Quantification of the Impact of Rail Traffic to Air Pollution at an Aboveground Train Station and its Surroundings

In Germany, rail traffic is crucial when it comes to land transport of passengers and goods, according to the last report of the Deutsche Bahn AG, in 2023 more than 5 million passengers and 540 kt per day were transported [1]. Although this type of transport has been at the forefront in terms of sustainability and environmental friendliness, it is not exempted from generating effects on the environment.
According to the national emission inventory, the estimation of particulate matter (PM) emissions from train fuel combustion have decreased over the last 25 years (from ~ 2 kt/year to ~0.1 kt/year), however in the case of non-exhaust-emissions they have remained relatively constant at about 8 kt/year. Similarly, nitrogen oxide (NOX) emissions have considerably fallen from > 45 kt/year in 1995 to < 10 kt/year in 2022 [2].
Despite these data, which are by the way estimates, are not that detailed aggregated, that they could show e.g. the distribution of the air pollutants within the vicinity of the rails.
This study addresses this gap by measuring air quality in different structures of the German railway network: plain line, freight station, underground- and aboveground station, and tunnel.
Methodology
Air pollutant measurements were carried out at Augsburg central train station (handling about 234,000 trains annually) from February to May 2023. Using a windward-leeward approach, four measurement stations were installed, two for measuring the urban background concentrations and two directly on train platforms.
PM was measured by gravimetry (24 – 72 h averages) and continuous light scattering spectrometers and NOx with a chemiluminescence monitor (continuously) at one station and with passive samplers (2 – 4 weeks averages) at all stations.
Some filters from the gravimetric measurements were analyzed in the laboratory for a broad spectrum of trace elements (e.g., Fe, Cu, Mg, etc.). Ultrafine particles and black carbon were also measured at one station.
A motion sensor camera recorded train passages to differentiate impacts from passenger/freight trains and diesel/electric locomotives.
Results
The results show a relatively low additional load of PM at around 2 μg/m³, while in the case of NOx the value was between 17 and 20 μg/m3. On the other hand, when the short-term influence was assessed, following train passages showed significant peaks, the concentrations of PM rose to almost 100 μg/m³ and NOx even up to 600 μg/m³ for several minutes.
As it was not the case that all trains generated the same increase in pollutant concentration, a statistical analysis was carried out in which more than 10,000 events (train passages) were evaluated. The events were categorized by train type (S-Bahn, IC/ICE, regional, freight) and locomotive (diesel/electric). By this means means, probabilities of additional pollutant concentrations were also calculated.
The results showed that one in 20 trains produced an additional PM load exceeding 10 μg/m3 for all train types and in the cases of diesel trains, one in five trains caused an increase in NOX concentration of at least 50 μg/m3.