Black carbon over a central Himalayan Glacier (Satopanth): Pathways and direct radiative impacts

Assessment of Black Carbon, optical properties and aerosol radiative forcing at Pranmati basin Himalayan critical zone observatory

The study aimed to understand the optical properties of Black Carbon (BC) and radiative forcing over a data deficient Himalayan region focusing on critical zone observatory employing ground-based measurements by Aethalometer for BC and satellite retrieval techniques for optical properties during mid-May-June 2022 and January-May 2023. BC mass concentration ranged from 0.18 to 4.43 μgm-3, exhibit a mean of 1.47 ± 0.83 μgm-3 with higher summer concentration (1.51 ± 0.94 μgm-3) than winter (1.39 ± 0.61 μgm-3). The average Absorption Ångström Exponent observed to be significantly higher than unity (1.77 ± 0.31) over the studied high-altitude Himalayan region, suggesting the dominance of biomass-burning aerosol. Higher aethalometer derived compensation parameter (K) in winter suggesting locally originated BC while, lower K value in summer suggesting aged BC transported from Indo-Gangetic Plains. Optical properties calculated from "Optical Properties of Aerosol and Cloud" (OPAC) model are used in the "Santa Barbara DISORT Atmospheric Radiative Transfer" (SBDART) model to calculate the aerosol Direct Radiative Force (DRF). The entire studied period is characterized by the predominance of absorbing aerosols, particularly BC, increasing Aerosol Optical Depth, Asymmetric Parameters and decreasing Single Scattering Albedo, leading to a considerable increase in atmospheric radiative forcing (+0.9 Wm-2, top of atmosphere) and Heating Rate (0.36 KDay-1). The mean radiative forcing within atmosphere during summer was higher (+14.29 Wm-2) relative to the winter (+12.00 Wm-2), emphasizing the impact of absorbing aerosols on regional warming and potential glacier melting in the Himalayas at a faster rate. Urgent policy consideration for the reduction of absorbing aerosols is highlighted, recognizing the critical roles of Black Carbon in the changing behaviour of Critical Zone observatory. The study's data serve as a valuable resource to understanding and addressing uncertainties in climate models, aiding effective policy implementation for Black Carbon reduction.

Particulate pollution over an urban Himalayan site: Temporal variability, impact of meteorology and potential source regions

Five-year (2013-2017) particulate matter (PM) data observed at an urban site, Srinagar, Kashmir Himalaya, India was used to examine the temporal variability, meteorological impacts and potential source regions of PM. The daily mean PM₁₀ and PM_2.5 concentration was 135 ± 112 μg/m³ and 87 ± 93 μg/m³ respectively with significant intra- and inter-daily variation. The annual PM₁₀ and PM_2.5 concentration was 2.0-3.2 and 1.7-2.8 times higher than the annual Indian National Ambient Air Quality Standards (PM₁₀ = 60 μg/m³ and PM_2.5 = 40 μg/m³). PM concentration shows a bimodal diurnal pattern with morning and evening peaks, which coincide with the increased anthropogenic activity and shallow planetary boundary layer (PBL). The combined effect of the low temperature, low wind speed, shallow and stable PBL and geomorphic setup of Kashmir valley leads to the accumulation of particulate pollution during autumn and winter and the converse meteorological conditions leads to dispersion, dilution and deposition during spring and summer. High precipitation rate (>15 mm/day) removes the coarse particles (PM₁₀) more efficiently than fine particles (PM_2.5), while as the moderate to high humid conditions (55-95%) leads to the accumulation and growth of more PM. It was observed that ~80% of the air masses arriving at the site during spring, autumn and winter are westerlies. Source contribution analysis revealed that highly potential source regions of PM at the site are neighboring Pakistan, Afghanistan, parts of Iran and Trans-Gangetic Plains, which could contribute high concentration of the PM₁₀ (>250 μg/m³) and PM_2.5 (>150 μg/m³) during autumn and winter. The high PM load observed at the site during autumn and winter, with major contribution from the anthropogenic source emissions like biomass and coal burning, fossil fuel combustion and suspension of road dust, is aggravated by the geomorphic and meteorological setup of the Kashmir valley.

