Satellite-based estimates of ground-level fine particulate matter during extreme events: A case study of the Moscow fires in 2010

We estimate fine particulate matter (PM2.5) concentrations daily using MODIS satellite observations of aerosol optical depth (AOD) for a major biomass burning event around Moscow during summer 2010. Evaluation of MODIS AOD with the Moscow AERONET site supports a MODIS-AOD error estimate of � (0.05 þ0.2 � AOD) for this event. However, since the smoke was often thick (AOD >4.0) and spatially variable, the standard MODIS algorithm incorrectly identifies some aerosol as cloud. We test relaxed cloud screening criteria that increase MODIS coverage by 21% and find excellent agreement with coincident operational retrievals (r 2 ¼0.994, slope ¼1.01) with no evidence of false aerosol detection. We relate the resultant MODIS AOD to PM2.5 using aerosol vertical profiles from the GEOS-Chem chemical transport model. Our estimates are in good agreement with PM2.5 values estimated from in-situ PM10 (r 2 ¼0.85, slope ¼1.06), and we find that the relationship between AOD and PM2.5 is insensitive to uncertainties in biomass burning emissions. The satellite-derived and in-situ values both indicate that peak daily mean concentrations of approximately 600 mgm �3 occurred on August 7, 2010 in the Moscow region of the Russian Federation. We estimate that exposure to air pollution from the Moscow wildfires may have caused hundreds of excess deaths.