Cold Light is the second book in the After Series by Traci L. Slatton. The first book is called Fallen, and I fell in love with it immediately.
I recommend reading Fallen before reading Cold Light, in order to get the full story. That being said, I think Cold Light might stand up on its own. Some of what happened in the first book is mentioned, or at least eluded to, in the second book.
Cold Light picks up not long after Fallen ends, in a post-apocalyptic world that is in constant danger. Mists that eat metal, turn buildings to dust, and dissolve people, are still roaming the world. In addition, there is the danger that happens when desperate people, struggling to survive, see others as their enemy.