The concept of Air Quality Management was introduced in the late 1990s. A statutory regime was introduced whereby Local Authorities have to assess the quality of the air within their areas on a regular basis. The assessment process has to take into account pollution from traffic, industrial processes, commercial premises and domestic premises. It also has to take into account such factors as the traffic speed, traffic flows, vehicle type and weather particularly wind speed and direction. The legislation specifies which pollutants should be assessed. They are:
- Carbon monoxide (CO),
- Sulphur dioxide (SO2),
- Nitrogen dioxide (NO2),
- 1,3 Butadiene,
- Benzene,
- Particles (PM10),
- Lead (Pb).
The legislation also lays down objectives for each pollutant. Each objective consists of a level of pollutant and a target date for reaching that specified level. The following is an example objective:
'There should be less than 40 µgm/m3 of nitrogen dioxide in air, expressed as an annual mean, before 31st December 2005'.
The last review and assessment concluded that the objective for Nitrogen Dioxide was likely to be exceeded in some parts of Bolton.
This same conclusion was reached in all of the Greater Manchester authorities. Where any objectives are likely not to be met then the local authority must declare an Air Quality Management Area (AQMA) and draw up an air quality action plan. Because of the nature of air pollution, the action plan can include measures which affect areas outside as well as inside the air quality management area. The objective for NO2 is 40 µg/m3 (micrograms per cubic metre) but, as a precaution, the Greater Manchester authorities agreed to draw the boundary of the AQMA according to the 35µg/m3 NO2 contour, so, in effect, the AQMA is slightly larger. See 'Links' for illustrative maps of the Bolton and Greater Manchester AQMAs.