Airborne particles from railroad traffic have been identified as an air pollution problem
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mainly in tunnel environments. In several subways around the world, the smell of brake
dust and high particle concentrations have focused attention on the sources of the
particles and the measures that can be taken to reduce emissions. But problems have
also been identified in railroad environments above ground. For instance, dust
deposition has been accused of damaging the enamel on cars parked closed to the
railroad. The deposition has been studied in a previous VTI report, where 15 of the
analysed metals were assigned to railroad traffic. As a result of the introduction of the
environmental quality standard for inhalable particles on 1st of January 2005, the
interest in railroad particle pollution has increased further.
The present report focuses on the variation of PM10 (inhalable particles) in some
railroad environments under and above ground, the way these relate to traffic and on the
particles'size distributions and elemental composition.
The results show that particle concentrations in above ground railroad environments
(Linköping, Stockholm, Lund and Eslöv), do not exceed the environmental quality
standard during the campaigns. Diurnal mean values of PM10 range between 19 to 25
μg/m3. On the contrary, the diurnal mean concentrations on the platforms of the
underground stations Arlanda Central and Arlanda South are far above the limit value
(237 and 88 μg/m3 respectively).
In the tunnel environments of Arlanda, clear diurnal and weekly patterns in PM10
concentration can be identified. These patterns co-fluctuate with traffic frequency. The
particle mass size distribution has an obvious peak around 5–7 μm at Arlanda C, and
slightly smaller, 2–3 μm, at Arlanda S. The concentrations of both PM10 and ultrafine
particles (< 0,1 μm) vary a lot depending on different trains. Especially the ultrafine
particles seem to be emitted from certain trains, but it has not been possible to identify
the source of these particles.
The tunnel measurements also give some interesting results regarding possible measures
against high particle concentrations. Washing of the tunnel walls and floor was carried
out on two consecutive nights, but it had no noticeable results on particle
concentrations. This implies that a dominant proportion of the particles is directly
emitted rather than resuspended. On certain nights, the concentrations of all particle size
fractions sank to very low levels, lasting till the morning traffic began. This implies
effective self ventilation during these hours.
The elemental composition of the particles in the tunnel environments was dominated
by iron (84 % and 74 % respectively in Arlanda C and Arlanda S), but also other metals,
like Cu, Zn, Cr, Ni and Sb (only at Arlanda C) have relatively high concentrations. The
ratios between metals indicate, hypothetically, that the sources of iron, manganese and
maybe also nickel are rails and wheels, while the sources of copper and zinc are the
Measurements in several different environments on Stockholm central station show that
PM10 vary several tens of μg/m3. Activity, related to both traffic and people, increases
particle concentration. The highest concentrations were measured inside the waiting
hall. Nevertheless, the concentrations on the platforms were generally at least as high as
in the busy street environment outside the station.
During a railroad travel, the PM10 and PM2,5 concentrations were generally low, but
increase at stops and, most prominently, on entering the Arlanda airport railroad
tunnels. The PM2,5 proportion is considered high, contributing to approximately
50–80 % of PM10.
All in all, the results of this study show that railroad traffic is a source of high
concentrations of iron-rich inhalable particles in railroad tunnel environments. Above
ground, in the often very open station environments, the emissions are probably
dispersed quickly, and higher concentrations therefore occur only during very short
periods. The sources of railroad emitted PM10 are likely to be rails, wheels and brakes,
but a source apportionment has not been accomplished in this project. The sources of
the ultrafine particles have not been identified.
For construction and operation of existing and future railroad- and subway tunnels and
their traffic, it is of great importance to investigate the importance of different particle
sources, the particles' health effects and possible measures to reduce emissions. Even
though no alarming. Also in above ground environment.