L ike an infection that grows more and more virulent, the continent-size hole in Earth’sozone layer keeps getting bigger and bigger.

Each year since the late 1970s, much of the protec-tive layer of stratospheric ozone above Antarctica hasdisappeared during September, creating what is popu-larly known as the ozone hole. The Antarctic hole nowmeasures about 9 million square miles, nearly the size of North America. Less dramatic, but still significant,depletion of ozone levels has been recorded around theglobe. With less ozone in the atmosphere, more ultravio-let radiation strikes Earth, causing more skin cancer,eye damage, and possible harm to crops.

What is ozone? How did researchers discover its rolein Earth’s atmosphere and the devastating consequencesof its depletion? The fol-lowing article, adaptedfrom an account by Dr. F.Sherwood Rowland, a pio-neering researcher in thefield who shared the 1995Nobel Prize in Chemistryfor his work, attempts toanswer these and otherquestions. In doing so, itdramatically illustrateshow science works and, inparticular, how basicresearch—motivated by adesire to understandnature—often leads topractical results ofimmense societal benefitthat could not have beenanticipated when theresearch first began.

The Problem

For four months of every year, Antarctica’sMcMurdo Research Station lies shrouded in dark-ness. Then the first rays of light peek out over thehorizon. Each day, the sun lingers in the sky just alittle longer and the harsh polar winter slowly givesway to spring.

Spring also brings another type of light to theAntarctic, a light that harms instead of nurtures. Inthis season of new beginnings, the hole in theozone layer reforms, allowing lethal ultraviolet radi-ation to stream through Earth’s atmosphere.

The hole lasts foronly two months, butits timing could not beworse. Just as sunlightawakens activity in dor-mant plants and ani-mals, it also delivers adose of harmful ultravi-olet radiation. Aftereight weeks, the holeleaves Antarctica, onlyto pass over more popu-lated areas, includingNew Zealand andAustralia. This biologi-cally damaging, high-energy radiation can

THE OZONE DEPLETION PHENOMENON

THE PATH FROM RESEARCH TO HUMAN BENEFIT

N A T I O N A L A C A D E M Y O F S C I E N C E S

A satellite image of theozone hole (pink area)over Antarctica taken onSeptember 25, 1995.

BEYOND DISCOVERYBEYOND DISCOVERY

cause skin cancer, injure eyes, harm the immune system,and upset the fragile balance of an entire ecosystem.

Although, two decades ago, most scientistswould have scoffed at the notion that industrialchemicals could destroy ozone high up in theatmosphere, researchers now know that chlorinecreates the hole by devouring ozone molecules.Years of study on the ground, in aircraft, and fromsatellites has conclusively identified the source ofthe chlorine: human-made chemicals called chloro-fluorocarbons (CFCs) that have been used in spraycans, foam packaging, and refrigeration materials.

All About Ozone

Ozone is a relatively simple molecule, consistingof three oxygen atoms bound together. Yet it hasdramatically different effects depending upon itslocation. Near Earth’s surface, where ozone comesinto direct contact with life forms, it primarily dis-plays a destructive side. Because it reacts stronglywith other molecules, large concentrations of ozonenear the ground prove toxic to living things. Athigher altitudes, where 90 percent of our planet’sozone resides, it does a remarkable job of absorbingultraviolet radiation. In the absence of this gaseousshield in the stratosphere, the harmful radiation hasa perfect portal through which to strike Earth.

Although a combination of weather conditionsand CFC chemistry conspire to create the thinnestozone levels in the sky above the South Pole, CFCs

are mainly released at northern latitudes—mostlyfrom Europe, Russia, Japan, and North America—and play a leading role in lowering ozone concentra-tions around the globe.

Worldwide monitoring hasshown that stratosphericozone has declined for at leasttwo decades, with losses ofabout 10 percent in the win-ter and spring and 5 percentin the summer and autumn insuch diverse locations asEurope, North America, andAustralia. Researchers nowfind depletion over the NorthPole as well, and the problemseems to be getting worseeach year. According to aUnited Nations report, theannual dose of harmful ultra-violet radiation striking thenorthern hemisphere rose by5 percent during the past decade.

During the past 40 years, the world has seen analarming increase in the incidence of malignant skincancer; the rate today is tenfold higher than in the1950s. Although the entire increase cannot be blamedon ozone loss and increased exposure to ultravioletradiation, there is evidence of a relationship. Scientistsestimate that for each 1 percent decline in ozone lev-els, humans will suffer as much as a 2 to 3 percentincrease in the incidence of certain skin cancers.

