Autumn and spring are the best seasons to visit Kathmandu: dry weather, festivals and Himalayan views. They are also the months when the valley’s air can turn hazy on some days. We’d rather you hear it from us than get surprised, so this guide gives the real figures month by month, explains the causes and shows how to plan so the haze doesn’t spoil your trip. On 4 November 2026, Kathmandu Metropolitan City also announced new measures against polluting vehicles and waste burning.
Quick answer
- Peak season (October–November) and spring (March–May) are still the best times to visit. October usually has fairly clean air and the clearest mountain views.
- Hazy days are most common from late November to January and in April.
- Cleanest air: the monsoon months (June–August), though that also means rain and clouds.
- Main causes: traffic, dust, brick kilns and industry, waste and biomass burning and forest-fire smoke in spring. The valley’s bowl shape traps all of it.
- Easy to plan around: check the live AQI (Air Quality Index) on IQAir Kathmandu, pack a mask for busy roads and save temples and indoor sights for hazy days.
How bad is air pollution in Kathmandu?
Kathmandu regularly appears on lists of the world’s most polluted cities on bad days. Averaged over a whole year, the figures look like this:
- 2024: an average PM2.5 concentration of 45.1 µg/m³, about 9 times the WHO annual guideline of 5 µg/m³ (IQAir).
- 2025: an average of 39 µg/m³, about 7.8 times the WHO guideline (IQAir).
PM2.5 means fine particles small enough to go deep into the lungs. It’s the main pollutant in Kathmandu. Yearly averages hide big swings between seasons, though. A summer day can be quite clean, while a December evening can be very hazy.
Kathmandu air quality by month
The table shows average PM2.5 by month at the Ratnapark monitoring station in central Kathmandu, based on 2020–2022 data analysed in a 2024 study. Individual years differ, but the pattern repeats every year.
| Month | Avg PM2.5 (µg/m³) | What to expect |
|---|---|---|
| January | 69.5 | Quiet season, hazy days common |
| February | 50.1 | Improving, sunny winter days |
| March | 46.4 | Spring season starts |
| April | 65.4 | Warm and blooming; forest-fire haze some days |
| May | 31.7 | Improving |
| June | 26.3 | Monsoon starts, clean air |
| July | 14.7 | Among the cleanest |
| August | 13.2 | Usually the cleanest month |
| September | 31.4 | Monsoon ending |
| October | 39.3 | Peak season, clear post-monsoon days |
| November | 67.4 | Peak season; haze builds later in the month |
| December | 71.7 | Crisp days, hazy evenings common |
Source: Sah Telee et al., Monitoring Air Quality in Kathmandu with Trend and Public Health Risks, Journal of Nepalese Management Academia (2024). Data: Ratnapark station, 2020–2022.
Other sources describe the same pattern. IQAir notes higher readings from January to May and in November and December and calls August historically the cleanest month. Nepal News calls it a U-shaped cycle, with peaks in March–April and December–January and cleaner air during the June–October monsoon. For the full travel picture, including mountain views, trekking and festivals, see our month-by-month guide to the best time to visit Nepal.
Why the Kathmandu Valley traps pollution
Kathmandu sits in a bowl with hills on every side. On cold, still days, cool air settles over the valley floor and holds pollution near the ground. The city notice puts it simply: cold conditions stop pollutants from dispersing. Rain and strong winds clear the air for a while, which is why the monsoon months are so much cleaner.
The main sources, according to Kathmandu Metropolitan City and published research, are:
- Vehicle exhaust: a large and growing fleet, many of them older vehicles.
- Dust from roads and construction.
- Brick kilns and industry.
- Burning waste and biomass, including open burning of plastic.
- Forest-fire smoke in spring, especially March to May, plus smoke from crop burning carried in from the plains of northern India.
