Kathmandu sits in a bowl-shaped valley where dust, traffic fumes and smoke can become trapped. Air quality varies a lot by season, so it's worth knowing when it's worst.
Quick answer: air pollution is usually worst in winter and spring. Cold air traps pollution in the valley in winter, and from March to May, smoke from forest fires and crop burning adds to it, sometimes pushing the AQI to very unhealthy or hazardous levels. Air is usually cleanest during the monsoon and just after.
Why the air gets bad
- Vehicle exhaust and road dust
- Brick kilns and industry around the valley
- Forest fires and agricultural burning, especially in spring
- The valley's shape and cold winter air, which trap pollution
Protecting yourself
- Check the AQI on a reliable app each day.
- Wear a well-fitting N95/KN95 mask on bad days, especially in traffic.
- Plan outdoor activities for early mornings or after rain.
- Spend smoggy days in the hills: Nagarkot, Dhulikhel or Pokhara often have cleaner air.
- If you have asthma or heart or lung conditions, take extra care and bring medication.
Effect on trips
Haze can hide mountain views in spring. The clearest skies are usually October–November. See Kathmandu weather by month and best time to visit.