3
Science Scientists detail chlorofluorocarbon research Controversy continues on the compounds' ability to destroy ozone in the stratosphere, and thus reduce earth's UV shield f 169th ACS NATIONAL MEETING With study groups being formed, hear- ings being held, and more articles ap- pearing in the general press, events surrounding the chlorofluorocarbon controversy continue to accumulate. The focus of this controversy settled early this month on Philadelphia, where a Division of Physical Chemistry symposium on chlorine reactions and stratospheric ozone provided details of current research efforts. At a heavily attended press conference, symposium participants reflected the current sci- entific thinking about the problem. Meanwhile, during the same week, members of a panel formed by the Na- tional Research Council to assess strat- ospheric pollution were announced. Joining Dr. H. S. Gutowsky, director of the school of chemical sciences at the University of Illinois, who had pre- viously been chosen as chairman (C&EN, March 31, page 14), are 11 scientists from the U.S., Canada, the U.K., and West Germany. The panel is charged with assessing the potential effects of stratospheric pollution from natural as well as man- made sources. With funding from the National Aeronautics & Space Admin- istration, National Science Founda- tion, Environmental Protection Agen- cy, and National Oceanic & Atmo- spheric Administration, the panel will give principal attention to the large- scale use of chlorofluoromethanes and emissions from NASA's upcoming space shuttle. The chlorofluorocarbon problem first surfaced last June when Dr. F. Sher- wood Rowland and Dr. Mario Molina announced their theory of ozone de- struction by chlorofluoromethane gas. However, the issue didn't draw major public attention until Rowland and Molina presented their findings at the American Chemical Society's national meeting last September in Atlantic City (C&EN, Sept. 23, 1974, page 27). Since then, the issue has been contin- ually in the headlines and it has gal- vanized studies and research on nu- merous fronts. The main concern is with the chloro- fluoromethanes fluorocarbon-11 (CFC1 3 ) and fluorocarbon-12 (CF2CI2)— FC-11 and FC-12. The problem arises with the extreme inert- ness of the compounds. Used as aerosol propellants and as refrigerants—per- haps best known are the Du Pont Freons—the compounds escape to the lower atmosphere. But because of their inertness, they do not decompose there. Slowly but inexorably they find their way into the stratosphere. There, after absorbing short-wave-length ul- traviolet radiation (1900 to 2250 A), they decompose to free radical atomic chlorine and other products. The chlo- rine radical then acts as a catalyst and attacks ozone through a chain of reac- tions to form oxygen. That, at least, is the theory. What makes it an issue is that no reduction in the ozone layer by this means has been directly measured as yet, and the question still remains as to whether chlorine atoms react in the strato- sphere as they do in the lab. What makes the issue serious is that the stratospheric ozone layer is a shield against ultraviolet radiation and its re- duction could result in increased inci- dences of skin cancer, weather modifi- cation, and agricultural damage. The fluorocarbon industry doesn't deny the seriousness of the problem. Indeed, as Dr. Raymond L. McCarthy, technical director of Du Pont's Freon products division, told the press con- ference at the ACS meeting, if the the- oretical models are correct, there is no question that production of chlorofluo- romethanes must end. But faced with the lack of proof, the industry urges caution lest severe economic disloca- tions be caused needlessly from a ban on the products. The models have been developed, McCarthy says, and the next step now is to make measurements. A number of competent experimenters, he notes, are developing techniques for measuring the CI and CIO species. Faced with the same lack of direct proof, many scientists are calling for a ban on production and use of chloroflu- oromethanes. Armed with the theoreti- cal models and experimental results, they contend that every year spent in discussion and additional research on the problem will result in a greater ultimate effect on ozone levels. Even significant errors in current calculations will have little effect on the eventual fate of the ozone layer, Rowland says. He maintains that worldwide manufacture of chlorofluo- romethanes already is about 25 times the level that the atmosphere can ab- sorb without significant reduction in average ozone concentration. Even if Johnston, Rowland, Wofsy, McCarthy, Cicerone, and Kaufman (left to right) at ACS news conference on stratospheric ozone

