earth’s surface), ozone is a major air pollutant in the lower atmosphere. Ozone depletion in the stratosphere is a serious matter. The ozone layer serves two important functions: it protects life on earth from harmful ultraviolet (UV) radiation and helps maintain stable earth temperatures. CFC and HCFC refrig- erants are known to damage the ozone layer and have come under increasing governmental regu- lation worldwide. Stratospheric ozone depletion is a global problem that may cause: • Crop loss. • Increased eye diseases. • Skin cancer and other radiation-related diseases. • Reduced marine life. • Increased ground-level ozone. • Deforestation. Much attention has focused on the destruc- tiveness of widely used CFCs such as R-11 and R-12. Chlorine, a chemical element of many refrig- erants, is the primary culprit. CFCs are very stable, chlorine-containing compounds that do not break up in the atmosphere as do other, less- stable refrigerants. Unlike other chlorine compounds and naturally-occurring chlorine, the chlorine in CFCs neither dissolves in water nor breaks down into compounds that dissolve in water. This means it does not “rain out” of the atmosphere. Normally, chlorine in the lower atmosphere cannot reach the ozone layer. However, CFC molecules act as “carriers,” lifting chlorine atoms to the ozone layer. These stable refrigerant mole- cules may float around for more than 40 years in the upper stratosphere, where they absorb energy from the sun’s ultraviolet radiation and break into individual atoms. As the refrigerant mole- cules break up, chlorine atoms are released and attack the protective ozone molecules. Each chlo- rine atom combines with one oxygen atom (O1) from an ozone molecule (O 3 ), forming chlorine monoxide (ClO) and oxygen (O 2 ). The subject of ozone depletion has been controversial. Some investigators contend the chlorine found in the stratosphere comes from natural sources, such as volcanic eruptions. However, air samples taken over erupting volca- noes show that volcanoes contribute a small amount of chlorine compared to the amount of chlorine produced by CFCs. Also, the rise in the amount of chlorine measured in the stratosphere over the past two decades matches the rise in the amount of fluorine over the same period. Fluorine (also a refrigerant chemical) and chlorine do not originate from the same natural source. Furthermore, the rise in the amount of chlorine measured in the stratosphere over the past 20 years matches the rise in CFC emissions over the same period. To express the risk to the ozone layer caused by the chlorine in refrigerants, each refrigerant has been assigned a number called its ozone depletion potential (ODP). See Figure 15-2 for a partial list of these numbers. ODP is a measure- ment of a refrigerant’s ability to destroy ozone. The three primary types of refrigerants differ greatly in ODP: • Chlorine-fluorine-carbon (CFC) = high ODP. • Hydrogen-chlorine-fluorine-carbon (HCFC) = low ODP. • Hydrogen-fluorine-carbon (HFC) = no ODP. R-11, R-12, and R-500 are examples of CFCs. R-22 and R-123 are examples of HCFCs. R-134a is an HFC. CFCs have the highest ODP. HCFCs have a hydrogen atom in the molecule, making the molecule unstable. Therefore, HCFCs tend to break up quickly when released to the atmosphere. HCFCs have a low ODP. HFCs contain no chlo- rine, so they have no ozone depletion potential. Many scientists agree that certain chemical compounds have another damaging effect on the earth’s environment. Global warming, also called the greenhouse effect, occurs when long-wave (infrared) radiation from the sun reaches the earth but cannot escape. Trapped radiation causes a gradual buildup of heat on the earth’s surface. Several refrigerants are suspected of contributing to global warming. To express the risk of a refrig- erant contributing to global warming, each one has been assigned a number called its global warming potential (GWP). The higher the GWP, the greater the risk. Refer to Figure 15-2. Refrigerants with high ODP and GWP ratings are systematically being phased out. Refrigerants with lower ratings are replacing them. The phaseout is the result of a significant piece of national legis- lation called the Clean Air Act (CAA). Its rules largely resulted from an international agreement called the Montreal Protocol. The Clean Air Act is having a profound impact on new equipment manufactured, lubricants used, and procedures required for installation and service of air condi- tioning and refrigeration systems. 260 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.