Air Quality Index (AQI)
Weather index for activity planning
What is the Air Quality Index (AQI)?
The Air Quality Index (AQI) is an essential public health tool that measures and communicates the concentration of dangerous atmospheric pollutants in the air, including fine particles (PM2.5 and PM10), ground-level ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO). This index is converted to a 0-10 scale where higher values indicate cleaner, healthier air, while low values signal dangerous conditions that can cause acute and chronic respiratory problems, especially in vulnerable groups such as children, elderly, people with cardiorespiratory diseases, and pregnant women. Air quality affects not only respiratory health but also visibility, overall comfort, and the ability to safely perform outdoor physical activities.
How is the Air Quality Index (AQI) calculated?
- PM2.5 (fine particles): Particles smaller than 2.5 micrometers penetrate deeply into lungs and bloodstream. High concentrations (above 55 µg/m³) drastically reduce the index, causing respiratory and cardiovascular problems.
- PM10 (inhalable particles): Particles up to 10 micrometers can be inhaled and cause irritation. Values above 150 µg/m³ significantly reduce the index and affect respiratory health.
- Ground-level ozone (O3): Tropospheric ozone is formed by the reaction of pollutants with sunlight. Concentrations above 100 ppb reduce the index and cause respiratory problems, especially on hot and sunny days.
- Nitrogen dioxide (NO2): Emitted by vehicles and industries, concentrations above 200 µg/m³ reduce the index and cause airway inflammation, aggravating existing respiratory conditions.
- Carbon monoxide (CO): Emitted mainly by vehicles, high concentrations (above 9 ppm) reduce the index and can cause headaches, dizziness, and cardiovascular problems, especially in areas with heavy traffic.
Understanding the Air Quality Index (AQI) Scale (0-10)
0-2
Very Poor - Hazardous for everyone
3-4
Poor - Unhealthy
5-6
Fair - Sensitive groups at risk
7-8
Good - Acceptable
9-10
Excellent - Clean air
Air Quality Index (AQI): Top Cities Comparison
Compare Air Quality Index (AQI) values for the most popular cities ranked by search volume
| City | Country | Today | Tomorrow | Change |
|---|---|---|---|---|
| Tokyo | Japan | 8 / 10 Excellent | 4 / 10 Fair | -4 |
| Osaka | Japan | 8 / 10 Excellent | 6 / 10 Good | -2 |
| Kyoto | Japan | 10 / 10 Excellent | 8 / 10 Excellent | -2 |
| London | United Kingdom | 8 / 10 Excellent | 10 / 10 Excellent | +2 |
| Rome | Italy | 8 / 10 Excellent | 10 / 10 Excellent | +2 |
| Paris | France | 8 / 10 Excellent | 10 / 10 Excellent | +2 |
| Delhi | India | 4 / 10 Fair | 6 / 10 Good | +2 |
| Florence | Italy | 8 / 10 Excellent | 10 / 10 Excellent | +2 |
| New York City | United States | 8 / 10 Excellent | 10 / 10 Excellent | +2 |
| Hanoi | Vietnam | 8 / 10 Excellent | 8 / 10 Excellent | 0 |
Air Quality Index (AQI): Tips & Recommendations
- Check air quality before outdoor activities
- Avoid intense outdoor exercise when AQI is low
- People with asthma should be cautious when AQI is moderate
- Wear protective masks on poor air quality days
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