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Who's at risk and why?

Background papers: Lifestyle and wider determinants :: Air Quality [Update in progress] :: Who's at risk and why?

The impact of air quality upon health is unquestionable, and indeed has been a major driver in national and international attempts to reduce levels of air pollution. Long and short term exposure to poor air quality can have health impacts ranging from premature death due to cardiovascular disease[1] and lung cancer,[2] aggravation of asthma and other allergic illnesses,[3] and reduced quality of life.[4] Recent research has also linked air pollution to low birthweight.[5]

The human, and economic cost is considerable. The Committee on the Medical Effects of Air Pollutants (COMEAP) has calculated that in 2008, the long–term health effects on air pollution was the equivalent of 29,000 deaths at typical ages, and an associated loss of total population life of 340,000 life–years. This burden can also be represented as a loss of life expectancy from birth of approximately six months.[6] In economic terms, the Department for Environment, Farming and Rural Affairs (DEFRA) reports that the annual cost is £15 billion, within the range of £8–17 billion. To put this in perspective, they compare this to the economic costs of obesity and physical activity in urban areas, which is estimated as in excess of £10 billion per annum.[4]

The arguments for improving air quality on both public health and economic grounds are therefore strong, and European agreement on reduction of air pollution is predicated on analysis by the World Health Organisation. The 2008 ambient air quality directive (2008/50/EC) sets legally binding limits for concentrations in outdoor air of major air pollutants. At a national level, DEFRA monitors national air quality objectives,[7] and the Environment Act 1995 and Air Quality (Standards) Regulations 2010 provide a framework for local management of air quality and translate the EU directives into English legislation.

Both indoor and outdoor pollution impact upon people's health. Indoor air pollution may include particulate matter from domestic gas combustion (cooking and heating), volatile organic compounds (VOCs) from cleaning and decoration products, wood and coal fires, and second-hand smoke.[8] It is more difficult to monitor and legislate, but significant health gains have been achieved through, for example, smokefree legislation in England since 2007.

Outdoor pollution includes nitrogen oxides (NOX), particulate matter (PM10, PM2.5), sulphur dioxide (SO2) and ozone (O3). Nitrogen oxides (nitric oxide (NO) and nitrogen dioxide (NO2)) are produced by combustion of fossil fuels i.e. heating, power generation and the internal combustion in motor vehicles. The most harmful nitrogen oxide for human health is NO2, and short-term impacts include shortness of breath, and irritation of the eyes and respiratory system.

Particulate matter consists of those compounds which are emitted directly into the atmosphere and those which are formed within the atmosphere as a result of chemical reactions. Of greatest concern to public health are particles measuring less than 2.5 micrometres in diameter (PM2.5), small enough to be inhaled into the deepest parts of the lung. Studies link this fine particulate matter with asthma, bronchitis, acute and chronic respiratory symptoms such as shortness of breath and painful breathing, and premature deaths. The young and elderly are most at risk, the former because their lungs and respiratory systems are still developing, and the latter because of comorbidities and declining immune systems.[9] As a consequence, PM2.5 and its impact upon mortality is a new indicator in the Public Health Outcomes Framework (3.01).[10] Air Quality Objectives for local authorities are also in place for the protection of human health for PM2.5 and PM10 (particles of less than 10 micrometres in diameter).

Sulphur dioxide is an acidic gas which combines with water vapour to produce acid rain. It is associated with asthma and chronic bronchitis.

Ozone is a secondary pollutant and is formed by reactions between NO2, hydrocarbons and sunlight. Ozone can have an impact upon health in terms of respiratory irritation and airway inflammation, and can cause summer smog. However, formation of ozone can take place over several hours or days and may have arisen from emissions many hundreds of miles away. For this reason ozone is not considered to be a 'local' pollutant. The overall health effects of air pollution by severity and incidence are helpfully summarised by the American Thoracic Society[11]:

Figure 1: Health effects of air pollution
Figure 1: Health effects of air pollution

Susceptibility to the adverse health effects of air pollution varies for different population groups. The young, older people, pregnant women, and those with pre–existing respiratory conditions and chronic illnesses such as asthma and chronic obstructive pulmonary disease are most at risk.

