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Comment by bearforcenine | Hacker News Reader

Based on my reading of the table, the PurpleAir II sensors seemed to be the best of the sub $300 for PM1.0 (field R^2 of 0.96 to 0.98) and PM2.5 (field R^2 of 0.93 to 0.97). The PM10 readings were not as good (field R^2 of 0.66 to 0.70).

After skimming the rest of the table, it looks like the PurpleAir II sensors might have some of the best field R^2 for PM 2.5 and PM 1.0

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That sensor is also available from Adafruit: https://www.adafruit.com/product/3686 I got it hooked up to a RaspberryPi that exposes sensor readings in Prometheus format.

Do you have a PurpleAir II to compare against? I suspect that there will be some extra calibration or signal processing some to make it more accurate that will be missing in the raw sensor.

EDIT: The link we're discussing says this explicitly: "[...] These particle counts are processed by the sensor using a complex algorithm to calculate the PM1.0, PM2.5 & PM10 mass in ug/m3. [...] PurpleAir PA-II uses two identical PMS5003 sensor units attached to each other and placed in the same shelter. [...]"

I don't think you can recommend the PMS5003 as a substitute for the PurpleAir II.

That sensor available at Adafruit uses the same algorithm for calculating PM levels, it's literally the same chip. Maybe using 2 of them yields more accurate results though.

The specs for particulate matter are identical:

https://www2.purpleair.com/collections/air-quality-sensors/p...

https://cdn-shop.adafruit.com/product-files/3686/plantower-p...

The Adafruit sensor is just the sensor, the PurpleAir II is two sensors plus extra logic that processes the readings to give extra accuracy.

You can't expect one sensor to give the same performance as two sensors plus correction logic. If it was that easy, PurpleAir could just put a case on a PMS sensor and be done with it.

If that was true, then why are the specs for the PurpleAir II identical with the Adafruit sensor ?

You provide absolutely no data to back up your claims that there is extra logic on the PAII or that 2 sensors are better than one.

I agree, looking at devices around the sub-$300 price point that were lab tested, PA-II has good performance and seems to be readily available.

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