Condensed fog

Condensed fog is a junk item in Fallout 4 add-on, Far Harbor.

Characteristics
It can be used to create different sludge based chems.

Locations
Condensed fog can be found in the basins of the fog condenser machines. Far Harbor, Longfellow's cabin, the National Park Visitor's Center, Dalton Farm and Echo Lake Lumber has condensers.

It is implied that condensed fog is what is left over after the fog has been removed from a settlement. Most likely, it is just the collected "fog", once it has been condensed from a vapor into liquid form.