Small airborne particles made of black carbon (BC) have important effects on the Earth’s climate system. BC particles influence clouds, precipitation and atmospheric circulations in numerous ways. They also deposit on snow, sea ice and glaciers, accelerating melting, which can produce additional impacts on the climate through positive feedback mechanisms. To better assess the response of climate to uncertainties and potential future changes in BC emissions, scientists at DOE’s Pacific Northwest National Laboratory developed and applied an explicit emission tagging technique in the Community Atmosphere Model (CAM5) to explicitly track BC particles emitted from major source regions and their transport to receptor regions of interest, focusing on the Arctic in this study. 

Their analysis shows that the contributions from major source regions to the global BC burden are not always directly proportional to their respective emissions because particles from some regions are removed much more rapidly compared to other regions. The BC effects on energy reaching the Earth’s surface is however proportional to the burden. Concentrations and deposition of BC in the Arctic and source contributions from different regions all have strong seasonal variations. Eastern Asia contributes the most to the wintertime Arctic BC burden, but has much less impact on concentrations near the surface and on deposition to the surface. Northern Europe emissions are more important to both surface concentration and deposition in winter than in summer. The largest contribution to Arctic BC in the summer is from Northern Asia. Although the relatively small Arctic emissions contribute less than 10% to the annual mean BC burden and deposition within the Arctic, the per-emission efficiency is much greater than for non-Arctic sources. The year-to-year variability of annual mean Arctic BC burden and radiative forcing due to meteorology during 1996-2005 is small, but seasonal means have significant interannual variability. 

Compared to conventional emission perturbation approaches, the new explicit tagging technique allows deriving source-receptor relationships without actually perturbing emissions. As a result, it is not only physically more consistent but also much more efficient computationally than the conventional approaches, making it affordable for studying interannual variability in computationally demanding high-resolution global simulations and/or with numerous source regions or types.