Researchers at the American Institute of Standards and Technology (NIST) have further developed a laser frequency comb that can simultaneously measure three greenhouse gases in the air – nitrous oxide, carbon dioxide and concentrations of water vapor, as well as the main air pollutants, ozone and carbon monoxide, in the atmosphere.
Combined with an earlier methane-measuring version of the system, NIST’s double-comb technology now it can detect four primary greenhouse gases, which can help to understand and monitor emissions of heat trapping gases that play a role in climate change. The latest comb system can also help assess urban air quality.
These NIST instruments identify gas signals by accurately measuring the amount of light absorbed in each color of the broad laser spectrum while specially prepared beams follow a path. they follow, combing the air. Current applications include the detection of leaks in oil and gas facilities and the measurement of livestock emissions. Comb systems are capable of measuring a larger number of gases than conventional sensors that sample air at specific locations. Combs also offer greater accuracy and longer range than similar techniques using other light sources.
NIST’s latest development, described in a new study, shifts the analyzed light from the near-infrared to the mid-infrared range. spectrum, which allows the identification of several and different gases. Older near-infrared comb systems identify carbon dioxide and methane, but not nitrous oxide, ozone, or carbon monoxide.
Researchers have shown orbits of 600 meters and 2 kilometers introduce the new system. The light from the two frequency combs was combined in optical fiber and transmitted from a telescope located on top of the NIST building in Boulder, Colorado. One beam was sent to a reflector on the balcony of another building and the other to a reflector on a hill. The comb light bounced off the reflector and returned to the original site where it was analyzed to identify gases in the air. The frequency comb is a very accurate “ruler” for measuring the exact color of light. Each comb tooth has a different color
The system is accurate enough to capture changes in atmospheric levels of all measured gases and is the same as a conventional point sensor for carbon monoxide and nitrous oxide. with the results obtained. The great advantage of sensing multiple gases simultaneously is that correlations can be measured between them. For example, the measured proportions of carbon dioxide and nitrous oxide were the same as in other studies on emissions from transport. In addition, the proportions of excess carbon monoxide and carbon dioxide were the same as in similar urban studies, but were only about one-third of the levels predicted by the U.S. National Emission Inventory (NEI). These levels show how efficiently fuel is burned in emissions such as cars.
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