By 1970 it was well established that ultraviolet light from the sun co

By 1970 it was well established that ultraviolet
light from the sun contributes to skin cancer.
Fortunately, much of the sun's most damaging
ultraviolet radiation is screened out by a thin, diffuse
(5) layer of ozone-a toxic form of oxygen-in the
stratosphere, 10 to 25 miles above the earth's surface.

During the 1970s, however, public policy makers
worldwide were alerted to the fragility of the ozone
layer through the pioneering research and advocacy of
(10) two Nobel Prize-winning scientists, Mario Molina and
F. Sherwood Rowland. In the absence of pollutants,
stratospheric ozone concentrations should remain
stable over time, with natural production and
destruction of the gas in rough equilibrium. Molina
(15) and Rowland showed how manufactured
chlorofluorocarbons (CFCs)-highly volatile
chemicals, millions of tons of which had been used
each year in products such as aerosol sprays and
refrigerants-chemically attack and deplete the ozone
(20) layer, diminishing its effectiveness as a shield against
ultraviolet radiation. Studying two freon gases-types
of CFCs-they observed that, when released into the
lower atmosphere (troposphere), these gases slowly
diffuse upward into the stratosphere. There, subjected
(25) to massive ultraviolet radiation, they break down into
their constituent elements, including chlorine. The
resulting increase in the concentration of chlorine in
the stratosphere is devastating to the ozone layer.
Chlorine and ozone chemically react in a way that
(30) both destroys the ozone and regenerates the chlorine
atoms. As a result of this chemical reaction, each
chlorine atom could destroy as many as 100,000 ozone
molecules before becoming inactive.

In 1974 the two scientists estimated that the
(35) atmosphere contained the accumulation of five years
of global CFC production. This meant that, given the
rate of diffusion and breakdown of CFCs in the
atmosphere, the depletion of the ozone layer would
continue for years, if not decades, even if the
(40) production and use of CFCs were to cease
immediately. Recognizing this as a pressing
environmental threat, Molina and Rowland became
public advocates for a prompt and proportionate public
policy response. As a result, Molina was invited to
(45) testify before the U.S. Congress and was later
appointed to the U.S. National Science Foundation
Committee on Fluorocarbon Technology Assessment.

Predictably, the work of Molina and Rowland and
their advocacy of dramatic policy changes were
(50) subjected to attacks by critics, especially scientists
with ties to the CFC industry. However, over time their
views were corroborated, especially by the discovery
of a hole in the ozone layer over Antarctica, and this
led to the development of an international agreement
(55) (the Montreal Protocol of 1987) to ban the production
of ozone-depleting gases. In North America, CFCs
were banned in the late 1970s, leading to a
transformation in packaging for consumer spray
products and the development of more
(60) environmentally friendly refrigerant chemicals.

1 . The information in the passage most helps to answer which one of the following questions?

(A) What laboratory experiments were conducted by Molina or Rowland in their research on CFCs?
(B) What was the estimated concentration of CFCs in the atmosphere in 1987?
(C) In what year did Molina testify before the U.S. Congress?
(D) Does any chemical that does not contain chlorine contribute to the destruction of ozone molecules?
(E) Which constituent element of CFCs is most damaging to ozone?


2. Which one of the following, if true, would most strengthen the conclusions of Molina and Rowland concerning the long-term effects of CFCs in the stratosphere?

(A) The hole in the ozone layer over Antarctica continued to grow for years after CFC emissions had almost ceased.
(B) Other manufactured chemicals have been found to diffuse upward into the stratosphere when released into the troposphere.
(C) Ozone has been shown to react more violently with chlorine than with many other chemicals.
(D) Many scientists who in the 1970s were highly critical of the research methods of Molina and Rowland have come to accept the soundness of their methods.
(E) Current CFC levels in the troposphere suggest that not all nations currently abide by the Montreal Protocol.


3. Which one of the following statements is most strongly supported by the information in the passage?

(A) Little or no ozone destruction occurs naturally in the stratosphere unless chlorine is present.
(B) Skin cancers occur primarily because of excessive absorption of ultraviolet light.
(C) Few chemicals besides CFCs can result in the release of chlorine in the upper atmosphere.
(D) Regulating the use of CFCs contributes indirectly to lowering the incidence of skin cancer.
(E) The upward flow of CFCs into the stratosphere occurs mainly in Antarctica.


4. Based on the passage, the information yielded by which one of the following experiments would be most useful in determining whether a particular chemical could replace CFCs without damaging the ozone layer?

(A) testing to see whether the chemical is capable of reacting with forms of oxygen other than ozone
(B) testing to see whether the chemical, when released into the lower atmosphere, would react with other chemicals commonly found there
(C) testing the chemical to determine whether it would chemically react with chlorine testing to see what chemical properties the
(D) chemical or its constituent elements share with chlorine
(E) testing the chemical to see if it would break down into its components when subjected to ultraviolet radiation


5. Which one of the following statements is most strongly supported by the information in the passage?

(A) No refrigerant chemicals other than CFCs had been discovered when Molina and Rowland suggested that CFC production cease.
(B) Refrigerant chemicals developed as substitutes for CFCs after 1987 release fewer chlorine atoms into the stratosphere than CFCs do.
(C) CFCs were originally used in refrigeration components because they provided the most energy-efficient means of refrigeration.
(D) The Montreal Protocol led to the cessation of CFC production in North America.
(E) Some of the refrigerant chemicals being manufactured today contain chemicals known to be environmentally damaging.