Hydrofluorocarbons (HFCs) were developed because they could perform many of the same functions as chlorofluorocarbons (CFCs) while causing much less depletion of stratospheric ozone. However, many HFCs are potent greenhouse gases, so replacing CFCs with HFCs solved one environmental problem while contributing to another.
Level: HL only; Subtopic 6.4 Stratospheric ozone
The Reasoning
CFCs were widely used as refrigerants, aerosol propellants and foam-blowing agents because they were stable, non-flammable and effective. Their stability allowed them to remain in the atmosphere long enough to reach the stratosphere.
There, high-energy ultraviolet radiation broke down CFC molecules and released chlorine radicals. These radicals catalysed the destruction of ozone, meaning one chlorine radical could destroy many ozone molecules before being removed. Ozone depletion allowed more harmful UVB radiation to reach Earth's surface, increasing risks such as skin cancer, cataracts, DNA damage and reduced phytoplankton photosynthesis.
HFC molecules contain hydrogen, fluorine and carbon but no chlorine. They therefore do not release the chlorine radicals responsible for CFC-driven ozone destruction and have much lower ozone depletion potential.
| Property | CFCs | HFCs |
|---|---|---|
| Chlorine present | Yes | No |
| Effect on stratospheric ozone | Strong ozone depletion | Much less ozone depletion |
| Practical use | Refrigeration, air conditioning and foams | Similar applications |
| Wider environmental problem | Ozone-depleting substances | Potent greenhouse gases |
The Montreal Protocol restricted CFCs and other ozone-depleting substances, encouraging the adoption of alternatives such as HFCs. Because HFCs can have high global warming potentials, they were later controlled through the Kigali Amendment to the Montreal Protocol.
Exam Technique
For an IB ESS explanation, link molecular composition to environmental impact: HFCs contain no chlorine, so they do not release ozone-destroying chlorine radicals. Avoid the misconception that HFCs are environmentally harmlessasthey protect stratospheric ozone but can intensify the enhanced greenhouse effect.
