The assessment of personal exposure to air pollution is a critical component of epidemiological studies associating air pollution and health effects. This paper critically reviewed 157 studies over 29 years that utilized one of five categories of exposure methods (proximity, air dispersion, hybrid, human inhalation, and biomarkers). Proximity models were found to be a questionable technique as they assume that closer proximity equates to greater exposure. Inhalation models and biomarker estimates were the most effective in assessing personal exposure, but are often cost prohibitive for large study populations. This review suggests that: (i) factors such as uncertainty, validity, data availability, and transferability related to exposure assessment methods should be considered when selecting a model; and (ii) although an entirely discreet new class of approach is not necessary, significant progress could be made through the development of a 'hybrid' model utilizing the strengths of several existing methods. Future work should systematically evaluate the performance of hybrid models compared to other individual exposure assessment methods utilizing geospatial information technologies (e.g. geographic information systems (GIS) and remote sensing (RS)) to more robustly refine estimates of ambient exposure and quantify the linkages and differences between outdoor, indoor and personal exposure estimates.
1. Introduction
By the mid-20th century, there had been several pronounced air pollution 'events' resulting in substantial adverse effects on human health. The most well-known were the 1930 event in the Meuse Valley of Belgium, 1 the toxic smog in Donora, Pennsyl-vania in October 1948, 2 as well as the 1952 London event known as the 'killer fog' which resulted in over 4000 deaths. 3 As a result of these events and others, the 1950s saw the first studies examining the association between human health and air pollution. 4 It is now well known and widely accepted that air pollution is associated with mortality 5,6 and morbidity, including asthma, 7,8 chronic bronchitis and emphysema, 7,9 myocardial infarction, 10 cardiovascular disease, 11 neurotoxicity, 12 and lung cancer, 13,14 among other ailments and forms of disease. [15][16][17][18][19][20][21][22] The World Health Organization (WHO) 23 estimates that around 1.4 billion urban residents are living in areas with air above WHO air quality guidelines (AQG), and consequently, outdoor air pollution is associated with approximately 200 000 to 570 000 annual deaths representing about 0.4 to 1.1% of the total annual deaths in urban areas worldwide. The health effects related to outdoor air pollution are now recognized as a focus-area for reducing the global burden of disease, though governments have only begun to acknowledge this fact through enacting policy. 24