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PurpleAir Flex & PurpleAir Zen Review

When I first started this website back in 2020, there were two air quality companies that I was well aware of even before writing my first articles – IQAir and PurpleAir. While I got a chance to test monitors from the former earlier this year, until recently, I never got to test anything from PurpleAir, which is quite a surprise considering how well-known and respected its monitors are!

After many years, I finally got my hands on a few PurpleAir monitors about one month ago, and I’ve been testing them since. I received three monitors: 2x PurpleAir Zen (PA-II-Zen) and one PurpleAir Touch (PA-I-Touch). While I haven’t had a chance to test the Flex, this review will focus on the Flex and the Zen, as they are the same in most regards, with the only key difference being that the Flex is exclusively an outdoor monitor, while the Zen sports the same hardware but can double as an indoor monitor.

PurpleAir Monitor Comparison

Comparison of PurpleAir monitors. As you can see, the PurpleAir Flex and Zen have very few differences.

PurpleAir’s Flex and Zen are perhaps the world’s most famous outdoor air quality monitors, which is one reason I’ve always been so interested in testing them. While I’ve tried many indoor air quality monitors, I’ve only tried a few outdoor monitors, such as the AirGradient Open Air and CO2 Click Model X. In the parts of the world where I live, however, outdoor air pollution is a big issue, and having an outdoor monitor is invaluable for knowing when it’s okay to open my windows or when I should ‘lockdown’.

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.

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In today’s review, I want to dive deep into the performance, functionality, and usability of PurpleAir’s outdoor air quality monitors – the PurpleAir Flex and PurpleAir Zen. I’ve been using my Zen monitor for around a month, and I’ve been impressed and disappointed by some aspects of the device, which surprised me. What am I talking about? Read on to learn more!

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

PurpleAir Sensors PMS6003

The most important aspect of any air quality monitor is accuracy. After all, without knowing if a monitor is accurate, we have no way of knowing if we can trust it! With that in mind, let’s get started by examining how the PurpleAir Flex and PurpleAir Zen perform in terms of precision and accuracy.

Both monitors use two Plantower PMS6003 laser particle sensors, which are common in outdoor air quality monitors (Plantower sensors can also be found in the AirGradient Open Air and AirBeam3). While only one sensor is needed in most cases, a second is included for redundancy and to ensure sensor agreement because having a second sensor allows us to identify if there is an issue with the device, as we’d typically expect low inter-device variability between two identical sensors in the same location. The vast majority of the time, this is the case. However, if one sensor begins to drift and the inter-device variability grows, we know there is an issue with one of the device’s sensors.

PurpleAir Sensor Agreement

The PurpleAir map shows a ‘confidence’ percentage, which compares sensor A and sensor B readings. If these readings don’t demonstrate a strong correlation, one of the sensors has a fault.

While this does add to the cost, I’m a fan of having a second sensor for redundancy, and I believe it should be standard practice in all outdoor air quality monitors. While these sensors should prove accurate for at least a few years, knowing when they begin to fail is vital to continued trust in the monitor and its data. One of my favourite aspects of this dual-sensor setup is that PurpleAir allows you to export individual data from both sensors to do further comparisons yourself.

Alongside the dual Plantower PMS6003 sensors is a BOSCH BME688 that is used to monitor temperature, humidity, and volatile organic compounds (VOCs). Since temperature and humidity sensors can easily be influenced by heat generated by themselves and other components, PurpleAir has placed the probe slightly outside the device. Between these two types of sensors, you will find all the readings you need from your PurpleAir device.

Now that we’ve discussed the sensor tech used in the monitor let’s take a deeper look into how the sensors perform and whether their data is trustworthy. We will start with the more interesting sensor, the Plantower PMS6003. This sensor and its siblings, the PMS5003 and PMS7003, are well-studied, and there is much literature to discuss.

Plantower PMS5003 PMS6003 and PMS7003

PMS7003 (top left), PMS5003 (top right), PMS6003 (bottom).

