Most people, when they hear the word Ozone, immediately think of air pollution and global warming. This is just a small part of the story. Ozone also has many useful applications. Let's take a deeper look.
Ozone, or tri-oxygen, is a triatomic molecule made of three atoms of oxygen. It is an unstable molecule and is constantly being generated and then destroyed in the atmosphere. Ozone comprises a tiny 0.00006% of the atmosphere.
The highest levels of ozone are in the stratosphere, commonly called the ozone layer between about 6 and 31 miles up. Ozone serves as a natural filter of ultraviolet (UV) light from the Sun. These rays are harmful to us in large doses.
Ozone in produced when the UV rays react with oxygen (click here for a great diagram that summarizes the chemistry). The radiation first splits an oxygen molecule and then allows the formation of the triatomic struture:
O2 + photon (UV radiation < 240 nm) → 2 O
O + O2 + M → O3 + M
Ozone can also be destroyed by a reaction with atomic oxygen in the presence of one of a variety of catalyzing agents (including hydroxyl, nitric oxide, chlorine and bromine):
O3 + O → 2 O2
In recent decades, we have heard more and more about the "hole" in the ozone layer. Scientists suspect the stratospheric levels of ozone have declined in part due to emissions of CFCs and other chlorinated and brominated organic molecules. The presence of these catalyists increase the rate at which ozone is destroyed and decrease the overall concentration of ozone in the stratosphere.
While low levels of ozone are an issue in the stratosphere, here on the ground, it is high levels that present health risks. Ozone is formed when sunlight reacts with air containing hydrocarbons and nitrogen oxides to form ozone. Ground ozone can take 22 days to be destroyed and can cause effects from smog to reduction in agricultural yields (due to the effects on photosynthesis).
Despite the negative press, ozone is used successfully in many applications (beyond its effects as a sunscreen for the planet in the stratosphere). The largest use of ozone is in industrial applications. It can cleave carbon bonds, facilitate the breakdown of agricultural organic wastes, sanitize and deodorize items and kill bacteria in drinking water. Next time, I'll take a look at how ozone can be created and measured for these purposes.
There are many resources to further investigate the positive and negatives that surround this molecule. Here are just a few: