Ozone-oxygen cycle

Ozone-oxygen cycle in the ozone layer.

The ozone-oxygen cycle is the process by which ozone is continually regenerated in Earth's stratosphere, all the while converting ultraviolet radiation into heat. In 1930 Sydney Chapman resolved the chemistry involved. The process is commonly called the Chapman cycle by atmospheric scientists.

Most of the ozone production occurs in the tropical upper stratosphere and mesosphere. The total mass of ozone produced per day over the globe is about 400 million metric tons. The global mass of ozone is relatively constant at about 3 billion metric tons, meaning the Sun produces about 12% of the ozone layer each day.[1]

Contents

Chemistry

The ozone molecules formed by the below reaction absorb ultraviolet radiation having wavelengths between 240 and 310 nm. The triatomic ozone molecule becomes diatomic molecular oxygen plus a free oxygen atom:

O3 + (240 nm < radiation < 310 nm) → O2 + O

The atomic oxygen produced immediately reacts with other oxygen molecules to reform ozone:

O2 + O + M → O3 + M

where "M" denotes the third body that carries off the excess energy of the reaction. In this way, the chemical energy released when O and O2 combine is converted into kinetic energy of molecular motion. The overall effect is to convert penetrating UV light into heat, without any net loss of ozone. This cycle keeps the ozone layer in a stable balance while protecting the lower atmosphere from UV radiation, which is harmful to most living beings. It is also one of two major sources of heat in the stratosphere (the other being the kinetic energy released when O2 is photolyzed into O atoms).

Removal

If an oxygen atom and an ozone molecule meet, they recombine to form two oxygen molecules:

O3 + O· → 2 O2

And if two oxygen atoms meet, they react to form one oxygen molecule:

2 O· → O2

The overall amount of ozone in the stratosphere is determined by a balance between production by solar radiation, and removal. The removal rate is slow, since the concentration of O atoms is very low.

Certain free radicals, the most important being hydroxyl (OH), nitric oxide (NO), and atoms of chlorine (Cl) and bromine (Br), catalyze the recombination reaction, leading to an ozone layer that is thinner than it would be if the catalysts were not present.

Most of the OH and NO are naturally present in the stratosphere, but human activity, especially emissions of chlorofluorocarbons (CFCs) and halons, has greatly increased the Cl and Br concentrations, leading to ozone depletion. Each Cl or Br atom can catalyze tens of thousands of decomposition reactions before it is removed from the stratosphere.

External links

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Oxygen cycle — The oxygen cycle. The Oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within its three main reservoirs: the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all… …   Wikipedia

  • Ozone depletion — Image of the largest Antarctic ozone hole ever recorded (September 2006) Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth s… …   Wikipedia

  • Ozone — For other uses, see Ozone (disambiguation). Ozone …   Wikipedia

  • Ozone layer — The ozone layer is a layer in Earth s atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 97–99% of the Sun s high frequency ultraviolet light, which is potentially damaging to the life forms on Earth.[1] It …   Wikipedia

  • Oxygen — This article is about the chemical element and its most stable form, O2 or dioxygen. For other forms of this element, see Allotropes of oxygen. For other uses, see Oxygen (disambiguation). nitrogen ← oxygen → fluorine ↑ O ↓ …   Wikipedia

  • Oxygen concentrator — A home oxygen concentrator in situ in an emphysema patient s house. The model shown is the DeVILBISS LT 4000 …   Wikipedia

  • Dobson ozone spectrophotometer — Original Dobson Spectrometer, using photographic plates The Dobson spectrophotometer, also known as Dobsonmeter or Dobson spectrometer, is the earliest instrument used to measure atmospheric ozone. It was invented in 1926 by Gordon Dobson.[1] A… …   Wikipedia

  • Nitrogen cycle — Schematic representation of the flow of nitrogen through the environment. The importance of bacteria in the cycle is immediately recognized as being a key element in the cycle, providing different forms of nitrogen compounds assimilable by higher …   Wikipedia

  • OTEX Ozone Laundry System — is an ozone disinfection laundry system developed by the commercial laundry equipment, dishwasher and service provider, JLA Group. OTEX was launched in June 2004, after a £3m development programme.[1] Contents 1 Application 2 Properties …   Wikipedia

  • Human impacts on the nitrogen cycle — Agricultural and industrial nitrogen (N) inputs to the environment currently exceed inputs from natural N fixation (Galloway 2003). As a consequence of anthropogenic inputs, the global nitrogen cycle (Fig. 1) has been significantly altered over… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.