Abstract: Magnetic analyses offer a valuable avenue for obtaining physical and chemical information not typically provided by standard air pollution analyses. In a series of works conducted inside tunnels in São Paulo, we aimed to chemically characterize particulate matter emissions from the vehicular fleet. Alongside chemical analyses, we also conducted magnetic characterizations on the same samples used in the research. This study delved into the correlation between magnetic data and chemical data, aiming to bridge interpretative gaps between particulate matter characteristics and magnetic parameters. Our findings revealed that specific magnetic parameters respond to brake and tire wear, enabling the effective distinction between exhaust and non-exhaust emissions in tunnel experiments. Additionally, we identified two primary magnetic particle populations—one associated with vehicular emissions and the other indicative of urban background. The ratio between these populations holds promise for source apportionment applications. Lastly, our investigation shed light on an iron discrepancy within one of the tunnels, potentially resolving an open question in the article series. Acknowledgements: The authors would like to thank the Wellcome Trust program and Yale University for the grant n° UNS81697. This work was part of the “Chemical and toxicological SOurce PROfiling” of particulate matter in urban air project (SOPRO, Grant no. POCI-01-0145-FEDER-029574), supported by the Portuguese Foundation for Science and Technology from the Ministry of Science, Technology, and Higher Education (FCT/MCTES), and by the São Paulo Research Foundation (FAPESP; Grant #2018/07848-9). SOPRO project is also funded by FEDER, through COMPETE2020—Programa Operacional Competitividade e Internacionalização (POCI), and by national funds (OE), through FCT/MCTES. The authors were also supported by FAPESP for Grants #2016/18438-0 (Metroclima project, for research resources) and #2019/01316-8 (URBESP project, scholarship); the Brazilian National Council for Scientific and Technological Development (CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico), CNPq Research Productivity Fellowship and Scholarship grants #165393/2020-3, #301503/2018-4, #303891/2018-1, and #167722/2018-2; and the Klimapolis Joint Project. The authors are grateful to the São Paulo state Companhia de Engenharia de Tráfego (CET, Department of Transportation) and CCR RodoAnel for the provided support during the sampling campaigns and would also like to thank Rosana Astolfo for her support during the tunnel campaigns. Ana Vicente is subsidized by national funds (OE), through FCT, I.P., in the framework contract foreseen in the article 23 (n°s 4, 5, and 6) of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. We are also grateful for the support to CESAM by FCT/MCTES (UIDP/50017/2020+UIDB/50017/2020+LA/P/0094/2020) through national funds, and co-funding by FEDER, within the PT2020 Partnership Agreement and Compete 2020. Finally, the authors thank the Geoanalítica-USP Core Facility, as well as the staff of the Instituto de Geociências-USP for their support in ICP-MS analysis.

Keywords: Alternative analysis, Environmental Magnetism, Tunnel experiment, Vehicular emissions, Particulate Matter.