CHAPTER 4
A HOLE IN THE SKY: OZONE DEPLETION

EARTH'S PROTECTIVE OZONE LAYER

Ozone is a gas naturally present in Earth's atmosphere. Unlike regular oxygen, which contains two oxygen atoms (O₂), ozone contains three oxygen atoms (O₃). A molecule of regular oxygen can be converted to ozone by ultraviolet (UV) radiation, electrical discharge (such as from lightning), or complex chemical reactions. These processes split apart the two oxygen atoms, which are then free to bind with other loose oxygen atoms to form ozone.

Ozone exists in Earth's atmosphere at two levels: the troposphere and the stratosphere. (See Figure 4.1.) Tropospheric (ground-level) ozone accounts for only a small portion of Earth's total ozone, but it is a potent air pollutant with serious health consequences. Ground-level ozone is the primary component in smog and is formed via complex chemical reactions involving emissions of industrial chemicals and through fossil fuel combustion. Ozone formation is intensified during hot weather, when more radiation reaches the ground. Smog retards crop and tree growth, impairs health, and limits visibility.

Approximately 90% of the Earth's ozone lies in the stratosphere at altitudes greater than about twenty miles. (See Figure 4.2.) Ozone molecules at this level protect life on Earth by absorbing UV radiation from the sun and preventing it from reaching the ground. The so-called ozone layer is actually a scattering of molecules constantly undergoing change from oxygen to ozone and back. Even though most of the ozone changes back to oxygen, a small amount of ozone persists. As long as this natural process stays in balance, the overall ozone layer remains thick enough to protect the Earth from harmful UV radiation from the sun. The amount of ozone in the stratosphere varies greatly, depending on location, altitude, and temperature.

EVIDENCE OF OZONE DEPLETION

Many scientists believe that the introduction of certain chemicals into the stratosphere alters the natural ozone balance by depleting ozone molecules. Chlorine and bromine atoms are particularly destructive. They can bind to loose oxygen atoms and prevent them from reforming either oxygen or ozone. Chlorine and bromine are found in the sea salt from ocean spray. Chlorine is also present in the form of hydrochloric acid, which is emitted with volcanic gases. These are natural sources of ozone-depleting chemicals.

In the mid-1970s scientists began to speculate that the ozone layer was rapidly being destroyed by reactions involving industrial chemicals that contained chlorine and bromine. Two chemists, F. Sherwood Rowland (1927–) and Mario Molina (1943–), discovered that chlorofluorocarbons (CFCs) could break down in the stratosphere, releasing chlorine atoms that could destroy thousands of ozone molecules. This discovery led to a ban on CFCs as a propellant in aerosols in the United States and other countries.

In 1984 British scientists at Halley Bay in Antarctica measured the ozone in the air column above them and discovered alarmingly low concentrations. Measurements indicated ozone levels about 50% lower than they had been in the 1960s.

Scientists report ozone concentrations in Dobson units. The unit is named after Gordon M. B. Dobson, a British scientist who invented an instrument for measuring ozone concentrations from the ground. One Dobson unit (DU) corresponds to a layer of atmospheric ozone that would be 0.001 millimeters thick if it was compressed into a layer at standard temperature and pressure at the Earth's surface. Atmospheric ozone is considered "thin" if its concentration falls below 220 DU. A thin spot in the ozone layer is commonly called an ozone hole.

The extreme cold and unique climate conditions over the poles are thought to make the ozone layers there particularly susceptible to thinning. Where cloud and ice particles are present, reactions that hasten ozone destruction also

FIGURE 4.1

FIGURE 4.2

occur on the surface of ice particles. Since 1982 an ozone hole has appeared each year over Antarctica (the South Pole) beginning in August and lasting until November. The hole formation is linked to polar clouds that form during the dark Antarctic winter (May through September). These clouds provide reaction surfaces for chlorine-containing compounds to release their chlorine. As sunlight returns in August or September, the released chlorine begins destroying ozone molecules.

