Abstract
Abstract. We use a global chemical transport model (GEOS-Chem CTM) to interpret observations of black carbon (BC) and organic aerosol (OA) from the NASA ARCTAS aircraft campaign over the North American Arctic in April 2008, as well as longer-term records in surface air and in snow (2007–2009). BC emission inventories for North America, Europe, and Asia in the model are tested by comparison with surface air observations over these source regions. Russian open fires were the dominant source of OA in the Arctic troposphere during ARCTAS but we find that BC was of prevailingly anthropogenic (fossil fuel and biofuel) origin, particularly in surface air. This source attribution is confirmed by correlation of BC and OA with acetonitrile and sulfate in the model and in the observations. Asian emissions are the main anthropogenic source of BC in the free troposphere but European, Russian and North American sources are also important in surface air. Russian anthropogenic emissions appear to dominate the source of BC in Arctic surface air in winter. Model simulations for 2007–2009 (to account for interannual variability of fires) show much higher BC snow content in the Eurasian than the North American Arctic, consistent with the limited observations. We find that anthropogenic sources contribute 90% of BC deposited to Arctic snow in January-March and 60% in April–May 2007–2009. The mean decrease in Arctic snow albedo from BC deposition is estimated to be 0.6% in spring, resulting in a regional surface radiative forcing consistent with previous estimates.
Highlights
Aerosol pollution in the Arctic peaks in winter-spring, when transport from mid-latitudes is most intense and removal by deposition is slow (Barrie et al, 1981; Quinn et al, 2002, 2007; Law and Stohl, 2007)
Fires were a dominant source of organic aerosol (OA) during Aircraft and Satellites (ARCTAS)/ARCPAC, but we show that anthropogenic sources were more important for black carbon (BC), near the surface
Open fires in Russia were the dominant source of OA in ARCTAS (Warneke et al, 2009, 2010), and we find from tagged source attribution that OA emissions from Russian fires must be reduced by an additional 36 % to match the ARCTAS observations
Summary
Aerosol pollution in the Arctic peaks in winter-spring, when transport from mid-latitudes is most intense and removal by deposition is slow (Barrie et al, 1981; Quinn et al, 2002, 2007; Law and Stohl, 2007). Two coordinated aircraft campaigns with carbonaceous aerosol measurements were conducted in April 2008 out of Fairbanks, Alaska: the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) (Jacob et al, 2010) and the NOAA Aerosol, Radiation and Cloud Processes affecting Arctic Climate (ARCPAC) (Brock et al, 2011) These two campaigns were part of the international program Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport (POLARCAT) (http://www.polarcat.no). They provided extensive vertical profiling of trace gases and speciated aerosols through the depth of the Arctic troposphere. Our results suggest that Russian anthropogenic sources are a major source of Arctic BC in winter, and that BC concentrations in Arctic air and snow are highest in the Eurasian sector in both winter and spring
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