<p>Above accepted answer provide very good explanation to the question. I did some research on it and found some reasons <em>why</em> Ozone layer stays there instead somewhere else.</p>
<p><strong>TL;DR :</strong> Higher the altitude, higher the solar radiation energy. That makes <span class="math-container">${O_2}$</span> more excited and easier to break <span class="math-container">${O-O}$</span> bond. Also the concentration of oxygen need to be sufficient, but higher the altitude lower the oxygen as atmosphere become less dense. The equilibrium is where the Ozone layer is.</p>
<p>Following image from <a href="https://ozonewatch.gsfc.nasa.gov/facts/NH.html" rel="noreferrer">NASA Ozone Watch</a> shows the <span class="math-container">$\ce{O_3}$</span> concentration with altitude
<a href="https://i.sstatic.net/LeHba.gif" rel="noreferrer"><img src="https://i.sstatic.net/LeHba.gif" alt="enter image description here" /></a></p>
<p>Center for Coastal Physical Oceanography's <a href="http://www.ccpo.odu.edu/SEES/ozone/class/Chap_5/5_2.htm" rel="noreferrer">website</a> has some nice explanation why 40km altitude has highest <span class="math-container">$\ce{O_3}$</span> concentration.</p>
<blockquote>
<p>Ozone photochemistry is driven by the interaction of the Sun's
radiation with various gases in the atmosphere, particularly oxygen.
The understanding of the basics of ozone photochemistry began with
Chapman (1930), who hypothesized that UV radiation was responsible for
ozone production and proceeded to lay the foundation of stratospheric
photochemistry: the Chapman reactions. He proposed that atomic oxygen
is formed by the splitting (dissociation) of <span class="math-container">$\ce{O_2}$</span> by high energy
ultraviolet photons (i.e., packets of light energy with wavelengths
shorter than 242 nanometers) via</p>
<p><span class="math-container">$\ce{O_2 + hc/\lambda -&gt; O + O}$</span></p>
<p>Where h is the Planck constant, c is the
speed of light, and <span class="math-container">${\lambda}$</span> is the wavelength of the photon, given in
nanometers (abbreviated nm, where 1 nm=10-9 meter). Collectively,
<span class="math-container">$\ce{hc/\lambda}$</span> represents the photon of light that breaks up the <span class="math-container">$\ce{O_2}$</span>
molecule. The top panel of Figure 5.01 displays the absorption cross
section for oxygen multiplied by 10,000. The cross-section is
proportional to the probability that a photon from the Sun will be
absorbed by an oxygen molecule. While this probability increases for
the shorter, more energetic photons, the amount of UV radiation with
wavelength shorter than 242nm reaching into the atmosphere falls
dramatically with decreasing altitude.</p>
<p>The bottom of Figure 5.01 shows the amount of solar energy per unit
area (the flux) of different wavelengths reaching to three different
altitudes: the top of the atmosphere, 30 km, and the surface. The
amount of very energetic UV (&lt; 242 nm) radiation falls off sharply.
Thus, the splitting apart or photolysis of oxygen molecules by solar
radiation is relatively slow in the lower and middle stratosphere
because the photons of sufficient energy have already been absorbed by
molecular oxygen in the upper stratosphere in the Chapman reaction
given above. Few such photons are able to penetrate deeply into the
atmosphere</p>
<p>Figure 5.01 is below</p>
<p><a href="https://i.sstatic.net/zEPhY.jpg" rel="noreferrer"><img src="https://i.sstatic.net/zEPhY.jpg" alt="Figure 5.01" /></a></p>
</blockquote>

