What gets tested · Core
Ozone depletion on the EPA 608 Core
Ozone depletion on the EPA 608 Core comes down to one chain and one ranking: how chlorine from a released refrigerant ends up destroying ozone high in the atmosphere, and how CFCs, HCFCs and HFCs rank by ozone depletion potential. Atmospheric chemistry beyond that isn't on the test.
The chain every question sits on
A chlorine-bearing refrigerant escapes during service, a leak or disposal. The molecule is stable enough to survive the trip up to the stratosphere, and once its chlorine is set free there, the ozone around it starts to disappear. The health and environmental effects the Core asks about all follow from that thinner ozone overhead.
This section doesn't reward chemistry depth. EPA's test topics list (EPA test topics, checked October 7, 2026) asks for the role of chlorine, the class of a refrigerant, the ranking of the classes, and the effects and evidence of depletion. Reaction rates and altitudes aren't on it.
Ground-level ozone is a different problem
The stratosphere is the one place on this exam where ozone is the hero. Ground-level ozone is a smog pollutant regulated for air quality under separate rules. Every ozone question here means the layer high overhead.
The ranking on one scale
Classes you'll be asked to sort
Refrigerant classes by ozone depletion potential, with examples and current status
| Class | ODP | Examples | Where it stands |
|---|---|---|---|
| CFC, chlorofluorocarbon | Highest; CFC-11 = 1.0 | R-11, R-113 | US production and import ended January 1, 1996 |
| HCFC, hydrochlorofluorocarbon | 0.01 to 0.1 | R-123, R-124 | HCFC-22 production and import ended January 1, 2020 |
| HFC, hydrofluorocarbon | 0 | R-32, R-407C | Not ozone-depleting; still under the 608 venting and sales rules |
Dates: EPA Class I phaseout page and EPA Class II phaseout page (checked October 7, 2026). Phaseouts end production and import; existing equipment can still be serviced. A zero ODP doesn't exempt an HFC from venting rules, as the venting prohibition page explains.
Trace the chain
Before you answer, place each item on the chain: release, stratosphere, chlorine, ozone loss or effect.
0 right · 0 of 15 answered
Which layer of the atmosphere contains the ozone that protects Earth from harmful ultraviolet radiation?
Why each option is right or wrong
Answer: B. Stratosphere
- AThe mesosphere lies above the ozone layer and is not where protective ozone is concentrated.
- BCorrect: the protective ozone layer sits in the stratosphere, where it absorbs UV radiation.
- COzone in the troposphere, near the ground, is smog-forming pollution, not the protective layer.
- DThe thermosphere is far above the ozone layer.
The stratosphere contains the ozone layer that shields Earth from harmful UV radiation. This is the layer damaged by chlorine released from refrigerants like CFCs and HCFCs.
What is the primary function of the stratospheric ozone layer?
Why each option is right or wrong
Answer: A. Filtering harmful ultraviolet radiation
- ACorrect: stratospheric ozone absorbs most of the sun's harmful UV radiation before it reaches the surface.
- BThe ozone layer does not supply the oxygen we breathe; plants and plankton produce it.
- CRegulating climate is linked to greenhouse gases, not the ozone layer's main job.
- DPrecipitation forms in the lower atmosphere and has nothing to do with the ozone layer.
The stratospheric ozone layer protects Earth by filtering harmful ultraviolet radiation from the sun.
Evaluate the potential environmental impacts listed below and determine which are most likely attributed to a reduction in the Earth's protective ozone layer.
Why each option is right or wrong
Answer: A. Increased rates of skin cancer and eye disease
- ACorrect: a thinner ozone layer lets more UV radiation reach the surface, raising rates of skin cancer and eye diseases such as cataracts.
- BDeforestation is caused by land clearing, not ozone loss.
- CRising sea levels are linked to global warming, not ozone depletion.
- DAcid rain comes from sulfur and nitrogen oxides, not ozone depletion.
Thinning of the stratospheric ozone layer lets more ultraviolet (UV) radiation reach Earth's surface, and that is linked to higher rates of skin cancer and eye disease.
Which chemical element in refrigerants is most responsible for ozone depletion?
Why each option is right or wrong
Answer: B. Chlorine
- AHydrogen actually makes a molecule break down sooner in the lower atmosphere, which lowers its ozone impact.
- BCorrect: chlorine released in the stratosphere destroys ozone, which is why CFCs and HCFCs deplete it and HFCs do not.
- CCarbon is in nearly every refrigerant, including HFCs with zero ODP, so it is not the culprit.
