White noise machines are widely used for sound masking, increasing privacy in offices and helping people sleep. The classic approach is a fan in a box, though in the past ten years people have mostly switched over to electronic ones. But a fan is really a great approach; you just need to put it to better use: have the fan clean the air.

Instead of spinning a fan in free air to make noise, you can have it pull air through a filter. A small purifier sounds a lot like a classic noise machine, is only a bit larger and more expensive, and removes smoke and infectious particles from the air. For example, here's a $47 purifier with a 6.5" diameter, cleaning 34 cubic feet of air per minute ("CADR") at 45dB. For most circumstances where someone would use a white noise machine, this kind of small purifier is all-around better.

Now, 34 CFM is not very much air cleaning. I usually run an AirFanta 3Pro and it cleans ~6x more air for the same amount of noise, or ~12x more air with much more noise (~56dB). On the other hand it's more expensive ($165) and bulkier (12.6" square), and arguably uglier.

Still, even a 34 CFM purifier helps a lot with smoke. If you have a 10ft square room with an 8ft ceiling and a reasonably typical 0.5 air changes per hour through leakage from outdoors, this small purifier will cut particulate levels to 16% of the outdoor level. In AQI terms (not linear) this is like going from AQI 200 to 72 or AQI 100 to 31.