PA-II-FLEX vs PA-II according to AQ-SPEC - help me decide

I’m looking at getting my first PurpleAir monitor and was set on the PA-II-Flex model with the latest (PMS6003) sensor offered. However, I noticed that on the AQ-SPEC evaluation table it seems to score lower than the regular PA-II model. I don’t know a lot about the methodology of the testing or if the folks here agree with it, but I thought I’d ask.

Which one is thought to be the most accurate amongst folks here? If you were getting your first one now, what would you get?

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The choice ultimately depends on the mission the sensor is purchased for.

If comparability to other sensors is paramount, go with the older PA-II; its a known quantity (many, MANY scholarly articles exist discussing calibration and performance both in the field and in the lab) and there are more of the older sensor out there to compare apples-to-apples.

If the unit is running isolated in a residential or light commercial setting where the internal quality indicator will be seen and SD storage will be used, you need more accurate environmental data, and/or you have trouble with the PA-II sensors fouling quickly, then the PA-II-FLEX is a good choice.

As time goes on we’ll learn more about the -FLEX’s performance.


Thanks for the great reply. This will be used in a residential setting (Salt Lake City, UT) in an area where there is pretty good saturation of other sensors - many of the PA-II variety. The geek in me is mostly interested in tracking my own local variations during our horrible inversion seasons and such. I’m sure that the differences between the sensors will matter little for my purposes, but I figured I may as well may an educated decision before spending money! Would having more of the -FLEX sensors in an area such as mine be helpful for the community at-large?

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I recently tested the Flex model using two Flex monitors running side by side with three PA-II monitors. The test was over two months and very high concentrations were occasionally created using marijuana vape pens, heated laboratory hotplates with miniature cast iron pans, etc. Except for the very highest concentrations (1-10 mg/m3!) all monitors agreed very well. An upper maximum around 500 ug/m3 was indicated. So if the Flex model has any additional features beyond the PA-II that you like, it would be a good choice.


I dug up the SCAQMD AQ-SPEC results for the PA-II and PA-II-FLEX monitors so that anybody who checks this thread in the future has easy access to the documents:


I’ve got both types of monitors on my front porch and find that the PA-II-FLEX tends to read a little higher than my PA-II, but there are a lot of reasons why that could be the case. I’m also more interested in PM1.0 and PM2.5 than I am PM10, so I’m still kinda leaning towards the PA-II-FLEX because of the bright LED status indicator and the easy maintenance design, but I just wish it scored a little better on the tests. Perhaps the good folks at PurpleAir would consider offering the PA-II-FLEX with the original PA-II laser counters inside? Or maybe even offer an upgrade to sensors that test better than both the current PA-II and PA-II-FLEX laser counters?

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