There can be numerous reasons why the AQI can vary significantly from one station to another, even when they are close by. Hyperlocal air quality differences due to hyperlocal air pollution sources. Stations that are very close to a busy street, close to hyperlocal industrial pollution, a restaurant kitchen exhaust, a home burning wood, a construction site or a bus stop might show higher air pollution than stations that are slightly further away.
 
Some air quality stations, especially those from air quality agencies, may have delays in reporting air quality due additional quality control procedures. This can lead to the air quality being reported having been measured one or more hours earlier. IQAir removes stations from the map, when they have not reported data for more than 6 hours. IQAir provides a timestamp on top of every station page and visibility in the history graph of the last station data available.
 
Most stations on the IQAir map measure fine dust (PM2.5), which is the most harmful of common air pollutants. There are some stations that measure more pollutants than PM2.5, such as ozone (O3), NO2, SO2 and CO. While PM2.5 is the dominant pollutant for most of the world for most of the time, there can on occasion be other air pollutants that become the dominant pollutant and that determine the AQI. Typically these are PM10 or O3. There are yet other stations that do not measure PM2.5, but instead measure only ozone and report the AQI based on the ozone concentration. This can mean that during high PM2.5 and low O3 periods, these stations show a better AQI than surrounding stations that measure PM2.5.
 
Finally, there is the possibility that some stations reporting data, due to a lack of maintenance, some malfunction or a move by the station owner report wrong data. IQAir has an automatic station quality control validation procedure in place that helps to remove most invalid station data, but may not always identify an issue. This is why every station page on the IQAir website and mobile app allows users to report data inconsistency or a station issue.
 
We strive to display these different data sources as transparently as possible, to give due credit to those who make this data publicly available. For detailed information on how to find these data credits within the AirVisual app and website, visit this page:
 
 
How is air quality data validated before publishing on the AirVisual platform?

 
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