Socioeconomic position and outdoor nitrogen dioxide (NO2) exposure in Western Europe: A multi-city analysis

Background: Inconsistent associations between socioeconomic position (SEP) and air pollution have been reported in Europe, but methodological differences prevent any direct between-study comparison. Objectives: Assess and compare the association between SEP and air pollution exposure at residential address across 20 cities from eight European countries. Methods: Three SEP indicators, defined at individual-level (education and occupation) and area-level (unemployment rate) were assessed in three European multicenter cohorts. NO2 exposure was estimated at participants’ addresses with land use regression models developed within the European Study of Cohorts for Air Pollution Effects (ESCAPE). Pooled and cityspecific linear regressions were used to analyze associations between each SEP indicator and NO2. Heterogeneity across cities was assessed using a random-effects meta-analysis. Results: 8277 participants were included. Pooling the data, participants with lower individual-SEP indicators tended to be less exposed to NO2. Conversely, participants living in neighborhood characterized by higher unemployment rate were more exposed. However, in both cases, city-specific results exhibited heterogeneity across areas (I2>75%). When having individual- and area-SEP indicators in the same model, estimates were similar compared to the simple regression model (individual- and area-SEP in separate models), suggesting independent associations between individual-SEP and unemployment rate with NO2. Conclusions: At European level, associations between SEP and NO2 were heterogeneous and no geographical or urban pattern could be identified. Our results showed that individual- and area-SEP indicators capture different aspects of the SEP distribution regarding exposure to air pollution, stressing the importance of considering both in air pollution epidemiological studies.