Last week I flew on a BA A320 and A319. About 0.25 and 0.75 of the way down the cabin there is a small vent located in the dividing wall between two of the overhead racks. On the 319, for example, there is one around row 16. They were definitely present on the right-hand-side rack (facing forward), I didn’t check the left side.
At this location, as well as the vent, there is a wider than normal gap between the overhead rack doors and ‘not a permitted location for cabin divider’ signage. There seemed to be a slight outflow of air from the vent.
I have noticed the same thing on BA’s CFM A320s, and on BD and EI A320 family aircraft.
I assume this is where the various gases to keep us docile are pumped in – am I correct?
Seriously though, what is it actually for?