In order to distinguish the railway emissions from the regional background, simultaneous samples were also taken at a near urban background site in Zürich. PM10 concentrations were found to be only moderately higher at the railway influenced sites compared to the urban background site. However, from the iron data it can be seen, that this increase is to a large extent caused by iron. This finding is in line with the expecta-tions, because the most plausible sources of the railway emissions are abrasion particles from tracks, brakes and wheels. It should be noted that in Switzerland trains are operated nearly exclusively by electric locomo-tives and consequently no diesel particle emissions from railways have to be considered.
The concentration differences between the railway exposed sites and the background site Zeughaus show that the railway contribution to the ambient concentrations of PM10 and iron was in the range of 1-2 ug/m3 and is decreasing quite rapidly with increasing distance from the railway tracks. It can thus be concluded that measurable exposition to PM10 caused by railway traffic occurs only in the immediate vicinity of very busy railway lines, consists mainly of iron in the coarse fraction and is quantitatively moderate.