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Model X Review – An Affordable Outdoor Air Quality Monitor

A few years ago, when I first began reviewing carbon dioxide monitors, I heard about some monitors being hand-made using high-quality sensors and 3D-printed parts in Canada. While I didn’t expect much at first, I got a chance to test the monitor myself, and I was impressed by how well it performed. While it was made using 3D-printed parts and didn’t come from a big company, it had best-in-class performance regarding the sensor and did exceptionally well regarding internal data storage and connectivity – especially when using multiple devices.

The monitor in question is the CO2.Click Model C. Fast forward a few years, and the catalogue of air quality monitors from CO2.Click is extensive. Not only can you find dedicated carbon dioxide sensors (both with connectivity and not), but you can also find outdoor air quality monitors and a whole selection of indoor air quality monitors. Across the selection, a few things have remained consistent, but the most important is the quality of the components. In these monitors, you will only find high-quality sensors from the likes of Senseair and Sensirion.

BreatheSafeAir Award
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Best User Experience
Qingping AQ Monitor

With a beautiful display, this is the best standlone indoor AQ monitor.

* This link may be an affiliate link. I can earn from qualifying purchases at no extra cost to you.

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Best Enthusiast
AirGadient ONE

An indoor air quality monitor with great performance.

* This link may be an affiliate link. I can earn from qualifying purchases at no extra cost to you.

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Best Outdoor
PurpleAir Zen/Flex

With dual-PM sensors, this monitor emphasises accuracy.

* This link may be an affiliate link. I can earn from qualifying purchases at no extra cost to you.

Recently, I received the Model F (standalone CO2 monitor), Model G (indoor air quality monitor), and Model X (outdoor air quality monitor) from Andre at CO2.Click. While I will have reviews of all three monitors coming soon, today, I want to focus on the Model X outdoor air quality monitor as this is the one that interests me the most at the moment- mainly because I recently reviewed PurpleAir’s outdoor air quality monitors.

So, what makes the Model X such an interesting outdoor air quality monitor? Well, while far from exhaustive, here are a couple of key points that interest me about this outdoor air quality monitor:

  • Sensor – the Model X uses the SPS30 from Sensirion (AirGradient, PurpleAir, and AirBeam all use Plantower sensors). This is a more expensive sensor with extra functionality, such as a self-cleaning function.
  • Lower price – The Model X costs less than half the price of a PurpleAir monitor and is only slightly pricer than a DIY outdoor AirGradient monitor.

While these two points interest me the most about the monitor, there’s much to discuss here, so let’s dive into the full review. Is the CO2.Click Model X a good alternative outdoor air quality monitor to more established monitors such as those from PurpleAir and AirGradient, or is it best to stick with larger brands? In this review, I will give you all the information you need to make your own decision!

This post contains affiliate links. For more information, please refer to my affiliate disclaimer. I was sent a product for review, but the article is not sponsored. All opinions expressed in this post are my honest thoughts. I only recommend products that I genuinely believe in.

Information on this blog is for informational purposes only. Readers are encouraged to confirm the information herein with other sources. Furthermore, this information is not intended to replace medical advice from professionals. This website assumes no responsibility for the accuracy of the information, and information is subject to change without notice. Devices mentioned on this website are not medical devices and do not guarantee protection.

Accuracy & Sensors

Co2 Click Model X Sensor

As with all air quality monitors, the sensor tech and its accuracy are the most important aspects to consider. After all, if we can’t trust our monitors’ readings, they’re not very useful at all! With that said, let’s first discuss the sensor used in the CO2.Click Model X and then discuss how it performs in the real world. If this all sounds technical, don’t worry; I will do my best to make it easy to follow.

The Model X uses a single sensor for all measurements (particulate matter of all sizes, temperature, relative humidity and barometric pressure). In this case, the sensor is the Sensirion SPS30, a sensor I don’t have much experience with but one I’ve wanted to test for a while. This sensor makes this outdoor air quality monitor unique, as nearly all other outdoor air quality monitors, such as those from AirGradient, PurpleAir and AirBeam, all use Plantower sensors.

The SPS30 is a more expensive sensor than the Plantower sensors used by the competition, and, as I will discuss soon, I believe it may perform better than the Plantower sensors out of the box. Plantower sensors are known to overreport significantly without compensation algorithms, but from my experience, the raw output from Model X appears far closer to the truth. However, I’m getting ahead of myself; more on that soon!

