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COMEAP statement on banding of air quality

1. The system of Air Quality Banding used by the Department of the Environment since 1990 has been revised to take into account the new Air Quality Standards, recommended by the DOE Expert Panel on Air Quality Standards (EPAQS) outlined in the Air Quality Strategy for the UK. The revised system, like the old, is intended to provide guidance as to the effects of air pollutants on health and is linked with health advice provided via the Air Quality Helpline. Revision of the banding system has been based on advice from the Department of Health and its Committee on the Medical Effects of Air Pollutants (COMEAP).

2. A system of bands to describe air pollution in terms of concentrations of particulate matter and carbon monoxide has been added. The system is thus more comprehensive than formerly and should provide better insight into the possible effects of exposure to air pollution. The bands for each pollutant, and how they were determined, are discussed briefly below.

Ozone

3. The Air Quality Standard (AQS) for ozone is expressed as an eight hour average concentration: 50 parts per billion (ppb). This standard includes a margin of safety below the lowest level at which significant effects on health have been described and thus when concentrations of ozone are less than 50ppb (8 hour average) air pollution will be described as "low". The European Union has accepted a Directive on ozone which specifies two higher concentrations: 90 and 180 ppb, 1 hour average concentrations, at which information must be provided to the public. Thus these concentrations have been incorporated into UK legislation and the following bands are defined:

50 ppb (running 8 hour average) - 89 ppb (1 hour average): "moderate" levels of air pollution

90 - 179 ppb (1 hour average): "high" levels of air pollution

greater than 180 ppb (1 hour average): "very high" levels of air pollution.

4. At concentrations of ozone of less than 90 ppb it is very unlikely that anyone will notice any adverse effects though effects are detectable at a population level. As concentrations rise towards 180 ppb some individuals, particularly those exercising out of doors, may experience eye irritation, coughing and discomfort on breathing deeply. At more than 180 ppb these effects may become more severe. Individuals suffering from asthma and other respiratory disorders associated with a reduction in respiratory reserve, may experience earlier and more marked effects.

Sulphur dioxide

5. Sulphur dioxide is a respiratory irritant and causes tightening of the airways when inhaled at high concentrations. Those suffering from asthma are significantly more sensitive to sulphur dioxide than other people. This special sensitivity was taken carefully into account in devising the standard recommended by EPAQS, 100 ppb (15 minute average), and in devising the following bands:

less than 100 ppb (15 minute average): "low" levels of air pollution. At these concentrations it is most unlikely that anyone, even those suffering from asthma would experience any adverse effects. The figure of 100 ppb thus includes a safety margin.

100 - 200 ppb (15 minute average): "moderate" levels of air pollution. There is little evidence to suggest that those suffering from asthma would be significantly affected by exposure to concentrations of sulphur dioxide of less than 200 ppb. This figure was accepted by EPAQS as the lowest level at which clear though rather small effects had been described.

200 - 400 ppb (15 minute average): "high" levels of air pollution. The World Health Organisation has suggested that exposure to 400 ppb sulphur dioxide may lead to significant narrowing of the airways in those suffering from asthma. For most people the effects expected would not be large though some individuals may be clinically affected. The effects would be reversed by use of the "reliever inhalers" used by those suffering from asthma. Exposure to such concentrations may add to the effects of exposure to other pollutants and allergens and thus asthmatics should be warned that they may need to increase their medication.

greater than 400 ppb (15 minute average): "very high" levels of air pollution. As concentrations rise above 400 ppb then more asthmatic individuals may experience adverse effects and should be encouraged to ensure that they have an adequate supply of their "reliever inhaler". At any concentrations likely to be experienced in the UK it is very unlikely that normal individuals will experience any adverse effects.

Nitrogen dioxide

6. Nitrogen dioxide is a common air pollutant in urban areas and indoors but studies of its effects on either those suffering from asthma or other individuals are more difficult to interpret than those of sulphur dioxide. Evidence of effects at lower levels (200-300 ppb)is inconsistent. Many studies show no effects and, in those which do the effects described are generally very small and likely to be insignificant.These studies were examined closely by EPAQS in recommending a standard of 150 ppb (1 hour average).

less than 150 ppb (1 hour average): "low" levels of air pollution. At these concentrations it is very unlikely that anyone will experience any adverse effects.

