I was given the chance to review the brand new Flow 2 by Plume Labs and I took the opportunity to review it on my trip to Athens, Greece while visiting my family. Flow 2 is a small handheld AQ monitor that can follow you almost anywhere through the day and it tracks Particulate Matter, Nitrogen Dioxide and VOCs.
Technical Specifications
- Particulate Matter Sensor
- Nitrogen Dioxide NO2 Sensor
- Volatile Organic Compound VOC Sensor
- 12+1 RGB LED Array
- Bluetooth Low Energy (BLE)
- USB-C & Custom metal contacts for charging
- Charging base
Hardware
There some new feature in the second version of Flow.
The old version Flow 1 used to take measurements every minute all day long but now thanks to the custom battery management the device enters in idle mode and takes fewer samples during the night at home, as a result, the battery can now run longer between 24 and 72h.
The Particulate Matter sensor is a custom design, I haven’t opened the device to check it myself but this is what I was being told by a trustful person. The company says on their website that the device “is at 90 to 95% correlation with static reference monitors in benchmark tests for the core pollutants we measure”. Sounds amazing but the Lab evaluations are very different from the Field evaluations, so I will keep an open mind until a field evaluation is published because I don’t have a reference monitor in order to do it myself. However, I will try to compare the data with other stations/monitors later on.
Flow 2 is now featuring PM1.0 measurments which indicates to me that the company is moving forward to even smaller particle sensing. A prediction of mine is that the next best thing in low-cost PM sensing is nano particle sensing.
My opinion on correlations is well known, I am not searching for a 100% correlation, it is not possible to achieve and propable utopian but I am keen on devices with a correlation greater than ±80%.
The RGB LED ring can provide instant AQI feedback to the user.
The charging base is a great addition to the device because you can easily leave the Flow on top of it and it starts to charge right away.
Software
I think the Flow 2 features the most advanced app for Air Quality monitoring so far thanks to Neural Engine and Machine Learning algorithms Plume Labs has developed.
The information that is displayed on the mobile app is mostly location-based which means that the app will spot polluted areas and will inform you about them. In the screenshot below you can see my long walk around Athens and how exposed I was to the various pollutants –mostly from the vehicles. The app always displays the average exposure but when you click on the timeline (second screen) you can see your exposure at that particular time too.
In case you want to build a case about the air pollution that you are exposed, the app enables you to export the data via email with maps, user position (.kml and .csv files) and all the sensors data in .csv file in order for the users to document their report.
Plume Labs has developed its own AQ Index number so-called Plume AQI based on World Health Organisation (WHO) guidelines as well as international standards developed by the United States Environmental Protection Agency (EPA) and other scientific studies.
My Experience
The whole experience with the device is pleasant, it is a quite light device 70g, so it is easy to attach on your pants, bag, suitcase, etc.
Sometimes and for some strange reason, the device loses the GPS connection which is strange because my Phone and Flow 2 were always together. From what I understand the issue is on the way the phone manages the Bluetooth devices, maybe it tries to save power and the connection is lost temporarily.
The app really helps you to map your commute very well and also decipher the pollutants. I love the location-base approach.
I would like to see a future update where the app will allow users to give some feedback by naming the places they visit the most, like home, gym, workplace, etc… that way the feedback that the user is going to receive from the ML will be much more precise in the future. Finally, I would like to see a dark mode app, but it isn’t something that I can’t live without.
The first half of the graph above is what the device measured during the night and the other half represent my walk in Athens. The PM10 concentrations reached 128μg/m³ and 50μg/m³ for the PM2.5 correspondingly. The NO2 concentrations were high as well breaking the annual WHO guideline of 20ppb with an average value of 46ppb for the 3 hours walk. Life and traffic never ends in Athens.
In case you decide to purchase the device or you already have it, I will recommend you to allow the device to operate for a week before you make conclusions about the AQ because the sensors need to auto-adjust to the new environment and the Neural Engine to learn about your routes.
Conclusion
Flow 2 is a great device for those who want to track air pollutants indoors and outdoors. The outdoor mapping is designed to make the average user’s life very easy. I would recommend this device for anyone who spends a lot of time outdoors especially if the user cycles or walks.
See The Air 
The new power save mode is nothing like you describe. Basically it is an option to activate idle mode for 2, 4 or 8 hours. it doesn’t do any measurements during that period, and it will go back to normal sampling after this period. Apparently it is hard to make a good power save, as heating up the sensors for 15 minutes before it starts measuring takes a lot of power. In my opinion it would have been better if during power save, it idles for a few hours, heats up, does one or two measurements and goes back to idle mode, effectively taking measurements only every few hours.
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and this is where the base offers a solution, by placing the device on the easy charger base it continues measuring pollutants during night in my case at least I had this expirence.
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Using the base, isn’t the same as a power saving feature, which is what I was referring to. The base is really nice and very easy to use . I like it.
Please note that I was explicitly told by support not to leave it on its base for extended periods of time.
The only workable way of using it, is by charging it during the night, and remove it from its base during the day. For that way of using it, the power save feature doesn’t help at all. In fact it is hard to think of any plausible scenario where it is a good idea to automatically resume normal operation after a few hours.
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[…] portable devices and miniaturisation is a thing of the future. In this post, I am going to compare Flow 2 and Atmotube Pro side by side. Both devices are two portable Air Quality Monitors that can easily […]
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[…] consumer-grade monitors that I placed in the reference AQ station were the Atmotube Pro and the Flow 2. Of course, I placed them outside the station and I attached them to the PM2.5 beta attenuation […]
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Thanks Sotirios for the review of the Flow 2.
My experience with the Flow is not really positive. I explain why.
I have bought three Flows in the last 12 months: two of the first generation, and one Flow Gen 2. I lost the Flow Gen 2 while riding the bicycle just one month after I bought it, because the silicon strap is not as safe as the leather/plastic strap of Flow 1st gen.
The two Flows 1st Gen have serious issues: one is reading the NO2 all over the place, very very high, and the second does the same with the PM2.5 and PM10. And there is no way to reset them. So they are not reliable in the real world for me.
My AtmoTube Pro instead, which I carry with me on my bag every day since more than 1 year now, is still reading the PM2.5, PM1 and PM10 very accurately (I know this because I can I compare with other air monitors that I have at home like the Uhoo, PurpleAir, iQAir and others). It is therefore more reliable than the Flows, but it does not have a NO2 sensor and doesn’t have the very helpful map feature.
Also, I have been writing to the Flow team about the issues with my Flows, but they don’t care to reply, so I am not trusting this company anymore. Not to mention that the Flow 2 costs now 199 Euro when it used to cost 159 Euro until just a month ago. That’s too expensive now. Too bad because I really would like to have a Flow monitor that can work properly, because with its features I find that it would be a perfect air monitor if it worked properly.
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