Abstract
Traffic-related nitrogen dioxide (NO2) has been traditionally estimated using surfaces generated through land-use regression (LUR). Recently, air pollution dispersion has been used to derive NO2 exposures in urban areas. There is evidence that data collection protocols and modelling assumptions can have a large effect on the resulting NO2 spatial distribution. This study investigates the effects of various NO2 surfaces on the risk estimates of postmenopausal breast cancer (BC) and prostate cancer (PC), both of which have already been associated with traffic-related air pollution. We derived exposures for individuals in two case control studies in Montreal, Canada using four different surfaces for NO2. Two of the surfaces were developed using LUR but employed different data collection protocols (LUR-1 and LUR-2), and the other two surfaces were generated using dispersion modelling; one with a regional model (dispersion-1) and another with a street canyon model (dispersion-2). Also, we estimated separate odds ratios (ORs) using concentrations of NO2 as measures of exposure for both cancers. While the range of NO2 concentrations from dispersion (4–26 ppb) was lower than the range from LUR (4–36 ppb), the four surfaces were found to be moderately correlated, with Spearman correlation coefficients ranging from 0.76 to 0.88. The ORs for BC were estimated to be 1.26, 1.10, 1.07, and 1.05 based on LUR-1, LUR-2, dispersion-1, and dispersion-2. In contrast, the ORs for PC were estimated to be 1.39, 1.30, 1.13, and 1.04 based on LUR-1, LUR-2, dispersion-1, and dispersion-2. The four exposure measures indicated positive associations but we observed higher mean ORs based on the LUR surfaces albeit with overlapping CIs. Since LUR models capture all sources of NO2 and dispersion models only capture traffic emissions, it is possible that this difference is due to the fact that non-road sources also contribute to the spatial distribution in NO2 concentrations.
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