A forecast of air pollution for the following 24 hours is prepared each afternoon, for inclusion in the 16:00 air pollution bulletin. A revised forecast is also issued at 11:00 if VERY HIGH air pollution is being measured or is expected. It is also possible to issue new or revised forecasts at any hour of the day.
The air pollution forecasts are based on information from a number of sources. The forecast is prepared with reference to all available information and on the basis of a number of years of 'hands on' experience of UK air pollution monitoring (Stedman and Willis, 1994). Sources of information include:
On-line measured concentrations from the UK monitoring networks, for all pollutants. Data are averaged for comparison with the relevant bandings (ie 15-minute, hourly, 8-hourly or 24-hourly averages).
Weather forecasts for the following day, provided by the UK Meteorological Office (MO).
'Real time' results from the trajectory ozone forecasting model (Stedman and Williams, 1992). The model is run each day during the summer by the MO, taking the output of numerical weather prediction models as its input, with the results automatically transferred to NETCEN via a computer link. This model provides estimates of ozone concentration for one day ahead for 20 sites and for two days ahead for five sites.
Ozone data from selected monitoring sites in North West Europe is available each day via email. Moves towards the co-ordination of ozone data exchange in North West Europe are discussed in Section 6.5.
Results from the urban pollutants forecasting box model, also provided by MO. The NO
x emissions estimates used in this model are provided by the National Atmospheric Emissions Inventory. This model provides estimates of NOx and NO2 concentration and meteorological parameters for 10 sites for one day ahead for the whole year and meteorological parameters for 10 sites for two days ahead during the winter.
Carbon monoxide concentrations are forecast using the box model by assuming that the dispersion and emission conditions that are likely to lead to elevated CO are similar to those likely to lead to high concentrations of NO
x and NO2.
2 concentrations can result from poor dispersion of low level emission sources and forecasts of such episodes are based on the box model results and a knowledge of local low level emissions (which are significant in cities such as Belfast). SO2 episodes due to the impact of plumes from individual major point sources are predicted by reference to meteorological forecasts, and further research is under way to improve the reliability of these forecast (see Section 6.2).
Results from a trajectory model adapted to forecast particulate sulphate are used in the forecasting of secondary PM
10. Primary PM10 is forecast using the results from the urban pollutants forecasting box model. Both of these are discussed in more detail in Section 5.