https://www2.purpleair.com/products/list A me sembrano un'azienda che vende prodotti e la loro mappa è secondaria. Pubblicizzano persino le loro cose sulla mappa stessa.

“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) – based on that maybe 4/5 blocks would be accurate. There do not seem to be any trackers or advertisements on the site.