A volatile organic compound (VOC) is a portion of matter consisting of organic compounds that is capable of producing photochemical oxidants by reactions with nitrogen oxides in the presence of sunlight. Hence it can act as an air pollutant.
A portion of matter is an aggregate of material entities that have a state of matter.
Editor note:
Portions of matter describe mass nouns like e.g. water, air and fuel. Mass nouns are uncountable, but portions of these can be quantified, like 1 glass of water, 1 m³ of air or 1 barrel of fuel. For further explanation please refer to: https://github.com/OpenEnergyPlatform/ontology/wiki/Explanation-on-mass-nouns
Ontology