How AirQuality.city processes data
AirQuality.city combines measurements from its own Sensorbox stations with publicly available data from official monitoring networks. This page provides a short overview of what happens between the source measurement and the value shown on the website.
A detailed list of sources, technical rules, and the calculation formula is available on the Data sources and methodology page.
Data sources
The website uses two main groups of data:
- measurements from Sensorbox stations
- data from official and other clearly identified external stations
Sensorbox stations use an SDS011 sensor for PM2.5 and PM10 and a BME280 sensor for temperature, humidity, and pressure. These are lower-cost sensors intended for following local changes, not for official regulatory assessment.
Official-station data may be preliminary. The competent institution may correct or invalidate them after review.
Processing Sensorbox measurements
A Sensorbox station collects several readings during one cycle, checks the message integrity, and sends an average value. Measurements are normally repeated every two to three minutes.
The website rejects technically invalid or incomplete records and tracks the time of the latest valid measurement.
An unavailable value is not displayed as zero. Zero would mean a measured concentration of 0 µg/m³, while an unavailable value means there is no valid reading.
AQI calculation
A separate AQI is calculated for PM2.5 and PM10 using U.S. EPA concentration breakpoints. The station's overall AQI is the higher of the two.
overall AQI = max(PM2.5 AQI, PM10 AQI)
The website uses the official AQI categories:
- 0-50: Good
- 51-100: Moderate
- 101-150: Unhealthy for sensitive groups
- 151-200: Unhealthy
- 201-300: Very unhealthy
- 301-500: Hazardous
NO₂, O₃, SO₂, and CO are not included in the website's overall AQI.
Near-current display and official indices
The website AQI is calculated from the latest processed value available for a station, unless a different averaging period is stated alongside the data.
It is therefore a near-current indicator. It should not be treated as the same thing as an official daily AQI, which may use 24-hour averages, NowCast, or another method.
Differences between websites may also result from update times, later validation, different stations, and different sets of pollutants.
What may affect a reading
The project's optical sensors may be affected by:
- high humidity and condensation
- sensor position and shielding
- nearby local sources
- contamination and device ageing
- differences between units of the same model
A station describes its own location. It does not necessarily represent an entire city, especially where terrain, traffic, and heating patterns vary between neighbourhoods.
For official, regulatory, health, or emergency decisions, check the data and guidance issued by competent authorities.