Testing and evaluation of a new airborne system for continuous Nsub2/subO, COsub2/sub, CO, and Hsub2/subO measurements: the Frequent Calibration High-performance Airborne Observation System (FCHAOS)

摘要

We present the development and assessment of a new flight system that uses a commercially available continuous-wave, tunable infrared laser direct absorption spectrometer to measure Nsub2/subO , COsub2/sub , CO, and Hsub2/subO . When the commercial system is operated in an off-the-shelf manner, we find a clear cabin pressure–altitude dependency for Nsub2/subO , COsub2/sub , and CO. The characteristics of this artifact make it difficult to reconcile with conventional calibration methods. We present a novel procedure that extends upon traditional calibration approaches in a high-flow system with high-frequency, short-duration sampling of a known calibration gas of near-ambient concentration. This approach corrects for cabin pressure dependency as well as other sources of drift in the analyzer while maintaining a ～90 % duty cycle for 1?Hz sampling. Assessment and validation of the flight system with both extensive in-flight calibrations and comparisons with other flight-proven sensors demonstrate the validity of this method. In-flight 1 σ precision is estimated at 0.05?ppb, 0.10?ppm, 1.00?ppb, and 10?ppm for Nsub2/subO , COsub2/sub , CO, and Hsub2/subO respectively, and traceability to World Meteorological Organization (WMO) standards (1 σ ) is 0.28?ppb, 0.33?ppm, and 1.92?ppb for Nsub2/subO , COsub2/sub , and CO. We show the system is capable of precise, accurate 1?Hz airborne observations of Nsub2/subO , COsub2/sub , CO, and Hsub2/subO and highlight flight data, illustrating the value of this analyzer for studying Nsub2/subO emissions on ～100 km spatial scales.