Since I don’t have a reference monitor to compare to, I turned to the literature to see how accurate the SPS30 is. While some studies find the Plantower sensors to be more accurate or similarly accurate, there seem to be more studies that point towards the SPS30 being a more accurate sensor in various cases. Here are a couple of these studies:

However, as I mentioned, some studies show very similar performance between the two. I also found one study that pointed towards the Plantower sensors as being slightly more accurate. Either way, at worst, these sensors are comparable, but the SPS30 does offer a few other unique features, such as a self-cleaning function, which boosts sensor lifespan and decreases drift. These extra features likely explain the increased cost of the SPS30 and why only one sensor is present in this monitor as opposed to the two sensors found in AirGradient and PurpleAir monitors.

AQMD has also tested the SPS30 as part of its AQ-SPEC program and found that this sensor is very accurate for lower concentrations of PM1.0 and PM2.5, with accuracy decreasing at higher concentrations. However, it exhibited a medium to strong correlation with reference monitors even at these higher concentrations. It’s also important to note that decreasing accuracy at higher concentrations is standard across all consumer-grade sensors. When it comes to PM10, the sensor performs poorly, and this is because, as with most low-cost sensors, PM10 concentrations are interpolated from PM2.5 data.

Sensirion SPS30 AQMD Report

AQMD report of the Sensirion SPS30.

Furthermore, the SPS30 is the only low-cost sensor currently holding an MCERTS certification (albeit only when installed following the guidelines) for the PM2.5 range of 0 to 75μg/m3. This again shows the performance of the SPS30, at least for smaller particle sizes and at lower concentrations. That said, I would argue that accuracy at these lower concentrations is more important for the typical user than at higher concentrations.

While these studies point to the SPS30 being a trustworthy sensor with high precision and good accuracy (at least for PM1.0 and PM2.5), I was curious and wanted to do some of my own testing, too. As such, I decided to compare the Model X’s accuracy to a few of my PurpleAir monitors. Below are the initial results, but make sure to read on to learn why this occurred!

SPS30 Accuracy vs Raw PurpleAir Data

The above graph shows the Model X and Model G (also with an SPS30) compared to two outdoor PurpleAir monitors and one indoor PurpleAir monitor.

As you can see, the SPS30 monitors (the Model X and Model G) provided significantly lower readings than the two PurpleAir Zen outdoor air quality monitors and vastly lower readings than the PurpleAir Touch indoor air quality monitor. When I first ran this test, I was worried that either the Model X wasn’t particularly accurate or that mine was faulty.

However, as I progressed through my PurpleAir Zen review, I quickly learned that by default, the PurpleAir outdoor air quality monitors aren’t particularly accurate when measuring smoke particles (which are the primary form of particle pollution where I currently live). Therefore, the EPA created a correction formula that can be applied to PurpleAir raw outputs to provide a more accurate measurement. If you want to read more about this, please refer to my PurpleAir review. For now, let’s retake a look at the comparison after the PurpleAir monitors are corrected.

PurpleAir vs SPS30 EPA Adjusted

As you can see, with the exception of the red line (the PurpleAir Touch, an indoor air quality monitor), the CO2 Click monitors and the PurpleAir monitors now provide very similar readings. While the SPS30 does appear to overreport at high concentrations (as found in the AQMD study), the PM2.5 readings from this sensor are very similar to the Plantower sensors at normal and, for most people, more common concentrations. While I am unsure what corrections Sensirion performs on its data, it looks like an out-of-the-box SPS30 is more accurate than an uncorrected Plantower sensor.

PurpleAir vs SPS30 Woodsmoke

At this point, mostly out of curiosity, I applied the ‘Woodsmoke’ correction to the PurpleAir data and got similar results. This correction formula was developed in Australia to improve the accuracy and modelling of the impacts of wildfire smoke. At first glance, it looks to give very similar results to the EPA formula, and I would assume both of these formulas provide far more accurate readings of my air quality as the high PM2.5 concentrations are primarily from smoke.

Since it’s hard to see all of the details on the above graphs, I also created one more graph showing the monitors’ readings (the PurpleAir monitors are EPA-corrected here) over a 24-hour period. While there is an anomaly between 3 pm and 9 pm with the Model G data (no data was reported over this period for some reason), you can still see that the Model X provides very similar readings to EPA-corrected PurpleAir monitors. Still, it looks to overreport at higher concentrations. This is likely why the SPS30 is only MCERTS certified for PM2.5 up to 75μg/m3.

