Environmental Protection Agency (EPA) MVAC Certification

Which of the following compounds is the most stable in the lower atmospheres of Earth?

1. Hydrochlorofluorocarbons (HCFCs)

2. Chlorofluorocarbons (CFCs)

3. Hydrofluorocarbons (HFCs)

4. Perfluorocarbons (PFCs)

The correct answer is: Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are considered the most stable compounds in the lower atmosphere due to their chemical structure and the absence of hydrogen atoms in their formulation. CFCs contain carbon, chlorine, and fluorine, but the lack of hydrogen means they do not readily react with other atmospheric components. This stability allows them to persist in the atmosphere for extended periods, often leading to their accumulation and contributing to environmental concerns such as ozone depletion. In comparison, Hydrochlorofluorocarbons (HCFCs) include hydrogen in their formulation, which makes them more susceptible to atmospheric degradation via reactions with hydroxyl radicals and other compounds. Hydrofluorocarbons (HFCs) are also less stable than CFCs when considering the entire atmospheric sequence because they can break down in the atmosphere over time, albeit at a slower rate than HCFCs. Perfluorocarbons (PFCs) are highly stable in the atmosphere, but they are not as widely discussed in the context of ozone depletion and are also less prevalent in atmospheric concentrations compared to CFCs. The historical usage and examination of CFCs in the context of their chemical stability and environmental impact solidify their standing as the