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Tyre wear in particulate matter – No need to panic!

von Prof. Dr. Günter Stein, Dipl.-Ing. Erik Wünstel, Dipl.-Ing., M.Sc. Wilma Travnicek-Pagaimo

Accurate knowledge of the composition of particulate matter is becoming more and more important within the framework of environmental legislation. For this reason, the Laboratory for Environmental Analysis of the Faculty of Engineering at the RheinMain University of Applied Sciences, Rüsselsheim Study Site, in cooperation with the Hessian State Office for Environment and Geology (HLUG), Wiesbaden, wants to make a contribution to the analytical quantification of tyre wear material in particulate matter.

For this purpose, in the context of several diploma-, master- and bachelor theses, an analytical chemical measurement method based on pyrolysis-GC/MS was developed and combined with a statistical design of experiments (DoE) instead of the classical calibration. On the basis of indicator substances specific for rubber pyrolysis, it was possible to determine both the percentage of tyre wear material in the particulate matter as well as the contribution of tyre wear material to the particulate matter concentration in μg/m3 for real claimed samples of particulate matter determined at locations exposed to considerable traffic in the cities of Wiesbaden and Darmstadt. As a convenient side effect, this analytical method also allows the determination of the average composition of tyre wear material regarding the NR/IR, BR and SBR (E-SBR + S-SBR) polymers used.

The outstanding result of this research work is the proof that although tyre wear material is present in particulate matter as predicted by modelling, it is predominantly present in the form of larger particles. Hence, while as a rule it is mostly not present in the PM10 fraction and only in traces in the finer PM_2.5 fraction (PM = particulate matter), it is found in the toxicologically less critical TSP (= total suspended particulates). Under conditions of a “worst case scenario” an average of only 0.5 % of tyre wear material in PM₁₀ was found (the literature indicates an average of about 8 %). The corresponding contribution to the concentration of PM₁₀ was on average roughly 0.1 μg/m³; the highest single value found was 0.3 μg/m³. These amounts are practically negligible in relation to the corresponding critical value of 50 μg/m³ which may not be exceeded for more than 35 days per year.