In-train particulate matter (PM₁₀ and PM_2.5) concentrations: Level, source, composition, mitigation measures and health risk effect – A systematic literature review

<jats:p> Exposure of commuters to pollutants on trains has been an essential topic of discussion in recent years due to its health implications. This review summarizes literature that measures particulate matter (PM) in trains to understand the concentration levels and health effects caused due to exposure. The databases searched were Scopus, Web of Science (WOS) and Google Scholar. Articles, conference papers and textbooks written in English, measuring PM in train carriages and published between 1998 and 2022 were selected for this review. Out of the 3247 articles identified, only 73 were included in this study. 15/20 articles agreed that concentration is significant at the underground segment by a factor of 7 than the counterpart above/ground levels. The review observed that 80% of the publication of in-train concentrations of PM<jats:sub>10</jats:sub> and PM<jats:sub>2.5</jats:sub> were above the WHO standard. In-train PM<jats:sub>2.5</jats:sub> concentration ranges from 2 μgm<jats:sup>−3</jats:sup> to 563 μgm<jats:sup>−3</jats:sup>, and in-train PM<jats:sub>10</jats:sub> concentration ranges from 6 μgm<jats:sup>−3</jats:sup> to 997 μgm<jats:sup>−3</jats:sup>. People’s activities, mechanical movement of train parts, train operation conditions and local emissions were the primary source of PM. Future research should focus on health damage due to PM exposure and the effect of the filtration system on PM levels in trains. </jats:p>