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Page 1: Scientists detail chlorofluorocarbon research

Science

Scientists detail chlorofluorocarbon research Controversy continues on

the compounds' ability

to destroy ozone in the

stratosphere, and thus

reduce earth's UV shield

f 169th ACS NATIONAL MEETING

With study groups being formed, hear­ings being held, and more articles ap­pearing in the general press, events surrounding the chlorofluorocarbon controversy continue to accumulate. The focus of this controversy settled early this month on Philadelphia, where a Division of Physical Chemistry symposium on chlorine reactions and stratospheric ozone provided details of current research efforts. At a heavily attended press conference, symposium participants reflected the current sci­entific thinking about the problem.

Meanwhile, during the same week, members of a panel formed by the Na­tional Research Council to assess strat­ospheric pollution were announced. Joining Dr. H. S. Gutowsky, director of the school of chemical sciences at the University of Illinois, who had pre­viously been chosen as chairman (C&EN, March 31, page 14), are 11 scientists from the U.S., Canada, the U.K., and West Germany.

The panel is charged with assessing the potential effects of stratospheric pollution from natural as well as man-made sources. With funding from the National Aeronautics & Space Admin­istration, National Science Founda­

tion, Environmental Protection Agen­cy, and National Oceanic & Atmo­spheric Administration, the panel will give principal attention to the large-scale use of chlorofluoromethanes and emissions from NASA's upcoming space shuttle.

The chlorofluorocarbon problem first surfaced last June when Dr. F. Sher­wood Rowland and Dr. Mario Molina announced their theory of ozone de­struction by chlorofluoromethane gas. However, the issue didn't draw major public attention until Rowland and Molina presented their findings at the American Chemical Society's national meeting last September in Atlantic City (C&EN, Sept. 23, 1974, page 27). Since then, the issue has been contin­ually in the headlines and it has gal­vanized studies and research on nu­merous fronts.

The main concern is with the chloro­fluoromethanes fluorocarbon-11 (CFC13) and fluorocarbon-12 (CF2CI2)— FC-11 and FC-12. The problem arises with the extreme inert­ness of the compounds. Used as aerosol propellants and as refrigerants—per­haps best known are the Du Pont Freons—the compounds escape to the lower atmosphere. But because of their inertness, they do not decompose there. Slowly but inexorably they find their way into the stratosphere. There, after absorbing short-wave-length ul­traviolet radiation (1900 to 2250 A), they decompose to free radical atomic chlorine and other products. The chlo­rine radical then acts as a catalyst and attacks ozone through a chain of reac­tions to form oxygen.

That, at least, is the theory. What makes it an issue is that no reduction in the ozone layer by this means has been directly measured as yet, and the

question still remains as to whether chlorine atoms react in the strato­sphere as they do in the lab. What makes the issue serious is that the stratospheric ozone layer is a shield against ultraviolet radiation and its re­duction could result in increased inci­dences of skin cancer, weather modifi­cation, and agricultural damage.

The fluorocarbon industry doesn't deny the seriousness of the problem. Indeed, as Dr. Raymond L. McCarthy, technical director of Du Pont's Freon products division, told the press con­ference at the ACS meeting, if the the­oretical models are correct, there is no question that production of chlorofluo­romethanes must end. But faced with the lack of proof, the industry urges caution lest severe economic disloca­tions be caused needlessly from a ban on the products.

The models have been developed, McCarthy says, and the next step now is to make measurements. A number of competent experimenters, he notes, are developing techniques for measuring the CI and CIO species.

Faced with the same lack of direct proof, many scientists are calling for a ban on production and use of chloroflu­oromethanes. Armed with the theoreti­cal models and experimental results, they contend that every year spent in discussion and additional research on the problem will result in a greater ultimate effect on ozone levels.