The Antarctic ozone hole increased in size throughout the 1980s. By the early 1990s it was consistently larger than the area of Antarctica. Throughout most of the early 2000s the hole has been larger in size than the continent of North America. In 2002 the size of the hole dropped dramatically because of unusually warm weather at the South Pole. As shown in Figure 4.3, the 2006 hole measured twenty-six million square kilometers (ten million square miles) in size, constituting the largest area recorded since 1998.

In 1995 scientists first detected thinning of the ozone over the Arctic (the North Pole). Historically, Arctic winters have been warmer than those in Antarctica (the South Pole). This helped protect the northern pole from ozone depletion. However, during the 1990s and early 2000s scientists reported increasingly colder temperatures over the Arctic region and the formation of more polar clouds. In April 2005 European researchers reported the lowest Arctic levels of ozone since monitoring began decades ago.

The World Meteorological Organization (WMO) notes in Scientific Assessment of Ozone Depletion: 2002 (2002, http://www.esrl.noaa.gov/csd/assessments/2002/) that the average total ozone column on a global-wide basis was approximately 3% lower between 1997 and 2001 when compared with pre-1980 average values. The most dramatic changes were recorded in the polar regions and midlatitudes (between the tropics and the poles). Most of the global population lives in the midlatitudes of the Northern and Southern Hemispheres. For instance, mainland United States lies approximately in the range of 30 degrees and 50 degrees north latitude.

CONSEQUENCES OF OZONE DEPLETION

The sun emits radiation at a variety of wavelengths. The ozone layer acts as a protective shield against UV radiation (i.e., radiation with wavelengths of approximately 290 to 400 nanometers; a nanometer is one billionth of a meter). As ozone diminishes in the upper atmosphere, the Earth could receive more UV radiation. In "Ozone Science: The Facts behind the Phaseout" (December 26, 2006, http://www.epa.gov/ozone/science/sc_fact.html), the U.S. Environmental Protection Agency (EPA) reports that the amount of UV radiation reaching the ground in Antarctica can double during the existence of its annual ozone hole.

Scientists are particularly worried about the increased exposure to radiation in the ultraviolet-B (UVB) spectrum (i.e., wavelengths of approximately 190 to 320 nanometers). This wavelength can be damaging to human health, because it is linked with adverse effects to deoxyribonucleic acid (DNA), skin, eyes, and the immune system.

FIGURE 4.3

In addition, excessive exposure to UV radiation can negatively affect terrestrial and aquatic ecosystems and damage synthetic materials.

UV radiation alters photosynthesis, plant yield, and growth in plant species. Phytoplankton (one-celled organisms found in the ocean) are the backbone of the marine food web. According to the EPA, excessive exposure to UVB radiation reduces the productivity and survival rate for these organisms. Diminishing phytoplankton supplies would likely harm many fish species that depend on them for food. Studies performed in the mid-1990s blamed the rise in UV radiation caused by the thinning of the ozone layer for the decline in the number of frogs and other amphibians.

Increased UV radiation also affects synthetic materials. Plastics are especially vulnerable, tending to weaken, become brittle and discolored, and break.

OZONE-DEPLETING CHEMICALS

Most ozone destruction in the atmosphere is believed to be anthropogenic (caused by humans). In 1998 the WMO estimated in Scientific Assessment of Ozone Depletion: 1998 (http://www.esrl.noaa.gov/csd/assessments/1998/ExecSum98.pdf) that only 18% of the sources contributing to ozone depletion were natural. The remaining 82% of sources contributing to ozone depletion were industrial chemicals. The blame is largely placed on chemicals developed by modern society for use as refrigerants, air conditioning fluids, solvents, cleaning agents, and foam-blowing agents. These chemicals can persist for years in the atmosphere. Thus, there is a significant lag between the time that emissions decline at the Earth's surface and the time at which ozone levels in the stratosphere recover.

Table 4.1 lists the chemicals of particular concern to scientists. Each chemical is assigned a value called an ozone depletion potential (ODP) based on its harmfulness to the ozone layer. The most common depleters are the chlorofluorocarbons CFC-11, CFC-12, and CFC-13. Each of these

TABLE 4.1

chemicals is arbitrarily assigned an ODP of 1. The ODPs for other chemicals are determined by comparing their relative harmfulness with that of CFC-11. In general, Class I chemicals are those with an ODP value greater than or equal to 0.2, and Class II chemicals have ODP values less than 0.2.