What Kathmandu is doing about it (November 2026)
In its 4 November 2026 notice, the Environment Management Department of Kathmandu Metropolitan City:
- banned open burning of plastic and other waste;
- warned that anyone burning waste or running a vehicle that smokes beyond emission standards, will face legal action;
- told construction firms not to store materials on roads and footpaths and to control dust while transporting and loading;
- ordered industries, factories and hospitals to follow the city’s Pollution Control Standards 2025 and use pollution-control equipment.
Sources: OnlineKhabar, Nepal Press, Radio Nepal.
Is it safe to visit Kathmandu with the pollution?
For most healthy travellers on a short visit, yes. Nepal welcomes more than a million international visitors a year, and most of them pass through Kathmandu. The city notice names children, older people, people with asthma or other breathing problems and people with chronic diseases as most at risk. If that includes you, talk to your doctor before you travel and bring any medication you use. For crime, traffic and other practical safety questions, see Is Kathmandu Safe for Tourists in 2026?
8 practical tips for travellers
- Check the AQI every day. The AQI (Air Quality Index) turns pollution levels into one number from 0 to 500: the higher the number, the worse the air. See the live reading for Kathmandu on IQAir Kathmandu (also available as a free app). 0–50 is good, 51–100 moderate, 101–150 unhealthy for sensitive groups, 151–200 unhealthy, 201–300 very unhealthy and above 300 hazardous.
- Pack proper masks. A well-fitting N95, KN95 or FFP2 mask filters fine particles much better than a cloth or surgical mask.
- Swap your plans around on bad days. Save temples, museums and cafés for high-AQI days. Keep long walks and viewpoints for clearer ones.
- Cut your time in traffic. Busy roads are where exhaust and dust are worst. Walking the quieter old lanes or using a car with the windows up for longer trips helps.
- Pick a hotel room away from the main road and keep the windows closed when the air is bad.
- Time your trip for mountain views. Haze hides the Himalaya. If clear views matter to you, see our guide to Himalayan views without trekking.
- Drink plenty of water and give yourself rest days. Dry winter air and dust can irritate your throat.
- Use a short stay well. Our 2-day Kathmandu itinerary fits the main sights into two days, so you spend less time in the city on hazy days.
See the highlights without the traffic stress
Patan, Pashupatinath and Boudhanath in one guided small-group tour from Thamel. 5.5 hours, transport included, max 10 guests.
View the tourBest time to visit Kathmandu and how the air fits in
October and November are the most popular months for good reason: dry, sunny weather, big festivals and the clearest Himalayan views. October usually has the cleaner air of the two. Haze tends to build later in November. Spring (March–May) brings warm days and rhododendrons in bloom, with some hazy days around April when forest fires burn across Nepal. Winter (December–February) is quieter, with crisp sunny days and hazier evenings. If clean air matters most to you, the monsoon (June–August) is cleanest, but expect rain and clouds over the mountains. Planning around festivals too? See our Nepal festival calendar.
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Frequently asked questions
What is AQI?
AQI stands for Air Quality Index, one number from 0 to 500 that shows how polluted the air is. Up to 50 is good, above 150 is unhealthy and above 300 is hazardous. You can check Kathmandu’s live AQI on IQAir Kathmandu.
What is the worst month for air pollution in Kathmandu?
Readings are usually highest in December and January, with some hazy weeks in April because of forest-fire smoke. October, one of the most popular months to visit, is relatively clean.
What is the cleanest month in Kathmandu?
August is usually the cleanest, followed by July. Monsoon rain washes particles out of the air.
Should I wear a mask in Kathmandu?
On high-AQI days, especially near busy roads, a well-fitting N95/KN95/FFP2 mask is a good idea.
Why is Kathmandu so polluted?
The valley is a bowl that traps pollution on cold, still days. Traffic, dust, brick kilns, industry, waste burning and seasonal forest-fire smoke all add to it.
Does pollution affect mountain views from Kathmandu?
Yes. Haze often hides the Himalaya in winter and spring. Views are usually clearest after rain and in the post-monsoon weeks of October.
Main photo; The Kathmandu Valley seen from above. Its bowl shape traps pollution on cold, still days. Photo: Pritush Munankarmi / Unsplash
