Source apportionment and ecotoxicity of particulate pollution events in a Major Southern Hemisphere Megacity: influence of biomass burning and a biofuel impacted fleet

Abstract. The Metropolitan Area of São Paulo (MASP) in Brazil has reduced its vehicular emissions in the last decades. However, it is still affected by air pollution events, mainly in the winter, characterized as a dry season. The chemical composition of fine particulate matter (PM_2.5) was studied in the MASP during a 100-day dry period in 2019. PM_2.5 samples underwent an extensive chemical characterization (including inorganic and organic species), and submicrometer particle number size distributions were simultaneously monitored. PM_2.5 concentrations exceeded the new World Health Organization's daily guidelines on 75% of sampling days, emphasizing the need for strengthening local regulations. Source apportionment (Positive Matrix Factorization, PMF5.0) was performed, and the sources related to vehicular emissions remain dominant (over 60% of PM_2.5). A high contribution of biomass burning was observed, reaching 25% of PM_2.5 mass and correlated with sample ecotoxicity. This input was associated with north and northwest winds, suggesting other emerging sources besides sugarcane burning (forest fires and sugarcane bagasse power plants). A mixed factor of road dust and vehicular emissions increased throughout the campaign was related to stronger winds, suggesting a significant resuspension. The sulfate secondary formation was related to humid conditions. Additionally, monitoring size particle distribution allowed the observation of particle growth on days impacted by secondary formation. The results pointed out that control measures of high PM_2.5 events should include the control of emerging biomass burning sources in addition to stricter rules concerning vehicular emissions.