Ppm 18 : Parts per million; a unit for measuring the concentration of a gas or vapour in air; parts (by volume) of the gas or vapour in a million parts of air. Concentration of a particular substance in a liquid or solid
The Association of Petrochemicals Producers in Europe (APPE), The European petrochemical industry, Glossary of Terms on Chemical Safety for Use in IPCS Publications, van Nieuwenhuyse, Brussels 2006. http://www.petrochemistry.eu/glossary.html, (Petrochem Ind - Brit) {473}