This graph shows how the amount of ozone in the air is greater in the stratosphere. The most ozone is found at an altitude between 20 and 25 km (12 and 16 miles).
Click on image for full size
Image courtesy of NOAA, modified by Windows to the Universe staff.

Ozone Layer

The ozone layer is a range of altitudes in Earth's stratosphere which has a higher concentration of ozone molecules. Ozone is an unusual type of oxygen molecule. It is created when high-energy ultraviolet light from the Sun strikes a normal oxygen molecule.

The ozone layer extends from roughly 15 to 35 km (9 to 22 miles) above sea level. The peak of ozone concentration is between 20 and 25 km (12 and 16 miles). Concentrations typically range between 2 and 8 parts per million, though they can rise as high as 15 parts per million. About 90% of the ozone in our atmosphere is contained in the stratosphere. The ozone layer isn't actually a separate layer of Earth's atmosphere; it is a region within the stratosphere.

Ozone in the stratosphere protects us from ultraviolet radiation in sunlight. The ozone layer is sort of like sunscreen for planet Earth. It absorbs most of the incoming UV "light" before it reaches the ground. The ozone layer stops almost all of the incoming UV-C, about 90% of the UV-B, and roughly half of the UV-A radiation. The ozone molecules which absorb UV radiation later re-radiate the energy as heat, warming the stratosphere.

Various chemicals that humans release into the atmosphere can destroy ozone in the stratosphere. That is a problem since it allows more UV radiation to make it to the surface. In the 1980s, scientists noticed that the ozone layer was thinning. They also noticed huge holes in the ozone layer, especially over Antarctica. They convinced people and governments around the world to reduce emissions of ozone-destroying chemicals. They hope the ozone layer will heal itself over time.

Last modified February 27, 2009 by Randy Russell.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Ozone

Ozone is a special kind of oxygen molecule. Normal oxygen molecules (O2), the kind we need to breathe, have two oxygen atoms. Ozone molecules (O3) have three oxygen atoms. Ozone forms when a photon of...more

Oxygen

Oxygen (O2) is a kind of gas. A lot of the air you breathe is oxygen. That's a good thing, since we need oxygen to stay alive! About 4/5ths of the air in Earth's atmosphere is nitrogen (N2). Almost all...more

Ozone in the Stratosphere

Most of the ozone that we know about is found in the the stratosphere, the second layer of the Earth's atmosphere. Ozone forms a kind of layer in the stratosphere. This layer shields us from the Sun's...more

Air Pollution

Have you ever heard of air pollution? Air pollution is not new. 700 years ago, when people started burning large amounts of coal 700 years ago in London, England, they complained about the dust and soot...more

Rainbows

Rainbows appear in the sky when there is bright sunlight and rain. Sunlight is known as visible or white light and is actually a mixture of colors. The sun's rays pass through millions of raindrops. A...more

The Four Seasons

It takes the Earth one year to travel around the sun one time. During this year, there are four seasons: summer, autumn, winter, and spring. Each season depends on the amount of sunlight reaching the...more

Research Aircraft

Scientists sometimes travel in airplanes that carry weather instruments in order to gather data about the atmosphere. These research aircraft bring air from the outside into the plane so scientists can...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF