| 15 Oct 2026
Technical note: Assessing CO2 fluxes over Greece using CTDAS-WRF – A sensitivity analysis
Abstract. CO2 is a key driver of climate change and knowledge of its emissions is a prerequisite for climate mitigation. CO2 emissions over Greece in 2019 are assessed using a regional atmospheric inversion framework based on the CarbonTracker Data Assimilation Shell coupled with the Weather Research and Forecasting model (CTDAS-WRF). Ground-based CO2 measurements from an urban background site (Thissio), a regional background site (Finokalia), and a high-altitude station (Helmos), together with satellite-derived column-averaged CO2 observations from OCO-2, are assimilated to optimize CO2 emissions by allowing 50 % of uncertainty on CAMS anthropogenic CO2 emissions. Biospheric and fire fluxes are kept fixed. Sensitivity tests of localization length and anthropogenic emissions uncertainty assess parameter choices and results robustness. For 600 km localization, annual posterior anthropogenic emissions over Greece are 55.6 ± 1.9 Mt, close to CAMS prior (55.0 Mt) and below EDGAR (61.5 Mt) and Greece's reported total (65.7 Mt). The corresponding total CO2 net flux over Greece is 118.3 ± 1.9 Mt. Since natural fluxes are not optimized, inferred adjustments cannot be attributed solely to anthropogenic emissions. Optimization reduces mean model bias by 80 % and RMSE by about 40 % at Thissio. This study demonstrates a CTDAS-WRF framework for regions with strong mesoscale variability and complex airflow. Urban background observations strongly reduce emission uncertainty around Athens, while regional background observations inform long-range transport and have less effect on local emission inversions. Denser observation network is therefore needed covering major local emission sources. Future work should optimize anthropogenic emissions jointly with biospheric and fire fluxes.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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