A Novel Airborne Carbon Isotope Analyzer for Methane and Carbon Dioxide Source Fingerprinting

Abstract:

Recent field studies on major sources of the important greenhouse gas methane (CH₄) indicate significant underestimation of methane release from fossil fuel industrial (FFI) and animal husbandry sources, among others. In addition, uncertainties still exist with respect to carbon dioxide (CO₂) measurements, especially source fingerprinting. CO₂ isotopic analysis provides a valuable in situ measurement approach to fingerprint CH₄ and CO₂as associated with combustion sources, leakage from geologic reservoirs, or biogenic sources. As a result, these measurements can characterize strong combustion source plumes, such as power plant emissions, and discriminate these emissions from other sources.

As part of the COMEX (CO2 and MEthane eXperiment) campaign, a novel CO₂ isotopic analyzer was installed and collected data aboard the CIRPAS Twin Otter aircraft. Developing methods to derive CH₄ and CO₂ budgets from remote sensing data is the goal of the summer 2014 COMEX campaign, which combines hyperspectral imaging (HSI) and non-imaging spectroscopy (NIS) with in situ airborne and surface data. COMEX leverages the synergy between high spatial resolution HSI and moderate spatial resolution NIS.

The carbon dioxide isotope analyzer developed by Los Gatos Research (LGR) uses LGR’s patented Off-Axis ICOS (Integrated Cavity Output Spectroscopy) technology and incorporates proprietary internal thermal control for high sensitivity and optimal instrument stability. This analyzer measures CO₂ concentration as well as δ¹³C, δ¹⁸O, and δ¹⁷O from CO₂ at natural abundance (100-3000 ppm). The laboratory accuracy is ±1.2 ppm (1σ) in CO₂ from 370-1000 ppm, with a long-term (1000 s) precision of ±0.012 ppm. The long-term precision for both δ¹³C and δ¹⁸O is 0.04 ‰, and for δ¹⁷O is 0.06 ‰. The analyzer was field-tested as part of the COWGAS campaign, a pre-cursor campaign to COMEX in March 2014, where it successfully discriminated plumes related to combustion processes associated with dairy activities (tractor exhaust) from plumes and sources in air enriched in methane and ammonia from bovine activities including waste maintenance.

Methodology, laboratory data, field data from COWGAS, and field data from the COMEX campaign acquired by LGR’s carbon isotope analyzer as well as other COMEX analyzers are presented.