Even significant errors in current calculations will have little effect on the eventual fate of the ozone layer, Rowland says. He maintains that worldwide manufacture of chlorofluo­romethanes already is about 25 times the level that the atmosphere can ab­sorb without significant reduction in average ozone concentration. Even if

Johnston, Rowland, Wofsy, McCarthy, Cicerone, and Kaufman (left to right) at ACS news conference on stratospheric ozone

Page 2: Scientists detail chlorofluorocarbon research

Rowland: persist through next century

use of the chemicals ceased immedi­ately, the long life of chlorofluo-romethanes in the lower atmosphere would mean that the effects of current production wouldn't show up until later this century and would persist through the next century, he says.

One problem with gathering direct proof of ozone depletion is that there is a natural variability of ozone in the stratosphere of possibly more than 10%. Thus, Dr. Ralph Cicerone of the University of Michigan told the press conference, if it is necessary to show actual harm, it is necessary to have a lot of harm. Scientists have come to realize in the past several months, he says, that scientific proof will be diffi­cult and may take years. But, he says,

decision-makers do not have much room to hedge their bets. All the theo­retical models, he points out, indicate that the effects of chlorofluorocarbons will persist for decades.

In a like vein, Dr. Fred Kaufman, a chemical kineticist at the University of Pittsburgh and organizer of the Phila­delphia symposium, notes that the problem involves a complex scheme in which it is difficult to measure the final product. But a decision must be made at some point, he says, and there is a large body of knowledge to rely on. Admitting to being bothered by the "man-from-Missouri" approach, he pleads that the show-me attitude not become excessive. "From the kineti-cist's point of view," he says, "there is nothing on the horizon that would change matters."

Kaufman notes that many new ex­periments and measurements are being made. There is, he says, "a rapid con­vergence of various laboratories on the truth."

His own research group, for example, described at the symposium experi­ments it is carrying out. Kaufman notes that the catalytic removal of "odd oxygen"—03 and O—by chlorine species formed in photolysis of chlo­rofluorocarbons in the stratosphere in­volves seven or eight key reactions. In these reactions, CI or CIO is formed or destroyed or interacts with "odd oxy­gen."

The Pittsburgh group is in one stage or another of studying four of the reac­tions in a discharge-flow apparatus using resonance fluorescence detection of atom or radical species such as CI, O, or OH. The radicals are measured at the downstream end of a tempera­ture-controlled tube at concentrations

upwards of one part in 100 million and at pressures about 1% of atmospheric. The results so far:

• Work is completed on the reaction OH + HC1 — H 2 0 + CI, which regen­erates reactive CI from relatively inert HC1. A total of 60 experiments show the reaction to be fast, in good agree­ment with measurements made by oth­ers using a different method.

• Work is just about complete on the principal CI reaction in the strato­sphere, CI + 0 3 — CIO 4- 0 2 . Some 73 experiments at 200 to 370° K have shown the reaction to be very rapid, al­though about 30% lower than the one reported room-temperature measure­ment. It is, the group says, a fast first step in the catalytic chain.

• Work is in progress on the reac­tion CIO + NO — CI + N 0 2 , in which CI is regenerated. Initial experiments have shown it to be very rapid.

• Work on the reaction CIO + O -* CI -I- O2 is just getting under way.

All told, says the Pittsburgh group, the general conclusion that can be drawn at this stage is that none of the laboratory results so far contradict the seriousness of the projected ozone re­moval problem.

Dr. Julian Heicklen of Pennsylvania State University's chemistry depart­ment and ionosphere research labora­tory told the symposium of work car­ried out by his group on the photoox-idation of chlorofluoromethanes. In studying the photodissociation of FC-11 and FC-12, the group found that the photodissociation efficiency to give chlorine atoms is unity. The group also measured the rates of attack of O on CF3CI, CF2CI2, CFCI3, and CCU and found the reactions to give CIO all the time.

