That was my thought which is one reason I mentioned having the air pump and filter in my earlier post. The greenhouse is really an enclosure to reduce direct contamination while topside servicing the "air handler". It also serves to protect the solar panels while allowing them to continue working.

I'm a bit surprised the bunker didn't have a filter of some sort when built. They have a contamination wash-down area outside the main room of the bunker, so fallout was considered in their planning, which makes the lack of an air filter puzzling.