NSF/NCAR airborne facility observations of carbon monoxide and nitrous oxide enhancements in biomass burning plumes in the Northwestern United States in the summer of 2018

Abstract:

Recent improvements to NSF/NCAR facility CO and the novel offering of N₂O measurements are described, along with quantification of enhanced mole fractions within relatively fresh biomass burning plumes. A commercial Aerodyne Research Inc. QCL direct absorbance (mini-QCL) instrument was added in 2018 to the NSF/NCAR requestable measurements suite. Initial measurement characterization results are presented, including laboratory environmental chamber characterizations, test flight air motion sensitivity characterization and a summary of performance metrics observed during the 2018 WE-CAN C-130 research flights and the 2020 GV ACCLIP-test flights.

Chamber studies allowed implementation of configuration modifications to optimize the accuracy of airborne carbon monoxide measurements. Careful alignment of the etalon wavelength tuning standard, in-flight purging of the free space optics with CO-scrubbed and N₂O quantified dry gas produced the highest accuracy of CO determination. The efficacy of this configuration was validated using data from in-flight test maneuvers and CO measurement intercomparison between the NSF/NCAR C-130 and University of Wyoming King Air during the simultaneous and co-located WE-CAN and Biomass Burning FLUX (BB-FLUX) field experiments.

The improved fit accuracy and biomass burning sampling objectives allowed demonstration of the ability to accurately quantify small (a few ppbv) changes in ambient N₂O concentrations in a high CO environment (several ppmv). The resultant overall uncertainty of carbon monoxide and nitrous oxide measurements are +/- 1 ppbv for CO and +/- 0.6 ppbv for N₂O, while precision of 1-second data from each spectral quantification was 0.1 ppbv for each measurand. Finally, observed nitrous oxide emission factors will be presented and compared to prior observations and emission inventories for this important long-lived greenhouse gas.