above: Relative ozone levels, October 1998. From the Total Ozone Mapping Spectrometer Earth Probe (TOMS EP). Low ozone levels are transparent (blue) while high levels are opaque (white).


Ozone (O3) is a relatively unstable molecule made up of three atoms of oxygen (O). Although it represents only a tiny fraction of the atmosphere, ozone is crucial for life on Earth.

Depending on where ozone resides, it can protect or harm life on Earth. Most ozone resides in the stratosphere (a layer of the atmosphere between 10 and 40 km above us), where it acts as a shield to protect Earth's surface from the sun's harmful ultraviolet radiation. With a weakening of this shield, we would be more susceptible to skin cancer, cataracts, and impaired immune systems. Closer to Earth in the troposphere (the atmospheric layer from the surface up to about 10 km), ozone is a harmful pollutant that causes damage to lung tissue and plants.

The amounts of "good" stratospheric and "bad" tropospheric ozone in the atmosphere depend on a balance between processes that create ozone and those that destroy it. An upset in the ozone balance can have serious consequences for life on Earth, as scientists are finding evidence that changes are occurring in ozone levels—the "bad" tropospheric ozone is increasing in the air we breathe, and the "good" stratospheric ozone is decreasing in our protective ozone layer. This article describes processes that regulate "good" ozone levels.

next: Ozone Balance in the Stratosphere


by Steve Graham
July 30, 1999


Ozone: What is it, and why do we care about it?
Ozone Balance in the Stratosphere
Ozone Depletion
Monitoring Ozone from Space