Development of a Novel Trace Methane/Carbon Dioxide Analyzer and Results of Field Validation Studies for the Determination of Methane Flux

"We report the development, and field validation, of a recently commercially available, portable and rugged, trace gas analyzer for the measurement of atmospheric methane (and carbon dioxide). Supported in part under the DOE/ARPA-E, MONITOR1 program, the purpose of the development was to make available a low-cost, high-sensitivity instrument that would become the core of a complete system for the localization and quantification of methane leaks from industrial sites related to oil & gas operations and other sources of fugitive methane emissions.

Based on Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS), the resulting analyzer (LI-7810) offers both sensitivity and stability for long-term measurement of background atmospheric methane, meeting the measurement compatibility goals as defined by WMO/GAW, and also the sampling rate, response time, and dynamic range, to act as the core of a complete system for determination of industrial methane flux.

We begin the presentation with a brief introduction to the now commercially available trace gas analyzer, before re-visiting deployment details and results from extensive field trials completed during the development process. Finally, performance characterization of the commercial analyzer is presented in detail. Field validations of the analyzer were completed at test sites simulating methane emissions from natural gas storage and transmission infrastructure sites. In both situations, set-up of the complete measurement system was guided by EPA OTM 33A. A brief introduction to the determination of methane flux using OTM 33A is provided.

Under the ARPA-E program, and in collaboration with Colorado State University, a prototype analyzer was deployed at the METEC site, located in Fort Collins, Colorado. This prototype was co-located with LI-COR's LI-7700 open-path methane analyzer, and the two units, along with sampling system, 3-axis sonic anemometer, and other ancillary meteorological equipment, were located in accordance with OTM 33A. The system was then challenged with test site releases; varying emissions source location, height, and release rate. Averaged over 20 tests, flux estimated with OTM33A and data from the trace gas analyzer prototype agreed to within in 5 %. Individual tests were typically within 20-25% of the release rate. Larger errors occurred under stable, low-wind speed conditions and when the fetch exceeded 90 meters.

We conclude the presentation with results of performance testing of the commercial analyzer. Results include data from long-term measurement stability tests for methane at approximately atmospheric background concentration. Allan deviation plots for measurements of methane, at similar concentrations, are also presented. In conclusion, the work presented here has resulted in a commercially available trace gas analyzer (LI-7810) for the measurement of methane (and carbon dioxide). For methane, the portable and rugged instrument exceeds requirements for both long-term atmospheric background measurements, and as part of a complete system including the aforementioned meteorological equipment, for the quantification, and potentially location, of emissions from a variety of sources.

1The initial principles and some portions of the new technology presented herein were developed in part based on the grant from the MONITOR Program by the U.S. Department of Energy Advanced Research Projects Agency - Energy (ARPA-E), under award number DE-AR0000537."