Healthy
Environments

 

Health Evidence Bulletins - Wales (logo)
Team Leaders: Dr Meirion Evans. Mr Alan Bennett

Literature searches completed on 12 February 1998

6: Air Quality - Environmental Exposure to Pollutants

This document is a supplement to, not a substitute for, professional skills and experience. Users are advised to consult the supporting evidence for a consideration of all the implications of a recommendation.

The Statements The Evidence
6.1 Air Quality
6.1a. Air quality remains a key element in the reduction of risks to health from environmental hazardsi. Recent studies suggest that, even at the substantially lower levels of airborne pollution experienced today compared with the 1950s, there are associations with premature mortality, chronic illness and discomfort for sensitive groupsii,iii,iv. Exposure to levels of air pollution that are capable of adversely affecting lung function may also be associated with long term as well as short term health effectsiii,iv. i. Department of the Environment. The United Kingdom National Air Quality Strategy. London: Department of the Environment, 1997
(Type V evidence - expert opinion)
ii. Anderson HR, Ponce de Leon A, Bland JM, Bower JS, Strachan DP. Air Pollution and daily mortality in London: 1987-92. British Medical Journal 1996; 312: 665-669
http://www.bmj.com/cgi/content/full/312/7032/665
(Type IV evidence – observational studies)
iii. Department of Health. Committee on the Medical Effects of Air Pollutants. Quantification of the effect of air pollution on health in the United Kingdom. London: HMSO, 1998
(Type IV and V evidence – review of observational studies, statistical data and expert opinion)
iv. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)

6.1b. The major contaminants of air are:

  • suspended particulate matter (SPM)-mainly from motor vehicles, particularly diesel powered vehicles

  • sulphur dioxide-derived from power generation, industrial processes and heating

  • ozone and other oxidants-formed by the reaction of oxides of nitrogen in the presence of volatile organic compounds and sunlight, of particular concern in industrial settings

  • nitrogen dioxide-generated indoors by smoking, gas-fired appliances and oil stoves, and outdoors by power generation, heating and motor vehicles

  • carbon monoxide-derived mainly from the incomplete combustion of vehicle fueli

i. Department of the Environment. The United Kingdom National Air Quality Strategy. London: Department of the Environment, 1997
(Type V evidence - expert opinion)

Literature searches completed 12.2.98
Top

6.1c. Historically, in industrial societies, the major sources of air pollution have been fossil fuel combustion and the manufacture and use of chemicals. Pollution from household emissions, industry and power generation has increased in the past few years, e.g. nitrogen oxides, though other pollutants such as smoke and sulphur dioxide have decreased. The contribution of vehicle emissions is becoming increasingly important. Recent legislation aimed to stabilise and reduce emissions during the 1990si. i. Department of the Environment. The United Kingdom National Air Quality Strategy. London: Department of the Environment, 1997
(Type V evidence - expert opinion)
6.1d. Indoor air pollutant concentrations including nitrogen dioxide, carbon monoxide, formaldehyde and particulates are often higher than those outdoors, particularly at work i. There are relatively few studies of the potential adverse health effects of indoor exposureii.
Research is needed on:
  • personal exposure to pollutant mixtures during pollution episodes, assessed using personal monitors and statistical modelling of outdoor and indoor measurements
  • measuring ratios of indoor to outdoor pollutants
  • assessing spatial variability of pollutant concentrations in urban areas during pollution episodes and detecting hot-spots
  • establishing the relationship between fixed point pollutant measurements and personal exposure measurements
i. Department of the Environment. The United Kingdom National Air Quality Strategy. London: Department of the Environment, 1997
(Type V evidence - expert opinion)
ii. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)

Literature searches completed 12.2.98
Top

6.2 Air Pollutants
6.2a. Suspended particulate matter (SPM) is a complex mixture of organic substances. Particles less than 10 m in diameter (PM10) and those less than 2.5 m (PM2.5) are thought to be potentially most harmful. Particles are directly emitted from sources such as non-nuclear power stations, motor vehicles, cement factories and open-cast coal mines. They also occur naturally as airborne spores and pollen grains. In urban areas motor vehicles, particularly diesel powered vehicles, are the major source of particulates. An estimated 20-50% of urban PM10 particulates are due to motor vehicles. Domestic coal burning is an important source in some areas i. i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)
6.2b. Sulphur dioxide (SO2) is the principal pollutant associated with acid deposition, usually after oxidation to sulphuric acid. Sulphuric acid is generally present as an acid aerosol, often associated with other pollutants in droplets of solid particles of various sizes. In the UK, SO2 still arises principally as a result of combustion of fossil fuels. Non-nuclear power stations account for 66% of total UK emissions and other industrial combustion 16% (1993 figures). Vehicles are not a significant source of SO2 (2%) although diesel engines produce more than petrol engines. Emissions declined by 50% between 1970 and 1993i. i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)

 

Literature searches completed 12.2.98
Top

 

6.2c. Ground level ozone (O3) is a highly reactive oxidising agent formed indirectly by the action of sunlight on nitrogen dioxide (NO2). Peak pollution episodes occur in summer when there are long hours of bright sunlight, temperatures above 20oC and light winds. Ozone tends to build up downwind of urban connurbations (where most oxides of nitrogen are emitted by road transport). Once formed, ozone can travel long distances and peak levels tend to occur in rural areas i.