The risks to pregnant women and their unborn child(ren) of prolonged exposure to air pollutants include low birthweight, intrauterine growth retardation, and an increased risk of chronic diseases in later life.[12]

While two independent reviews by COMEAP[13] and the Health Effects Institute (HEI) of the evidence around onset of asthma and air pollution both concluded that there was insufficient evidence of a causative link, the latter reported a link with exacerbation of symptoms amongst asthmatic individuals, in particular children.[14]

Currently, there is insufficient evidence available to attribute outdoor air pollution as the causative factor for COPD due to the lack of long–term studies, but there is an association between air pollution and acute exacerbation of existing COPD. This includes increasing symptoms to A&E visits, hospital admissions and even mortality.[15]

Research conducted on behalf of the Environment Agency suggests a close link between air quality and deprivation. It concluded that in the 10 per cent of most deprived wards, the air quality was poorest (interestingly, the least deprived 10 per cent also experience above average concentrations of pollutants, although not as acutely as the most deprived).[16] Sir Michael Marmot's report on health inequalities, Fair Society, Healthy Lives reports that “Poorer communities tend to experience higher concentrations of pollution and have a higher prevalence of cardio-respiratory and other diseases … 66 per cent of carcinogenic chemicals emitted into the air are released in the 10 per cent most deprived wards."[17]


[1]   Shah et al. Global association of air pollution and heart failure: a systematic review and meta-analysis The Lancet 2013; 382 (9897): 1039 - 1048.
[2]   Raaschou-Nielsen et al. Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE) Lancet Oncology 2013; 14(9): 813-822.
[3]   Krzyzanowski K.-D. Health effects of transport-related air pollution 2005; World Health Organization.
[4]   Department for Environment, Food and Agricultural Affairs. Air Pollution: Action in a Changing Climate 2010; Department for Environment, Food and Agricultural Affairs.
[5]   Pedersen et al. Ambient air pollution and low birthweight: a European cohort study (ESCAPE) Lancet Respiratory Medicine 2013; 1(9): 695-704.
[6]   Committee on the Medical Effects of Air Pollutants. The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the United Kingdom 2010; Committee on the Medical Effects of Air Pollutants.
[7]   Department for Environment, Food and Agricultural Affairs. National air quality objectives 2010; Department for Environment, Food and Agricultural Affairs. .
[8]   British Lung Foundation. Indoor Air Pollution
[9]   Air Quality Expert Group. Fine Particulate Matter (PM2.5) in the United Kingdom 2012; Department for Environment, Food and Agricultural Affairs. .
[10]   Department of Health. Public Health Outcomes Framework 2012;
[11]   World Health Organisation. Air Quality Guidelines: Global Update 2005 2006; World Health Organisation. .
[12]   British Medical Association. Healthy Transport = Healthy Lives 2010; British Medical Association. .
[13]   The Committee on the Medical Effects of Air Pollutants. Does outdoor air pollution cause asthma? 2010;
[14]   Health Effects Institute. Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposure, and Health Effects: A Special Report of the HEI Panel on the Health Effects of Traffic-Related Air Pollution 2010; Health Effects Institute. .
[15]   Ko F, Hui D. Air pollution and chronic obstructive pulmonary disease Respirology 2012; 17: 395-401.
[16]   Walker G, Fairburn J, Smith G, et al. Environmental Quality and Social Deprivation: Phase II: National Analysis of Flood Hazard, IPC Industries and Air Quality 2003; Environment Agency. .
[17]   Marmot M. Fair Society, Healthy lives 2010; Strategic Review of Health Inequalities in England post-2010. .