Pollution by chlorofluorocarbons may parallel well-understood natural NOx cycle

Catalytic cycle Neutral cycle

NO + O, N02 + 0 2

NO + O3

N02 + 0

• N02 + 0 2

•NO + 0 ,

N02 + UV -» NO + O

O + 0 2 - » 0 3

• 0 2 + 0 2 Net: 0 3 + O

Destroys 70% of ozone formed

Net: Zero

N20 UV

0(1D) #

NO, 5% 1 million tons per year

Catalytic cycle

CI +03-»CIO + 02

CI0 + O-*Cl + 0 ,

Neutral cycle

CI + 0 3 - > C I O + 0 2

CIO + NO- * CI + N 0 9

N02 + UV-

0 + 0 , -

• NO + O

Net: 0 3 + O - • 0 „ + O, Net: Zero

CF2CI2

Stratosphere

CH4

c i ; HC

HO

100% 0

CITCIO 10%

N20 HNOa

Inert in troposphere

N20

Rainout in troposphere

CF?CI 500,000

2 tons per year

Inert in troposphere

HCI

CF2CI2

Rainout in troposphere

N20, N2 NO", N02 in soil Note: CF2 C 1 3 represents chlorofluorocarbons.

22 C&EN April 21, 1975

Page 3: Scientists detail chlorofluorocarbon research

The significance of the group's find­ings, Heicklen says, is that the chloro-fluoromethanes are removed very effi­ciently to produce CI or CIO both by photodissociation and by 0 attack. In fact, he says, the rates of these pro­cesses are as fast as theoretically possi­ble. Thus, the molecules are indeed a threat to the ozone layer.

Dr. Harold S. Johnston of the Uni­versity of California, Berkeley, says that more has been learned about the stratosphere in the past three years than was ever known before. He cites a three-year, $50 million study made by the Department of Transportation through its Climatic Impact Assess­ment Program. That program included research on the stratosphere, strato­spheric ozone, and the vulnerability of stratospheric ozone to future fleets of supersonic transports (C&EN, Jan. 27, page 8).

The new data from the DOT study, Johnston says, are directly applicable to the chlorofluorocarbon problem. Johnston draws a direct parallel be­tween the now well-understood role of natural stratospheric nitrogen oxides and the problem of stratospheric pollu­tion by chlorofluorocarbons.

Nitrous oxide is released from the

NRC picks panel members for study of stratosphere Chairman, Dr. H. S. Gutowsky, di­rector, school of chemical sciences, University of Illinois, Urbana

Dr. Julius Chang, University of Cali­fornia, Lawrence Livermore Labora­tory

Dr. Robert Dickinson, National Center for Atmospheric Research, Boulder, Colo.

Dr. James P. Friend, department of chemistry, Drexel University, Phila­delphia

Dr. Christian E. Junge, Max-Planck Institut fur Chemie, Mainz, West Germany

Dr. Frederick Kaufman, department of chemistry, University of Pitts­burgh

Dr. R. A. Marcus, department of chemistry, University of Illinois, Ur­bana

Dr. George Pimentel, department of chemistry, University of California, Berkeley

Dean H. I. Schiff, York University, Downsview, Ont.

Dr. John H. Seinfeld, division of chemistry and chemical engineer­ing, California Institute of Technolo­gy, Pasadena

Dr. Brian Thrush, department of chemistry, Cambridge University, England

Dr. Cheves Walling, department of chemistry, University of Utah, Salt Lake City

soil by natural processes. Inert in the lower atmosphere, it slowly moves into the stratosphere where it is partially converted to nitric oxide plus nitrogen dioxide (NOx). The NOx destroys some 70% of the ozone, which is formed from solar radiation and oxygen. The global rate of formation of stratospheric NOx , Johnston notes, has been found to be 1 million tons per year. This rate, he says, constitutes a simple, firm refer­ence point for comparison against pos­sible stratospheric pollutants, includ­ing chlorofluorocarbons.

