<p>BrO and ClO significantly deplete ozone from the atmosphere.</p>

<p>Researchers at <a href="https://www.arp.harvard.edu/research/climate-change-atmospheric-chemistry" rel="noreferrer">Harvard University</a> state:</p>

<blockquote>
  <p>It is a remarkable fact that perhaps the most important observation coupling climate forcing to UV dosage levels at the surface at mid-latitudes is the observation of high (e.g. > 10 ppmv) water vapor and low temperatures (&lt; 210 K) with the simultaneous determination of BrO and ClO in the lower stratosphere at mid-latitudes.</p>
</blockquote>

<p>Similarly, <a href="https://science.sciencemag.org/content/266/5184/398.abstract" rel="noreferrer">Science magazine</a> states:</p>

<blockquote>
  <p>Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O<sub>3</sub>; reactions involving BrO account for one-half of this loss. </p>
</blockquote>

<p><a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/halogen" rel="noreferrer">Additonally</a>,</p>

<blockquote>
  <p>... where the chlorine and bromine thus released participate in the catalytic destruction of ozone.</p>
</blockquote>

<p><a href="https://core.ac.uk/display/18454995?source=3" rel="noreferrer">Kinetic studies of the BrO plus ClO cross-reaction over the range T=246-314 K</a> </p>

CC BY-SA 4.0
2020-02-22T06:42:37.143Z
2020-02-22T06:42:37.143Z
Fred
<p><em>pretext:</em> Seeing this question on the list of network questions caught my interest to the site.</p>

<p>I agree with the arguments put forward in the answer by Fred, gravitating on the <a href="https://en.wikipedia.org/wiki/Radical_(chemistry)" rel="noreferrer">radical</a> character of halogene oxides listed (e.g., BrO, ClO), where unpaired electrons contribute to reactivity to the specis.  Some of them are created <em>in situ</em> under light radiation and hence may interfere in the constant generation and decomposition of ozone in the <a href="https://en.wikipedia.org/wiki/Ozone-oxygen_cycle" rel="noreferrer">Chapman cycle</a>.  </p>

<p>To expand the picture, there is a large «family» of chlorine oxydes, for some of them the structural formulae are given below (each containing a dot already is a radical in a chemical sense) and <a href="https://en.wikipedia.org/wiki/Chlorine_oxide" rel="noreferrer">individual details</a> (chlorine oxides), and <a href="https://en.wikipedia.org/wiki/Bromine_dioxide" rel="noreferrer">bromine dioxide</a> in addition:</p>

<p><a href="https://i.sstatic.net/Z2kiI.png" rel="noreferrer"><img src="https://i.sstatic.net/Z2kiI.png" alt="enter image description here"></a></p>

<p>(<a href="https://de.wikipedia.org/wiki/Chloroxide" rel="noreferrer">image credit</a>)</p>

<p>However, I would point out that the original listing on OSCAR about GEMS' mission as-such <em>accidentally may</em> contain errors as it lists <code>HC3Br Mole Fraction</code>.  For one, there isn't such a compound as a stable one you could store in a bottle like copper sulfate.  Indeed I speculate, in analogy to <a href="https://en.wikipedia.org/wiki/Chlorofluorocarbon" rel="noreferrer">CFCs</a> like <a href="https://en.wikipedia.org/wiki/Dichloromethane" rel="noreferrer">methylene chloride</a> and <a href="https://en.wikipedia.org/wiki/Chloroform" rel="noreferrer">chloroform</a>, their target is <a href="https://en.wikipedia.org/wiki/Bromoform" rel="noreferrer">bromoform</a>, <span class="math-container">$\ce{CHBr3}$</span> which has natural sources, and is relevant to atmospheric ozone, too.</p>

<p><em>side note:</em>
Similar to the putative chemical error here, <em>some</em> elder data entries in crystallographic databases erroneously state a symmetry in <span class="math-container">$P1$</span>. While initially submitted by the authors as <span class="math-container">$P\bar{1}$</span>, the bar sometimes was lost during the processing (mentioned, for example, by Hofman <a href="https://link.springer.com/chapter/10.1007/978-3-642-04759-6_4" rel="noreferrer">here</a>), like the first <a href="https://en.wikipedia.org/wiki/Second-harmonic_generation" rel="noreferrer">SHG signal</a> described by <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.7.118" rel="noreferrer">Franken <em>et al.</em></a></p>

