How to read the AQI
| US AQI | Category | What to do |
|---|---|---|
| 0–50 | Good (राम्रो) | Air quality is satisfactory — enjoy normal outdoor activities. |
| 51–100 | Moderate (मध्यम) | Acceptable for most people; unusually sensitive individuals should consider limiting prolonged outdoor exertion. |
| 101–150 | Unhealthy for Sensitive Groups (संवेदनशील समूहलाई अस्वस्थ) | Children, older adults and people with heart or lung disease should reduce prolonged or heavy outdoor exertion. |
| 151–200 | Unhealthy (अस्वस्थ) | Everyone may begin to feel effects — limit prolonged outdoor exertion; sensitive groups should avoid it and consider a mask outdoors. |
| 201–300 | Very Unhealthy (धेरै अस्वस्थ) | Health alert — avoid outdoor exertion, keep windows closed, use a well-fitted mask (KN95/N95) outside and an air purifier if available. |
| 301+ | Hazardous (खतरनाक) | Emergency conditions — stay indoors with windows closed; everyone should avoid outdoor activity. |
Air pollution in Nepal — what drives the number
Kathmandu regularly ranks among the world’s most polluted capitals in winter. The main sources are vehicle exhaust, brick kilns, road and construction dust, open waste burning and — in the dry spring — forest-fire smoke carried across the hills. Geography makes it worse: the valley’s bowl shape traps a layer of cold air overnight (temperature inversion) that holds pollutants near the ground until the sun or wind breaks it up. Terai cities like Birgunj and Biratnagar also see high PM2.5 from industry and regional haze crossing the border.
The seasonal pattern is strong: expect the worst air from Mangsir to Baisakh (roughly December–April, peaking during fire season), and the cleanest air during the monsoon (Asar–Bhadau) when rain scrubs the atmosphere.
Sources & disclaimer
- Open-Meteo Air Quality API — live modelled data (Copernicus CAMS), fetched directly in your browser; no key, no tracking by Tools Pasal.
- Air Quality Monitoring — Ministry of Forests and Environment (pollution.gov.np) — Nepal’s official ground-station network; use it for regulatory or health-decision readings.
Sources last reviewed 2026-07-03. Modelled AQI can differ from a nearby ground station, especially during sharp pollution episodes — treat this page as a planning tool, and official monitors as authoritative.
Frequently asked questions
Why is Kathmandu's air quality so bad in winter?
The Kathmandu Valley is a bowl surrounded by hills. In winter (roughly Mangsir to Falgun), temperature inversion traps cold air — and the smoke, vehicle exhaust and dust in it — close to the ground, so PM2.5 accumulates for days. Forest fires in the dry months (Chait–Baisakh) often push AQI into the unhealthy range across the country, while monsoon rain washes the air cleanest from Asar to Bhadau.
What is PM2.5 and why does it matter most?
PM2.5 means particles smaller than 2.5 micrometres — small enough to pass deep into the lungs and bloodstream. It is the pollutant that drives most of Nepal's health burden from air pollution and usually determines the AQI number in Kathmandu.
Which AQI scale does this page use?
The US EPA AQI scale (0–500), computed by the data provider from modelled pollutant concentrations. Other apps may show different numbers if they use another country's index or a specific ground station — always compare like with like.
Is this an official government reading?
No. Live values come from the CAMS atmosphere model via the Open-Meteo Air Quality API — a modelled estimate for your location, not a ground station. Nepal's official monitoring network is the Ministry of Forests and Environment's pollution.gov.np, which this page links for reference readings.
At what AQI should I wear a mask or keep children indoors?
From the 'Unhealthy for Sensitive Groups' band (AQI 101–150), children, older adults and people with asthma, COPD or heart disease should cut back outdoor exertion. From 'Unhealthy' (151–200) everyone should limit time outdoors and a well-fitted KN95/N95 helps. 'Very Unhealthy' and above: avoid outdoor activity, close windows and use an air purifier if you have one.