According to ISO 8573-1, oil is the sum of all hydrocarbons – liquid and vaporous ones – starting from C₆ (from n-hexane).

It can be subdivided into the follwoing states of aggregation.

• liquid oil (measurement according to ISO 8573-2) and
• oil vapor (measurement according to ISO 8573-5).

Oil vapor is the sum of all gaseous hydrocarbons or organic compounds starting from n-hexane, which can again be subdivided into

	VOCs – «volatile organic compounds» C6 (n-hexane C6H14) up to C16 (n-hexadecane C16H34) and
	SVOCs – «semi-volatile organic compounds» C16 (> n-hexadecane) up to C22 (n-docosane C22H46),

or – to keep it short and simple – all volatile organic compounds from n-hexane up to n-docosane. Organic compounds less volatile than C₂₂ are unlikely to be in the gaseous phase but may be present and, if so, should be reported.

VVOCs – «very volatile organic compounds» C1 (methane CH4) to C6 (< n-hexane) do not belong to the oil content according to ISO 8573-1 . This exclusion absolutely makes sense since corresponding compounds could not be found in the vapor of compressor oils, investigated by headspace measurements.

If in general the sum of all VOCs or SVOCs shall be considered, this may also be expressed as TVOCs or TSVOCs, respectively – «total (semi) volatile organic compounds».

Thus, oil vapor in compressed air, according to the before mentioned definitions, not only consists of compounds from the “vaporized compressor oil” itself but also all corresponding compounds within the suction air of compressors, e.g.:

• pollutants in the ambient air,
  e.g. toluene, ethylbenzene, xylene, …..
• pollutants in the ambient air caused by traffic,
  e.g. vapors or ashes from fuel, kerosene, diesel, …..
• natural and synthetic flavors,
  e.g. essential oils, flavor of conifers (terpenes), citrus flavor (limonene), …..
• …

Oil vapor in compressed air is expected to be present in a range of <0,001 mg/m³ up to 10 mg/m³, without dedicated treatment typically 0,1 mg/m³ up to 1 mg/m³.