<h2>Carbon monoxide (CO), natural gas &amp; hydrocarbons, VOCs, ammonia, etc.</h2>

<p>In <a href="https://chemistry.stackexchange.com/a/118050/16035">this Chemistry SE answer</a> and <a href="https://electronics.stackexchange.com/q/302225/102305">this Electronics SE question</a> I discuss how the family of MOS gas sensors work. They can measure a large variety of different gasses that can react with atomic oxygen (O rather than <span class="math-container">$\small\mathsf{O_2}$</span>). </p>

<blockquote>
  <p>I'll quote from <a href="https://electronics.stackexchange.com/q/302225/102305">this question</a>:</p>
  
  <blockquote>
    <p>...sintered composite based on the semiconductor material <span class="math-container">$\small\mathsf{SnO_2}$</span>, which is the metal oxide. The different sensors have different admixtures and operating conditions to achieve different sensitivities to different gasses. </p>
    
    <p>The principle of operation of MOS-type gas sensors is explained in Figaro sensors' <a href="http://www.figaro.co.jp/en/technicalinfo/principle/mos-type.html" rel="noreferrer">Operating principle; MOS type</a>.</p>
  </blockquote>
  
  <p>The Figaro link shows the operating principle in the GIF below:</p>
  
  <p><img src="https://i.sstatic.net/qH4H5.gif" alt="enter image description here"> GIF (Source: <a href="https://www.figaro.co.jp/en/technicalinfo/principle/mos-type.html" rel="noreferrer">Figaro</a>)</p>
  
  <p>When the <span class="math-container">$\small\mathsf{SnO_2}$</span> is heated by the (usually 5V but not always) heater supply, oxygen in the air will dissociate at the surface and oxygen ions will stick to the surface, depleting the semiconductor and cutting off the flow of current. When a carbon-containing gas (e.g. <span class="math-container">$\small\mathsf{CO}$</span> or <span class="math-container">$\small\mathsf{C_xH_y}$</span> (but not <span class="math-container">$\small\mathsf{CO_2}$</span>)) comes along, it will combine with the adsorbed oxygen and remove it from the surface. The more gas, the lower the equilibrium concentration of adsorbed oxygen and the higher resulting current flow through the semiconductor. </p>
</blockquote>

<h2>Carbon dioxide (<span class="math-container">$\small\mathsf{CO_2}$</span>)</h2>

<p>The <span class="math-container">$\small\mathsf{CO_2}$</span> sensor works on a totally different principle because <span class="math-container">$\small\mathsf{CO_2}$</span> is fully oxidized carbon, it will not react further with atomic oxygen.</p>

<p>Instead the <span class="math-container">$\small\mathsf{CO_2}$</span> sensors are either solid electrolyte chemical cells like the MG-811 or newer versions (see <a href="https://chemistry.stackexchange.com/q/89726/16035">this question</a>) or they are <a href="https://en.wikipedia.org/wiki/Carbon_dioxide_sensor#Nondispersive_Infrared_(NDIR)_CO2_Sensors" rel="noreferrer">Non-dispersive Infrared Light sensors (NDIRs)</a> based on optical absorption of a certain wavelength of infrared light, using a hot filament or other light source to produce IR and a narrow multilayer optical filter to select one of the strong absorption lines of <span class="math-container">$\small\mathsf{CO_2}$</span>. The more <span class="math-container">$\small\mathsf{CO_2}$</span>, the more the reduction in the transmission of light in the optical path of the sensor. </p>

CC BY-SA 4.0
2019-12-06T14:30:56.460Z
2020-01-02T19:10:46.737Z
2020-01-02T19:10:46.737Z
uhoh
<p>I think the core of the answer should lie in what was already stated in the comments. These detectors are not scientific instruments. For air quality monitoring <a href="https://www.thermofisher.com/order/catalog/product/48I" rel="nofollow noreferrer">much more sophisticated analyzers</a> are needed to measure the concentration of the gases. The example in the link works on a basis of gas filter (filled with CO) and it can just as well be used for <span class="math-container">$\small\mathsf{CO_2}$</span> if you fill the filter with this gas instead. Analyzers like this can cost around 20 000 USD (very rough estimate based on prices in my national currency).</p>

