Drawings of Girls Wearing Gas Masks - Heart-wrenching Contrast

Gas masks can be used to filter out all manner of unpleasantness from the air, including dangerous fumes, toxins, particulates, and even biohazardous materials. When you see a seemingly normal girl with a gas mask, it makes you wonder just what her situation is.

As you look over the illustrations below, what sort of backstory comes to mind for each of the characters?