150 - 300 ppb (1 hour average): " moderate" levels of air pollution. Studies of volunteers, including those with asthma, exposed to concentrations of up to 300 ppb for one hour do not provide convincing evidence that significant effects on health are likely. Some increase in the response of the lung to substances which produce narrowing of the airways have been recorded on exposure to nitrogen dioxide at these concentrations. Again the studies are inconsistent and the effects are small.

300 - 400 ppb (1 hour average): "high" levels of air pollution. Around 300 ppb a few studies have shown small direct effects on indices of lung function. In addition, there is evidence from epidemiological studies of the effects of mixtures of pollutants characterised by concentrations of nitrogen dioxide in this range that adverse effects on health may occur. Should effects occur then those with pre-existing disease of the heart or lungs would be likely to be most at risk: see below.

more than 400 ppb (1 hour average): "very high" levels of air pollution. At these concentrations epidemiological studies have provided evidence of effects. These included increased admissions to hospital and consultations of General Practitioners. The air pollution episode experienced in London in 1991 was characterised by an increase in concentrations of both nitrogen dioxide and particulate matter and though a possible effect of nitrogen dioxide cannot be excluded, it is not clear which pollutant was responsible for the adverse effects on health. Those suffering from long standing diseases of the heart and lungs should be aware that their condition may worsen as concentrations of nitrogen dioxide move into the "very high" band. Individuals suffering from asthma do not appear to be at such increased risk on exposure to nitrogen dioxide as they are on exposure to sulphur dioxide.

Particulate matter

7. Particulate matter is monitored in the UK as PM₁₀: ie particles generally less than 10 microns in diameter. A large number of epidemiological studies have shown that day to day variations in concentrations of particles are associated with adverse effects on health. These include increased daily deaths, increased admissions to hospital of patients suffering from heart and lung disorders, and a worsening of the condition of those with asthma. This evidence was reviewed in detail by COMEAP in the report "Non-Biological Particles and Health" published by DH in 1995.

8. A remarkable feature of the evidence is that even at low concentrations of particles effects remain. Of course, as concentrations fall so effects decrease. In a specially commissioned study of the effects of air pollution in Birmingham, a city with a population of 1 million, it was shown that on a day when the concentration of particles rose from the annual average concentration of 25 µg/m3 to 50 µg/m3 (24 hour average)then one more admission to hospital for treatment of respiratory diseases might be expected. 50 µg/m3, 24 hour average concentration, was accepted by EPAQS as a lowest effect level and was recommended as the EPAQS air quality standard. EPAQS also advised that efforts should be made to reduce annual average concentrations of particles in the UK.

9. Because of the continuous relationship between concentrations of particles and effects on health a different approach to devising bands of air quality has been advised by COMEAP. The following break points between bands were agreed: 50, 75 and 100 µg/m3. Thus the bands are:

less than 50 µg/m3 (running 24 hour average): "low" levels of air pollution.

50-75 µg/m3 (running 24 hour average) : "moderate" levels of air pollution.

75-100 µg/m3 (running 24 hour average): "high" levels of air pollution

more than µg/m3: "very high" levels of air pollution.

10. It is accepted that these figures are in a sense arbitrary in that they describe increments of effect along a continuum. As concentrations enter the "very high" band those suffering from disease of the heart and lungs may experience a worsening of their symptoms and should if necessary, consult their doctors. Such concentrations occur fairly frequently in the UK but the great majority of people will experience no adverse effects at all. It is fair to say that our knowledge of the effects of particulate matter on health is evolving rapidly and this advice and the bands defined above may require revision in the light of new evidence.

Carbon monoxide

11. Carbon monoxide is perhaps the best understood of the pollutants discussed here. The most significant exposure to carbon monoxide occurs in the general population as a result of cigarette smoking. Carbon monoxide interferes with the transport of oxygen by the blood and at high concentrations produces unconsciousness and death. Some 60 accidental deaths occur in the UK each year as a result of exposure to carbon monoxide indoors.

