Which Sensor to Choose

PurpleAir offers different sensors that can all uniquely suit different needs. Once connected to WiFi, all of these sensors appear on the PurpleAir map, where data can be viewed and shared. With proper installation, PurpleAir sensors are weather resistant. You can view details about each sensor model below and purchase your own sensors here.

You can learn more about what PurpleAir sensors measure and how they work here.

PurpleAir Touch

The PurpleAir Touch contains a single laser counter and a full-color LED that will glow the color associated with the current air quality (green, yellow, orange, red, purple, maroon). It is designed to sit comfortably on a counter or tabletop. Double-tapping the sensor will cycle the brightness level through several options. This sensor also includes a BME680 from Bosch. This component is responsible for measuring temperature, humidity, pressure, and total volatile organic compounds (VOC). The VOC readings are currently experimental. This sensor is specifically meant for use indoors.

PurpleAir Zen

The PurpleAir Zen contains two laser counters and a ring of LEDs that will glow the color associated with the current air quality (green, yellow, orange, red, purple, maroon). It has two bases that can be swapped for indoor and outdoor use. The indoor base is designed to sit comfortably on a counter or tabletop. The outdoor base is designed to be mounted onto a wall or post. Double-tapping the sensor will cycle the brightness level through several options. This sensor also includes a BME688 from Bosch, which is responsible for measuring temperature, humidity, pressure, and total volatile organic compounds (VOC). The VOC readings are currently experimental. The sensor has an SD logger to store offline data but does not come with a micro SD card. The laser counters are built into a quick-release system, so they are easy to access and replace. This sensor can be used both indoors and outdoors.

PurpleAir Flex

The PurpleAir Flex has two laser counters, allowing the Confidence Score to be reported. It also includes a full-color LED that shines out of the underside of the device. This LED will glow the color associated with the current air quality (green, yellow, orange, red, purple, maroon). The PurpleAir Flex also contains a microSD card logger and a real-time clock, and the data can be viewed the same way as mentioned above for the PurpleAir Classic SD. This sensor also includes a BME688 from Bosch. This component measures temperature, humidity, pressure, and total volatile organic compounds (VOC). The VOC readings are currently experimental. The bracket on the device can be removed easily for quick maintenance on the sensor, and the laser counters are built into a quick-release system, so they are easy to access. This sensor can be used both indoors and outdoors.

The full-color LEDs display the air quality color using the US EPA PM2.5 AQI scale.

PurpleAir Classic

The PurpleAir Classic contains two laser counters, whose numbers are compared to each other to return a self-rating Confidence Score. The PurpleAir Classic does not have a full-color LED. This sensor can be used both indoors and outdoors.

PurpleAir Classic SD

The PurpleAir Classic SD is identical to the PurpleAir Classic, with the addition of a microSD card and a real-time clock. While still capable of sending data to the PurpleAir map, this sensor will log its data to the internal SD card, with or without a WiFi connection. To read the data on the SD card, the SD card must be removed and plugged into a computer. This sensor could prove helpful in areas with a poor WiFi connection or serve as a backup if the WiFi connection is lost. This sensor can be used both indoors and outdoors.

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It looks like the Flex contains PMS-6003 laser counters while the old PA-II devices use the PMS-5003 laser counters. Can anybody confirm that form me and also potentially dive into the nuanced differences between those two types of laser counters? If I have a bunch of both types deployed in the field, will I be able to notice a difference in readings? Will they be reasonably comparable or more like apples to oranges?

Thanks!

Always monitoring,
Mark

Here is a link I found that describes the difference. Curious to know if this holds up to scrutiny from others on this forum: Review: Node-S by Clarity – See The Air.

Quoting from the page: “The PMS6003 is a dual laser version of the PMS5003, for longer lifetime and has been proved to be very accurate and a better fit for particles with an aerodynamic diameter smaller than 2.5 microns (PM2.5) which makes it a perfect candidate for urban environments and vehicle emissions. Of course, it can also measure PM10 and PM1.0.”

I would like to get the Flex as well, for reasons you’ve highlighted, plus the VOC measurement. But as understood, determination of actual accuracy numbers is pending some testing Purple Air is either doing, or waiting on a 3rd part to do.

Regards,
Robert

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We are told that the accuracy of the PMS6003 laser counters should be improved, especially with PM10 measurements. However, @Robert is correct that they are being evaluated, and we are waiting to hear results back.

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Hi Ethan,

Did you have an ETA on those results?

Thanks,
Robert

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Will the improvement be a firmware update or …? any updates on this?

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Do you have those results in yet? Is the PMS6003 accuracy updated to better match the original PA-II readings with PMS5003 units?

Our apologies for the delay. AQ-SPEC has released an evaluation on the PurpleAir Flex sensor here: PurpleAir PA-II-FLEX.

Thanks! I reviewed the PA-II classic and FLEX models on that AQ-SPEC website and found that the PA-II-FLEX seems to have worse performance than the PA-II classic, at least as indicated in the language in the “Discussion” for each monitor for PM1.0, PM2.5, and PM10. I made a chart to highlight the differences:

(EDITED ORIGINAL POST TO SWAP IN GRAPHICAL VERSION OF TABLE BELOW)
Screenshot 2023-03-01 at 11.47.20 AM

Do you have any comments on these differences? I would prefer to go with the PA-II FLEX for future purchases, but this information gives me pause. How will they compare to the PA-II classic models? Do you plan any updates to the FLEX that could potentially remedy this difference?

Here are the exact documents that I’m using to assemble this information:

http://www.aqmd.gov/docs/default-source/aq-spec/field-evaluations/purple-air-pa-ii—field-evaluation.pdf?sfvrsn=11

http://www.aqmd.gov/docs/default-source/aq-spec/field-evaluations/purpleair-pa-ii-flex—field-evaluation.pdf?sfvrsn=8

Thanks for your input!

Best,
Mark

One addition - it also seems to me that the FLEX I have at my home tends to show higher EPA PM2.5 AQI scores than the PA-II Classic (also at my home) when the levels are in the high yellow or orange. The levels correspond well in the green zone. Has anybody else noticed a similar kind of issue?
Screenshot 2023-03-01 at 11.55.28 AM

Here’s another visual examples of the difference between the Classic and Flex. Note how the divergence gets bigger at higher pollution levels…
Screenshot 2023-03-03 at 7.57.06 PM

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Thanks for the helpful comparison.

I have to replace the laser counters in my Classic, and was wondering whether it was worth upgrading to the Flex instead, but based on your postings it sounds like it is worth hanging on to my Classic and getting new PMS5003 sensors.

I am interested in any updates on comparing the different monitors if anyone has any.

so if buying today, which should Ibuy?

Resurrecting a post that has been quiet, but rather important (in my mind) since I am looking to add another sensor now has this been addressed in the Flex / Zen? I would very much like to get the Zen, but the classic is clearly the better performing model unless something has changed when I review the reports.

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any updates on stats or firmware fixes for this?