How are the forecasts produced?
Defra’s air quality forecasts are produced by the Met Office. Forecasts are produced early in the morning for the current day as well as for the next 4 days.
The Met Office weather forecast and climate prediction model has been developed to include air quality forecasting in a new model configuration called AQUM.
Air quality is determined by the following factors:
- Emissions of pollutants
- Transport and dispersion of pollutants by winds
- Chemical reactions amongst reactive gases and aerosols
- Removal processes, such as rain and deposition on surfaces.
The Met Office model uses UK and European maps of annual average pollutant emissions to simulate the release of chemical species into the atmosphere. These are then allowed to chemically react according to prescribed reaction rates which depend on factors including the concentration of the species, the temperature and the amount of sunlight. Species are then transported and dispersed within the model according to the winds and the concentrations are re-evaluated. Using the concentrations calculated in this way throughout the forecast period, the Daily Air Quality Index is calculated as an average over prescribed time periods (see DAQI for more information).
The forecast is improved by incorporating recent observations of air quality from across the UK from the Automatic Urban and Rural Network (AURN).