Class I Chemicals

Even though a number of chemicals can destroy stratospheric ozone, CFCs are the main offenders because they are so prevalent. When CFCs were invented in 1928, they were welcomed as chemical wonders. Discovered by Thomas Midgley Jr. (1889–1944), they were everything the refrigeration industry needed at the time: nontoxic, nonflammable, noncorrosive, stable, and inexpensive. Their artificial cooling provided refrigeration for food and brought comfort to warm climates. The compound was originally marketed under the trademark Freon.

Over time, new formulations were discovered, and the possibilities for use seemed endless. CFCs could be used as coolants in air conditioners and refrigerators, as propellants in aerosol sprays, in certain plastics such as polystyrene, in insulation, in fire extinguishers, and as cleaning agents. World production doubled every five years through 1970, and another growth spurt occurred in the 1980s as new uses were discovered—primarily as a solvent to clean circuit boards and computer chips.

CFCs are extremely stable; it is this stability that allows them to float intact through the troposphere and into the ozone layer. The National Aeronautics and Space Administration (NASA) estimates in "Peering into the Ozone Hole" (October 2, 2000, http://science.nasa.gov/headlines/y2000/ast02oct_1.htm) that it can take up to two years for CFC molecules to reach the stratosphere. Once there, some can survive for hundreds of years. CFCs do not degrade in the lower atmosphere but, after entering the stratosphere, they encounter the sun's UV radiation and eventually break down into chlorine, fluorine, and carbon. Many scientists believe it is the chlorine that damages the ozone layer. (See Figure 4.4.)

Even though CFCs are primarily blamed for ozone loss, other gases are also at fault. One of these gases is halon, which contains bromine. As shown in Table 4.1, halons have much higher ODP values than do CFCs. The bromine atoms in halons destroy ozone in a manner similar to that shown in Figure 4.4 for chlorine, but they are chemically more powerful. This means that the impact to ozone of a particular mass of halon is more destructive than a similar mass of a CFC. Halons are relatively long-lived in the atmosphere, lingering for up to sixty-five years before being broken down. Halon is used primarily for fighting fires. Civilian and military firefighting training accounts for much of the halon emission.

FIGURE 4.4

Other Class I ozone destroyers include carbon tetrachloride, methyl bromide, and methyl chloroform. These chemicals are commonly used as solvents and cleaning agents.

Class II Chemicals

The most common Class II ozone-depleting chemicals are hydrochlorofluorocarbons (HCFCs). HCFCs contain hydrogen. This makes them more susceptible to atmospheric breakdown than CFCs. As shown in Table 4.1, most HCFCs have a lifetime of less than six years. The most long-lived, HCFC-142b, lasts for only 17.9 years. HCFCs have much lower ODP values than CFCs, halons, and industrial ozone depleters. HCFCs are considered good short-term replacements for CFCs. Even though HCFCs are less destructive to ozone than the chemicals they are replacing, scientists believe that HCFC use must also be phased out to allow the ozone layer to fully recover.

A LANDMARK IN INTERNATIONAL DIPLOMACY: THE MONTREAL PROTOCOL

CFCs and halons were widely used in thousands of products and represented a significant share of the international chemical industry, with billions of dollars in investment and hundreds of thousands of jobs. Ozone depletion was a global problem that necessitated international cooperation, but nations mistrusted one another's motives. As with the issues of global warming and pollution, developing countries resented being asked to sacrifice their economic development for a problem they felt the industrialized nations had created. To complicate matters, gaps in scientific proof led to disagreements over whether a problem actually existed.

In 1985, as the first international response to the ozone threat, twenty nations signed an agreement in Vienna, Austria, calling for data gathering, cooperation, and a political commitment to take action at a later date. In a 1987 negotiators meeting in Montreal, Canada, the participants finalized a landmark in international environmental diplomacy: the Montreal Protocol on Substances That Deplete the Ozone Layer. It is generally referred to as the Montreal Protocol. The protocol was signed by twenty-nine countries, including the United States, Canada, Mexico, Japan, Australia, all of western Europe, the Russian Federation, and a handful of other countries around the world.