<p>This is what is relevant to Earth Science SE, the questions about the price should really be asked on a different site.</p>

CC BY-SA 3.0
2017-06-29T11:56:24.847Z
I would also like to know what makes the scientific and more accurate instruments so expensive compared to the simple commercial ones (parts, working principle rights/complexity, large scale production.. ?). Given the special use of CO2 analyzers in Earth Science this is probably as relevant here as it would be in Engineering SE.
Communisty
CC BY-SA 3.0
2017-06-29T20:57:27.547Z
@Communisty It's worth comparing your average off-the-shelf CO detector and how it's used to the equipment and practices used at places like the Keeling Curve operation on Mauna Loa: http://scrippsco2.ucsd.edu/assets/publications/manometry_report_scripps_ref_gas_calibration_revision_of_2012_pub_2016.pdf Mauna Loa is used because it's isolated from nearby transient sources of CO2 such as rush-hour traffic or growing/decaying agriculture and someone is on site to monitor conditions.
jeffronicus
CC BY-SA 4.0
2017-06-29T11:44:07.300Z
2020-01-02T19:00:30.800Z
2020-01-02T19:00:30.800Z
Janina
<p>First you need to make the difference between a detector and a sensor, while the first one only shows that some gas is present, the second has to show the amount of gas.</p>

<p>Usually a sensor needs calibration, where you must give two points with different concentrations, this is not easy and you need a known source of concentration. Also this means that a sensor requires more electronics for its human-machine interaction.<br>
A detector only needs to trigger an alarm, nothing else.</p>

CC BY-SA 3.0
2017-06-29T16:48:54.923Z
2017-06-29T16:48:54.923Z
Santiago
<p>In the Arduino compatible sensors I've found, CO, methane, and other common raw sensors are as little as US\$1 from China. The cheapest <span class="math-container">$\small\mathsf{CO_2}$</span> sensor (also from China) I found was around US\$35.  Otherwise, raw sensors components are around US\$100.  The only real difference between the raw sensors and scientific instruments are that the instruments are obviously finished units that are certified and calibrated, like (for example) are raw Geiger tubes (US\$5) vs calibrated and certified Geiger counters (US$300). I have several DIY Geiger counters (US\$35) and calibrated Geiger counter instruments.</p>

CC BY-SA 4.0
2019-12-06T05:05:29.207Z
2020-01-02T19:00:02.543Z
2020-01-02T19:00:02.543Z
Tweeks
<p>Please excuse me if Earth Science is not the correct place to ask this question.</p>

<p>I read a New York Times article about increasing <span class="math-container">$\small\mathsf{CO_2}$</span> levels in the atmosphere: "<a href="https://www.nytimes.com/2017/06/26/climate/carbon-in-atmosphere-is-rising-even-as-emissions-stabilize.html" rel="nofollow noreferrer">Carbon in Atmosphere Is Rising, Even as Emissions Stabilize</a>" (26 June 2017)</p>

<p>According to the article, there are not enough <span class="math-container">$\small\mathsf{CO_2}$</span> monitoring stations for scientists to have a detailed understanding of where <span class="math-container">$\small\mathsf{CO_2}$</span> is being emitted/absorbed (e.g. by landmasses and oceans)</p>

<p>This got me thinking, would it be possible to design a dual-use product that integrates a <span class="math-container">$\small\mathsf{CO_2}$</span> sensor (e.g. a solar powered garden lamp) from which we could crowd source <span class="math-container">$\small\mathsf{CO_2}$</span> data for scientists? Perhaps a bit naive, since the sensors may not be accurate enough for scientific studies, and if it's a consumer product they would likely have a dense install base in metropolitan areas and less in the countryside/oceans.</p>

<p>But that isn't the biggest flaw in this idea. No, that came when I looked up <span class="math-container">$\small\mathsf{CO_2}$</span> sensor prices:</p>

<p><a href="https://i.sstatic.net/pI8mK.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/pI8mKm.jpg" alt="CO2 sensors - Digikey"></a> (click for full size)</p>

