The ozone depletion process begins when CFCs and other ozone-depleting substances (ODS) are emitted into atmosphere. It is caused by the release of chlorofluorocarbons (CFCs), hydrofluorocarbons (HCFCs), and other ozone-depleting substances (ODS), which were used widely as refrigerants, insulating foams, and solvents. The discussion below focuses on CFCs, but is relevant to all ODS. Although CFCs are heavier than air, they are eventually carried into the stratosphere in a process that can take as long as 2 to 5 years. Measurements of CFCs in the stratosphere are made from balloons, aircraft, and satellites.

When CFCs and HCFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to break apart and release chlorine atoms which react with ozone, starting chemical cycles of ozone destruction that deplete the ozone layer. One chlorine atom can break apart more than 100,000 ozone molecules.

Other chemicals that damage the ozone layer include methyl bromide (used as a pesticide), halons (used in fire extinguishers), and methyl chloroform (used as a solvent in industrial processes for essential applications). As methyl bromide and halons are broken apart, they release bromine atoms, which are 60 times more destructive to ozone molecules than chlorine atoms.

Ozone in the lower atmosphere is formed during electrical discharge from high voltage appliances as shown in the equations below:

O2(g) → 2O(g)

O2(g) + O(g) → O3(g)

Ozone in the Upper Atmosphere (stratosphere)

About 90% of all ozone (O3) in the atmosphere is found in the stratosphere (16 to 32 km above the earth's surface).

In the stratosphere ozone acts as the primary UV radiation shield, short wavelength UV radiation from the sun provides the energy to split oxygen molecules into oxygen atoms:

Oxygen atoms then react with oxygen molecules to form ozone:

O(g) + O2(g) → O3(g)

Ozone can absorb harmful UV-B and UV-C radiation, preventing it from reaching the earth's surface:

The constant formation and destruction of ozone maintains a balance over time. Human acitivities, such as the release of chlorofluorocarbons in to the atmosphere, have disturbed this balance.