Inter-comparison of different sensors for in-situ airborne measurements of Carbon Monoxide during ACCLIP campaign

A series of in-situ Carbon Monoxide (CO) observations were recently performed in the Western Pacific region, during summer 2022, in the framework of the ACCLIP project (Asian summer monsoon Chemical and CLimate Impacts Project). During the ACCLIP measurements campaign, located in Osan (South Korea), two different research aircraft were employed with a set of sensors installed onboard. The NASA WB-57 aircraft carried out 15 research flights (reaching a maximum altitude of about 19 km), and the NSF/NCAR Gulfstream (GV) aircraft carried out 14 research flights (reaching a maximum altitude of about 15 km), covering a large region near Korea and Japan. We report on the inter-comparison between five different instruments for in-situ CO mixing ratio measurements: three installed onboard WB-57 (ACOS, COLD2 and COMA), and two installed onboard GV (Aerodyne-CO and Picarro G2401-m). COLD2 (Carbon Oxide Laser Detector 2) [1] and Aerodyne-CO [2] are mid-infrared Quantum Cascade Laser spectrometers, based on direct absorption in combination with a multipass cell. ACOS (Carbonyl Sulfide Analyzer) [3] and COMA (Carbon mOnoxide Measurement from Ames) [4] are mid-infrared absorption spectrometers based on Off-Axis ICOS (Integrated Cavity Output Spectroscopy) technology. The Picarro sensor is a cavity ring down absorption spectrometer [5]. The in-flight CO mixing ratio values measured by the five spectrometers will be compared, with particular attention to both the accuracy of each instrument and the adopted or not-adopted calibration procedures, as, in principle, for many measurement environments the two sensors based on direct absorption do not need in-flight calibration. Laboratory measurements of common primary and secondary calibration standards made by the five CO measurement groups will be presented to increase confidence in method accuracy.