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.