Modeling Transport and Processing of Light Absorbing Aerosols Deposited on the Greenland Ice Sheet in 2013

The processes that result in aerosol deposition within the Arctic are important for understanding how mid-latitude pollution impacts and modifies the natural Arctic environment. Aerosol deposition is a dominant source of light-absorbing impurities, including black carbon, found in Arctic ice and snow. Trace amounts of light absorbing impurities in snow are important because they are used to interpret past pollution trends (e.g. fire frequency) using ice cores and because they have important climate impacts (warming) due to their modification of snow and ice albedo. Here, we focus on the role of biomass burning in controlling the amount of black carbon deposited on the Greenland ice sheet. Biomass burning is known to modify the Arctic aerosol burden, but large uncertainties remain with respect to the specific processes and impacts. In this presentation, a specific case of light absorbing aerosol deposition to the Greenland ice sheet is studied by combining extensive snow pit measurements with simulations using the regional model WRF-Chem. Light absorbing impurities were measured in snow pits (in 2014) and snow accumulation rates (2013-2014) were monitored at several remote sites on the Greenland ice sheet as part of the SAGE project. The largest black carbon deposition quantity measured was traced to a snow accumulation event that occurred in early August 2013, which included snow deposition having 2-4 cm water equivalent with BC concentrations of up to 40ng/g . In order to understand the origin and identify the processes controlling the observed deposition event, the regional model WRF-Chem is used (run from 17 July - 5 August 2013). The model simulation includes anthropogenic and fire emissions in North America as well as transport and chemical/physical transport processes for both trace gases and aerosols. Model results show that the observed deposition event can be traced to fires burning in northern Canada in late July 2013. The processes controlling aerosol deposition will be discussed including the critical role of transport pathways and storm systems, which are essential in controlling the fate of emissions within the Arctic region.