<p>I was able to find some Arduino compatible sensors from a Google search for around 50USD at the low end, but looking at electronics distributors, a more reasonable price for a raw <span class="math-container">$\small\mathsf{CO_2}$</span> sensor seems to be at least 70USD.</p>

<p>Carbon Monoxide detectors which you are encouraged to install in your home are much less expensive!</p>

<p><a href="https://i.sstatic.net/GGWWo.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GGWWom.png" alt="Carbon Monoxide detectors - Amazon"></a> (click for full size)</p>

<ol>
<li>How can it be that <span class="math-container">$\small\mathsf{CO_2}$</span> sensors are so expensive compared to CO detectors? </li>
<li>Is this due to the fact that carbon monoxide sensors use a detection
method which cannot accurately determine the PPM of CO?</li>
</ol>

CC BY-SA 3.0
2017-06-26T23:29:40.277Z
Detectors are not well-structured measurement devices. Measuring real CO requires sophisticated equipment than just home based detectors. Your question is not about Earth science, it is an enquiry into the price of sensors/detectors.
Gemechu Fanta Garuma
CC BY-SA 3.0
2017-06-27T06:27:32.600Z
I think this is a good question that emerges from interest towards earth science, but is actually as much about the sensor/detector engineering. Some earth scientist with an measurement device background could have a great answer to this.
Communisty
CC BY-SA 3.0
2017-06-27T12:59:42.753Z
Technically, this question is not a question on Earth Science. However, it is related to dealing with some current Earth Science-related questions. A similar question is dealt with in some project on urban air quality (a discussed at scientific conferences): Can we equip public transport buses, citizens or bikes with small, robust and maintenance-free (and cheap) devices to measure air pollutants such as NOx or PM with adequate accuracy? Currently, the answer is no. Either the instrument do not provide adequate accuracy or they are too expensive or ... .
daniel.heydebreck
CC BY-SA 3.0
2017-06-27T13:03:03.433Z
As @GFG pointed out (but to emphasize it): You are right with your second question. There is a difference between a detector, which should just give a qualitative response (CO above a rough threshold: YES/NO), and measurement device, which should give a quantitative output on the CO concentration.
daniel.heydebreck
CC BY-SA 3.0
2017-06-27T13:13:23.313Z
As final note: The problem is not only the lack of good spatial coverage of CO2 measurements but also the lack of spatio-temporal data, which is consistent over a reasonable time span (i.e. 50 years). Consistency is a bit problem: if we switch from one measurement device to another (at one measurement location), how well would it reproduce the measurements of its predecessor? Therefore, short-term data from lots of CO2 instruments might be of limited value from a scientific point of view. For 'why do we need long term data?' the space for comments is too short.
daniel.heydebreck
CC BY-SA 3.0
2017-06-28T04:53:40.007Z
I would suspect the major reason CO detectors are less expensive than CO2 detectors is simply that millions of people DO install them, enabling mass production and economies of scale.  Also, they don't need to be all that accurate, just sound an alarm if the concentration goes over some minimum threshold.
jamesqf
<climate-change><co2><instrumentation>
Why are CO2 sensors so expensive when CO sensors aren't?
hwmartin
# Why are CO2 sensors so expensive when CO sensors aren't?

(Asked by: username_0 on 2017-06-26)

Please excuse me if Earth Science is not the correct place to ask this question.

I read a New York Times article about increasing $\small\mathsf{CO\_2}$ levels in the atmosphere: "[Carbon in Atmosphere Is Rising, Even as Emissions Stabilize](https://www.nytimes.com/2017/06/26/climate/carbon-in-atmosphere-is-rising-even-as-emissions-stabilize.html)" (26 June 2017)

According to the article, there are not enough $\small\mathsf{CO\_2}$ monitoring stations for scientists to have a detailed understanding of where $\small\mathsf{CO\_2}$ is being emitted/absorbed (e.g. by landmasses and oceans)

This got me thinking, would it be possible to design a dual-use product that integrates a $\small\mathsf{CO\_2}$ sensor (e.g. a solar powered garden lamp) from which we could crowd source $\small\mathsf{CO\_2}$ data for scientists? Perhaps a bit naive, since the sensors may not be accurate enough for scientific studies, and if it's a consumer product they would likely have a dense install base in metropolitan areas and less in the countryside/oceans.

