You might find https://jamanetwork.com/journals/jama/fullarticle/2763852 of interest in the discussions as well. Both related to the question of just how fast the droplets might dry in air and how well the masks might work in terms of protecting others.
As I read the bit we might need to consider the protection as asymmetric—keeps more out than, possible, in even without considering an exhaust valve.
It looks like an exhaust port that incorporated a heat sink and moisture separator is plausibly more effective at preventing pathogen escape, but it has to be high-volume enough to pass a sneeze without it blowing out along the face.
You might find https://jamanetwork.com/journals/jama/fullarticle/2763852 of interest in the discussions as well. Both related to the question of just how fast the droplets might dry in air and how well the masks might work in terms of protecting others.
As I read the bit we might need to consider the protection as asymmetric—keeps more out than, possible, in even without considering an exhaust valve.
It looks like an exhaust port that incorporated a heat sink and moisture separator is plausibly more effective at preventing pathogen escape, but it has to be high-volume enough to pass a sneeze without it blowing out along the face.