Hi again, njb, and thanks for your response. I did not mean to imply you weren't familiar with humidifiers, I am sorry if you got that impression. The published article (from asthma.net), included good information about air purifiers so I felt you would want to read that part of the article.
There is a wealth of information on the internet which focuses on air purifiers. In fact, if you were to do your own search, using the key words 'air purifiers UL listed', I think you will find most of the information you may need to make a good decision for purchase. You will find in the search, there are several reviews of the top purifiers on the market. It also includes listings of units which are, in fact, UL approved. That may be a good place to start.
Sadly, I do not work with these devices at all. I would be doing the same thing you are to try to find the one that would be best suited for me.
Please do check back and let us know how you do in your search. We all can benefit from the research you do.
Good luck!
Leon (site moderator COPD.net)