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Similar term(s): ppm.
A weight to weight ratio used to describe concentrations. Parts per million (ppm) is the number of units of mass of a contaminant per million units of total mass.
Source: GreenFacts
ppm (or ppmm) is used to measure the concentration of a contaminant in soils and sediments. In that case 1 ppm equals 1 mg of substance per kg of solid (mg/kg).
ppm (or ppmm) is also sometimes used to describe small concentrations in water, in which case 1 ppm is equivalent to 1 mg/l because a liter of water weighs approximately a 1000 g. This use of ppm tends to be phased out in favour of mg/l.
ppm (or ppmV) is often used to describe concentrations of contaminants in air (as a volume fraction). In this case the conversion of ppm to mg/m3 depends on the molecular weight of the contaminant.
For example, 1 ppm chlorine represents one part of chlorine in one million parts of air by weight, which is 1.45 mg/m3.
The ppm unit is mainly used in North America.
Source: GreenFacts
Concentration - Contaminant(s) - Environmental media
Español: Partes por millón
Français: Parties par million
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