Above: Image © iStock, toskov

Let's start by looking at what ozone is.

What do we breathe? Air. And what part of the air do we need? Oxygen.

Just under 21 per cent of the air is made up of oxygen. Oxygen is a gas consisting of two oxygen atoms, and is therefore its chemical form is shown as O2. Ozone is also a gas, consisting of three oxygen atoms stuck together (O3). Now, these two compounds, O2 and O3, can — and do — change into each other under intense ultraviolet (UV) radiation. This is where our atmosphere and our Sun come in. UV radiation from the sun splits the O2 molecules into two single oxygen atoms. These singular atoms don't like to hang out alone and attach themselves either to another atom to re-form O2, or to an O2 molecule to form O3. Et voila, ozone is born.

So why is ozone important?

UV radiation is a type of energy that travels through space at different wavelengths. UV radiation is divided into three ranges of wavelengths (measured in nanometers (nm) or 0.0000004 meters), called UV-A (320-400 nm), UV-B (290-320 nm) and UV-C (100-290 nm). These groupings are based on the energy they contain and the effects they have on biological systems.

UV-C has the most energy and is the most harmful to life on our planet, whereas the reverse is true for UV-A. Since UV-A has so little energy, it is unable to break ozone or oxygen molecules apart and therefore is not absorbed by the reaction.

Did you know? If you go out in the sun, especially close to the poles where the ozone layer is thinner, always wear long clothes and a hat to protect your skin from harmful UV rays.Instead, most UV-A passes through the ozone to the earth. High energy UV-C radiation, on the other hand, is able to break the bonds holding O2 and O3 molecules together, which helps remove the dangerous radiation from the atmosphere. Ozone is even better in adsorbing UV-C radiation than oxygen gas, as it requires more energy to split O3 into O2 molecules. In fact, ozone is so effective that it can eliminate almost all of the UV-C radiation in our atmosphere, keeping it from reaching us on earth.

This back-and-forth ping pong game of the conversion between oxygen to ozone back to oxygen can be severely influenced by a range of chemicals released into the atmosphere. One group of chemical compounds that has received a lot attention are chlorofluorocarbons (CFCs), which have been used in such products as spray cans and fridges. When emitted into the atmosphere, the CFCs react with UV radiation, resulting in the release of chlorine (Cl) atoms.

Did you know? While many countries ratified the ban of CFCs, they are still standard production material in many countries.

Chlorine is highly reactive and can easily break apart ozone (O3) to form O2 and ClO (chlorine monoxide). The ClO will then interact with single oxygen atoms to form more O2 and the Cl atom that is also released is now free to break down even more ozone molecules. Over time, there has been a net depletion of ozone in the atmosphere. As a result, there is a higher risk of exposure to harmful UV radiation from the sun. Only a big international ban on CFCs prevented further destruction of ozone.

Learn More!

Ozone Layer (Wkipedia) Ozone Layer (NASA) Ozone Layer (Meteorological Service of Canada)

Lars Rose

Lars Rose is a PhD candidate in high temperature Solid Oxide Fuel Cell research (that is sustainable energies), at the Department of Materials Engineering in the Faculty of Applied Science at the University of British Columbia (UBC), and at the National Research Council Canada, Institute for Fuel Cell Innovation (NRC-IFCI). He enjoys teaching fun stuff and is the current Media Relations and Human Resources coordinator of the outreach program Let's Talk Science at UBC. He enjoys writing science in a fun way for CurioCity, UBC Terry, the Science Creative Quarterly, Fuel Cell Today and Ubyssey.

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