CC BY-SA 4.0
2020-08-29T19:54:04.263Z
2020-08-29T19:54:04.263Z
Salitha
<p>For the ozone layer to dissolve, it would need something to bind to. <a href="https://en.wikipedia.org/wiki/Chlorofluorocarbon" rel="noreferrer">Chloroflurocarbons</a> are one very notable thing that it can bind to, but that doesn't exactly answer the question.</p>
<p>While the ozone layer would be 3 mm thick if it was compressed down to the pressure of earth's surface, since it is further up in the atmosphere, it can take up a larger volume (like 20 km thick). The ozone layer is maintained by the <a href="http://glossary.ametsoc.org/wiki/Chapman_mechanism" rel="noreferrer">Chapman cycle</a>.</p>
<p>That is, the oxygen molecule (<span class="math-container">$\ce{O_2}$</span>) is dissociated by UV radiation (photolysis) to oxygen atoms (<span class="math-container">$\ce{2O}$</span>). Then the photolyzed oxygen atoms (<span class="math-container">$\ce{2O}$</span>) can bond with two oxygen molecules (<span class="math-container">$\ce{2O_2}$</span>) to make an two ozone molecules (<span class="math-container">$\ce{2O_3}$</span>), provided another molecule can take away some excess energy.</p>
<p>Since it is a cycle, there has to be a way for the ozone to return to oxygen. One ozone molecule (<span class="math-container">$\ce{O_3}$</span>) can photolyze to make an oxygen atom (<span class="math-container">$\ce{O}$</span>) and oxygen molecule (<span class="math-container">$\ce{O_2}$</span>). The oxygen atom (<span class="math-container">$\ce{O}$</span>) can react with another ozone molecule (<span class="math-container">$\ce{O_3}$</span>) to make two oxygen molecules (<span class="math-container">$\ce{2O_2}$</span>).</p>
<p>To just answer your question directly, the ozone layer is replenished by the sun's UV energy reacting with the oxygen in the atmosphere.</p>

CC BY-SA 4.0
2020-08-29T06:24:06.563Z
Thanks for the explanation. Just side question. If Ozone layer "regenerates", we can restore it by  stop emitting harmful gases like CFC. Isn't?
Salitha
CC BY-SA 4.0
2020-08-29T12:47:38.630Z
@Salitha [that's the plan](https://www.nasa.gov/feature/goddard/2019/2019-ozone-hole-is-the-smallest-on-record-since-its-discovery): *"The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons— banned chlorine-containing synthetic compounds that were once frequently used as coolants—continue to decline. Scientists expect the Antarctic ozone to recover back to the 1980 level around 2070."*
Robotnik
CC BY-SA 4.0
2020-08-29T16:41:20.400Z
Looking at [the picture here](https://www.pd.co.ke/business/science-tech-innovation/kenya-boasts-healthy-ozone-layer-5593/), what stops the ozone layer _diffusing_ (which is possibly what the OP meant by _dissolving_) into the stratosphere and/or the troposphere? Or does it, but the above reactions keep replacing it at that boundary (in which case, why is ozone created _there_ and not elsewhere)?
TripeHound
CC BY-SA 4.0
2020-08-29T19:55:30.010Z
@TripeHound  Ozone is created in other places (like the troposphere, but by a different process). Why the stratosphere? I've found it is because of the [density of oxygen](https://uk-air.defra.gov.uk/research/ozone-uv/ozone-concerns). Go higher and there isn't enough oxygen to start a reaction (See [Hydrostatic Equation](http://glossary.ametsoc.org/wiki/Hydrostatic_equation)). Go any lower and the UV radiation would be filtered out by the ozone above (exponentially- see [Beer-Lambert Law](https://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law)).
BarocliniCplusplus
CC BY-SA 4.0
2020-08-29T21:58:17.283Z
When you say "the pressure of earth's surface", do you mean "the atmosphere pressure at earth's surface"?
Pedro A
CC BY-SA 4.0
2020-08-30T08:46:28.307Z
@PedroA Yes. [NASA](https://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html) says that *"The Dobson Unit is the most common unit for measuring ozone concentration. One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere (the air pressure at the surface of the Earth)..... The average amount of ozone in the atmosphere is roughly 300 Dobson Units"*
Salitha
CC BY-SA 4.0
2020-08-28T20:04:37.763Z
2020-08-28T20:04:37.763Z
BarocliniCplusplus
<p><a href="https://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html" rel="noreferrer">It is said</a> about ozone:</p>
<blockquote>
<p>a layer in the earth's stratosphere at an altitude of about 10 km (6.2 miles) containing a high concentration of ozone</p>
</blockquote>
<blockquote>
<p>Over the Earth’s surface, the ozone layer’s <em>average</em> thickness is about 300 Dobson Units or a layer that is 3 millimetres thick. (nasa)</p>
</blockquote>
<p>So, how does the Ozone gas stays in that altitude without dissolving?</p>

