Air Quality Challenges in Gangtok, Sikkim Himalaya: A Study of Aerosol Variability and Impacts

The study investigates the spatial and altitudinal variability of aerosol components, including Black Carbon (BC), PM1, PM2.5, PM10, Total Suspended Particles (TSPM), respirable, thoracic, and inhalable particulate matter, across different sites in Gangtok, Sikkim Himalaya. The monitoring locations - Residential (Site 1, 900 m), Commercial (Site 2, 1800 m), and Control (Site 3, 2200 m) demonstrate distinct altitudinal gradients in ambient aerosol concentrations. The measurements were conducted during the winter of 2024 using an Aethalometer AE-33 to measure BC and an EDM 264 to analyse various size of aerosols in the ambient atmosphere. BC associated with PM2.5 decrease from 4.94 µg/m³ at Site 1 to 2.62 µg/m³ at Site 2 and 1.49 µg/m³ at Site 3, while PM2.5 concentrations follow a similar pattern, declining from 84.88 µg/m³ to 18.62 µg/m³. Comparable trends are observed for PM1, PM10, and TSPM, with higher concentrations at lower altitudes indicating the dominance of anthropogenic activities and population density. These components also exhibited strong diurnal variability, with daytime levels consistently higher than night-time levels across all sites. For instance, at Site 1, the mean daytime BC concentration is 5.59 µg/m³, compared to 3.63 µg/m³ at night. This variation is attributed to increased vehicular emissions and other human activities during the day. Additionally, a strong correlation is observed between BC and PM_2.5 levels indicating common sources such as combustion-related activities. Lower temperatures and higher RH at each site, enhanced aerosol condensation and particle deposition, resulting in reduced pollutant concentrations. Components like respirable, thoracic, and inhalable particulates, critical for assessing health impacts, also show decreasing trends with altitude but remain concerning in residential areas at lower altitudes due to their ability to penetrate the respiratory system. BC's role as a short-lived climate pollutant with high radiative forcing potential further emphasizes its environmental significance in the ecologically sensitive Himalayan region. Addressing the sources of aerosols, particularly in densely populated lower-altitude areas, is vital for improving air quality and mitigating health and climate impacts in the Sikkim Himalaya.