Redistribution of traffic related air pollution associated with a new road tunnel.

The aim of this study was to assess the effect of a new road tunnel on the concentration and distribution of traffic-related air pollution (TRAP), specifically nitrogen dioxide (NO(2)) and particulate matter (PM), and to determine its relationship to change in traffic flow. We used continuously recorded data from four monitoring stations at nonroadside locations within the study area and three regional monitors outside the area. The four monitors in the study area were in background locations where smaller pollutant changes were expected compared with changes near the bypassed main road. We also deployed passive samplers to assess finer spatial variability in NO(2) including application of a land use regression model (LUR). The study was conducted from 2006 to 2008. Analysis of the continuously recorded data showed that the tunnel intervention did not lead to consistent reductions in NO(2) or PM over the wider study area. However, there were significant decreases in NO(2), NO(x), and PM(10) in the eastern section of the study area. Analysis of passive sampler data indicated that the greatest reductions in NO(2) concentrations occurred within 100 m of the bypassed main road. The LUR model also demonstrated that changes in NO(2) were most marked adjacent to the bypassed main road. These findings support the use of methods that highlight fine spatial variability in TRAP and demonstrate the utility of traffic interventions in reducing air pollution exposures for populations living close to main roads.