Mario Molina is walkingme through his laboratoryat the Massachusetts In-

stitute of Technology, which is overflow-ing with exotic equipment. He makeshis way to a small room in the back ofthe lab where he points out one of hislatest toys, a powerful microscopehooked up to a video camera. He de-tails how he and his students designedthis high-tech setup to watch the for-mation of cloud particles. Despite hisenthusiastic description, my mind wan-ders—I’m distracted by the dazzlingclouds visible (without magnification)through the large window over Moli-na’s shoulder. Somehow I did not ex-pect that the man who suggested thatchlorofluorocarbons (CFCs) were de-stroying the ozone layer, some 20 kilo-meters above our heads, would use amicroscope to probe the vast expansesof the atmosphere.

But within the confines of his labora-tory, the Nobel Prize–winning Molinahas seen quite a bit—much of it trou-bling. Molina is not an alarmist by tem-

perament: “I’ve never claimed the worldwas coming to an end,” he chuckles,yet a hint of seriousness remains in hisgentle voice. When Molina and his col-league F. Sherwood Rowland of theUniversity of California at Irvine an-nounced their CFC findings in 1974, itseemed to many people that, in fact, thesky was falling.

Damage to the protective ozone layer,which shields the earth’s surface fromharmful ultraviolet radiation, wouldmean outbreaks of skin cancer andcataracts as well as the loss of cropsand wildlife. So great was the concernthat 10 years ago this fall, governmentsaround the globe outlawed CFCs bysigning the Montreal Protocol on Sub-stances That Deplete the Ozone Layer.

The reluctant Cassandra of the chem-istry world started out just having fun.As a young boy, he showed an interestin chemistry, so his indulgent parentsallowed him to convert one bathroomin the spacious family home in MexicoCity into a private laboratory.

After boarding school in Switzerland

and graduate schools in Germany andFrance, Molina made his way to theUniversity of California at Berkeley tocomplete his Ph.D. in physical chem-istry. When he arrived in 1968, thecampus was embroiled in student un-rest about the Vietnam War. His time atBerkeley served as an awakening forhim about the significance of scienceand technology to society. (Molina’stime there had a personal significanceas well: fellow graduate student LuisaTan would later become his wife andfrequent research collaborator.) Moli-na’s project was rather academic: usinglasers to study how molecules behaveduring chemical reactions. But becauselaser technology also can be used inweapons, the work was unpopular withstudent activists.

“We had to think of these issues: Whyare we doing what we are doing? Wouldthe resources be better spent in someother way? Is science good or bad?”Molina asks, waxing philosophical. “Icame to the conclusion that science it-self is neither good nor bad.” Technolo-gy—what people do with science—wasanother story.

A desire to understand the implica-tions of technology led Molina to studyCFCs during a postdoctoral fellowshipunder Rowland. “All we knew is thatthese industrial compounds were un-usually stable. We could measure themeverywhere in the atmosphere,” Moli-na says. “We wondered: What happensto them? Should we worry?”

The irony of CFCs is that years agothey were initially valued precisely be-cause there seemed to be no need toworry. At a 1930 meeting the inventorof the compounds inhaled CFC vaporsand then blew out a candle to showthat the chemicals were neither toxicnor flammable. Over the next 50 years,CFCs made an array of new technolo-gies possible: modern refrigerators,household and automobile air condi-tioners, aerosol spray cans, Styrofoam,cleaning techniques for microchips andother electronic parts.

Most emissions, such as exhaust fromcars and smokestacks, actually never getvery high in the air—the pollutants reactwith the hydroxyl radical (OH), whichis essentially an atmospheric detergentthat makes compounds soluble in rain-water. Molina checked to see how fastCFCs would react with hydroxyl radi-cals. The answer: zip. “It seemed that

News and Analysis40 Scientific American November 1997

PROFILE:

MARIO MOLINA

Rescuing the Ozone Layer

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maybe nothing whatsoever interestingwould happen to them,” he says.

If chemicals could not break downCFCs, perhaps sunlight would. Basedon their laboratory observations, Row-land and Molina realized that in thestratosphere, ultraviolet radiation is suf-ficiently energetic to break apart CFCmolecules, releasing, among other sub-stances, highly reactive chlorine atoms.Small amounts of chlorine can destroyozone by acting as a catalyst (that is,the chlorine is not used up in the pro-cess of breaking down ozone).

In June 1974 Rowland and Molinapublished their paper in the journal Na-ture proposing a connection betweenCFCs and destruction of the ozone lay-er. Much to their surprise, the article re-ceived little notice. A few months laterthe two held a press conference at achemistry meeting. “Eventually, wecaught people’s attention,” Molina says.

