The Hulk has allergies just like many people we know, but with gamma ray bombarded allergies you have to be careful, or so were taught the late people of Coast City. That is if deceased can learn a thing. Again.
This city is infamous for being under the protection of one of Earth's Green Lanterns, with such bad luck that it has been targeted by every monster in the block and blown off the face of Earth one time too many.
Yesterday morning, the Hulk was jumping around apparently attracted by all the green in the scenery when something in the air made him sneeze. Two sneezes later, the city was gone.
Oh, we're going to have a real pi$$ed off Hal Jordan when he comes back from his Secret Origin storyline.