Pollution dispersion at an urban motorway tunnel portal: Comparison of the small-scale predictive study with the actual conditions measured on the site

This paper presents a study on the environmental impact of vehicle exhausts at the south portal of the Landy tunnel located north of Paris, France. This study is based on a 1995 dispersion study using a hydraulic model and a 2002 campaign of in situ measurements.The 1995 study, conducted before the motorway covering was built, was aimed at comparing the theoretical NO2 concentrations, obtained with a hydraulic scale model, with the permissible thresholds imposed by French regulations. The NO2 concentrations obtained with the scale model were found to be reasonable, but as a precaution it was decided to retain a contingency option to subsequently install a massive extraction chimney to reduce exhaust emission levels at the portal.The 2002 in situ measurement campaign was aimed at measuring the actual pollution levels in the vicinity of the Landy tunnel south portal. The statistical analysis showed that the NO2 concentrations were higher on the east side of the road than the west, but still 5 to 10 times lower than at the exhaust, and are of the same order of magnitude as alongside other major Paris motorways. The PM10 measurements were in line with regulatory reference values on both sides of the road.Comparing the 1995 study and the 2002 in situ measurements showed a certain consistency but also highlighted the complexity of the phenomena involved and the difficulty of identifying the influence of the tunnel exhaust on the NO2 levels at the roadside.