Experimental Reduction of Snow Surface Albedo by Local Black Carbon and Mineral Dust Deposition in the Andes of Laguna del Maule, Chile

Snowmelt from the Andes is the primary source of freshwater for central Chile, a region experiencing prolonged drought and increasing anthropogenic pressures. Light-absorbing particles (LAPs), such as black carbon (BC) from mining vehicles and locally derived mineral dust (MD), accelerate snowmelt by reducing surface albedo. This study presents experimental results from a field campaign conducted on 27 August 2025 near Laguna del Maule, where controlled deposits of BC and MD were applied to the snow surface to quantify their impact on spectral albedo. BC (simulating mining truck emissions) and MD (local soil) were deposited cumulatively at masses of 1, 2, 3, 5, and 7 grams over a defined snow area. Surface albedo was measured using a spectroradiometric system consisting of six synchronized spectroradiometers covering 300–2500 nm. For each contamination level, 12 replicate measurements were taken. Broadband albedo (300–2500 nm) was averaged across replicates to evaluate the reduction induced by each LAP type. Due to wind-driven dispersion, the average effective mass deposited on the snow surface was 58% of the applied BC and 93% of the applied MD. Results show a consistent decrease in average broadband albedo with increasing deposition mass. A linear regression between broadband albedo and the effective surface concentration (accounting for wind loss) yielded an average albedo reduction slope of 0.014 ± 0.002 per gram of BC and 0.011 ± 0.001 per gram of MD. This indicates that, under these experimental conditions, BC exerts a stronger per-mass darkening effect than MD. These findings demonstrate that vehicular BC and wind-blown MD from mining and disturbed soils can significantly darken snow surfaces, thereby enhancing melt rates. In a region already affected by megadrought and shrinking snowpack, such albedo reductions threaten to further diminish freshwater availability. This study emphasizes the need to integrate local aerosol emissions—particularly from mining and transport activities—into hydrological and climate models for the Central Andes. The authors acknowledge the support of the National Research and Development Agency of Chile (ANID), namely, ANID-FONDECYT 3230555, ANID-FONDECYT 11220482, ANID-FONDECYT 11220525, ANID Vinculación Internacional FOVI240088, and ANID FONDEQUIP EQM250078, as well as the Multidisciplinary Research Project PI_M_24_03 from Universidad Técnica Federico Santa Maria (Chile). The spectroradiometric system was funded by the Spanish Ministry of Science and Innovation through the Acquisition of Scientific-Technique Equipment (2019) grant (ref. EQC2019-006105-P).