From Dust Rising — Cy Bishop

The end of the world was heralded by bombs. Not nukes as most assumed, but chemical bombs that devastated the planet's surface, leaving behind a slowly dying world with caustic gas constantly rising from the ground and dissipating into the air. Any form of shelter, where the gas can condense into a deadly fog, has become too dangerous to risk. The remaining survivors have adapted to life outdoors, on the move, doing their best to stay alive in a world of murderers, Slavers, and zombie-like Ragers that mindlessly destroy anything and anyone they come across.

Ronan has long survived by keeping to himself, happy to use whatever underhanded tricks he can to get the upper hand of anyone he crosses paths with. But then he finds himself stuck with Lily, a pampered lady who knows nothing of survival. Worse, her particular sensitivity to the gas constantly slows them down. Getting her back to her people means riches beyond his dreams, but it also means traveling a little too close to a deadly gang that's gunning for Ronan. Can he get her safely home before her ignorance gets them both killed?