Variability of levels and composition of PM10 and PM2.5 in the Barcelona metro system 1Institute of Environmental Assessment and Water Research, IDAEA, CSIC, C/Jordi Girona 18–24, 08034 Barcelona, Spain
08 Jun 2012
2Transports Metropolitans de Barcelona, TMB Santa Eulàlia, Av. del Metro s/n L'Hospitalet de Llobregat, 08902, Spain
Received: 26 Jan 2012 – Published in Atmos. Chem. Phys. Discuss.: 02 Mar 2012 Abstract. From an environmental perspective, the underground metro system is one of
the cleanest forms of public transportation in urban agglomerations. Current
studies report contradicting results regarding air quality in the metro
systems: whereas some reveal poor air quality, others report PM levels which
are lower or of the same order of magnitude than those measured in traffic
sites above ground level. The present work assesses summer and winter indoor
air quality and passenger exposure in the Barcelona metro, focusing on PM
levels and their metal contents. In addition, the impact on indoor air
quality of platform screen door systems (automated systems consisting of
closed rail track and platforms) is evaluated, to determine whether these
systems reduce passenger exposure to PM when compared with conventional
systems (open tracks and platforms). In the Barcelona metro PM levels inside
the trains in summer are amongst the lowest reported for worldwide metro
systems (11–32 μg m−3 PM2.5). This is most likely due to the air
conditioning system working in all carriages of the Barcelona metro during
the whole year. Levels were considerably higher on the platforms, reaching mean
levels of 46 and 125 μg m3 in the new (L9) and old
(L3) lines, respectively. PM10 data are also reported in the present study,
but comparison with other metro systems is difficult due to the scarcity of
data compared with PM2.5. Results showed distinct PM daily cycles, with a
drastic increase from 06:00 to 07:00 a.m., a diurnal maximum from
07:00 to 10:00 p.m., and marked decrease between 10:00 p.m. and 05:00 a.m. The elements
with the highest enrichment were those associated with wheel or brake
abrasion products (Ba, Fe, Cu, Mn, Cr, Sb, As, Mo, Co, Sr, among others).
Laminar hematite (Fe2O3) was the dominant particle type, being
mainly originated by mechanical abrasion of the rail track and wheels.
Regarding passenger exposure to PM, the contribution of commuting by metro
was estimated to account for around 10% of the daily exposure.
However, this contribution may be one order of magnitude higher when specific matals are considered. Finally,
we conclude that the implementation of platform screen door systems results
in reductions of both PM levels and metal concentrations. In addition an
advanced optimized ventilation system gave even a much higher efficiency in
reducing exposure to PM of metro commuters. Combining these two features PM
exposure levels in the platforms may be reduced down by a factor of 7 with
respect the old subway lines in Barcelona.
Revised: 03 May 2012 – Accepted: 16 May 2012 – Published: 08 Jun 2012
Citation: Querol, X., Moreno, T., Karanasiou, A., Reche, C., Alastuey, A., Viana, M., Font, O., Gil, J., de Miguel, E., and Capdevila, M.: Variability of levels and composition of PM10 and PM2.5 in the Barcelona metro system, Atmos. Chem. Phys., 12, 5055-5076, doi:10.5194/acp-12-5055-2012, 2012.