CC BY-SA 4.0
2020-02-23T00:50:19.700Z
That's great news, welcome to the site and thank you for your answer!
uhoh
CC BY-SA 4.0
2020-02-23T00:57:51.940Z
fyi I've just asked [Are atmospheric halogen oxides "supposed to be" in the atmosphere? Where do they come from?](https://earthscience.stackexchange.com/q/19274/6031)
uhoh
CC BY-SA 4.0
2020-02-22T17:45:26.273Z
2020-02-22T17:45:26.273Z
Buttonwood
<p>Regarding the Geostationary Environmental Monitoring Spectrometer (GEMS) itself:</p>

<blockquote>
  <p>The instrument's purpose is given as</p>
  
  <blockquote>
    <p>Ozone profile and total-column or gross profile of other species. Tracked species: BrO, NO2, O3, OClO, SO2 and aerosol</p>
  </blockquote>
</blockquote>

<p>That is rather inaccurate and misleading. GEMS does not track BrO or OClO (or ClO). It does track ozone, but the target is tropospheric rather than stratospheric ozone. GEMS is a satellite instrument whose primary goal is tropospheric air quality monitoring rather than stratospheric chemistry.</p>

<p><br></p>

<blockquote>
  <p>I think that "Mole fraction" is a relative concentration and "Total column" is absolute?</p>
</blockquote>

<p>Mole fraction is the relative concentration of some atmospheric component as a function of altitude. Converting this relative concentration to an absolute quantity (e.g., number of moles, or mass) and integrating from the bottom of the atmosphere to the top yields the "total column" quantity for that component.</p>

<p><br></p>

<blockquote>
  <p>Why are atmospheric BrO and ClO important to measure by satellite?</p>
</blockquote>

<p>This is the question raised in the title of the question.</p>

<p>A large number of halogenated hydrocarbons indirectly contribute to ozone depletion. Those halogenated hydrocarbons by themselves are not ozone-depleting substances. But if those compounds reach the upper stratosphere, sunlight can split a halogen atom off of those components. Split-off fluorine atoms tend to bind rather quickly with hydrogen and form an extremely stable hydrogen fluoride molecule. Fluorine barely registers as an ozone-depleting substance because hydrogen fluoride is so stable. Stratospheric hydrogen fluoride eventually diffuses into the troposphere, where it gets dissolved by water and falls as rain.</p>

<p>Split-off chlorine and bromine atoms have a different fate. Hydrogen chloride and hydrogen bromide aren't nearly as stable as is hydrogen fluoride. Chlorine and bromine instead alternate between reservoirs such as HCl and hBr and atomic/oxide forms that catalytically deplete ozone. The key reason it is important to monitor these halogens is that most (about 80%) of the chlorine and almost half (40-50%) of the bromine in the stratosphere is anthropogenic.</p>

<p><br>
References:</p>

<p><a href="https://science.sciencemag.org/content/238/4831/1253.short" rel="nofollow noreferrer">Molina, Mario J., et al. "Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride, and ice: Release of active chlorine." Science 238.4831 (1987): 1253-1257.</a></p>

<p><a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92GL00781" rel="nofollow noreferrer">Poulet, Gilles, et al. "Role of the BrO+ HO2 reaction in the stratospheric chemistry of bromine." Geophysical research letters 19.23 (1992): 2305-2308.</a></p>

<p><a href="https://www.spiedigitallibrary.org/journals/Introducing-the-geostationary-environment-monitoring-spectrometer/volume-12/issue-04/044005/Introducing-the-geostationary-environment-monitoring-spectrometer/10.1117/1.JRS.12.044005.full?webSyncID=9a0ce46e-9e6e-c7a4-9dab-6a0cbad05932&amp;sessionGUID=9ad883c9-d902-bc99-93ce-d268bead49a2&amp;SSO=1" rel="nofollow noreferrer">Choi, Won Jun, et al. "Introducing the geostationary environment monitoring spectrometer." Journal of Applied Remote Sensing 12.4 (2018): 044005.</a></p>

<p><a href="https://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-18-0013.1" rel="nofollow noreferrer">Kim, Jhoon, et al. "New era of air quality monitoring from space: Geostationary Environment Monitoring Spectrometer (GEMS)." Bulletin of the American Meteorological Society 2019 (2019): 00.</a></p>