But that isn't the biggest flaw in this idea. No, that came when I looked up $\small\mathsf{CO\_2}$ sensor prices:

[![CO2 sensors - Digikey](https://i.sstatic.net/pI8mKm.jpg)](https://i.sstatic.net/pI8mK.jpg) (click for full size)

I was able to find some Arduino compatible sensors from a Google search for around 50USD at the low end, but looking at electronics distributors, a more reasonable price for a raw $\small\mathsf{CO\_2}$ sensor seems to be at least 70USD.

Carbon Monoxide detectors which you are encouraged to install in your home are much less expensive!

[![Carbon Monoxide detectors - Amazon](https://i.sstatic.net/GGWWom.png)](https://i.sstatic.net/GGWWo.png) (click for full size)

1. How can it be that $\small\mathsf{CO\_2}$ sensors are so expensive compared to CO detectors?
2. Is this due to the fact that carbon monoxide sensors use a detection
   method which cannot accurately determine the PPM of CO?

**Tags:** climate-change, co2, instrumentation

> **Comments:**
> **username_1**: Detectors are not well-structured measurement devices. Measuring real CO requires sophisticated equipment than just home based detectors. Your question is not about Earth science, it is an enquiry into the price of sensors/detectors.  
> **username_2**: I think this is a good question that emerges from interest towards earth science, but is actually as much about the sensor/detector engineering. Some earth scientist with an measurement device background could have a great answer to this.  
> **username_3**: Technically, this question is not a question on Earth Science. However, it is related to dealing with some current Earth Science-related questions. A similar question is dealt with in some project on urban air quality (a discussed at scientific conferences): Can we equip public transport buses, citizens or bikes with small, robust and maintenance-free (and cheap) devices to measure air pollutants such as NOx or PM with adequate accuracy? Currently, the answer is no. Either the instrument do not provide adequate accuracy or they are too expensive or ... .  
> **username_3**: As @GFG pointed out (but to emphasize it): You are right with your second question. There is a difference between a detector, which should just give a qualitative response (CO above a rough threshold: YES/NO), and measurement device, which should give a quantitative output on the CO concentration.  
> **username_3**: As final note: The problem is not only the lack of good spatial coverage of CO2 measurements but also the lack of spatio-temporal data, which is consistent over a reasonable time span (i.e. 50 years). Consistency is a bit problem: if we switch from one measurement device to another (at one measurement location), how well would it reproduce the measurements of its predecessor? Therefore, short-term data from lots of CO2 instruments might be of limited value from a scientific point of view. For 'why do we need long term data?' the space for comments is too short.  
> **username_4**: I would suspect the major reason CO detectors are less expensive than CO2 detectors is simply that millions of people DO install them, enabling mass production and economies of scale.  Also, they don't need to be all that accurate, just sound an alarm if the concentration goes over some minimum threshold.  

---

## 4 answers

### Answer by username_5 on 2019-12-06. Score: 8

## Carbon monoxide (CO), natural gas & hydrocarbons, VOCs, ammonia, etc.

In [this Chemistry SE answer](https://chemistry.stackexchange.com/a/118050/16035) and [this Electronics SE question](https://electronics.stackexchange.com/q/302225/102305) I discuss how the family of MOS gas sensors work. They can measure a large variety of different gasses that can react with atomic oxygen (O rather than $\small\mathsf{O\_2}$).

