parts per million

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parts per million (PPM, ppm)

the ratio of the amount of one substance to the amount of another, expressed as a unit of solute dissolved in one million units of solution. It denotes the number of units of one substance relative to one million units of another substance. It may be further expressed in terms of mass-to-mass, volume-to-volume, or another relationship of units of measure.

parts per million

(părts),

PPM; ppm

The concentration of a solute in a liquid or gas. For example, a pollutant such as soot may be said to be present in air at a level of 50 parts per million (parts of air). The units also may be expressed as weight of one substance to the weight of another or the volume of a fluid in the volume of another.

parts per million

mg/kg or ml/l; see ppm.