I have recently started to measure the fine dust in the air with two rather old “PurpleAir Flex Air Quality Monitor”-sensors:
The local measuring stations with professional sensors give a value of 5-15. The purple air sensor give a value 40-70. I have thought of two possible problems:
Have you got an idea where the problem is?
Make sure you define the units/options you are looking at in the map. The default is AQI (Air Quality index).
5-15 ug/m3 of PM2.5 is about 50 - 75 AQI.
Thank you for the hint. Do you mean this option?:“Tasmanian PM2.5 scale (ug/m^3)”
When I apply this the values are still a bit to high but now much lower.
Who is your local air quality authority? And you have PA-II Classic sensors, not Flex
You might try setting the map as follows, if you are looking for PM2.5 in μg/m³ to compare with locally calibrated equipment:
- Data layer: Raw PM2.5
- Apply conversion: US EPA
It may be difficult to get close agreement if your air pollutants require specialized correction factors. US EPA’s adjustment was developed with wood smoke as a primary pollutant.
You might also try performing the sensor maintenance described here, especially if the A and B sensors are wildly different: