A Car-Mounted Sensor Can Sniff Out Methane Leaks While Driving at Highway Speed

Methane, a potent greenhouse gas released from natural gas infrastructure, livestock farms, landfills and coal mines, is often invisible to the naked eye and can pose fire and explosion hazards when it leaks from underground pipelines. Researchers at East China Normal University have built a vehicle-mounted spectroscopy system, described in the journal Optics Express, that can reliably detect methane in real time while driving, making it easier to locate hidden emissions across large areas.

"Dual-comb spectroscopy uniquely enables simultaneous, high-precision measurement of multiple gases, but is sensitive to environmental noise, which can degrade its performance. Our work addresses and overcomes this key challenge," said team leader Wenxue Li. "SUVs equipped with our spectroscopy system could cruise residential streets day and night. If an underground gas pipeline has a methane leak, the system could capture the concentration of the gas, record the GPS coordinates and notify maintenance crews." The system is based on mid-infrared dual-comb spectroscopy, which uses two precisely matched frequency combs — light sources producing many evenly spaced wavelengths — to detect gases; the mid-infrared range is useful because many molecules have strong, distinctive absorption signatures there.

Taking dual-comb spectroscopy out of the lab is difficult because such systems typically rely on precisely aligned optics that limit their ability to move freely. To solve this, the team used vibration-resistant fiber lasers to generate the frequency combs and developed a method that keeps the two light sources naturally synchronized, removing the need for complex hardware to actively keep them in phase. The light travels through a compact, open-path gas cell providing an effective 25-meter path through the surrounding air, increasing sensitivity without a large instrument.

In road tests, including a 47-kilometer drive on urban roads and expressways at speeds up to 100 km/h, the system measured methane with a precision of 66 parts per billion and matched the accuracy of typical laboratory-based systems. In controlled release tests, the researchers drove past two simulated leaks and mapped the gas plume around one of them by circling it, producing a concentration map that closely matched local wind patterns.