The effect of wildfires on air quality in Kathmandu, Nepal

Air pollution spikes in the central Himalayas' southern regions, including Nepal and northern India, occur mainly from wildfires during March to May. Despite being a significant contributor to pre-monsoon pollution, wildfire smoke remains under-researched. This study used multiple datasets and trajectory analysis to examine hazardous air pollution levels in Nepal's Kathmandu Valley from 2018-2022. It found 47 days exceeding the daily PM2.5 limit of 100 μg/m³, peaking at 305 μg/m³. The pollution was largely due to wildfire smoke from neighboring and transboundary areas, with a strong correlation between active fire counts and pollution levels. The correlation peaked at 0.89 (p<0.05) when lagged by two days during high fire years, like 2021, highlighting the valley's vulnerability due to its bowl-shaped structure. Our findings can inform legislation to mitigate wildfire-induced air pollution, which impacts both public health and the economy.