During the pandemic I took 2 clear tubes, and put PM meters in them. I used tape to tape various COVID masks between them and to seal them kind of air tight. Th

During the pandemic I took 2 clear tubes, and put PM meters in them. I used tape to tape various COVID masks between them and to seal them kind of air tight. Then I placed computer fans at each end to push air through. I learned that the best filters I could get only worked down to 2.5 microns.