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A Hole in the Sky: Ozone Depletion - Substitutes And New Technologies

hfcs environmental refrigeration chemical

As pressure increased to discontinue 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. They are also 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. HFCs have ODP values of zero.

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

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 FIGURE 3.5
Emissions of ozone-depleting substances, 1990–2001
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.

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