Macropores: The pores in activated carbon which have diameters exceeding 1000 Angstrom units. An Angstrom unit is 1 x 10^-8 meters.

Magnehelic: Registered trade name for a diaphragm activated, dial guage for measuring resistance.

Make-up Air: Air that is supplied to a building to replace the air that has been removed by an exaust system.

Manometer: Instrument for measuring pressure of gases and vapors. Gas pressure is balanced against a column of liquid in a U-shaped tube.

Media Area: Gross: The total area of media used in the production of a filter. Net effective: The measure of usable media in a filter.

Median Efficiency: In a series of effeciency tests, the median efficiency is the one which has an equal number of test results higher and lower than it.

Membrane Filter: A solid continuous material (film) in which microscopic pores of controlled size are created by a variety of methods.

Meter (Metre): An SI linear measurement equal to 39.37 inches. Metre is the prefered spelling.

Microbe: A microscopic single cell organism.

Micron: One millionth of a meter. A micron is more correctly known as a micrometre (µm).

Micropores: Pores in activated carbon ranging in diameter from 10 to 1000 angstrom units. An angstrom unit is 1 ten-billionth of a metre.

Mist: An aerosol formed by the dispersion of a liquid into very fine particles.

Modacrylic (Fibre): A manufactured fiber in which the fiber-forming substance is any long-chain synthetic polymer composed of less than 85% but at least 35% by weight of acrylontrile units [-CH₂CH(CN)-]. Other chemicals such as vinyl chloride are incorporated as modifiers.

Mold: A fungus which grows on damp decaying organic matter. It is characterized by a fuzzy mat surface.

Molecular Weight: The sum of the individual atomic weights of the atoms which make up a molecule.

Molecule: The smallest portion of an element or compund which retains the identity and characteristics of the element or compound.

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