I use these with a box fan to bring cool night air into my apartment, while filtering out the smoke particles from the wildfire smoke being blown into my area.

They come in a number of sizes that allow you to open a window to a minimum, and keep the worst of the air pollution out.  I use a 20x20 and a 20x25 to cover a 20x45 opening.

Once, overnight, the air quality unexpectedly went from mod to unhealthy, and my apartment was filled with smoke.  Ran my fan with the filter after closing all the windows, and it cleared it up.

I advise all my co-workers to use this method, and filters, to protect their lung health. [This review was collected as part of a promotion.]