<p>In addition to the above scientific articles, there are many web pages on stratospheric chemistry. For example, <a href="https://personal.ems.psu.edu/~brune/m532/meteo532_ch7_stratospheric_chemistry.htm" rel="nofollow noreferrer">https://personal.ems.psu.edu/~brune/m532/meteo532_ch7_stratospheric_chemistry.htm</a></p>

CC BY-SA 4.0
2020-02-24T02:41:33.257Z
yikes! it's going to take me a few days just to download and/or skim these, but I'm looking forward to it, thanks!
uhoh
CC BY-SA 4.0
2020-02-23T18:53:34.397Z
2020-02-23T18:53:34.397Z
David Hammen
<p>The announcement <a href="https://www.arianespace.com/press-release/ariane-5-success-va252/" rel="noreferrer">Arianespace orbits two satellites – JCSAT-17 and GEO-KOMPSAT-2B – to support connectivity and environmental monitoring in Asia</a> mentions <a href="https://www.wmo-sat.info/oscar/satellites/view/35" rel="noreferrer">GEO-KOMPSAT-2B</a> which hosts the <a href="https://www.wmo-sat.info/oscar/instruments/view/145" rel="noreferrer">Geostationary Environmental Monitoring Spectrometer</a> or GEMS UV/Vis (300-500 nm) imaging spectrometer for hyperspectral imaging of Earth's atmosphere.</p>

<p>The instrument's <strong>purpose</strong> is given as</p>

<blockquote>
  <p>Ozone profile and total-column or gross profile of other species. Tracked species: BrO, NO<sub>2</sub>, O<sub>3</sub>, OClO, SO<sub>2</sub> and aerosol</p>
</blockquote>

<p>and its <strong>primary mission objectives</strong> are listed as</p>

<ul>
<li>BrO Mole Fraction</li>
<li>ClO Mole Fraction</li>
<li>H<sub>2</sub>O Mole Fraction</li>
<li>HC<sub>3</sub>Br Mole Fraction</li>
<li>HCHO Mole Fraction</li>
</ul>

<p>with the following as other mission objectives</p>

<ul>
<li>HCHO Total Column</li>
<li>NO Mole Fraction</li>
<li>NO<sub>2</sub> Total Column</li>
<li>NO<sub>2</sub> Mole Fraction</li>
<li>O<sub>3</sub> Mole Fraction</li>
<li>O<sub>3</sub> Total Column</li>
<li>SO<sub>2</sub> Mole Fraction</li>
<li>SO<sub>2</sub> Total Column</li>
</ul>

<p>I think that "Mole fraction" is a relative concentration and "Total column" is absolute? </p>

<p>I see that some of the species listed in the instrument's purpose are not in its primary objectives, but oh well.</p>

<p><strong>Question:</strong> Why exactly are atmospheric BrO and ClO so important to measure, and measure by satellite, and what is the difference between ClO in the "objectives" and OClO in the "purpose"?</p>

CC BY-SA 4.0
2020-02-22T06:00:42.600Z
A *guess* (I don't have to research at the moment): BrO and ClO play a role in ozone destruction (→ ozone hole).
njuffa
CC BY-SA 4.0
2020-02-24T01:02:27.763Z
As noted in my answer, the OSCAR entry on the GEMS instrument is severely flawed: GEMS will not measure BrO or ClO. Those flaws do not detract from the primary question regarding the importance of measure atmospheric BrO and ClO, or from the auxiliary question regarding molar fraction vs total column.
David Hammen
<atmosphere><atmospheric-chemistry><satellites><upper-atmosphere>
Why are atmospheric BrO and ClO important to measure by satellite?
uhoh
# Why are atmospheric BrO and ClO important to measure by satellite?

(Asked by: username_0 on 2020-02-22)

The announcement [Arianespace orbits two satellites – JCSAT-17 and GEO-KOMPSAT-2B – to support connectivity and environmental monitoring in Asia](https://www.arianespace.com/press-release/ariane-5-success-va252/) mentions [GEO-KOMPSAT-2B](https://www.wmo-sat.info/oscar/satellites/view/35) which hosts the [Geostationary Environmental Monitoring Spectrometer](https://www.wmo-sat.info/oscar/instruments/view/145) or GEMS UV/Vis (300-500 nm) imaging spectrometer for hyperspectral imaging of Earth's atmosphere.

