That's actually a good question and has to do with the physics of respiration. When you inhale, you're creating negative pressure that pulls particles closest to you into your lungs, leaving a void that other particles fill as they randomly redistribute themselves. This causes aerosolized droplets to follow the path of least resistance around the mask, as if they are pulled, rather than landing against it. That's why real N95/100 masks require a proper fit: if there's even a sliver of space between the mask and face, inhaling will simply suck air in through that space instead of through the filter, which has a higher "resistance".
When you exhale, on the other hand, you create positive pressure which violently expels the droplets regardless of what's in the way. This creates droplets with high velocity and turbulent flows within the mask that prevent them from traveling a straight path through the mask and cause most of them to collide with the fabric.
Basically, once it's exhaled it's a hazard to anyone who doesn't have a properly fitted N95/100 mask (which requires specialized equipment, though it's relatively common)
Those guys who used to say 2+2=5 might have been on to something, but more correctly, it was probably 3 for fluid dynamics here.
I remember as an OTR driver the truckstop bathrooms I survived each day. The olfactory violence was palpable enough to feel it crawling through the mask and see it grinning as it coursed through what must have been an unusual ratio of gas to air. I'd think to myself in that sometimes surreal environment where photons seemed to sweat and stagger, that even an n95 was pointless, perhaps life itself. If rona be here, every particle is riding a pale horse in a hazmat suit. I'll always consider myself a permanent petri dish for that.
When you exhale, on the other hand, you create positive pressure which violently expels the droplets regardless of what's in the way. This creates droplets with high velocity and turbulent flows within the mask that prevent them from traveling a straight path through the mask and cause most of them to collide with the fabric.
Basically, once it's exhaled it's a hazard to anyone who doesn't have a properly fitted N95/100 mask (which requires specialized equipment, though it's relatively common)