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Satellite aerosol products have been widely used to retrieve ground PM2.5concentration because of its wide coverage and continuously spatialdistribution. While more and more studies focus on the retrieval algorithm, wefind that the relationship between PM2.5 concentration and satellite AOD hasnot been fully discussed in China. Is satellite AOD always a good indicator forPM2.5 in different regions and can AOD still be employed to retrieve PM2.5 withpollution conditions changing in these years remain unclear. In this study, therelationships between PM2.5 and AOD were investigated in 368 cities in Chinafor a continuous period from February 2013 to December 2017, at different timeand regional scales. Pearson correlation coefficients and PM2.5/AOD ratio wereused as the indicator. Firstly, we concluded the relationship of PM2.5 and AODin terms of spatiotemporal variations. Then the impact of meteorologicalfactors, aerosol size and topography were discussed. Finally, a GWR retrievalexperiment was conducted to find out how was the retrieval accuracy changingwith the varying of PM2.5-AOD relationship. We found that spatially thecorrelation is higher in Beijing-Tianjin-Hebei and Chengyu region and weaker incoastal areas such as Yangtze River Delta and Pearl River Delta. The PM2.5/AODratio has obvious North-South difference with a high ratio in north China and alower ratio in south China. Temporally, PM2.5/AOD ratio is higher in winter andlower in summer, the correlation coefficient tends to be higher in May andSeptember. As for interannual variations from 2013 to 2017, we detected adeclining tendency on PM2.5/AOD ratio. The accuracy of GWR retrievals weredecreasing too, which may imply that AOD may not be a good indicator for PM2.5in the future.

The relationships between PM2.5 and AOD in China: About and behind spatiotemporal variations