Question: Questions about Plantower sensors from the University of Wisconsin - Eau Claire

OrionAllgaier is asking a question about air-monitoring: Subscribe to answer questions on this topic

OrionAllgaier asked on March 13, 2019 20:46
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Hi All,

This seems to be a very promising development towards affordable particulate counters as well as understanding their basic function and analysis. Regarding these "Simple Air Sensors", I am curious...

1. In the Plantower manual (for the PurpleAir monitor), we haven't been able to find the conversion between # of particles per liter to micrograms per liter. This conversion includes assumed particle density [e.g., "Arizona Road Dust" of 2.65 g/mL] and average volume per particle for each of the size ranges measured. Does anyone have this information?

2. Is the sensor interpreting results using Rayleigh, Mie, or some other combination of scattering?

Thank you,

Orion Allgaier | orionallgaier@gmail.com



5 Comments

Hi @OrionAllgaier, It's great to be curious and I'm sorry I can't answer your questions. But I am also curious. To my mind if one is trying to produce a low cost and usable particulate monitor I would expect one to use reasonably accurate and inexpensive methods to calibrate the output and, also to my mind, the simplest way would be to co-locate with a federally accepted monitor and use the data to develop a relationship from counts, the output of my counter, to µg/m3, the output of the more expensive monitor. This would seem to me to be easier and quicker than starting from scratch with some theory and assumptions about particle density,"Arizona Dust" eg, and average volume, etc. In fact in my correspondence with Purple Air, this is what they recommend for users of their monitors so that the user can develop a relationship that more accurately gives densities that relate to the particulate generally in the air in their geographic location, ie they advise relating the purple air output to an accepted regulation monitor output. (Which, of course, prompts one to wonder how many users actually go through this process!) To my mind also, if one wants to use an inexpensive monitor in environmental health related research, this is the only way to develop confidence in the data gathered. And the only way to be able to include a reasonable variablilty, ie error, analysis. I'd be curious as to what you think about this. Thanks.

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Hi all, great questions here. Pinging in a couple people who might be able to help provide some insight @cfastie @guolivar

Best, Stevie

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@nanocastro @cbarnes9 @ag8n @wu_ming2 @bigmit37 might also know a bit about this?

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I believe your first question was answered in general terms here: https://publiclab.org/questions/Ag8n/08-18-2018/pharmaceutical-class-100000-particulate-as-compared-to-pm2-5

I had short conversations with the sensor manufacturer reps in Beijing and Shenzhen and if I were you wouldn’t expect to find exact information. They may be commercially sensible and haven’t find any willing to go beyond what’s written on the spec sheet.

Your second question was answered here: https://publiclab.org/notes/guolivar/01-08-2018/thoughts-on-low-cost-air-quality-sensors

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The only other thing to point out- all these calculations assume the particles are spheres. We had particle surface area measuring equipment. The particles are rarely spheres. Sometimes the variation is minor, but in materials like activated charcoal, it can be dramatic.

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