Thanks very much for this suggestion. I bought one of them based on your comments (they can be bought through Lazada as well, which is what I did), and I am very satisfied with it. It is, as you say, a no-frills device. I consider it to be a very elegant solution to the air quality issue. After all, an air purifier is essentially a filter and a fan. I must say that it is quite noisy when it is turned up all the way, but it is fairly quiet on its mid-range setting. So I only turn it up all the way when I am out, and when I am home I keep it on half speed. It cost me around 1,800 baht including delivery, which is a fraction of what the other devices cost. And it uses the Xaomi filters, which are readily available. (Basically, it's a nicely designed fan on top of a Xaoimi filter.) Thanks again for the suggestion.