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Graphical abstract Highlights • Particulate pollution was evaluated both inside and outside of public rapid transits. • No systematic air quality gains could be attributed to public rapid transit systems. • Air quality at the users' scale depended on the indoor accumulation of outdoor pollution and in-vehicle PM generation. • Enforcing standards does not ensure a reduced lung accumulation, and vice versa. • In densely trafficked areas, it is preferable for pedestrians to use the available public transport system. Abstract Airborne particulate matter (PM) and particle-bound polycyclic aromatic hydrocarbons (PAHp) were monitored both inside and outside of a tramway and two types of high-level service buses within a major French conurbation. The air quality variations among tramway and the different bus rapid transit systems were large and significant. This proved to be a complex issue involving contamination and clearance processes, as evidenced by mechanisms like in-vehicle PM generation and indoor accumulation of the outdoor PAHp pollution. Given these empirical results, a simple lung-accumulation model has been formulated in order to estimate the public transport users' (PTU) exposure during their journey. Calculations draw attention to situations and categories of individuals to be targeted by clean air policies. For instance, despite being chronically exposed to excessive concentrations in heavily built-up and trafficked areas, PTU would accumulate in their lungs 4–11 times less PM and PAHp than nearby pedestrians walking the same route. These pedestrians are more likely to experience short episodes of strong lung accumulations. Moreover, the numerical approach employed herein allowed: (i) estimating a distance at which walking could be considered a viable alternative to the use of public transport services; (ii) probing the relevance (in terms of lung accumulations) of both EU and US standards; and (iii) proposing exposure reduction strategies. [ABSTRACT FROM AUTHOR]