> I'll quote from [this question](https://electronics.stackexchange.com/q/302225/102305):
>
> > ...sintered composite based on the semiconductor material $\small\mathsf{SnO\_2}$, which is the metal oxide. The different sensors have different admixtures and operating conditions to achieve different sensitivities to different gasses.
> >
> > The principle of operation of MOS-type gas sensors is explained in Figaro sensors' [Operating principle; MOS type](http://www.figaro.co.jp/en/technicalinfo/principle/mos-type.html).
>
> The Figaro link shows the operating principle in the GIF below:
>
> ![enter image description here](https://i.sstatic.net/qH4H5.gif) GIF (Source: [Figaro](https://www.figaro.co.jp/en/technicalinfo/principle/mos-type.html))
>
> When the $\small\mathsf{SnO\_2}$ is heated by the (usually 5V but not always) heater supply, oxygen in the air will dissociate at the surface and oxygen ions will stick to the surface, depleting the semiconductor and cutting off the flow of current. When a carbon-containing gas (e.g. $\small\mathsf{CO}$ or $\small\mathsf{C\_xH\_y}$ (but not $\small\mathsf{CO\_2}$)) comes along, it will combine with the adsorbed oxygen and remove it from the surface. The more gas, the lower the equilibrium concentration of adsorbed oxygen and the higher resulting current flow through the semiconductor.

## Carbon dioxide ($\small\mathsf{CO\_2}$)

The $\small\mathsf{CO\_2}$ sensor works on a totally different principle because $\small\mathsf{CO\_2}$ is fully oxidized carbon, it will not react further with atomic oxygen.

Instead the $\small\mathsf{CO\_2}$ sensors are either solid electrolyte chemical cells like the MG-811 or newer versions (see [this question](https://chemistry.stackexchange.com/q/89726/16035)) or they are [Non-dispersive Infrared Light sensors (NDIRs)](https://en.wikipedia.org/wiki/Carbon_dioxide_sensor#Nondispersive_Infrared_(NDIR)_CO2_Sensors) based on optical absorption of a certain wavelength of infrared light, using a hot filament or other light source to produce IR and a narrow multilayer optical filter to select one of the strong absorption lines of $\small\mathsf{CO\_2}$. The more $\small\mathsf{CO\_2}$, the more the reduction in the transmission of light in the optical path of the sensor.


---

### Answer by username_6 on 2017-06-29. Score: 3

I think the core of the answer should lie in what was already stated in the comments. These detectors are not scientific instruments. For air quality monitoring [much more sophisticated analyzers](https://www.thermofisher.com/order/catalog/product/48I) are needed to measure the concentration of the gases. The example in the link works on a basis of gas filter (filled with CO) and it can just as well be used for $\small\mathsf{CO\_2}$ if you fill the filter with this gas instead. Analyzers like this can cost around 20 000 USD (very rough estimate based on prices in my national currency).

This is what is relevant to Earth Science SE, the questions about the price should really be asked on a different site.

> **Comments:**
> **username_2**: I would also like to know what makes the scientific and more accurate instruments so expensive compared to the simple commercial ones (parts, working principle rights/complexity, large scale production.. ?). Given the special use of CO2 analyzers in Earth Science this is probably as relevant here as it would be in Engineering SE.  
> **username_7**: @username_2 It's worth comparing your average off-the-shelf CO detector and how it's used to the equipment and practices used at places like the Keeling Curve operation on Mauna Loa: http://scrippsco2.ucsd.edu/assets/publications/manometry_report_scripps_ref_gas_calibration_revision_of_2012_pub_2016.pdf Mauna Loa is used because it's isolated from nearby transient sources of CO2 such as rush-hour traffic or growing/decaying agriculture and someone is on site to monitor conditions.  

---

### Answer by username_8 on 2017-06-29. Score: 2

First you need to make the difference between a detector and a sensor, while the first one only shows that some gas is present, the second has to show the amount of gas.

Usually a sensor needs calibration, where you must give two points with different concentrations, this is not easy and you need a known source of concentration. Also this means that a sensor requires more electronics for its human-machine interaction.  
A detector only needs to trigger an alarm, nothing else.


---

### Answer by username_9 on 2019-12-06. Score: 2

In the Arduino compatible sensors I've found, CO, methane, and other common raw sensors are as little as US\$1 from China. The cheapest $\small\mathsf{CO\_2}$ sensor (also from China) I found was around US\$35. Otherwise, raw sensors components are around US\$100. The only real difference between the raw sensors and scientific instruments are that the instruments are obviously finished units that are certified and calibrated, like (for example) are raw Geiger tubes (US\$5) vs calibrated and certified Geiger counters (US$300). I have several DIY Geiger counters (US\$35) and calibrated Geiger counter instruments.


---

