Monitoring and modeling seasonally varying anthropogenic and biogenic CO₂ over a large tropical metropolitan area

Abstract. Atmospheric CO₂ concentrations over urban areas indirectly reflect local fossil fuel emissions and biogenic fluxes, offering a potential approach to assess city climate policies. However, atmospheric models used to simulate urban CO₂ plumes face significant uncertainties, particularly in complex urban environments with dense populations and vegetation. This study aims to address these challenges and fill the research gap regarding such vegetated and urbanized areas by conducting a comprehensive analysis of atmospheric CO₂ dynamics in the Metropolitan Area of São Paulo, Brazil, and its surroundings, using the WRF-GHG atmospheric model. The simulations are evaluated using observations from ground stations collected across the METROCLIMA GHG network, the first greenhouse gas monitoring network in South America, and column concentrations (XCO₂) from the OCO-2 satellite spanning February to August 2019. We also assess and improve the performances of the biospheric model Vegetation Photosynthesis and Respiration Model (VPRM) by optimizing the model parameters of the dominant vegetation types (Atlantic forest, cerrado, sugarcane) using flux measurements from multiple eddy-covariance flux towers. We evaluate the atmospheric model's ability to replicate seasonal variations in CO₂ concentrations by comparing the simulations with measurements from two sites part of the GHG network in São Paulo. We conclude here that atmospheric concentrations over metropolitan areas located in tropical areas largely depend on our ability to represent the biogenic contribution from the surrounding vegetation, the large-scale contribution in global models, and the model’s ability to represent the local atmospheric dynamics.