CO2 Click Model X Accuracy EPA Corrected

The Model G data shows an anomaly between 3 p.m. and 9 p.m. (no data was reported over this period for some reason).

So, what can we conclude here? Well, I think we can say that the SPS30, and by extension, the CO2.Click Model X is accurate in most cases. While the sensor struggles with higher concentrations of PM2.5 and all concentrations of PM10, it does well in other cases, according to studies and my own findings. I would also argue that the decreasing performance at higher concentrations is not particularly important for most users.

Taking the example from the graph above, whether the actual concentration was 120μg/m3 or 160μg/m3 at the peak, my actions wouldn’t change. Either way, I should avoid outdoor activities (especially exercise) and lock down my home if possible. On the other hand, the accuracy at lower concentrations is much higher, and the difference between 10μg/m3 and 20μg/m3 is far more significant to me than the difference between 120μg/m3 and 160μg/m3.


CO2 Click Model X

The CO2.Click Model X is the simplest outdoor air quality monitor I’ve reviewed. While there isn’t much to discuss here, I’m a fan of the design and want to discuss it briefly. So, what makes the Model X’s design so simple? Well, the monitor is housed in a pipe with a head on top. While this is an easier (and cheaper) approach for a small company like CO2.Click, I appreciate the simplicity for a few reasons I will discuss soon.

Every other CO2.Click device I’ve tried to date (Model C, Model G and Model F) have been 3D-printed, but I assume a different decision was made here as this monitor will be exposed to the elements. While I don’t know the exact plastic used for the housing on the other monitors, I assume it’s probably less UV-resistant, hence the choice to opt for a pipe on the Model Instead.

On the bottom of the device, you will find the Type-C USB port for powering the device and an intake and vent for the Sensirion SPS30. Obviously, for accurate measurements, this sensor must be exposed, but it also needs to be protected from water, which is why it’s placed on the bottom of the monitor, similar to every other outdoor air quality monitor I’ve tried to date.

While incredibly simple in design, I am a fan of this on an outdoor air quality monitor. Why? Because it blends in. Except for the USB cable that powers the device, this looks identical to a piece of pipe and is very unassuming. While this likely won’t matter if the monitor is installed in private areas, I’ve set up monitors on the edge of my property before that have been damaged by people wondering what they are (usually at night, as most outdoor monitors have at least a small LED). For this reason, I love the lack of an LED or anything else that stands out about this monitor. You can put it anywhere, and it will be left untouched.

While a status LED that can be disabled would be helpful in some circumstances, I don’t think it’s essential, and I never felt a need for it. With that in mind, I believe this super-minimalist approach is fine, and I prefer it to monitors such as the PurpleAir Zen (although I don’t mind the less obvious design of the Flex).

CO2 Click Model X Bottom

Since it’s difficult to mount a round pipe, there is also a bracket included in the box which will allow you to screw the device onto any wooden surface. Alternatively, you can combine zip ties with this bracket (as I did) to mount it wherever you want without drilling any permanent holes. I also prefer this approach as it allows me to mount the monitor to everything from poles to fence posts.

That leads me to weatherproofing – this monitor is very sturdy and should be entirely weatherproof in its intended position (sensor facing downwards). There is a significant recess on the bottom of the device before the sensor inlet, so even if the rain is coming down from an angle, the monitor should be safe.

Of course, the monitor will need to be paired with a waterproof power supply if you intend to place it in an exposed position. Only a standard-length USB cable and adapter are included in the box, so this is something you will want to consider when purchasing the device. That said, if you have an outdoor location that isn’t exposed to the elements and is within a metre of a power outlet, you can use the included cable.

Co2 Click Solar Panel Kit

There is also an option to purchase the monitor with a solar panel, which allows it to sit away from any power outlet (but you will still want a WiFi connection, so it can’t be too far away from your house). This kit is much more expensive, but the freedom of being able to place the monitor in many more locations will appeal to some.

Overall, I appreciate the minimalist design of the CO2.Click Model X, and I believe this is one of the device’s strengths. It doesn’t attract attention and feels among the most weatherproof outdoor air quality monitors I’ve tested to date. I also appreciate the inclusion of a mounting bracket, as otherwise, it would not be easy to find a good spot for this monitor!

