Data aggregation
IQAir publishes air quality data for both individual stations and cities on an hourly basis, displaying timestamped values corresponding to the last full hour. This article explains how IQAir aggregates data from multiple sources to ensure consistent, reliable air quality information.
Data sources
IQAir gathers air quality data from two primary sources:
- Government reference stations, which provide high-precision readings.
- Low-cost sensors, such as IQAir’s Airvisual Outdoor monitors, as well as devices from other manufacturers.
For low-cost sensors, model-specific correction factors are applied to PM2.5 concentrations to correct for the well-known sensor measurement bias that occurs during high humidity conditions. This correction is based on co-located low-cost sensor and reference station measurements, and further ensures more accurate data in our platform.
You can find detailed information about a station’s contributors, sponsors, and data sources on each station or city page. Simply click on the link that lists the contributors to see more.
Station data aggregation
IQAir publishes real-time air quality data from over 30,000 stations world-wide. All station data, regardless of its original reporting frequency, is aggregated into 1-hour averages and reported with a retrospective timestamp. For instance, a value displayed at 11:00 represents the average of all measurements recorded between 10:00 and 10:59. This ensures consistency and allows for comparability across stations that may report data at varying frequencies.
Stations that fail to report data for several hours or show unusual readings (such as consistently static values), are temporarily excluded from the display to maintain data quality. Additionally, we cross-check station readings with neighboring stations to filter out significant discrepancies.
City data aggregation
For cities, IQAir calculates air quality based on the median of all hourly aggregated concentration data from stations within that city’s area. In cities without any monitoring stations, IQAir uses satellite data estimations to provide air quality values, which are processed and aggregated in a similar way. Read more this topic here: What does the asterisk (*) mean on some locations' AQI? (iqair.com).
Calculating AQI
IQAir calculates the AQI for each pollutant from the concentration data collected for each station and identifies the "dominant" pollutant which determines the overall AQI. For city data, we first calculate the AQI for each individual pollutant first, then report the overall city AQI based on the pollutant that producing the highest AQI value.
For more details on how AQI is calculated, including the difference between AQI and AQI⁺, read our detailed guide on What is the air quality index (AQI)? | IQAir.
Want to know more?
Check the Knowledge Base