https://www2.purpleair.com/products/list To me they seem like a company who sells products and their map is secondary. They even advertise their stuff on the map itself.

“PurpleAir is built on the ideal of sharing data and by doing this, empowering individuals to effect change. All public PurpleAir data is available to download under various licenses from private, not for profit use to educational and commercial use. The common element between these uses is to share attribution.” (https://community.purpleair.com/t/about-the-data-category/70) – berdasarkan itu mungkin 4/5 blok adalah tepat. Nampaknya tiada penjejak atau iklan di tapak.