Research and/or engineering questions/objective: The issue of air pollutant emissions from rail transport or from its infrastructure is a field that has been neglected and therefore existing databases are very little and heterogeneous. The objective of the research is, to gain more results and knowledge to close these gaps. Among others measurements of particulate matter emissions while braking on a brake test bench will finally deliver emission factors which will be applied in dispersion models. Thus, the contribution of railway traffic on the particulate matter pollution close to railway tracks will be determined and compared to measurements performed in the ambient air. Methodology: A comprehensive literature review and standardised protocols (UIC – International Union of Railways, UIC 541-4) were used to develop a criteria catalogue with decision tree for a measurement programme to investigate braking profiles and stop braking in freight traffic. The programme was carried out based on an existing test programme and included seven different stop brakings and three regulation brakings. An organic brake pad COSIT 810 (1xBGU) in combination with a Ö 874 mm Lucchini wheel set were used as test specimens. The abrasion of the brake pads was determined after each cycle to validate the particle measurements and wear simulations. The investigations focused on brake profiles at stops and stations with different intensity of use. The applied mechanical braking energy was used to determine the abrasion. The programme was developed to cover scenarios and braking conditions as close to reality as possible. Results of the brake test bench measurements: The particle measurements with a four-stage impactor showed that mainly coarser particles > 10 µm and very fine particles < 1 µm were measured. Especially when stopping at high speeds of 100 km/h, there was a shift in particle distribution away from coarse particles towards fine particles < 1 µm. While similar particle masses per braking were found for the 30 km/h and 60 km/h speed ranges, this value increased tenfold at an initial speed of 100 km/h. The content analyses of the particle samples from the brake test stand contained iron (approx. 30 %), barium and aluminium (3 % each) as well as magnesium and zinc (approx. 1 % each), regardless of the particle size. Copper (0.2 %), chromium (0.2 %) and nickel (0.1 %) was also detected. For molybdenum and calcium, the mass fractions were below 0.1 %. In addition, the VOC content was measured, but all VOC values were below the detection limit of 0.5 ppm. Limitations of this study: Within the study only two different types of brakes can be determined, due to the limitations of time and finances. Further types of brakes resp. further brake pad materials and combinations with wheels have to be simulated with the help of an abrasive wear model. The results of the abrasive wear model and the measurements done at the brake test bench will be compared to each other to validate the abrasive wear model with two different brake pad materials. Further validations of the abrasive wear model were done in previous projects. What does the paper offer that is new in the field in comparison to other works of the author? Not much focus was set on the air pollution caused by rail traffic in general up to now. This gap of knowledge and data will be reduced, but for sure not be closed entirely. What is new in this study is the combination of outdoor measurements close to railway tracks, the performance of brake test bench measurements, the application of an abrasive wear model in combination with dispersion modelling as well as toxicological risk assessment of the results. Conclusion: The brake test bench measurements proved, that higher speed and higher load per wheel deliver more abrasion and higher mass loss of the brake pads. Particle emissions are higher and of smaller size with higher speed. With the help of the findings determined in this project, not only with the one from the brake test bench measurements, but also from the air quality measurements close to sites (free railway tracks, freight yard, passenger station and underground passenger station), modelling with an abrasive wear model, specific emission factors are to be derived.

Dr.-Ing. Ulrich Vogt, Head of Department of Flue Gas Cleaning and Air Quality Control, University of Stuttgart; Mr. Daniel Ricardo Obando Nunez, PhD student, University of Stuttgart/Germany, Institute of Combustion and Power Plant Technology; Mr. Dieter Straub, co-worker, University of Stuttgart/Germany, Institute of Combustion and Power Plant Technology; Dr. Ingo Duering, head of office, Lohmeyer Ltd, engineering office; Dipl.-Ing. Wolfram Schmidt, co-worker, Lohmeyer Ltd, engineering office; Dr. Annette Bitsch, Head of department, Fraunhofer Institute for Toxicology and Experimental Medicine; Dipl.-Ing. Eckert Fritz, head of division, Institute of Railway Technology; Dr. Sabrina Michael, head of division, German Centre for Rail Traffic Research