Wool by Hugh Howey

This is the first in a series.  The protagonist, Holston, a sheriff in an underground world, is about to kill himself.  He doesn't think he's killing himself, but society sure does.  Nobody can go above ground because of the toxic air, but condemned criminals go up as their death sentence and must clean the device that monitors the outside world before they die.  Holston's wife three years ago begged to be let out because she said that she had discovered a secret, and Holston trusts that she found something worth him following her.

I loved Wool from the start to the finish.  It seemed to be going one way through the whole book, but the last few sentences changed everything.  My only question is exactly what the wife discovered that made her want out so badly.  Read it and you'll see why that's a valid concern.