High levels of air pollution are a common problem in both road and railroad tunnels. Sources and emission processes however differ significantly, as reflected by aerosols physical and chemical properties. As particle concentrations and properties affect exposure of and health effects for people on platforms and in vehicles, effective ways to reduce emissions and exposure are important. This study aims to improve the knowledge of the differences between PM10 in the rail and road tunnel environments, their sources and the possibilities to address problems with high particulate levels. Measurement campaigns were carried out at Arlanda Central, a railroad tunnel station below Arlanda airport and in Söderleden road tunnel, a road tunnel in central Stockholm.
The results show large differences in concentration levels, size distributions and in composition of the particles. The railroad tunnel aerosol consisted of coarse particles with high iron content, while the properties of the coarse particles in the road tunnel were strongly influenced by whether the road surface was wet or dry. In wet conditions, concentrations were relatively low and iron and sulfur dominating elements, while silicon, potassium, calcium and iron from suspension and road wear dominated during dry conditions. The content of elemental carbon, most likely from the pantograph, were unexpectedly high in the railroad tunnel. An older type of train with a large proportion of mechanical brakes were suggested to be responsible to the main particle emissions in the railway tunnel. The report concludes with a discussion and proposals for action against particle sources in the various underground environments.