Before continuing, however, it’s important to note that the performance of the PMS5003, PMS6003, PMS7003, and even other sensors in the family is almost identical. While the naming scheme is somewhat misleading, and I would expect the PMS7003 to be a higher-end model or successor to the PMS6003, the differences are only in size and connection options. Therefore, aside from monitor manufacturer corrections, we can expect similar accuracy across these sensors.

That said, we might expect slightly better performance from the PMS5003 and PMS6003 as they house larger sensors, meaning they are less susceptible to noise in their readings. While this can be somewhat offset by taking multiple readings or averaging values, less noise is generally better, and the PMS5003 and PMS6003 are both larger sensors.

While I can’t measure accuracy without reference grade equipment, I can measure precision, and I was curious to see how the two PA-II-Zen (PurpleAir Zen) monitors compared to one another and also how similar the readings they provide to the PA-I-Touch (PurpleAir Touch) when placed in a sheltered outdoor area. As you can see from the graph below, the two Zen monitors (in blue) provided remarkably consistent readings over three days, and they never showed a concentration difference of more than 2µg/m3 – a result I was very impressed with.

PurpleAir Sensor Precision

However, both monitors showed significant differences when compared to the Purple Air Touch indoor air quality monitor, and perhaps that monitor should not have been included in this comparison. This could be due to differences in corrections between the devices (the Touch is intended solely as an indoor monitor). Still, since the Zen is supposed to be an indoor and outdoor air quality monitor, I found these differences interesting and worth including. However, I will discuss them in more detail in my PurpleAir Touch review. Regarding the PurpleAir Flex and Zen, the readings between devices and even between sensors are very consistent, and while I’ve just shared one graph here, I can conclude that the devices are precise.

Now that we know the PurpleAir monitors provide consistent readings between all three devices, it’s time to discuss whether the monitors are accurate. Since I don’t have access to any reference equipment, I decided to look through the literature for this section. Long story short, the PurpleAir monitors are decently accurate, but there are a few essential things to remember.

PurpleAir Accuracy AQMD

AQMD test results. The first column after PM categorisations is field results, followed by lab results.

AQMD (South Coast Air Quality Management District) tested the PA-II-Flex and found it one of the most accurate monitors in its database for PM1 and PM2.5. While the Zen has not been tested, PurpleAir devices have consistently performed well in these tests. Considering the similarities between the two monitors, I would expect the Zen to do similarly well. There is a small surprise here: the previous PA-II monitor performed better in all tests, but I would guess this is due to different conditions at the time of testing.

One interesting finding from the AQMD AQ-SPEC testing was that at lower particulate matter concentrations, the PurpleAir devices tend to overestimate particle counts, while at higher concentrations, the devices tend to underestimate. The former of these findings is especially important because it’s also been confirmed by other studies and can cause some issues with raw data from the PurpleAir Flex and PurpleAir Zen.

For example, another study by the EPA (United States Environmental Protection Agency) found that PurpleAir devices can overestimate PM2.5 concentrations by as much as 60%! This study was carried out on a much larger scale, and actual monitors used across the PurpleAir network were compared to colocated and nearby reference-grade monitors.

So, why is there a discrepancy between these two reports? Well, it’s important to note that half of AQMD’s testing is done in a lab, and the other half is done during (I believe) ‘typical’ outdoor conditions near the organisation’s offices, which likely means most of the pollutants monitored by the devices during testing are those commonly found in urban areas such as traffic emissions. On the other hand, the EPA study was carried out during wildfire smoke events.

While we discuss ‘PM2.5’ and other particle categories as if they’re uniform, there is nothing at all uniform about PM2.5 particles. Particles from different sources have different sizes (depending on how they’re measured), compositions, weights, and more. This means that while specific sensors may be sensitive to certain types of PM2.5, they are less sensitive to other types.

Based on these two test reports, it looks like the raw data from the PMS6003 sensors in the PurpleAir monitors is accurate enough during urban air pollution events, but the sensors quickly lose accuracy when it comes to wildfire smoke events (and, from my findings, many forms of smoke). Before you despair, though, two notes! Firstly, this is common across all Plantower sensors (they’re known not to be particularly accurate out of the box), and secondly, this can be corrected!