Connectivity & Dashboard

CO2.Click Dashboard

The Model X connects via WiFi to an online dashboard, which can be used to view data from the device. Since the monitor doesn’t have a screen or Bluetooth, this is the only way you can view data from the device, and you will be referring to the dashboard frequently once you have your Model X setup!

I first used this dashboard a couple of years ago when I tried the Model C for the first time; however, just last week, the dashboard for all CO2.Click devices was updated with an improved user interface. At the moment, the dashboard is very simple, but it does offer the needed functionality.

CO2.Click PM2.5 Graph

From the dashboard, you can examine the data from your sensor over the past hour, five hours, 12 hours, 24 hours, 48 hours, and the past week. Since the Model X monitors temperature, humidity, and barometric pressure alongside particulate matter, you will also be able to find those measurements here. However, these three parameters are relegated to a second graph, which displays them together, as shown below.

While I would love to see more detail on the dashboard (for example, I wish I could zoom in or change the intervals), I don’t think this is too big of a deal as it’s very easy to export data from the monitor and graph it yourself. Since this is the most powerful way to analyse data anyway, I don’t mind the dashboard being somewhat limited.

Co2.Click Temperature air pressure RH

The dashboard is also where you will change device settings. While I’m not sure if it’s due to the new dashboard still being in the early stages, there are significantly fewer options than on the previous dashboard, where I could also change measurement intervals, upload intervals, and more. I would love to see these features re-introduced with the new dashboard if possible.

Interestingly, there is also an option to add your Model X to a public map. While the map is still very much in the early stages and data is very limited (and mostly in North America), I always love being able to contribute to such maps, and once I get my monitor set up in a more permanent position, I will be sure to enable it on the public map.

Co2.Click Model X Settings

At the moment, I feel that the dashboard is very simple, but I also don’t think it lacks any significant functionality. While I would like to see the abovementioned features implemented, they’re not vital, and the dashboard already works well. I’ve also found that the WiFi connectivity of the Model X is good, and it rarely ever drops the connection, even where my other monitors do (I have a very unstable connection where I am).

Co2.Click Map

CO2.Click Map.

It’s worth noting that since the monitor uses a web dashboard, it’s a more pleasant experience on a PC. While you can access the dashboard on your phone (from anywhere), it’s a better experience on a PC – especially if you want to view the graphs and other more detailed information.

Overall, the dashboard is solid, but I would like to see it expanded with more features. Off the top of my head, I would love to be able to adjust measurement intervals, measurement time, and upload intervals. I would also like extra options when exporting data (such as which parameters to export and for which period).

Pricing & Competition

CO2 Click Model X and PurpleAir

The CO2.Click Model X retails for 209 CAD, approximately 150 USD at the time of writing. This price point is quite competitive because there are no decent outdoor air quality monitors (to my knowledge) below this price point – unless you opt for the AirGradient Open Air DIY Kit. Regarding pre-built monitors, you’re looking at spending $190 – $320 with other brands, depending on whether you opt for AirGradient, PurpleAir, AirBeam, or IQAir alternatives.

Air Quality MonitorPollutants MeasuredSensorsCost
AirGradient Open AirPM (PM1.0, PM2.5, PM10) & CO2 (on newer models)PMS5003T, S8$125 (DIY), $190 (Assembled)
AirVisual OutdoorPM (PM1.0, PM2.5, PM10), temperature, humidity, air pressure, & CO2 (optional)(Unsure. Likely IQAir co-developed sensors as with the AirVisual Pro)€319.00
PurpleAir ClassicPM (PM1.0, PM2.5, PM10)2x PMS5003$229
PurpleAir FlexPM (PM1.0, PM2.5, PM10), Pressure, Temperature, Humidity & Gas2x PMS6003, BME688$289
PurpleAir ZenPM (PM1.0, PM2.5, PM10), Pressure, Temperature, Humidity & Gas2x PMS6003, BME688$299
CO2 Click Model XPM (PM1.0, PM2.5, PM10), Pressure, Temperature, HumiditySPS30$150 (approx)
AirBeam 3PM (PM1.0, PM2.5, PM10), Temperature, HumidityPMS7003$229

Do these monitors have some advantages? Yes. AirGradient, PurpleAir, and IQAir all offer dual sensor configurations, which allows for redundancy and easy identification of a faulty sensor. They also have more powerful software platforms with many more options – especially in the case of PurpleAir. Some of these monitors also offer extra sensors, such as CO2, VOCs, and NOx.

