Characterization of Source-Specific Air Pollution Exposure for a Large Population-Based Swiss Cohort (SAPALDIA)

Abstract

Background

Although the dispersion model approach has been used in some epidemiologic studies to examine health effects of traffic-specific air pollution, no study has evaluated the model predictions vigorously.

Methods

We evaluated total and traffic-specific particulate matter < 10 and < 2.5 μm in aero-dynamic diameter (PM ₁₀, PM _2.5), nitrogren dioxide, and nitrogen oxide concentrations predicted by Gaussian dispersion models against fixed-site measurements at different locations, including traffic-impacted, urban-background, and alpine settings between and across cities. The model predictions were then used to estimate individual subjects’ historical and cumulative exposures with a temporal trend model.

Results

Modeled PM ₁₀ and NO ₂ predicted at least 55% and 72% of the variability of the measured PM ₁₀ and NO ₂, respectively. Traffic-specific pollution estimates correlated with the NO _x measurements ( R ² ≥0.77) for background sites but not for traffic sites. Regional background PM ₁₀ accounted for most PM ₁₀ mass in all cities. Whereas traffic PM ₁₀ accounted for < 20% of the total PM ₁₀, it varied significantly within cities. The modeling error for PM ₁₀ was similar within and between cities. Traffic NO _x accounted for the majority of NO _x mass in urban areas, whereas background NO _x accounted for the majority of NO _x in rural areas. The within-city NO ₂ modeling error was larger than that between cities.

Conclusions

The dispersion model predicted well the total PM ₁₀, NO _x, and NO ₂ and traffic-specific pollution at background sites. However, the model underpredicted traffic NO _x and NO ₂ at traffic sites and needs refinement to reflect local conditions. The dispersion model predictions for PM ₁₀ are suitable for examining individual exposures and health effects within and between cities.