<p>Let us suppose, that the pollutant distributes in the lower 10 km
layer (H), and its concentrations (C) are equal on each altitude for more simple calculations. [mol/m<sup>2</sup>] must be converted to [mg/m<sup>3</sup>] for comparison with national threshold standards. Therefore, the near-ground value in [mg/m<sup>3</sup>] is:</p>
<p>C = (C<sub>col</sub>/H) * M * A,</p>
<p>where,</p>
<ul>
<li>C<sub>col</sub> is the pollutant column content [mol/m<sup>2</sup>],</li>
<li>M is the molar mass [g/mol],</li>
<li>A is a constant, equals to 1000, for conversion from [g/m<sup>3</sup>] to [mg/m<sup>3</sup>].</li>
<li>H is expressed in [m].</li>
</ul>
<p>REF:
DOI:10.28974/idojaras.2021.2.6</p>

CC BY-SA 4.0
2022-01-28T10:04:41.683Z
Although it seems so simple, it may actually work for me. Still, I need to try this method in practice. I don't mark it as the right answer for letting other people suggest alternative solutions.
Yaroslav
CC BY-SA 4.0
2022-01-26T13:39:12.517Z
2022-01-26T22:38:14.387Z
2022-01-26T22:38:14.387Z
user26314
<blockquote>
  <p>...measured in mol/m² within the total or tropospheric column. Is it possible to deduce concentrations for a specific slice of the troposphere?</p>
</blockquote>

<p>Not really, since you have a crucial bit of information missing: the vertical distribution.</p>

<p>Your alternatives are:</p>

<ul>
<li>Combine satellite data with a model to estimate near-surface NO₂.  The model may be able to estimate what surface conditions may be associated with what total column conditions, depending on other factors.</li>
<li>Stick with total column data.</li>
<li>Use a different data source, preferably ground-based measurements.  Although a limb sounder does a much better job at getting a high vertical resolution (at expense of horizontal resolution), below 50 metre is too close to the surface.</li>
</ul>

<p>Measuring the vertical distribution with a down-looking sensor is difficult.  You can get some information with vertical sounding by having many closely-spaced channels along a spectral line, but the vertical resolution is going to be very poor, <em>in particular</em> from space.  Vertical sounding is common practice for temperature and water vapour, but if you search for NO₂ vertical sounding, you will find mostly, probably exclusively, ground-based measurements.  I've tried to do CH₄ sounding and you're lucky if you can get 2 degrees of freedom of signal (DOFS), meaning a rough split in "lower half" or "upper half", but usually you get much less than that:</p>

<p><a href="https://i.sstatic.net/1sFuf.png" rel="noreferrer"><img src="https://i.sstatic.net/1sFuf.png" alt="information content"></a><br>
<em>Source: <a href="https://www.atmos-meas-tech.net/9/1961/2016/" rel="noreferrer">Holl et al., (2016)</a></em></p>

<p>TANSO-FTS is a spectrometer carried on a satellite, PEARL-FTS is a ground-based instrument looking up.  Now this was for CH₄ (not NO₂) and for a station in the Arctic at night.  Hopefully you're not trying to do this in the Arctic and not at night, so if you try to retrieve profiles from a spectrometer (AIRS, IASI, CrIS) you can do a better job, but near-surface, probably not.  Looking up, such as PEARL-FTS does, tends to be easier than looking down because you don't have a background surface to deal with.</p>

<p>There are plenty of  <a href="https://www.wmo-sat.info/oscar/gapanalyses?variable=106" rel="noreferrer">instruments that can retrieve NO₂ total column</a>:</p>

<p><a href="https://i.sstatic.net/3WTRV.png" rel="noreferrer"><img src="https://i.sstatic.net/3WTRV.png" alt="total column from WMO Oscar"></a><br>
<em>Source: <a href="https://www.wmo-sat.info/oscar/gapanalyses?variable=106" rel="noreferrer">WMO Oscar</a></em></p>

<p>However, to get a good quality profile from space you need a limb sounder, <a href="https://www.wmo-sat.info/oscar/gapanalyses?mission=25" rel="noreferrer">such as these</a>:</p>

<p><a href="https://i.sstatic.net/drTRB.png" rel="noreferrer"><img src="https://i.sstatic.net/drTRB.png" alt="limb sounders, WMO oscar"></a><br>
<em>Source: <a href="https://www.wmo-sat.info/oscar/gapanalyses?mission=25" rel="noreferrer">WMO Oscar</a></em></p>

