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. An airborne trace gas sensor based on mid-infrared technology is presentedfor fast (1 s) and high-precision ethane measurements during theAtmospheric Carbon and Transport-America (ACT-America) study. TheACT-America campaign is a multiyear effort to better understand andquantify sources and sinks for the two major greenhouse gases carbon dioxideand methane. Simultaneous airborne ethane and methane measurements provideone method by which sources of methane can be identified and quantified. Theinstrument described herein was operated on NASA's B200 King Air airplanespanning five separate field deployments. As this platform has limitedpayload capabilities, considerable effort was devoted to minimizinginstrument weight and size without sacrificing airborne ethane measurementperformance. This paper describes the numerous features designed to achievethese goals. Two of the key instrument features that were realized wereautonomous instrument control with no onboard operator and theimplementation of direct absorption spectroscopy based on fundamental firstprinciples. We present airborne measurement performance for ethane basedupon the precisions of zero air background measurements and ambientprecision during quiescent stable periods. The airborne performance wasimproved with each successive deployment phase, and we summarize the majorupgraded design features to achieve these improvements. During the fourthdeployment phase in the spring of 2018, the instrument achieved 1 s(1σ) airborne ethane precisions reproducibly in the 30–40parts per trillion by volume (pptv) range in both the boundary layer and theless turbulent free troposphere. This performance is among some of the bestreported to date for fast (1 Hz) airborne ethane measurements. In both thelaboratory conditions and at times during calm and level airborne operation,these precisions were as low as 15–20 pptv.

Autonomous airborne mid-infrared spectrometer for high-precision measurements of ethane during the NASA ACT-America studies