Abstract

Background: In epidemiological studies of the potential health effects of traffic related air pollution, self reported traffic intensity is a commonly used, but rarely validated, exposure variable.

Methods: As part of a study on the impact of Traffic Related Air Pollution on Childhood Asthma (TRAPCA), data from 2633 and 673 infants from the Dutch and the German-Munich cohorts, respectively, were available. Parents subjectively assessed traffic intensity at the home address. Objective exposures were estimated by a combination of spatial air pollution measurements and geographic information system (GIS) based modelling using an identical method for both cohorts.

Results: The agreement rates between self reported and GIS modelled exposure—accumulated over the three strata of self assessed traffic intensity—were 55–58% for PM_2.5, filter absorbance (PM_2.5 abs), and nitrogen dioxide in Munich and 39–40% in the Netherlands. Of the self reported low traffic exposed group, 71–73% in Munich and 45–47% in the Netherlands had low modelled exposure to these three air pollutants. Of the self assessed high exposed subgroups in Munich (15% of the total population) and the Netherlands (22% of the total population), only 22–33% and 30–32% respectively had high modelled exposure to the three air pollutants. The subjective assessments tend to overestimate the modelled estimates for PM_2.5 and NO₂ in both study areas. When analysis was restricted to the portion of the Dutch cohort living in non-urban areas, the agreement rates were even lower.

Conclusions: Self reported and modelled assessment of exposure to air pollutants are only weakly associated.