Thanks for the comment! I get the impression that people in Asia (well, I only have limited experience of Shanghai and various cities in south-west Japan) are

Thanks for the comment! I get the impression that people in Asia (well, I only have limited experience of Shanghai and various cities in south-west Japan) are quite aware. I saw a lot of air purifiers (for instance in hotels) in Japan. And in Shanghai they showed PM2.5 predictions as part of the weather forecast. And I noticed that a lot of people know about formaldehyde (a specific chemical / VOC that can be problematic in indoor air). Although, an old guy I met in Shanghai told me "I don't really like air purifiers, you have to clean them all the time, I rather just open the window" ;) But in Germany where I live, or Sweden where I'm from, few people I know ever thought about this. I suppose the air is just too good for people to bother thinking about it. But as observed in https://sciencenordic.com/chemistry-denmark-environment/our-homes-are-filled-with-soot-nanoparticles-from-candle-flames/1390377 https://sciencenordic.com/chemistry-denmark-environment/our-... it might still be worth spending a few thoughts about it: “Our indoor UFP levels are close to those in Beijing apartments but the pollution sources are completely reversed,” says Bekö, explaining that 70 percent of all UFPs in Beijing are from outdoor sources while in Denmark it’s the other way around. (they looked at indoor pollution in Copenhagen, and UFP stands for ultrafine particles (here defined as "Ultrafine particles (UFPs) are particles with a diameter of less than 100 nanometres.", so kind of PM0.1)) I would be really happy if I could create low-cost air purifiers or DIY solutions (I have quite good success with a Pringles can made an air purifier to reduce PM2.5 ;) ). Not sure if that will happen, but, luckily others do it already: https://smartairfilters.com/ https://smartairfilters.com/ IKEA also have an air purifying curtain (https://www.ikea.com/us/en/rooms/living-room/how-to/purify-your-air-with-gunrid-curtains-pubc73769b0 https://www.ikea.com/us/en/rooms/living-room/how-to/purify-y...) at a decent price - but don't know how good it is and it won't work for particles, but just chemicals/gases. They recently also released an air purifier https://newsroom.inter.ikea.com/news/ikea-committed-to-make-clean-indoor-air-accessible-for-the-many-by-launching-new-air-purifier/s/dbb71fb7-97f5-484e-a496-a61b45abe983 https://newsroom.inter.ikea.com/news/ikea-committed-to-make-... which is fairly cheap (49.99EUR/~60USD), especially the filter (HEPA H12) sticks out a bit to me just costing 4.99EUR (6USD) in Germany. Spontaneously, SmartAirFilters feels like a better choice for people that live where they sell it cheaply though. You are still right of course, more money can give better stuff, and both IKEA and SmartAirFilters might still be way too expensive for many.