Indeed. Over the next few years, let-ters about CFCs poured into Congress—

the final tally is second only to the num-ber received about the Vietnam War.The government responded quickly,passing amendments to the Clean AirAct in 1977 that called for the regula-tion of any substance “reasonably an-

ticipated to affect the stratosphere.”Soon the use of CFCs as propellants inspray cans was banned in the U.S.Chemical companies began to seek al-ternatives to CFCs; compounds knownas hydrochlorofluorocarbons (HCFCs)and hydrofluorocarbons (HFCs) are themost common choices. (AlthoughHCFCs still contribute to ozone deple-tion because they contain chlorine, theyare not as hazardous as CFCs, becausethey typically fall apart before reachingthe stratosphere. The HFCs pose nothreat to the ozone layer.)

Significantly, this flurry of action tookplace despite the fact that no one hadever observed any loss of stratosphericozone. The famous hole in the ozonelayer above Antarctica was not even de-tected until 1985. Molina commendsthis “important precedent in the use ofprecautionary principles” and suggeststhat the need to “do something eventhough the evidence is not there [is]very typical of environmental issues.”

A more comprehensive internationaltreaty regulating CFCs took longer tonegotiate. But in September 1987 morethan two dozen countries signed theMontreal Protocol. The agreement im-posed an immediate reduction in the

production and use of CFCs; subsequentamendments led to a total phaseout ofCFCs in developed countries in 1995(developing countries have until 2010).

Although the Montreal Protocol wassigned after the discovery of the Antarc-tic ozone hole, many scientists and pol-icymakers at the time were still unsurewhether the ozone hole had been causedby CFCs or whether it was just part ofa natural cycle. Molina himself remem-bers that when he first heard news ofthe ozone hole he “had no idea” wheth-er CFCs were truly to blame. To provethe connection between CFCs and theAntarctic ozone hole, Molina and hiswife proposed a new series of chemicalreactions in 1987 that measurementsconfirmed in 1991.

That satisfied most science and policyexperts, although a few critics still per-sist. As late as 1995 (ironically, the sameyear Molina won the Nobel Prize forChemistry, along with Rowland andPaul J. Crutzen of the Max Planck Insti-tute for Chemistry in Mainz, Germany),Congress held hearings questioningwhether the ozone hole was real and, ifso, whether CFCs were really the cul-prit. The state of Arizona declared theMontreal Protocol invalid within its

Copyright 1997 Scientific American, Inc.

boundaries. Molina’s patience is clearlytried by these suggestions. “You can goto the stratosphere and see how muchchlorine there is and convince yourselfthat it’s coming from CFCs,” he says,his voice rising.

In the scientific community, the ozoneproblem is basically settled. Today thechallenges lie more in the area of en-forcing the Montreal Protocol. (The lat-est concern: a burgeoning black marketin CFC trade.) Molina and his research

group have moved on as well, inves-tigating a wide range of reactionsthat occur in the atmosphere, in-cluding some that are important inurban air pollution. And Molinanow spends less time in the lab andmore time speaking to governmentofficials on policy questions. In 1994President Bill Clinton appointedhim a science and technology advis-er to the administration.

Molina also encourages studentsfrom developing countries, particularlyin Latin America, to study environ-mental sciences. (He is the first Mexi-can-American to win a Nobel Prize andthe first person born in Mexico to winin the sciences.) Part of his prize moneyhas gone to create a fellowship for thesestudents to study in the U.S. Given theenvironmental problems faced by de-veloping nations, including deforesta-tion, desertification, and worsening wa-ter and air pollution, Molina considers

it crucial to involve people from theseregions when crafting solutions.

Molina’s smog-choked hometownoffers a poignant tale. “When I was akid in Mexico City, [pollution] was nota problem,” he recalls. Over the past 50years, of course, that has changed. Mo-lina finds it puzzling that more is notdone to combat pollution in cities,which is so plainly obvious comparedwith CFC pollution in the stratosphere.“You can already see it and smell it andbreathe it,” he comments.

Molina hopes this argument will con-vince policymakers, specifically in thedeveloping world, to reduce emissionsof fossil fuels now, a move that shouldalso help alleviate global warming. Al-though Molina sees the evidence link-ing fossil fuels and climate change asstill somewhat tentative, the connectionbetween fossil fuels and urban pollutionis unequivocal—and thereby on muchfirmer footing than the CFC-ozone de-pletion connection was when controlson CFCs were established. “If we takea look at the whole picture, it is muchclearer to me that some strong actionneeds to be taken on the energy issue.”Interesting what shows up in Molina’smicroscope. —Sasha Nemecek

CHLORINE OZONE OXYGEN

CHLORINE PEROXIDE

CHLORINEMONOXIDE

SUN

CHLORINE FREED TO BEGINREACTION 1 AGAIN

REACTION 1

REACTION 2

REACTION 3

CHLORINE DESTROYS OZONEbut is not consumed in the process. Mario and Luisa T. Molina proposed this series of reactions to explain how CFCs caused

the Antarctic ozone hole.

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Copyright 1997 Scientific American, Inc.