Initiating the magnetic characterization of particulate matter in the Metropolitan Area of São Paulo, Brazil.

Abstract:

The environmental magnetism is showing a growing range of applications in airborne pollution studies. There is a need for the characterization of the magnetic properties of the airborne particles and their potential sources. In the Metropolitan Area of São Paulo (MASP, 4th biggest megacity in the world), Brazil, we had started the characterization of the main protagonist sources in the city: the transport sector. In this study, we characterize the airborne particulate matter (PM) inside and outside of two tunnels in the MASP region. These tunnels have been part of a series of experiments to chemically characterize the vehicular fleet emissions since 2001. The Jânio Quadros Tunnel has exclusively light-duty vehicles, and the Rodoanel 2 Tunnel has both light and heavy-duty vehicles. The sampling took eight days in each tunnel in the period of October-November 2018 (late spring). We used high volume samples (ThermoFisher Scientific, 1130 L/min) to obtain PM in two aerodynamic diameter distribution sizes: 0 – 2.5 μm and 0 – 10 μm. The PM was collected in quartz fiber filters. We made a series of chemical analyses in the filters (X-ray diffraction spectrometry, and mass spectrometry) and magnetic parameters measurements (Low field magnetic susceptibility and ARM spectra). Other analyses as IRM spectra, SIRM, and hysteresis are programmed to be made after the current COVID-19 pandemic. Early results consist of the coercivity spectra (up to 1000 oe) and king plot (Fig. 1). The weekly variation of the fleet traffic is visible in the susceptibility. We found three coercivity populations with peaks in 60, 300, and 600 oe. This study is the beginning of a series of magnetic source characterizations in the MASP. The upcoming phases will consist in the analysis of in-lab vehicular emissions, soil dust resuspension, local cooking methods, and an extensive ambient air sampling, These measurements are part of the SOPRO (Chemical and toxicological SOurce PROfiling of particulate matter in urban air) project, a collaboration between Sao Paulo University and Aveiro University (Portugal) funded by Compete2020, FCT/MCTES, and FAPESP.