# Question: What do the different colors mean on the Simple Air Sensor?

stevie is asking a question about pm

by stevie |

Collaborators at UW Eau Claire (@crispinpierce and his students @Aleah and @Cbarnes9) are interested in using the Simple Air Sensor for demonstrations in their presentations around the Purple Air Monitor. What do the colors on the sensor mean? What causes the sensor to change colors? and what's a good way to describe this to people in a demonstration?

These particular sensors, the way they are programmed, is to test a range between 0 and 20 micrograms per cubic meter, where 0 is green, and red is 20 (or anything beyond 20). You will also see a range of colors between green and red as the sensor detects more particulate matter. It's important to note these sensors don't take into account humidity or other factors that might alter what the sensor reads.

@warren any edits or additions?

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Just that a really in-depth discussion on how this works can be found here: https://publiclab.org/questions/warren/04-18-2019/brainstorm-on-ways-to-use-colored-light-to-show-sensor-readings

which gets at both the programming behind it and some of the considerations of colorblindness, color meanings, etc that may be good justifications to decide to do things differently! Thanks!

This wheel shows the range of values from 0-140 that correspond to the 0-20 values from the sensor:

Thanks @stevie and @warren. So green is 140 degrees and represents 0 ug/m3 and red is zero degrees and >= 20 ug/m3? I'm curious about how the calibration was done by you.

It would be very cool if you could program the simple air sensor to reflect the EPA air quality index (AQI) using the following chart (from, https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=2ahUKEwjknY6R5pnkAhUkhOAKHR2_ClUQFjADegQIDRAG&url=https%3A%2F%2Fwww.epa.gov%2Fsites%2Fproduction%2Ffiles%2F2016-04%2Fdocuments%2F2012_aqi_factsheet.pdf&usg=AOvVaw3korf91hVoSvvEiD4o2GKV):

I've also emailed Plantronics to see what dust standard they used ("Arizona road dust"), what their particle density conversion algorithm is, and if they assume Rayleigh and/or Mie scattering. No response.

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We didn't do any calibration at all, and are just reporting out the values produced by the sensor. Purple Air does a conversion to AQI, but do you think 1 sensor with no temp/humidity correction is good enough to make such a conversion possible?

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