Air Pollution and the AQI, Explained Without the Jargon
Air Pollution and the AQI: what it is, why it matters, and what published guidance actually asks of you.
Polluted air is linked to asthma attacks, heart attacks and strokes, and checking the daily AQI lets you plan activity to cut your exposure.
Key takeaways
- Good (green): 0 to 50
- Moderate (yellow): 51 to 100
- Most useful single change: Check the AQI daily on AirNow or a weather app, especially in wildfire season.
- Commonest mistake: Hard outdoor exercise when the AQI is orange or worse if you are in a sensitive group.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
The short answer
Outdoor air pollution such as ozone, fine particles and wildfire smoke, and the Air Quality Index used to report it.
Where it fits
This is part of Environmental Health. Guidance sets out what to look for and what to do about it, which is what the rest of this page covers.
The numbers, in one place
| Measure | Figure |
|---|---|
| Good (green) | 0 to 50 |
| Moderate (yellow) | 51 to 100 |
| Unhealthy for sensitive groups (orange) | 101 to 150 |
| Unhealthy (red) | 151 to 200 |
| Very unhealthy (purple) and hazardous (maroon) | 201 to 300, and 301 or higher |
| Sensitive groups | people with heart or lung disease, children, older adults, pregnant people and outdoor workers |
What that means in practice
Put another way, here is what it asks of you:
- Check the AQI daily on AirNow or a weather app, especially in wildfire season
- Move exercise indoors or to times when pollution is lower; ozone is often highest on summer afternoons
- Keep windows closed on smoky days and run a portable HEPA air cleaner or a MERV 13 filter in your HVAC system
- Wear a well-fitting N95 respirator if you must be outdoors in heavy smoke
- Keep rescue inhalers and other medicines on hand and follow your asthma action plan
What gets people into trouble
The pitfalls worth knowing about:
- Hard outdoor exercise when the AQI is orange or worse if you are in a sensitive group
- Relying on cloth or surgical masks for smoke protection
- Burning wood, candles or frying food indoors on smoky days
Related topics
- Air Quality: What the Evidence Actually Says (Respiratory Health)
- Wildfire Smoke: What Published Guidance Supports (Heat, Cold and Weather Safety)
- What the Guidance Really Says About Asthma and Allergy (Allergies)
- COVID-19: What the Evidence Actually Says (Infectious Diseases)
Where to go next
- Starting Out With Air Pollution and the AQI
- Your Questions About Air Pollution and the AQI, Answered
- Air Pollution and the AQI — the reference entry
- Environmental Health: The Complete Guide
- What the Guidance Really Says About Indoor Air and Gas Stoves
- The Evidence on Pesticides at Home, Without the Hype
When to speak to a doctor
See your doctor if poor air days regularly worsen your asthma, COPD or heart symptoms, so your treatment plan can be adjusted. Call 911 for chest pain, severe shortness of breath, an asthma attack not relieved by your rescue inhaler, or signs of a stroke.
Where this comes from
- AirNow — Air Quality Index (AQI) Basics
- EPA — Wildfires and Indoor Air Quality
- CDC — Wildfire Smoke and Your Health
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.
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