Hello,
I have been comparing different data layers on the PurpleAir map and noticed something that I would like to understand better.
When I look at real-time readings for the same sensor at the same moment, or “1-week / averaging period”, variables that display µg/m³ values (such as Tasmania, Canada, British Columbia and Raw PM2.5) all show the same reading (for example, 4 µg/m³). However, the Brazilian PM2.5 (µg/m³) layer consistently shows a higher value for the same sensor at the same time (for example, 6 µg/m³).
My question is: why does the Brazilian PM2.5 layer produce a different (higher) µg/m³ numeric value compared to other layers that also report in µg/m³?
I understand that different AQI layers use different breakpoints to classify air quality categories, but this seems to be a difference in the actual concentration value displayed, not just in how the value is categorized. Is the Brazilian layer applying a different conversion formula, a different CF (correction factor), or using a different PM2.5 field (such as cf=1 vs ATM) compared to the other µg/m³ layers?
Any clarification on the methodology behind this layer would be greatly appreciated.
Thank you.