Carbon dioxide plume dispersion simulated at hectometer scale using DALES: model formulation and observational evaluation

Abstract. Developing effective global strategies for climate mitigation requires an independent assessment of green-house gas emission inventory at the urban scale. In the framework of the Dutch Ruisdael Observatory infrastructure project, we have enhanced the Dutch Large-Eddy Simulation (DALES) model to simulate carbon dioxide (CO₂) plume emission and three-dimensional dispersion within the turbulent boundary layer. The unique ability to explicitly resolve turbulent structures at the hectometer resolution (100 m) makes DALES particularly suitable for detailed realistic simulations of both singular high-emitting point sources and urban emissions, aligning with the goals of Ruisdael Observatory. The model setup involves a high-resolution simulation (100 m × 100 m) covering the main urban area of the Netherlands (51.5°–52.5° N, 3.75°–6.45° E). The model integrates meteorological forcing from the HARMONIE-AROME weather forecasting model, background CO₂ levels from the CAMS reanalysis, as well as point source emissions and downscaled area emissions derived from 1 km × 1 km emission inventory from the national registry. The latter are prepared using a sector-specific downscaling workflow, covering major emission categories. Biogenic CO₂ exchanges from grasslands and forests are interactively included in the hectometer calculations within the heterogeneous land-surface model of DALES. Our evaluation strategy is twofold, comparing DALES simulations with: (i) the state-of-the art LOTOS-EUROS model simulations and (ii) in-situ Cabauw tower measurements and Ruisdael surface observations of the urban background in the Rotterdam area at Westmaas and Slufter. Our comprehensive statistical analysis confirmed the effectiveness of DALES in modeling the urban-scale CO₂ emission distribution and plume dispersion under turbulent conditions, but also revealed potential limitations and areas for further improvement. Thus, our new model framework provides valuable insights into emission transport and dispersion of CO₂, in support of emission uncertainty reduction using atmospheric measurements and the development of effective climate policies.