Description and validation of a carbon monoxide and nitrous oxide instrument for high-altitude airborne science (COMA)

Abstract. In this work, we describe the development of the Carbon monOxide Measurement from Ames (COMA) instrument for measurement of carbon monoxide (CO) and nitrous oxide (N2O) aboard NASA's WB-57 high-altitude research aircraft. While COMA has previously flown in the cabin of the NASA P3 platform, here the instrument was modified to operate in a significantly different environment – an unpressurized pallet flying primarily above 12 km (40 000 ft). Modifications were made to the laser to allow for detection of CO and N2O, ruggedization and thermal management were addressed, and a calibration system was designed to quantify the measurement stability in-flight. Testing was conducted in a thermal vacuum chamber to mimic anticipated ambient conditions experienced inside the WB-57 pallet bay and found that the electronic components remained within the thermal limits. COMA was operated successfully during 9 unattended transit flights to and from South Korea and 15 research flights during NASA's Asian summer monsoon Chemical & CLImate Project (ACCLIP) 2022 campaign, which was focused on studying the Asian summer monsoon anticyclone in the western Pacific. The CO measurement has an overall uncertainty ranging between 4.1 ppb (at 50 ppb CO) and 5.6 ppb (at 200 ppb CO). N2O has an overall uncertainty of 2.7 ppb (at 320 ppb N2O). In addition, COMA observations were compared with two other in situ CO instruments co-located on the WB-57: the Carbon Monoxide Laser Detector 2 (COLD2) and the Airborne Carbonic Oxides and Sulfide Spectrometer (ACOS). Comparisons for the 15 flights during the ACCLIP campaign indicate ranges in slope of 1.10–1.15 for COLD2 vs. COMA and 0.94–1.10 for ACOS vs. COMA.