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Reduction of nitrogen oxide pollution in the vicinity of road tunnels using photocatalytic reactors

Problem definition:

In road tunnels in general, a high volume of pollutants is to be expected, which are difficult to remove and thus concentrate. Due to the high concentration at the tunnel portals, the environment can be severely affected. City tunnels and tunnels that are close to residential developments are particularly hazardous. Therefore, the controlled removal of pollutants and, consequently, the improvement of the exhaust systems at existing and new tunnels is important.

Project Objective:

The overall objective of the project is to investigate ways to reduce vehicle-induced NOₓ pollution in the exhaust air of road tunnels. Furthermore, the aim of the project is to gain knowledge in the field of the use of linear photocatalytic reactors. Here, the focus is on the possibility of retrofitting existing tunnels and the possibility of integrating these innovative technologies in new construction tunnels.


The project, which is based on extensive experimental and numerical investigations, will be carried out in two parts. In the first part, approaches and concepts for photocatalytic exhaust air treatment of pollutants generated in tunnels will be developed and associated solutions for integration in road tunnels will be worked out. Based on this, a real-scale implementation of the designed solution will be carried out in the second part, and the nitrogen oxide degradation capacity will be measured and optimized. In this context, ISAC will characterize the exhaust gas dispersion of stationary traffic and perform numerical simulations. The characterization is to be used to determine a target position for the extraction of pollutants in the tunnel. Furthermore, a test rig is created to experimentally determine a section of the real-scale exhaust system and the decomposition rates. Subsequently, the cost-benefit ratio of such a developed exhaust air treatment will be estimated.


RWTH Aachen University

ISAC - Institute for Road Engineering Aachen

AIA - Aerodynamic Institute

University of Wuppertal (BUW)

IAU - Physical and Theoretical Chemistry
Institute for Atmospheric and Environmental Research

ISAC GmbH - Engineering Company for Road Systems Aachen


Federal Highway Research Institute
Federal budget, chapter 1214, title 68601, budget year 2020, for the composite system:
"TunNOₓ - Reduction of nitrogen oxide pollution in the vicinity of road tunnels by means of photocatalytic reactors - Subproject RWTH Aachen: Experimental and numerical investigations of the development of the reactor".
FE-No.: 88.0170/2018

Year of Completion / Publication



Nils Lichtenberg
Moritz Berghaus