What Is AQI?
The Air Quality Index is a standardised scale that communicates how polluted the air is and what health effects might occur. It measures key pollutants including ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulphur dioxide, and nitrogen dioxide.
AQI Scale
| AQI Range | Level | Health Guidance |
|---|---|---|
| 0-50 | Good | Air quality is satisfactory; no risk |
| 51-100 | Moderate | Acceptable; sensitive groups may notice effects |
| 101-150 | Unhealthy for Sensitive Groups | Active children, asthmatics, elderly should reduce outdoor exertion |
| 151-200 | Unhealthy | Everyone should reduce prolonged outdoor exertion |
| 201-300 | Very Unhealthy | Everyone should avoid outdoor exertion |
| 301-500 | Hazardous | Health emergency; stay indoors |
PM2.5 — The Key Number
PM2.5 refers to particulate matter smaller than 2.5 micrometres. These tiny particles penetrate deep into your lungs and even enter your bloodstream. PM2.5 is the primary driver of AQI readings in most cities.
What Worsens Air Quality?
- Traffic: Vehicle exhaust is the top urban polluter
- Wildfires: Can send AQI above 300 hundreds of kilometres away
- Industrial emissions: Factories and power plants
- Weather: Temperature inversions trap pollution near the ground
- Agriculture: Crop burning and ammonia from fertilisers
Practical Tips
- Check AQI before outdoor exercise, especially if you have asthma
- Use N95 or KF94 masks when AQI exceeds 150
- Keep windows closed on high-AQI days
- Run an air purifier with a HEPA filter indoors
- Exercise indoors when AQI exceeds 100
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