Researchers at the National Institute of Standards and Technology (NIST) have upgraded their laser frequency-comb instrument to simultaneously measure three airborne greenhouse gases — nitrous oxide, carbon dioxide and water vapor — plus the major air pollutants ozone and carbon monoxide.

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Combined with an earlier version of the system that measures methane, NIST’s dual comb technology can now sense all four primary greenhouse gases, which could help in understanding and monitoring emissions of these heat-trapping gases implicated in climate change. The newest comb system can also help assess urban air quality.

These NIST instruments identify gas signatures by precisely measuring the amounts of light absorbed at each color in the broad laser spectrum as specially prepared beams trace a path through the air. Current applications include detecting leaks from oil and gas installations as well as measuring emissions from livestock. The comb systems can measure a larger number of gases than conventional sensors that sample air at specific locations can. The combs also offer greater precision and longer range than similar techniques using other sources of light.

NIST’s latest advance, described in a new paper, shifts the spectrum of light analyzed from the near-infrared into the mid-infrared, enabling the identification of more and different gases. The older, near-infrared comb systems can identify carbon dioxide and methane but not nitrous oxide, ozone or carbon monoxide.

Researchers demonstrated the new system over round-trip paths with lengths of 600 meters and 2 kilometers. The light from two frequency combs was combined in optical fiber and transmitted from a telescope located at the top of a NIST building in Boulder, Colorado. One beam was sent to a reflector located on a balcony of another building, and a second beam to a reflector on a hill. The comb light bounced off the reflector and returned to the original location for analysis to identify the gases in the air.

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