Modeling plumes containing black-carbon from Siberian sources to the Arctic

There are currently large uncertainties in global climate model predictions of black carbon (BC) in the Arctic. These differences are in part due to uncertainties in anthropogenic and biomass burning emissions, errors arising from model parameterizations, and inadequate spatial resolution in large scale models. In addition to the contribution to aerosol radiative forcing, black carbon deposited on snow alters its albedo and consequently the rate of melting. Our study presents the main pollution transport pathways from Siberia to the Arctic and how they impact the Arctic air composition in summer and spring. We focus on two periods (summer 2012 and spring 2008) when field campaigns took place in the Arctic. As part of the Arctic Climate Change, Economy and Society (ACCESS) project, an aircraft campaign was conducted in July 2012 in Andoya, Norway. The main focus of the campaign was to investigate the role of current and future anthropogenic activities in and near the Arctic on regional air pollution and to analyze potential connections to Arctic climate. To put the emerging local pollution within a broader context, biomass burning plumes containing black carbon imported from Siberian wildfires were sampled during the campaign. Two flights north of Norway into the Arctic, with a refueling stop in Spitsbergen focused specifically on biomass burning pollution transported across the North Pole from Siberia. To simulate the emission, transport, and fate of black carbon, we use a regional chemical transport model, the Weather Research and Forecasting model with chemistry (WRF-Chem), with a model domain that encompasses most of the northern hemisphere. The model is able to represent the most intense plumes sampled during the flights in the North of Spitsbergen, with ~120 ppb CO enhancement. The simulations show a clear connection of these plumes to fires in Siberia and Central Russia and are complemented by a more detailed comparison to airborne observations and satellite measurements in terms of spatial and vertical distributions (MODIS, CALIPSO). We also present the main pollution transport pathways from Siberia to the Arctic throughout the spring, when seasonal Arctic Haze occurs. Spring 2008 period is chosen because a number of field campaigns (e.g. ARCTAS, ISDAC) took place as part of the International Polar Year that collected measurements of BC and other aerosols that can be used to evaluate model performance in this region. Sensitivity simulations are performed that examine the impact of emission estimates and wet removal on BC concentrations over the Arctic in relation to the observations. The model is driven with a new emission dataset, which includes emissions from gas flaring (ECLIPSE: Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants). Flaring dominates the estimated BC emissions in the Arctic (North of 66 °N) and has been previously underestimated by most studies.