TECHNOLOGY: Scientists prepare an inexpensive, accurate regulatory tool to track greenhouse gas concentrations. Researchers at the National Institute of Standards and Technology (NIST) and the National Oceanic and Atmospheric Administration are refining a method using two frequency combs to indirectly measure the amount of carbon dioxide, methane and water vapor over a substantial distance. A single frequency comb emits a laser beam that contains many different wavelengths or frequencies of light, with each tooth of the comb representing a different frequency. The concentration of the different gases is measured by how much light is absorbed. The more of a gas that is present, the higher the amount of absorption. To make the frequency comb better able to identify gas absorption signatures, the laser beam contained light frequencies too high to be directly detected. In order to see what light had been absorbed at what wavelength, the researchers needed a way to spread out the frequencies. To do this, the researchers used a second frequency comb with slightly differently spaced teeth. The researchers brought the laptop-sized sensors to the roof of the NIST laboratory in Boulder, Colo. They directed the laser beams toward a mirror on a mesa, which reflected the beams back to a detector in the lab. The difference in spacing between the combs corresponded with certain radio frequencies that were measurable and could be correlated to specific greenhouse gases. The demonstration was the first time that the technique had been shown to work over long distances outdoors. Researchers have been using frequency comb technology to study greenhouse gases. However, these are the first portable sensors that are able to detect multiple gases over a relatively long distance. Combing the atmosphere with lasers Today, scientists measure the concentrations of greenhouse gases in the air by taking samples using single-point sensors. In order to estimate how much CO2 is around a power plant, or how much methane is being emitted from a feedlot, researchers would have to take multiple measurements from around the desired area with ground-based sensors and extrapolate from those measurements what the overall amount of CO2 or methane might be within the given area. Eventually, the instrument would be part of the global greenhouse gas reference network maintained by NOAA. But scientists and regulators already feel a great need for it to monitor the oil and gas industry, said Pieter Tans, a scientist in the Global Monitoring Division at NOAAs Earth System Research Laboratory and a co-author of the study. The industry is the second-highest emitter of methane, a greenhouse gas that is 86 times as potent as carbon dioxide on a 20-year time scale. Companies report their emissions to U.S. EPA every year, but scientists have recently found that they are likely lowballing their numbers. eenews.net/stories/1060008188
Posted on: Sun, 02 Nov 2014 20:22:36 +0000
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