<p>A limb sounder gets a much better vertical resolution, but a much worse horizontal and temporal resolution (there are no geostationary limb sounders, and the concept wouldn't make much sense).  You can find <a href="https://www.researchgate.net/figure/Limb-viewing-geometry-for-a-limb-sounder-The-instrument-measures-the-radiance-emitted-by_fig9_261013184)" rel="noreferrer">a limb viewing geometry illustration here</a>:</p>

<p><a href="https://i.sstatic.net/mpz17.png" rel="noreferrer"><img src="https://i.sstatic.net/mpz17.png" alt="limb geometry"></a><br>
<em>Source: <a href="https://www.researchgate.net/figure/Limb-viewing-geometry-for-a-limb-sounder-The-instrument-measures-the-radiance-emitted-by_fig9_261013184)" rel="noreferrer">Riese et al. (2014)</a></em></p>

<p>The best signal to noise ratio are from solar occultation limb sounders such as <a href="https://www.wmo-sat.info/oscar/instruments/view/6" rel="noreferrer">ACE-FTS</a>, but those can only measure at sunrise and sunset.  And close to the surface is difficult with any limb sounder, solar occultation or not, so it is unlikely that a limb sounder would even work in your case of measurements within 50 metre from the surface.</p>

<p>Depending on your scientific background, I would either look for model data or use ground-based measurements.</p>

<hr>

<ul>
<li><p><a href="https://www.atmos-meas-tech.net/9/1961/2016/" rel="noreferrer">Holl</a>, G., Walker, K. A., Conway, S., Saitoh, N., Boone, C. D., Strong, K., &amp; Drummond, J. R. (2016). Methane cross-validation between three Fourier transform spectrometers: SCISAT ACE-FTS, GOSAT TANSO-FTS, and ground-based FTS measurements in the Canadian high Arctic. Atmospheric Measurement Techniques, 9(5), 1961-1980. </p></li>
<li><p>Riese, M. &amp; Oelhaf, H. &amp; Preusse, P. &amp; Blank, Joerg &amp; Ern, M. &amp; Friedl-Vallon, Felix &amp; Fischer, H. &amp; Guggenmoser, Tobias &amp; Höpfner, Michael &amp; Hoor, Peter &amp; Kaufmann, M. &amp; Orphal, Johannes &amp; Ploeger, Felix &amp; Spang, Reinhold &amp; Suminska-Ebersoldt, O. &amp; Ungermann, Jörn &amp; Vogel, B. &amp; Woiwode, W.. (2014). Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) scientific objectives. Atmospheric Measurement Techniques. 7. 1915-1928. 10.5194/amt-7-1915-2014. </p></li>
</ul>

CC BY-SA 4.0
2020-03-06T18:31:54.770Z
I think I'll stick with the option to combine Sentinel-5P data with some model to estimate near-surface NO₂. Thank you for the detailed answer.
Yaroslav
CC BY-SA 4.0
2020-03-06T09:10:27.937Z
2020-03-06T12:34:43.350Z
2020-03-06T12:34:43.350Z
gerrit
<p><strong>Sentinel-5P</strong> satellite provides <a href="https://sentinels.copernicus.eu/web/sentinel/technical-guides/sentinel-5p/products-algorithms" rel="noreferrer">high-resolution data products</a> on concentration levels for several atmospheric trace gases (NO<sub>2</sub>, SO<sub>2</sub>, O<sub>3</sub>
, and others), which are measured in <strong>mol/m<sup>2</sup></strong> within the total or tropospheric column. Is it possible to deduce concentrations for a specific slice of the troposphere?</p>

<p>Namely, I'm interested to get NO<sub>2</sub> raster to work in GIS, where each pixel of it will contain NO<sub>2</sub> level in <strong>μg/m<sup>3</sup></strong>, 0–50 meters above the ground. I've already read <em>Product User Information</em>, <em>Algorithm Theoretical Basis Document</em>, and <em>Input Output Data Definition</em> related to the corresponding Sentinel-5 NO<sub>2</sub> product. However, it didn't give me an idea of how to get μg/m<sup>3</sup> for the near-ground level. Is it feasible at all? I guess it is, as in the <a href="https://regional.atmosphere.copernicus.eu" rel="noreferrer">Copernicus European air quality portal</a>, which uses Sentinel-5P data for the air pollution forecast, I see that they show NO<sub>2</sub> concentrations in μg/m3.</p>

<p><strong>Is there some workflow to do it?</strong></p>

<p><em>A screenshot from the Copernicus European air quality portal:</em>
<a href="https://i.sstatic.net/J79rd.png" rel="noreferrer"><img src="https://i.sstatic.net/J79rd.png" alt="A screenshot from the Copernicus European air quality portal"></a></p>

