Results of a micro-simulation dispersion model study of portal emissions using GRAL.

As urban populations increase, the need for more efficient and less-polluting transport follows. Local air quality considerations are a crucial factor in the design and assessment of transport systems and infrastructure. Road tunnels play an important role in our built environment. In recent years Australia, and Sydney in particular, has seen a rise in road tunnels built in densely populated areas. Air pollution from tunnels longer than one kilometre is usually dispersed through elevated ventilation outlets which, whilst effective, often have large implications for design and operation. The venting of tunnel exhaust air from portals is common in other parts of the world, but it remains an operating restriction for several recent tunnels in NSW. For this reason, the air quality impacts of tunnel portals emissions have not been extensively assessed in Australia. The GRAL model was developed at the Graz University of Technology in 1999, with one of the main drivers for its development being the need to assess dispersion from road tunnel portals. GRAL has been used for this purpose across Europe, and now more widely. This paper summarises the results of a micro-simulation dispersion modelling study using GRAL for a small urban area. The focus of the study was to test the sensitivity of the concentrations predicted by GRAL to model configuration, inputs and assumptions. The effects of topography, receptor placement and the portal air temperature increment are discussed. [ABSTRACT FROM AUTHOR]