Which element in CFC and HCFC refrigerants is responsible for destroying ozone in the stratosphere?
Chlorine. Ultraviolet light breaks CFC and HCFC molecules apart in the stratosphere, and the chlorine atoms released attack ozone. Refrigerants with no chlorine, such as HFCs, have an ozone depletion potential of zero.
- Fluorine
- Carbon
- ChlorineCorrect answer
- Hydrogen
Why “Chlorine” is correct
CFCs and HCFCs contain chlorine. When ultraviolet light breaks these molecules apart high in the stratosphere, the chlorine atoms that are freed attack ozone. That is why chlorine-free refrigerants such as HFCs have an ozone depletion potential of zero.
Source: EPA: Test Topics
Why the other answers are wrong
- Fluorine — Fluorine is in CFCs, HCFCs and HFCs alike, yet HFCs do not deplete ozone, so fluorine is not the culprit.
- Carbon — Carbon is the backbone of the molecule but does not attack ozone.
- Hydrogen — HFCs contain hydrogen and have an ozone depletion potential of zero, so hydrogen is not the culprit.
The source, word for word
They move to the stratosphere and are broken down by strong ultraviolet (UV) light, where they release chlorine atoms that then deplete the ozone layer.
They contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs.
Which elements each family contains
Fluorine and carbon are in all three families, so they cannot be what separates ozone-depleting refrigerants from the rest. Chlorine does.
| Family | Elements | Ozone depletion potential |
|---|---|---|
| CFC | Chlorine, fluorine, carbon | Up to 1 |
| HCFC | Hydrogen, chlorine, fluorine, carbon | 0.01 to 0.1 |
| HFC | Hydrogen, fluorine, carbon | 0 |
What ODP measures
Ozone depletion potential compares a substance with the same mass of CFC-11, whose ODP is defined as 1.0. Zero ODP does not exempt a refrigerant from recovery: all three families must be recovered.
Keep practicing
- Refrigerant types: CFC, HCFC, HFC and HFO
- What CFCs, HCFCs and HFCs have in common
- Which family R-12 belongs to
- EPA 608 Core practice test
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.