Study guide
3.1 The Science of Ozone Depletion (ODP and GWP)
EPA 608 Technician Certification Exam
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1 Introduction to EPA 608 Certification
1.1 What EPA 608 Is and Who Needs It 1.2 Exam Format, Scoring, and Administration 1.3 How to Study for EPA 608
2 Regulations and the Clean Air Act
2.1 Clean Air Act Overview 2.2 Penalties and Enforcement 2.3 Montreal Protocol and International Agreements 2.4 AIM Act and HFC Phasedown Schedule 2.5 SNAP Program and Refrigerant Transitions
3 Refrigerants and Ozone Science
3.1 The Science of Ozone Depletion (ODP and GWP) 3.2 Refrigerant Classification, ASHRAE Numbering, and Safety Groups 3.3 Common Refrigerants: Properties, Applications, and Phaseout Status 3.4 Refrigerant Blends: Glide, Fractionation, and Liquid Charging
4 The Refrigeration Cycle
4.1 The Basic Refrigeration Cycle 4.2 System Components in Detail 4.3 Heat Transfer and Pressure-Temperature Relationships
5 Refrigerant Safety and Handling
5.1 Refrigerant Hazards and Health Effects 5.2 Safe Handling Practices, PPE, and Cylinders 5.3 A2L (Mildly Flammable) Refrigerant Safety
6 Recovery, Recycling, and Reclaiming
6.1 The Three Rs: Recover, Recycle, Reclaim 6.2 Recovery Equipment Requirements 6.3 Required Levels of Evacuation 6.4 Refrigerant Sales Restrictions and Recordkeeping
7 Leak Detection and Repair
7.1 Leak Detection Methods 7.2 Leak Repair Requirements and Trigger Rates 7.3 Leak-Rate Calculation, Recordkeeping, and Reporting
8 Type I — Small Appliances
8.1 What Counts as a Small Appliance 8.2 Type I Recovery Requirements 8.3 Type I Procedures, Access Valves, and the Open-Book Exam
9 Type II — High-Pressure Appliances
9.1 What Type II Covers: High-Pressure System Overview 9.2 Type II Recovery Methods and Required Evacuation Levels 9.3 Leak Detection, the Repair Triggers, and Recordkeeping 9.4 The R-22 Phaseout, Retrofits, and the Move to Lower-GWP A2Ls
10 Type III — Low-Pressure Appliances
10.1 Low-Pressure System Fundamentals 10.2 Purge Units and Air Management 10.3 Type III Recovery and Procedures 10.4 Type III Leak Testing
11 10. Disposal, Shipping, and Compliance
11.1 Equipment Disposal Requirements 11.2 Refrigerant Shipping and Transport 11.3 Compliance Checklist and Best Practices
12 Final Review and Exam Strategy
12.1 High-Yield Core Section Review 12.2 Type I vs Type II vs Type III: Side-by-Side Review 12.3 How the Exam Works and Exam-Day Strategy
3.1 The Science of Ozone Depletion (ODP and GWP)
Key Takeaways Explain This Topic AI
The ozone layer sits in the stratosphere (roughly 7-31 miles up) and absorbs harmful UV-B radiation before it reaches the surface
Chlorine and bromine atoms freed from CFCs/HCFCs catalytically destroy ozone — one chlorine atom can destroy about 100,000 ozone molecules
Ozone Depletion Potential (ODP) is measured relative to CFC-11 (R-11), which is defined as 1.0; HFCs and HFOs have ODP of zero because they contain no chlorine
Global Warming Potential (GWP) is measured relative to CO2 (R-744 = 1) over 100 years; ODP and GWP are independent — a refrigerant can have zero ODP but very high GWP
Bromine is roughly 40-60 times more destructive to ozone per atom than chlorine, which is why halons carry ODP values of 3-10
Last updated: October 2026
Understanding ozone depletion is the foundation of the entire EPA 608 certification. Every recovery rule, venting prohibition, and refrigerant phaseout in the Clean Air Act exists because certain refrigerants damage the atmosphere. The Core section tests this science directly, and Type-specific sections assume you already understand why venting is illegal. This section explains the chemistry behind two independent measurements you must master: Ozone Depletion Potential (ODP) and Global Warming Potential (GWP) .
Where the Ozone Layer Lives
The atmosphere is layered, and knowing where ozone resides is a frequently tested fact. The ozone layer is in the stratosphere , not the troposphere where we live and breathe.
