---
title: "Ozone-Depleting Substances | Honors Biology"
description: "Ozone-depleting substances are chemicals that break down stratospheric ozone, letting more UV reach Earth. In Honors Biology, they connect to ecosystems and human health."
canonical: "https://fiveable.me/hs-honors-biology/key-terms/ozone-depleting-substances"
type: "key-term"
subject: "Honors Biology"
unit: "Unit 20"
---

# Ozone-Depleting Substances | Honors Biology

## Definition

Ozone-depleting substances are chemicals that destroy ozone in the stratosphere, thinning the ozone layer. In Honors Biology, they show how human-made compounds can disrupt atmospheric protection and increase UV exposure.

## What It Is

In Honors Biology, ozone-depleting substances are human-made chemicals that release reactive chlorine or bromine in the stratosphere and damage ozone molecules faster than they are replaced. The main examples you will see are chlorofluorocarbons (CFCs), halons, and related compounds used in older refrigeration, foam blowing, and aerosol systems.

The key idea is not just that these chemicals exist, but that they travel upward first. Many ODS are stable in the lower atmosphere, so they do not break down quickly near the ground. Once they reach the stratosphere, strong UV light splits them apart and frees chlorine or bromine atoms. Those atoms then act like catalysts, meaning one atom can destroy many ozone molecules without being used up right away.

That matters because the ozone layer absorbs a lot of the Sun’s harmful ultraviolet radiation, especially UV-B. When ozone is depleted, more UV reaches Earth’s surface. In biology terms, that raises the risk of DNA damage in living things, which can increase skin cancer and cataracts in humans and also stress plants, plankton, and other organisms at the base of food webs.

A common misconception is that ozone-depleting substances are the same thing as greenhouse gases. Some chemicals can affect both systems, but ozone depletion is a different process from warming caused by heat-trapping gases. Here, the main issue is chemical destruction of ozone in the stratosphere, not just trapping infrared heat.

This topic often shows up alongside environmental chemistry and ecology because it connects human industry to a change in the atmosphere that affects whole ecosystems. The ozone layer can recover, but slowly, because many ODS persist for a long time and can keep causing damage after they are released.

## Why It Matters

Ozone-depleting substances show how a single class of chemicals can change conditions for entire ecosystems. In Honors Biology, that connects molecular behavior to big biological outcomes: more UV radiation means more risk for DNA damage, cell mutation, and health problems in humans and other organisms.

This term also gives you a clear example of cause and effect across Earth systems. A chemical released from a spray can or refrigerator foam does not stay local. It can move through the atmosphere, react in the stratosphere, and weaken the ozone layer that protects life at the surface.

The topic fits into climate and environmental units because it shows how biology is shaped by atmospheric chemistry, policy, and human activity. When you study the Montreal Protocol, you are seeing a real-world response to an environmental problem that scientists measured, explained, and tracked over time.

It also helps with data interpretation. If you see a graph of ozone concentration over time, or a case study about UV exposure, you should be able to connect the pattern back to ODS, ozone loss, and the chain reaction that makes the effect spread.

## Connections

### Chlorofluorocarbons (CFCs)

CFCs are the most familiar ozone-depleting substances, so they are often the first example you name. They were widely used because they are chemically stable and useful in refrigeration and aerosol products. That stability is part of the problem, since it lets them reach the stratosphere before UV light breaks them apart and releases chlorine.

### Ozone Layer

The ozone layer is the part of the stratosphere that absorbs much of the Sun’s harmful UV radiation. Ozone-depleting substances matter because they thin this protective layer. If the ozone layer drops, the biological consequences show up in higher UV exposure, which affects DNA, skin, eyes, and photosynthetic organisms.

### Montreal Protocol

The Montreal Protocol is the international agreement that limited many ozone-depleting substances. In an environmental biology unit, it is the policy response to the science. It shows how countries reacted after scientists linked ODS to ozone loss and rising UV risk, and it is a major reason the ozone layer is recovering slowly.

### [negative feedback](/hs-honors-biology/key-terms/negative-feedback)

Negative feedback is a useful comparison because it describes a system response that reduces a change, while ozone depletion does the opposite. ODS add a harmful pressure to the atmosphere instead of balancing it out. If your class asks you to compare environmental mechanisms, this term helps you separate stabilizing loops from damaging human-caused disruptions.

## On the AP Exam

A quiz question may give you a chemical name, a diagram of the stratosphere, or a scenario about increased UV exposure and ask you to identify the cause. You should be able to trace the chain: ODS are released, drift upward, break apart in UV light, and free atoms that destroy ozone. If the question includes health or ecosystem effects, connect ozone loss to more UV-B reaching Earth.

On a lab, graph, or data response, you may need to explain why ozone dropped in a certain period or why the ozone layer recovered after policy changes. In a short essay or class discussion, this term can also support a human impact argument, especially when you explain how industry, atmosphere, and living systems are linked.

## ozone-depleting substances vs greenhouse gases

Ozone-depleting substances and greenhouse gases both involve human emissions, but they affect the atmosphere in different ways. ODS break down stratospheric ozone, which increases UV radiation at Earth’s surface. Greenhouse gases trap heat in the lower atmosphere and drive warming. A chemical can sometimes be part of both discussions, but the mechanism is not the same.

## Key Takeaways

- Ozone-depleting substances are chemicals that destroy ozone in the stratosphere, especially CFCs and halons.
- They matter because ozone blocks harmful UV radiation, so ozone loss increases exposure to DNA-damaging sunlight.
- Most ODS were used in products like refrigeration, foam production, and aerosol sprays because they were stable and useful.
- These chemicals are dangerous in the stratosphere because UV light can free chlorine or bromine atoms that keep breaking down ozone.
- The Montreal Protocol cut many ODS emissions, and that is why the ozone layer is slowly recovering.

## FAQs

### What is ozone-depleting substances in Honors Biology?

Ozone-depleting substances are human-made chemicals that break apart ozone in the stratosphere. In Honors Biology, they come up when you study how atmospheric changes affect living things, especially because less ozone means more UV radiation reaches Earth.

### Are ozone-depleting substances the same as CFCs?

Not exactly. CFCs are the classic example, but ozone-depleting substances also include halons and other related compounds. If your teacher says ODS, think of the whole group of chemicals that can damage stratospheric ozone.

### How do ozone-depleting substances damage the ozone layer?

They often stay stable near Earth’s surface, then break apart in the stratosphere when UV light hits them. That releases chlorine or bromine atoms, which act like catalysts and destroy ozone molecules over and over again.

### What are the effects of ozone depletion on living things?

Less ozone means more UV-B radiation reaches Earth. That can increase skin cancer and cataracts in humans, and it can also harm plants, algae, and other organisms that depend on steady sunlight conditions.

## Related Study Guides

- [20.2 Climate Change and Global Environmental Issues](/hs-honors-biology/unit-20/climate-change-global-environmental-issues/study-guide/IKJDry1GzODmz3Ve)

## About This Document

Canonical Fiveable pages are available as Markdown at the same path plus `.md`.

- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
- [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`)
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