Atmospheric helium levels are rising, research confirms

The study’s lead author, Benni Birner, of the Scripps Institution of Oceanography at UC San Diego. Credit: Erik Jepsen/UC San Diego

Scientists at UC San Diego’s Scripps Institution of Oceanography have used an unprecedented technique to detect that helium levels are rising in the atmosphere, solving a problem that has persisted among atmospheric chemists for decades.

The atmospheric abundance of helium 4 (4He) the isotope increases because 4It is released during the combustion and extraction of fossil fuels. The researchers report that it is increasing at a very small but, for the first time, clearly measurable rate. the 4The isotope itself does not add to the global-warming greenhouse effect, but measurements of it could serve as proxy markers of fossil fuel use.

The study appears today in the journal nature geoscience.

“The main motivation was to resolve a long-standing controversy in the scientific community over helium concentrations in the atmosphere,” said study lead author Benni Birner, a former graduate student and now a postdoctoral researcher at the Scripps Institution of Oceanography at UC San Diego.

The isotope 4It is produced by radioactive decay in the earth’s crust and accumulates in the same reservoirs as fossil fuels, especially those of natural gas. When extracting and burning fossil fuels, 4It is released by coincidence, which creates another way to gauge the scale of industrial activity.

The breakthrough of the study lies in the technique used by the Scripps Oceanography team to measure the amount of helium in the atmosphere. Birner and Scripps geoscientists Jeff Severinghaus, Bill Paplawsky and Ralph Keeling have created an accurate method for comparing 4It isotopes to levels of common atmospheric nitrogen gas. Because nitrogen levels in the atmosphere are constant, an increase in He/N2 is indicative of the rate of 4It accumulates in the atmosphere.

Ralph Keeling, co-author of the study and geochemist at Scripps Oceanography, responsible for the famous measurement of carbon dioxide known as the Keeling Curve, describes the study as a “masterpiece of fundamental geochemistry “. Although helium was relatively easy for scientists to detect in air samples, present at levels of five parts per million in air, no one had done the work to measure it carefully enough to observe a atmospheric increase, he said.

The study also provides a basis for scientists to better understand the valuable 3-helium (3He) isotope, which has uses for nuclear fusion, cryogenics, and other applications. Proposals to acquire the moon’s noble gas are an indication of how far manufacturers will go to harvest it.

According to previous work by other researchers, the 4The isotope He exists in the atmosphere in what appears to be an invariable relationship with 3He. The atmospheric rise of 4The He isotope measured at Scripps therefore implies that the 3The He isotope should increase at a rate comparable to 4He. Birner’s team’s research raises several questions about the accuracy of scientists’ previous assumptions about how 3It is produced and in what quantity.

“We don’t know for sure, but I wonder if there’s more 3It’s coming out of the Earth more than we previously thought, which could perhaps be harvested and fuel our nuclear fusion reactors in the future,” Birner said.

“Study highlights controversy surrounding rare helium isotope 3It,” Keeling said. “The implications are far from clear, but it takes some extra work.”

Ancient helium escaping from core offers clues to Earth’s formation

More information:
Benjamin Birner, Increase in atmospheric helium due to exploitation of fossil fuels, nature geoscience (2022). DOI: 10.1038/s41561-022-00932-3.

Provided by University of California – San Diego

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