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Light-absorbing particles in snow can significantly reduce the snow albedo. Quantification of the influence of black carbon (BC), one of the most important light-absorbing particles, on snow albedo is essential for understanding the budgets of solar radiation on snow-covered areas. We measured BC concentration in snow at 28 sites and snow albedo at 18 sites in a vast region across northwestern China in January 2018. The BC concentration was in a wide range of 40-1,850 ng g(-1). The presence of the BC reduced the snow albedo by 0.01-0.20 at the visible wavelength band (400-750 nm). The reduction differed from sites to sites with large values close to industrial areas that are characterized by high pollutants emission. Albedos simulated with a Snow, Ice, and Aerosol Radiation model based on the measured BC agreed well with the measured albedos, with the deviation within +/- 0.03 and the average underestimation of <0.002. It worth noting that the retrieved optical effective snow grain radius was the key factor in snow albedo calculation. The BC-induced radiative forcing was estimated to be 0.2-6.9 W m(-2), indicating strong acceleration of snowmelt due to BC in northwestern China. All obtained data are extremely valuable for climate model validation associated with the albedo of BC-contaminated snow cover.

Plain Language Summary Snow cover on the Earth system is one of the most reflective surfaces and plays a crucial role in the budget of solar radiation energy in the atmosphere. Studies with controlled experiments and model simulations have shown the reductive effect of BC pollution on snow albedo, but the reduction has rarely been assessed with in situ observations. For the first time, we measured both snow albedo and BC concentration in snow in a vast area across northwestern China. Results show a good correlation between the two variables, which is consistent with previous studies, that is, the more BC, the larger reduction. We found that the retrieved optical effective snow grain radius was the key factor to enhance the albedo simulation. We also estimated the radiative forcing of BC in snow and got a nonignorant absorptive effect, which indicates a possible accelerated snowmelt. All the data are extremely valuable for climate model validation associated with the reflection by BC-contaminated snow cover.