Individual Exposure to NO₂ in Relation to Spatial and Temporal Exposure Indices in Stockholm, Sweden: The INDEX Study

<div><p>Epidemiology studies of health effects from air pollution, as well as impact assessments, typically rely on ambient monitoring data or modelled residential levels. The relationship between these and personal exposure is not clear. To investigate personal exposure to NO₂ and its relationship with other exposure metrics and time-activity patterns in a randomly selected sample of healthy working adults (20–59 years) living and working in Stockholm. Personal exposure to NO₂ was measured with diffusive samplers in sample of 247 individuals. The 7-day average personal exposure was 14.3 µg/m³ and 12.5 µg/m³ for the study population and the inhabitants of Stockholm County, respectively. The personal exposure was significantly lower than the urban background level (20.3 µg/m³). In the univariate analyses the most influential determinants of individual exposure were long-term high-resolution dispersion-modelled levels of NO₂ outdoors at home and work, and concurrent NO₂ levels measured at a rural location, difference between those measured at an urban background and rural location and difference between those measured in busy street and at an urban background location, explaining 20, 16, 1, 2 and 4% (R²) of the 7-day personal NO₂ variation, respectively. A regression model including these variables explained 38% of the variation in personal NO₂ exposure. We found a small improvement by adding time-activity variables to the latter model (R² = 0.44). The results adds credibility primarily to long-term epidemiology studies that utilise long-term indices of NO₂ exposure at home or work, but also indicates that such studies may still suffer from exposure misclassification and dilution of any true effects. In contrast, urban background levels of NO₂ are poorly related to individual exposure.</p>