It’s hard to pin down a threshold of a specific time of exposure because it depends on the minimum infectious dose, which varies widely among people, at least for lots of diseases. Also, the rate of shedding varies widely based on the progression of the disease, whether the person is talking, how far away the person is, etc. Furthermore, the HVAC system causes additional variation. So I think when you add all these uncertainties, a 16 times reduction in emission/​inhalation would correspond to very roughly a 16 times reduction in infection, but I would be very interested to see if someone has run the math on this.
It’s hard to pin down a threshold of a specific time of exposure because it depends on the minimum infectious dose, which varies widely among people, at least for lots of diseases. Also, the rate of shedding varies widely based on the progression of the disease, whether the person is talking, how far away the person is, etc. Furthermore, the HVAC system causes additional variation. So I think when you add all these uncertainties, a 16 times reduction in emission/​inhalation would correspond to very roughly a 16 times reduction in infection, but I would be very interested to see if someone has run the math on this.