Abstract: In most Latin American metropolises, the largest source of pollutant emissions is the vehicle fleet. Atmospheric concentrations of primary pollutants emitted by vehicular exhaust have been reduced after the enforcement of emission control laws, although some pollutant levels are still above the values recommended by the World Health Organization (WHO). An extensive monitoring has been performed with the measurement of particulate matter in the Faculty of Medicine of the University of São Paulo, located in the central area of São Paulo (Brazil), since 2021, allowing us to observe the effects of the changes in the fleet circulating in the city. Fine particulate matter (PM2.5) was collected with low-volume samplers (Low-Vol) and then subjected to analysis with an XRF (X-ray fluorescence) spectrometer to determine element concentrations. Black carbon (BC) was monitored with an aethalometer and biomass burning-related BC was estimated. Sugar compounds are being quantified, after aqueous extraction and analysis with high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC). PM2.5 concentrations increased with northeast winds, where the central area of São Paulo is located, with intense vehicle traffic. The most abundant elements in PM2.5 between 2021 and 2022 were S, Na, K, Fe, Si, Zn, and Al. The profile is similar to a previous study performed in the same sampling site when an abundance of Al, K, Fe, and Ca was observed in PM2.5. The high abundance of sulfur is associated with the presence of secondarily formed sulfate – in the aerosol and elements such as Si, Al, and K may have crustal origin. In addition to marine aerosol, sodium has already been linked to resuspension associated with paving, vehicular emissions and, specifically, the combustion of ethanol and gasohol. Potassium may also be associated with biomass burning and marine aerosol. The element Fe has already been associated with emissions from vehicles powered by ethanol and gasohol, widely used in Brazil, and is also related to crustal sources. Receptor model Positive Matrix Factorization (PMF) was applied and five factors were obtained for the period between 2021 and 2022. Adding the sources related to vehicle emissions, such as vehicle exhaust, non-exhaust, secondary formation and lubricating oil, and lubricating oil exhaust, it is possible to observe that it represents the majority of the contribution for fine particulate matter in the city (above 60%), while the other sources were biomass burning + soil resuspension and marine aerosol. Vehicular-related sources remain a dominant source after the pandemic lockdown period and are associated with the high particulate matter levels measured in the site.

Keywords: Particulate matter, source apportionment, receptor model, positive matrix factorization, black carbon.