Arctic air pollution seen from space

Arctic Amplification is a phenomenon linked to complicated, non-linear processes and feedback mechanisms between surface and atmosphere in the Arctic regions. Aerosols are one of the largest sources of uncertainty for those processes and feedbacks due to spatial/temporal coverage and quality of the available observations. Aerosol optical properties, especially Aerosol Optical Thickness (AOT), over the Arctic are currently sparsely provided by ground-based measurements or active remote sensing observations with very limited spatial coverage for a relative short time period. Arctic aerosol observations from passive remote sensing are needed to fill the data gaps both temporally and spatially to reduce the uncertainty in the knowledge of Arctic aerosol during the recent Arctic amplification. Retrieval of AOT over snow-covered Arctic regions from passive remote sensing is very challenging due to 1) lack of aerosol information content; 2) large surface contribution to passive satellite observations; 3) similarities between snow and cloud properties. All above require precisely decoupling of surface contribution from Top Of Atmosphere (TOA) reflectance and good performance of cloud screening algorithm in advance. In this paper, we present a method for the AOT retrieval over snow/ice-covered surfaces trying to address all three aspects listed above utilizing a dual-viewing technique. Satellite-based MODIS and AATSR retrievals of AOT over snow-covered Arctic regions are in close agreement with ground-based measurements. Smooth transition of AOT between new-derived snow-covered regions AOT and mature oceanic regions AOT product is achieved, indicating trustable quality of the satellite derived AOT over Arctic regions. Arctic air pollution can be seen from space using the satellite-derived AOT product. Arctic haze event in spring is analyzed using the time-series dataset created by both satellite-derived and ground-based observations. A case study of the transportation of Russian wildfire in 2010 into the Arctic regions is also presented.