Relationships between fixed-site ambient measurements of nitrogen dioxide, ozone, and particulate matter and personal exposures in Grand Paris, France: the MobiliSense study.

Background: Past epidemiological studies, using fixed-site outdoor air pollution measurements as a proxy for participants' exposure, might have suffered from exposure misclassification.

Methods: In the MobiliSense study, personal exposures to ozone (O₃), nitrogen dioxide (NO₂), and particles with aerodynamic diameters below 2.5 μm (PM_2.5) were monitored with a personal air quality monitor. All the spatial location points collected with a personal GPS receiver and mobility survey were used to retrieve background hourly concentrations of air pollutants from the nearest Airparif monitoring station. We modeled 851,343 min-level observations from 246 participants.

Results: Visited places including the residence contributed the majority of the minute-level observations, 93.0%, followed by active transport (3.4%), and the rest were from on-road and rail transport, 2.4% and 1.1%, respectively. Comparison of personal exposures and station-measured concentrations for each individual indicated low Spearman correlations for NO₂ (median across participants: 0.23), O₃ (median: 0.21), and PM_2.5 (median: 0.27), with varying levels of correlation by microenvironments (ranging from 0.06 to 0.35 according to the microenvironment). Results from mixed-effect models indicated that personal exposure was very weakly explained by station-measured concentrations (R² < 0.07) for all air pollutants. The R² for only a few models was higher than 0.15, namely for O₃ in the active transport microenvironment (R²: 0.25) and for PM_2.5 in active transport (R²: 0.16) and in the separated rail transport microenvironment (R²: 0.20). Model fit slightly increased with decreasing distance between participants' location and the nearest monitoring station.

Conclusions: Our results demonstrated a relatively low correlation between personal exposure and station-measured air pollutants, confirming that station-measured concentrations as proxies of personal exposures can lead to exposure misclassification. However, distance and the type of microenvironment are shown to affect the extent of misclassification.