Abstract
Abstract. An airborne trace gas sensor based on mid-infrared technology is presented for fast (1 s) and high-precision ethane measurements during the Atmospheric Carbon and Transport-America (ACT-America) study. The ACT-America campaign is a multiyear effort to better understand and quantify sources and sinks for the two major greenhouse gases carbon dioxide and methane. Simultaneous airborne ethane and methane measurements provide one method by which sources of methane can be identified and quantified. The instrument described herein was operated on NASA's B200 King Air airplane spanning five separate field deployments. As this platform has limited payload capabilities, considerable effort was devoted to minimizing instrument weight and size without sacrificing airborne ethane measurement performance. This paper describes the numerous features designed to achieve these goals. Two of the key instrument features that were realized were autonomous instrument control with no onboard operator and the implementation of direct absorption spectroscopy based on fundamental first principles. We present airborne measurement performance for ethane based upon the precisions of zero air background measurements and ambient precision during quiescent stable periods. The airborne performance was improved with each successive deployment phase, and we summarize the major upgraded design features to achieve these improvements. During the fourth deployment phase in the spring of 2018, the instrument achieved 1 s (1σ) airborne ethane precisions reproducibly in the 30–40 parts per trillion by volume (pptv) range in both the boundary layer and the less turbulent free troposphere. This performance is among some of the best reported to date for fast (1 Hz) airborne ethane measurements. In both the laboratory conditions and at times during calm and level airborne operation, these precisions were as low as 15–20 pptv.
Highlights
The Atmospheric Carbon and Transport-America (ACTAmerica) campaign was a 4-year study composed of five different aircraft campaigns over the continental US to quantify sources, sinks, and transport of carbon dioxide (CO2) and methane (CH4), two of the major greenhouse gases
We present in this study a new autonomous airborne ethane instrument for fast 1 s measurements on the NASA B200 aircraft for ACT-America studies based upon the CAMS-2 difference frequency generation (DFG) spectrometer
The airborne performance was significantly improved with each successive field deployment phase study, and we summarized the major upgraded design features to achieve these improvements
Summary
The Atmospheric Carbon and Transport-America (ACTAmerica) campaign was a 4-year study composed of five different aircraft campaigns over the continental US to quantify sources, sinks, and transport of carbon dioxide (CO2) and methane (CH4), two of the major greenhouse gases. Kostinek et al (2019), and references therein, discuss the fact that airborne measurement precisions of these spectrometers are dramatically affected by cabin pressure changes as the aircraft ascends and descends to different flight levels or altitudes To address this, these researchers carried out the frequent addition of calibration standards every 5–10 min for a total duration of 20 s, which includes a 10 s flush time. We discuss the numerous designs implemented to reduce weight and size as well as to incorporate autonomous instrument control without the need for an onboard operator This system reliably acquired high-precision and fast ethane measurements (30–40 pptv) on the B200 aircraft over several hundred flight hours during the first to. We present comparisons with NOAA/ESRL Global Monitoring Division programmable flask package (PFP) ethane measurements acquired on the same aircraft and show example correlations with methane in providing methane source characterizations
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