Anyone suffering from wildfire smoke this week: You can make a really cheap air purifier by taping a HEPA filter (from the furnace section of a hardware store) to a box fan: https://www.youtube.com/watch?v=kH5APw_SLUU

I made one last summer, and it really helps. And it's cheap enough that you can make several if you need to clean the air in a larger space.

You might want to tape the filter to the back of the fan (instead of the front, as in the video), so it stays better.