Methane Emissions: Remote Mapping and Source Quantification Using an Open‐Path Laser Dispersion Spectrometer. Issue 10 (20th May 2020)

• Record Type: Journal Article
• Authors: Hirst, Bill; Randell, David; Jones, Matthew; Chu, Johnny; Kannath, Arun; Macleod, Neil; Dean, Marcella; Weidmann, Damien
• Is Part Of: Geophysical research letters. Volume 47:Issue 10(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-05-20
• Subjects: methane -- emission quantification -- emission localization -- open‐path measurements -- Dispersion spectroscopy; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL086725
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Reducing man‐made greenhouse gas emissions depends on the effective detection and location of sources. We present a new method that remotely detects, locates, and quantifies gas emission rates by sequentially steering an optical beam between multiple retro‐reflectors. The novel open‐path laser gas sensor uses Laser Dispersion Spectroscopy (LDS), with seven beams up to 98 meters long deployed across open, flat terrain. LDS offers high precision (10–20 ppb), high dynamic range and linearity, enhanced immunity to atmospheric perturbations, with fast response to probe an area in 3 s. Simultaneous wind and concentration data were collected for four calibrated methane gas release schemes with emission rates of ~1.3 kg/hr. The resulting data were processed using a Bayesian, Markov chain Monte‐Carlo inverse solver to locate the sources and quantify their mass emission rates and uncertainty bounds. All the sources were located to within a few meters and mass emission rates established within the associated confidence bounds. Plain Language Summary: The Earth's atmosphere contains 600 times as much CO2 as methane (by mass), but the warming effect due to the small amount of methane is 58% of that due to all the CO2 . Furthermore, methane's atmospheric lifetime is ~10 yr whereas CO2 's is ~100 yr. So, reducing methane emissions not only provides much greater impact per unit mass but that reduction in atmospheric warming is realized in years not centuries. Many industrial activities produce methane emissions, but difficulties in remotely attributing and quantifying emission rates have severely impeded effective remedial action. We present a novel method to continuously detect, locate, and quantify methane emission sources distributed across extensive areas. We demonstrate its performance in simple controlled tests using a novel optical beam gas sensor to measure path‐averaged gas concentrations. The data are analyzed using advanced statistical methods to locate and quantify the emission rates of the sources. Key Points: Seventeen calibrated methane releases of ~1.3 kg/hr per source in four release schemes of single and dual sources distributed across a 120 × 120 m 2 area Tunable laser dispersion spectrometer operating at 3.3 μm is used in seven open paths, with sequential scanning of the full beam array in 3 s Sources located to few meters accuracy and emission rates quantified with 0.1 to 0.5 kg/hr uncertainty, including sources outside the beam array