Original spectrum on paper from 1951. Credit: IUP

An international research team led by the University of Bremen has detected chlorofluorocarbons (CFCs) in Earth’s atmosphere for the first time in historical measurements from 1951—20 years earlier than previously known. This surprising glimpse into the past was made possible by analyzing historical measurement data from the Jungfraujoch research station in the Swiss Alps. The study has now been published in Geophysical Research Letters.

"This discovery provides quantitative data for the concentration of a CFC for the year 1951," explains Professor Justus Notholt from the Institute of Environmental Physics at the University of Bremen. "Without the archived measurements from the Jungfraujoch station, this unique look into the past would have been impossible."

What are CFCs—and why are they important?

CFCs are artificially produced chemical substances that were once frequently used as coolants in refrigerators and air conditioning systems and also as propellants in spray cans. It was later discovered that they destroy the protective ozone layer in the stratosphere, which protects against dangerous ultraviolet radiation. For this reason, many countries decided to ban the production of CFCs worldwide in 1987 under the Montreal Protocol. Since then, the ozone layer has been slowly recovering.

Looking back 70 years

Until now, 1971 was considered the date of the first measurement of CFCs in the atmosphere. At that time, the British scientist James Lovelock achieved this breakthrough with a newly developed measuring device. The new study now provides results for the year 1951.

In 1950 and 1951, solar measurements were carried out with a spectrometer at the high-altitude Jungfraujoch research station (3570 meters above sea level). The original aim was to study the sun’s atmosphere and the measurements were recorded and archived on long rolls of paper.

These measurements not only provided results about the solar atmosphere, as planned at the time, but also contained additional signatures of Earth’s atmosphere. At the time, this extra input was rather disruptive, whereas now it was the scientists’ focus. Researchers from the University of Bremen, together with scientists from the Department of Astrophysics at the University of Liege in Belgium and the School of Earth and Environment at the University of Leeds in the UK, have now scanned the spectra, digitized them, and re-evaluated them using modern analysis methods. They discovered traces of the CFC "Freon-12" in Earth’s atmosphere at the time.

Surprisingly high concentration

The concentration measured in 1951 was around 26 "pptv"—that is, 26 molecules of CFC per trillion air molecules. Model calculations had expected only around 9 pptv for this time. The researchers emphasize that the models probably did not take all emission sources at the time into account.

The discovery shows how valuable historical measurement data can be for today’s research. "These old records allow us to trace the history of air pollution more accurately," explain the researchers. This helps to improve climate models and better understand how quickly harmful substances spread in the atmosphere. In addition to CFCs, other gases in Earth’s atmosphere can also be detected in the historical spectra, which is the objective of further research projects.

Publication details

Jamal Makkor et al, First Measurements of CFC‐12 in 1951 at Jungfraujoch and Comparison to Current Measurements and Atmospheric Models, Geophysical Research Letters (2026). DOI: 10.1029/2025gl117453

Citation: Ozone-depleting CFCs detected in historical measurements—20 years earlier than previously known (2026, February 3) retrieved 3 February 2026 from https://phys.org/news/2026-02-ozone-depleting-cfcs-historical-years.html

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