To account for the significant overreporting of PurpleAir monitors during wildfire smoke events, the EPA developed a correction formula that significantly improves the accuracy of PurpleAir monitors – but only when impacted by wildfire smoke (it performs significantly worse during dust events).

Since these findings, PurpleAir allows you to apply the EPA correction within the map, making it super quick and easy to toggle between raw, uncorrected readings and EPA-corrected readings. This ensures you get decently accurate data whatever the conditions. While it is an extra step to take (and sometimes easy to forget!), there is no one-size-fits-all when it comes to monitoring something as vague as PM2.5.

PurpleAir Uncorrected Data

Uncorrected PurpleAir data (the blue line is the Model X with a Sensirion SPS30).

During this review, I was preparing data for another review on the CO2 Click Model X, and I found that my PurpleAir devices were constantly showing readings as much as double the Sensirion SPS30 within that monitor. I spent more than a few hours thinking that the Model X was simply inaccurate before discovering the EPA correction formula and applying it to the PurpleAir data. When I applied the formula, I graphed the data again, and the results were vastly different.

PurpleAir Corrected Data

Corrected data using the EPA Conversion.

While the SPS30 is just another consumer-grade low-cost particle sensor and a far cry from any reference equipment, I was curious to see the difference with the PurpleAir monitors both before and after the conversion. While not everyone will want to apply this algorithm as it depends on your local pollution composition, I found it to make a big difference as I’m primarily affected by smoke.

Overall, the PurpleAir Flex and PurpleAir Zen can provide accurate data, but you should know the different corrections and when to use them. While PurpleAir has made it very easy to filter the data however you want to, I think many people overlook how important this feature is. By default, PM concentration readings taken by PurpleAir monitors of wildfire smoke vastly overstate the concentration.

As mentioned previously, the temperature, relative humidity, atmospheric pressure and VOC readings are all collected from the BOSCH BME688. To ensure the temperature readings aren’t too heavily influenced by heat generated by the components within, the temperature probe extrudes slightly from the bottom of the device. While I’ve read some complaints about issues with the sensor and/or their algorithm on the PurpleAir forums, I’ve found it to generally perform well and to give similar readings to my Aranet2.

We need to be careful regarding VOC readings from the PurpleAir Flex and PurpleAir Zen. In PurpleAir’s own words about the experimental VOC readings: ‘This parameter is experimental, and we are still evaluating what it means’. To explain, VOC readings from this sensor are normally displayed with a 0-500 index, regularly updating the baseline values to show a relative reading of your VOC levels. In other words, it helps show if your VOC levels are increasing, decreasing, or stable.

However, PurpleAir appears to have opted to use Bosch’s sIAQ (static indoor air quality), which does not as frequently update and has a larger range of potential values. With that said, VOC sensors still have questionable importance since they can’t differentiate between VOCs and have differing sensitivities to different gases.

VOC sensor readings

For example, the above image is from Sensirion and shows how a VOC sensor would consider both of the above situations the same. However, the first composition is dominated by ethanol (harmless), whereas the second is mostly toluene (harmful). With these caveats in mind, VOC sensors may have some benefits, but the data is only truly meaningful if we already know the composition of the gases we monitor (which we don’t in real life – especially outdoors). However, this is not a PurpleAir-unique issue and applies to all low-cost sensors.

I’ll be curious to see what PurpleAir decides to do with the VOC readings from these monitors, as they currently seem unsure and are researching the best way to use these readings (if at all). In the meantime, it’s best to stick with the PM, temperature and relative humidity readings from our monitors, which are all decently accurate – as long as the right corrections are applied.


PurpleAir Zen AQ Monitor

Before explaining the design differences between the Flex and the Zen, it’s important to note that PurpleAir intends the Flex to be a solely outdoor monitor, the Touch to be a solely indoor monitor, and the Zen to be a monitor capable in both situations. However, since the Touch is an indoor-focused monitor, I’ve used my Zen outdoors and have decided to review it as an outdoor monitor – I think this is how most people will use it, too.

