Germicidal UV could make airborne diseases as rare as those carried by water

No mention of ozone. The more directly dangerous 254nm UV light has the advantage that it doesn't create ozone.

Viruses and bacteria aren't the only bad things you don't want in your air. Ozone is thought to be a carcinogen in its own right and aggravate the health effects of particulate pollution. We want filtering and air circulation anyway, we don't want anything that makes it worse. The consumer electronics industry is all too willing to try to sell us things that make our problems worse, such as ultrasonic humidifiers, or ionizing air purifiers with special chambers for your aromatherapy oils, so it's best to be careful.

Could accumulate in an isolated room, but following normal building ventilation standards, really shouldn't be an issue as shown by Brenner in 2023: https://pubmed.ncbi.nlm.nih.gov/38037431/

article specificaly mentions rooms with poor ventilation. if you have proper ventilation, then you don't need this system in the first place, because you will get ouside air UV sterilised by the sun...

> things that make our problems worse, such as ultrasonic humidifiers, or ionizing air purifiers

What is bad about these?

Ultrasonic humidifiers require ridiculously clean water. Even regular distilled water is scarcely clean enough. You need to clean the water tank ridiculously well, ridiculously often. No one actually uses an ultrasonic humidifier like it's "supposed" to be used. When the water isn't industrially clean, everything dissolved in it is turned very efficiently into tiny particles. You'll get a fine white mineral dust everywhere.

Ionizing air purifiers make ozone and the makers claim either that it's a good thing or that it's too little to worry about. The first is wrong, the second is a bad sell because the thing it's supposed to be removing is also (by itself) not a big health risk on any single day; the health benefit from removing particles is likely eaten up by the negative health effects of the ozone. You can clean air without ionization, so why? As far as I can tell, it's a pure marketing gimmick, the need to seem high-tech outweighs the actual utility of the thing. (That's also probably why ultrasonic humidifiers are popular, you can see the fog)