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Abstract
The total suspended particulate (TSP) samples were collected from April 2013 to April 2014 at the urban location of Pokhara valley in western Nepal. The major aims were to study, quantify, and understand the concentrations and variations of TSP and major water-soluble inorganic ions (WSIIs) in the valley with limited data. The annual average TSP mass concentration was 135.50 ± 62.91 µg/m3. The average analyzed total WSIIs accounted for 14.4% of total TSP mass. Major anions and cations in TSP samples were SO42− and Ca2+, respectively. Seasonal differences in atmospheric conditions explain the clear seasonal variations of ions, with higher concentrations during pre-monsoon and winter and lower concentrations during the monsoon period. Neutralization factor calculations suggested that Ca2+ in the Pokhara valley mostly neutralizes the acidity in the atmosphere. Principle component analysis, NO3−/SO42− ratio, and non-sea salt fraction calculations suggested that the WSIIs in the valley were mostly derived from anthropogenic activities and crustal mineral dust, which was also supported by the results from precipitation chemistry over the central Himalayas, Nepal. In addition, back trajectories analysis has suggested that the air pollution transported from and through Indo-Gangetic Plains (IGP) during the dry periods, which has resulted in high ionic loadings during this period. Average NO3−/SO42− ratio was found to be 0.69, indicating the dominance of stationary sources of TSP in Pokhara valley. Secondary inorganic aerosols can have an adverse health impact on the human population in the valley. The data set from this one-year study provides new insights into the composition of WSIIs in the foothills of the Himalayas, which can be of great importance for understanding the atmospheric environment in the region.
Highlights
Airborne particulate matter plays a vital role among their sources, transport, and deposition mechanisms of various pollutants in the atmosphere [1]
The values of total suspended particulate (TSP) mass concentration throughout the year have been presented in Figure S3, in which five analyzed samples exceeded the World Health Organizations (WHO) regulation limits which were during pre-monsoon and winter
Prior studies have suggested that westerlies prevail during non-monsoon seasons in Nepal that bring little precipitation and more aerosols, and during predominant westerlies, dust aerosols could be transported to Nepal from arid regions [10,23], which may be responsible for higher concentrations of crustal-derived aerosols
Summary
Airborne particulate matter plays a vital role among their sources, transport, and deposition mechanisms of various pollutants in the atmosphere [1]. This study will provide the dataset for major water-soluble ionic species in atmospheric aerosol for a yearlong period in the second largest valley in the foothills of the Himalayas, Pokhara valley, Nepal. For the first time, total suspended particulate (TSP) samples were systematically collected for a year, from April 2013 to April 2014, at an urban residential area of the core city in the Pokhara valley with the aim of investigating the ambient suspended particles and related chemical composition with a focus on water-soluble inorganic ions. The results from this study are useful to extend the knowledge on major water-soluble ionic species of TSP in the urban Himalayan environment and their temporal distribution (variability) and differences depending on the sources
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