Description and Validation of a Carbon Monoxide and Nitrous Oxide Instrument for High-Altitude Airborne Science (COMA)

Abstract. In this work, we describe 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 P-3 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 electronic components remained within thermal limits. COMA successfully operated during nine unattended transit flights to and from South Korea and fifteen 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 5.9 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: Carbon Monoxide Laser Detector (COLD) 2 and Airborne Carbonic Oxides and Sulfide Spectrometer (ACOS). Comparisons for 15 flights during the ACCLIP campaign indicate a range in slope of 1.10–1.15 for COLD2 vs. COMA and 0.94–1.10 for ACOS vs COMA.