Year-round optical properties and source characterization of Arctic organic carbon aerosols on the North Slope Alaska

Long-term data on organic aerosol concentration and optical properties are needed in the Arctic to improve characterization of radiative forcing by atmospheric aerosols. This study presents the seasonal trends (summer 2012 to summer 2013) of organic carbon (OC) and water-soluble organic carbon (WSOC) along with optical properties of light-absorbing OC from a yearlong sampling campaign in Utqiagvik, AK. Ambient OC concentrations for the year range from 0.008 +/- 0.002 mu g m(-3) to 0.95 +/- 0.06 mu g m(-3) with peaks in late summer, early fall, and late winter. On average, WSOC accounted for 57 +/- 11% of the total OC burden throughout the sampling campaign, which is consistent with previous WSOC values. In order to understand the potential radiative impacts of light-absorbing OC, the light absorption properties of WSOC were determined. Seasonal averaging revealed that the highest average mass absorption efficiency value of 1.54 +/- 0.75 m(2) g(-1) was in the fall, with an annual range of 0.70 +/- 0.44 to 1.54 +/- 0.75 m(2) g(-1). To quantify the contributions of fossil and contemporary carbon sources to OC, radiocarbon abundance measurements were performed. For OC, fossil contributions were the greatest for select samples in the fall at 61.4 +/- 9.8%, with contemporary contributions dominating OC in the spring and summer (68.9 +/- 9.8% and 64.8 +/- 9.8%, respectively). Back trajectories identified five major source regions to Utqiagvik throughout the year, with a marine influence from the Arctic Ocean potentially present in all seasons. All these results point to impact from primary and secondary sources of OC in the Arctic. Plain Language Summary In this study, trends and sources of atmospheric organic aerosols, or small particles in the atmosphere, are explored in the North American Arctic region (i.e., within the Arctic Circle). Organic aerosols can absorb sunlight and heat the atmosphere, cause snow and ice surfaces to darken, and act as seed particles for cloud formation. Aerosol samples were collected from summer 2012 to summer 2013 and analyzed to determine the sources of the particles: fossil fuel combustion (i.e., burning natural gas flares, diesel, or coal), biomass combustion (the burning of grass, trees, or biofuels), and biogenic emissions (aerosols derived from marine and terrestrial plant emissions). It was determined that fossil fuel combustion was an important source of aerosols in the fall, while nonfossil sources of organic aerosols, including biogenic emissions and biomass combustion events, were dominant in the spring and summer. Major source regions of these aerosols to the North American Arctic include the Russian Arctic, Canadian Arctic, the Alaskan Arctic, the Arctic Ocean, and western interior Alaska. This study highlights the potential climatic effects of light-absorbing organic aerosols and their sources in the North American Arctic and can be useful for determining climate mitigation strategies in this region.