The only difference between PurpleAir’s two outdoor monitors – the Flex and the Zen is the design. While the Flex is inconspicuous, with all of the components hidden in a simple white case that looks like it’s from a pipe, the Zen uses a semi-transparent plastic case with an LED ring near the bottom. This LED ring lights up based on the air quality detected by the monitor (or a range of other settings, which can be decided when setting up the monitor), and you can adjust the brightness by tapping on the top of the monitor.

I prefer the Flex design for an outdoor monitor. While the LED ring in the Zen might be a nice addition for some, I don’t see the appeal unless using the monitor indoors. Sure, having the LEDs isn’t a disadvantage, but I prefer a monitor that people don’t notice for outdoor use. Luckily, it is possible to entirely disable the LEDs (but choose this option at setup; otherwise, you can only disable them until the device is restarted, which happens quite often to me in the Philippines due to blackouts).

PurpleAir Zen Monitor

On the Zen, you can also change the brightness and disable the LED by double-tapping the top of the device. However, I’ve found this control scheme to be infuriating sometimes, as it’s very unresponsive. In fact, when I had it sitting on a table next to my PurpleAir Touch, I could double tap the Zen, and it wouldn’t respond, but the Touch next to it would – very frustrating! Anyway, as soon as I have the LED on the lowest brightness level or off, I leave it untouched, so this isn’t a big deal.

Thankfully, PurpleAir hasn’t intended for this device as a replacement, and the Flex is still available at a slightly lower price than the Zen. I am a bit confused as to why PurpleAir introduced the Touch alongside the Zen, but I can only assume they wanted to create a lower-cost monitor for users who only want to monitor indoor air quality.

One final difference between the Zen and the Flex is that the Zen comes with two different attachments for mountain – a bracket for wall/post mounting (similar to the Flex) and a ‘foot’ mount, which allows you to sit the monitor on a surface without restricting airflow to the sensors. On the other hand, the Flex only has a wall/pole mount, and it’s not designed to sit on a surface. Again, this design choice appears to have been made to ensure the device can be used indoors or outdoors.

PurpleAir Zen and Touch

PurpleAir Zen (centre) and Touch (left).

Now that we’ve discussed the differences, let’s dive into the similarities. Both monitors sit in weather-resistant housing with an open bottom. Since airflow is required for accurate air samples, this approach makes sense, but I am surprised not to see some mesh guard as this design makes it easy for insects to enter the device (and they’ve been known to get lodged in PM sensors and cause issues!).

The flip side is that the monitor’s PM modules are incredibly easy to replace. On both monitors, the two PMS6003 sensors are mounted on a ‘quick release’ plate, which allows you to slide the sensors out and replace them when needed effortlessly. While the sensors shouldn’t need to be replaced too frequently, this system is incredibly easy and makes any future replacements effortless. Aside from the sensor modules, you can also quickly and easily insert, remove, or change the SD card, but you might need a pair of tweezers as finger room is minimal.

PurpleAir Zen Sensors

Looking at the monitor from the bottom also highlights one of my common complaints with air quality monitors – the Micro USB port. If you’ve ever read any of my reviews before, you’ll know exactly what I’m about to say, and it comes down to this. It’s 2024, and I hate seeing this outdated standard still used. Type-C is so cheap these days that I’m sure an extra-long, weather-proof adapter could be found for the same price as the current Micro USB one. I understand if PurpleAir doesn’t want to leave users with older Micro USB cables behind, but at a point, you need to update outdated features.

This brings me to powering the device. By default, the monitor doesn’t come with a Micro USB cable, and you will either need to purchase the 12-foot IP68 weather-resistant cable for $40 from PurpleAir or purchase your own. While you can, in theory, use any Micro USB cable and adapter, you will want something that’s weather-resistant if you decide to use the monitor outdoors. If you plan to house the monitor somewhere not exposed to rain (or indoors), you can use any Micro USB cable you choose. Since no data is transferred over the cable and the device is low-power, cheap cables should work fine!

