Mario Molina: What makes his discovery so important?

Today’s Google Doodle celebrates the life and work of Mario José Molina Henríquez, a Mexico-born chemist who played a pivotal role in the discovery of the depletion of the ozone layer of Earth’s atmosphere and what was causing this. He was a co-recipient of the 1995 Nobel Prize in Chemistry for his role in discovering the threat to the Earth's ozone layer from chlorofluorocarbon (CFC) gases. He was the first Mexican-born scientist to receive a Nobel Prize in Chemistry and the third Mexican-born person to receive a Nobel prize. Molia died of a heart attack in 2020 at the age of 77. He would have been 80 today. 

What was his research based on?

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In 1973, having completed his Ph.D. in physical chemistry, Molina joined a research program at UC Berkeley under fellow chemist F. Sherwood Rowland, who was conducting pioneering research into "hot atom" chemistry, which is the study of chemical properties of atoms with excess translational energy owing to radioactive processes. They shared a topic of interest — Chlorofluorocarbons or CFCs, widely used at the time as refrigerants, propellants (in aerosol applications), and solvents, and considered ‘harmless’. CFCs were being released into the atmosphere and were accumulating in its upper layers. The basic scientific question Molina asked was "What is the consequence of society releasing something to the environment that wasn’t there before?", says a profile of Molina on the website of the American Academy of Achievement.

What did they find?

Rowland and Molina had investigated compounds similar to CFCs before. As their study of these compounds and their interaction with the atmosphere continued, they found that CFCs ascend intact into the stratosphere. Molina predicted that chlorine atoms, produced by this decomposition of CFCs, would act as a catalyst for the destruction of ozone.

Why had everyone missed this?

Earlier, the scientific community and by extension the producers of CFCs were working on the theory that solar radiation would destroy the compounds in CFCs. But Molina found that CFCs exposed to solar radiation in the stratosphere break down into their component elements, producing a high concentration of pure chlorine atoms, which destroy ozone. Molina and Rowland put together the various pieces of the puzzle and figured out that at the rate at which humans were putting out CFCs into the atmosphere, CFCs could start a chain reaction that would ultimately damage the ozone layer in the stratosphere.

What does the ozone layer do?

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The ozone layer absorbs 97% to 99% of the Sun's medium-frequency ultraviolet light (UV-B light), which is harmful for biological life-forms. The most common forms of skin cancer in humans, basal and squamous cell carcinomas, have been strongly linked to UV-B exposure. Additionally, it can cause a host of other relatively minor issues like sunburns and cataracts in the eye.

So what happened when Molina made his discovery?

Molina and Rowland published their findings in a 1974 issue of Nature. It drew considerable attention — and, initially, ridicule and criticism. Eventually, stories about the findings started appearing in the mainstream press and Molina testified before a committee of the U.S. Congress, leading to the U.S. National Academy of Sciences (NAS) releasing a report in 1976 that confirmed the essential premises of Molina’s ozone depletion hypothesis. Then, in 1985, something truly startling happened: scientists of the British Antarctic Survey detected a large and growing gap in the ozone layer over Antarctica, which was correlated with a dramatic increase in skin cancer rates in Australia and other countries of the Southern Hemisphere.

Finally, the world recognised the importance of Molina and his co-authors' work and in 1987, 56 countries adopted the Montreal Protocol, an agreement to cut CFC production and use and to work towards the worldwide elimination of CFCs from aerosol cans and refrigerators. The establishment of this protocol has led to the amount of CFCs being emitted into the atmosphere decrease significantly, halting slowing down the rate of ozone depletion considerably. It has also had a positive effect on the rate of climate change.

For this work, Molina shared the Nobel Prize in Chemistry in 1995 with Paul J. Crutzen and F. Sherwood Rowland, his co-authors on this life-changing study.