update docstring of `emission_rate_per_aerosol_when_present` and `aerosol`
Changed to:
def emission_rate_per_aerosol_when_present(self) -> _VectorisedFloat:
"""
The emission rate of virions in the expired air per aerosol volume,
if the infected population is present, in (virion.cm^3)/(mL.h).
This method includes the diameter-independent variables of the emission rate.
It should not be a function of time.
"""
And
def aerosols(self):
"""
Total volume of aerosols expired per volume of exhaled air (mL/cm^3).
"""