Understanding the forecasts
What is the AQI?
The AQI (Air Quality Index) summarises air quality as a single number: the higher it is, the more polluted the air and the greater the health risk. It is computed from pollutant concentrations; the pollutant giving the highest value sets the index.
On this site, the AQI curve shows the hour-by-hour evolution over 4 to 5 days. The main pollutant and its maximum expected concentration are given with matching advice.
The six levels
Good · 0 – 50Satisfactory air quality, little or no risk.
Moderate · 51 – 100Acceptable; possible discomfort for very sensitive people.
Unhealthy for sensitive groups · 101 – 150Sensitive people may experience health effects.
Unhealthy · 151 – 200Everyone may experience health effects.
Very unhealthy · 201 – 300Health alert: increased risk for everyone.
Hazardous · 301 and aboveHealth emergency: the whole population is affected.
Pollutants we track
Fine particles (PM2.5)
Where does it come from?
Particles under 2.5 µm released by combustion: road traffic (especially diesel), wood heating, industry, agricultural burning. They also form in the air from other gases. Episodes are common in cold, dry, windless weather.
Health effects
They penetrate deep into the lungs and can enter the bloodstream. Short term: irritation of eyes, nose and throat, cough, worsening asthma. Long term: respiratory and cardiovascular disease. Children, older adults, pregnant women and people with chronic conditions are the most exposed.
Ozone (O₃)
Where does it come from?
A gas formed in the air by sunlight from nitrogen oxides and volatile organic compounds (traffic, industry, solvents). Peaks occur in the afternoon and early evening in hot, sunny weather, especially in summer.
Health effects
An irritant gas: cough, discomfort or pain when breathing deeply, eye and throat irritation, a temporary drop in breathing capacity during exercise, worsening asthma. It also harms vegetation and crops.
How to read the curves
Coloured bands in the background match the AQI levels. Hover or touch the curve to read the value at a given hour. Times are shown in your device’s time zone. Concentrations (the “Concentrations” tab) are expressed in µg/m³; the dashed line shows the WHO guideline value.
Where does the data come from?
Forecasts come from air quality models (ECMWF) and are updated regularly. They cover major European cities as well as major cities worldwide (air pollution only outside Europe): your position is matched with the nearest city (up to 100 km away). A forecast is an estimate: actual air quality may differ, especially near a local source (busy road, industry, fires).
Pollen forecasts (grass, ragweed, alder, mugwort, birch) also come from ECMWF and are expressed in pollen grains per cubic metre of air. The pollen seasons and thresholds shown are indicative.
iOS app
The iOS app — maPollution iOS
Take air quality forecasts in your pocket with our iPhone app.
- Your city’s forecast at a glance
- Advice tailored to your sensitivity
- Designed to be simple and light
Download on the App Store
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Legal information
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Publisher: ZLIKA SAS — 63 bis rue d avron, 75020 PARIS. Publication director: Ronald Van Assche. Contact: contact@mapollution.fr.
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Disclaimer
The forecasts and advice published are for information only. They are neither medical advice, nor an official alert, nor a guarantee of accuracy. If in doubt about your health, consult a healthcare professional; during a pollution episode, follow your local authorities’ guidance. The publisher cannot be held liable for decisions made on the basis of this information.
Intellectual property
The texts, illustrations and graphics of the site are protected. Any reproduction without permission is prohibited, except for extracts shared using the share button.
Personal data and cookies
Geolocation: your position is requested only with your browser’s consent. Coordinates are sent to the server solely to find the nearest city; they are neither recorded nor retained.
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Reference values
The concentration references shown are World Health Organization guideline values (2021 guidelines). They are indicative and are not regulatory limits.
