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Climate and Water Resource Case Study

Definitions
Overview of Climate Change
Greenhouse Effect and Climate Change
What is the world doing about climate change?
Investigating Regional and Local Projected Climate Change
Consequences of Projected Climate Change
Conclusions
Chapter 7 title
Chapter 8 title

Chapter 2 - D2. Greenhouse Gases: HFCs, PFCs, and SF6

Introduction

Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and aerosols are very important greenhouse gases. CFCs, HFCs, and PFCs are all human made and are not produced by any other process but our activities. Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants. CFCs owe their existence to accidents that occurred in the early 1900s. Refrigerators in the late 1800s and early 1900s used the toxic gases, ammonia (NH3), methyl chloride, and sulfur dioxide, as refrigerants. After a series of fatal accidents in the 1920s when methyl chloride leaked out of refrigerators, a search for a less toxic replacement begun as a collaborative effort of three American corporations - Frigidaire, General Motors, and Du Pont. CFCs were first synthesized in 1928 by Thomas Midgley, Jr. of General Motors, as safer chemicals for refrigerators used in large commercial applications.

Hydrofluorocarbons - HFCs, Perfluorocarbons - PFCs, Sulfur Hexafluoride - SF6

            Hydrofluorocarbons (composed of hydrogen, fluorine, and carbon) and perfluorocarbons (composed of fluorine and carbon) have been created for industrial applications and been adopted as ozone safe replacements for chlorofluorocarbons and thus are growing in atmospheric concentration (Figure 13).  Even though hydrofluorocarbons and perfluorocarbons are emitted in relatively small quantities, they have a disproportionate effect on the greenhouse effect. As a greenhouse gas, the most potent hydrofluorocarbons and perfluorocarbons are 11,700 times and 7000 to 9000 times per molecule as effective as a molecule of carbon dioxide, respectively. Also, perfluorocarbons have relatively long atmospheric lifetimes (up to 50,000 years).  Rated as the most powerful greenhouse gas ever released to the atmosphere, sulfur hexafluoride is used as an electric insulator, heat conductor, and a freezing agent.  In comparison to one molecule of carbon dioxide, the global warming potential of one sulfur hexafluoride molecule is approximately 24,000 times greater. Sulfur hexafluoride has now been banned from use due to its global warming potential.

Figure 13. Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) atmospheric concentrations.. Concentrations given in parts per trillion (ppt).

 

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