Defense
Student: Caroline Fernanda Hei Wikuats
Program: Meteorologia
Title: “Interação entre composição química, fontes de emissão e potencial oxidativo do MP2,5 no ambiente urbano de São Paulo”
Advisor: Profa. Dra. Maria de Fátima Andrade - IAG/USP
Judging Comitee:
Titular members:
- Profa. Dra. Maria de Fátima Andrade – Presidente e Orientadora - IAG/USP
- Profa. Dra. Nilmara de Oliveira Alves Brito - Institut Pasteur de Lille (por videoconferência)
- Profa. Dra. Pamela Alejandra Dominutti - IGE (por videoconferência)
- Profa. Dra. Rita de Cássia Marques Alves – UFRGS (por videoconferência)
- Profa. Dra. Luciana Varanda Rizzo - IF/USP
Abstract:
Air pollution is one of the most significant current challenges and has been a critical issue for the city of São Paulo, especially concerning particulate matter. The composition and emission sources of fine particulate matter (PM2.5) can influence the severity of its adverse health effects, mainly through oxidative stress, a biological mechanism triggered by an excess of reactive oxygen species (ROS). Oxidative potential (OP), which assesses PM2.5’s capacity to generate ROS and induce oxidative stress, is considered a more robust indicator of its health impacts than mass concentration alone. Thus, this study aimed to estimate the OP of PM2.5 and investigate its relationship with chemical composition and emission sources during a sampling campaign conducted from May 2021 to August 2022 in a densely urbanized area near downtown São Paulo. PM2.5 concentrations were, on average, 55.5% higher in the dry season than in the rainy season, ranging from 9 to 21.1 µg m-3, with episodes of elevated concentrations associated with local sources and the transport of pollutants originating mainly in the north and northeast. Chemical analysis revealed a predominant composition of organic carbon (OC) (50.9%), metals (20.2%), and black carbon (BC) (12.8%). Positive matrix factorization (PMF) identified six major emission sources: secondary aerosols (28.5%), biomass burning (24.3%), resuspended soil dust (15.5%), vehicle exhaust emissions (14.1%), marine aerosols (11.6%), and vehicle non-exhaust emissions (6.2%). OP was evaluated using electron spin resonance (OP-ESR) and dithiothreitol (OP-DTT) assays. Overall, OP values were higher during the dry season, although the seasonal pattern was less pronounced than that observed for PM2.5. Moreover, no correlation was found between OP and PM2.5 mass concentration. Multiple linear regression (MLR) analysis indicated that, contrary to expectations, OP-DTT did not exhibit a strong correlation with OC. On the other hand, OP-ESR was influenced not only by metals but also by the BC from biomass burning (BCBB), suggesting a broader range of oxidative mechanisms. These findings highlight that different OP assays can capture distinct reactive pathways, which vary according to the period and specific characteristics of atmospheric aerosols in the region. Thus, using multiple OP techniques provides a more comprehensive assessment of the oxidative capacity of PM2.5. Vehicle emissions and marine aerosols were the primary contributors to OP throughout the study. However, during an intense biomass burning event, this source accounted for 31.3% of the OP-DTTv. The results reinforce the role of OP as a more sensitive metric of PM2.5-related health impacts than mass concentration alone, being driven by chemical composition and mission sources. Integrating OP into air quality assessments can enhance exposure assessment and improve the understanding of health effects, particularly those linked to oxidative stress. Therefore, regulating emission sources associated with high OP values, such as vehicle emissions and biomass burning, is essential for implementing effective air quality management strategies in São Paulo. Finally, despite time constraints, the pilot study involving kidney cells exposed to PM2.5 shows the importance of investigating the impacts of air pollution on various human organs beyond the well-studied pulmonary effects.
Keywords: fine inhalable particles, oxidative stress, health effects of aerosols, chemical characterization, source apportionment.