Health · Explainer · · Mirror News Today
Air Quality Index: How to Read the Number That Matters
An air-quality reading is most useful when it connects a pollutant, a location and the people affected. A color alone is incomplete context.
Written with AI assistance using the primary sources below. Recommendations are analysis; examples are hypothetical.
What the US AQI tells you
The US Air Quality Index translates monitored pollution into six categories, from good to hazardous. AirNow explains that values above 100 indicate unhealthy conditions, initially for sensitive groups and then for everyone as values rise. The index communicates conditions and guidance; it cannot diagnose how an individual will respond.
Other countries may calculate and display their indices differently. Before comparing numbers, check the publisher, scale, location and time. Two apps labeled "air quality" may use different measurements or give different instructions.
AQI values and health guidelines use different measures
The World Health Organization's air-quality guidelines recommend health-based pollutant concentrations, including for fine particles and ozone. Those concentrations have different units and purposes from an AQI value. Some also concern exposure averaged over different periods.
Check the pollutant and averaging period before comparing readings or guidelines. A summary app can help you find a number quickly; the local public agency's explanation supplies the context for interpreting it.
Read the advice for the pollutant being reported
AirNow identifies groups that may be more affected by particular pollutants and gives advice on reducing exposure. Read the guidance attached to the reported pollutant. People with an existing condition should also follow their clinician's plan and local public-health advice.
Schools, workplaces and sports organizers can identify the relevant official guidance before conditions worsen. Decide who will monitor updates and communicate any change of plan. That avoids leaving the first discussion of a concerning reading until an activity is underway.
Check the place and timestamp
A regional reading may not describe the air beside a busy road or inside a building. An old reading cannot establish current conditions. Check whether the display shows an observation, a forecast or a broader regional summary.
An organizer choosing between morning and afternoon activities, for example, would need updated official information and the applicable guidance. That example does not imply one time of day is always safer. The decision depends on conditions at the time.
Explain changes to activities clearly
An air-quality notice should name the source, the condition being tracked and the action being taken. Say when the next update is expected so people know when to check again.
Follow the relevant official source and its matching guidance as conditions change. One improved reading should not be presented as an all-clear beyond what authorities advise. This is general information; individual medical decisions need advice suited to the person.
Main points
- The US AQI is a communication scale, rather than a personal diagnosis.
- Above 100, air is unhealthy first for sensitive groups and then more broadly as values rise.
- AQI systems and health guidance can differ across countries.
Common questions
Can AQI values from different countries be compared?
First check whether their calculations, thresholds and labels match. The same number may mean different things on different scales.
Does the AQI predict exactly how I will feel?
It describes pollution conditions and gives general guidance. Your susceptibility and medical advice also matter.
How does a forecast differ from a reading?
A forecast estimates future conditions. A monitoring reading describes observations for a stated place and period.