Not everyone has neighbors, or neighbors who spray weird stuff, I could see how that would be problematic though if you did. You bring up a good point about running air purifiers and/or filtration on intake air, I bet that could improve things significantly.
I think "clean" is a subjective term, the idea of bug shit,(not that I grow buggy plants) or pine needles on my buds doesn't bother me near as much as the idea of human dander, dust, or zipper threads, but to each their own. That's the great thing about growing your own, you don't have to rely on anyone else's idea of what is "clean".
It sounds like you really care about the cleanliness of your pot. You probably grow some amazing, clean, weed, I'd love to try it. Wish you could try mine.
I should change my previous statement from, "Indoor pot is much dirtier than outdoor.", to, A lot of indoor pot is much dirtier than outdoor pot.