Performance of an open-path near-infrared measurement system for measurements of CO₂ and CH₄ during extended field trials

Nicholas M Deutscher (1) , Travis A Naylor (1) , Christopher G R Caldow (1, 2) , Hamish L Mcdougall (1) , Alex G Carter (1) , David W T Griffith (1)

1 CAC - Centre for Atmospheric Chemistry [Wollongong]
2 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]

Open-path measurements of atmospheric composition provide spatial averages of trace gases that are less sensitive to small-scale variations and the effects of meteorology. In this study we introduce improvements to open-path near-infrared (OP-NIR) Fourier transform spectrometer measurements of CO 2 and CH 4. In an extended field trial, the OP-NIR achieved measurement repeatability 6 times better for CO 2 (0.28 ppm) and 10 times better for CH 4 (2.1 ppb) over a 1.55 km one-way path than its predecessor. The measurement repeatability was independent of path length up to 1.55 km, the longest distance tested. Comparisons to co-located in situ measurements under well-mixed conditions characterise biases of 1.41 % for CO 2 and 1.61 % for CH 4 relative to in situ measurements calibrated to World Meteorological Organisation-Global Atmosphere Watch (WMO-GAW) scales. The OP-NIR measurements can detect signals due to local photosynthesis and respiration, and local point sources of CH 4. The OP-NIR is well-suited for deployment in urban or rural settings to quantify atmospheric composition on kilometre scales.

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Nicholas M Deutscher, Travis A Naylor, Christopher G R Caldow, Hamish L Mcdougall, Alex G Carter, et al.. Performance of an open-path near-infrared measurement system for measurements of CO₂ and CH₄ during extended field trials. Atmospheric Measurement Techniques, 2021, 14 (4), pp.3119 - 3130. ⟨10.5194/amt-14-3119-2021⟩. ⟨hal-03242044⟩