Air quality at metro platforms is influenced by train‑induced particle resuspension, abrasion processes, and complex airflow patterns. Within the Horizon Europe project AeroSolfd, we assessed how filtration solutions and optimized purifier placement can reduce PM exposure in semi‑enclosed underground stations. CFD simulations were applied to identify zones of high particle concentration and guide the placement of air purifiers, followed by a month‑long demonstration at a Lisbon metro station using both scientific‑grade instruments and distributed low‑cost sensors.

The AeroSolfd measurements confirmed two characteristic PM zones predicted by CFD: an HVAC‑supported cleaner zone and a high‑exposure zone where the ventilation system has limited effect. Scientific grade instruments were placed in one location, while low‑cost sensors enabled detailed spatial mapping. To compare similar use cases with and without air filtration, a detailed test plan was developed and optimized during the campaign. Duration of one operation mode could be one full day, half a day or two hours thereby also accounting for weekdays and weekends or holidays.

We will present results of the data analysis, show the challenges of measuring particle concentrations at metro stations, and discuss in detail the consequences of different approaches for data analysis to obtain solid values for evaluating filtration efficiency. The study shows that care must be taken in attempting to correct measurements from different devices. The results demonstrate the potential of well-placed air purifiers and hybrid operation with a stationary HVAC system to improve air quality at the platform.