With that said, the SPS30 in the CO2.Click is supposed to have a lifespan of around eight years (according to Sensirion), which is vastly superior to the two to three-year lifespan we usually see with Plantower sensors. This is largely due to the SPS30’s self-cleaning functionality. I still would like to see an option with a second sensor because I’m all for redundancy and long-term use. Still, I understand this price point wouldn’t be achievable in such a configuration – especially for a smaller brand that can’t purchase large quantities of sensors.

Regarding software, I believe that AirGradient and PurpleAir offer more fleshed-out platforms, but I also think this won’t matter for many users. If all you want to do is see the current PM concentrations and historical data, the CO2.Click platform performs well. The ability to export data also makes it a great monitor to use to collect data for further analysis. With that said, I would like to see the platform expanded in the future.

On the other hand, the CO2.Click has some advantages, too. Most significantly, I think the sensor in this monitor performs better than the outdoor monitors that rely on Plantower sensors – at least when they aren’t corrected. This isn’t the case for PurpleAir, as they allow you to apply the corrections easily, but not all monitors have the corrections already applied or as an option.

Of course, since the CO2.Click is also significantly more affordable than some of these other monitors; it’s a tempting offer. I don’t think you can go wrong with any of the monitors I’ve discussed here (as long as you know how to use them!), but it will really come down to what you value most. I believe the Model X makes quite a compelling purchase at its price point.


Co2 Click Model X Outdoor Air Quality Monitor 2

If you’re looking for an affordable outdoor air quality monitor, I think the CO2.Click Model X is a monitor that should be on your radar. While it isn’t perfect – no monitor is – I have enjoyed using this monitor for the past few weeks and haven’t found any major downsides. On the other hand, I have been impressed with its performance, especially regarding accuracy.

While there are quite a few other outdoor air quality monitor options out there, many cost twice the price, and I think, when put that way, I would take two of these monitors over a PurpleAir or IQAir monitor in most situations. With that said, if you want the best user experience, the PurpleAir platform is more well-established. I haven’t used an IQAir outdoor monitor yet, so I can’t comment on the experience with them.

Of course, in this lower-cost category, there is also AirGradient (if you purchase the DIY kit), but as of the time of writing, I’ve found the CO2.Click monitor to provide more accurate and precise readings (when compared to the Model X). With that said, the AirGradient monitors also have a CO2 and NOx sensor, which might prove helpful if you live near a highway or other pollutant source.

At the end of the day, the deciding factor will be your personal needs. After using this device for a few weeks, I would probably say this is the best outdoor air quality monitor I’ve used for monitoring PM2.5, but some people will appreciate the extra sensors that some other monitors come with. Price is also a significant factor, and for the price that you can get a PurpleAir or IQAir monitor with a second sensor for redundancy, you can purchase two of these and place them right next to each other to achieve the same result.

Model X FAQ

What Does the Model X Monitor?

It monitors particulate matter (PM1.0 – PM10), barometric pressure, temperature and relative humidity.

What Alternatives Are There to the Model X?

The most popular alternatives are the AirGradient Open Air, PurpleAir Zen and Flex, Habitatmap AirBeam, and IQAir Outdoor Monitor.

Is the Model X Accurate?

Yes, based on both studies and my own findings, it provides accurate readings.

Where Can I Buy the Model X?

You can purchase it from CO2.Click.

What Sensor Does the Model X Use?

The Sensirion SPS30.

Model X Review - An Affordable Outdoor Air Quality Monitor
Co2 Click Model X Outdoor Air Quality Monitor 1

The Model X from CO2.Click is an outdoor air quality monitor at half the price of the competition. Is it worth it? In this post, I will do a deep dive into how this air quality monitor performs.

Product Brand: CO2 Click

Editor's Rating:


  • Accurate sensor
  • Long sensor life expectancy
  • WiFi connectivity
  • Web dashboard
  • Simple Design
  • Cheaper than the competition


  • Dashboard lacks advanced functionality
  • No extra sensors (CO2, NOx, or otherwise)

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