Optical and Physico-chemical Characteristics of Ambient Aerosols Along Gangotri Glacier Valley in Western Himalaya, India

The optical, morphological, and elemental characteristics of aerosols from the pristine Gangotri Glacier Valley (GGV) are reported. To our knowledge, this is the first study to examine the morphological and elemental components of aerosols in the northwestern Indian Himalayas. Located far from any anthropogenic air pollution hotspot, this glacier valley in the Himalayas provides an ideal setting for research on aerosol characterization. The observations are made using an optical attenuation-based real-time black carbon monitor (aethalometer type AE 33). The scanning electron microscope equipped with an energy dispersive X-ray spectroscope (SEM–EDX) was utilized to analyze the morphology and elemental composition of individual particles. This analysis focused on the total suspended particles (TSP) that were deposited on the quartz filter tape of the aethalometer. The scanned electron micrographs reveal variable morphological structures in submicron particles. Morphological parameters (viz., aspect ratio (AR) and circulatory factor (CIR)) were computed after careful analysis of electron micrographs using ImageJ software. The frequency distribution of morphological parameters reveals that the AR peaked between 1.1 and 1.3, while the CIR peaked between 0.95 and 1.1. The results are compared to other studies and reveal that GGV particles are more spherical than Indo-Gangetic Basin samples. Energy dispersive X-ray analysis of electron micrographs provides elemental identification and quantitative composition. During the study period (May 2016), the air surrounding GGV was observed to be rich in fluorine, oxygen, carbon, silica, sodium, aluminum, magnesium, sulfur, iron, zinc, potassium, calcium, and barium. Synoptic scale analyses of thermal anomalies and aerosol optical depth were also carried out using MODIS and MERRA-2 satellite data sets, respectively. HYSPILT backward air mass cluster trajectory analysis reveals that air mass transported from south-western Asia and the Indo-Gangetic basin dominated the glacier valley throughout the study period. The current research initiates an important step in our understanding of the aerosol properties in Himalayan glacier valleys. These findings also highlight the importance of understanding regional-scale processes that alter aerosol composition and concentrations in this ecologically vulnerable region. This investigation lays the groundwork for future long-term, multi-seasonal studies. These scientific studies may help environmental regulators protect the Himalayan cryosphere and glacier habitat.