- DFluorine is in HFCs too, which have zero ODP, so it is not what depletes ozone.
Chlorine is the chemical element in refrigerants most responsible for ozone depletion. When released into the atmosphere, chlorine atoms break down ozone molecules in the stratosphere.
How does chlorine from CFCs act as a catalyst in ozone depletion?
Why each option is right or wrong
Answer: C. Chlorine atoms repeatedly catalyze the destruction of ozone molecules.
- AChlorine's effect is high in the stratosphere; it does not work by making the lower atmosphere denser.
- BChlorine does not react once and stop; it is freed again after each reaction.
- CCorrect: chlorine acts as a catalyst, freed again after each reaction, so a single atom can destroy thousands of ozone molecules.
- DForming stable compounds would take chlorine out of action; ozone damage comes from chlorine staying active.
Chlorine atoms released from CFCs act as catalysts that repeatedly destroy ozone molecules.
What role does ultraviolet radiation play in ozone depletion?
Why each option is right or wrong
Answer: D. It breaks down CFC and HCFC molecules, releasing chlorine atoms that destroy ozone
- AUV radiation is the trigger that breaks CFC molecules apart, so it plays a central role.
- BUV does not help refrigerants form ozone; the chlorine it frees destroys ozone.
- CRefrigerants are not converted into ozone; their chlorine destroys it.
- DCorrect: in the stratosphere, UV light splits CFC and HCFC molecules and frees chlorine atoms, which then destroy ozone.
Ultraviolet radiation breaks down CFC and HCFC molecules in the stratosphere, releasing chlorine atoms that then destroy ozone molecules.
Explain why hydrofluorocarbons (HFCs) are less harmful to the ozone layer compared to chlorofluorocarbons (CFCs).
Why each option is right or wrong
Answer: B. HFCs do not contain chlorine, which breaks down ozone.
- ASolubility in water is not why HFCs are safer for the ozone layer.
- BCorrect: HFCs contain no chlorine, so they do not destroy ozone and have an ODP of zero.
- CBeing heavier does not keep a gas out of the stratosphere; CFCs are heavy and still reach it.
- DSunlight is not what makes HFCs harmless; they simply have no chlorine to release.
HFCs are considered less harmful to the ozone layer because they lack chlorine, the element in CFCs and HCFCs that leads to ozone depletion. Chlorine atoms released from CFCs and HCFCs break down ozone molecules in the stratosphere.
Which of the following refrigerants is a CFC?
Why each option is right or wrong
Answer: A. R-12
- ACorrect: R-12 is a CFC (dichlorodifluoromethane), with chlorine and no hydrogen.
- BR-22 is an HCFC: it contains hydrogen as well as chlorine.
- CR-410A is an HFC blend with no chlorine.
- DR-134a is an HFC with no chlorine.
R-12 is a CFC (chlorofluorocarbon) once common in older refrigeration. R-22 is an HCFC, and R-134a and R-410A are HFCs.
What distinguishes a CFC from an HCFC refrigerant?
Why each option is right or wrong
Answer: B. HCFCs contain hydrogen atoms while CFCs do not
- ABoth CFCs and HCFCs contain carbon; the 'C' is in both names.
- BCorrect: HCFCs contain hydrogen, which makes them break down sooner in the lower atmosphere, so less chlorine reaches the stratosphere.
- CBoth contain fluorine; the 'F' is in both names.
- DCFCs do contain chlorine; that is why they have the highest ODP.
HCFCs contain hydrogen atoms while CFCs do not, making HCFCs less stable and less harmful to the ozone layer.
What is the primary environmental concern with HFC refrigerants?
Why each option is right or wrong
Answer: D. They have high global warming potential
- AWrong: HFCs are released as gases, not as groundwater contaminants.
- BWrong: acid rain comes from sulfur and nitrogen oxides, not from HFC refrigerants.
- CWrong: HFCs contain no chlorine, so their ozone depletion potential is zero.
- DCorrect: HFCs don't harm the ozone layer, but many have a high global warming potential, which is the main environmental concern with them.
While HFCs don't deplete the ozone layer, they are potent greenhouse gases with high global warming potential, contributing to climate change when released into the atmosphere.
Which environmental problem is directly associated with the release of chlorine-containing refrigerants into the atmosphere?
Why each option is right or wrong
Answer: A. Ozone layer depletion
- ACorrect: chlorine from released CFCs and HCFCs rises to the stratosphere and destroys ozone.
- BAcid rain comes from sulfur and nitrogen oxides, not chlorine-containing refrigerants.
- COcean acidification is driven by carbon dioxide dissolving in seawater.
