In 2011, Jeffrey E. Terrell, M.D. of the University of Michigan demonstrated the effectiveness of using a cheap box fan with furnace filter to improve indoor air quality. In his video he reduces particulate matter in a room by 90% using nothing more than a box-fan and filter.
The recent poor air quality in the bay area has caused many to wonder if this really works. So I've run a replication of that experiment.
A simple fan and MERV >=12 filter can significantly reduce indoor particulate matter by 90% in small tightly-sealed room. Compared to having no filter at all, this is a dramatic improvement.
The principal downside of this filter compared to a more expensive filter is that a box-fan filter will have a hard time keeping up with polluted air leaking in. A door being open for just a few seconds will very quickly reduce the air quality significantly. With normal traffic in and out of room, the box fan may never bring the air to a "good" quality level.
I accidentally left the window cracked open for the AustinAir trial. Darn.