Study by TU Graz shows that exhaust particles account for less than ten per cent of fine dust emissions from cars and trucks. Compliance with new air quality limits to take effect in 2030 will be nevertheless difficult to achieve.
Exhaust gases are no longer the most important emission factor from motor vehicles by far when it comes to particulate matter. This is shown by a large-scale study carried out by Graz University of Technology (TU Graz) for the FVV eV.in Germany, in which the non-exhaust emissions for the current European car fleet were also recorded. Due to the increasing proportion of electric vehicles and the reduction in exhaust emissions since the introduction of exhaust particulate filters with the EURO 5 and EURO 6 emissions standards, emissions from combustion engines now account for less than ten per cent of total vehicle emissions in the most common traffic situations. Instead, brake emissions, tyre and road abrasion and the resuspension of particles by car traffic are responsible for most of them.
Brake and exhaust emissions will decrease significantly
“However, with the introduction of the Euro 7 emissions standard in 2026, we expect a reduction in brake emissions of around 80 per cent in new vehicles by 2040,” says study leader Stefan Hausberger from the Institute of Thermodynamics and Sustainable Propulsion Systems at TU Graz. “This will be achieved through new braking technologies, such as hard metal coatings, as well as the increasing electrification of the car fleet, as electric cars generate a lot of braking energy through recuperation instead of conventional braking. And because particulate filter technology will continue to improve and the number of electric cars will increase, our simulations suggest that exhaust particulate emissions could fall by up to 90 per cent by 2040.”
The situation is different with tyre wear. The need for good grip and high safety does not go hand in hand with the desire for greatly reduced tyre wear. The tyres must interact with the road by means of friction so that the vehicles do not slide around on it as if on clear ice. The authors of the study therefore expect a maximum reduction potential of ten to 20 per cent over the next decade. Lower speed limits would achieve more. On the vehicle side, it is almost impossible to influence road abrasion and resuspended particles, which is why these will probably make up the largest proportion of traffic emissions in the future.
New limit values as of 2030 difficult to achieve
Due to the limited options for tyre and road abrasion and resuspended particles, the authors of the study expect that it could be difficult to comply with the new EU air quality limits as of 2030 at many measuring points, despite the calculated reductions in exhaust and brake emissions. The limit values for the mass of particles smaller than ten micrometres (PM10) will then be halved from 40 to 20 micrograms per cubic metre. “Our calculations show that compliance with EU air quality limits will be extremely tight as of 2030. Especially at locations with high traffic volumes and unfavourable conditions, such as tunnel portals or street canyons,” says Stefan Hausberger.
For the study, the researchers used the PHEM (Passenger car and Heavy duty Emission Model) software developed by TU Graz together with the Research Association for Combustion Engines and Thermodynamics (FVT). Originally developed for the simulation of exhaust emissions from a wide range of vehicle types, the researchers have expanded the software to include non-exhaust emissions by means of measurements they carried out themselves and data collected in the TU Graz Lead Project NExT as well as projects for the Swiss FOEN and EU Horizon, in order to simulate these consistently and on the basis of physical relationships. Thanks to the cooperation with the colleagues involved in the EU project LENS at the Institute of Thermodynamics and Sustainable Propulsion Systems, these simulations are also possible for two-wheelers.