A review of intraurban variations in particulate air pollution: Implications for epidemiological research

Epidemiological studies typically utilise one or few central monitoring stations as a proxy for personal exposure to particulate matter air pollution. However, recent research indicates that central monitoring sites may not accurately characterize the spatial complexities of the particulate field across an urban area. Consequently, intraurban assessment of exposure to air pollution has become a priority area of study. This paper reviews particulate air pollution exposure studies with a focus on monitored-data studies at the intraurban spatial scale. Portions of the literature provide contradictory conclusions as to the homogeneity of intraurban particulate concentrations, due in part to local conditions such as source composition, meteorology, locations of monitoring sites and topography, but which may also be a result of the methods and definitions used to quantify relative and absolute spatial concentration variations. Comparative analyses of the literature by particle size fraction, method of determining heterogeneity, and sampling characteristics were performed. We find that particular attention should be given to local conditions and methods when using one or few monitoring sites to characterise wider population exposures. The utilisation of absolute and relative measures of homogeneity such as the coefficient of divergence which are based on data from several monitoring sites (e.g., n>4n>4) in combination with an appropriate sample size (e.g., n⩾50n⩾50) may reduce the possibility of misclassification based on incorrect assumptions about heterogeneity. The errors in exposure misclassification based on these assumptions about intraurban concentration variations are especially critical in long-term cohort epidemiological analyses that assess the effects of exposure variations in air pollution upon health.