How do CFCs destroy the ozone layer?

Here’s the explanation of how natural gases and chemical substances, including nitrogen and chlorine, cause the depletion of the ozone layer.

Ozone has always had natural enemies in the atmosphere. One of them is nitrogen (NO), but chlorine (Cl) has been added to the list over the past century. In fact, its concentration has increased due to human-related activities, breaking the delicate balance of the stratosphere.

Let’s see in detail how CFCs, combined to ozone molecules, cause the ozone depletion.

The introduction of ozone into the stratosphere occurs through CFCs (Chlorofluorocarbons). CFCs, composed by chlorine, fluorine, and carbon, have a long lifecycle, which favours their accumulation. CFCs do not easily react with other substances. In fact, they break up only through sunlight, which divides their molecules, causing the release of chlorine (Cl). Once the chlorine is released, it is able to react with ozone (O3), to form chlorine monoxide (ClO) and oxygen (O2).

Cl + O3 = ClO + O2

When the molecule of chlorine monoxide (ClO) meets another molecule of oxygen (O) it breaks up, releasing chlorine (Cl), which can “destroy” another molecule of ozone (O3), creating the catalytic cycle of chlorine.

ClO + O = Cl + O2

The industrial production of CFCs started in the 1920’s, causing an average reduction of the ozone layer of 3 per cent.

Fortunately, chlorine has “natural enemies” as well, such as methane (CH4). Thanks to them, the natural ozone layer could recover over 50 years, as long as CFCs are no longer used on a global level.

The ozone depletion is also referred to as the “ozone hole”, due to the fact that its reduction is not uniform, but mainly concentrated in the Antarctic region, with reductions up to 70 per cent.

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