A Direct Absorption Spectrometer for Low Drift and High Accuracy Measurements of Methane Isot

Atmospheric methane (CH4) is a potent greenhouse gas and ozone precursor that is
increasingly important in our understanding and modeling of climate change. Identifying and
differentiating methane sources are crucial to any strategies aimed at reducing CH4 emissions.
Isotopic composition and ethane content are both dependent upon methane origin, making them
valuable diagnostics for source attribution. Instrumentation capable of fast, high precision
quantification of CH4 isotopes and ethane aboard an aircraft platform will advance scientifically
backed methane mitigation strategies.

This proposal aims to develop a flight-capable laser-based monitor for 12CH4, 13CH4, CH3D, and
C2H6. The 1 Hz standard deviation performance targets of d-13CH4 precision of 0.5 per mil and
d-CH3D precision of 10 per mil delta units, and C2H6 mixing ratio precision of 10 parts per
trillion will be achieved in this work. These performance goals will be met using direct absorption
infrared spectrometry, which has been demonstrated to achieve the desired precision under
laboratory conditions. As outlined in the proposal, the technical challenges are:
i) identifying and eliminating sources of measurement drift due to aircraft motion, temperature and
pressure changes, ii) developing innovative zeroing and calibration methods amenable to
these high precision measurements, and iii) designing a flight-ready instrumentation package.