What measure is used to identify the particle diameter, which corresponds to the most typical settling behavior of an aerosol?

a. Mean mass velocity coefficient (MMVC)
b. Logarithmic standard diameter (LSD)
c. Mean mass aerodynamic diameter (MMAD)
d. Geometric standard deviation (GSD)

ANS: C
Because medical aerosols contain particles of many different sizes (are heterodisperse), the aver-age particle size is expressed with a measure of central tendency, such as MMAD for cascade impaction or volume median diameter (VMD) for laser diffraction.