Measuring 13 C-enriched CO2 in air with a cavity ring-down spectroscopy gas analyser: Evaluation and calibration.

13 C-enrichement in CO2 leads to minor errors in CRDS measurements of x12 CO2 . We propose an empirical correction for measurements of 13 C-enriched CO2 in air by CRDS instruments such as the Picarro G2131-i.