AQI explainer tool
What is the Air Quality Index? A practical AQI explainer
An Air Quality Index turns pollutant-specific rules into a public communication scale. It is useful for comparing categories and changes, but it is not a universal measurement unit, a diagnosis, or a promise that one number is safe for everyone.
Named scale
AQI ≠ µg/m³
Compare within one scheme, with pollutant, time, and source.
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AQI is a communication scale, not a pollutant unit
A concentration such as micrograms per cubic metre describes a pollutant quantity. AQI applies a published set of pollutant breakpoints, averaging periods, and labels to communicate concern. That means the index is derived from pollutant information but should not be mistaken for the physical concentration itself.
AirAgora’s runtime preserves OpenWeather’s official 1–5 value and category for display. It separately uses the provider’s documented pollutant concentration bands to derive continuous component severity and explain the main pollutant without mixing raw concentration units.
European and U.S. AQI use different bands
The EEA documents European AQI categories and AirNow documents the U.S. AQI categories. The systems use different breakpoints, labels, pollutant treatment, and communication context.
Those numbers cannot be converted by a simple multiplier. The systems differ in breakpoints, pollutant treatment, terminology, and communication context. A value of 70 on one scale is not the same claim as 70 on the other.
| Scheme | Lower categories | Higher categories |
|---|---|---|
| European AQI | Good · Fair · Moderate | Poor · Very poor · Extremely poor |
| U.S. AQI | Good · Moderate | Unhealthy for sensitive groups · Unhealthy · Very unhealthy · Hazardous |
How AirAgora labels the runtime scale
AirAgora displays OpenWeather’s official air-pollution scale from 1 to 5 in every supported country. The interface language translates the category, but it does not relabel the provider value as U.S. AQI, European AQI, or a local regulatory index.
European and U.S. AQI remain useful educational systems on this page. They are not the live product scale, and AirAgora does not publish a synthetic conversion from OpenWeather’s provider value to either regulatory AQI.
What a category can help you decide
A category makes an hourly pattern easier to read. It can show that modeled conditions are changing, that a pollutant component is controlling the aggregate result, or that all practical periods remain poor. It can also provide a common label for alert crossings.
A category cannot determine personal exposure, indoor conditions, symptoms, or treatment. The WHO guideline context is one reason AirAgora avoids a universal “safe” threshold. Better means lower within the available forecast, not risk-free.
How the AQI explainer connects to the planner
AirAgora derives continuous severity for each supported pollutant from OpenWeather’s documented concentration bands before comparing hours. It evaluates complete two-hour windows, weights the mean more heavily than the worst hour, preserves an earlier tied window, and requires a meaningful improvement before naming a precise best time.
This normalized score is an internal comparison aid, not an AQI. The result continues to display the original OpenWeather 1–5 value and category, pollutant concentrations, source, and timestamp.
- Always keep the OpenWeather scale beside the number.
- Do not add or average European and U.S. AQI values together.
- Check whether a screen shows an aggregate or a pollutant component.
- Use official warnings for urgent decisions.
Common mistakes when reading AQI
One mistake is treating every value below a round number as universally harmless. Another is comparing screenshots from different times, locations, or index schemes. A third is assuming that a modeled grid and a nearby monitor should match exactly.
A careful reading asks five questions: which scheme, which pollutant, which averaging period, which timestamp, and which provenance? AirAgora puts those answers near the result so the index remains interpretable rather than decorative.
Direct answers
Frequently asked questions
What does AQI stand for?
AQI stands for Air Quality Index. It is a public communication scale built from pollutant-specific rules, not a pollutant concentration unit.
Is a lower AQI always better?
Within the same named scheme and comparable time/location, lower generally represents less modeled pollution concern. It still does not guarantee zero risk or personal safety.
Can European AQI be converted directly to U.S. AQI?
No. The systems use different breakpoints, labels, pollutants, and averaging conventions. AirAgora normalizes within one scheme for ranking rather than publishing a fake conversion.
Which scale does AirAgora show live?
OpenWeather’s official air-pollution scale from 1 to 5. It is not labeled as U.S., European, or local regulatory AQI.
Is the OpenWeather value a street-level measurement?
No. AirAgora labels it as a modeled forecast value; a point monitor or street can differ.
Does a “good” category mean safe for everyone?
No. It is a category within a communication system. AirAgora avoids universal-safe claims and directs users to official or professional guidance for personal needs.
Evidence register
Sources and further reading
The links below identify the primary references used on this page. Selection, summary, and presentation are AirAgora modifications.
Keep exploring
AirAgora provides informational planning guidance, not medical advice. Local conditions can differ from modeled forecasts; follow official guidance during severe events.