PM2.5 masks can prevent viruses, PM2.5 masks generally refers to be able to completely block <2.5μm particle size particles, droplets are the main new coronavirus transmission mode, droplets the vast majority of >5μm, so for completely block <2.5μm particle size particles of the masks can be prevented almost all droplets. Ordinary gauze masks can not play a role in defending PM2.5 particles, medical ordinary masks can not prevent haze but can prevent viruses, that is, to prevent the spread of droplets.N95 masks are PM2.5 defense better masks, medical grade masks can defend almost all droplet transmission. Source: Dr. Yurai