CC BY-SA 4.0
2024-10-17T11:14:07.320Z
In Australia, we have strict (VERY strict) rules when using refrigerants because we have holes in the ozone here that we did not cause. How did the holes in the ozone get here when we are only 250 years old in development? And we have the strictest rules in the world probably when it comes to pollutants, especially chloroflourocarbons.
I can get fined as a person who handles refrigerant something like AU$10,000 for one offence. The company I work for can get fined much worse. (Also need to renew a license annually to work with refrigerants)
How is it that you can buy R134A off the shelf as an
Beano
<ozone>
How does the ozone layer "stay in place"?
Salitha
# How does the ozone layer "stay in place"?

(Asked by: username_0 on 2020-08-28)

[It is said](https://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html) about ozone:

> a layer in the earth's stratosphere at an altitude of about 10 km (6.2 miles) containing a high concentration of ozone

> Over the Earth’s surface, the ozone layer’s *average* thickness is about 300 Dobson Units or a layer that is 3 millimetres thick. (nasa)

So, how does the Ozone gas stays in that altitude without dissolving?

**Tags:** ozone

> **Comments:**
> **username_1**: In Australia, we have strict (VERY strict) rules when using refrigerants because we have holes in the ozone here that we did not cause. How did the holes in the ozone get here when we are only 250 years old in development? And we have the strictest rules in the world probably when it comes to pollutants, especially chloroflourocarbons. I can get fined as a person who handles refrigerant something like AU$10,000 for one offence. The company I work for can get fined much worse. (Also need to renew a license annually to work with refrigerants) How is it that you can buy R134A off the shelf as an  

---

## 2 answers

### Answer by username_2 on 2020-08-28. Score: 17 | Accepted answer

For the ozone layer to dissolve, it would need something to bind to. [Chloroflurocarbons](https://en.wikipedia.org/wiki/Chlorofluorocarbon) are one very notable thing that it can bind to, but that doesn't exactly answer the question.

While the ozone layer would be 3 mm thick if it was compressed down to the pressure of earth's surface, since it is further up in the atmosphere, it can take up a larger volume (like 20 km thick). The ozone layer is maintained by the [Chapman cycle](http://glossary.ametsoc.org/wiki/Chapman_mechanism).

That is, the oxygen molecule ($\ce{O\_2}$) is dissociated by UV radiation (photolysis) to oxygen atoms ($\ce{2O}$). Then the photolyzed oxygen atoms ($\ce{2O}$) can bond with two oxygen molecules ($\ce{2O\_2}$) to make an two ozone molecules ($\ce{2O\_3}$), provided another molecule can take away some excess energy.

Since it is a cycle, there has to be a way for the ozone to return to oxygen. One ozone molecule ($\ce{O\_3}$) can photolyze to make an oxygen atom ($\ce{O}$) and oxygen molecule ($\ce{O\_2}$). The oxygen atom ($\ce{O}$) can react with another ozone molecule ($\ce{O\_3}$) to make two oxygen molecules ($\ce{2O\_2}$).

To just answer your question directly, the ozone layer is replenished by the sun's UV energy reacting with the oxygen in the atmosphere.

