The effects of variations in buffer gas mixing ratios on commercial carbon dioxide cavity ring-down spectroscopy sensors

Primary gas standards, gas chromatography, and frequency-stabilized cavity ring-down spectroscopy measurements have been used to assess the effect of variations in the argon mixing ratio on the CO2 mixing ratios reported by commercial cavity ring-down spectroscopy sensors. Supporting calculations demonstrate that the use of argon-free, synthetic air standards can lead to a bias of '0.7μmolmol-1 at atmospheric concentration levels of CO2 as a result of pressure-broadening effects. This bias is an order of magnitude greater than the precision of the best commercial sensors and significantly exceeds the World Meteorological Organization's target compatibility goal. © 2013 American Meteorological Society.