First compare the place and the time
Four details that make a reading useful
- 01Pollutant
- PM2.5, PM10 or another pollutant?
- 02Unit / index
- µg/m³ or a named AQI scale?
- 03Time
- Current hour, daily average or forecast?
- 04Source
- A station observation or a model?
Two services may use different monitors, update at different times or show a nearby location rather than the same point. Compare the coordinates or station name, timestamp and data source before comparing values. A monitor observation and a regional model should not be expected to match exactly.
Then compare the thing being displayed
One screen may show PM2.5 concentration, another an AQI, and another a forecast. AQI rules also differ across jurisdictions: the US AQI is EPA’s system, while the EEA maintains a European index. A shared colour name or a similar number does not make the scales equivalent.
Look for method labels, not a winner
Check pollutant, unit, averaging period and whether the data are measured, modelled or forecast. AirNow’s current NowCast itself uses multiple recent hours rather than a raw instant value. Clear labels let you decide which source best fits the question you have, instead of treating every difference as evidence of bad faith.
Sources
Educational information; personal health questions belong with your clinician.
Explore next
- Air quality index: what AQI means
- Air quality forecast in the Atmiq app: how to read it
- PM2.5: what it means and how to use the reading
- PM10: what it is and how it differs from PM2.5
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