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PROFESSOR: So having
established the importance

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of airborne transmission in
the spreading of COVID-19

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specifically, and more
generally in the spreading

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of respiratory
pathogens, let's proceed

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to analyze airborne transmission
in a well-mixed room.

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So we're thinking
of a situation where

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a certain number of people
are sharing an indoor space.

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And the air in that room
is well-mixed enough

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that as pathogen-containing
droplets are released

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from the breath of one
person, it's quickly spread

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throughout the whole room.

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And by the time someone
else breathes it,

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they're essentially exposed
to the average concentration of

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pathogen in the air
after accounting

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for such effects as the
settling, the evaporation,

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the ventilation, filtration,
and other effects,

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but still at the level
of a well-mixed space.