• A further step of this project is the proposal and field implementation of mitigation strategies to reduce the effect on indoor air quality of pollution-generated activities, which is referred by action B2. The addition of new ballast to tunnels has been selected as a key activity, likely to alter the air quality at platforms. Thus, this activity was planned to be developed under two different methodologies to assess differences: 1) adding ballast under normal conditions (ballast+water), 2) adding ballast using a commercial available antiresuspension polymer (ballast +water + dust suppressant). The standard method (ballast + water) was applied at the metro system of Palau Reial (L3), where air quality measurements were performed from 1st April to 14th May.

B2. Measuring equipments at Palau Reial platform (left) and new ballast applied in the railtrack of the station.

  • The addition of ballast previously treated with the dust suppressant has been applied in the metro station of Maria Cristina (L3). This station is adjacent to Palau Reial, both stations have a similar design (one wide tunnel with two rail tracks separated by a middle wall), depth and ventilation system. The measurement campaign started on 14th May and finished on 9th of June 2015. According to the established IMPROVE air quality monitoring method, equipment deployed both at the platforms of Palau Reial and Maria Cristina consist of: i) a light-scattering laser photometer for PM1, PM2.5 and PM10 (particulate matter with aerodynamic diameter less than 1 µm, 2.5 µm and 10 µm, respectively) mass concentrations; ii) an optical particle sizer for the determination of the number size distributions in the size range 0.3–10 μm; iii) an indoor air quality meter for CO, CO2, T and RH values; iv) a high volume sampler with a PM2.5 head for off-line gravimetric and chemical analysis; and v) NO2 diffusion tubes for off-line NO2 levels. High-resolution data is being processed, while the analyses to determine off-line parameters are underway.


B2. Measuring equipments at Maria Cristina platform (left), mixing process of dust suppresant nanopolymer with water (middle) and application to the untreated ballast.

  • Measurements were done at Poble Sec station (L3) from 14th September to 11th October 2016. Tests aimed to investigate the effects on air quality linked to the addition of ballast to tunnel, and were designed following the methodology previously performed at Palau Reial and Maria Cristina stations in summer 2015. Accordingly, two different methods were compared: 1) addition of ballast under normal conditions (ballast +water), and 2) addition of ballast using a commercial available anti-resuspension polymer (ballast +water +dust suppressant). Each method was applied at a different side of the tunnel. Instruments were moved from one platform to the opposite one, following the schedule of the tunnel works. The sampling periods included days under normal conditions and days affected by works (comprising adding and levelling ballast). The analysis of the results is now in progress, combining this campaign with that performed at Palau Reial and Maria Cristina. Information on the kilometric points where works were carried out each night is being compiled.

B2. Effect of ballast addition on air quality on Poble Sec´s platform

  • Sampling equipments were moved to the station of Tarragona (L3) on the 29th of February. During this campaign a study on air quality conditions in the platform when the ventilation regime is changed from the normal conditions, introducing outdoor air into the tunnel and/or platform (impulsion), to a different experimental condition removing indoor air towards the outdoor environment (extraction). Measurements progressed until 11th of May in order to complete all the proposed tests. The main goal of the measurements was to assess the repeatability of the results on air quality variations obtained in this station in summer 2015.

B2. Effect of changing air flow direction on air quality on Tarragona´s platform

  • The effect of air purifiers was studied against the air quality in the platform under normal conditions. An average reduction on PM2.5 concentrations of 30% was recorded when one of the purifiers was functioning closed to the air quality instrumentation. This finding promoted the completion of an additional test to assess how the effectiveness varies with the distance. During these tests, purifiers were placed in the middle of the platform and a portable automatic PM monitor was used to measure in 8 different positions, approximately equidistant, along the platform; the first measurement being located at the air quality sampling site, at one end of the platform.
  • In order to further assess the role of ventilation on air quality, measurements were also carried out at one platform of Collblanc station from 11th May to 11th July 2016. This platform belongs to the newest metro line of the city (L9S), opened in February 2016 to connect the city centre with the airport. The design of the station is characterised by driverless trains running through a single tunnel with one rail track separated from a single platform by a wall with a full length platform screen door (PSD) system. The organisation of L9S at Collblanc is unusual because at this end of the line the two railtracks run one above the other in vertically separated 12-metre-wide tunnels, rather than side by side. In Collblanc the situation is complicated by the fact that only the lower rail track and platform are currently open for public use, so that trains run in both directions using the same tunnel. The upper station is currently only used for maintenance works. This station is ventilated by stronger and more numerous fans than the older conventional lines.

All platform measurements scheduled under Action B2 were successfully completed on November 2016.