Parts Per Million (ppm)

The English expression parts per million (ppm, literally translated as “parts every million”) is used in science and technology to refer to the millionth part (10-6) − similar to percent for the hundredth part (10-2). The problem is the different uses in concentration specifications as a volume, mass or particle concentration measure. In chemistry ppm is used for concentrations of aqueous solutions of dissolved substances. The specification of 1 ppm means that one gram of a substance is contained in a million grams of the solution or mixture.