From the Super Mario Wiki
Purple Bombers are ghosts found in Luigi's Mansion. Purple Bombers are purple colored Ceiling Surprises and are usually found in the same places as them, but appear more often in later areas. One major difference between Ceiling Surprises and Purple Bombers is that, while Ceiling Surprises simply tend to be annoying, Purple Bombers can attack with dropping a bomb. Purple Bombers have zero Heart Points and can be sucked up without effort. It is easier for the player if they point the nozzle up to suck this ghost in, or they can just spray it with an element. Unfortunately, it will come back as long as the area that Luigi is in is dark.