The first one is my guess. They're kinda similar to ones I've seen in tunnels. I wouldn't have really thought it would be a long enough distance that they'd have problems with buildup though. Maybe it's a requirement given that they're under taxiways.

And the airport isn't in Detroit, so it's not their power bills (or the fact that their power company can't keep the power on regardless of whether people pay bills or not either, given the number of buildings that have been without power the last couple days).