Exploring Earth’sAtmosphere

Like many lines of scientific inquiry, research lead-ing to the prediction and discovery of global ozonedepletion and the damaging effects of CFCs followeda path full of twists and turns. Investigators did not setout to determine whether human activity affects ourenvironment nor did they know much about chemicalpollutants. Instead, they began with basic questionsabout the nature of Earth’s atmosphere—its composi-tion, density, and temperature distribution.

B E Y O N D D I S C O V E R Y2

Although, two

decades ago, most

scientists would

have scoffed at

the notion that

industrial chemi-

cals could destroy

ozone high up in

the atmosphere,

researchers now

know that chlo-

rine creates the

hole by devouring

ozone molecules.

UV-B radiation

Troposphere

10 km

Stratospheric ozone

Mt. Everest

Stratosphere

50 km

Stratospheric ozone occupies the region of the atmospherebetween 10 and 50 kilometers from Earth's surface and provides a shield against damaging ultraviolet radiation.

The composition of our planet’s atmosphere fas-cinated humans long before chemistry became aformal science. “The storm thundered and light-ened, and the air was filled with sulfur,” Homerwrote in the Odyssey, referring to the sharp odor,created during thunderstorms, of what later becameknown as ozone.

By the late 1800s, atmospheric scientists had iso-lated carbon monoxide and inferred the existence ofa second combustible gas in the air, which they ten-tatively identified as methane, the simplest hydrocar-bon. But in attempting to further analyze the com-position of the atmosphere, researchers at the turnof the century faced a major stumbling block: virtu-ally all gases, except for molecular nitrogen and oxy-gen, exist in such minute concentrations that avail-able equipment could not detect them.

Help, however, was on the way. During the1880s, scientists had begun perfecting a new, highlyprecise method of identifying a compound byrecording a special kind of chemical fingerprint—theparticular pattern of wavelengths of light it emits orabsorbs. Scientists call this pattern a spectrum.

In the 1920s, G.M.B. Dobson developed a spec-trometer that could measure small concentrations ofozone. By measuring the spectrum of air, theBelgian scientist M.V. Migeotte demonstrated in1948 that methane is a common constituent of theatmosphere with a concentration of about one partper million by volume. Soon, scientists had the toolsto detect other atmospheric gases that occur in con-centrations one-tenth to one-hundredth as great asthat. By the 1950s, researchers had identified 14atmospheric chemical constituents.

Despite this progress, researchers were still miss-ing a major piece of the atmospheric puzzle. All ofthe compounds detected possessed an even numberof electrons, a characteristic which typically giveschemical stability. Other less common compoundswith an odd number of electrons—known as freeradicals—readily undergo chemical reactions and donot survive for long. These compounds play crucialroles in such phenomena as urban smog, the loss ofstratospheric ozone, and the global removal ofatmospheric impurities.

Scientists had not detected free radicals becausethey reside in the atmosphere at concentrations wellbelow the part-per-million level that state-of-the-artequipment in 1948 could detect. But unrelatedresearch in an entirely different field, analytical chem-istry, soon came to the rescue. Analytical chemists

had begun developing a cavalcade of new instru-ments and methods to measure minute quantities ofcompounds in the laboratory.

Such research spurredadvances on two fronts: a substantial increase in theprecision and accuracy of mea-surements of atmosphericgases and a striking decreasein the minimum concentrationof a compound that must bepresent to be detected. As a result, the number ofatmospheric compounds iden-tified by scientists hasincreased from 14 in the early1950s to more than 3,000today. Detectors today rou-tinely measure compounds atconcentrations below one partper trillion, and some can record gases that occur inconcentrations one-thousandth as great at that.

Even in some of the most remote locations onEarth, scientists have detected hundreds of com-pounds. Curiously, some of the substances that occurin the smallest concentrations rank as some of thebiggest players in altering the atmosphere. A case inpoint: the group of chemicals known as CFCs.

N A T I O N A L A C A D E M Y O F S C I E N C E S 3

Frequency (in hertz)

Wavelength (in centimeters)

high frequency short wavelength

low frequency long wavelength

1020

1010 1

Ultraviolet light

Infrared rays

Radar wavesMicrowaves

X–rays

105

1025

Gamma rays

10-10

105

10-15

1 1010

AM radio waves

1015 10-5 VISIBLE LIGHT

Television and FM radio waves

Cancer-causing ultraviolet radiation occupies the region of the spectrum between visible light and even higher frequency radiation such as x-rays and gamma rays.

