International comparison CCQM-K84—carbon monoxide in synthetic air at ambient level

Abstract

Carbon monoxide (CO) is reported to mainly be emitted from industries, transportation, and burnings for various usages. Its atmospheric lifetime varies from weeks to months, depending on the mixing ratio of the highly reactive hydroxyl radical. Even though the ambient level of CO varies as a function of regional sources, the mixing ratio ranges from 30 nmol/mol to 300 nmol/mol at the marine boundary layers and from 100 nmol/mol to more than 500 nmol/mol in urban areas(1). In order to study temporal trends and regional variations of the level of CO, the National Oceanic & Atmospheric Administration/Earth System Research Laboratory-Global Monitoring Division (NOAA/ESRL-GMD(2)) has played a key role as the designated Central Calibration Laboratory (CCL) within the frame of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) program. NOAA/ESRL-GMD provides natural air standards, analyzed for CO, to WMO GAW participants. Since the structure of WMO traceability chain appears hierarchical and explicit all over the world, WMO intends to improve the CO measurement compatibility to up to 2 ppb (in case of extensive compatibility goal: 5 ppb, GAW report No. 213(3)) in order to ensure compatibility through the GAW network. Nevertheless, accurate measurement of CO at an ambient level has proven to be difficult due to the lack of stability in cylinders. For these reasons, it is necessary that measured results are compared among the values assigned by various NMIs.This key comparison was initially proposed to be aimed at a CO/N2 standard in the 2010 CCQM meeting by KRISS. With participation of FMI, NOAA, and Empa, a modified scheme of CO/air standards was developed for the purpose of atmospheric observations and co-operative support to WMO/GAW activities. Therefore, the purpose of the comparison is to support the measurement capability of CO at an ambient level of 350 nmol/mol. Further, this key comparison is expected to contribute to the establishment of traceability to a single scale of CO between NMIs by means of harmonizing the results from different national standards. The Empa result lies in a different report.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).