Nitrogen dioxide levels estimated from land use regression models several years apart and association with mortality in a large cohort study

BACKGROUND Land Use Regression models (LUR) are useful to estimate the spatial variability of air pollution in urban areas. Few studies have evaluated the stability of spatial contrasts in outdoor nitrogen dioxide (NO₂) concentration over several years. We aimed to compare measured and estimated NO₂ levels 12 years apart, the stability of the exposure estimates for members of a large cohort study, and the association of the exposure estimates with natural mortality within the cohort. METHODS We measured NO₂ at 67 locations in Rome in 1995/96 and 78 sites in 2007, over three one-week-long periods. To develop LUR models, several land-use and traffic variables were used. NO₂ concentration at each residential address was estimated for a cohort of 684,000 adults. We used Cox regression to analyze the association between the two estimated exposures and mortality. RESULTS The mean NO₂ measured concentrations were 45.4 μg/m³ (SD 6.9) in 1995/96 and 44.6 μg/m³ (SD 11.0) in 2007, respectively. The correlation of the two measurements was 0.79. The LUR models resulted in adjusted R2 of 0.737 and 0.704, respectively. The correlation of the predicted exposure values for cohort members was 0.96. The association of each 10 μg/m³ increase in NO₂ with mortality was 6 % for 1995/96 and 4 % for 2007 LUR models. The increased risk per an inter-quartile range change was identical (4 %, 95 % CI:3-6 %) for both estimates of NO₂. CONCLUSIONS Measured and predicted NO₂ values from LUR models, from samples collected 12 years apart, had good agreement, and the exposure estimates were similarly associated with mortality in a large cohort study.