Investigation of Aerosol Climatology and Long-Range Transport of Aerosols over Pokhara, Nepal

Abstract

This study presents the spectral monthly and seasonal variation of aerosol optical depth (τAOD), single scattering albedo (SSA), and aerosol absorption optical depth (AAOD) between 2010 and 2018 obtained from the Aerosol Robotic Network (AERONET) over Pokhara, Nepal. The analysis of these column-integrated aerosol optical data suggests significant monthly and seasonal variability of aerosol physical and optical properties. The pre-monsoon season (March to May) has the highest observed τAOD(0.75 ± 0.15), followed by winter (December to February, 0.47 ± 0.12), post-monsoon (October and November, 0.39 ± 0.08), and monsoon seasons (June to September, 0.27 ± 0.13), indicating seasonal aerosol loading over Pokhara. The variability of Ångström parameters, α, and β, were computed from the linear fit line in the logarithmic scale of spectral τAOD, and used to analyze the aerosol physical characteristics such as particle size and aerosol loading. The curvature of spectral τAOD, α’, computed from the second-order polynomial fit, reveals the domination by fine mode aerosol particles in the post-monsoon and winter seasons, with coarse mode dominating in monsoon, and both modes contributing in the pre-monsoon. Analysis of air mass back trajectories and observation of fire spots along with aerosol optical data and aerosol size spectra suggest the presence of mixed types of transboundary aerosols, such as biomass, urban-industrial, and dust aerosols in the atmospheric column over Pokhara.

Aerosols over the Foothills of the Eastern Himalayan Region during Post-monsoon and Winter Seasons

“…This variation in AOD, α, and β is due to differing atmospheric conditions driven by seasonal meteorology as well as changes in sources and types of aerosol emissions over the IGP (Tiwari et al, 2018(Tiwari et al, , 2016. Moreover, the seasonal average value of β shows that the aerosol loading during post-monsoon (0.33±0.19) is higher compared to winter (0.27±0.16), which is contrary to the results obtained from the central Himalayan foothills region, Pokhara (Regmi et al, 2020). The β values show significant correlation (R 2 =0.964) with AOD and anti-correlation with α on majority of the days during study period.…”

Analysis of Surface Level PM2.5 Measured by Low-Cost Sensor and Satellite-Based Column Aerosol Optical Depth (AOD) over Kathmandu

“…The city of Kathmandu is Nepal's largest metropolitan area and is highly polluted. Nepal is surrounded by the Indo-Gangetic Plain in the south and the large Himalayas in the north (Sarkar et al, 2017;Regmi et al, 2020). High mountains surround the Kathmandu valley, ranging from 2000 meters to 2800 meters, and the valley is shaped like a bowl, trapping pollution.…”

Atmospheric Turbidity of Solar Radiation over Langtang National Park

“…Linke turbidity is 5.7 ± 2.5 on Bhaktpur on 2013 [13]. Average seasonal value of Angstrom exponential (α) are 1.14 ± 0.01 in winter, 1.17 ± 0.07 in the pre monsoon season, 1.10 ± 0.08 in monsoon and 1.22 ± 0.08 in the post monsoon season on Pokhara between 2010 and 2018 [14].…”