Meanwhile, as studies are made and data come in, Rowland proposes pin­ning down the chlorofluorocarbon ques­tion with experiments that could be performed during the next few months. He suggests use of special techniques and equipment to detect the amounts of radioactive chlorine in fresh samples of stratospheric air. The radioactive chlorine is formed in small amounts in the stratosphere when molecules of trace argon are struck by cosmic rays. The radioactive chlorine decomposes quickly with a half-life of less than an hour. But if air samples were analyzed quickly for key compounds in the ozone destruction sequence, the pres­ence of radioactive chlorine in the

Hypertensives work by

169th ACS NATIONAL MEETING

The underlying causes of essential hy­pertension, or high blood pressure, are still largely unknown. But the chemi­cal and physical changes that occur in the body with the onset of hyperten­sion have been observed with some de­gree of precision. This knowledge has enabled pharmaceutical researchers to synthesize antihypertensive drugs to treat the symptoms of this disease that affects millions of people worldwide.

By class, antihypertensive drugs fall roughly into three classes of com­pounds: adrenoceptor antagonists, pe­ripherally acting compounds, and cen­trally acting compounds. Adrenoceptor antagonists inhibit the action of nor­adrenaline, a chemical messenger that carries sympathetic nerve impulses to the various organs of the body—par­ticularly the heart and blood vessels, which play a key role in blood pressure control. Peripherally acting drugs work by increasing the degree of vasodila­tion—in other words, decrease the de­gree of blood vessel constriction in the hypertensive patient. Centrally acting antihypertensives, on the other hand, get right to the root of the problem, so to speak. They work on the vasomotor center of the lower brain, the section directly responsible for blood pressure control.

Drugs acting by these several mecha­nisms were discussed at a Medicinal

compounds would constitute evidence that the ozone-depleting reactions are indeed occurring in the stratosphere.

Rowland also proposes as a short-term solution to the chlorofluo-romethanes problem the substitution of FC-22 for FC-12. He notes that FC-22 (CHF2C1) is one of three com­mercial chlorofluorocarbons containing a C—H bond. Chlorofluorocarbons with this or C = C bonds can react, he says, with OH radicals in the lower at­mosphere and be destroyed there, un­like chlorofluoromethanes.

Even so, it would be just a short-term solution. Rowland estimates that about 10% of FC-22 will reach the stratosphere and react there. But since it can release only one chlorine atom per molecule, compared to two for FC-12, the relative atmospheric hazard is half of 10%, or 5%. On this basis, he estimates that FC-22 is 20 times less hazardous than FC-12 per molecule. He notes, however, that considerable uncertainty remains in the calculations and the added safety factor could easi­ly be 10 or 40 rather than 20. He also estimates that the safety factor for FC-21 (CHFCI2) and FC-31 (CH2FC1) should be even higher by another fac­tor of five—that is, 50 to 200. •

several mechanisms Chemistry Division symposium on re­cent advances in antihypertensive therapy. Dr. Richard Clarkson of Im­perial Chemical Industries' pharma­ceutical division in the U.K. led off the program with a discussion of beta-adrenoceptor antagonist compounds that show promise for human use. The initial search for a specific beta-adre-noceptor antagonist, Clarkson says, centered on a means of protecting the myocardium (heart muscle) from sym­pathetic nerve stimulation that would be useful for treating angina pectoris and for patients recovering from heart attacks.

Trials with the early compounds synthesized for this purpose proved successful. But these drugs exhibited antihypertensive activity as well. One drug in particular, propranolol, in 1964 was discovered to have antihyperten­sive activity. It is now marketed in the U.S. as Inderal by Ayerst under license from ICI. Followup studies with other compounds of the propanolamine class, to which propranolol belongs, showed that antihypertensive activity is typi­cal of the class.

The specific mechanism by which the beta-blockers act, according to Clarkson, is still uncertain. But there is speculation that they work by one or a combination of modes. These include reduction of cardiac output; suppres­sion of renin release (a proteolytic en­zyme responsible for some forms of hy­pertension); by direct central effects on the brain area responsible for blood

April 21, 1975 C&EN 23