"unprotected in the acid rain."
Trees killed by acid rain
Creative Commons Attribution Share AlikeTrees killed by acid rain - Credit: bdk/wikimedia commons

 Acid rain is rain which is unusually acidic, caused when carbon dioxide, sulfer dioxide and nitrogen oxide emissions react with the water molecules in the air. Acid rain is very harmful to plants and animals, and corrodes structures and buildings. This story envisions a future in which the rain has become so acidic that it is dangerous for people to walk around unprotected.