Duringthe summer and winter periods of 2019-2020, we conductedsampling of fine mode ambient aerosols in the western Himalayan glacialregion (WHR; Thajiwas glacier, 2799 m asl), central Himalayan glacialregion (CHR; Gomukh glacier, 3415 m asl), and eastern Himalayan glacialregion (EHR; Zemu glacier, 2700 m asl). We evaluated the aerosol opticalproperties, which included the mass absorption coefficient, mass absorptionefficiency, mass scattering efficiency, absorption angstrom exponent,single scattering albedo, as well as their simple radiative forcingefficiencies. We observed the highest absorption in the near ultraviolet-visiblewavelength range (200-400 nm), with CHR showing the highestabsorption compared to the other two sites, WHR and EHR, respectively.Across the wavelength range of 200-1100 nm, the overall contributionof black carbon to light attenuation was greater than that of browncarbon. However, brown carbon dominated the absorption in the nearUV-visible wavelengths, providing evidence of its non-trivialpresence over the Himalayan region. Additionally, we observed a positiveradiative forcing (W/g), which leads to net warming at these sites.The findings of this ground-based study contribute to our understandingof the light-absorbing nature of carbonaceous aerosols and their impacton the Himalayan glacier regions.

This study inspects the concentrations of fine particulate matter (PM2.5) mass and carbonaceous species, including organic carbon (OC) and elemental carbon (EC), as well as their thermal fractions in the Indian Himalayan glacier region at the western Himalayan region (WHR; Thajiwas glacier, 2799 m asl), central Himalayan region (CHR; Gomukh glacier, 3415 m asl), and eastern Himalayan region (EHR; Zemu glacier, 2700 m asl) sites, throughout the summer and winter periods of 2019-2020. Ambient PM2.5 samples were collected on quartz fiber filters using a low-volume sampler, followed by carbon (OC and EC) quantification using the IMPROVE_A thermal/optical reflectance methodology. Different seasonal variations in PM2.5 and carbonaceous species levels were found at all three sites investigated. Averaged PM2.5 mass ranged 55-87 mu g m-3 with a mean of 55.45 +/- 16.30 mu g m-3 at WHR, 86.80 +/- 35.73 mu g m-3 at CHR, and 72.61 +/- 24.45 mu g m-3 at EHR. Among the eight carbon fractions, high-temperature OC4 (evolved at 580 degrees C in the helium atmosphere) was the most prevalent carbon fraction, followed by low-temperature OC2 (280 degrees C) and EC1 (580 degrees C at 2% oxygen and 98% helium). Char-EC representing incomplete combustion contributed to 56, 67, and 53% of total EC, whereas soot EC contributed to 38, 26, and 43% of total EC in WHR, CHR, and EHR, respectively. The measured OC/EC ratios imply the presence of secondary organic carbon, whereas char-EC/soot-EC ratios suggested that biomass burning could be the predominant source of carbon at CHR, whereas coal combustion and vehicular emission might be dominant sources at WHR and EHR sites.

Forests, though very critical for life on Earth, are threatened by various factors and the frequently occurring forest fires are one of the significant causes. Forest fires drastically contribute to climate change on both regional and global scales. Forest fires-of both natural and anthropogenic origins-induce aerosols in the atmosphere and have a significant impact on the health and climate of the region. In this study, we simulate the Uttarakhand (29-31 degrees N, 78-80 degrees E) fire event in India, which occurred in April 2016, using the Weather Research and Forecasting with Chemistry (WRF-Chem) model to estimate the radiative impact of the aerosols emitted due to this fire event and probe into the extent of their transport into the atmosphere. Multiple data from ground-based and satellite observations are used to access the model performance. Our analysis showed that the high values of aerosol optical depths (AODs) during the fire event simulated by WRF-Chem compared very well with MODIS AODs over the Uttarakhand region. The model simulations of the vertical profile of BC corroborate with elevated smoke aerosols derived from CALIPSO. An enhancement of smoke aerosols is observed up to 5-km altitude during the fire event both in the model simulations and observations. The fire has increased the near-surface air temperatures by 1-3 degrees C and decreased the relative humidity by similar to 10% over the affected areas. The NET (shortwave + longwave) atmospheric radiative forcing due to fire varied between similar to 10 and similar to 40 Wm(-2) in the entire affected areas, with the highest values over the source region. The fire-induced atmospheric heating rate varied between 0.5 and 1.4 K/day over the Uttarakhand region.

Ambient equivalent black carbon (BC) measurements spanning from June to October have been carried out over an adjoining location of Satopanth and Bhagirath-Kharak Glaciers (3858m, amsl) of Central Himalaya during the year 2019. Hourly BC varied from 12 ng m- 3 to 439 ng m- 3 during the entire period of observation. Monthly averaged BC values showed the highest concentration during June (230.96 +/- 85.46 ng m- 3) and the lowest in August (118.02 +/- 71.63 ng m- 3). The decrease in BC during monsoon months is attributed to limited long-range transport and rapid wet scavenging processes. Transport model studies indicate a higher retention time of tracer in Uttarakhand, Punjab, Haryana, and adjacent polluted valley regions with increased biomass burning (BB) incidences. The high rate of BC influx during June, September, and October was attributed to transport from the polluted Indo-Gangetic Plain (IGP) region, wildfires, and vehicular emissions in the valley region. Higher equivalent brown carbon (BrC) influx is linked to BB, especially wood-burning, during intense forest fires at slopes of mountains. Data obtained from limited BC observations during the 2011-19 period showed no significant BC influx change during post-monsoon. The strong correlation between BC mass and BB affirms the dominant role of BB in contributing BC to the Glacier region. Increased TOA forcing induced by surface darkening and BC atmospheric radiative heating indicate an additional warming and possible changes of the natural snow cycle over the glacier depending on the characteristics and extent of debris cover.

Simultaneous measurements of ambient atmospheric black carbon (BC) mass concentrations and radiative fluxes were carried out over Satopanth glacier in the central Himalayas from September 22 to October 2, 2016, as a part of a glacier campaign experiment. The daily mean atmospheric BC concentrations varied between 165 +/- 20-263 +/- 32 ng m(-3) with a mean of 199 +/- 54 ng m(-3) during the observational period. The measured average surface albedo was found to be 0.24 +/- 0.11 during the entire period of observation. Spectral albedo from Moderate Resolution Imaging Spectroradiometer - Bidirectional Reflectance Distribution Function (MODIS-BRDF) satellite observation and net radiometer derived glacier albedo was found to be in good agreement with a correlation of 0.64 over the region. Concentration weighted trajectory analysis (CWT) over the site indicates a 70% BC transport from the Indo-Gangetic plain, Pakistan, and the Middle East region. BC radiative forcing was estimated using an optical model along with a radiative transfer model. An average BC direct radiative forcing of -5.4 +/- 0.25 W m(-2) and 2.4 +/- 0.19 W m(-2) was found respectively in the surface and at the top of the atmosphere (TOA) during the experimental period. The estimated average BC induced heating rate was found to be 0.33 +/- 0.04 K day(-1) over the region.