The hole lasts for

only two months,

but its timing

could not be

worse. Just as

sunlight awakens

activity in dor-

mant plants and

animals, it also

delivers a dose of

harmful ultravio-

let radiation.

Enter the CFCs

CFCs were invented about 65 years ago during asearch for a new, nontoxic substance that could serveas a safe refrigerant. One of these new substances,often known by the DuPont trademark Freon, soonreplaced ammonia as the standard cooling fluid inhome refrigerators. It later became the main coolantin automobile air conditioners.

The 1950s and 1960s saw CFCs used in a varietyof other applications: as a propellant in aerosol sprays,in manufacturing plastics, and as a cleanser for elec-tronic components. All this activity doubled the world-wide use of CFCs every six to seven years. By the early1970s, industry used about a million tons every year.

Yet as recently as the late 1960s, scientistsremained unaware that CFCs could affect theatmosphere. Their ignorance was not from lack ofinterest, but from lack of tools. Detecting theminuscule concentrations of these compounds inthe atmosphere would require a new generation ofsensitive detectors.

After developing such a detector, the British sci-entist James Lovelock, in 1970, became the first todetect CFCs in the air. He reported that one ofthese compounds, CFC-11, had an atmospheric

concentration of about 60 parts per trillion. To putthat measurement in perspective, the concentrationof methane (natural gas) is 25,000 times greater.Twenty years earlier, merely detecting methane hadbeen considered a major feat.

Lovelock found CFC-11 in every air sample thatpassed over Ireland from the direction of London.That was not surprising, because most major cities,including London, widely used CFCs. However,Lovelock also detected CFC-11 from air samples

20

15

10

5

00 5 10 15 20 25 30 35

Ozo

ne p

artia

l pre

ssur

e (m

Pa)

Altitude (km)

Ozone loss over the South Pole in 1995 (in green) comparedwith 1993 (in red). The blue line shows values before ozonedestruction began. SOURCE: National Oceanic and Atmospheric Administration.

1840 Christian FriedrichSchönbein identifiesozone as a compo-nent of the loweratmosphere andnames it.

1881 W.N. Hartley identifiesozone as the substancethat absorbs ultravioletradiation from the sunat wavelengths below290 nanometers. Healso shows that ozoneresides primarily athigh altitudes.

1913–1932 C. Fabry and M. Buisson showthat the total amount of ozonein a vertical column of theatmosphere can be measuredand that it equals (in modernunits) 300 Dobson units.

1924 G.M.B. Dobson setsup a regular programof ozone measure-ments at Oxford withhis newly developedspectrophotometer.

1930 Sydney Chapmanexplains how sun-light striking mol-ecular oxygen inthe atmospheregenerates ozone.

1957 As part of theInternationalGeophysical Year, fourto five research sta-tions in Antarcticabegin making regularozone measurements.

1970 The Nimbusseries of satel-lites beginsmaking ozonemeasurements.

1973 Richard Stolarskiand RalphCicerone discoverstratosphericchlorine chainreaction.

1970 James Lovelock uses his electroncapture detector to measure chloro-fluorocarbons(CFCs).

Advances in Atmospheric Science and Policy Decisions Through 1996

This timeline shows the chain of events leading to prediction of the ozone depletionphenomenon, recognition of its consequences, and eventual actions to avert athreatened disaster. It is rich in examples of how basic research often contributesto unanticipated outcomes of immense societal benefit.

directly off the North Atlantic, uncontaminated byrecent urban pollution.

This unexpected discovery prompted Lovelockto do further studies. Accordingly, he asked theBritish government for a modest sum of money toplace his apparatus on board a ship traveling fromEngland to Antarctica. His request was rejected;one reviewer commented that even if such a mea-surement succeeded, he could not imagine a moreuseless bit of knowledge than finding the atmos-pheric concentration of CFC-11.

But Lovelock persisted. Using his own money,he put his experiment aboard the research vesselShackleton in 1971. Two years later the Britishresearcher reported that his shipboard apparatus haddetected CFC-11 in every one of the more than 50air samples collected in the North and SouthAtlantic. Lovelock correctly concluded that the gaswas carried by large-scale wind motions. He alsostated that CFCs were not hazardous to the envi-ronment, a conclusion soon to be proven wrong.