The protocol called for industrial countries to cut CFC emissions in half by 1998 and to reduce halon emissions to 1986 levels by 1992. Developing countries were granted deferrals to compensate for their low levels of production. Industrial countries agreed to reimburse developing countries that complied with the protocol for "all agreed incremental costs," meaning all additional costs above any they would have expected to incur had they developed their infrastructure in the absence of the protocol. More important, the protocol also called for further amending as new data became available.

Throughout the 1990s and early 2000s new scientific information revealed that ozone depletion was occurring faster than expected. This news spurred calls to revise the

TABLE 4.2

treaty. In total, four amendments to the Montreal Protocol have been adopted. These are known as the London Amendment (effective 1992), the Copenhagen Amendment (effective 1994), the Montreal Amendment (effective 1999), and the Beijing Amendment (effective 2002). The final phaseout schedule for ozone-depleting substances is shown in Table 4.2.

According to the United Nations Environment Program (UNEP), in "Evolution of the Montreal Protocol: Status of Ratification" (August 6, 2007, http://ozone.unep.org/Ratification_status/index.shtml), as of 2007, 191 countries had ratified the original Montreal Protocol, whereas only 130 nations had ratified the Beijing Amendment. The United States has ratified all the amendments to the Montreal Protocol.

The Montreal Protocol has been hailed as a historic event—the most ambitious attempt ever to combat environmental degradation on a global scale. It ushered in a new era of environmental diplomacy. Some historians view the signing of the accord as a defining moment, the point at which the definition of international security was expanded to include environmental issues as well as military matters. In addition, an important precedent was established: that science and policy makers had a new relationship. Many observers thought that the decision to take precautionary action in the absence of complete proof of a link between CFCs and ozone depletion was an act of foresight that would now be possible with other issues.

MONTREAL PROTOCOL IMPLEMENTATION

In 2007 the UNEP marked the twentieth anniversary of the Montreal Protocol with issuance of the report A Success in the Making (http://ozone.unep.org/Publications/MP_A_Success_in_the_making-E.pdf), which details the progress made and the challenges remaining to be solved for complete implementation. According to the UNEP, the Montreal Protocol had been ratified by 191 countries by 2006, and those countries had phased out the production and consumption of more than 95% of the chemicals controlled by the agreement. The UNEP reports high levels of compliance in both developed and developing countries. The latter have been aided financially with money from the Multilateral Fund—a fund established under the protocol to assist developing nations with phaseout costs. The UNEP indicates that atmospheric levels of major ozone-depleting substances (ODS) have decreased and projects that full implementation of the protocol will return the ozone layer to pre-1980 levels by 2050 to 2075.

Despite these successes the UNEP recognizes that the program faces ongoing challenges to its full implementation. As shown in Table 4.2, developing nations must phase out CFCs, halons, and carbon tetrachloride by 2010. In A Success in the Making, the UNEP estimates that as of 2006 these countries had eliminated 72% of their usage, leaving sizable progress to be made within only four years. Furthermore, the UNEP notes in the press release "Backgrounder: Basic Facts and Data on the Science and Politics of Ozone Protection" (August 2003, http://www.unep.ch/ozone/pdf/Press-Backgrounder.pdf) that the use of CFCs is increasing, not decreasing, in many developing countries because of demand from growing middle-class populations for consumer products that use refrigerants. The UNEP complains that much of this demand is being met by the exportation of used and older refrigeration units that still use CFCs instead of acceptable alternatives. This is expected to make it much more difficult for the developing countries to reduce their demand for CFCs by the phaseout deadline.

