Maintenance Mindset: The future of emissions monitoring — Exploring NIST’s game-changing spectroscopy technology

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What if we could see greenhouse gases? Better yet, what if plant staff could identify toxic plumes or areas of high emissions through machine sensors?

Scientists at the National Institute of Standards and Technology (NIST) are working on it, specifically upgrading our ability to measure and analyze greenhouse gas (GHG) emissions. They have their sights set on the more problematic of GHGs to measure—methane—and one that, at this point, could be doing more potential damage long-term than carbon dioxide.

Scientists do have methods for gas measurement, but free-form dual-comb spectroscopy will be faster, more flexible and can perform more sensitive analysis (22 times higher sensitivity than traditional methods), potentially making it easier to identify emissions at the source.

Measuring vs. calculating GHG emissions

For many process-based facilities, GHG emissions are already a reality. Commitments to the 2015 Paris Agreement or Paris Climate Accord and achieving net zero GHG emissions by 2050, with a 50% reduction by 2030, will require much deeper emissions monitoring and reductions in industry and beyond.
 
Many industries are reporting annual GHG emissions, a total of more than 8,000 facilities as part of the EPA’s Greenhouse Gas Reporting Program (GHGRP). Every October EPA releases GHG emissions data from the previous year. Currently, power plants are the largest emitters, followed by oil and gas, and non-fluorinated chemical manufacturers, which produce ammonia, hydrogen, ethylene and other chemicals. GHG emissions are trending downward, according to GHGRP reporting, but not quickly enough.
 
EPA says: “For sources reporting to the GHGRP, emissions decreased by 4.4% from 2022 to 2023. Over the past thirteen reporting years (2011-2023), GHGRP reported direct emissions from sectors other than oil and gas (also excluding suppliers) declined by 27.1%. This decline is primarily caused by a 33.8% decline in reported power plant emissions since 2011.”
 
There are seven gases that collectively make up GHGs: carbon dioxide (CO2), methane (CH4), nitrous oxide (N20) and fluorinated man-made gases, such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3). While CO2 has been the primary culprit for climate change, methane gas is more efficient at trapping radiation, and therefore, 25 times more efficient at causing global warming than carbon dioxide, over a 100-year period. 
 
Methane is also harder to measure, in part, because of the diversity of its sources and geographic spread. CH4 largely comes from livestock farms, natural gas systems, and landfill sites, and methane concentrations in the atmosphere are also increasing more rapidly than carbon dioxide. Our atmosphere is already highly saturated with CO2, and there’s essentially a lot more room for CH4 absorption, so it has a much larger chance to impact global warming moving forward. Methane concentrations are already 2.5 times higher than in preindustrial periods, compared to a 150% increase in carbon dioxide. 
 
EPA does support initiatives to reduce methane emissions, which have lowered by 19% from 1990 to 2022, including technology like vapor recovery units for centrifugal compressors. EPA says: “Crude oil and condensate production into atmospheric pressure fixed roof storage tanks creates a substantial volume of low-pressure methane gas emissions to the atmosphere. Vapor recovery units (VRUs) are commonly used to capture methane emissions from these tanks and a variety of other low pressure vented gas sources found across oil and gas operations, including pipeline pigging operations, compressors, and dehydrators.”
 
GHG emissions reporting has been ongoing in many industries since 2010, but questions remain about the true accuracy of that data. Reporting involves emissions from different levels—Scope 1, Scope 2 and Scope 3. The later represents the environmental impact up and down the supply chain and is often hard to untangle and decipher accurately.
 
GHG reporting can also be a time-consuming and resource-intensive activity, and may not result in 100% accurate data for many reasons, such as data availability, quality and consistency, complex value chains that challenge Scope 3 identification, and the many methodologies for GHG calculations, which may not always correlate one-to-one.

Advances in spectroscopy

Much of GHG data is calculated rather than measured, but we do have methods to measure greenhouse gases. Spectroscopy can measure and identify different materials by observing how they interact with light. As a prism separates white light into a rainbow of colors, spectroscopy does a similar process with light passing through a substance, revealing information about the substance’s properties and composition.
 
Dual-comb spectroscopy is a method for examining many colors of light simultaneously in high resolution, and NIST scientists’ recent improvements have made this technology even more accurate and faster.
 
At the heart of dual-comb spectroscopy is the Nobel Prize-winning optical frequency comb. This laser tool resembles the teeth of a comb, as it produces light in a series of equally spaced frequencies. Dual-comb means two optical frequency combs, which can analyze how substances interact with the light from both combs for faster and more precise results.
 
The latest advances in “free-form” dual-comb spectroscopy can emit super-fast light pulses (and, I mean, really fast), and this high precision control can improve measurements. The new frequency comb can emit light pulses that are 100 femtoseconds (one millionth of one billionth of a second, 10^-15). It can show real-time images of methane plumes or the distribution of any gases and can quickly measure gas by zeroing in on the most data-rich parts of the sample. This smart measurement technology takes some of the guess work out of where to look for gas that’s not visible to the naked eye.
 
Fabrizio R. Giorgetta, Simon Potvin, Jean-Daniel Deschênes, Ian Coddington, Nathan R. Newbury and Esther Baumann published their work on free-form dual-comb spectroscopy in September 2024 in Nature Photonics.
 
As a monitoring tool, the technology also has potential. It can create detailed images of a variety of gas clouds, like this real-time image of methane plumes (Figure 1).