Black carbon pollutants in pristine Himalayan ecosystem: a pilot study along Gangotri Glacier Valley

The present study provides the first multi-year (2015-2020) random observation of black carbon (BC) aerosols from pristine localities along the Gangotri Glacier Valley in the north-western Indian Himalaya. Due to the harsh climatic conditions and inaccessible terrain, hardly any BC observation is available from glaciated Himalaya. To investigate the background concentration of BC in the high Himalaya, random measurements are conducted at five locations at variable microclimates with different anthropogenic influences along a 24-km-long Gangotri Glacier Valley trek, viz. Gangotri (~ 3200 m amsl), Chirbasa (~ 3600 m amsl), Bhojbasa (~ 3800 m amsl), Gaumukh (~ 4000 m amsl), and Tapovan (~ 4400 m amsl). A relatively high concentration of BC (up to 2.23 ± 0.57 μg m^-3) was recorded at Gangotri which is a famous Indian pilgrimage centre which remains highly crowded during the peak tourist season, i.e. May-June and Oct-Nov every year. Surprisingly, we also recorded high BC (up to 1.27 ± 0.57 μg m^-3) at Tapovan, which is a high altitude meadow surrounded by high ice-snow peaks, viz. Bhagirathi Peak (6856 m amsl), Shivling (6543 m amsl), and Meru Parvat (6660 m amsl). The HYSPLIT cluster trajectory and CALIPSO data images suggest that besides local anthropogenic activities, polluted air mass-produced due to burning of forest and agriculture biomass and fossil fuels, etc. transported from Indo Gangetic Basin might be playing a potential role in ambient BC concentration in the study area. The present preliminary investigations of BC in the Gangotri Glacier Valley open new vision and possibilities for further extensive ground-based observation of aerosol air pollutants in Himalayan glacier valley systems.

A Response of Snow Cover to the Climate in the Northwest Himalaya (NWH) Using Satellite Products

The Himalayan region is one of the most crucial mountain systems across the globe, which has significant importance in terms of the largest depository of snow and glaciers for fresh water supply, river runoff, hydropower, rich biodiversity, climate, and many more socioeconomic developments. This region directly or indirectly affects millions of lives and their livelihoods but has been considered one of the most climatically sensitive parts of the world. This study investigates the spatiotemporal variation in maximum extent of snow cover area (SCA) and its response to temperature, precipitation, and elevation over the northwest Himalaya (NWH) during 2000–2019. The analysis uses Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra 8-day composite snow Cover product (MOD10A2), MODIS/Terra/V6 daily land surface temperature product (MOD11A1), Climate Hazards Infrared Precipitation with Station data (CHIRPS) precipitation product, and Shuttle Radar Topography Mission (SRTM) DEM product for the investigation. Modified Mann-Kendall (mMK) test and Spearman’s correlation methods were employed to examine the trends and the interrelationships between SCA and climatic parameters. Results indicate a significant increasing trend in annual mean SCA (663.88 km2/year) between 2000 and 2019. The seasonal and monthly analyses were also carried out for the study region. The Zone-wise analysis showed that the lower Himalaya (184.5 km2/year) and the middle Himalaya (232.1 km2/year) revealed significant increasing mean annual SCA trends. In contrast, the upper Himalaya showed no trend during the study period over the NWH region. Statistically significant negative correlation (−0.81) was observed between annual SCA and temperature, whereas a nonsignificant positive correlation (0.47) existed between annual SCA and precipitation in the past 20 years. It was also noticed that the SCA variability over the past 20 years has mainly been driven by temperature, whereas the influence of precipitation has been limited. A decline in average annual temperature (−0.039 °C/year) and a rise in precipitation (24.56 mm/year) was detected over the region. The results indicate that climate plays a vital role in controlling the SCA over the NWH region. The maximum and minimum snow cover frequency (SCF) was observed during the winter (74.42%) and monsoon (46.01%) season, respectively, while the average SCF was recorded to be 59.11% during the study period. Of the SCA, 54.81% had a SCF above 60% and could be considered as the perennial snow. The elevation-based analysis showed that 84% of the upper Himalaya (UH) experienced perennial snow, while the seasonal snow mostly dominated over the lower Himalaya (LH) and the middle Himalaya (MH).