Illegal Trade Problems

Illegal black market trading of ODS is another frequently mentioned challenge associated with implementing the Montreal Protocol. The Environmental Investigation Agency (EIA) is a London-based nonprofit organization that works to expose international environmental crimes. Tom Maliti notes in "Illegal Trade in Ozone-Depleting Substances Is Thriving over Three Continents, Says Report" (Associated Press, November 11, 2003) that in 2003 the EIA reported that international trade in illegal ozone-depleting substances was detrimental to achieving progress under the Montreal Protocol. The EIA noted that demand for illegal CFCs remained high in the United States, Russia, China, Vietnam, Cambodia, and Nepal. Ezra Clark of the EIA, in "Preventing Illegal Trade in ODS: Strengthening the Montreal Protocol Licensing System" (June 2007, http://www.eia-international.org/files/reports138-1.pdf), indicates that weaknesses in the agreement's licensing system have allowed ODS smuggling to flourish. The EIA recommends tightening record keeping and enforcement requirements to help alleviate these problems.

the u.s. black market

the u.s. black market. In 1996 the ban on CFCs was implemented in the developed countries, including the United States. The CFC called Freon was widely used in automobile air conditioners before that time. After the ban went into effect, there were still millions of Americans with cars that used Freon as a refrigerant. Even though alternative refrigerants were available, they were more expensive than Freon. The result was a black market for the product. This market expanded in the United States during the early 2000s with the boom in the illegal production of methamphetamine at so-called meth labs. Freon is commonly used in meth labs as part of the production process.

Several U.S. government agencies—the EPA, the U.S. Customs and Border Protection, the U.S. Departments of Commerce and Justice, and the Internal Revenue Service—began intensive antismuggling efforts. The Internal Revenue Service became involved because of the Revenue Reconciliation Act of 1989, which imposes an excise tax on most U.S. manufacturers, producers, and importers of ODS. During the early 2000s U.S. law enforcement officials broke up a massive Freon-smuggling ring based in Panama that operated during the 1990s to supply Freon to customers in southern Florida. The U.S. Department of Justice (DOJ) reports in "Defendant to Serve 17 Years in Prison for Smuggling Freon" (May 21, 2004, http://www.usdoj.gov/opa/pr/2004/May/04_tax_354.htm) that the ring leader was sentenced to seventeen years in prison and ordered to pay a $20.3 million fine. He also had to pay $6.5 million in restitution to the Internal Revenue Service for tax evasion. In another case, the DOJ notes in "Businessmen Sentenced to 88 Months in Prison for Scheme to Evade Taxes on Sales of Ozone-Depleting Chemical" (March 22, 2006, http://www.usdoj.gov/opa/pr/2006/March/06_enrd_164.html) that in 2005 two New York businessmen were convicted of dozens of counts in an ODS scheme. The two purchased large quantities of CFC-113 and avoided the excise tax by claiming that they intended to export the chemical. Instead, they sold it to U.S. buyers, including a laboratory supply company indicted in a separate investigation for selling CFC-113 to meth labs. In 2006 the two men received prison sentences of more than one year and were ordered to pay $1.9 million in restitution.

MONITORING DATA SHOW PROGRESS

The National Oceanic and Atmospheric Administration (NOAA) operates the Earth System Research Laboratory (ESRL), which is headquartered in Boulder, Colorado. The ESRL collects data at its observatories around the world and does research related to global trends in air quality.

Figure 4.5 shows atmospheric data collected by the ESRL for five ozone-depleting chemicals: CFC-11, CFC-12, CFC-113, methyl chloroform (CH₃CCl₃), and carbon tetrachloride (CCl₄). The data were collected at five ESRL observatories:

• Point Barrow, Alaska
• Niwot Ridge, Colorado
• Mauna Loa, Hawaii

FIGURE 4.5

• Cape Matatula, American Samoa
• South Pole, Antarctica

After peaking in the 1990s, the atmospheric concentrations of CFC-11 began to decline. Concentrations of CFC-113, methyl chloroform, and carbon tetrachloride have declined dramatically since 1990. CFC-12 concentrations began to level off in 2002, after climbing steadily for decades. CFC-12 has the longest atmospheric lifetime (one hundred years) of the five compounds.

