title: Factors controlling air quality in different European subway systems.
abstract: Sampling campaigns using the same equipment and methodology were conducted to assess and compare the air quality at three South European subway systems (Barcelona, Athens and Oporto), focusing on concentrations and chemical composition of PM2.5 on subway platforms, as well as PM2.5 concentrations inside trains. Experimental results showed that the mean PM2.5 concentrations widely varied among the European subway systems, and even among different platforms within the same underground system, which might be associated to distinct station and tunnel designs and ventilation systems. In all cases PM2.5 concentrations on the platforms were higher than those in the urban ambient air, evidencing that there is generation of PM2.5 associated with the subway systems operation. Subway PM2.5 consisted of elemental iron, total carbon, crustal matter, secondary inorganic compounds, insoluble sulphate, halite and trace elements. Of all metals, Fe was the most abundant, accounting for 29-43% of the total PM2.5 mass (41-61% if Fe2O3 is considered), indicating the existence of an Fe source in the subway system, which could have its origin in mechanical friction and wear processes between rails, wheels and brakes. The trace elements with the highest enrichment in the subway PM2.5 were Ba, Cu, Mn, Zn, Cr, Sb, Sr, Ni, Sn, Co, Zr and Mo. Similar PM2.5 diurnal trends were observed on platforms from different subway systems, with higher concentrations during subway operating hours than during the transport service interruption, and lower levels on weekends than on weekdays. PM2.5 concentrations depended largely on the operation and frequency of the trains and the ventilation system, and were lower inside the trains, when air conditioning system was operating properly, than on the platforms. However, the PM2.5 concentrations increased considerably when the train windows were open. The PM2.5 levels inside the trains decreased with the trains passage in aboveground sections.
authors.affiliation: Institute of Environmental Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain; Department of Analytical Chemistry, Faculty of Chemistry, University of Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain. Electronic address: vania.ferreira@idaea.csic.es.
authors.forename: Vânia
authors.initials: V
authors.lastname: Martins
authors.affiliation: Institute of Environmental Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Moreno
authors.affiliation: Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, Environmental Radioactivity Lab, N.C.S.R. "Demokritos", Agia Paraskevi, 15310 Athens, Greece; University of the Aegean, Department of Environment, 81100 Mytilene, Greece.
authors.forename: Luís
authors.initials: L
authors.lastname: Mendes
authors.affiliation: Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, Environmental Radioactivity Lab, N.C.S.R. "Demokritos", Agia Paraskevi, 15310 Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Eleftheriadis
authors.affiliation: Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, Environmental Radioactivity Lab, N.C.S.R. "Demokritos", Agia Paraskevi, 15310 Athens, Greece.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Diapouli
authors.affiliation: Centre for Environmental and Marine Studies (CESAM), Department of Environment, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Célia A
authors.initials: CA
authors.lastname: Alves
authors.affiliation: Centre for Environmental and Marine Studies (CESAM), Department of Environment, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Márcio
authors.initials: M
authors.lastname: Duarte
authors.affiliation: Transports Metropolitans de Barcelona, TMB Santa Eulàlia, Av. Del Metro s/n L'Hospitalet de Llobregat, 08902, Spain.
authors.forename: Eladio
authors.initials: E
authors.lastname: de Miguel
authors.affiliation: Transports Metropolitans de Barcelona, TMB Santa Eulàlia, Av. Del Metro s/n L'Hospitalet de Llobregat, 08902, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Capdevila
authors.affiliation: Institute of Environmental Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Querol
authors.affiliation: Institute of Environmental Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
authors.forename: María Cruz
authors.initials: MC
authors.lastname: Minguillón
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D016902:Air Pollution, Indoor / Q000032:analysis*; D004784:Environmental Monitoring; D006115:Greece; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D011174:Portugal; D011890:Railroads; D013030:Spain; D062206:Spatial Analysis; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter
keywords: Commuting; Exposure; PM(2.5); Subway stations; Trains