While it is a significant extra cost on top of the monitor itself, I quite like the cable that PurpleAir sells, but I’m sure you can find much cheaper alternatives online. Whatever your situation, ensure you get a weather-resistant cable unless your device is sheltered or you plan only to use it indoors.

At the end of the day, both the PurpleAir Flex and Zen are simple devices in design. However, they don’t need to be anything more, and I appreciate their simple and minimalist designs. While I haven’t been able to ‘weather test’ my monitors for extended durations yet, the plastic seems sturdy, and I can imagine it will last many years – especially if placed in a sheltered area. If you plan to use the monitor outdoors, I would recommend just getting the Flex because the design changes of the Zen are not particularly important for outdoor usage – at least, in my opinion. Some people may appreciate the easily visible LEDs.

For indoor usage, I’m still uncertain about the design of the Zen, mostly due to the unresponsive double-tap feature. With that said, I much prefer the design of the PurpleAir Zen to the dedicated indoor monitor, the PurpleAir Touch and with the other added features of the Zen, it’s an easy choice which one I would prefer to use indoors, even with the extra cost.

Connectivity & Map

PurpleAir Map

PurpleAir map.

Now, let’s get to the biggest advantages and downsides of the PurpleAir Flex and PurpleAir Zen air quality monitors. The chances are you’re already aware of the PurpleAir Map, and if not, you’ll quickly find out that it’s one of, if not the most populated, community-sourced air quality maps on the internet. I think the map alone causes a lot of people to turn to PurpleAir because it’s a fantastic demonstration of how community scientists can contribute to a larger cause. It also shows just how popular PurpleAir monitors are.

However, before we discuss the map, let’s discuss how the monitor uploads data. Every PurpleAir Flex or Zen monitor has a WiFi chip that connects to a local 2.4 GHz WiFi network. This connection will upload data to the PurpleAir platform, which can (optionally) display your data to anyone viewing the map. The setup process is painless, but you will need the Device ID, printed on the sticker on the outside and inside of your monitor to register your monitor.

Once you’ve connected the device to WiFi, you can go to the map and create an account. Once this is done, you must enter your monitor’s device ID and tie it to your Google Account. Unfortunately, you need a Google Account (there doesn’t appear to be any other way to create an account) and must use the email under which you purchased the monitors. I found this to be a very frustrating decision, as all the monitors I obtained were under my email address, which isn’t a Google address, and I had to go out of my way to create a Google Account with that email address.

PurpleAir Data

Once you’ve added your sensor(s), you can choose to publicly show them on the map or keep them private. Even if you decide to keep your monitor’s data private, you will need to use the map platform to view the data from your monitor; hence, you still need to set a location. The only difference is that you won’t be able to view your monitor’s data unless you log in. On the other hand, if it’s public, everyone can view the data and location.

Overall, the map is very powerful, and I can see why PurpleAir is so famous. There are so many options on the map, and you can apply thousands of different filter combinations. Want to view raw PM2.5 concentration data averaged over 10-minute periods? You can. Want to view EPA-adjusted PM10 data over daily periods? No problem. There are so many options with this dashboard, and it’s one of the strongest aspects of the PurpleAir devices.

PurpleAir EPA Conversion

Applying the U.S EPA conversion.

However, I started to have issues with downloading the data. I regularly download data from my air quality monitors, and I want to access it easily. Unfortunately, PurpleAir only lets you see recent data on the dashboard – two days for real-time readings, one week for 30-minute readings, and one year for one-day readings (among other options). While I don’t see an issue with the longer options, I wish I could see at least a week of real-time data for deeper analysis. Of course, you can use the API to access data, but this will cost you after you use your free credits.

Luckily, you can access data from your monitors for free, but again, this is all done through the API, which I had a lot of difficulties with. Even using the PurpleAir Download Tool, I couldn’t download my data through the API even after trying tens of times. I’m not exactly sure what the issue is, but I don’t seem to be able to use the API, no matter which method I use. This is likely just an issue on my end, but I’m still not a fan that in-depth data for my own monitors is all behind an API. I understand the need to make money, and I believe having only limited data from other monitors behind a paid API is acceptable. Still, I want my data to be easy to access and download, like it is for most other monitors.