<p>P.S. I have good experience in remote sensing of land surface and geographic information systems, but I've never worked with weather/atmosphere data before.</p>

CC BY-SA 4.0
2020-03-06T10:04:57.360Z
To clarify, do you mean completely *at* ground level (where we breath), or more generally near the surface?
gerrit
CC BY-SA 4.0
2020-03-06T12:30:15.560Z
Near the surface, like from 0 to 50 m above the ground. It's needed to study the air we breathe.
Yaroslav
CC BY-SA 4.0
2022-01-05T23:12:45.807Z
Have you find a way to make the conversion from mol/m2 to ug/m3? I am facing the same problem and I do not know how to do it
Amirdudu
CC BY-SA 4.0
2022-01-06T00:41:40.140Z
related question: https://earthscience.stackexchange.com/questions/8860/convert-omi-no2-vertical-column-density-molecules-cm2-into-mixing-ratio-ppm?noredirect=1&lq=1
f.thorpe
<atmosphere><atmospheric-chemistry><air-pollution><satellites><weatherdata>
Convert NO2 concentration in Sentinel-5P data from mol/m2 to μg/m3 on the ground level
Yaroslav
# Convert NO2 concentration in Sentinel-5P data from mol/m2 to μg/m3 on the ground level

(Asked by: username_0 on 2020-03-06)

**Sentinel-5P** satellite provides [high-resolution data products](https://sentinels.copernicus.eu/web/sentinel/technical-guides/sentinel-5p/products-algorithms) on concentration levels for several atmospheric trace gases (NO2, SO2, O3
, and others), which are measured in **mol/m2** within the total or tropospheric column. Is it possible to deduce concentrations for a specific slice of the troposphere?

Namely, I'm interested to get NO2 raster to work in GIS, where each pixel of it will contain NO2 level in **μg/m3**, 0–50 meters above the ground. I've already read *Product User Information*, *Algorithm Theoretical Basis Document*, and *Input Output Data Definition* related to the corresponding Sentinel-5 NO2 product. However, it didn't give me an idea of how to get μg/m3 for the near-ground level. Is it feasible at all? I guess it is, as in the [Copernicus European air quality portal](https://regional.atmosphere.copernicus.eu), which uses Sentinel-5P data for the air pollution forecast, I see that they show NO2 concentrations in μg/m3.

**Is there some workflow to do it?**

*A screenshot from the Copernicus European air quality portal:*
[![A screenshot from the Copernicus European air quality portal](https://i.sstatic.net/J79rd.png)](https://i.sstatic.net/J79rd.png)

P.S. I have good experience in remote sensing of land surface and geographic information systems, but I've never worked with weather/atmosphere data before.

**Tags:** atmosphere, atmospheric-chemistry, air-pollution, satellites, weatherdata

> **Comments:**
> **username_1**: To clarify, do you mean completely *at* ground level (where we breath), or more generally near the surface?  
> **username_0**: Near the surface, like from 0 to 50 m above the ground. It's needed to study the air we breathe.  
> **username_2**: Have you find a way to make the conversion from mol/m2 to ug/m3? I am facing the same problem and I do not know how to do it  
> **username_3**: related question: https://earthscience.stackexchange.com/questions/8860/convert-omi-no2-vertical-column-density-molecules-cm2-into-mixing-ratio-ppm?noredirect=1&lq=1  

---

## 2 answers

### Answer by username_1 on 2020-03-06. Score: 8 | Accepted answer

> ...measured in mol/m² within the total or tropospheric column. Is it possible to deduce concentrations for a specific slice of the troposphere?

Not really, since you have a crucial bit of information missing: the vertical distribution.

Your alternatives are:

* Combine satellite data with a model to estimate near-surface NO₂. The model may be able to estimate what surface conditions may be associated with what total column conditions, depending on other factors.
* Stick with total column data.
* Use a different data source, preferably ground-based measurements. Although a limb sounder does a much better job at getting a high vertical resolution (at expense of horizontal resolution), below 50 metre is too close to the surface.

