Quantifying black carbon deposition over the Greenland ice sheet from forest fires in Canada

Black carbon (BC) concentrations observed in 22 snowpits sampled in the northwest sector of theGreenland Ice Sheet in April, 2014 have allowed us to identify a strong and widespread BC aerosol deposition event, which was dated to have accumulated in the pits from two snow storms between 27 July and 2 August, 2013. This event comprises a significant portion (57% on average across all pits) of total BC deposition over 10 months (July, 2013 – April, 2014). Here we link this depositional event to forest fires burning in Canada during summer 2013 using modeling and remote sensing tools. Aerosols were detected by both the CALIOP (onboard CALIPSO) and MODIS (AQUA) instruments during transport between Canada and Greenland, confirming that this event involved emissions from forest fires in Canada. We use high resolution regional chemical transport modeling (WRF-Chem) combined with high resolution fire emissions (FINNv1.5) to study aerosol emissions, transport, and deposition during this event. The model accurately captures the timing of the deposition event and shows that the major contribution to BC deposition during the second snow storm is emissions originating from fires in Canada. However, the model under estimates BC deposition compared to measurements at all sites by a factor of 2–100. Under prediction of modeled BC deposition originates from uncertainties in fire emissions combined with uncertainties in aerosol scavenging by clouds. This study suggests that it is possible to simulate the transport of a major wildfire smoke event on regional and continental scales. Improvements in model descriptions of precipitation scavenging and emissions from wildfires are needed to correctly predict deposition, which is critical for determining the climate impacts of aerosols that originate from fires.