Humidity effect on PurpleAir PA-II sensor

Humidity affects the PA-II sensor, but is there a breakoff point where it is most affected? For example, does the PM 2.5 concentrations it measures deviate significantly from federally regulated monitors at a specific or range of humidity?

Hi @DTapia,

From our experience, we have seen that humidity does not have much of an effect on particulate matter measurements. In the example below, it appears that the spikes in the AQI do not have a strong correlation with the humidity level.

While on the PurpleAir map, we recommend switching from the humidity data layer to your desired AQI data layer to compare. Several very humid regions show similar AQI values to regions with low humidity.

Studies have shown that humidity has an effect on the readings, but it is likely minor. The US EPA conversion factor on the PurpleAir map uses relative humidity in its formula. More information on this conversion factor is available in the US EPA’s nationwide study.

Screen Shot 2022-10-12 at 3.01.36 PM
Screen Shot 2022-10-12 at 3.01.55 PM