2.1 The Science of Ozone Depletion

2.1 The Science of Ozone Depletion

Understanding ozone depletion is fundamental to the EPA 608 certification. The science behind it explains why refrigerant regulations exist and why proper handling is a federal requirement.

Atmospheric Layers

The atmosphere is divided into distinct layers, and understanding where ozone exists is critical:

The ozone layer resides in the stratosphere, not the troposphere. This distinction is important for the exam.

What Is Ozone (O3)?

Ozone is a molecule composed of three oxygen atoms (O3), compared to the normal oxygen we breathe (O2), which has two oxygen atoms. In the stratosphere, ozone is continuously created and destroyed in a natural cycle:

1. UV radiation splits O2 molecules into individual oxygen atoms
2. These individual atoms combine with O2 to form O3 (ozone)
3. UV radiation also breaks apart O3, releasing energy (heat) and absorbing the harmful UV rays

This natural cycle keeps the ozone layer in balance — until man-made chemicals disrupt it.

The Ozone Destruction Cycle

When CFC or HCFC molecules reach the stratosphere, UV radiation breaks them apart, releasing free chlorine atoms. The destruction cycle works like this:

1. Cl + O3 → ClO + O2 (Chlorine atom attacks ozone, creating chlorine monoxide and oxygen)
2. ClO + O → Cl + O2 (Chlorine monoxide reacts with an oxygen atom, releasing the chlorine atom)
3. The free chlorine atom repeats Step 1 — attacking another ozone molecule

This catalytic cycle means one chlorine atom is recycled and can destroy ozone repeatedly. Scientists estimate that a single chlorine atom can destroy approximately 100,000 ozone molecules before it is eventually deactivated.

Ozone Depletion Potential (ODP)

ODP measures a substance's ability to destroy ozone relative to CFC-11 (R-11), which has an ODP of 1.0:

For the Exam: HFCs have ZERO ozone depletion potential because they contain no chlorine. However, they still have high GWP, which is why they are being phased down under the AIM Act. CFCs have the highest ODP.

Global Warming Potential (GWP)

While ODP measures ozone destruction, GWP measures a substance's contribution to global warming over 100 years, relative to CO2, which has a GWP of 1:

The Greenhouse Effect Connection

Refrigerants contribute to global warming when released into the atmosphere. HFCs, while not harming the ozone layer, can be hundreds to thousands of times more potent than CO2 as greenhouse gases. This is why the AIM Act focuses on phasing down HFCs even though they have zero ODP — their climate impact is severe.