Arctic aerosols: origins and direct radiative forcings

Long-range transport of anthropogenically-emitted aerosols contaminates the Arctic's naturally pristine environment, perturbing its radiative balance. Although several limitations and uncertainties restrict the ability to quantify direct radiative forcings, this study provides an additional method for determining the impact of Arctic aerosols.

The GFDL global climate models (CM2.1 and AM3) are used to assess the origin and climatic impact of sulfate and black carbon aerosols in the Arctic during the years 1980-2000. Different experiments are run using AM3 (atmospheric model, cubed-sphere, 2° latitude x 2.5° longitude, 32 levels, simplified chemistry, aerosol interactions, AR5 emissions inventory) to trace emissions from various Northern Hemispheric source regions, identifying transport pathways of aerosol species. Results show that aerosol sources contribute non-uniformly to the Arctic region and that sulfate and black carbon have different transport pathways in the northern high-latitudes. Although this approach for determining aerosol origins is innovative and thus difficult for comparison with similar analyses, the results support previous studies.

A two-stream approximation 1-D radiative transfer model is used to evaluate the direct shortwave aerosol radiative forcing in two Arctic locations (Barrow, Alaska and Ny-Alesund, Norway) during the springtime. In order to quantitatively assess the aerosol forcing across the globe and Arctic, the CM2 radiation code is implemented. Sulfate and black carbon optical depths are taken from both the AM3 and CM2.1 results. CM2.1 (coupled atmosphere and ocean model, spherical Earth, 2° latitude x 2.5° longitude, 24 levels, AR4 emissions inventory) results show that the Arctic is saturated with excess black carbon, whereas AM3 results show depleted black carbon. In addition, results show that black carbon has a significantly larger forcing per optical depth than sulfate, and thus a much stronger forcing tendency.