The nature of air pollution has changed over the past 40 years. Emissions of smoke and sulphur dioxide associated with smogs of the past have declined, while the proportion of pollution from vehicles has increased. The health effects of air pollution are still, however, significant. Evidence from the Government’s Committee on the Medical Effects of Air Pollution (COMEAP) suggests that some 29,000 deaths per year (4,000 in London alone) are brought forward by exposure to man-made particulate air pollution at current levels. Their current work suggests that a similar scale of premature deaths are caused by NO2 pollution, although further work is being carried out to establish to what extent these impacts overlap.
Health effects are the primary, although not the only, reason for work to improve air quality. In order to be able to assess the effect of air pollutants on health, accurate measurement of personal and population exposure to indoor and outdoor air pollution is necessary. Also, the response of individuals to air pollutants varies widely. Other factors such as smoking, pet ownership and diet may influence the incidence of respiratory disease such as asthma.
As is the case in many fields our knowledge of the health effects of air pollution is developing and current information only represents the best that we know at present. Recent developments and questions that are still being studied include:
- the effects of short term exposure to high concentrations of pollution compared with long term exposure to “normal” concentrations;
- there is growing evidence that air pollution can actually cause people to develop asthma rather than merely triggering attacks;
- it is now accepted that nitrogen dioxide (NO2) has actual health effects rather than, as has been often thought, acting as a marker for some other pollutant(s); and,
- the question of which size fraction(s) and which metric(s) for particulate matter are responsible for adverse health effects.
Health Effects of Air Pollutants
The table below shows the effects of several common air pollutants:
|Pollutant||Observed effects on asthma sufferers|
|Nitrogen oxides (NOx) vehicles and industry||Respiratory irritant.|
|Ozone (O3) (formed from nitrogen oxides in sunlight)||Causes inflammation and consequent narrowing of the airways after short exposure and can increase response to irritants. Asthma symptoms can be exacerbated.|
|Particles (PM10 and PM2.5)||Long-term exposure to particles (especially PM2.5) is associated with premature mortality, especially from heart and lung conditions. Recent studies have also suggested that high levels of PM2.5 in childhood can permanently impair lung function. High levels of particles can affect asthma sufferers.|
|Sulphur dioxide (SO2) coal burning||Causes narrowing of the airways of asthma sufferers, through the immune response of the airway to the irritant.|
|Air Pollution Episodes (periods of exceptionally high pollution levels)||Air pollution episodes are thought to trigger asthma attacks and other allergic reactions in many people. It is not thought however that long-term exposure to high levels of air pollution causes asthma itself.|
|Allergens (tree and grass pollen)||Pollens can trigger an allergic response in the airways of susceptible asthmatics, causing inflammation and consequent narrowing. At high concentrations air pollutants can enhance the effect of some pollens. Air pollution may also affect the concentration of pollens|