Trafic - oil drip from underside open-ended hose

Hi



Could somebody please explain to me what the open-ended rubber hose is on the underside of my Renault Trafic (DCI) bonnet?



This vertical hose is located below the engine, and has been dripping a bit of oil...not a lot, but enough to mark my drive.



What is the likely reason for it to drip oil?



many thanks