Black carbon concentrations in surface snow and ice in the Arctic and modeled biomass burning smoke deposition fluxes

Intensifying high latitude Arctic wildfires are increasing the potential for deposition of black carbon (BC) on the Arctic cryosphere. When deposited on snow and sea ice, the dark BC aerosols absorb more solar radiation than the surrounding snow/ice surface, causing a localized radiative forcing that can enhance melt. Here we present refractory black carbon (rBC) concentration and size distributions with a Single Particle Soot Photometer from snow sampled across multiple locations of the Arctic from 2014 to 2018, along with modeled wet and dry smoke deposition from the Navy Aerosol Analysis Prediction System model. Samples analyzed include surface hoar in the bare ice dark zone of the Greenland Ice Sheet, snow on sea ice in the Chuckchi Sea, and fresh and aged seasonal snow across Svalbard. On the Greenland Ice Sheet (GrIS), the size distributions from the surface hoar samples appear unimodal, and were overall smaller than the fresh snow sample, with a peak around 0.3 µm. Whereas a fresh snow sample contained very large rBC particles that had a pronounced bimodality in peak size distributions, with peaks around 0.2 µm and 2 µm. BC concentrations ranged from a minimum of 0.3 µg-rBC/L-H2O in a sub-surface layer of a snowpit on Holdtedahlfonna Glacier, to a maximum of 48 µg-rBC/L-H2O in surface snow collected near the town of Longyearbyen, both on Svalbard. On the GrIS, concentrations ranged from 3 µg-rBC/L-H2O in light-colored patches of surface hoar to a maximum of 32 µg-rBC/L-H2O in a dark patch in early August. Additionally, rBC concentrations peaked on the GrIS in light and dark patches in early August, which is likely due to smoke transport from wildfires in Northern Canada and Alaska, which wasby the Navy Aerosol Analysis and Prediction System (NAAPs) model. According to NAAPs deposition fluxes, the model suggests 26 mg/m3 of biomass burning derived smoke was deposited on this region of the GrIS between April 1st and August 30th. Of the total smoke deposited, 85% came from wet deposition and 67% was during our sample collection timeframe. These rBC concentrations, size distributions, and deposition fluxes provide insight into the seasonal evolution of impurities in the Arctic, which are needed to constrain snow and ice albedo-feedbacks and radiative forcing responses.