I have the Zen sensor for measuring my indoor air quality. My understanding is that the sensors overestimate PM2.5 and thus AQI values, especially at higher concentrations, and that is why the conversion factors exist.
So, when the AQI is roughly displayed via the color changing LEDs (i.e. green = good, yellow = moderate, etc.) is it using one of the conversion factors (e.g. “US EPA”) or is there no conversion factor applied (equivalent on the map of “Apply conversion: No”)?
Much appreciated
Hi @moeck602, the LEDs on PurpleAir devices display the US EPA PM2.5 AQI with no conversion factor applied. We hope to include a feature in the future to change the AQI scale and conversion factor it displays.
This would be so useful for users outside the US who have different AQ indices!
Hi @Ethan, can you please expand on this? It’s my understanding that the purple air data needs the US EPA PM2.5 AQI conversion factor to more accurately reflect concentrations that regulatory monitors read (especially in high concs). You said no conversion factor is applied but they display the US EPA PM2.5 AQI. Is the Zen light displaying the raw AQI Purple Air data or is it displaying the Purple Air data with the US EPA conversion factor applied? Thank you!
Hi @missoulaair
The US EPA AQI and the US EPA conversion for PurpleAir data are two different things. The AQI is a scale that is meant to convey health recommendations at different levels of air quality. The scale goes from 0 to 300+ and has associated color changes at set breakpoints (0-50, 50-100, etc.). This is raw PA data that has just been converted into the AQI scale.
The US EPA conversion factor, on the other hand, actually changes the data. In cases of heavy wildfire smoke, PurpleAir sensor have a tendency to overestimate particulate levels. The US EPA conversion was developed to curb that overestimation.
The LEDs on the Zen, Touch, and Flex reflect the US EPA AQI and its associated breakpoints, but they do not use the EPA conversion.