This study discusses year-long (October 2016-September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28 degrees 12'49.21 '' N, 85 degrees 36'33.77 '' E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 mu g m(-3)) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96-542 ng g(-1) and 152-827 ng g(-1), respectively. The source apportionment study using the absorption Angstrom exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated similar to 14% contribution of BC from open-burning and similar to 77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model - Snow, Ice, and Aerosol Radiation - was in the range of 0.8-3.8% during the pre-monsoon season. The glacier mass balance analysis suggested that BC contributed to approximately 39% of the total mass loss in the pre-monsoon season. (C) 2021 The Authors. Published by Elsevier Ltd.

Snow and ice albedo reduction due to deposition of absorbing particles (snow darkening effect [SDE]) warms the Earth system and is largely attributed to black carbon (BC) and dust. Absorbing organic aerosol (BrC) also contributes to SDE but has received less attention due to uncertainty and challenges in model representation. This work incorporates the SDE of absorbing organic aerosol (BrC) from biomass burning and biofuel sources into the Snow Ice and Aerosol Radiative (SNICAR) model within a variant of the Community Earth System Model. Additionally, 12 different emission regions of BrC and BC from biomass burning and biofuel sources are tagged to quantify the relative contribution to global and regional SDE. BrC global SDE (0.021-0.056 Wm(-2) over land area and 0.0061-0.016 Wm(-2) over global area) is larger than other model estimates, corresponding to 37%-98% of the SDE from BC. When compared to observations, BrC simulations have a range in median bias (-2.5% to +21%), with better agreement in the simulations that include BrC photochemical bleaching. The largest relative contributions to global BrC SDE are traced to Northern Asia (23%-31%), Southeast Asia (16%-21%), and South Africa (13%-17%). Transport from Southeast Asia contributes nearly half of the regional BrC SDE in Antarctica (0.084-0.3 Wm(-2)), which is the largest regional input to global BrC SDE. Lower latitude BrC SDE is correlated with snowmelt, in-snow BrC concentrations, and snow cover fraction, while polar BrC SDE is correlated with surface insolation and snowmelt. This indicates the importance of in-snow processes and snow feedbacks on modeled BrC SDE.

This study discusses year-long (October 2016-September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28 degrees 12'49.21 '' N, 85 degrees 36'33.77 '' E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 mu g m(-3)) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96-542 ng g(-1) and 152-827 ng g(-1), respectively. The source apportionment study using the absorption Angstrom exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated similar to 14% contribution of BC from open-burning and similar to 77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model - Snow, Ice, and Aerosol Radiation - was in the range of 0.8-3.8% during the pre-monsoon season. The glacier mass balance analysis suggested that BC contributed to approximately 39% of the total mass loss in the pre-monsoon season. (C) 2021 The Authors. Published by Elsevier Ltd.