Since the PurpleAir Flex and Zen both support micro SD cards, this is another approach you can take to access data from your monitors. Unfortunately, I don’t have a micro SD card reader on me at the moment, and while this admittedly might solve my issue, I wish there were an easier way to access data online.

I’m also not particularly a fan of needing to use the map for my own data. While I understand that PurpleAir wants to push the map to encourage adoption and that maintaining two platforms would be difficult, I prefer having a dashboard like AirGradient, CO2.Click or even Airthings offers for my private monitors. After all, when I want to view data from my own monitor, I don’t need the map taking up 70% of my screen as I am already well aware of where the monitor is situated!

For example, while it’s easy enough to filter out indoor monitors (the PurpleAir Touch or indoor PurpleAir Zen monitors), I don’t see why they should be added to the map in the first place. Indoor monitors don’t add valuable information to the map because indoor conditions vary so much. However, even if you want to view data from your indoor monitors, you’ll need to use the map. In this case, I would much prefer a simple dashboard and I have no need at all for the map.

PurpleAir Map Data

Data viewing screen on the PurpleAir map.

Anyway, I digress. My issues with data access are significant, but the dashboard is a minor gripe. I appreciate the map, and I think it’s one of the best (if not the best) on the internet for crowd-sourced data. However, I wish a screen was dedicated to just viewing data and trends from my devices (especially indoor monitors). I admit, though, that I am a ‘power user’ and that most people will appreciate the map. It is fantastic; it’s just built with community at its core, which has advantages and disadvantages.

On the flip side, the depth that the map offers is unparalleled. As an air quality advocate, I love having so many different options and filters that can be applied. Of course, having the largest AQ map platform on the internet also means that there is lots of support and a strong community supporting it. It also gets the most attention from organisations such as the EPA, leading to awesome things like the development of the EPA correction formula.

I think it comes down to this: If you want to use an indoor air quality monitor, there is much better software out there from other companies. However, if you want to get an outdoor monitor – and especially if you want to make your monitors public – the PurpleAir map is probably the best there is. It would be nice if they made data easier to access, though!

Price & Competition

PurpleAir Zen Monitor 1

I finally understand the name!

While there is much competition for indoor air quality monitors, there is significantly less for ‘affordable’ outdoor air quality monitors. As I mentioned at the beginning of this article, the PurpleAir range of monitors is probably the most well-known outdoor air quality monitor on the market. However, they certainly aren’t the only options.

I haven’t had a chance to test the IQAir outdoor air quality monitor yet, so I can’t speak on that option. However, I have personally tried everything else on the list below, and I think each has significant advantages. Let’s discuss how the monitors compare to the PurpleAir Flex and PurpleAir Zen.

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

The first comparison is to the AirGradient Open Air. To be transparent, I now work part-time for AirGradient (but I didn’t when I wrote my initial reviews) as they’re a very transparent and open company (as can be seen by its open-source hardware and software). While I will remain as unbiased as possible here, please keep this fact in mind.

The AirGradient Open Air is significantly cheaper (especially if you get the DIY kit, which is less than half the price), and it either comes with two particle sensors or one particle sensor and one CO2 sensor. Both options have merits, and I think they’re worth considering instead of the PurpleAir monitors.

However, the PurpleAir monitors have some features that I’ve come to love – the ability to save data to an SD card is invaluable for connection outages, the map is much better implemented and offers much more functionality than AirGradient’s dashboard, and the overall experience feels more polished (I’ve had difficulty using my AirGradient Open Air monitors this week due to technical issues).

On the other hand, the fact that PurpleAir limits data to the previous few days (unless you use the API, which is frustrating to do in my experience) and that everything is hosted on the map also frustrates me – I would love to see a typical dashboard, too. Which monitor you opt for is entirely up to you, and I think both are great monitors.

