descriptor of an individual, organ, or tissue). For example: mg of particles deposited in the subject; μg of particles deposited in the respiratory tract; μg of particles in the tracheobronchial region; or number of viable organisms in the alveolar spaces of the lung.

geometric standarddeviation (GSD) A measure of dispersion for a log-normal distribution that is analogous to the standard deviation for a normal distribution. The GSD is the ratio of the 84.13 percentile to the 50 percentile.

mass median aerodynamicdiameter (MMAD) For aerosols, the MMAD equals the particle diameter at which particles larger than the MMAD contribute half of the collected mass and particles smaller than the MMAD contribute the other half.

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