Metrological Traceability in Eddy Covariance Measurements of CO2 Flux

The Eddy Covariance (EC) technique is widely used to quantify carbon dioxide (CO2) fluxes between the atmosphere and terrestrial ecosystems, playing a crucial role in climate research and carbon cycle studies. To maximize the impact and the meaningfulness of these measurements, they have to be comparable in time and space. The reliability and comparability of EC data critically depend on ensuring metrological traceability to SI units through national standards or internationally agreed references by means of rigorous calibration practices.This study examines the traceability chain for key EC components (air temperature and pressure, wind components and CO2 concentration in air), emphasizing calibration processes for gas analyzers. Gas analyzers, which measure CO2 amount fractions, are calibrated using traceable gas mixtures, such as Certified Reference Materials, linked to primary national standards, ensuring accuracy and minimizing biases. We assess the impact of the calibration uncertainty on overall flux estimates and propose a methodology for periodic recalibration of the analysers to account for their drift and response to environmental influences.By establishing robust links to national metrology standards, this work enhances the traceability and reliability of EC data across diverse ecosystems and temporal scales. The outcomes provide a foundation for harmonizing EC networks globally, improving confidence in CO2 flux measurements and their role in shaping evidence-based climate policies. This focus on calibration underscores the importance of metrology in advancing the precision and usefulness of environmental measurements.