1 IntroductionAEAT-3844
The Department of the Environment, Transport and the Regions (DETR) provides an hourly update on air pollution levels, together with a 24-hour air pollution forecast, which is widely disseminated through the media. An air pollution forecast allows individuals who may be affected by episodes of high air pollutant concentrations to take preventative measures. These can include increasing medication or taking steps to reduce exposure and dose.

Air Pollution Bulletins continue to be made available to the public each day by the DETR's Data Dissemination Unit (DDU), via television teletext, newspapers and a free telephone information service (currently 0800 556677). Teletext pages have been updated hourly since June 1994. Information on current air pollution and forecasts are also made available on the World Wide Web:
This site also includes a comprehensive Air Quality Archive. Air pollution information is always made available for inclusion in television, and radio weather forecasts and is usually broadcast during periods of HIGH air pollution.

Detailed, region by region, forecasts of air pollution for inclusion in these bulletins are provided by AEA Technology, National Environmental Technology Centre (NETCEN). The forecast consists of an air pollution band for each pollutant for the following 24 hours, for each geographical region. During the period covered in this report there were 9 geographical regions (see Figure 1.1) but in February 1998 the new region of East Anglia was introduced (see Figure 1.2).

From January 1st to November 18th 1997 air quality was classified according to four banding levels set out by the DETR, with the forecasters aiming to predict POOR and VERY POOR levels of O
3, NO2 and SO2. On 19 November 1997 a new set of bandings were brought in by DETR, including levels for CO and particles (PM10) as well as re-defined bandings for O3, NO2 and SO2. Under the new bandings forecasters are aiming to predict HIGH and VERY HIGH levels of air pollution. At the same time the term 'air pollution' has been substituted for the term 'air quality'.

In addition to the public dissemination of the daily air quality forecast, NETCEN also provides DETR with an 'early warning' forecasting service of major air pollution episodes.

Our first report (Stedman and Willis, 1994) described the techniques that are used to forecast air quality in the UK and presented an analysis of the forecasting success rate for the year from April 1992 to March 1993. Subsequent reports (Stedman and Willis, 1995; Stedman and Willis, 1996, Stedman et al, 1997) presented analyses of the forecasting success rate and discussed modifications to the forecasting system. This report, the fifth on air pollution forecasting in the UK, presents an analysis and some discussion of the forecasting success rate for the year period from January to December 1997. We consider the new bandings introduced in November 1997, and the likely changes to episode frequencies. The forecasting success rate is discussed in two sections: one for each set of bandings. The testing and implementation of modelling to aid in the forecasting of PM
10 is discussed in Section 5 and Section 6 covers a number of other forecasting issues, including other models and data exchange.

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