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.