Traffic, Outdoor Air Pollution, and Asthma

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The epidemiology of asthma and outdoor air pollution has shown that respiratory health effects can vary in relation to different emission sources, types of pollutants, underlying nutritional status, medication use, and genetic polymorphisms. Using sophisticated exposure assessment methods in conjunction with clinical tests and biomarkers that provide mechanistic information, the study of outdoor epidemiology and asthma has evolved into a complex multidisciplinary field. This article presents an overview of the mechanisms by which outdoor air pollution and traffic-related emissions lead to changes in respiratory health and lung function in subjects with asthma.

Section snippets

The outdoor air pollution mix

Polluted outdoor air contains a complex mixture of particle and gas-phase pollutants. Most epidemiologic studies on asthma and air pollution have focused on understanding the health effects of criteria air pollutants, which are routinely monitored by the Environmental Protection Agency and include ozone, nitrogen dioxide, sulfur dioxide, lead, carbon monoxide, and particulate matter (PM) [2], [3]. PM is further subdivided into coarse particulate matter or PM10 (PM with an aerodynamic diameter

Airway inflammation

Outdoor air pollutants are known to exacerbate asthma by causing inflammation in the airways [8], [9]. Even short-term exposures to vehicular traffic emissions (PM2.5, PM1.0, elemental carbon, and nitrogen dioxide) in subjects with asthma are associated with evidence of neutrophilic inflammation and reduced airway pH [7]. Evidence that outdoor air pollution leads to airway inflammation in asthma is also supported by studies using exhaled nitric oxide as a biomarker. In a panel of 19 children

Acute changes in lung volumes

Subjects with asthma are far more susceptible than healthy subjects to the effects of outdoor air pollution. Most studies have found that increased concentrations of outdoor air pollution can be associated with acute reductions in forced vital capacity (FVC) and forced exhaled lung volume in one second (FEV1) among persons with asthma. The magnitude and lag between exposure and change in lung function varies considerably according to the exposure assessment (type of pollutants being measured)

Asthma and traffic-related emissions

Evidence that there is considerable spatial variability in the concentration of traffic-related pollutants has sparked interest in assessing the health effects associated with vehicular emissions. Several studies have found that exposure to traffic-related emissions are associated with higher rates of adverse respiratory health outcomes in comparison with background air pollution exposure [47], [48], [49], [50], [51]. This phenomenon may be explained by the pollutant mix properties near

Summary

There is growing evidence that exposure to traffic-related emissions is different than that of background air pollutants in terms of the composition of the pollution mix and the health risks. However, given the broad differences in methodology and exposure assessment, it is difficult to reach a consensus on what constitutes an exposure to “traffic- or vehicle-related emission.” This limitation leaves many important questions unanswered and hampers the capacity of research to translate results

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