The COllaborative Carbon Column Observing Network (COCCON) quality management.

Year after year, the effects of climate change are more dramatic and evident, and it is no longer possible to hide them, which requires immediate action against anthropogenic emissions of greenhouse gases (GHGs) in Earth’s atmosphere, mainly carbon dioxide (CO2) and methane (CH4). The scientific community plays an important role in continuously developing and improving current instrumentation and methods, which enable high-resolution measurements to monitor, track, quantify, and verify the concentration and emissions of GHGs in the atmosphere. Measuring GHGs with high accuracy in the atmosphere is challenging, but achieving measurements with global coverage is even more demanding, and only satellites can provide such data sets. However, they require ground-based column-integrating measurements for validation. For this purpose, the Total Carbon Column Observing Network (TCCON) was created; however, due to its high operational costs and the need for trained expertise on-site, the number of sites is limited (~ 26). Moreover, these stations are stationary, so performing observations of selected GHG source regions with several spectrometers is impossible. The COllaborative Carbon Column Observing Network (COCCON) was initiated to overcome these limitations and to supplement the existing TCCON stations. The standard instrument used by COCCON is the portable FTIR spectrometer EM27/SUN, developed by KIT in cooperation with Bruker Optics from 2011 onwards. Although this instrument has a lower spectral resolution (0.5 cm-1) in comparison to the TCCON instrument (0.002 cm-1), it delivers XCO2, XCH4, XH2O, and XCO with sufficient quality to complement TCCON satellite validation efforts. COCCON data are tied to the trace gas scale as realized by the TCCON reference. COCOON ensures a high degree of internal consistency across the participating spectrometers, defines common standards for data processing, and performs quality assurance checks on individual spectrometers to ensure the quality of the network. The services of COCCON are enabled by ESA support. Meanwhile, one hundred twenty spectrometers have been optimized and characterized by the centralized testing facility operated at KIT, and many more units are expected to be commissioned in the months ahead. This contribution presents the current status of the activities of the central QA/QC facility: methods, results, and foreseen improvements.