Carbon dioxide (CO₂) is the greenhouse gas with the largest contribution to global warming. New initiatives to measure emissions and assess the impact of mitigation policies foresee an increase in the number of in situ monitoring sites, and consequently an increased requirement for CO₂ in air calibration standards. A newly developed facility at the BIPM Headquarters will allow National Metrology Institutes around the world to demonstrate consistency of their standards and enable uniformity in emission measurements and calculations.

The facility, described in the Metrologia paper, is based on pressure, volume and temperature measurements of CO₂ in air and cryogenically extracted CO₂. Use of the facility enables the determination and comparison of amount fraction (concentration) values with those of gas cylinder standards. It can operate over a wide range of CO₂ concentrations, from those found in background “clean” air to urban sites. The facility was developed by scientists at the BIPM Headquarters together with visiting scientists from the NIST (USA) and RISE (Sweden).