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Modelling tunnel jet emissions with LASAT: evaluation study with two Austrian data sets (Ehrentalerbergtunnel and Kaisermuhlentunnel)

By Marcus Hirtl

Abstract

Two comprehensive data sets are used to investigate the ability of the Lagrangian particle diffusion model LASAT to simulate the dispersion of plumes emitted from tunnel jets. The data sets differ in traffic volume, tunnel geometry and temporal resolution of the measurement data. In the framework of the measurement campaign at the Ehrentalerbergtunnel in Carinthia, seven trace gas experiments with SF6 were conducted in 2001. Short term averages (30 minutes) of concentrations were measured at 25 air quality stations in the vicinity of the tunnel portal during different meteorological conditions. In general the dispersion of the plume depends on the meteorological conditions (wind, stability) and the modification of the flow by terrain and buildings in the vicinity of the portal. The influence of the exit velocity of the tunnel jet must also be considered as well as the difference between the exhaust temperature and the ambient air temperature to account for buoyancy effects. The temperature increment cannot be provided directly as input parameter to LASAT as in case of the tunnel jet velocity although it is an important parameter. With LASAT, the model user can adjust two empirical input parameters to the tunnel specifications. Relationships between these model parameters and the tunnel parameters are developed in this study. They are based on the data set Ehrentalerbergtunnel and provide reasonable input values for the model user. The simulations with LASAT show that the model is able to reproduce the location and the height of the observed peak concentrations very well. The second data set was generated from January to October 2001 at the Kaisermühlentunnel in Vienna. Measurements of NOx at four air quality stations near the portal are available. Because of uncertainties in the emission data caused by vehicle counts in only one direction, only long term averages of concentrations are compared for this data set. The functions between tunnel and model parameters derived for the Ehrentalerbergtunnel are also applied to this site. It is shown that LASAT is able to simulate the position of the plume and that the modelled and the measured concentration values do not deviate more than 30 %. This study reveals that LASAT can be applied to tunnel portal emissions. The model simulations for both the Ehrentalerbergtunnel and Kaisermühlentunnel meet the requirements specified in the Austrian design guideline RVS 9.263 “Ventilation Systems - Pollutant burden at portals”

Topics: Meteorology. Climatology, QC851-999
Publisher: Borntraeger
Year: 2011
DOI identifier: 10.1127/0941-2948
OAI identifier: oai:doaj.org/article:e9c9479376e54650aab0a4821247b56e
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