- DRefrigerant releases are an air problem; water pollution is not the issue linked to them.
The release of chlorine-containing refrigerants (CFCs and HCFCs) into the atmosphere contributes to ozone layer depletion. The chlorine atoms break down ozone molecules in the stratosphere.
What effect does ozone depletion have on the environment?
Why each option is right or wrong
Answer: C. It allows more harmful ultraviolet radiation to reach Earth's surface
- AAcid rain is not caused by ozone depletion.
- BOzone loss does not lower the oxygen we breathe.
- CCorrect: less ozone means more UV radiation reaches the surface, harming people, crops and marine life.
- DOzone depletion is not a direct cause of rising global temperatures; that is the greenhouse effect.
Ozone depletion allows more harmful ultraviolet (UV) radiation to reach Earth's surface, which can increase skin cancer rates, damage crops and marine ecosystems, and contribute to various environmental problems.
A technician sorts three cylinders by refrigerant class before recovery: R-12, R-22, and R-134a. Which label is correct?
Why each option is right or wrong
Answer: D. R-22 is an HCFC
- AR-12 has no hydrogen and does contain chlorine, so it is a CFC, not an HFC.
- BR-134a contains no chlorine, so it is an HFC, not an HCFC.
- CR-22 contains hydrogen, which places it in the HCFC class rather than the CFC class.
- DCorrect: R-22 contains hydrogen, chlorine, fluorine, and carbon, which makes it an HCFC.
R-12 is a CFC, R-22 is an HCFC, and R-134a is an HFC. The hydrogen atom is what separates an HCFC from a CFC, and the absence of chlorine is what makes an HFC.
HCFCs such as R-22 break down in the lower atmosphere faster than CFCs do. Why are they still regulated as ozone-depleting substances?
Why each option is right or wrong
Answer: B. Some of their chlorine still reaches the stratosphere
- AOzone depletion is about chlorine in the stratosphere, not fluorine acting on ground-level ozone.
- BCorrect: HCFCs are less stable than CFCs, but part of their chlorine still reaches the stratosphere and destroys ozone.
- CR-22 contains no bromine; bromine is found in halons, not in HCFC refrigerants.
- DAbsorbing UV is what ozone itself does; that would not make a refrigerant ozone-depleting.
HCFCs carry chlorine, and the share that survives the lower atmosphere is carried up and releases chlorine that destroys stratospheric ozone. Their ozone depletion potential is lower than that of CFCs, but it is not zero.
Apart from higher rates of skin cancer and cataracts, which effect is linked to the loss of stratospheric ozone?
Why each option is right or wrong
Answer: A. Lower crop yields and harm to marine life
- ACorrect: more UV-B reaching the surface can reduce crop yields and damage plankton and other marine life.
- BAcid rain comes from sulfur and nitrogen oxides, not from thinning of the ozone layer.
- CSea-level rise is tied to climate warming, not to the extra UV that ozone loss lets through.
- DSmog is ground-level ozone formed from pollution; it is not caused by stratospheric ozone loss.
A thinner ozone layer lets more UV-B radiation reach the surface. Besides human health effects, that UV can reduce crop yields and harm aquatic ecosystems.
More practice across all four sections: Practice test · Timed mock
The concept that trips this topic
Why this still matters on the job
If new equipment uses HFCs, why does the Core still test ozone?
Installed equipment still holds CFCs and HCFCs. HCFC-22 production and import ended on January 1, 2020 (EPA Class II phaseout page, checked October 7, 2026), yet existing systems are still serviced, and appliances holding 50 lb or more of ozone-depleting refrigerant fall under the 608 leak-repair rules, with leak-rate triggers of 20%, 30% or 10% by appliance type (40 CFR 82.157, eCFR as of October 5, 2026). The percentages are explained on the leak-rate thresholds page.
Does this topic test climate change too?
Only as a contrast. Ozone depletion potential and global warming potential are separate scales, and questions like to swap them; ODP vs GWP sorts them out. AIM Act HFC rules aren't on the 608 exam (ESCO Institute via ACHR News, September 19, 2026).
Key takeaways
- The ozone on this exam is the stratospheric layer; ground-level ozone belongs to air-quality rules.
- ODP ranks CFC above HCFC above HFC, with CFC-11 at 1.0 (EPA test topics, checked October 7, 2026).
- Phaseouts stop production and import; the dates and what they allow are on the refrigerant phase-out page, the law behind them on Clean Air Act and Montreal Protocol.
- This topic is one slice of the EPA 608 Core section; the rest of Core is mapped there.