Investigating the Benefits of Large-Eddy Simulation for Simulating Urban CO2 Emissions Using WRF-LES Over the Paris Area

Urban areas are significant contributors to global CO₂ emissions, and simulating CO₂ dispersion in these regions, especially near emission hotspots, presents considerable challenges due to the complex dynamics at small scales. High-resolution simulations are crucial for accurately capturing the dispersion of CO₂ in urban environments. As part of the Carbon Atmospheric Tracer Research to Improve Numerics and Evaluation (CATRINE) project, this study employs the Weather Research and Forecasting model with the Large-Eddy Simulation mode (WRF-LES) to simulate CO₂ concentrations over the Paris area, aiming to improve plume simulation accuracy. The study evaluates the model's performance in urban environments and investigates the added value of LES by comparing simulation results with those from mesoscale configurations. A series of simulations using five nested domains, with resolutions ranging from 8.1 km to 100 m, were performed to examine the sensitivity of plume structures to model resolution. The study also investigates the propagation of errors when running a pseudo-data CO₂ inversion using high-resolution 100-m resolution WRF outputs to generate data, but inverting using lower resolution simulations (300-m and 900-m resolutions). The focus is on understanding how resolution influences inversion model results and quantifying aggregation errors introduced when aggregating higher-resolution outputs to coarser resolutions. 

Preliminary findings emphasize the advantages of LES in capturing complex plume features, reducing numerical diffusion, and producing more concentrated, well-defined CO₂ plumes. Resolution intercomparisons highlight that higher resolutions better capture sharp concentration gradients, localized dispersion patterns, significantly outperforming traditional mesoscale models. Additionally, WRF model outputs were validated against observations from various sources, including the Paris Mid-cost CO₂ sensor network, total column of CO₂ measurements from EM27 and Total Carbon Column Observing Network (TCCON), and wind LIDAR data from six stations across Paris and Île-de-France, collected during the URBISPHERE project. Future studies will extend this research to other urban cities, utilizing different LES models such as WRF-LES, Micro-HH, and Parallelized Large-Eddy Simulation Model (PALM). Intercomparing these models will provide performance metrics on model resolution when assimilating complex urban plumes combining multiple diffuse sources and point sources, thereby further refining the accuracy of CO₂ dispersion models for urban emissions monitoring and climate mitigation strategies.