The west coast now has some of the worst air quality in the world caused by the forest fires. Much of this air pollution is particulates and can be filtered out. There has been research on DIY filters by residents of Beijing. Beijing DIY filter. Ideally you will have a device for measuring and test the air quality improvement with your filter. The brand name to look for is Dylos; this can also be DIYed using cheap Arduino or Raspberry pi computers. Don’t let the lack of a air quality monitor stop you.
The simplest filter can work pretty well:
take a 20”x20” box fan;
tape a 20”x20” furnace filter to the fan;
use a MERV 13 filter if available (the higher the number the better the filtration), but use what you can get.
This will work best for cleaning the air in a small single room with closed windows. I would do a better job of taping the filter to the fan than the picture; the goal is to have all the air moved by the fan to go through the filter. From what I’ve read, thicker filters put less load on the fan so the fan will last longer and you can run it at a lower speed; 4” is recommended, but 1” thick should work and is much easier to find. You can use any fan you have if you can jury rig something to ensure that almost all the air pushed by the fan goes through the fan.
There are commercial air cleaners and they work ok, but they are a lot more expensive and the replacement filters are expensive. When I lived next door to a halfway house for addicts (20 women who smoked constantly), I was having constant asthma attacks. Using the largest Honeywell air cleaner that Home Depot sold , I was able to survive in my smallest bedroom. It was like living inside a vacuum cleaner, but it worked. The goal is to stay as healthy as possible in this emergency.
wirecutter diy filter.
More detailed DIY filter article.
I have not tried these filters, but here are some examples:
amazon filter
home depot filter
example of Home Depot box fan.
Using MERV less than 13 will work, but higher merv numbers filter better.
I use a commercial air cleaner when I need one, not a DIY, but these should work. Similar things have been used by people in Beijing and they find that the reduction in particulates can be as good or better than commercial units.
Of course, an alternative is to always wear a good mask such as an N95 mask or better; they are hard to find because of the virus.