Air Quality Sensor

Here is another article on PurpleAir that was just published yesterday

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Why Purple Air and Air Now may have different values:

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Thinking of Purple Air or Plume Labs Flow. Not sure if the Flow 2 is worth $70 more than the Flow 1, main difference seems to be that Flow 2 also measure PM1, in addition both Flow 1&2 measuring PM2.5, PM10, NO2, VOCs.

I had the flow 1 before the flow 2. In my opinion it wasn’t worth the upgrade. It’s battery operated, therefore mobile, but lasts only a day, so basically it is always in the charger. At some point the battery will give up. I would have preferred if it used wifi for 24/7 operation. Currently it only transmits data when my phone is in range and bluetooth is on (which most of the time it isn’t). Other than that, it is working fine

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Liking the Flow, or Flow 2, since it also Measures NO2.

Excellent new online map available at https://fire.airnow.gov/ lets you drill down visually, and includes permanent, temporary, and low-cost (Purple Air etc.) sensors.

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I posted earlier about the California Wildfires and Air Quality. Got some good suggestions on Air Quality sensors. Purchased the Plume Labs Flow 2.

But I’m confused. It does not appear values such at PM 2.5 are equivalent on Flow 2 vs. what Purple Air publishes online. And the AQI numbers seem to be calculated differently.

Help, I just want to check my local Air Quality, and compare to what’s online.

Thanks for your thoughts.

long discussion in Air Quality Sensor and a link to a page that explains the differences…

Here near Tacoma we just went from AQI of 20 to AQI of 300 as a wall of smoke from the central Washington fires hit us. You could see it coming, the Cascades and MtRainier disappeared and we couldn’t even see the landing lights of the planes going in to SeaTac Airport. Amazing.

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there are many (too many) different AQIs in the world. Plume uses their own.


What you can see in the last graph on that page is that the none of the AQI is linear depend on the concentration of pm2.5.
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For example, there is a sharp bend in the orange (USA(24)) curve at 150 and again at 200. The Plume index also isn’t linear. If you scroll down on that page there is a little table that give you the values of when there is a bend in the Plume curve. You could use that, to get from the plume values to the concentration of pm2.5.

Or you could use the download data in your app, and you get the data that does include the concentrations.

I wish they would also display the concentration in ug/m3 (please do bug them about that… more than once!).

btw if you install the Plume labs Air Quality App(beta) you can select the USA aqi in the settings. but that doesn’t show your own device

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Isn’t PM2.5 equal to PM2.5?
Right now the Purple Air devices near me read 93, 92, 99 for PM2.5. The devices are all about 2 miles away.
But my Plume Labs Flow 2 reads 4 for PM2.5. Flow 2 is outside in the backyard.

And the Flow 2 AIR app say it’s 45 for PM 2.5. for my street. (The AIR app is different from my Flow 2 device app, anyone can use the Plume Labs AIR app. )

Crazyland between SeaTac airport and Tacoma - wind blew in a wall of smoke, humidity at 15%, and check out this AQI graph from the last 2 hours.

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Now winds 30+ ‘of course’ on the day guys are supposed to work on the roof, but at least it’s not trash day which is when we normally get the winds :slight_smile:

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Here is a link the the whole white paper that Sunny referenced. https://plumelabs.zendesk.com/hc/en-us/article_attachments/360039609054/Article_Plume_Index_.pdf

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that can’t be right. A value of 4 for pm2.5 in flow 2 is about 2 ug/m3.
The value of 90 you see in pleasanton is the usa AQI. You have to go to ug/m3 to compare. 90 boils down to about 30 ug/m3, but that is still way off. Contact support I would say. Or give it a few more days to settle in.

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Well, it just jumped a LOT, from PM 2.5 of 4, to values much higher for all the PMs.
Before I could write them down, all the PMs are back down low.

Give it a week to calibrate itself. (If I remember correctly it mentions that in the manual)

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(if you click on the values in the flow app, you get a graph and you can see the values by scrolling the cursor along the time axis)

You might have figured that out by now but the way AQI works is that any raw data like PM2.5 or VOC or NO2 value is non-uniformly scaled (that’s what is in the graph above). but something like NO2 has different health impacts then PM2.5, that’s why it uses a different scale. So each parameter is converted to some AQI value on its own. The general AQI is just the maximum of those converted values. For example, a NO2 aqi of 20, a pm2.5 aqi of 40 and an VOC aqi of 35 would result in a general AQI of 40 (the max of 40 and 35 and 20).
Many authorities have their own idea of how unhealthy NO2 or PM2.5 is, that’s why there are so many different AQIs.

I read that about letting NO2 settle down, but no sure it applies to PM values and Flow 2. I almost got ahold of Plume Labs live today, but it’s challenging, as they are on Paris time.

And OMG, this AQ stuff is a bit hard to compare, with so many different interpretations of AQ.

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I just found this website where you can convert USA AQI values to concentrations https://www.airnow.gov/aqi/aqi-calculator/

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