Outdoor Air Quality Monitors

[Ethan]

While my website initially focused mostly on outdoor air quality, that changed over time as the pandemic hit. Despite my interest in outdoor air pollution ([that is the reason I started my blog] (BreatheSafeAir • About Me)!), I recognised that there was a much more pressing matter at hand: indoor air pollution.

While the pandemic is far from over, I now have more time to focus on outdoor air quality monitors again. Recently, I was finally able to review my first dedicated outdoor air quality monitor - the AirGradient Open Air. I was impressed with the monitor and loved how much insight it gave me into the concentrations and make-up of outdoor air. Since that review, I’ve wondered how other outdoor air quality monitors perform.

I have the Purple Air Zen on the way for testing. Still, in the meantime, I wanted to start compiling a list of outdoor air quality monitors that are in a relatively similar price range (within reach for most consumers) and have a similar feature set. While I’m sure I’ve missed many, as this list is just off the top of my head, here are the monitors I’ve looked at so far.

Air Quality Monitor	Pollutants Measured	Sensors	Cost
AirGradient Open Air	PM (PM1.0, PM2.5, PM10) & CO2 (on newer models)	PMS5003T, S8	$125 (DIY), $190 (Assembled)
PurpleAir Classic	PM (PM1.0, PM2.5, PM10)	2x PMS5003	$229
PurpleAir Flex	PM (PM1.0, PM2.5, PM10), Pressure, Temperature, Humidity & Gas	2x PMS6003, BME688	$289
PurpleAir Zen	PM (PM1.0, PM2.5, PM10), Pressure, Temperature, Humidity & Gas	2x PMS6003, BME688	$299
AirVisual Outdoor	PM (PM1.0, PM2.5, PM10), temperature, humidity, air pressure, & CO2 (optional)	(unsure. Likely IQAir co-developed sensors as with the AirVisual Pro)	€319.00

As I mentioned, this list of outdoor air quality monitors is far from complete, and I’m sure I’ve missed many. However, both for my own sake and anybody considering an outdoor air quality monitor, I will update this in the future as more monitors come across my radar!

[Ethan]

I forgot to add the Model X from CO2 Click to the list. The Model X is another great, affordable option.

For Canadian $209, you can get a monitor with a Sensirion SPS30 and Bosch BME280. I haven’t yet tried this monitor either, but it’s small form factor and inconspicuous look could make it ideal for some uses.

[Ethan]

I am currently testing the Purple Air Zen (Purple Air’s newest outdoor air quality monitor). So far, I am still in the early phases of testing, so I won’t go into details yet, but I do have a few first thoughts.

For anyone wondering, the Zen and the Flex are quite similar, but the Zen looks to be positioned as the successor to the Flex as it’s both slightly more expensive and has a few extra features. However, both monitors have the same sensors (two Plantower PMS6003 sensors and a Bosch BME688).

Interestingly, however, the Zen seems to be an incredibly incremental update, and I have to wonder why the choice to release it and sell it alongside the Flex was made. As per this post on PurpleAir’s forum, the only two major differences are the LED ring and double-tap functionality (to change LED brightness) on the Zen.

Based on this, I have to assume the Flex is meant more for applications where people don’t want the monitor to be noticed as it’s very inconspicuous. On the other hand, the Zen is made to stand out.

I will be sharing more thoughts soon!

[Ethan]

Over the past few weeks, I’ve had a chance to try a few more outdoor air quality monitors, including the PurpleAir Zen, CO2 Click Model X and AirBeam 3. After using AirGradient Open Airs as outdoor monitors almost exclusively for many months, I have quite a few thoughts to share. While I have full reviews upcoming, I want to discuss the CO2 Click Model X in particular, as it’s impressed me so far.

This CAD 209 monitor comes in at roughly half the price of the PurpleAir monitors, and it’s even cheaper than the AirBeam and AirGradient monitors (unless you get the DIY kit, which is slightly cheaper). While it only has a single sensor, it is a more expensive Sensirion SPS30 (as opposed to the Plantower sensors used in all other monitors mentioned here). I’ll discuss the accuracy in more detail soon, though, as that has left me the most impressed about this device.

You are trading some other features, such as local data storage (on the PurpleAir monitors), cellular connectivity (AirBeam 3), and the ability to monitor CO2 or NOx (AirGradient Open Air), but there are also a few key benefits to the Model X - in particular, the pricing and the completely free dashboard with up to four years of data.

While each monitor certainly has advantages, and I would argue that the Model X has the least developed platform (due to it being newer and managed by a much smaller team), I have been very impressed with the device’s performance, so let’s discuss that!

All the other monitors I listed use Plantower sensors, but they use different models. AirGradient uses the PMS5003, PurpleAir the PMS6003, and AirBeam the PMS7003. However, despite the naming scheme, each of these sensors has very similar performance, with the key differences being in size and connection options. On the other hand, the Model X uses the Sensirion SPS30.

Which of these sensors is more accurate is still up in the air, as some studies point to the SPS30 performing better while others have found better performance with Plantower sensors. Either way, I tend to look at the sensors as roughly comparable - at least for PM2.5.

https://www.scirp.org/journal/paperinformation?paperid=107924

I wanted to make some comparisons, so I decided to graph the PM2.5 concentrations recorded by the Model X and a couple of PurpleAir monitors over the same period. At first, I found that the sensors recorded vastly different values, but after doing some research, I found it’s common knowledge that the PurpleAir monitors (and likely most Plantower-based devices) significantly overreport PM concentrations. For this reason, the EPA developed a correction formula to bring their readings more in line with federal reference equipment (at least for smoke and urban pollution).

Before the EPA correction. Please note that Model G is mislabeled (it should be Model X)

After EPA correction. Also, sorry for the imperfect ChatGPT graphs…

After exporting data that had been EPA-corrected, I was surprised to find that the Model X with the SPS30 and the PurpleAir devices showed very similar readings. While I’m unsure what corrections Sensirion applies, I was impressed at these results and, while I lack access to reference equipment, I would take this to mean the Model X accuracy is good.

A full review is coming up soon, but I was impressed to see the similarities in readings, and I think the Model X might be another good (lower cost) outdoor air quality monitor option!

[Ethan]

PurpleAir Flex and Zen review:

PurpleAir Flex & PurpleAir Zen Review

These are probably the most popular outdoor air quality monitors on the market, and after spending some time with them (and continuing to use them daily), I think they’re a great option - potentially the best for many users.

[Ethan]

Another option that I thought was purely a portable air quality monitor, but that turns out to have some great features that can be used as a static outdoor air quality monitor, is the AirBeam 3.

This ghostly monitor is intended firstly as a portable air quality monitor, but due to it having a built-in GPS, SD card for local storage, and SIM connectivity, it becomes a good option as an outdoor monitor, too. On top of that, it’s weather sealed, and comes with a karabiner so it can be hung anywhere. When needed, you can opt to use it as a portable monitor instead.

I am currently working on a full review for this monitor and will share it when complete.