Organic Chlorofluoro Hydrocarbons

Abstract

The chlorofluorocarbons (CFCs) were introduced in the 1930s as “safe” replacements for refrigerants such as sulfur dioxide, ammonia, carbon tetrachloride, and chloroform. In World War II, they were used to produce insecticide aerosols to protect the troops in tropical areas against malaria and other insectborne diseases. During the next 40–50 years, the number and type of applications expanded to include foam blowing, precision cleaning, and propellants for medicinal, cosmetic, and general-purpose aerosols, air conditioning, and refrigeration. These uses eventually resulted in emission of the CFCs into the atmosphere. Because of their low chemical reactivity, they typically have long atmospheric residence times, and as a consequence, they are distributed globally. In 1974 Molina and Rowland hypothesized that, once the CFCs reach the stratosphere, they will undergo breakdown to release chlorine atoms. The chlorine atoms could then react with the stratospheric ozone breaking it down into oxygen. Since the stratospheric ozone absorbed much of the sun's ultraviolet β radiation (UVB), decreased ozone levels would lead to increases in ground-level UVB. This could affect crop growth and lead to increases in cataracts and nonmelanoma skin cancers. Following reports of a marked drop in column ozone over Antarctica (the “ozone hole”) during the Antarctic winter, in 1987 most of the nations of the world drafted and signed an agreement calling for the phaseout of CFCs. This agreement is known as the Montreal Protocol. Development was initiated on two types of “in-kind” replacements. The first were the hydrochlorofluorocarbons (HCFCs) and the second were the hydrofluorocarbons (HFCs). Both contain hydrogen and are susceptible to attack by hydroxyl radicals present in the atmosphere. Therefore, they have a shorter atmospheric lifetime and either are not transported to the stratosphere or are transported there only in small amounts. The HCFCs contain chlorine and are still capable of causing ozone depletion, although, since their atmospheric lifetimes are short, their ozone-depleting potential (ODP) is lower than those associated with the CFCs. The HFCs do not contain chlorine (or bromine, also associated with ozone depletion). They, therefore, do not cause ozone depletion. A ranking scale has been developed using CFC11 as the reference compound, with an assigned value of 1. These values are also presented. A second concern, regarding both CFCs and their replacements, is that they are greenhouse warming gases. They, along with other substances such as carbon dioxide, trap the sun's infrared radiation and convert it to heat. However, they are also good insulating materials, and frequently their use as foam blowing agents in refrigeration equipment can lead to considerable energy savings, reducing carbon dioxide emissions. The greenhouse warming potentials (GWPs) for many of the CFCs, HCFCs, and HFCs are given. Many methods have been developed for atmospheric monitoring of these substances. Because of their widespread use and concerns about their environmental effects and health effects, several reviews have been written on these materials. From the reviews as well as the data presented later in this chapter, it can be seen that many of these chemicals are not highly toxic. Some, in fact, do not show significant signs of toxicity at air exposure levels up to a few percent or even over 5 or 10%. The most typical response seen following overexposure is CNS depression related to the anesthetic properties of many of these chemicals. Also, some have caused hepatotoxicity and occasionally reproductive effects. Each compound is discussed individually. They have been divided into three general areas: chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons. Keywords: CFC 11-13; CFC 112-115; HCFC 21, 22, 123, 124, 132, 133a, 141b, 142b, HFC 32, 125, 1344a, 152a, 245fa; Ozone depletion potential; Chlorofluorcarbons; Greenhouse effect; Global warming; Atmospheric lifetime