TRAPOS: Optimisation of modelling methods for traffic pollution in streets

• Research unit: EU RFP
• Project number: 97.0136

Key words (English)

Urban air pollution; turbulent dispersion; street canyons; roughness sublayer

Alternative project number (English)

EU project number: FMRXCT970105

Research programs (English)

EU-programme: 4. Frame Research Programme - 10.1 Stimulation of training and mobility

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
ETH Zürich
Institute for Atmospheric and Climate Science - IACETH

Partners and International Organizations (English)

Coordinator: National Environmental Research Institute (DK)

Abstract (English)

The TMR-network TRAPOS aims at improving the understanding and hence modelling capability of processes contributing to the dispersion of air pollutants from traffic within street canyons. The various institutions within the network use field measurements, wind tunnel experiments and CFD/ numerical models to attack to the problem. The main focus of the network is to combine the results and concepts from these different approaches in order to benefit from the advantages of all of them.
The Swiss contribution focused on two main topics: i) To investigate the turbulence structure within and above typical street canyons and hence derive simple algorithms for length and velocity scales to describe the flow in such an environment. ii) To investigate the relative importance of traffic produced turbulence (TPT) for the process of pollutant dispersion in street canyons.
For i) data from full-scale and wind tunnel experiments were combined. For the first time wind tunnel data from a real-array urban model (rue de Strasbourg, Nantes) were analysed in terms of turbulence characteristics. Typically, the user of a street level dispersion model needs to specify a reference velocity and very often, this information is not readily available, but the wind speed from another street, another height or another position within the canyon is at disposition. Therefore, average characteristics of the flow within and above this complex geometry are necessary not only for the model development but also to fulfil the modelling needs during its application.
As for ii) different approaches were investigated to parameterise the contribution of TPT. In this area ETH had the leading role within TRAPOS due to the experience of the involved postdoc. The physical background of parameterisations for different traffic densities were verified and a concept to combine turbulent components due to wind- and traffic-induced motions was established. Parameterisations for CFD models were developed and tested against field and laboratory data. Neglecting TPT parameterisations in dispersion models causes significant over-predictions of pollutant concentrations in urban street canyons that range up to a factor of 4 to 5

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0136