Towards traceability in CO2 line strength measurements by TDLAS at 2.7 µm

- Line strengths of the P36e and P34e lines in the 2.7 µm ν1+ν3 CO2 band were measured.
- GUM-compliant uncertainties of 1-1.3% have been determined.
- Line strengths uncertainties reduced by a factor of two compared to literature.
- Traceability of the results has been addressed.

Direct tunable diode laser absorption spectroscopy (TDLAS) was combined in this study with metrological principles on the determination of uncertainties to measure the line strengths of the P36e and P34e line of 12C16O2 in the ν1+ν3 band at 2.7 µm. Special emphasis was put on traceability and a concise, well-documented uncertainty assessment. We have quantitatively analyzed the uncertainty contributions of different experimental parameters to the uncertainty of the line strength. Establishment of the wavenumber axis and the gas handling procedure proved to be the two major contributors to the final uncertainty. The obtained line strengths at 296 K are 1.593×10-20 cm/molecule for the P36e and 1.981×10-20 cm/molecule for the P34e line, with relative expanded uncertainties of 1.1% and 1.3%, respectively (k=2, corresponding to a 95% confidence level). The measured line strength values are in agreement with literature data (line strengths listed in the HITRAN and GEISA databases), but show an uncertainty, which is at least a factor of 2 lower.