Ozone Loss: The ChemicalCulprits

In 1972, the life of atmospheric scientist F.Sherwood Rowland took a critical turn when he heard

a lecture describing Lovelock’s work. Like otherresearchers at the time, Rowland had no inkling thatCFCs could harm the environment, but the injectioninto the atmosphere of large quantities of previouslyunknown compounds piqued his interest. What wouldbe the ultimate fate of these compounds? Rowland,joined by Mario Molina, a colleague at the Universityof California, Irvine, decided to find out.

The scientists showed that CFCs remainedundisturbed in the lower atmosphere for decades.Invulnerable to visible sunlight, nearly insoluble inwater, and resistant to oxidation, CFCs display animpressive durability in the atmosphere’s lowerdepths. But at altitudes above 18 miles, with 99percent of all air molecules lying beneath them,CFCs show their vulnerability. At this height, theharsh, high-energy ultraviolet radiation from thesun impinges directly on the CFC molecules, break-ing them apart into chlorine atoms and residualfragments.

If Rowland and Molina had ended their CFCstudy with these findings, no one other than atmos-pheric scientists would ever have heard about it.However, scientific completeness required that theresearchers explore not only the fate of the CFCs,but also of the highly reactive atomic and molecularfragments generated by the ultraviolet radiation.

In examining these fragments, Rowland andMolina were aided by prior basic research on chemical

974 Sherwood

owland andMario Molinaiscover thatFCs canestroy ozonen the stratos-here.

1976 The National Academy ofSciences releases itsreport verifying theRowland-Molina finding.

1976 The Food and DrugAdministration andthe EnvironmentalProtection Agencyannounce a phase-out of CFCs inaerosols.

1978 CFCs used inaerosols arebanned in theUnited States.

1984 A British researchgroup led by JosephFarman detects a40 percent ozoneloss over Antarcticaduring spring in the southern hemi-sphere.

1985 NASA satellite dataconfirm the existenceof the ozone holeover the Antarctic.

1987 The MontrealProtocol issigned, callingfor eventualworldwide CFCreduction by50 percent.

1988 The UnitedStates ratifiesthe MontrealProtocol in aunanimous vote.

1995F. SherwoodRowland, MarioMolina, andPaul Crutzenawarded theNobel prize fortheir work inatmosphericchemistry.

1996Complete banon industrialproduction ofCFCs goesinto effect.

1988 Scientists presentpreliminary find-ings of a hole inthe ozone layerover the Arctic.

kinetics—the study of how quickly molecules reactwith one another and how such reactions takeplace. Scientists had demonstrated that a simple lab-oratory experiment will show how rapidly a particu-lar reaction takes place, even if the reaction involvesthe interaction of a chlorine atom with methane atan altitude of 18 miles and a temperature of -60degrees Fahrenheit.

Rowland and Molina did not have to carry outeven a single laboratory experiment on the reactionrates of chlorine atoms. They had only to look upthe rates already measured by other scientists. Basicresearch into chemical kinetics had reduced adecade’s worth of work to two or three days.

After reviewing the pertinent reactions, the tworesearchers determined that most of the chlorineatoms combine with ozone, the form of oxygenthat protects Earth from ultraviolet radiation. Whenchlorine and ozone react, they form the free radicalchlorine oxide, which in turn becomes part of achain reaction. As a result of that chain reaction, a

single chlorine atom canremove as many as 100,000molecules of ozone.

Unknown to Rowlandand Molina, the same chlo-rine atom chain reactionhad been discovered a fewmonths earlier by RichardStolarski and RalphCicerone. In 1974,Rowland and Molina madea disturbing prediction: Ifindustry continued torelease a million tons ofCFCs into the atmosphereeach year, atmosphericozone would eventuallydrop by 7 to 13 percent.

To make matters worse,other scientists haddemonstrated that an

entirely different group of compounds could fur-ther reduce ozone levels. Paul Crutzen first showedin 1970 that nitrogen oxides react catalytically withozone, playing an important role in the naturalozone balance. Soil-borne microorganisms producenitrogen oxides as a decay product, and Crutzen’swork spotlighted how microbe-rich agricultural fer-tilizers might lead to reduced ozone levels. His

research and that of Harold Johnston also focusedattention on the effect of nitrogen oxides spewedby high-altitude aircraft. These emissions may alsoreduce ozone levels in the stratosphere.

