The Role of Spectroscopy in Methane Detection and Climate Sustainability

Light-based measurement is essential for fostering sustainability and improving the economic potential of natural materials. As a result, many spectroscopic techniques are being used to detect methane in the environment, which help inform public policy decisions to safeguard the environment for future generations.

In this Q&A overview, we explore the role that spectroscopy has played in climate sustainability efforts.

Why has methane detection become a central focus for climate sustainability efforts?

Although carbon dioxide (CO₂) is often the primary focus of climate discussions, methane (CH₄) is a significantly more potent greenhouse gas, possessing over 25 times the warming potency of CO₂.¹ Although it has a much shorter atmospheric lifetime, its impact on radiative forcing is estimated at nearly 60% of that of CO₂.¹ Because the absorption bands of methane are not saturated, rising concentrations of methane have a disproportionately large impact on global warming. Consequently, experts believe that controlling methane emissions is one of the highest-impact levers available to slow climate change over the next 25 years.¹ This is why researchers are exploring new ways to use spectroscopy to help detect methane in the atmosphere.

What are the primary sources of methane emissions that need monitoring?

Methane sources are geographically dispersed and diverse. The main anthropogenic sources include oil and gas systems (22.5% of man-made emissions), livestock enteric fermentation (40%), landfills and waste treatment (20%), and coal production (12%).¹ Natural sources, such as wetlands and microbial action in bogs, account for approximately 40% of total atmospheric methane.^1,2 Additionally, methane is the most abundant component of natural gas extracted through unconventional oil and gas (UOG) exploration, making leak detection in these regions critical for environmental protection.^1,2

How does spectroscopy specifically facilitate the detection of methane?

Spectroscopy helps identify methane by measuring the absorbance of light at frequencies unique to its vibrational modes, primarily in the infrared (IR) region.^1,3 Methane has main H-CH stretching vibrational modes around 3.4 µm and deformation modes between 6.8–7.5 µm.¹ Advanced techniques, such as tunable diode laser absorption spectroscopy (TDLAS), use narrow wavelengths of light to achieve high selectivity for single compounds. Meanwhile, Fourier transform infrared (FT-IR) spectroscopy can measure dozens of compounds simultaneously, including methane and other short-chain hydrocarbons.^1,3

What is "fenceline monitoring," and which spectroscopic tools are used for it?

Fenceline monitoring refers to air quality measurements taken at the perimeter of industrial facilities like oil refineries.³ Open-path spectroscopy is ideal for this because it provides real-time data over paths up to 1000 meters, offering much better spatial coverage than traditional point monitors.³ FT-IR is a preferred technique for methane fenceline monitoring because it is a widely accepted U.S. Environmental Protection Agency (EPA) standard method.³ In these systems, a light source and detector measure the "spectral match" against reference gas-phase libraries to identify and quantify gas plumes crossing the facility boundary.³

How are mobile and remote sensing technologies advancing methane detection?

New portable devices are supplementing traditional laboratory-based gas chromatography. The Cavity Ring-Down Spectrometer (CRDS) is a highly precise tool that uses reflective mirrors to create an effective sample pathlength of up to 10 km, allowing for part-per-billion (ppb) methane level precision.¹ For even broader scales, satellite instruments measure methane in the shortwave IR using solar radiation backscatter. A major upcoming mission, the Methane Remote Sensing LIDAR Mission (MERLIN), will use differential absorption LIDAR to create daily global maps of methane distribution, providing unprecedented insight into geographic variations and emission control opportunities.¹

Can spectroscopy help distinguish between different origins of methane, such as biogenic vs. thermogenic?

Yes, it can. This is particularly important in groundwater monitoring near UOG sites. Biogenic methane is a byproduct of bacterial metabolism, while thermogenic methane is the target of fossil fuel recovery.² Spectroscopy, often coupled with gas chromatography (GC), can identify these origins by analyzing isotopic abundances or the ratio of methane to higher-chain hydrocarbons like ethane and propane.² For instance, a new vacuum ultraviolet (VUV) detector measures gas-phase absorption between 120–240 nm, offering unique qualitative and quantitative capabilities for monitoring the type of dissolved gases in water.²

Does spectroscopy play a role in monitoring natural carbon sinks like peatlands?

Spectroscopic methods are essential for studying humic acids in peat, which forms through the slow decomposition of plants in anaerobic environments.⁴ Researchers use ultraviolet-visible (UV-vis), FT-IR, and fluorescence (FL) spectroscopy to characterize the structural changes in these organic materials.⁴ Understanding the aromaticity and functional groups (like carboxyl and phenolic hydroxyl groups) of peat humic acids helps scientists evaluate the biological activity and carbon sequestration potential of peatlands, which is vital for long-term climate sustainability.⁴

What are the biggest challenges in implementing these spectroscopic solutions?

One primary challenge is the interference from other atmospheric compounds or "chemically similar" species, which can lead to false positives.^2,3 For example, in FT-IR analysis, some sensitive methane features can be obscured by CO₂. Additionally, real-world minimum detection limits (MDLs) are often higher than laboratory-derived limits because of environmental conditions.³ Ensuring robust infrastructure and automated data management systems is also critical, as fenceline networks can generate millions of data points that require real-time quality control for public reporting.³

References

1. Buckley, S. Detecting Methane Emissions: How Spectroscopy is Contributing to Sustainability Efforts. Spectroscopy 2022, 37 (4), 22–26. DOI: 10.56530/spectroscopy.zx3279o9
2. Schug, K. A.; Carlton Jr., D. D.; Hildenbrand, Z. L. Analytical Efforts Toward Monitoring Groundwater in Regions of Unconventional Oil and Gas Exploration. Spectrosc. Suppl. 2015, 30 (10). Available at: https://www.spectroscopyonline.com/view/analytical-efforts-toward-monitoring-groundwater-regions-unconventional-oil-and-gas-exploration-0
3. Schill, S. R.; McEwan, R. S.; Moffet, R. C.; et al. Real-World Application of Open-Path UV-DOAS, TDL, and FT-IR Spectroscopy for Air Quality Monitoring at Industrial Facilities. Spectrosc. Suppl. 2022, 37 (s11). DOI: 10.56530/spectroscopy.qz5173x6
4. Li, L.; Ma, L.; Lu, Y.; et al. Spectroscopic Analysis of the Effects of Alkaline Extractants on Humic Acids Isolated from Herbaceous Peat. Spectroscopy 2024, 39 (3), 20–25. DOI: 10.56530/spectroscopy.wk3774u5