A high-resolution urban CO ₂ transport model with anthropogenic and biogenic fluxes

Abstract. We develop PALM-CO2, a high-resolution urban carbon dioxide transport model with anthropogenic and biogenic carbon emissions. The PALM-CO2 model is implemented within the open-source urban-flow large-eddy simulation (LES) model PALM. Anthropogenic CO2 emissions are prescribed using an external emission inventory, while biogenic CO2 fluxes are computed online using the Vegetation Photosynthesis and Respiration Model (VPRM). In addition, custom output modules are developed to diagnose carbon fluxes. PALM-CO2 is validated through a case study in London, comprising an 8 by 8 km2 domain covering the borough of Camden at a resolution of 10 m. Simulations are driven by reanalysis meteorological forcing and background CO2 concentrations, while the hourly anthropogenic emissions at 10 m resolution are explicitly derived in this study. Validation against eddy-covariance flux measurements within the study region confirms that the model captures the diurnal variation of turbulent transport and anthropogenic emissions. The biogenic flux module is evaluated independently using observed monthly diurnal profiles of biogenic CO2 fluxes from a deciduous forest site in the Czech Republic. The comparison shows that the model captures realistic seasonal and diurnal variations in ecosystem carbon exchange. Analysis of the London simulations reveals strong spatial heterogeneity in near-surface CO2 concentrations arising from the interaction of building-induced turbulence, diurnal boundary-layer evolution, and emission patterns. PALM-CO2 provides a high-resolution framework for investigating CO2 transport processes in complex urban and vegetated environments, providing improved quantification of urban emission sources.