The association between indoor and outdoor NO2 levels: A case study in 50 residences in an urban neighbourhood in New Zealand

Background: In the context of inner-city housing intensification, exploring the association between outdoor and indoor air quality is important to quantify any potential health risks. Methods: We undertook a cross-sectional case study on 50 residences in an inner-city neighbourhood scheduled for urban development, bisected by a busy road. We measured indoor and outdoor NO2, indoor temperature, and undertook a survey on demographic factors and household NO2 sources. We performed a linear regression to examine the association between indoor and outdoor NO2 (measured at the building facade) adjusting for potential confounders. Results: Mean indoor and outdoor levels of NO2 were 8.4 and 12.5 mu g/m(3) respectively. The unadjusted model showed no significant association between indoor and outdoor NO2. In the fully-adjusted model, a 1 % increase in outdoor NO2 was associated with a 5 % increase in indoor NO2 (95 %CI: 1.2-8.8%). Conclusion: A weak association between indoor and outdoor NO2 was found. More intensive housing development in a transport corridor may be possible; however given the health risks of induced by air pollutants starts even at levels below WHO recommended levels, urban policy measures to reduce indoor and ambient air pollution are required.