Ultraviolet light breaks chlorofluorocarbon molecules apart once they drift up into the stratosphere, freeing an atom that then attacks ozone. Which atoms are released and do that damage?
- Chlorine atoms
- BFluorine atoms
Fluorine is held in a very stable bond within the molecule and is not the atom that drives stratospheric ozone loss, which is why fluorine-only refrigerants such as HFCs carry no ozone depletion potential.
- CHydrogen atoms
Hydrogen actually makes a refrigerant less harmful to ozone, because it lets the molecule break apart in the lower atmosphere before it can reach the ozone layer.
- DCarbon atoms
Carbon forms the backbone of the molecule but does not catalyze ozone destruction. Recovering refrigerant is about the halogen it carries, not the carbon.
Why A is correct
Free chlorine acts as a catalyst. It pulls one oxygen atom off an ozone molecule to form chlorine monoxide, then that compound reacts again and releases the chlorine atom unchanged. Because the chlorine is not consumed, one atom keeps cycling and destroys ozone molecules over and over, which is why very small amounts of CFC do outsized damage.
What this question is testing
This item checks that you know the mechanism behind the regulations, not just the rule itself. The exam expects you to link the letters in CFC and HCFC to the specific halogen that harms ozone, and to recognize that the destruction is catalytic rather than one-for-one.
On the job
Every recovery job you do is enforcement of this chemistry. When a supermarket rack still running R-22 gets torn out, the whole reason you are required to pull the charge into a cylinder instead of cracking a valve is that the chlorine in that charge would otherwise reach the stratosphere. Techs who understand the chain reaction tend to be the ones who take the time to pump down properly, because they know a pound vented is not a pound of damage, it is years of catalytic damage from one release.
Memory technique
The C in CFC stands for Chlorine and for Culprit.
Exam tip
If the refrigerant name has a C for chlorine in it, it hurts ozone. Watch for choices that blame fluorine, which is the classic trap.
Where to look it up
Chlorine is the ozone destroyer, and it works catalytically, so one atom kills many ozone molecules.