Thesis defense
Student: Rafaela Cruz Alvez Alberti
Program: Meteorology
Title: "Dynamics of CO2 Concentration in the Metropolitan Area of São Paulo"
Advisor: Profa. Dra. Rita Yuri Ynoue
Judging Committee
- Profa. Dra. Rita Yuri Ynoue – Presidente e Orientadora - IAG/USP
- Profa. Dra. Maria de Fátima Andrade - IAG/USP
- Prof. Dr. Thomas Lauvaux - University of Reims Champagne Ardenne
- Dr. Angel Liduvino Vara Vela – IF/USP
- Dra. Alba Badia Moragas - Barcelona Supercomputing Center
Abstract:
This study investigated the atmospheric concentrations of carbon dioxide (CO2) in the Metropolitan Region of São Paulo (MASP) and its surroundings, using the Weather Research and Forecasting model coupled with the greenhouse gas module (WRF-GHG). The primary objective was to quantify anthropogenic emissions and biogenic fluxes, as well as to understand the spatial and temporal dynamics of CO2 in one of the largest and most complex urban areas in Latin America. Biogenic fluxes were simulated using the Vegetation Photosynthesis and Respiration Model (VPRM), with optimized parameters to represent tropical ecosystems (Atlantic Forest, Cerrado, and sugarcane) based on local flux tower data. Parameter optimization significantly improved the representation of CO2 fluxes for the Cerrado and sugarcane ecosystems, capturing seasonal dynamics such as higher CO2 uptake during the rainy season. However, the model faced challenges in representing the Atlantic Forest. The simulated net fluxes for the Atlantic Forest showed that this biome may be a source of CO2, rather than a sink. In some periods, this overestimation overshadowed the productivity of this ecosystem, highlighting the need for advanced methods to improve flux estimations. CO2 simulations using WRF-GHG, integrating biogenic fluxes and anthropogenic emissions, captured distinct seasonal and diurnal patterns. At the urban site (IAG), the model underestimated CO2 concentrations, showing a negative bias due to the complexity of dense vehicular traffic emissions. In contrast, at the vegetated and elevated site (PDJ), the simulations showed excellent agreement with observational data, with very small positive biases. These results highlight the model’s ability to reproduce CO2 dynamics in less urbanized areas influenced more by atmospheric mixing and regional transport processes. Seasonality analyses showed higher CO2 concentrations in winter, associated with greater atmospheric stability and less uptake from vegetation, particularly in August. In summer, lower atmospheric stability, higher wind speeds, and humidity contributed to lower concentrations, as well as higher agricultural productivity, absorbing CO2 from the atmosphere. Furthermore, the comparison between biogenic and anthropogenic scenarios demonstrated the contributions of both fluxes to CO2 dynamics in MASP, emphasizing the importance of incorporating combined emissions into atmospheric models. As the first evaluation of CO2 dynamics in São Paulo, this study provides an essential foundation to understand the complex interactions between biogenic fluxes, anthropogenic emissions, topography, and meteorology in the largest urban area in South America.
Keywords: CO2 concentration, biogenic fluxes, WRF-GHG, VPRM