Keywords: airborne particles, composition, legislation, morphology, rail traffic.

Emission of airborne particles is a side effect from rail transport. This paper reviews recent research on particle emissions from rail vehicles. Both exhaust and non-exhaust particle emissions are characterized by size, morphology, composition, and size distribution. Current legislation, knowledge of adverse health effects, and available and proposed solutions for emission reductions are also considered. Furthermore, various alternatives for reducing particle emissions from rail transport are discussed.

Only a few studies have been done on non-exhaust emissions, and they are almost exclusively related to road transport, e.g., airborne particles from tyre, braking materials, and roads. Particle mass is considered in most research and regulations. But other characteristic properties, such as size, shape, number, and composition, have been poorly investigated and they are not considered in current regulations. The development of efficient and proactive countermeasures calls for further studies of particle characteristics, generation mechanisms, and exposure factors, particularly by focusing on non-exhaust emissions from rail transport. Furthermore, there is no accepted methodology available for how to measure the emissions and how to assess the results. A method to measure the airborne wear particle emission rate (AWPER) from wheel-rail and braking contact is suggested. This method can be used by manufacturers to demonstrate the advantage of their product. This method could also be used in legislations to force manufacturers to consider the wear particle emission rates of their products and to optimize their products in accordance with the proposed regulations.

Iron is the dominant element identified in almost all reviewed studies. Some of the studies considered the characteristics of iron to be the main source of its adverse health effects. However, if we compare the manganese/iron, copper/iron, and chromium/iron ratios with the predetermined occupational exposure limits (OELs) for these materials, we understand that the risks caused by those non-ferrous materials are markedly higher than that of iron, particularly on subway platforms. Furthermore, the concentrations of these elements can be increased by road traffic or other pollutant sources. The magnitudes of calcium, silicon, aluminium, and sodium are also significant. So instead of focusing on the concentrations of single elements, the combined, cumulative concentrations of elements such as iron, copper, chromium, manganese, sodium, aluminium, silicon and calcium as well as soot should be considered, i.e., the summation ratios of OEL concentrations must be less than unity. Furthermore, the adverse health effects of particles from rail vehicles on more sensitive people, such as children and people with pre-existing respiratory problems or diabetes, must be studied in depth, which most likely means that not just combinatory effects but also interaction effects must be considered.

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