The instrument's **purpose** is given as

> Ozone profile and total-column or gross profile of other species. Tracked species: BrO, NO2, O3, OClO, SO2 and aerosol

and its **primary mission objectives** are listed as

* BrO Mole Fraction
* ClO Mole Fraction
* H2O Mole Fraction
* HC3Br Mole Fraction
* HCHO Mole Fraction

with the following as other mission objectives

* HCHO Total Column
* NO Mole Fraction
* NO2 Total Column
* NO2 Mole Fraction
* O3 Mole Fraction
* O3 Total Column
* SO2 Mole Fraction
* SO2 Total Column

I think that "Mole fraction" is a relative concentration and "Total column" is absolute?

I see that some of the species listed in the instrument's purpose are not in its primary objectives, but oh well.

**Question:** Why exactly are atmospheric BrO and ClO so important to measure, and measure by satellite, and what is the difference between ClO in the "objectives" and OClO in the "purpose"?

**Tags:** atmosphere, atmospheric-chemistry, satellites, upper-atmosphere

> **Comments:**
> **username_1**: A *guess* (I don't have to research at the moment): BrO and ClO play a role in ozone destruction (→ ozone hole).  
> **username_2**: As noted in my answer, the OSCAR entry on the GEMS instrument is severely flawed: GEMS will not measure BrO or ClO. Those flaws do not detract from the primary question regarding the importance of measure atmospheric BrO and ClO, or from the auxiliary question regarding molar fraction vs total column.  

---

## 3 answers

### Answer by username_3 on 2020-02-22. Score: 11

BrO and ClO significantly deplete ozone from the atmosphere.

Researchers at [Harvard University](https://www.arp.harvard.edu/research/climate-change-atmospheric-chemistry) state:

> It is a remarkable fact that perhaps the most important observation coupling climate forcing to UV dosage levels at the surface at mid-latitudes is the observation of high (e.g. > 10 ppmv) water vapor and low temperatures (< 210 K) with the simultaneous determination of BrO and ClO in the lower stratosphere at mid-latitudes.

Similarly, [Science magazine](https://science.sciencemag.org/content/266/5184/398.abstract) states:

> Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O3; reactions involving BrO account for one-half of this loss.

[Additonally](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/halogen),

> ... where the chlorine and bromine thus released participate in the catalytic destruction of ozone.

[Kinetic studies of the BrO plus ClO cross-reaction over the range T=246-314 K](https://core.ac.uk/display/18454995?source=3)


---

### Answer by username_4 on 2020-02-22. Score: 5

*pretext:* Seeing this question on the list of network questions caught my interest to the site.

I agree with the arguments put forward in the answer by username_3, gravitating on the [radical](https://en.wikipedia.org/wiki/Radical_(chemistry)) character of halogene oxides listed (e.g., BrO, ClO), where unpaired electrons contribute to reactivity to the specis. Some of them are created *in situ* under light radiation and hence may interfere in the constant generation and decomposition of ozone in the [Chapman cycle](https://en.wikipedia.org/wiki/Ozone-oxygen_cycle).

To expand the picture, there is a large «family» of chlorine oxydes, for some of them the structural formulae are given below (each containing a dot already is a radical in a chemical sense) and [individual details](https://en.wikipedia.org/wiki/Chlorine_oxide) (chlorine oxides), and [bromine dioxide](https://en.wikipedia.org/wiki/Bromine_dioxide) in addition:

[![enter image description here](https://i.sstatic.net/Z2kiI.png)](https://i.sstatic.net/Z2kiI.png)

([image credit](https://de.wikipedia.org/wiki/Chloroxide))

However, I would point out that the original listing on OSCAR about GEMS' mission as-such *accidentally may* contain errors as it lists `HC3Br Mole Fraction`. For one, there isn't such a compound as a stable one you could store in a bottle like copper sulfate. Indeed I speculate, in analogy to [CFCs](https://en.wikipedia.org/wiki/Chlorofluorocarbon) like [methylene chloride](https://en.wikipedia.org/wiki/Dichloromethane) and [chloroform](https://en.wikipedia.org/wiki/Chloroform), their target is [bromoform](https://en.wikipedia.org/wiki/Bromoform), $\ce{CHBr3}$ which has natural sources, and is relevant to atmospheric ozone, too.

