PT146.S4.P4.Q23 > Analytics

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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 layer of ozone—a toxic form of oxygen—in the stratosphere, 10 to 25 miles above the earth's surface.

Background · Ozone protects from UV radiation from sun

Ozone is a toxic kind of oxygen 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 two Nobel Prize-winning scientists, Mario Molina and F. Sherwood Rowland. …

Spotlight · Molina and Rowland warned about fragility of ozone layer in 1970s

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 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 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 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 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.

M's and R's findings · CFCs deplete ozone layer because of chlorine in CFCs

CFCs break down into constituent elements in UV radiation. One element, chlorine, reacts to ozone in way that destroys ozone.

In 1974 the two scientists estimated that the 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 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 testify before the U.S. Congress and was later appointed to the U.S. National Science Foundation Committee on Fluorocarbon Technology Assessment.

M's and R's advocacy · Advocated public policy response to accumulation of CFCs in atmosphere

Predictably, the work of Molina and Rowland and their advocacy of dramatic policy changes were 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 (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 environmentally friendly refrigerant chemicals.

M's and R's success · International ban on ozone-depleting gases passed; CFCs banned in North America

Passage Style

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23.

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

What laboratory experiments were conducted by Molina or Rowland in their research on CFCs?

The author doesn’t discuss the laboratory experiments Molina and Rowland conducted. What kinds of experiments? What did they do in those experiments? We have no information about this.

11%

What was the estimated concentration of CFCs in the atmosphere in 1987?

The author doesn’t discuss the estimated concentration of CFCs in the atmosphere in 1987. The author mentions the level of CFC accumulation in the atmosphere in 1974, but not 1987.

In what year did Molina testify before the U.S. Congress?

The author doesn’t mention the year in which Molina testified before the U.S. Congress.

Does any chemical that does not contain chlorine contribute to the destruction of ozone molecules?

The author doesn’t mention whether chemicals that don’t contain chlorine can contribute to the destruction of ozone molecules.

Which constituent element of CFCs is most damaging to ozone?

Answered — chlorine. The author doesn’t explicitly say it’s the “most” damaging, but in discussing the damage caused to the ozone layer, the author mentions only chlorine and discusses only the effects of chlorine. This is the best answer. Don’t think the correct answer needs to be explicitly stated or that it must be logically proven in the same way a MBT answer in logical reasoning must be logically proven.

77%

PrepTest 146 - Section 4 - Passage 4 - Question 23

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