A selective laser-based sensor for fugitive methane emissions

Abstract

A mid-infrared laser-based sensor is reported for the quantification of fugitive methane emissions. The sensor is based on a distributed feedback inter-band cascade laser (DFB – ICL) operating near 3.3 µm. Wavelength tuning with cepstral analysis is employed to isolate methane absorbance from (1) fluctuations in the baseline laser intensity, and (2) interfering species. Cepstral analysis creates a modified form of the time-domain molecular free-induction-decay (m-FID) signal to temporally separate optical and molecular responses. The developed sensor is insensitive to baseline laser intensity imperfections and spectral interference from other species. Accurate measurements of methane in the presence of a representative interfering species, benzene, are performed by careful selection of the scan index (ratio of laser tuning range to spectral linewidth) and initial and final time of m-FID signal fitting. The minimum detection limit of the sensor is ~ 50 ppm which can be enhanced with an optical cavity. The proposed sensing strategy can be utilized to measure methane leaks in harsh environments and in the presence of interfering species.

Drone-Assisted Monitoring of Atmospheric Pollution—A Comprehensive Review

“…In order to achieve high accuracy, the measurements had to be performed at flight altitudes between 4 and 15 m above the ground. These results were in agreement with investigations performed earlier [142], in which a similar set-up was used to detect subsurface and surface methane leaks. The authors also reported that the system was not able to discriminate between low and high concentration methane plumes.…”

A laser-based sensor for selective detection of benzene, acetylene, and carbon dioxide in the fingerprint region

“…Laser-based sensors can thus overcome many of the limitations associated with other speciation techniques [7]. Given these advantages, laser-based sensors have garnered attention from researchers and have been proven to be a useful tool for quantitative analysis of gaseous species in numerous elds, such as chemical analysis [8], monitoring of agricultural emissions [9], control of industrial processes [10], breath analysis [11], pollution monitoring [12][13][14], and combustion diagnostics [15][16][17][18].…”

A laser-based sensor for selective detection of benzene, acetylene, and carbon dioxide in the fingerprint region

“…In particular, the mid-infrared (MIR) region contains the fundamental vibrational bands of most of the atmospheric species and VOCs (e.g., CO 2 , H 2 O, hydrocarbons, etc.) [19,20]; the absorption coe cients of these species are orders of magnitude stronger in this region than in the near-infrared region [21]. A speci cally interesting region in the MIR is the molecular ngerprint region (6.7-20 m) which includes strong bending vibrational modes of many air pollutants and the C-halogen stretching modes of most halocarbons [22].…”

“…show overlapping absorption features over most of the IR range, which necessitates the use of advanced post-processing techniques in order to selectively measure BTEX species [23][24][25]. However, standard scanned-wavelength absorption spectroscopy would be su cient for selective detection due to the isolated, distinct features of BTEX in the molecular ngerprint region.…”