Simulations of black carbon (BC) aerosol impact over Hindu Kush Himalayan sites: validation, sources, and implications on glacier runoff

Abstract

Abstract. We estimated the black carbon (BC) concentration over the Hindu Kush Himalayan region (HKH), its impact on snow albedo reduction, and sensitivity on annual glacier runoff over the identified glaciers. These estimates were based on free-running aerosol simulations (freesimu) and constrained aerosol simulations (constrsimu) from an atmospheric general circulation model, combined with numerical simulations of a glacial mass balance model. BC concentration estimated from freesimu performed better over higher altitude (HA) HKH stations than that over lower altitude (LA) stations. The estimates from constrsimu mirrored the measurements well when implemented for LA stations. Estimates of the spatial distribution of BC concentration in the snowpack (BCc) over the HKH region led to identifying a hot-spot zone located around Manora Peak. Among glaciers over this zone, BCc (>60 µg kg−1) and BC-induced snow albedo reduction (≈5 %) were estimated explicitly being high during the pre-monsoon for Pindari, Poting, Chorabari, and Gangotri glaciers (which are major sources of fresh water for the Indian subcontinent). The rate of increase of BCc in recent years (i.e., over the period 1961–2010) was, however, estimated to be the highest for the Zemu Glacier. Sensitivity analysis with a glacial mass balance model indicated the increase in annual runoff from debris-free glacier areas due to BC-induced snow albedo reduction (SAR) corresponding to the BCc estimated for the HKH glaciers was 4 %–18 %, with the highest being for the Milam and Pindari glaciers. The rate of increase in annual glacier runoff per unit BC-induced percentage SAR was specifically high for Milam, Pindari, and Sankalpa glaciers. The source-specific contribution to atmospheric BC aerosols by emission sources led to identifying the potential emission source being primarily from the biofuel combustion in the Indo-Gangetic Plain south of 30∘ N, but also from open burning in a more remote region north of 30∘ N.

Wintertime radiative effects of black carbon (BC) over Indo-Gangetic Plain as modelled with new BC emission inventoriesin CHIMERE

“…However, it is also noted from the evaluation of BC concentration estimated from the free-running aerosol simulations using Laboratoire de Météorologie Dynamique atmospheric general circulation model (LMDZT-GCM) that simulated BC which is underestimated by a significant factor at stations which are close to emission sources (such as that over mainland India), exhibit a relatively lower discrepancy with observed BC concentration over the Indian oceanic regions (Reddy et al, 2004;Verma et al, 2007Verma et al, , 2011. The simulated BC distribution from LMDZT-GCM was also found to match consistently well the available observations at high altitude Himalayan Hindukush stations (e.g., Hanle, Satopanth)) which are relatively remotely located and mostly influenced by the transport of aerosols (Santra et al, 2019). The above evaluations, therefore, suggest that the large underestimation of BC concentration over the India mainland would primarily be due to BC emission dataset, instead of the model configurations.…”

“…Possible reasons suggested for the discrepancy between model and observations included, lack of BC emissions used as input, inadequate meteorology, and representation of aerosol treatment, and coarse resolution in the model (e.g. Santra et al, 2019;Kumar et al, 2018;Wang et al, 2016;Pan et al, 2015;Verma et al, 2011;Reddy et al, 2004).…”

Impact of light-absorbing particles on snow albedo darkening and associated radiative forcing over high-mountain Asia: high-resolution WRF-Chem modeling and new satellite observations

“…Firstly, LAPs can directly interact with incoming solar radiation and induce thermodynamical modifications to synoptic-scale circulations (Hansen et al, 1997;Ramanathan et al, 2001;Bond et al, 2013;Lau et al, 2006;Bollasina et al, 2011;Li et al, 2016). Secondly, acting as cloud condensation nuclei, changes in concentrations of these particles can lead to microphysical modification of cloud systems and precipitations Li et al, 2016;Qian et al, 2009;Sarangi et al, 2017). Finally, deposition of LAPs in the snowpack can also darken the snow, reduce its surface albedo, and accelerate snow warming and melting (Warren and Wiscombe, 1980;Qian et al, 2015Qian et al, , 2011Qian et al, , 2009Lau et al, 2010;B.…”

Black carbon sanitary burden in the Indo-Gangetic plain: exposures, risks and mitigation

“…Thereby, indicating that the inadequate BC distribution would lead to the dilution of the population exposure and the reduction of population-weighted concentration. A better agreement between model simulated and observed magnitude of atmospheric aerosol species was, however, delivered over the Indian region in a recent study using the constrained aerosol simulation approach 7,16 . Further, the constrained BC emissions were estimated over the Indian region constraining the simulated BC concentration in a general circulation model (Laboratoire de Météorologie Dynamique atmospheric General Circulation Model (LMDZT-GCM)) with the observed BC (observationally-constrained BC emissions) by combining forward and receptor modelling approaches 12 .…”

“…Available studies indicated that the most likely reasons for the discrepancy between model and observations include an underestimation of BC emissions used as input, inadequate meteorology and representation of aerosol treatment, and too coarse spatial resolution in the model 7,11,[16][17][18][19] . In a recent study 20 , an improvement in model performance relative to observations over the East and South Asia regions was shown with a high-resolution chemical transport model, revealing an overlap of high BC exposure concentration and population density.…”