A Multi-Model Comparison of Black Carbon Budgets in the Arctic Region.

Abstract:

In this study we quantify modeled aerosol processes related to black carbon (BC) concentrations in the Arctic region in several general circulation models used by the Expert Group on Arctic Monitoring and Assessment Program (AMAP). All models simulated well the observed seasonal cycle of BC concentrations in the high Canadian Arctic region, however, most models (except CanAM) underestimate the total concentrations. Transport of BC from lower latitudes is the major source for the Arctic region where emissions are small. The models produce similar seasonal cycle of BC transport towards the Arctic with maximum transport in July. However, substantial differences were found among the models in simulating BC burdens and vertical distributions with some models producing very week seasonal cycle while others producing stronger seasonality. The annual mean BC residence times in models also differs markedly with CanAM having the shortest residence times followed by SMHI-MATCH, CESM and NorESM. There are substantial differences among the models in simulating the relative role of wet and dry deposition rates which is one of the major factors causing variations in the seasonality of BC burdens in the models. Similarly, significant differences in wet deposition efficiencies among the models exist and are the leading cause of differences in simulated BC burdens. To further explore these processes, we performed several sensitivity tests in CanAM and CESM. Overall, the results indicate that scavenging of BC in convective clouds as compared to simulations without convective BC scavenging substantially increases the overall efficiency of BC wet deposition which leads to low BC burdens and a more pronounced seasonal cycle.