Aircraft cabin air quality  has generated considerable cabin crew and passengers' concern and controversy in the past years, with oil contamination by bleed air being one of the subjects.

Outline of bleed air system on a jet aircraft. (courtesy of Capt. Tristan Loraine).

Well, no more guessing.

Real time continuous monitoring of aircraft cabin air for oil free compliance is now possible with the Oil Supervisor.
 
The system has additional options to also monitor dew point, CO, CO2, etc.