PREDICTING THE BENEFITS OF THE MONTREAL PROTOCOL

The EPA uses the model called the Atmospheric and Health Effects Framework (AHEF) to evaluate the human health impacts expected to be gained from mitigating (correcting) ozone depletion. Specifically, the model estimates the incidence and mortality of skin cancer cases in the United States for different control scenarios under the Montreal Protocol. According to the latest available AHEF report, Human Health Benefits of Stratospheric Ozone Protection (April 24, 2006, http://www.epa.gov/ozone/science/AHEFDEC2003D3.pdf), earlier versions of the model also estimated the incidence of cataracts (clouding of the natural eye lens). However, the EPA notes that the link between UV exposure and cataracts is now considered "weak." The AHEF uses stratospheric ozone levels from 1979 to 1980 as the baseline for its analysis.

Figure 4.6 presents AHEF predictions of stratospheric ozone column levels at 40 degrees to 50 degrees north

FIGURE 4.6

latitude, assuming that the 1999 Montreal Amendment to the protocol is fully implemented. The EPA anticipates that ozone levels at this latitude range, which encompasses the northern U.S. mainland, will return to baseline levels by the 2040s. Figure 4.7 compares the original Montreal Protocol with its amendments in terms of the annual incidence of cutaneous malignant melanoma (CMM) cases. CMM is the least common but most dangerous form of skin cancer, because it can quickly spread to other parts of the body that are difficult to treat. As shown in Figure 4.7, the Montreal Amendment to the Montreal Protocol came closest to approaching the baseline incidence (for the period from 1979 to 1980), which is reflected in the y-axis. In other words, full implementation of the Montreal Amendment will come close to reducing the incidence of CMM to levels that occurred before 1980, when the ozone level had not yet been depleted. (Note that the Beijing Amendment is not included in the graph, because it would make only slight changes to the Montreal Amendment.)

THE LATEST SCIENTIFIC ASSESSMENT

Article 6 of the Montreal Protocol requires that the ratifying nations base their decision making on scientific information assessed and presented by an international panel of ozone experts. This panel includes the WMO, the UNEP, the European Commission, NOAA, and NASA.

In February 2007 the UNEP published the panel's latest findings in Scientific Assessment of Ozone Depletion: 2006 (http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/index.shtml). This is the sixth scientific assessment of the world's ozone condition and is based on analysis of data collected from satellites, aircraft, balloons, and ground-based instruments and the results of laboratory investigations and computer modeling.

The following are the major findings:

• Global emissions of CFC-11 and CFC-12 in 2003 were approximately 25% of their maximum values reported back around 1986. CFC-113 emissions declined approximately 3% over the same time period. Emissions of all three ODS have declined since 2000.
• Stratospheric abundance of all ODS has declined since peaking in the late 1990s.
• Total column ozone values averaged globally for 2002–05 were 3.5% less than 1964–80 values. Ozone values over the Northern Hemisphere reached a minimum in the early 1990s and have been increasing since that time. In the Southern Hemisphere the levels decreased through the late 1990s before leveling off.

FIGURE 4.7

• Total column ozone is projected to increase by 1% to 2.5% between 2000 and 2020. By 2100 total column ozone should be approximately 5% greater than values recorded in 1980.
• Stratospheric chlorine levels are expected to return to pre-1980 levels by 2049 at the midlatitudes and by 2065 over Antarctica.

U.S. EFFORTS TO END OZONE DEPLETION

In April 2005 the U.S. Food and Drug Administration (FDA) adopted a final rule banning the use of such ozone-depleting substances as propellants in medical inhalers. This use was exempted from the general ban on CFCs that went into effect during the 1990s. The FDA rule prohibits the distribution of metered-dose inhalers (commonly used for the medical treatment of respiratory problems) using CFCs after December 31, 2008. The agency reports that alternative acceptable propellants for the devices are available on the market and should adequately serve patient needs.

Even though CFCs are no longer used in new applications in the United States, existing users can continue using them, provided they are maintained under strict regulation, such as being replenished and "reclaimed" by authorized technicians. The EPA Office of Enforcement and Compliance Assurance can levy civil fines and criminal prosecutions against companies and individuals who violate regulations regarding ODS.

