A brief overview of CO2 scales for supporting atmospheric monitoring of carbon dioxide (CO2) at remote and urban areas

Carbon dioxide (CO₂) is a major greenhouse gas that significantly contributes to climate change. Atmospheric CO₂ concentrations are closely linked to human activities such as fossil fuel combustion, deforestation, and industrial processes. Precise and consistent atmospheric measurement of CO₂ concentrations is crucial for verifying global and national greenhouse gas emissions, particularly in the context of climate change mitigation. Both global and national greenhouse gas initiatives have been launched to enhance atmospheric greenhouse gas monitoring sites, improving the understanding of the impact of climate change mitigation actions. These efforts have led to an increased demand for CO₂ reference materials. The National Oceanic and Atmospheric Administration, designated as a Central Calibration Laboratory by the World Meteorological Organization (WMO), maintains and disseminates the WMO CO₂ scale (i.e., reference measurement standard) to atmospheric monitoring sites within the WMO Global Atmospheric Watch programme. National metrology institutes including the Korea Research Institute of Standards and Science (KRISS) are developing their own CO₂ scale to meet the growing demand for CO₂ reference materials. This paper provides a brief overview of the WMO CO₂ scale, the activities of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology, Gas Analysis Working Group Task Group, and the development and establishment of the KRISS CO₂ scale.