Abstract
Abstract. The Integrated Carbon Observation System Atmosphere Thematic Centre (ICOS ATC) automatically processes atmospheric greenhouse gases mole fractions of data coming from sites of the ICOS network. Daily transferred raw data files are automatically processed and archived. Data are stored in the ICOS atmospheric database, the backbone of the system, which has been developed with an emphasis on the traceability of the data processing. Many data products, updated daily, explore the data through different angles to support the quality control of the dataset performed by the principal operators in charge of the instruments. The automatic processing includes calibration and water vapor corrections as described in the paper. The mole fractions calculated in near-real time (NRT) are automatically revaluated as soon as a new instrument calibration is processed or when the station supervisors perform quality control. By analyzing data from 11 sites, we determined that the average calibration corrections are equal to 1.7 ± 0.3 µmol mol−1 for CO2 and 2.8 ± 3 nmol mol−1 for CH4. These biases are important to correct to avoid artificial gradients between stations that could lead to error in flux estimates when using atmospheric inversion techniques. We also calculated that the average drift between two successive calibrations separated by 15 days amounts to ±0.05 µmol mol−1 and ±0.7 nmol mol−1 for CO2 and CH4, respectively. Outliers are generally due to errors in the instrument configuration and can be readily detected thanks to the data products provided by the ATC. Several developments are still ongoing to improve the processing, including automated spike detection and calculation of time-varying uncertainties.
Highlights
Rising greenhouse gas (GHG) concentration in the atmosphere is a major source of forcing in the current changing climate (Intergovernmental Panel on Climate Change, 2013)
The provision of atmospheric GHG mole fractions in near-real time (NRT) is useful for early detection of anomalies, whether they are instrumental or geophysical, and data assimilation schemes
As part of the construction of the Integrated Carbon Observation System (ICOS) Atmosphere Thematic Centre (ATC) data center, we have developed a framework for fast delivery (24 h) of the atmospheric greenhouse gases dataset
Summary
Rising greenhouse gas (GHG) concentration in the atmosphere is a major source of forcing in the current changing climate (Intergovernmental Panel on Climate Change, 2013). In ICOS, consolidated data are expected to be produced on a 6-month basis They contain additional data treatment steps ensuring increased precision and confidence in the dataset. These steps include potential correction due to drift in the reference scales used to make the measurements and ”manual visual” inspection of the data to screen for potential problems that are difficult to detect automatically. ICOS atmospheric data are traceable to the Global Atmosphere Watch (WMO/GAW) international reference scales for GHG, and the history of data processing steps is archived. This allows full traceability and transparency of the consolidated dataset, which will be the basis for elaborated products and services. For these species, only cavity ring-down spectroscopy (CRDS) analyzers commercialized by the Picarro company meet the ICOS requirements, but other instruments may be added in the future
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