Atmospheric Abundance of PM_2.5 Carbonaceous Matter and Their Potential Sources at Three High-Altitude Glacier Sites over the Indian Himalayan Range

Abstract

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 μg m–3 with a mean of 55.45 ± 16.30 μg m–3 at WHR, 86.80 ± 35.73 μg m–3 at CHR, and 72.61 ± 24.45 μg m–3 at EHR. Among the eight carbon fractions, high-temperature OC4 (evolved at 580 °C in the helium atmosphere) was the most prevalent carbon fraction, followed by low-temperature OC2 (280 °C) and EC1 (580 °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.

Optical Properties of Fine Mode Aerosols over High-Altitude Himalayan Glacier Regions

“…Local sources such as wood burning, fossil fuel combustion, and increased vehicular emissions during the Chota-Char Dham Yatra in the valley region might contribute to the sources of BrC and BC over the Himalayas. Additionally, long-range transport of aerosols from the Indo-Gangetic Plain to the Himalayan region during the pre-monsoon season, as reported by previous researchers, ,, could also contribute to the presence of BrC and BC. Furthermore, the strong thermal valley-to-mountain winds played a vital role in the transportation of aerosols from the foothills of the Himalayas …”

“…Collection of PM 2.5 samples was carried out from July 2019 to March 2020 by using three sets of MiniVol air sampler (version 4.2, AirMetrics Model Oregon, USA, equipped with PM 2.5 inlets). Details of sampling periods and total number of samples have been given in Tables S1–S3 for individual sites and can also be found elsewhere …”

“…In this study, we evaluated the optical properties of fine aerosols over the Indian Himalayan region. Additionally, this study is part of our earlier research conducted during the summer and winter of 2019–2020 in three glacier regions of the Himalayas, where we quantified the mass of PM 2.5 , OC, and EC . Details regarding the sampling sites are provided in Section (study area) of the present study.…”

“…During the pre-monsoon period, the primary driver of carbonaceous aerosol abundance over the Himalayas is the long-range transport from the Indo-Gangetic plains. 3,4 In addition to long-range transport, local sources such as cooking and heating activities also contribute a significant amount of carbonaceous aerosols to the nearby atmosphere.…”

“…Additionally, this study is part of our earlier research conducted during the summer and winter of 2019−2020 in three glacier regions of the Himalayas, where we quantified the mass of PM 2.5 , OC, and EC. 3 Details regarding the sampling sites are provided in Section 2 (study area) of the present study. The findings of this study will contribute to estimating radiative forcing and understanding the impact on regional climate.…”