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1. The Committee's terms of reference are to advise on the effects on health of both outdoor and indoor air pollutants. The Committee has been asked by HSE/DTI for advice* on how to assess the effects on health of concentrations of nitrogen dioxide and carbon monoxide indoors, given there are no indoor air quality standards.
* Advice for the public on nitrogen dioxide and carbon monoxide indoors can be found at www.le.ac.uk/ieh/pdf/IAQ.pdf and www.hse.gov.uk/pubns/indg238.pdf respectively.

2. Members recommended comparing the concentrations of nitrogen dioxide and carbon monoxide indoors with standards set for outdoor air by the Expert Panel on Air Quality Standards (EPAQS) and with guidelines provided by the World Health Organisation (WHO). The relevant standards and guidelines are: EPAQS (CO: 10 ppm, 8-hour average; NO2: 150 ppb 1-hour average) [1,2] and WHO's Air Quality Guidelines for Europe (CO: 10 ppm, 8-hour average; NO2: 100 ppb, 1-hour average). [3] These standards and guidelines are based on studies of volunteers exposed to the relevant gas and have been developed to allow confidence that, if they are not exceeded, adverse effects on health are unlikely in the outdoor setting. Members agreed that exceedances of the EPAQS Standards and WHO Guidelines indoors were undesirable. It is known that exceedances of these standards and guidelines can occur indoors [4,5].

3. At concentrations of nitrogen dioxide above the standard, individuals suffering from asthma might experience a worsening of their condition, though chamber studies of volunteers have not produced entirely consistent results [6].

The possible health effects of nitrogen dioxide have been described previously by the Committee in relation to outdoor air. This information is attached. Members did not consider that epidemiological studies of the effects of day to day changes in nitrogen dioxide outdoors were helpful in considering indoor exposure. This was because the effects in these studies could be due to nitrogen dioxide acting as a marker for other components of traffic pollution rather than due to nitrogen dioxide itself.

4. The effects of carbon monoxide indoors (including coma and death in some cases) are well known and have been described elsewhere [1,3,5].

5. The Committee was informed that HSE/DTI were undertaking an investigation of emissions from gas appliances. It is the Committee's view that, pending the development of indoor air quality guidance, the EPAQS standards for nitrogen dioxide and carbon monoxide can be used to assess the likelihood, but not the magnitude, of effects on health as a result of emissions from gas appliances. Whilst this should assist in the interpretation of test results, it was accepted that detailed study would be needed to assess fully the possible risks to health posed by gas appliances, and to put these risks into context.

COMEAP
October 2004

References

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

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

3. World Health Organisation. Air Quality Guidelines for Europe. Second Edition. WHO Regional Publications, European Series, No 91. Copenhagen: WHO Regional Office for Europe, 2000.

4. MRC Institute for Environment and Health (1996) Assessment on Indoor Air Quality in the Home: Nitrogen Dioxide, Formaldehyde, Volatile Organic Compounds, House Dust Mites, Fungi and Bacteria (Assessment A2), Leicester.
www.le.ac.uk/ieh/pdf/ExsumA2.pdf

5. MRC Institute for Environment and Health (1998) Assessment on Indoor Air Quality in the Home (2): Carbon Monoxide (Assessment A5), Leicester.
www.le.ac.uk/ieh/pdf/ExsumA5.pdf

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

Extract from COMEAP Statement on Banding of Air Quality

Nitrogen dioxide

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.

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