> **Comments:**
> **username_0**: Thanks for the explanation. Just side question. If Ozone layer "regenerates", we can restore it by  stop emitting harmful gases like CFC. Isn't?  
> **username_3**: @username_0 [that's the plan](https://www.nasa.gov/feature/goddard/2019/2019-ozone-hole-is-the-smallest-on-record-since-its-discovery): *"The ozone hole over Antarctica is expected to gradually become less severe as chlorofluorocarbons— banned chlorine-containing synthetic compounds that were once frequently used as coolants—continue to decline. Scientists expect the Antarctic ozone to recover back to the 1980 level around 2070."*  
> **username_4**: Looking at [the picture here](https://www.pd.co.ke/business/science-tech-innovation/kenya-boasts-healthy-ozone-layer-5593/), what stops the ozone layer _diffusing_ (which is possibly what the OP meant by _dissolving_) into the stratosphere and/or the troposphere? Or does it, but the above reactions keep replacing it at that boundary (in which case, why is ozone created _there_ and not elsewhere)?  
> **username_2**: @username_4  Ozone is created in other places (like the troposphere, but by a different process). Why the stratosphere? I've found it is because of the [density of oxygen](https://uk-air.defra.gov.uk/research/ozone-uv/ozone-concerns). Go higher and there isn't enough oxygen to start a reaction (See [Hydrostatic Equation](http://glossary.ametsoc.org/wiki/Hydrostatic_equation)). Go any lower and the UV radiation would be filtered out by the ozone above (exponentially- see [Beer-Lambert Law](https://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law)).  
> **username_5**: When you say "the pressure of earth's surface", do you mean "the atmosphere pressure at earth's surface"?  
> **username_0**: @username_5 Yes. [NASA](https://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html) says that *"The Dobson Unit is the most common unit for measuring ozone concentration. One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere (the air pressure at the surface of the Earth)..... The average amount of ozone in the atmosphere is roughly 300 Dobson Units"*  

---

### Answer by username_0 on 2020-08-29. Score: 7

Above accepted answer provide very good explanation to the question. I did some research on it and found some reasons *why* Ozone layer stays there instead somewhere else.

**TL;DR :** Higher the altitude, higher the solar radiation energy. That makes ${O\_2}$ more excited and easier to break ${O-O}$ bond. Also the concentration of oxygen need to be sufficient, but higher the altitude lower the oxygen as atmosphere become less dense. The equilibrium is where the Ozone layer is.

Following image from [NASA Ozone Watch](https://ozonewatch.gsfc.nasa.gov/facts/NH.html) shows the $\ce{O\_3}$ concentration with altitude
[![enter image description here](https://i.sstatic.net/LeHba.gif)](https://i.sstatic.net/LeHba.gif)

Center for Coastal Physical Oceanography's [website](http://www.ccpo.odu.edu/SEES/ozone/class/Chap_5/5_2.htm) has some nice explanation why 40km altitude has highest $\ce{O\_3}$ concentration.

> Ozone photochemistry is driven by the interaction of the Sun's
> radiation with various gases in the atmosphere, particularly oxygen.
> The understanding of the basics of ozone photochemistry began with
> Chapman (1930), who hypothesized that UV radiation was responsible for
> ozone production and proceeded to lay the foundation of stratospheric
> photochemistry: the Chapman reactions. He proposed that atomic oxygen
> is formed by the splitting (dissociation) of $\ce{O\_2}$ by high energy
> ultraviolet photons (i.e., packets of light energy with wavelengths
> shorter than 242 nanometers) via
>
> $\ce{O\_2 + hc/\lambda -> O + O}$
>
> Where h is the Planck constant, c is the
> speed of light, and ${\lambda}$ is the wavelength of the photon, given in
> nanometers (abbreviated nm, where 1 nm=10-9 meter). Collectively,
> $\ce{hc/\lambda}$ represents the photon of light that breaks up the $\ce{O\_2}$
> molecule. The top panel of Figure 5.01 displays the absorption cross
> section for oxygen multiplied by 10,000. The cross-section is
> proportional to the probability that a photon from the Sun will be
> absorbed by an oxygen molecule. While this probability increases for
> the shorter, more energetic photons, the amount of UV radiation with
> wavelength shorter than 242nm reaching into the atmosphere falls
> dramatically with decreasing altitude.
>
> The bottom of Figure 5.01 shows the amount of solar energy per unit
> area (the flux) of different wavelengths reaching to three different
> altitudes: the top of the atmosphere, 30 km, and the surface. The
> amount of very energetic UV (< 242 nm) radiation falls off sharply.
> Thus, the splitting apart or photolysis of oxygen molecules by solar
> radiation is relatively slow in the lower and middle stratosphere
> because the photons of sufficient energy have already been absorbed by
> molecular oxygen in the upper stratosphere in the Chapman reaction
> given above. Few such photons are able to penetrate deeply into the
> atmosphere
>
> Figure 5.01 is below
>
> [![Figure 5.01](https://i.sstatic.net/zEPhY.jpg)](https://i.sstatic.net/zEPhY.jpg)


---

