Atmospheric CO2 monitoring over a large tropical metropolitan area: fossil fuel and biogenic CO2 fluxes over the Sao Paulo Metropolitan Area

Sao Paulo Metropolitan Area, with 39 municipalities and a population of about 22 million inhabitants, aims to reach carbon neutrality by 2050. More than half of its population resides in Sao Paulo city, which, in 2018, was responsible for emitting nearly 18 million tons of CO2 equivalent. Two high-accuracy CO2 sensors have been deployed (Picarro CRDS analyzers)  from the first conventional in situ measurement network installed in South America for GHG monitoring.  The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem V4.0) with a modified version of the greenhouse gas chemistry module (WRF-GHG) was used to simulate the transport of the mole fraction of carbon dioxide (CO2) at a horizontal resolution of 3 km in the São Paulo Metropolitan Area during August 2020. Biogenic CO2 fluxes were simulated using an improved version of the “Vegetation Photosynthesis and Respiration Model” (VPRM) (Mahadevan et al., 2008) included offline in WRF-GHG. The VPRM parameters were optimized using flux tower data (Net Ecosystem Exchange) for the three main vegetation types in the area (Atlantic Forest, Sugarcane, and Cerrado). Anthropogenic CO2 emissions were simulated with the vehicle emission model VEIN (Ibarra et al., 2018) combined with industrial emissions from EDGAR (Crippa et al., 2020) and ODIAC (Oda et al., 2018). The initial and lateral boundary conditions (IC-BCs) were imported from CAMS and from CARBON-TRACKER global reanalysis for greenhouse gases.

The simulated CO2 concentrations from the WRF-GHG model captured both day-to-day and diurnal variations compared to in situ observations in suburban and urban areas (Pico do Jaraguá and IAG). We examined the magnitude of the fossil fuel contribution compared to biogenic signals across the domain, and the anthropogenic signals are heavily influenced by local and nearby sources and sinks. Additionally, the signal includes respiration from vegetation that is carried by winds from vegetation regions.

 We conducted a long-term analysis of CO2 concentration measurements at the two stations (2019-2022) to determine the seasonality and its relationship with both flux variability and local circulation. Finally, we estimated CO2 concentration gradients from three additional measurement stations around the Sao Paulo metropolitan area to assess the potential of our future urban atmospheric inversion system.