[Havoc]

PM2.5 is quite challenging to miniaturize for a mobile & compact form factor like this - you need a fan of some sort.

[formerly_proven]

Not necessarily: https://www.bosch-sensortec.com/products/environmental-senso... (fits in an USB key: https://www2.purpleair.com/products/purpleair-pixel)

[Havoc]

Oh that's fun. Been meaning to get PM2.5 for my place but the one I've got has a whiny fan

Thanks for linking