12. Concentrations of carbon monoxide in the air are related to concentrations of carbon monoxide in the blood in a well understood and predictable way. In describing levels of exposure, it is usual to speak in terms of that percentage of haemoglobin, the essential oxygen-transporting protein of the blood, which is saturated with carbon monoxide. The effects of different percentage saturations have been studied in volunteers and EPAQS reviewed the results of these investigations closely in recommending a standard of 10 ppm (8 hour average concentration). At this concentration the blood would reach a saturation of less than 2% and effects of health would be unlikely even in those suffering from heart disease. However, recent epidemiological studies have reported associations between outdoor concentrations of carbon monoxide and admissions to hospital for treatment of heart disease and this new evidence needs to be kept under review.

13. Studies of the effects of higher saturations have been carried out and these form the basis of the following banding system:

less than 10 ppm (running 8 hour average): "low" levels of air pollution.

10-15 ppm (running 8 hour average): "moderate" levels of air pollution. This level of exposure leads to a saturation of haemoglobin of about 2.5%. At this level there is some evidence to show that those with angina and other heart diseases may experience a more rapid onset of chest pain on exercise.

15-20 ppm (running 8 hour average): "high" levels of air pollution. Exposure to 20 ppm of carbon monoxide leads to a saturation of 4.5%. At these saturations it has been shown that there is a reduction in peak exercise capacity of healthy subjects and a reduction in the time needed for anginal pain to appear on exercise in those with heart disease. Whether such patients are likely to take sufficient exercise to reveal these effects is questionable but they should be aware that such effects may occur.

more than 20 ppm (running 8 hour average): "very high" levels of air pollution. As concentrations of carbon monoxide rise above 20 ppm then so the percentage saturation of haemoglobin will increase. Effects on those with heart disease become more likely. It should be recalled that sufficient outdoor exposure to reach these levels of saturation is unlikely.

Bibliography

General

World Health Organization. Air Quality Guidelines for Europe. WHO Regional Publications, European Series No 21. Copenhagen: World Health Organization, 1987.

World Health Organization. Update and Revision of the Air Quality Guidelines for Europe. Meeting of the Working Group "Classical" Air Pollutants, Bilthoven, The Netherlands 11-14 October 1994. WHO Regional Office for Europe. Copenhagen: World Health Organization, 1995.

Department of the Environment. The Scottish Office. The United Kingdom National Air Quality Strategy. Consultation Draft. London: Department of the Environment, 1996.

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. Fourth Report. Health Effects of Exposure to Mixtures of Air Pollutants. London: HMSO, 1995.

Department of Health. Committee on the Medical Effects of Air Pollutants. Asthma and Outdoor Air Pollution. London: HMSO, 1995.

Ozone

Commission of the European Communities. 92/72/EEC. Air Pollution by Ozone.

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. First Report. Ozone. London: HMSO, 1991.

Department of the Environment. Expert Panel on Air Quality Standards. Ozone. London: HMSO, 1994.

Sulphur dioxide

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. Second Report. Sulphur Dioxide, Acid Aerosols and Particulates. London: HMSO, 1992.

Department of the Environment. Expert Panel on Air Quality Standards. Sulphur Dioxide. London: HMSO, 1995.

Nitrogen dioxide

Department of Health. Advisory Group on the Medical Aspects of Air Pollution Episodes. Third Report. Oxides of Nitrogen. London: HMSO, 1993.

Department of the Environment. Expert Panel on Air Quality Standards. Nitrogen Dioxide. London: HMSO, 1996.

Anderson HR, Limb ES, Bland JM, Ponce de Leon A, Strachan DP, Bower JS. The health effects of an air pollution episode in London, December 1991. London: St George's Hospital Medical School, 1994.

Particles

Department of Health. Committee on the Medical Effects of Air Pollutants. Non- Biological Particles and Health. London: HMSO, 1995.

Department of the Environment. Expert Panel on Air Quality Standards. Particles. London: HMSO, 1995.

Anderson HR, Limb ES, Bland JM, Ponce de Leon A, Strachan DP, Bower JS. The health effects of an air pollution episode in London, December 1991. London: St George's Hospital Medical School, 1994.

Carbon monoxide

Department of Health. Expert Panel on Air Quality Standards. Carbon Monoxide. London: HMSO, 1995.

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