An Overview of Snow Albedo Sensitivity to Black Carbon Contamination and Snow Grain Properties Based on Experimental Datasets Across the Northern Hemisphere

Purpose of Review Black carbon (BC) deposition in snow can trigger a significant reduction in snow albedo and accelerate snowmelt. As a result, numerous snow surveys have performed to measure BC concentrations in snow across the polar regions, the Tibetan Plateau, and other high-mountain regions. This review is aimed to synthesize the current progresses of the potential feedbacks of snow albedo and its sensitivity by BC in snow across the Northern Hemisphere. Recent Findings Generally, BC concentrations in snow are highest in the mid-latitudes of Northern China and North America, and reduce toward higher latitudes (e.g., Greenland and the rest of the Arctic). We found that the snow albedo reduction attributed to low BC contamination (< 20 ng g(-1)) in older snow (200 mu m snow grains) is 1.2%, compared with 0.6% in fresh snow (50 mu m snow grains). Non-spherical snow grains exhibit a significantly lower snow albedo reduction (2-6%) due to BC contamination compared with spherical snow grains with 100-500 ng g(-1)of BC in the snowpack. Snow-BC-internal mixing reduces the snow albedo (< 10%) more substantially than does external mixing in the case of 50-200 mu m snow grains and a given BC concentration (< 2000 ng g(-1)). Besides the BC and other light-absorbing particles (LAPs), the mixing state of LAPs in snow, snow grain properties, and the scavenging\washing effects are also major challenges in determining snow albedo, which need to be further investigated on a global scale.