Trends, optical properties, and source contributions to elemental and organic carbon influencing the North American Arctic.


Atmospheric aerosols are one of the greatest sources of uncertainty in current global climate models. Aerosols affect the earth’s radiative budget by scattering or absorbing incoming solar radiation and by acting as cloud condensation nuclei. Carbonaceous aerosols are dominated by two main components: organic carbon and elemental carbon. Traditionally, only elemental carbon aerosols acted as absorbing species in global climate models, causing models to underestimate warming in certain regions, particularly the Arctic. However, it is now known that a fraction of organic carbon, or brown carbon, absorbs incoming solar radiation mainly in the ultra-violet wavelengths, and is responsible for as much as 19% of total aerosol absorption resulting from anthropogenic activity globally. Primary aerosols are emitted directly into the atmosphere via natural and anthropogenic processes wildfires, fossil fuel combustion, and biomass burning, while secondary organic aerosols are formed in the atmosphere via gaseous emission partitioning into the condensed phase. Due to their short atmospheric lifespan, 1-2 weeks, it is thought that decreasing the emissions of elemental and brown carbon would immediately reduce climate forcing across the globe. The Arctic is particularly sensitive to anthropogenic climate forcing. It is warming at a rate nearly twice the global mean, with temperature increases of nearly 2 °C since 1970. Aerosols play a vital role in the radiative budget of the Arctic due to their direct and indirect effects. For example, deposition of atmospheric aerosols on snow and ice reduces surface albedo, contributing to changing melt patterns. In order to determine the contributions of fossil and contemporary sources to organic and elemental carbon in the North American Arctic, a combination of source apportionment strategies, including radiocarbon abundance, was applied to samples collected at Barrow, Alaska. Optical properties were also explored to determine the overall efficiency of light-absorbing particles in the region. Results indicate that fossil sources dominate the elemental carbon burden for much of the year, while organic carbon has more equal contributions of fossil and contemporary sources throughout the year. These apportionment results are more tightly constrained than current climate models, and can be used to improve the overall accuracy of these models.



Elemental carbon. Organic carbon. Aerosols. Radiocarbon. Aerosol optical properties.