Principles and methods for mapping air quality

The various air quality mappings provide information on observed or forecast pollution levels at any location within the region of Auvergne. There are three types of mapping:

• Observation mapping
• Forecast mapping
• Vigilance mapping

Observation mappings

Observation mapping, also referred to as monitoring mapping, gives an illustration of pollution levels recorded either the day before or on a previous day. It gives an estimate of concentrations across the region based on measurements taken at regular intervals at a limited number of sites. This estimate, or spatial interpolation as it is otherwise known, can be obtained using various techniques.

IDWA (Inverse Distance Weighted Averaging) interpolation was selected initially for its relatively simple implementation. This method is based on the assumption that the relative weight of a given observation point decreases with its linear distance from the point where an estimate is made.

More sophisticated and efficient geostatistical methods are currently in development and should eventually enable researchers to significantly improve observation mappings.

Example of observation mapping

Forecast mappings
Forecast mappings give an estimate of expected short-term pollution levels (for the same day, the following day, or two days later). They are generally based on numerical modelling systems that calculate changes in the range of concentrations using a pollutant emission estimate and weather forecasts.

Example of forecast mapping

Vigilance mappings
Vigilance mappings represent the risk of exceeding certain regulatory thresholds in various regional zones. They are generated by experts who base their estimate on observed pollution levels, weather forecasts and numerical air quality simulations.

Example of vigilance mapping