What are the pm2.5 levels used as breakpoints on Purple Map?

General
1

I have a Flex outside and I want to be sure I understand the pm2.5 levels being used to compute the US EPA AQI I see on the map for my sensor.

I am using real-time and applying the US EPA “conversion”.

Also, I am not sure which item(s) in the LAN JSON data is being used.

Can someone please help confirm all this? Thanks!

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2

I believe that the AQI reported in the local json from my Flex is NOT EQA corrected.But when I show the Real time, US EPA AQI layer on the map and ensure that the EPA correction is NOT APPLIED, the map’s AQI does not match that shown in the json. For example, right this moment, the map shows 53 while the A sensor shows 38 and the B 46.

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I understand that there is likely some processing/averaging between the A and B sensors in my Flex but this cannot account for the difference. I understand that the breakpoints for the US EPA PM2.5 AQI have been revised at some point and I suspect that these changes likely account for the difference in the readings.

Is this correct? And if so, is there a firmware update to the Flex that will bring the two data sources into congruence?

How to explain significant difference between Smoggie and Purple Flex Humidity?
3

Hi Dave,

Thanks for the post! Addressing each question:

  1. To view PM2.5 concentrations, change the data layer from “US EPA PM2.5 (AQI)” to “Raw PM2.5 (µg/m³).” You can keep the US EPA conversion applied if desired. You can hover over the tooltip next to that setting for more information. Also, you can see the PM2.5 breakpoints in the bottom left of the map.

  2. Could you clarify what you mean by “LAN JSON data” and the items it contains? Are you referring to the local sensor page or the sensor’s JSON endpoint? The JSON endpoint provides several particulate-matter fields, including pm2_5_atm and pm2_5_cf_1. You can read about these in our JSON documentation. Feel free to read about the differences between the formulas used as well. The local AQI values—both in the JSON endpoint and on the sensor’s local page—are calculated using pm2_5_atm.

Happy to clarify further if needed.

4

Thanks Shawn,

  1. I had not noticed the bottom left showing anything except AQI. But looking more closely now I do see that.
  2. I mean the values shown at http://PURPLE_LAN_IP/json?live=true so good to know that the atm value is what is used in computing US EPQ AQI results for outdoor sensors like mine.
  3. I do remain a bit confused by the values shown in the json: pm2.5_aqi and pm2.5_aqi_b. These are documented as “US EPA PM2.5 AQI”. This implies there is an onboard computation being performed as they seem to be filled even if I block my Purple from internet at my router. It would seem that any EPQ AQI computation will require the breakpoints to be known. My sensor shows “V7.04 3.0+OPENLOG+NO-DISK+RV3028+BME68X+PMSX003-A+PMSX003-B” so is it using the most recently adopted breakpoints? And does it apply any “correction/conversion”? Is there documentation on how these values are computed?

Thanks so much!