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> Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. That statement is logically hard to sw

• tzs 6y ago
  There are at least 5 mechanisms by which filters can filter out particles. Four of them are explained in this document [1]. Some filter materials also trap particles electrostatically. but I have no idea if that is relevant for masks filtering viruses. For at least some of the four mechanisms covered in that document (inertial impaction, diffusion, and interception) it seems plausible that once you have a particle caught that way any other similar particle that otherwise might have been caught at the same spot the same way might either bounce off the first particle or dislodge the first particle. This could eventually reach a steady state where as many particles are coming out as are coming in the other side, just with the individual particles being delayed. If the particles are small enough so that sieving isn't significant, then there would probably be little change in the ability of air molecules to get through regardless of whether or not the filter is in the early, nearly clean stage or is in the steady state late stage where there are plenty of particles trapped. [1] http://donaldsonaerospace-defense.com/library/files/documents/pdfs/042665.pdf http://donaldsonaerospace-defense.com/library/files/document...