[rofo1]

That depends on your location. I've built something similar to this tool that is discussed here and I've tested in multiple locations.

For example, Vienna air was so clean (<= 10 pm10 ug/m^3), that you don't need any purifiers or anything like that.

[MartinMond]

If you think Vienna's air is clean, you didn't measure during winter and/or during an inversion. You absolutely need air purifiers.