Air Purifier Glossary: M-P

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Media - Medium

Filtering material designed to capture and retain pollutants.

MERV

"Minimum Efficiency Reporting Value," an efficiency rating system applied to furnace filters. Irrelevant to room air purifiers.

MCS

Acronym for Multiple Chemical Sensitivity.

Micrometer (µm)

Technical measuring parameter for small particles. Same as Micron, below.

Micron

A micron is a technically obsolete shorthand for Micrometer. Since "micron" is still widely used in the room air cleaner business, it is applied here.

One-millionth of a meter.
One-thousandth of a millimeter.
.0025 inch.

A human hair averages around 75 microns in diameter.

Mold Abatement

The process of removing mold from building interiors. Often done by professional contractors, mold removal is a difficult, expensive process.

Mold will always return unless moisture sources are controlled.

Mold Remediation

Same as Abatement, above.

Mold Spore

Molds reproduce by exhaling tiny seeds called spores. These can become airborne, and are always present in indoor and outdoor air. Where mold colonies flourish, high indoor concentrations can become a health threat.

Most Penetrating Particle Size (MPPS)

Another area of mass confusion. MPPS is the particle size which most easily goes through a filter. .3 microns is used in the HEPA standard, but this does not mean that HEPA filters cannot retain particles smaller than .3 micron, as widely cited.

"down to .3 micron" "as small as .3 micron" are incorrect descriptions of a true-HEPA filter.

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Negative Ion

An atom with more electrons than protons.

Negative ions attach to positively charged airborne particles, causing groups to form which are too heavy to remain airborne.

These fall to the floor - they are not retained or removed.

Negative ions were once marketed as having health benefits, until the FDA restricted their marketing to air cleaning.