Abstract
Abstract. 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 N2O, CO2, CO, and H2O. When the commercial system is operated in an off-the-shelf manner, we find a clear cabin pressure–altitude dependency for N2O, CO2, 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 1σ precision is estimated at 0.05 ppb, 0.10 ppm, 1.00 ppb, and 10 ppm for N2O, CO2, CO, and H2O respectively, and traceability to World Meteorological Organization (WMO) standards (1σ) is 0.28 ppb, 0.33 ppm, and 1.92 ppb for N2O, CO2, and CO. We show the system is capable of precise, accurate 1 Hz airborne observations of N2O, CO2, CO, and H2O and highlight flight data, illustrating the value of this analyzer for studying N2O emissions on ∼100 km spatial scales.
Highlights
We present the Frequent Calibration High-performance Airborne Observation System (FCHAOS), utilizing a TILDAS instrument and an updated calibration technique, to make N2O measurements that can be utilized for calculating facility emissions, mass balance fluxes, and regional inversions
We performed pre-flight calibrations on the ground for both the FCHAOS and Picarro G2301-f using two air cylinders calibrated to a NOAA World Meteorological Organization (WMO) greenhouse gas scale
We present a continuous-wave, mid-IR laser spectrometer system that can measure continuous 1 Hz airborne mole fractions of N2O, CO2, CO, and H2O
Summary
Continuous, 1 Hz airborne observations of atmospheric greenhouse gases and pollutants provide essential information for direct quantification of emissions (Karion et al, 2015; Peischl et al, 2015; Smith et al, 2015; Kort et al, 2016), assessment of modeled representations of emissions and transport (Wofsy, 2011; O’Shea et al, 2014), and validation of remote sensing observations (Tanaka et al, 2016; Inoue et al, 2016; Frankenberg et al, 2016). Evaluation of these representations can happen at the larger scales, for which top-down atmospheric inversions (Kort et al, 2008, 2011; Miller et al, 2012; Thompson et al, 2014; Chen et al, 2016; Griffis et al, 2017; Nevison et al, 2018) have challenged modeled and inventoried emissions and often found large discrepancies exceeding 100 % (Miller et al, 2012) To better understand these divergences as well as to properly assess the representation of flux chamber and eddy covariance measurements, we need observational constraints at 10–100 km spatial scales. We present our solution to improve instrument performance with short, frequent calibrations and validation by in-flight calibrations and comparison with a flight-proven Picarro cavity ring-down spectrometer
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