ИСТИНА

We estimated the distribution of aerosol optical thickness (AOT) with a spatial resolution of 1 km over Moscow megacity using MAIAC aerosol product based on MODIS satellite data (Lyapustin et al., 2018) for the warm period of year (May-September). Its validation against AERONET (Aerosol Robotic Network) datasets near the city centre at Moscow_MSU_MO and over Moscow suburbs at Zvenigorod has revealed that MAIAC AOT at 470 nm values were in an agreement with AERONET data but were underestimated by 0.05-0.1 for AOT<1 and overestimated for smoke aerosol conditions with AOT>1. The AOT MAIAC retrieval biases were almost the same for Moscow_MSU_MO and Zvenigorod AERONET sites, which indicated that MAIAC effectively removed the effect of the bright urban surface reflectance in the city centre. Annual median AOT differences between Moscow_MO_MSU and Zvenigorod (dAOT) varied up to +0.03 with statistically significant positive bias for most years and the average dAOT of ~0.02 according to ground-based measurements. At the same time, according to the MAIAC algorithm the dAOT varied within ±0.01 and were not statistically significant. The dAOT started decreasing recently due to intensive urban development of the territory adjacent to the Zvenigorod site and the decrease of pollutant emissions in Moscow, which is mainly caused by environmental regulations. The difference between maximum AOT and mean AOT values for different (25%, 50%) quantiles within the Moscow region, was about 0.02-0.04 which could be attributed to local urban aerosol effects. This work is supported by the Russian Science Foundation under grant # 18-17-00149.