Forest fires have become more intense and frequent in recently changing climates. The wide variety of pollutants released by forest fire include greenhouse gases, photochemically reactive compounds, and fine and coarse particulate matter. This study investigated the impact of forest fire events on air quality in the Kathmandu Valley during March-April 2021 using ground air quality monitoring stations and satellite data. The three fire periods were studied (a) Pre-fire from 21st - 23rd March (b) first-fire episode from 24th -27th March and (c) second fire episode from 1st - 5th April of 2021. The concentrations of PM2.5 reached to maximum 199 μg/m3 during pre-fire period, 371 μg/m3 and 280 μg/m3 during first and second fire event respectively. The second fire episode had lower PM2.5 concentration despite higher fire counts (449) compared to the first episode suggesting influence of fire activities near to vicinity of Kathmandu valley during second fire episode. There was a two-day lag between the beginning of forest fire events and an increase in PM2.5 levels in Kathmandu. Satellite observation showed varying patterns for different pollutants. HCHO levels responded quickly to fire activity, while AOD and CO levels increased after a few days. Also, low wind speed, low temperature, and low relative humidity additionally elevated these pollutants in Kathmandu. This study emphasizes the extent of the impact of forest fires on air quality and the importance of considering meteorological and satellite data to understand the distribution of pollutants during such events.
Keywords: Air quality; Forest fire; Meteorology; PM(2.5); Pollutants.
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