Compared to the CO2 Click Model X, there are many more differences. The Model X is designed as a ‘personal’ monitor, whereas PurpleAir seems to have designed all its monitors with the map at the front and centre of its platform. This platform is, of course, inherently public. The Model X also uses a single SPS30, which, while I might be leaning towards it as being a slightly better performer, is similar overall and doesn’t have a second sensor for redundancy. On the other hand, it’s far cheaper than any PurpleAir monitor!

Finally, the AirBeam 3 is a slightly more accurate monitor (per AQMD’s testing) but only has a single sensor. It also has an internal (and included) SD card and SIM card connectivity, allowing it to be the perfect monitor for isolated locations (when paired with a solar panel, perhaps). It also has an internal battery and is doubled as a portable monitor, which can be incredibly handy. On the flip side, it doesn’t have a second sensor and relies entirely on an app instead of the web dashboard.

All these options, including the PurpleAir Flex and Zen, are great. Out of all of these monitors, I’ve enjoyed the user experience of the PurpleAir monitors the most, and they have the accuracy and performance to back this up. It will come down to what you value – do you need SIM connectivity? Would you prefer an open-source monitor? Do you want to save some money? These are valid questions and will steer you towards the best monitor for your needs.


After using the PurpleAir Zen for around a month, I’ve been surprisingly pleased with the device. While I always had high hopes for it (after all, how else could it be so famous?), I had some reservations and wasn’t convinced that I would be sold on it. Now, I think it’s a good monitor, and I agree with the majority of reviews out there, which are positive.

While there are much cheaper options which are also solid out there, the one thing I’ve particularly enjoyed about using PurpleAir is the ease of using the system. Besides being unable to view much historical data and needing to use the API to access older data from my own monitors, the monitors have just worked. One example is the many power and internet outages I’ve had this week – the monitors boot up and reconnect as if nothing ever happened, and I appreciate this ease of use.

Of course, the PurpleAir Flex and Zen aren’t perfect. I do have a few other gripes with them, such as the fact that you need a Google account to use the map (and that you must add the monitors to the Google account you used to purchase them). Still, none of these are big enough to change my overall positive opinions on the monitors. The biggest downside is undoubtedly the price, but I think you get some significant improvements alongside the price increase.

The best way to sum this review up would be to say that, to date, the PurpleAir Flex and Zen are probably the most well-rounded and solid outdoor air quality monitors I’ve tested. They’re not perfect, and I think AirGradient, AirBeam, and CO2 Click offer fantastic lower-priced alternatives. However, if you can afford the extra cost, I think the PurpleAir monitors are worth considering.

If you want to join the discussion about outdoor air quality monitors, please feel free to come to the forum to ask questions or comment! Thank you for reading.

PurpleAir Flex and Zen FAQ

What Is the Difference Between the PurpleAir Zen and PurpleAir Flex?

The monitors are very similar, with the key difference being that the Zen is designed to double as an indoor and outdoor sensor, while the Flex is designed to be outdoors only.

What Do PurpleAir Monitors Measure?

They measure particles (PM1 – PM10) temperature, humidity, air pressure, and VOCs.

What Sensors Do the PurpleAir Flex and PurpleAir Zen Use?

They both use the two Plantower PMS6003 sensors and a single Bosch BME688 sensor.

What Are Some PurpleAir Alternatives?

The AirGradient Open Air, IQAir Outdoor Air Quality Monitor, CO2 Click Model X and AirBeam 3 are all good alternatives.

PurpleAir Flex & PurpleAir Zen
PurpleAir Zen Air Quality Monitor

PurpleAir has become synonymous with air quality, but are the outdoor air quality monitors as good as people say? In this review, I test them and see how the PurpleAir Flex and PurpleAir Zen perform.

Product Brand: PurpleAir

Editor's Rating:


  • Accurate Sensors (when used correctly)
  • Well-supported and popular map
  • SD card slot
  • Replaceable PM sensor modules
  • Separate sensor for temperature, RH, and humidity


  • Uses Micro-USB
  • Does not come with an outdoor cable
  • Tap-control is frustrating
  • Requires a Google Account
  • API required for historical data

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