The overall aim of IMPROVE (Implementing Methodologies and Practices to Reduce air pollution Of the subway enVironmEnt) is to provide a benchmark study that will lead to real improvement in subway air quality.

Underground rail systems provide an environmental lifeline to our world cities

Travelling by rail subway helps to reduce traffic congestion above ground and offers millions of commuters a rapid, efficient and relatively inexpensive form of urban transport. Furthermore, the more people that travel by rail subway instead of car the fewer will be the exhaust emissions, enhancing breathable city air quality and reducing the climatic effects attributable to greenhouse gases. Travel by rail subway is therefore strongly to be encouraged.

We should all breathe clean air

City life has many advantages, and a majority of people in the world now live in cities. One of the clear disadvantages of an urban lifestyle, however, is that air quality tends to be poorer than in rural environments. Large amounts of breathable dust particles (“particulate matter”, “PM” or “aerosols”), produced by transport movement, construction activity, industrial emissions and so on are present everywhere. You cannot see them, but they are there. Road traffic is especially implicated in its impact on city air, not only in PM pollution but also the emission of irritant gases such as nitrogen dioxide NO2. The World Health Organisation has warned that breathing bad air shortens the lifespan of city dwellers, particularly those made more vulnerable from asthma or cardiovascular conditions. The need to improve city air above ground is obvious.

Air quality underground

But what about air quality underground? This is an aspect of subway rail travel that has received relatively little attention. Underground air can be contaminated with traffic polluted air entering the system via ventilation systems and access points. Also airborne particles can be generated by the trains themselves as they move through the tunnels. Congested platforms full of people need to be well ventilated in order to avoid stuffy air conditions uncomfortable to commuters. Although passengers usually spend only a small part of their day in underground rail system, any program trying to improve city air should also consider conditions underground.

Published work so far

Published research has shown that in some cases air quality in subway stations and access tunnels can be poor, although the amount of information available remains rather limited and piecemeal in character. Physical measurements frequently consider only one aerosol size fraction, sampling campaigns may be limited in time and place, and chemical analyses are usually partial and/or small in number. One aim of the IMPROVE LIFE project is to bring together all information published in different cities across the world over the last 20 years, identify the main pollution sources, and ascertain just where we are in our understanding of the subject. The understanding and conclusions reached from this initial state-of-the-art overview of the problem will then be applied to the underground rail system in Barcelona.

The Barcelona Metro

Barcelona has a particularly interesting subway system from an air quality viewpoint. Like all such systems it carries a large proportion of the daily commute (around 1.25 million people), but there are striking variations between different lines. Of special interest are the new, technologically advanced lines where a screen door system separates platform from tunnel air and where sophisticated ventilation systems control airflow. This platform screen door system is being increasingly introduced in cities worldwide and can have an enormous impact on PM loading breathed on platforms. The new, closed platforms have a ventilation system that channels the convective dynamics caused by the train approach to renew the air throughout lateral ventilation outlets. This system allows air renovation in the platform, but also produces convective dynamics in the tunnel that may cause the resuspension of tunnel dust and the subsequent arrival of this dust into the platforms. The advanced nature of this system can be contrasted with the more traditional technology of the older lines in Barcelona, built progressively since 1924 and themselves each with their own design characteristics. Trains from all lines are equipped with an efficient air conditioning system that work continuously throughout the year, but with higher intensity in the summer period, so that indoor carriage air quality varies depending on the time of the year.

Barcelona: a world leader in subway air quality

The investment of European money in our IMPROVE LIFE subway project will allow us to project Barcelona as a world leader in subway air quality. Our study will test and practice measures that can reduce PM concentrations in platforms and inside trains, taking into account variations in all the key factors such as station depth, date of construction, station design, type of ventilation, types of brakes used on the trains, train frequency and the presence or absence of platform screen door systems. We will prioritise cost-effective and energetically green air pollution mitigation strategies, and produce a Strategic Plan designed to reduce air contamination in subway systems worldwide.

CSIC and TMB: working together

The IMPROVE LIFE metro study necessitates a positive working relationship between the scientists of CSIC and the local transport authority TMB. Working closely together, these two groups have generated a successful research proposal recognized by the European Union as unusually promising and innovative. All information obtained during the various sampling campaigns will be shared openly by CSIC and TMB with the aim of improving air quality where needed. Using media such as television and radio, both partners will promote a better awareness of city air quality in staff, passengers and the general public. The outcomes of the project will be further communicated and promoted by a proactive outreach dissemination programme directly involving relevant transport authorities in European and other cities across the world.