好指标。
英文摘要：
Satellite aerosol products have been widely used to retrieve ground PM2.5 concentration because of its wide coverage and continuously spatial distribution. While more and more studies focus on the retrieval algorithm, we find that the relationship between PM2.5 concentration and satellite AOD has not been fully discussed in China. Is satellite AOD always a good indicator for PM2.5 in different regions and can AOD still be employed to retrieve PM2.5 with pollution conditions changing in these years remain unclear. In this study, the relationships between PM2.5 and AOD were investigated in 368 cities in China for a continuous period from February 2013 to December 2017, at different time and regional scales. Pearson correlation coefficients and PM2.5/AOD ratio were used as the indicator. Firstly, we concluded the relationship of PM2.5 and AOD in terms of spatiotemporal variations. Then the impact of meteorological factors, aerosol size and topography were discussed. Finally, a GWR retrieval experiment was conducted to find out how was the retrieval accuracy changing with the varying of PM2.5-AOD relationship. We found that spatially the correlation is higher in Beijing-Tianjin-Hebei and Chengyu region and weaker in coastal areas such as Yangtze River Delta and Pearl River Delta. The PM2.5/AOD ratio has obvious North-South difference with a high ratio in north China and a lower ratio in south China. Temporally, PM2.5/AOD ratio is higher in winter and lower in summer, the correlation coefficient tends to be higher in May and September. As for interannual variations from 2013 to 2017, we detected a declining tendency on PM2.5/AOD ratio. The accuracy of GWR retrievals were decreasing too, which may imply that AOD may not be a good indicator for PM2.5 in the future.
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