What makes stratospheric ozone

It occurs naturally in small trace amounts in the upper atmosphere the stratosphere. At ground level, high concentrations of ozone are toxic to people and plants. Ninety percent of the ozone in the atmosphere sits in the stratosphere, the layer of atmosphere between about 10 and 50 kilometers altitude.

The natural level of ozone in the stratosphere is a result of a balance between sunlight that creates ozone and chemical reactions that destroy it. Ozone is created when the kind of oxygen we breathe—O 2 —is split apart by sunlight into single oxygen atoms. Single oxygen atoms can re-join to make O 2 , or they can join with O 2 molecules to make ozone O 3. Ozone is destroyed when it reacts with molecules containing nitrogen, hydrogen, chlorine, or bromine.

Some of the molecules that destroy ozone occur naturally, but people have created others. They received a Nobel Prize in Chemistry in for this work. When catalytic cycles involving chlorine, nitrogen oxides, and OH are included with the theory, the agreement between the theory and the measurements gets much better. Note that the total ozone amount at midlatitudes is greater than the amount in the tropics. This should seem strange to you because the solar UV that is part of the Chapman mechanism is strongest in the tropics.

Why do you think that total ozone is distributed this way? ANSWER: In addition to the production and destruction processes described above, the ozone distribution in the stratosphere is due to the motion of air.

Air comes from the troposphere into the stratosphere mostly in the tropics and then slowly moves to middle and high latitudes, where it sinks and re-enters the troposphere.

This air motion is known as the Brewer—Dobson circulation. Even though most ozone is made in the tropical stratosphere, the production process is relatively slow, and hence ozone abundance in the tropical stratosphere is quite low. As the air moves poleward, the production process adds ozone to the air, leading to relatively high ozone abundance at midlatitudes. Video is not narrated:. The Antarctic ozone hole is an extreme example of the destructive power of chlorine catalytic cycles.

Different catalytic cycles dominate the ozone destruction over Antarctica and, to a lesser extent, the Arctic. But, when aided by chemistry on the surfaces of naturally occurring polar stratospheric clouds, all the Cl in the form of HCl is liberated so that the polar catalytic cycles are able to destroy a few percent of the ozone per day in a plug the size of Antarctica from an altitude of 12 km all the way up to 20 km.

Skip to main content. It has also been linked to damage to some materials, crops, and marine organisms. The ozone layer protects the Earth against most UVB coming from the sun. It is always important to protect oneself against UVB, even in the absence of ozone depletion, by wearing hats, sunglasses, and sunscreen. However, these precautions will become more important as ozone depletion worsens. UVB has been linked to many harmful effects , including skin cancers, cataracts, and harm to some crops and marine life.

Scientists have established records spanning several decades that detail normal ozone levels during natural cycles. Ozone concentrations in the atmosphere vary naturally with sunspots, seasons, and latitude. These processes are well understood and predictable.

Each natural reduction in ozone levels has been followed by a recovery. Beginning in the s, however, scientific evidence showed that the ozone shield was being depleted well beyond natural processes. When chlorine and bromine atoms come into contact with ozone in the stratosphere, they destroy ozone molecules. One chlorine atom can destroy over , ozone molecules before it is removed from the stratosphere.

Ozone can be destroyed more quickly than it is naturally created. Some compounds release chlorine or bromine when they are exposed to intense UV light in the stratosphere. These compounds contribute to ozone depletion, and are called ozone-depleting substances ODS ODS A compound that contributes to stratospheric ozone depletion.

ODS include chlorofluorocarbons CFCs , hydrochlorofluorocarbons HCFCs , halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone. ODS that release chlorine include chlorofluorocarbons chlorofluorocarbons Gases covered under the Montreal Protocol and used for refrigeration, air conditioning, packaging, insulation, solvents, or aerosol propellants.

Since they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. These gases are being replaced by other compounds: hydrochlorofluorocarbons, an interim replacement for CFCs that are also covered under the Montreal Protocol, and hydrofluorocarbons, which are covered under the Kyoto Protocol. All these substances are also greenhouse gases. See hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, ozone depleting substance.

CFCs , hydrochlorofluorocarbons hydrochlorofluorocarbons Compounds containing hydrogen, fluorine, chlorine, and carbon atoms. Although ozone depleting substances, they are less potent at destroying stratospheric ozone than chlorofluorocarbons CFCs.

They have been introduced as temporary replacements for CFCs and are also greenhouse gases. See ozone depleting substance. This is why the ozone layer exists in the lower part of the stratosphere. The lower layer of the atmosphere that immediately surrounds the Earth is called the troposphere. Stratospheric ozone is a naturally-occurring gas that filters the sun's ultraviolet UV radiation.

This is typically regarded as 'good' ozone since it reduces the harmful effects of ultraviolet UV-B radiation. A diminished ozone layer allows more radiation to reach the Earth's surface.