Earlier studies, which had investigated whetherexhaust emissions from the supersonic transportand other high-speed aircraft could damage theenvironment, had already begun to document theeffects of ozone loss. Compiled because of the per-ceived threat from these aircraft, the data werebrought to bear on the very real threat from CFCsand nitrogen oxides.

With less ozone in the atmosphere, more ultra-violet radiation reaches Earth. Scientists estimatedthat increased exposure would lead to a higher inci-dence of skin cancer, cataracts, and damage to theimmune system and to slowed plant growth.Because some CFCs persist in the atmosphere formore than 100 years, these effects would lastthroughout the twenty-first century.

Concluding that such long-term hazards wereunacceptable, Rowland and Molina called for a banon further release of CFCs. Alerted to this clearand present danger, the United States, Canada,Norway, and Sweden in the late 1970s banned theuse of CFCs in aerosol sprays.

B E Y O N D D I S C O V E R Y6

Even in some of

the most remote

locations on

Earth, scientists

have detected

hundreds of com-

pounds. Curiously,

some of the sub-

stances that occur

in the smallest

concentrations

rank as some of

the biggest play-

ers in altering the

atmosphere.

CFCs+

Sunlight

ChlorineAtoms

CCl3F + UV Light Cl + CCl2F

O2 + UV Light 2 O

+ 2O22ClOChlorineAtoms

DestroyOzone

Molecules

Cl

O O

CCl

ClF

Cl

CCl

Cl

F

2Cl + 2O3

2O3 3O2

+ 2O22Cl2ClO + 2O

2 3O O O

Net Reaction:

Chlorine atoms induce the decomposition of two ozone mole-cules into three oxygen molecules in a net chain reaction inwhich the chlorine atoms are regenerated so that decomposi-tion of ozone continues.

The Ozone Hole Emerges

As it turned out, the ozone problem was farworse than Rowland and Molina could have imag-ined. The first warning signs of a bigger crisis didnot appear until the late 1970s, but the studies thatuncovered these findings had their roots in researchdating back nearly a century.

In the 1880s, W.N. Hartley discovered that abroad band of ultraviolet light reaches Earthalmost unimpeded. This band, known as UV-A,has wavelengths just slightly shorter than ordinaryvisible light. The ozone layer partly absorbs anoth-er ultraviolet band, known as UV-B, before it canreach Earth. During the 1920s, G.M.B. Dobsonmanaged to measure the ratio of UV-A to UV-B inincoming sunlight. By doing so, he determined forthe first time the total amount of ozone in theatmosphere.

Dobson had hoped his study would lead to anew method of predicting the weather. Instead, he

became interested in theseasonal variations inozone concentrations. Aninstrument that he devel-oped, the Dobson spec-trometer, has become thestandard for monitoringozone from the ground.

The rapid developmentof new scientific tools afterWorld War II—many ofthem based on wartimeinstrumentation—led to aflowering of studies inearth science. In1957–1958, this led to aworldwide scientific effortknown as the InternationalGeophysical Year (IGY).IGY sparked an interna-

tional outpouring of research on the oceans, theatmosphere, and unexplored land areas of the planet.

Monitoring ozone levels in the south polarregion, researchers found them to be consistentlyabout 35 percent higher in late spring than in win-ter. Annual monitoring showed the same seasonalpattern through the late 1970s.

But in 1978 and 1979, the British scientistsfound something different. In October, the begin-ning of spring in the southern hemisphere, theresearchers detected less ozone than had beendetected during the past 20 years. During the nextseveral years, October ozone levels continued todecline.

In 1984, when the British first reported theirdisturbing findings, October ozone levels wereabout 35 percent lower than the average for the1960s. The U.S. satellite Nimbus-7 quickly con-firmed the results, and the term Antarctic ozonehole entered popular language.

The Evidence Mounts

By the mid 1980s, scientists had become expertin measuring the concentration of chlorine-con-taining compounds in the stratosphere. Some mon-itored the compounds from the ground; othersused balloons or aircraft. In 1986 and 1987, thesescientists, including Susan Solomon and JamesAnderson, established that the unprecedentedozone loss over Antarctica involved atomic chlorineand chlorine oxide radicals.

At the same time, measurements in the loweratmosphere established that CFC levels hadincreased steadily and dramatically since the firstrecordings taken by Lovelock in 1970. The conclu-sion was clear: The prime sources of the ozone-devouring chlorine atoms over Antarctica were theCFCs and two other pollutants, the industrial sol-vents carbon tetrachloride and methylchloroform.

A satellite operated by the National Aeronauticsand Space Administration appears to have removedany possible doubt about the role of CFCs. Datacollected over the past three years by the UpperAtmosphere Research Satellite revealed these com-pounds in the stratosphere. Moreover, the satellitehas traced the worldwide accumulation of stratos-pheric fluorine gases, a direct breakdown product of CFCs. The quantitative balance of CFCs and itsproducts eliminates the possibility that chlorinefrom volcanic eruptions or other natural sources created the ozone hole.

N A T I O N A L A C A D E M Y O F S C I E N C E S 7

When chlorine and

ozone react, they

form the free radi-

cal chlorine oxide,

which in turn

becomes part of a

chain reaction. As

a result of that

chain reaction, a

single chlorine

atom can remove

as many as

100,000 molecules

of ozone.

The Outcome: PotentialCatastrophe Averted

Painstaking research on ozone and the atmosphereover the past 40 years has led to a global ban on CFCproduction. Since 1987, more than 150 countrieshave signed an international agreement, the MontrealProtocol, which called for a phased reduction in therelease of CFCs such that the yearly amount added tothe atmosphere in 1999 would be half that of 1986.Modifications of that treaty called for a complete banon CFCs which began in January 1996. Even withthis ban in effect, chlorine from CFCs will continue toaccumulate in the atmosphere for another decade. Itmay take until the middle of the next century forozone levels in the Antarctic to return to 1970s levels.

More globally, ozone depletion is expected toremain a fact of life for several decades to come, butthanks to the research that led to early recognition ofthe problem and steps that have been taken toaddress it, the potential consequences are much lesssevere than they otherwise would have been.

Scientists estimate, for example, that if activeresearch in stratospheric chemistry had not been inplace at the time the ozone hole was discovered in1985 and confirmed in 1986, global ozone depletion,measuring 4 percent today, would be close to 10 per-cent by the year 2000. Even larger ozone depletionwould have been observed over the United States andEastern Europe, substantially exceeding the current

measurements there of about 10 percent loss in win-ter and spring and 5 percent in summer and autumn.These larger losses have been avoided because basicresearch in the atmospheric sciences had alreadyadvanced to a level where it was able to explain thechemical reactions occurring in the ozone layer. Thatknowledge allowed other informed political and regu-latory decisions to be made

In 1995, the Royal Swedish Academy of Sciencesawarded Rowland, Molina, and Crutzen the Nobelprize in chemistry for showing “how sensitive theozone layer is to the influence of anthropogenicemissions of certain compounds.” In explaining thechemical mechanisms that affect the thickness of theozone layer, “the three researchers have contributedto our salvation from a global environment problemthat could have catastrophic consequences,” theacademy noted.

As lawmakers and the public face new challenges inthe struggle to protect the environment, they willincreasingly rely on basic research to open new vistas andsuggest new solutions about these pressing concerns.

B E Y O N D D I S C O V E R Y8

Inset, from left: Paul Crutzen of the MaxPlanck Institute for Chemistry, Mainz,Germany, and Mario Molina of theMassachusetts Institute of Technology, co-recipients of the prize.(Photo of Paul Crutzen courtesy of National Center forAtmospheric Research/National Science Foundation.)

This article was adapted by Ron Cowen from an articlewritten by F. Sherwood Rowland for Beyond Discovery:The Path from Research to Human Benefit, a project of the National Academy of Sciences. The Academy, locatedin Washington, D.C., is a society of distinguished scholarsengaged in scientific and engineering research, and dedicatedto the use of science and technology for the public welfare. For over a century, it has provided independent, objective scientific advice to the nation.

“We were trying to figure out how the world

works without thinking specifically about

how to use the results. There are distinct

advantages to letting people try to under-

stand things and in doing so pursue ques-

tions that might later lead to applications.”

—F. Sherwood Rowland

© 1996 by the National Academy of Sciences

BSI@NAS.EDU (202) 334-1575 April 1996

Above left:F. Sherwood Rowland of the University ofCalifornia, Irvine,receiving the 1995 Nobel prize in chemistry.