Measuring the vertical distribution with a down-looking sensor is difficult. You can get some information with vertical sounding by having many closely-spaced channels along a spectral line, but the vertical resolution is going to be very poor, *in particular* from space. Vertical sounding is common practice for temperature and water vapour, but if you search for NO₂ vertical sounding, you will find mostly, probably exclusively, ground-based measurements. I've tried to do CH₄ sounding and you're lucky if you can get 2 degrees of freedom of signal (DOFS), meaning a rough split in "lower half" or "upper half", but usually you get much less than that:

[![information content](https://i.sstatic.net/1sFuf.png)](https://i.sstatic.net/1sFuf.png)  
*Source: [Holl et al., (2016)](https://www.atmos-meas-tech.net/9/1961/2016/)*

TANSO-FTS is a spectrometer carried on a satellite, PEARL-FTS is a ground-based instrument looking up. Now this was for CH₄ (not NO₂) and for a station in the Arctic at night. Hopefully you're not trying to do this in the Arctic and not at night, so if you try to retrieve profiles from a spectrometer (AIRS, IASI, CrIS) you can do a better job, but near-surface, probably not. Looking up, such as PEARL-FTS does, tends to be easier than looking down because you don't have a background surface to deal with.

There are plenty of [instruments that can retrieve NO₂ total column](https://www.wmo-sat.info/oscar/gapanalyses?variable=106):

[![total column from WMO Oscar](https://i.sstatic.net/3WTRV.png)](https://i.sstatic.net/3WTRV.png)  
*Source: [WMO Oscar](https://www.wmo-sat.info/oscar/gapanalyses?variable=106)*

However, to get a good quality profile from space you need a limb sounder, [such as these](https://www.wmo-sat.info/oscar/gapanalyses?mission=25):

[![limb sounders, WMO oscar](https://i.sstatic.net/drTRB.png)](https://i.sstatic.net/drTRB.png)  
*Source: [WMO Oscar](https://www.wmo-sat.info/oscar/gapanalyses?mission=25)*

A limb sounder gets a much better vertical resolution, but a much worse horizontal and temporal resolution (there are no geostationary limb sounders, and the concept wouldn't make much sense). You can find [a limb viewing geometry illustration here](https://www.researchgate.net/figure/Limb-viewing-geometry-for-a-limb-sounder-The-instrument-measures-the-radiance-emitted-by_fig9_261013184)):

[![limb geometry](https://i.sstatic.net/mpz17.png)](https://i.sstatic.net/mpz17.png)  
*Source: [Riese et al. (2014)](https://www.researchgate.net/figure/Limb-viewing-geometry-for-a-limb-sounder-The-instrument-measures-the-radiance-emitted-by_fig9_261013184))*

The best signal to noise ratio are from solar occultation limb sounders such as [ACE-FTS](https://www.wmo-sat.info/oscar/instruments/view/6), but those can only measure at sunrise and sunset. And close to the surface is difficult with any limb sounder, solar occultation or not, so it is unlikely that a limb sounder would even work in your case of measurements within 50 metre from the surface.

Depending on your scientific background, I would either look for model data or use ground-based measurements.

---

* [Holl](https://www.atmos-meas-tech.net/9/1961/2016/), G., Walker, K. A., Conway, S., Saitoh, N., Boone, C. D., Strong, K., & Drummond, J. R. (2016). Methane cross-validation between three Fourier transform spectrometers: SCISAT ACE-FTS, GOSAT TANSO-FTS, and ground-based FTS measurements in the Canadian high Arctic. Atmospheric Measurement Techniques, 9(5), 1961-1980.
* Riese, M. & Oelhaf, H. & Preusse, P. & Blank, Joerg & Ern, M. & Friedl-Vallon, Felix & Fischer, H. & Guggenmoser, Tobias & Höpfner, Michael & Hoor, Peter & Kaufmann, M. & Orphal, Johannes & Ploeger, Felix & Spang, Reinhold & Suminska-Ebersoldt, O. & Ungermann, Jörn & Vogel, B. & Woiwode, W.. (2014). Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) scientific objectives. Atmospheric Measurement Techniques. 7. 1915-1928. 10.5194/amt-7-1915-2014.

> **Comments:**
> **username_0**: I think I'll stick with the option to combine Sentinel-5P data with some model to estimate near-surface NO₂. Thank you for the detailed answer.  

---

### Answer by username_4 on 2022-01-26. Score: 2

Let us suppose, that the pollutant distributes in the lower 10 km
layer (H), and its concentrations (C) are equal on each altitude for more simple calculations. [mol/m2] must be converted to [mg/m3] for comparison with national threshold standards. Therefore, the near-ground value in [mg/m3] is:

C = (Ccol/H) \* M \* A,

where,

* Ccol is the pollutant column content [mol/m2],
* M is the molar mass [g/mol],
* A is a constant, equals to 1000, for conversion from [g/m3] to [mg/m3].
* H is expressed in [m].

REF:
DOI:10.28974/idojaras.2021.2.6

> **Comments:**
> **username_0**: Although it seems so simple, it may actually work for me. Still, I need to try this method in practice. I don't mark it as the right answer for letting other people suggest alternative solutions.  

---

