Purple Air

Just got this email from our local clean air agency.

Hi Mark,


Very interesting, thanks for posting that.

Yes, thanks indeed. Maybe someone should tell WUnderground? I seem to recall they were promoting Purple Air. . .

Now im not sure if i regret buying one or not now. :roll:

Thanks a lot for posting that. Has Purple Air been made aware of that finding? I’d like to know what their response is. Actually, mine doesn’t seem to be that far off compared to what AirNow shows for Fremont, CA. Of course, I have no idea exactly where their sensor is. Like right now, my sensor shows 54 AQI and Fremont is showing 59 AQI so, I am under what they are showing.

I’ll try to find it again but I have seen a study comparing the Plantower sensor (as used in the Purpleair) against big bucks pro sensors, and it came out very favorably. Purpleair uses two Plantowers and either averages or votes to improve the quality of the output so I’m kind of surprised that your guys got such a poor result :?

This topic refers to a more in-depth report, I think


Harry, I’ve not forwarded that email to purple rain yet. Im not sure if i should or not.

Harry, yup, we went around this block a year ago…

Here’s a report from the LA Air Quality folks actually comparing the Purpleair performance http://www.aqmd.gov/docs/default-source/aq-spec/summary/purpleair-pa-ii---summary-report.pdf?sfvrsn=4

Hmmmmm… strange how the people here had bad results.

Im going to reply to that email and attach those pdf files and then ask them if they have any data to show their findings with the sensor.

Ah, yes. Thanks, Niko. I guess my memory banks have overflowed or maybe it’s just old age. :frowning:

Yeah, I know just what you mean. I’m selective about what I choose to remember these days, at least, that’s what I tell my wife :lol:

@Mark: Don’t forget that the PA’s AQI is only based on particulates, but your local WA air quality station uses Ozone too. As I understand AQI it will be driven by whichever of the two is higher. When I looked his afternoon the dominant pollutant in your area was ozone.

That’s cool. But they “our local agency” shouldn’t be writing off a sensor that does actually work. They seem just to be comparing it to theirs and if this sensor doesn’t match their readings, they seem to think its junk.

Agree 100%. I would really like to see the methodology and quantified results of their study.

Im replying to their email now with 2 pdf files showing it holds up really good to the big boy sensors. I’ll post their response.

Here’s the response I got today from our local clean air agency regarding the purple air sensor and how it stood up against other sensors. I tried posting the PDF file that they sent showing their report of the purple air sensor, but the file is too big so I upload the file to my site and the link is below.

Hey Mark,

Thanks for contacting us. Just got back to the office today and am happy to share with you what we have found regarding the Purple Air monitors. I have attached a report that summarizes our experience with Purple Air monitors at three of our sites this past winter/spring. Purple Air monitors use two laser particle counters, these sensors shine a laser and read the amount of light scattered by particles

The raw data from the Purple Airs, as shown by the AQ-SPEC field tests, is generally 1.3-1.6x higher in California. To get this number calculate 1/slope using the slope in the linear regression equations. We have found that here in Washington the Purple Airs are closer to 1.9x higher. This value will change based on location since the [b]particle type is different between California and Washington[/b].

Interesting :?

Im at a loss and not sure what to think other than according to them the sensor should be calibrated to your area before setting it up. Which would mean the purple air company so to speak would need too calibrate the sensor according to your area before shipping it.