Recycled halon and inventories produced before January 1, 1994, are the only supplies now available. It is legal under the Montreal Protocol and the U.S. Clean Air Act to import recycled halon, but each shipment requires approval from the EPA. Certain uses, such as fire protection, are classified as "critical use" and are permitted as long as supplies remain. The EPA also maintains a list of acceptable substitutes for halon.

SUBSTITUTES AND NEW TECHNOLOGIES

As pressure increased to discontinue the use of CFCs and halons, substitute chemicals and technologies began to be developed. One of the most popular substitutes is a class of compounds called hydrofluorocarbons (HFCs). HFCs do not contain chlorine, a potent ozone destroyer. Furthermore, they are relatively short-lived in the atmosphere—most survive intact for less than twelve years. This means that HFCs do not directly impact Earth's protective ozone layer. As a result, HFCs have ODP values of zero.

During the 1990s the use of HFCs increased dramatically. NASA reports that atmospheric levels of HFCs

TABLE 4.3

also surged during this time period. This is a concern to scientists studying global warming because HFCs are believed to enhance atmospheric heating. Also, HFC breakdown in the atmosphere produces a chemical called trifluoroacetic acid, large concentrations of which are known to be harmful to certain plants (particularly in wetlands). Continued heavy use of HFCs during the twenty-first century could introduce or aggravate other environmental problems.

The development of effective chemical substitutes with acceptable health and environmental effects is an enormous challenge. Some experts propose returning to the refrigerant gases used before the invention of CFCs. These include sulfur dioxide, ammonia, and various hydrocarbon compounds. However, these chemicals have their own issues; for example, most are highly toxic.

The EPA's Significant New Alternative Policy program evaluates alternatives to ozone-depleting substances and determines their acceptability for use. Submissions for evaluation include those that could be used in a variety of industrial applications, including refrigeration and air conditioning, foam blowing, and fire suppression and protection.

Many industrial engineers are pursuing new technologies for cooling, including semiconductors that cool down when charged with electricity, refrigeration that uses plain water as a refrigerant, and the use of thermoacoustics (sound energy). Extensive investment in research and development of new technologies will be required to produce cooling methods acceptable to industry and environmentalists.

THE GLOBAL WARMING CONNECTION

In Scientific Assessment of Ozone Depletion: 2006, the UNEP notes that "changes in ozone affect climate; and changes in climate affect ozone." As described in Chapter 3, the Earth's climate has been warming in recent decades and is expected to continue to do so. Many scientists blame this warming on a buildup in the atmosphere of anthropogenic emissions of chemicals, such as carbon dioxide. Many ODS are believed to contribute to this warming effect. Table 4.3 shows the global warming potential (GWP) of some common ODS and alternatives compared with a GWP value of 1 for carbon dioxide. CFCs and HFCs have GWP values that are several thousand times that of carbon dioxide. The Montreal Protocol has and will decrease emissions of CFCs. However, HFC emissions and their associated contribution to global warming are expected to increase as HFCs become common replacements for CFCs. Table 3.1 in Chapter 3 lists emissions of HFCs and other ODS substitutes for various years between 1990 and 2005.

On the other side of the equation, scientists are not completely sure how continued global warming will affect stratospheric ozone levels. The UNEP assessment predicts that future increases in greenhouse gas concentrations will contribute to cooling in the stratosphere. This could actually aid recovery of the ozone layer by slowing the rate of photochemical ozone destruction.

PUBLIC OPINION ABOUT THE OZONE LAYER ISSUE

In March 2007 the Gallup Organization conducted its annual poll of Americans' beliefs and attitudes about environmental issues. The results show that damage to the Earth's ozone layer ranks low on the list of environmental problems about which Americans are worried. (See Table 1.6 in Chapter 1.) Only 43% of those asked in 2007 expressed a great deal of worry about damage to the ozone layer. As shown in Figure 4.8, this percentage

FIGURE 4.8

is down from a peak of 51% in 1989. In 2007 another 27% expressed a fair amount of concern about the problem, whereas 19% felt only a little concern and 11% felt no concern at all.