[tim333]

There's a fair network in London https://www.londonair.org.uk/london/asp/PublicEpisodes.asp

The pollution seems fairly spread out so I'm not sure how much having higher resolution would help. I think those are government/council owned.

I was toying with a commercial service where householders could pay a bit for measurements on their homes and could try to counter bad stuff with filters and the like. Not quite sure about the economics - the cost of sensors seems to be dropping rapidly. The government monitoring stations I think are like $25k but there's cheaper stuff out there.