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Reported AQI levels seem lower than it appears, visually
Reported AQI levels seem lower than it appears, visually

Reported air quality levels are too low. Published data appears to be incorrect.

Kelsey avatar
Written by Kelsey
Updated over a week ago

IQAir hosts the World’s largest platform for air quality information, an accomplishment only made possible by the efforts of governments, organizations, initiatives, and engaged users, who have made their air quality data public. Advanced data validation and calibration systems have been established to reduce erroneous reporting across global locations and monitors.

Sometimes air quality data is counter intuitive. It’s possible, for example, to see and/or smell air pollution, while the nearest air quality monitoring station reports data that seems overly optimistic. This discrepancy can usually be explained by a number of scenarios, which should be evaluated before reporting a station for inaccuracies. These scenarios include:

Clean air is blowing toward the monitoring station, polluted air is blowing away from the monitoring station.

Wind speed and direction is a key determinant in understanding how emissions will affect measured air quality at a given location. Wind blowing emissions away from a monitoring station can prevent pollution from rising measured air quality readings. EX: Easterly winds (blowing west) prevent wildfire smoke from affecting cities just miles west of the fire.

Air pollution (such as smoke) exists at higher elevations than ground-based air quality stations.

Smoke plumes from wildfires often exist at elevations much higher than monitoring stations, because hot wildfire smoke quickly rises over cooler, less dense ground level air. Between wind and the natural tendency for smoke to rise, air quality monitoring stations, which are based at the ground level, may not register a significant rise in particulates. In this scenario, readings measured at the ground level are representative of what residents are breathing.

The air quality data is not current, or hasn’t been updated recently.

Each city and station page on the IQAir platform has a clear indication of its last update time. This information can be found directly under the main air quality widget. It's important to check when a place's information was last updated, to ensure that data is conveying current conditions.

During periods of high pollution, such as wildfires, stations can go offline for maintenance purposes, or because they have lost power. Checking the last update time will help discern which data is most reliable.

Air quality has changed since the last update time.

Monitoring stations typically take numerous measurements throughout an hour. The data published on the IQAir platform represents the average of these measurements, and is posted at the end of the hour. For example, measurements taken from 2:00 PM to 2:59 PM are averaged and posted at 3:00 PM, with a 3:00 PM update time.

It can happen that air quality changes from the time of update, to the time of observation. In the previous example, the next air quality update won’t be until 4:00 PM. By 3:55 PM, data collected from 2:00 to 2:59 PM may no longer be representative. This tends to be particularly true when there are strong winds, precipitation, or drastic changes in emissions.

In this case, it is best to check the station’s data again at the turn of the hour or use forecast data to better understand how air quality is trending.

The nearby monitoring station does not measure PM2.5.

In some cases, governmental (US EPA) monitoring stations may not monitor pollutants directly created or released in wildfires, such as PM2.5.

The IQAir air quality map only displays stations that measure or estimate PM2.5 data. This is so that all stations compare "apples to apples." It is still possible, however, to search for stations using the search bar, which do not monitor PM2.5. During wildfires, these AQI readings may differ drastically from stations which do also monitor PM2.5.

While IQAir aggregates data from a range of sources, including governmental and community contributed monitors, there are still a number of places around the world that lack air quality data granularity.

If you happen to know of an open data source that shows PM2.5 data for your location, we would be interested to add it to our map. Please contact IQAir support to suggest governmental or third party data in your area.

If you are not aware of any monitoring stations in your area, and would like to contribute an air quality station to the global network, it is possible to purchase one of three supported monitors for public outdoor deployment. This way you can provide your family, your community and data researchers alike with live outdoor PM2.5 levels in your area. Learn more about becoming a data contributor here.


If data oddities cannot be explained, and a station problem is suspected, compare station data to the source data

If the data seems unusual, and the above scenarios do not provide an explanation for a station’s data, check to see if the data source is also reporting erroneously. Learn how to find a station’s source data here.

Sometimes data from the IQAir platform may differ from other data sources, even when data has been aggregated from these. Follow the links below to better understand these differences:

Report incorrect data

If you would like to report a station which seems to be publishing incorrect data, navigate to the city or station page on the IQAir app, and scroll down to the grey “Any problem with this place? Report --->” section (just below the “pollutants” section”). Click here to quickly describe the problem.

Reports can also be made by contacting IQAir support.

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