Question: What type of aerosol was used for the calibration of the purpleair lasers?

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Cbarnes9 asked on November 09, 2018 00:33
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The optical characteristics of aerosols such as organic carbon and silica would likely reflect differently considering the purple air monitor uses laser spectroscopy. I work for a research team for the University of Wisconsin Eau Claire, and we are attempting to discern the validity of the data that is generated from the purple air monitors. Listed following this is a link to the AQI field test of the purple air monitor. http://www.aqmd.gov/docs/default-source/aq-spec/field-evaluations/purple-air-pa-ii---field-evaluation.pdf?sfvrsn=2



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As far as I know Plantower hasn't disclosed that (to be fair, I don't think any of the low-cost manufacturers has done either). From the field tests I've conducted, it seems like their algorithm is based on combustion particles which would make sense if their testing facility is in China and they just use outside air to calibrate their algorithms. Also, I don't believe that the sensors are calibrated individually but rather, the algorithm was developed and then implemented in the microcontroller ... hence the inter-instrument variability that you see and part of the reason PurpleAir has 2 sensors in it


The purple air monitors have a low r2 value for the pm10 testing. This may lead to the skewing that you are talking about.

I corresponded with them on this issue. Let me see if that data is still around. Jeff, do you have a copy of that letter by chance?

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I could be wrong but I do not believe optical particle counters use spectroscopy as the method is usually described. At any rate a number of years ago when I did some research on the "dust" used in calibration of particulate monitors I often came across references to "arizona dust". Using a search engine should give you the relevant information. Google yields: https://www.reade.com/products/arizona-test-dust-ansi-ard-arizona-ashrae-iso-jis-mtd-nfpa-nist-rm-srm-sae

Whether it is what purpleair uses is another question.


I agree, i think it's laser scatter -- you can read @guolivar's post here for a bit more! https://publiclab.org/notes/guolivar/01-08-2018/thoughts-on-low-cost-air-quality-sensors


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