*side note:*
Similar to the putative chemical error here, *some* elder data entries in crystallographic databases erroneously state a symmetry in $P1$. While initially submitted by the authors as $P\bar{1}$, the bar sometimes was lost during the processing (mentioned, for example, by Hofman [here](https://link.springer.com/chapter/10.1007/978-3-642-04759-6_4)), like the first [SHG signal](https://en.wikipedia.org/wiki/Second-harmonic_generation) described by [Franken *et al.*](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.7.118)

> **Comments:**
> **username_0**: That's great news, welcome to the site and thank you for your answer!  
> **username_0**: fyi I've just asked [Are atmospheric halogen oxides "supposed to be" in the atmosphere? Where do they come from?](https://earthscience.stackexchange.com/q/19274/6031)  

---

### Answer by username_2 on 2020-02-23. Score: 3

Regarding the Geostationary Environmental Monitoring Spectrometer (GEMS) itself:

> The instrument's purpose is given as
>
> > Ozone profile and total-column or gross profile of other species. Tracked species: BrO, NO2, O3, OClO, SO2 and aerosol

That is rather inaccurate and misleading. GEMS does not track BrO or OClO (or ClO). It does track ozone, but the target is tropospheric rather than stratospheric ozone. GEMS is a satellite instrument whose primary goal is tropospheric air quality monitoring rather than stratospheric chemistry.

> I think that "Mole fraction" is a relative concentration and "Total column" is absolute?

Mole fraction is the relative concentration of some atmospheric component as a function of altitude. Converting this relative concentration to an absolute quantity (e.g., number of moles, or mass) and integrating from the bottom of the atmosphere to the top yields the "total column" quantity for that component.

> Why are atmospheric BrO and ClO important to measure by satellite?

This is the question raised in the title of the question.

A large number of halogenated hydrocarbons indirectly contribute to ozone depletion. Those halogenated hydrocarbons by themselves are not ozone-depleting substances. But if those compounds reach the upper stratosphere, sunlight can split a halogen atom off of those components. Split-off fluorine atoms tend to bind rather quickly with hydrogen and form an extremely stable hydrogen fluoride molecule. Fluorine barely registers as an ozone-depleting substance because hydrogen fluoride is so stable. Stratospheric hydrogen fluoride eventually diffuses into the troposphere, where it gets dissolved by water and falls as rain.

Split-off chlorine and bromine atoms have a different fate. Hydrogen chloride and hydrogen bromide aren't nearly as stable as is hydrogen fluoride. Chlorine and bromine instead alternate between reservoirs such as HCl and hBr and atomic/oxide forms that catalytically deplete ozone. The key reason it is important to monitor these halogens is that most (about 80%) of the chlorine and almost half (40-50%) of the bromine in the stratosphere is anthropogenic.

References:

[Molina, Mario J., et al. "Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride, and ice: Release of active chlorine." Science 238.4831 (1987): 1253-1257.](https://science.sciencemag.org/content/238/4831/1253.short)

[Poulet, Gilles, et al. "Role of the BrO+ HO2 reaction in the stratospheric chemistry of bromine." Geophysical research letters 19.23 (1992): 2305-2308.](https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92GL00781)

[Choi, Won Jun, et al. "Introducing the geostationary environment monitoring spectrometer." Journal of Applied Remote Sensing 12.4 (2018): 044005.](https://www.spiedigitallibrary.org/journals/Introducing-the-geostationary-environment-monitoring-spectrometer/volume-12/issue-04/044005/Introducing-the-geostationary-environment-monitoring-spectrometer/10.1117/1.JRS.12.044005.full?webSyncID=9a0ce46e-9e6e-c7a4-9dab-6a0cbad05932&sessionGUID=9ad883c9-d902-bc99-93ce-d268bead49a2&SSO=1)

[Kim, Jhoon, et al. "New era of air quality monitoring from space: Geostationary Environment Monitoring Spectrometer (GEMS)." Bulletin of the American Meteorological Society 2019 (2019): 00.](https://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-18-0013.1)

In addition to the above scientific articles, there are many web pages on stratospheric chemistry. For example, <https://personal.ems.psu.edu/~brune/m532/meteo532_ch7_stratospheric_chemistry.htm>

> **Comments:**
> **username_0**: yikes! it's going to take me a few days just to download and/or skim these, but I'm looking forward to it, thanks!  

---

