Chapman cycle

Figure 7.11 The Chapman cycle for the creation and destruction of odd oxygen in the stratosphere...

However, at the tropopause the temperature profile changes, increasing with altitude throughout the stratosphere. The reason for this increase is a critical series of photochemical reactions involving ozone and molecular oxygen. The Chapman cycle, reactions (l)-(4), hypothesized in the 1930 s by Sir Sydney Chapman,... 

As described earlier, in the stratosphere, a steady-state concentration of 03 is produced naturally by the Chapman cycle, reactions (l)-(4). Until about 1970, relatively little attention was paid to potential anthropogenic (i.e., man-made) perturbations of the stratosphere. At that time, Crutzen (1970) examined the potential role of NO and N02 formed in the stratosphere from reactions of N20 that was originally generated at the earth s surface. Because N20 is unre-active in the troposphere, it has a sufficiently long lifetime to end up in the stratosphere, where it can be converted into NO (see Chapter 12). Crutzen (1970) proposed that the NO and N02 formed from reactions of N20 can then participate in a chain reaction that destroys 03 ... 

Chapman (1930) first proposed the fundamental ozone-forming and destruction reactions that lead to a steady-state concentration of O, in the stratosphere. These reactions are now known as the Chapman cycle ... 

In this project students review the Chapman cycle mechanism in detail and some photochemistry concepts including the photostationary state. A key element of this project is its focus on an important chemical mechanism and the use of exploratory options for predicting ozone concentrations as a function of time while reviewing other fundamental chemical kinetics concepts. Mathcad is used as the symbolic mathematics engine for solving the requisite differential equations and ample instruction is provided to students to guide them on the use of the software in this project. 

A British scientist Sydney Chapman suggested the basic ideas of stratospheric ozone in the 1930s, which have become known as the Chapman cycle. Short wavelength UV hv) can dissociate molecular oxygen and the atomic oxygen fragments produced react with oxygen molecules to make ozone. 

On the surface there is now an apparent contradiction with only the Chapman cycle we produce too much ozone, whereas the catalytic cycles could destroy all the ozone There are a number of cycles that can interconvert the catalytic cycles without odd oxygen removal these will be in competition with the catalytic cycles, e.g. 

Ozone is formed and destroyed in a series of stratospheric reactions. Its steady state concentration is described by the Chapman cycle. 

Terrestrial stratospheric chemistry is closely linked to the ozone (O3) layer at 15-35 km, which shields the Earth s surface from harmful UV sunlight (X<300 nm) and dissipates the absorbed solar energy as heat. The abundance of O3 in the stratosphere is a balance between production, destruction, and lateral transport. Production and destruction of O3 in the absence of other perturbing influences is described by the Chapman cycle given in Table V. 

HOt cycle 1 is therefore about half as effective in destroying 03 at 35 km as the Chapman cycle. 

Ozone removal by catalytic chlorine chemistry and the Chapman cycle are, therefore, roughly equal at about 40 km. 

A slightly simplified version of the steady-state process for ozone formation (reactions 1 and 2) and destruction (reactions 3 and 4) is known as the Chapman cycle (shown in left margin) after the scientist who proposed it. 

An animation of the Chapman cycle is found at a NASA website. Click on Atmospheric Chemistry under the Atmosphere heading. Then click on ozone and follow by clicking on the panel showing ozone creation to watch a movie of ozone formation, http // visibleearth.nasa.gov/... 

Chapman Cycle The set of four reactions that represents the steady-state formation and destruction of ozone in the stratosphere. 

It is known that measured ozone concentrations are lower than can be accounted for by the simple Chapman cycle. This has led scientists to look for other influences on the concentration of ozone. First, let s briefly consider one of the natural reactions that destroys ozone. UV radiation can break the oxygen-hydrogen bond of a water molecule in the stratosphere to generate hydrogen atoms and hydroxyl radicals ( OH). These two species are involved in many reactions, some of which actually convert Og to Og. However, this process, which scientists now believe is an efficient process above 50 km, has been occurring since the ozone layer developed, and there is little, if anything, that humans can do about it. The system has obviously attained a steady state that includes this perturbation. 

Write out the reactions of the Chapman cycle and discuss the meaning of each. 

The Chapman cycle is a series of chemical reactions related to the oxygen-ozone screening... 

Chapter 7 is a new chapter on the relationship between GFGs and the ozone hole, expanded from the four pages in the previous edition. The mechanisms by which oxygen and ozone protect us are discussed in the context of the Chapman Cycle. Scientific responses to the issue and the replacement of CFCs are considered. There is also discussion addressing the relationship between UV exposure and skin cancer. 

In 1903, the British scientist, Sydney Chapman, first explained the chemistry of the formation of ozone in the upper atmosphere when he proposed what is now known as the Chapman cycle. Although Chapman s original proposal was quite speculative, modern measurements of a wide array of quantities support his hypothesis. The Chapman cycle begins and ends with oxygen, the more stable... 

The Chapman cycle begins with a UV photon dissociating a diatomic oxygen molecule. 

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