- Layer Altitude Key Feature
- Troposphere 0-7 miles Where weather occurs and we live
- Stratosphere 7-31 miles Contains the ozone layer
- Mesosphere 31-53 miles Meteors burn up here
- Thermosphere 53-375 miles Aurora borealis occurs here
A common exam trap is to confuse "good" stratospheric ozone (which protects us) with "bad" ground-level ozone (smog). EPA 608 is concerned only with the protective stratospheric layer.
What Ozone Is and Why It Matters
Ozone (O3) is a molecule of three oxygen atoms, unlike the oxygen we breathe (O2), which has two. In the stratosphere, ozone is continuously created and destroyed in a natural balance:
Ultraviolet (UV) radiation splits an O2 molecule into two free oxygen atoms.
Each free atom combines with an O2 molecule to form O3.
UV radiation also breaks O3 back apart, absorbing the harmful UV-B energy in the process.
That continuous absorption of UV-B is exactly what shields humans from increased skin cancer, cataracts, and crop damage. Man-made halogenated chemicals break this balance.
The Catalytic Destruction Cycle
When a CFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) molecule drifts up to the stratosphere, intense UV radiation breaks it apart and frees a chlorine atom . That chlorine then destroys ozone in a repeating two-step cycle:
Cl + O3 → ClO + O2 — chlorine strips an oxygen atom from ozone, forming chlorine monoxide.
ClO + O → Cl + O2 — the chlorine monoxide reacts with a free oxygen atom, releasing the chlorine atom again .
Because the chlorine atom is regenerated in step 2, it is a catalyst — it is not consumed. A single chlorine atom can cycle through this reaction repeatedly and destroy roughly 100,000 ozone molecules before it is finally deactivated and rained out. This catalytic recycling is why even small amounts of chlorine cause outsized damage.
Bromine , released from halon fire-suppression agents, works the same way but is far more aggressive — roughly 40 to 60 times more destructive per atom than chlorine. That is why halons carry the highest ODP values (about 3 to 10).
Ozone Depletion Potential (ODP)
ODP measures how effectively a substance destroys ozone, on a scale anchored to CFC-11 (R-11) , which is defined as ODP = 1.0 . The single most important pattern to memorize: ODP tracks chlorine and bromine content. No chlorine or bromine means zero ODP.
- Refrigerant Category Contains Chlorine? ODP Range Examples
- CFCs Yes (lots) 0.6 - 1.0 R-11 (1.0), R-12 (1.0)
- HCFCs Yes (some) 0.01 - 0.11 R-22 (0.055), R-123 (0.02)
- HFCs No 0 R-134a, R-410A, R-32
- HFOs No 0 R-1234yf, R-1234ze
- Natural No 0 R-717 (ammonia), R-744 (CO2), R-290
HCFCs have lower ODP than CFCs because the added hydrogen atom makes the molecule less stable, so most of it breaks down in the lower atmosphere before reaching the ozone layer.
Global Warming Potential (GWP)
GWP is a completely separate measurement. It rates how much heat a gas traps in the atmosphere over a 100-year period, relative to carbon dioxide (CO2, R-744) , which is defined as GWP = 1 . A refrigerant with a GWP of 1,430 traps 1,430 times more heat than the same mass of CO2.
The critical exam insight is that ODP and GWP are independent . HFCs were adopted because they have zero ODP — but many of them have GWP in the thousands. That is why the AIM Act now phases down HFCs even though they do no ozone damage at all.
- Refrigerant Type ODP GWP (100-yr)
- R-11 CFC 1.0 4,750
- R-12 CFC 1.0 10,900
- R-22 HCFC 0.055 1,810
- R-134a HFC 0 1,430
- R-410A HFC blend 0 2,088
- R-32 HFC 0 675
- R-454B HFC/HFO blend 0 466
- R-290 HC (propane) 0 3
- R-744 CO2 0 1
- R-717 Ammonia 0 0
- R-1234yf HFO 0 <1 (≈4)
Worked Example: A technician compares a leak of R-12 versus an equal mass of R-134a. Which does more damage, and to what? R-12 (ODP 1.0, GWP 10,900) harms both the ozone layer and the climate — it contains chlorine and is a potent greenhouse gas. R-134a (ODP 0, GWP 1,430) harms only the climate, because it contains no chlorine. This shows why ODP and GWP must be evaluated separately: R-12 is worse on both scales, yet R-134a is still a serious climate pollutant. Either way, the correct action is full recovery — venting either one is illegal under the Clean Air Act.
Putting It Together
For the Core exam, anchor everything to two reference points: R-11 = ODP 1.0 and CO2 = GWP 1 . Then remember the one-line rule — chlorine drives ODP, and a separate property drives GWP. CFCs are bad on both; HFCs traded ozone safety for a climate problem regulators now correct.