Background Commuting by underground rail is a daily activity for over one hundred million people worldwide. In Europe alone, more than 60 cities use underground rail to facilitate commuter movement. With average return journey times lasting around one hour, these underground commuters can routinely be exposed to inhalable particulate matter (PM) levels that are higher than the normal legal limits for outdoor air quality in European cities (50 μg/m3 mean PM10 (PM Moreover, when compared to outdoor air, subway air is not only overly-rich in iron but can also contain high levels of trace metals such as Mn, Cr, Cu, Ni and Zn, as well as the toxic metalloids, Sb and As. The physical form of these metalliferous micro-particles is typically highly angular, with abundant fresh fracture surfaces available for bio-molecular interaction. Such a metalliferous cocktail, especially given the high mass loadings being breathed, is likely to be unusually bio-reactive. From an environmental perspective, the subway system is relatively clean, with low emission electric trains and moving large numbers of passengers, which promotes less traffic congestion on the surface. However, in terms of air quality and personal exposure, breathing subway air is likely to present a greater respiratory health risk to the regular commuter. Objectives The overall aim of IMPROVE LIFE is to provide a benchmark study that will lead to real improvement in subway air quality. The project will be carried out in Barcelona, where the main pollutant sources will be identified in order to inform the prioritisation of cost-effective and low energy air pollution mitigation strategies. The project will work with public transport authorities in the city, to improve their awareness of air quality and encourage them to develop best practice policies for improving underground atmospheric conditions. The project’s specific objectives include: Determining emission sources and their contribution to air pollution in both platforms and trains, identifying those that have a potentially higher health risk; Evaluating the effect of air quality mitigation measures already used in other subway systems worldwide (such as different types of break pad compositions, air filters, platform designs, as well as monitoring techniques, etc..); Developing proposals for helping local/national authorities to implement effective air mitigation measures in subway systems; Assisting Barcelona’s local transport services to implement a Strategic Plan designed to reduce air contamination in subways; Acting as a catalyst for the allocation of local/national funds, allowing for the implementation of air improvement strategies. Expected results: Outcomes will include: A comprehensive database, identifying the main air pollution sources in both platforms and trains in underground transport systems worldwide, indicating which present potentially higher health risks to commuters, especially with respect to their chemical composition; An evaluation of the effect of air quality mitigation measures already used in some subway systems worldwide; New protocols for helping local and national authorities to achieve effective air pollution mitigation strategies for subway systems. The protocols will be tested through their real-time application in the Barcelona subway system under variable controlled conditions on both platforms and inside trains. These protocols will be made available in technical guides and reports, and widely distributed to promote and encourage effective mitigation strategies at both national and European level.