## Concept information

This concept has been deprecated.

### Preferred term

ratio

### Definition

- In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are ppm (parts-per-million, 10–6), ppb (parts-per-billion, 10–9), ppt (parts-per-trillion, 10–12) and ppq (parts-per-quadrillion, 10-15).

### Broader concept

### Creator

- herbert.schentz@umweltbundesamt.at

### URI

http://vocabs.lter-europe.net/EnvThes/EUUnits_007

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