DATA TRANSPARENCY

Air Quality Data & Methodology

AirQualityIndex.org distinguishes between observed monitoring data, modelled air-quality information, forecasts and calculated AQI values. The methodology shown on each feature should be read together with its named data source.

1. Observations and monitoring stations

Monitoring observations are measurements reported by air-quality monitoring networks. Coverage, update frequency, quality control and reporting delays vary by network and country. OpenAQ states that its API aggregates publicly available data it has discovered or received, and that its data does not represent all air-quality monitoring data worldwide.

OpenAQ documentation · OpenAQ API reference

2. Modelled and forecast information

Atmospheric models combine observations and physical/chemical modelling to estimate pollution across areas where direct measurements may be unavailable. Copernicus CAMS provides analyses and forecasts of atmospheric pollutants worldwide and regional air-quality information for Europe. Modelled values should therefore be labelled as modelled or forecast rather than presented as a direct station measurement.

Copernicus CAMS air quality · CAMS evaluation and quality control

3. AQI is an index, not a concentration

An AQI converts pollutant concentration information into an index designed for communication. The calculation depends on the jurisdiction and pollutant-specific averaging period and breakpoints. An AQI number from one methodology should not automatically be treated as equivalent to the same number from another methodology.

U.S. AQI: EPA/AirNow describes six health-concern categories from Good through Hazardous and explains the pollutant-specific reporting periods. Read EPA/AirNow AQI Basics
European Air Quality Index: EEA uses a separate index based on up to five pollutants and distinguishes station and modelled layers. Read the European Air Quality Index

4. Health guidance

Health information on this site should be treated as general public information, not individual medical advice. WHO identifies particulate matter, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide among major pollutants of public-health concern and publishes global air-quality guidelines.

WHO Global Air Quality Guidelines · WHO ambient air pollution fact sheet

5. Source and timestamp principles

  • Identify the named data provider where available.
  • Show the observation or forecast timestamp and timezone where available.
  • State units and averaging period where relevant.
  • Do not present modelled data as a monitoring-station measurement.
  • Do not manufacture missing observations or silently substitute one source for another.
  • Where an index is calculated, identify the AQI methodology.

Important limitations

Air-quality datasets can be incomplete, delayed, revised or unavailable in particular locations. Coverage differs by country and network. OpenAQ explicitly notes that its data does not represent all monitoring data globally and that users remain responsible for applicable third-party terms. Always consult the originating authority for official regulatory, compliance, emergency-response or legal decisions.