The Great Smog of London blanketed the capital for five days in 1952 and led to the Clean Air Act of 1956. However, problems with the quality of the air that we breathe and the impact it can have on our health have not gone away

Air pollution remains one of the biggest threats to public health in the UK, behind only cancer, obesity and heart disease.

Epidemiological studies have shown that long-term exposure to air pollution reduces life expectancy, mainly due to cardiovascular and respiratory diseases and lung cancer.¹ Short-term exposure (over hours or days) can affect lung function, exacerbate asthma, and push up respiratory and cardiovascular hospital admissions.

In January the Government published its Clean Air Strategy 2019,² which sets ambitious, long-term targets to reduce people’s exposure to particulate matter, which the World Health Organization has identified as the most damaging pollutant.

A model developed by the UK Health Forum and Imperial College London, in collaboration with Public Health England (PHE), estimates that a 1mcg/m³ reduction in fine particulate air pollution in England could prevent around 50,900 cases of coronary heart disease, 16,500 strokes, 9,300 cases of asthma and 4,200 lung cancers over an 18-year period.³

Key air pollutants

Particulate matter (PM) is a generic term used to describe a mixture of solid and liquid particles of varying size and composition. The composition of PM varies greatly and depends on many factors, such as geographical location, emission sources and weather.

The main sources of manmade PM are the combustion of fuels and other physical processes such as tyre and brake wear. Natural sources include wind-blown soil and dust, sea spray particles and burning vegetation.

The size of particles and the duration of exposure are key determinants of potential adverse health effects. Particles larger than 10mcg are mainly deposited in the nose or throat, whereas particles smaller than 10mcg pose the greatest risk because they can be drawn deeper into the lung.

The strongest evidence for effects on health is associated with fine particles (PM_2.5 – particles that are less than 2.5mcg in diameter).

After PM, gases such as nitrogen dioxide (NO2) and nitric oxide (NO), produced by combustion processes, are the major pollutants. The Department for Environment, Food and Rural Affairs (DEFRA) estimates that 80 per cent of NOx emissions in areas where the UK is exceeding NO₂ limits are due to transport, especially emissions from diesel cars and vans.⁴

Short-term exposure to NO₂, particularly at high concentrations, is a respiratory irritant that can cause inflammation of the airways leading to cough, production of mucus and shortness of breath. Studies have shown associations of NO₂ in outdoor air with reduced lung development, respiratory infections in early childhood and effects on lung function in adulthood.

Public Health England estimates that between 2017 and 2025 the total cost of air pollutants for the NHS and social care system in England, for which there is robust evidence, will be £1.69bn (£1.54bn for PM_2.5 and £60.81m for NO2).³

How air pollution harms health

The three main conditions associated with air pollution are respiratory conditions such as asthma, cardiovascular disease (CVD) and lung cancer. Emerging evidence suggests that air pollution may also affect the brain and is possibly linked to dementia and cognitive decline. There is also emerging evidence associating air pollution with early life effects such as low birth weight.

The Royal College of Physicians’ report, Every Breath We Take: the Lifelong Impact of Air Pollution⁶, presents the findings of a number of international studies regarding each of these health effects.

Pregnancy and early childhood are critical times for the formation and maturation of body systems. As well as potential effects on foetal growth, air pollution exposure is associated with low birth weight and premature birth^7,8 while, in the longer term, exposure to air pollution in early life can have a longlasting effect on lung function.

Throughout childhood, there is a natural development of lung function. Maximising this is important, as low lung function leads to less reserve if lung disease develops. There is evidence that the process of normal lung function growth in children is suppressed by longterm exposure to air pollution.

Lung function in adulthood slowly declines with age, and there is emerging evidence that air pollution and living near a busy road accelerate this decline, for both adults and older people.⁶

Asthma symptoms can be exacerbated by various stressors, including respiratory viral infection, allergen exposure and episodes of elevated air pollution. There is also increasing evidence of air pollution having a potential role in causing asthma, especially in people who live near busy roads, as well as being a trigger that can make an asthmatic’s symptoms worse.

There is strong evidence for the effects of both short- and long-term exposures to air pollution on CVD in adults. Air pollution can both contribute to the development of CVD and exacerbate heart conditions that already exist, with the strongest associations having been observed for PM.

The risk of heart failure, myocardial infarction, arrhythmias and stroke is increased by both shortand long-term exposure to air pollution in susceptible individuals. This includes older people and individuals with pre-existing cardiovascular and respiratory conditions. The strongest associations have been observed for fine PM, which is associated with both cardiovascular morbidity and a reduction in life expectancy as a result of increased death from CVD.⁹

Despite the robust evidence for adults, it remains unclear whether exposure to air pollution during childhood influences CVD development in later life.⁶

There is strong evidence that outdoor air pollution is linked to lung cancer and the International Agency for Research on Cancer has classified PM from outdoor air pollution as carcinogenic to humans.¹⁰

To avoid exposure to high levels of air pollution, it is important to be aware of air quality. People can do this by keeping an eye on online updates from relevant organisations, such as DEFRA’s pollution forecast and air quality updates on social media.^11,12 DEFRA’s Daily Air Quality Index (DAQI)¹³ provides recommended actions and health advice for both the general population and at-risk individuals.

References

1. Associations of long-term average concentrations of nitrogen dioxide with mortality. COMEAP report. PHE publication gateway reference: 2018238
   
2. Clean Air Strategy 2019. Policy paper 
   
3. Estimation of the costs to the NHS and social care due to the health impacts of air pollution. PHE Publications gateway number: 2017858
   
4. Improving air quality in the UK: tackling nitrogen dioxide in our towns and cities.DEFRA May 2017 
   
5. Quantification of mortality and hospital admissions associated with ground-level ozone. COMEAP report. ISBN 978-0-85951-776-8
   
6. Every breath we take: the lifelong impact of air pollution. Royal College of Physicians 
7. Shah PS, Balkhair T. Air pollution and birth outcomes: a systematic review. Environment International 2011; 37 (2): 498-516
8. Ha S, Hu H, Roussos-Ross D et al. The effects of air pollution on adverse birth outcomes. Environmental Research 2014; 134: 198-204
   
9. COMPEAP: cardiovascular disease and air pollution. PHE. Ref: 271067 1P 0.1k Feb 2006 (CWP)
   
10. Loomis D, Grosse Y, Lauby-Secretan B et al. The carcinogenicity of outdoor air pollution. The Lancet 2013; 14 (13): 1262-1263
    
11. DEFRA pollution forecast
    
12. DEFRA Air quality on Twitter. @DefraUKAir
    
13. Daily Air Quality Index. DEFRA.