A Particle mass analyser (PMA) is an instrument for classifying

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 ...

particles according to their mass-to-charge ratio using opposing

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

and

centrifugal force Centrifugal force is a fictitious force in Newtonian mechanics (also called an "inertial" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It appears to be directed radially away from the axi ...

s. This allows the classifier to select particles of a specified mass-to-charge ratio independent of particle shape. It one of the three types of monodisperse aerosol classifier, the others being the differential mobility analyser (DMA, for

electrical mobility Electrical mobility is the ability of charged particles (such as electrons or protons) to move through a medium in response to an electric field that is pulling them. The separation of ions according to their mobility in gas phase is called ion ...

size), and the

aerodynamic aerosol classifier An aerodynamic aerosol classifier (AAC) is an embodiment of a measurement technique for classifying aerosol particles according to their aerodynamic diameters. The technique allows online size classification of particles without requiring them to b ...

(AAC, for relaxation time, or

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 ...

). The corresponding three quantities are related by the expression ''τ'' = ''mB'', where ''τ'' is relaxation time, ''m'' is mass and ''B'' is mobility. Further work improved the technique by engineering the centrifugal force to match the electrostatic force across the whole classification region, thus increasing the throughput.

References

{{Reflist Measuring instruments Scientific instruments Scientific techniques Aerosol measurement