i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)
6.2d. Oxides of nitrogen comprise several gases including nitric oxide (NO) and nitrogen dioxide (NO2).  NO2 is probably the most important for health. It is mainly a secondary pollutant formed by spontaneous conversion of NO to NO2 in the presence of oxygen or ozone. In the UK, some 50% of NO2 is produced by motor vehicles and 25% by power stations. Concentrations are highest in urban areas, especially on busy streets. Peak levels occur in cold, still weather during morning and evening rush hours. High NO2 levels are often found in conjunction with high levels of particulates and carbon monoxide i. i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type IV and V evidence – statistics and expert opinion)
6.2e. Carbon monoxide (CO) is produced by the incomplete combustion of fossil fuel. Outdoor CO is mainly produced (90%) by petrol engines while idling or decelerating. The UK distribution of outdoor CO is not accurately known. Levels in urban areas are highly variable and depend on weather conditions and traffic density. 8 hour averages are generally < 10 ppm i. Peak CO levels in garage workshops can reach 500 ppmi.

Research is needed on:

  • assessing variability of carbon monoxide levels and the relationships between indoor and outdoor levels
  • assessing carboxyhaemoglobin levels in different population groups and the correlation with personal exposure to carbon monoxide
i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)

 

Literature searches completed 12.2.98
Top

6.2f. Air pollution episodes are characterised by raised concentrations of more than one pollutant. In the UK, three types of air pollution episodes can be identified according to the season i:
  • Type 1: Summer smog, a pollution mixture for which the main indicator pollutant is ozone
  • Type 2: Vehicle smog, the indicator pollutant being oxides of nitrogen
  • Type 3: Winter smog, the indicator pollutant being sulphur dioxide, with a contribution from oxides of nitrogen.

Elevated concentrations of particles may occur during all three types of air pollution episode.

i. Department of Health. Advisory Group on the Medical Aspects of Air Pollution. Fourth Report. Health effects of exposures to mixtures of air pollutants. London: HMSO, 1995
(Type IV evidence - systematic review of observational studies)
6.2g. Volatile organic compounds (VOCs) pose an air pollution hazard because of their potential for generating ozone. Some VOCs such as benzene, 1,3-butadiene, polycyclic aromatic hydrocarbons (PAH) and dioxins are hazardous in themselves i.
  • Benzene - comes mainly from petrol combustion, but some from cigarette smoke. Ambient UK levels are 1-40 ppb hourly. There is an increased risk of leukaemia from occupational exposure but no evidence of risk below 25-30 ppm i.
  • 1,3-butadiene - comes mainly from vehicle exhausts, but cigarette smoke is a major source indoors. Maximum UK levels are 10 ppb hourly. There is an increased risk of leukaemia and lymphoma from occupational exposure in the rubber production industry (around 1-10 ppm)i.
  • Polycyclic aromatic hydrocarbons (PAHs) come mainly from incomplete combustion of vehicle emissions in urban areas and coal and coke burning elsewhere. Total PAH levels are around 10-150 ng/m3 in the UK. There is an increased risk of lung cancer from occupational exposure in coke-oven and coal gas workers (around 30 m g/m3)i.
i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)

 

Literature searches completed 12.2.98
Top

6.2h. Lead in air occurs mainly as fine organic particles, but around 10% occurs as organic lead arising from petrol combustion. The main sources of lead in air are petrol-engined vehicles and non-ferrous metal smelting processesi. Concentrations in air have decreased significantly in the past decade with the introduction of unleaded fuel. Human exposure to lead is highly dependent on intake from other sources such as food, water and dust. The health impact of lead in air is therefore difficult to establish i,ii.

i. Department of Health. Committee on Medical Effects of Air Pollutants. Handbook on air pollution and health. London: HMSO, 1997
(Type V evidence - expert opinion)
ii. Dubourg WR. Estimating the mortality costs of lead emissions in England and Wales. Energy Policy 1996; 24: 621 – 625
(Type V evidence - expert opinion)
6.3 Ultraviolet radiation
6.3a. Changes in lifestyle such as more leisure opportunities and increased holidays abroad have led to increased exposure to ultraviolet radiation i. i. Melia J, Ellman R, Chamberlain J. Meeting The health of the nation target for skin cancer: problems with tackling prevention and monitoring trends. Journal of Public Health Medicine 1994; 16: 225 – 232
(Type V evidence - expert opinion)

6.3b. Ozone in the stratosphere protects us from the sun’s damaging rays and is vital to life on earth. Depletion of the ozone layer will lead to a large increase in exposure of skin and eyes to ultraviolet B radiationi,ii. Chlorofluorocarbons (CFCs) which catalyze the breakdown of ozone are a major cause of ozone depletion. CFCs are being phased out, but they persist for up to 100 years in the atmosphere i,ii. Even if changes are made now, ozone depletion is likely to continue for many years.

i. Department of the Environment. The United Kingdom National Air Quality Strategy. London: Department of the Environment, 1997
(Type V evidence - expert opinion)
ii. Lloyd SA. Stratospheric ozone depletion. Lancet 1993; 342: 1156 – 1158
(Type V evidence - expert opinion)

Literature searches completed 12.2.98
Top


Contents Home

Health Evidence Bulletins: Wales, Duthie Library, UWCM, Cardiff CF14 4XN. e-mail: weightmanal@cardiff.ac.uk