Median aerodynamic diameter (MAD) is one of two parameters influencing the deposition of inhaled particles, the other being the

geometric standard deviation In probability theory and statistics, the geometric standard deviation (GSD) describes how spread out are a set of numbers whose preferred average is the geometric mean. For such data, it may be preferred to the more usual standard deviation. Not ...

of the particle size distribution. The MAD is the value of

aerodynamic diameter An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be generated from natural or human causes. The term ''aerosol'' commonly refers to the mixture of particulates in air, and not to the par ...

for which 50% of some quantity in a given

aerosol An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...

is associated with particles smaller than the MAD, and 50% of the quantity is associated with particles larger than the MAD. It simplifies the true distribution of aerodynamic diameters of a given aerosol as a single value. It is also used to describe those particle sizes for which deposition depends chiefly on inertial impaction and sedimentation.IAEA Safety Glossary
/ref>

Activity median aerodynamic diameter

In the context of

radiation protection Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposu ...

, activity median aerodynamic diameter (AMAD) is the MAD for the airborne activity in a given

Internal dosimetry Internal dosimetry is the science of internal ionising radiation dose assessment due to radionuclides incorporated inside the human body. Radionuclides deposited within a body will irradiate tissues and organs and give rise to committed dose unt ...

uses it as a means of simplifying the true distribution of aerodynamic diameters of a given aerosol.

Count median aerodynamic diameter

Count median aerodynamic diameter (CMAD)Lognormal conversion equations for common types of diameters
/ref> is only used rarely. Half of the particles (by count) of a given aerosol have the aerodynamic diameter smaller than the CMAD, and the other half larger. A similar quantity, count median (geometric) diameter (CMD) is more common.

Mass median aerodynamic diameter

Mass median aerodynamic diameter (MMAD) is the MAD for mass.

References

Nuclear safety and security Radioactive contamination {{Radioactivity-stub