12 February 1993 Field measurements of atmospheric methane with a HeNe laser-based real-time instrument
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Abstract
We recently have conducted measurements of distributions and fluxes of methane in several small towns in the U.S. These measurements are made with a real-time methane instrument recently developed at Aerodyne Research. This instrument is based on absorption of infrared light from a Zeeman-broadened HeNe laser operating at 3.39 micrometers . A non-uniform magnetic field applied to the laser plasma results in a nearly flat gain profile, which allows piezoelectric tuning of the laser on and off a methane line. Long path (47 m) absorption occurs in a multipass cell. The instrument has a noise level of 5 ppbv (rms, 1 sec.) and a gas sampling time of 6 sec. The instrument is mounted in a van with a suite of other real-time instruments (CO2 and SF6) which can function while moving at roadway speeds. We map the methane distribution in towns, identify the primary methane sources, and measure fluxes with tracer methods. The simultaneous measurement of CO2 with a commercially available NDIR device is useful in identifying some sources of methane. An SF6 instrument (electron capture) allows precise location and measurement of tracer plumes during flux measurement experiments.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
J. Barry McManus, Jeff A. Shorter, Paul L. Kebabian, Charles E. Kolb, Byard Mosher, Robert C. Harris, Brian Lamb, Eugene Allwine, and Touche Howard "Field measurements of atmospheric methane with a HeNe laser-based real-time instrument", Proc. SPIE 1715, Optical Methods in Atmospheric Chemistry, (12 February 1993); doi: 10.1117/12.140179; https://doi.org/10.1117/12.140179
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