High levels of air pollution can affect human health, cause damage to crops and materials and degrade sensitive ecosystems. The Government, the European Community and the World Health Organisation set standards and guidelines for levels of air pollution. These are concentrations that are considered to be acceptable in the light of what is known about the effects of each pollutant on health and on the environment. The standards can be used to review air pollution and also to provide a benchmark to see if air pollution is getting better or worse.

The Environment Act of 1995 made wide-ranging provision for the management and improvement of air quality in Great Britain. The National Air Quality Strategy was adopted by the Government in July 1997, and now forms the framework of the Government's policy on air quality. The Strategy sets health based standards for eight priority pollutants and objectives to be reached by the year 2005. These are summarised in the table below. The Government has just completed a review of the strategy, to determine whether the any of objectives can be tightened. A summary of the standards, objectives and the recommendations of the review is shown in Fig 5.

The health based standards adopt the recommendations of the Expert Panel on Air Quality Standards - a group of independent medical and scientific experts who advise the Government on air quality standards. Where advice from the Panel was not available, advice from the World Health Organisation was used.

Click here to see a summary of the standards, objectives and the recommendations of the National Air Quality Strategy Review (Figure 5).

The Act also laid the foundations for a system of local air quality management, in which local authorities are obliged to review and assess the quality of the air in their area, and to take action if there is a risk that these standards may be breached.


Figure 6 shows where the standards were breached during 1997, for sites measuring for at least 75% of the year. In order to make useful comparisons between pollutants, for which the standards may be expressed in terms of different averaging times, the table gives the number of days when a breach has been recorded rather than the actual number of periods of time above the standard.

Click here for Figure 6

For carbon monoxide and nitrogen dioxide, no site had more than five days on which the standard was exceeded. Carbon monoxide exceedences were recorded on one day by 2 sites that measure concentrations next to roads. Slightly more exceedences (periods above the standard) were recorded for nitrogen dioxide, but again these were mostly recorded by sites measuring near roads, and in London, where traffic levels are generally high. A major source of both of these pollutants is emissions from road transport, hence the exceedences are measured close to their major sources.

For particles (PM₁₀), ozone and sulphur dioxide, a greater proportion of sites exceeded the standard. For ozone, the majority of the exceedences were observed in rural locations, whereas particles and sulphur dioxide standards were exceeded more often in cities. The two Belfast sites recorded the highest number of days in breach of the sulphur dioxide standard. This is likely to be due to the relatively high number of homes using solid fuel for domestic heating. The highest number of exceedences of the particles standards occurred in Leeds, Camden Roadside and Port Talbot, and of the urban locations, lowest in Edinburgh.

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