Several groups have increased susceptibility to air pollution

A number of groups within the population have potentially increased vulnerability to the effects of exposure to particulate air pollutants. These groups comprise those who are innately more susceptible to the effects of air pollutants than others, those who become more susceptible (for example as a result of environmental or social factors or personal behaviour) and those who are simply exposed to unusually large amounts of air pollutants. Members of the last group are vulnerable by virtue of exposure rather than as a result of personal susceptibility. Groups with innate susceptibility include those with a genetic predisposition that renders them unusually sensitive.

Young children are especialy sensitive

A WHO Working Group has concluded that very young children and unborn babies are most likely also particularly sensitive to some pollutants (see: Effects of air pollution on children's health and development).

The evidence is sufficient to infer a causal relationship between particulate air pollution and respiratory deaths in the post-neonatal period. Evidence is also sufficient to infer a causal relationship between exposure to ambient air pollutants and adverse effects on lung function development. Both reversible deficits of lung function as well as chronically reduced lung growth rates and lower lung function levels are associated with exposure to particulates.

People with lung and heart disease have enhanced susceptibility to particulate matter

The available evidence is also sufficient to assume a causal relationship between exposure to PM and aggravation of asthma, as well as a causal link between increased prevalence and incidence of cough and bronchitis due to particulate exposure. Groups that develop increased sensitivity include the elderly, those with cardiorespiratory disease or diabetes (Zanobetti & Schwartz, 2001), and those who are exposed to other toxic materials that add to or interact with air pollutants.

When compared with healthy people, those with respiratory disorders (such as asthma or chronic bronchitis) may react more strongly to a given exposure, either as a result of increased responsiveness to a specific dose or as a result of a larger internal dose of some pollutants. In short-term studies, elderly people (Schwartz, 1994) and those with pre-existing heart and lung disease (Dockery et al., 2001; Goldberg et al., 2001) were found to be more susceptible to effects of ambient PM on mortality and morbidity.

In panel studies, asthmatics have also been shown to respond to ambient PM with more symptoms, larger lung function changes and increased medication use compared with non-asthmatics (Pope et al., 2002; Boezen et al., 1999). In long-term studies, it has been suggested that socially disadvantaged and poorly educated populations respond more strongly in terms of mortality (Hoek et al., 2002; Pope et al., 2002; Krewski et al., 2000).

Increased particle deposition and retention has been demonstrated in the airways of people or patients suffering from obstructive lung disease (Brown et al., 2002).

Lastly, those exposed to unusually large amounts of air pollutants, including PM, perhaps as a result of living near a main road or spending long hours outdoors, may experience increased vulnerability as a result of their past exposure.