The evidence is shocking when viewed from the Salt Lake Valley’s canyons: A brown stew of stagnant air swallowing clean air and stealing views like a suffocating shroud. That gunky blanket, seen especially during steamy summer months and winter inversions, is nearly as visible from the valley floor. And it has persuaded Salt Lake City Mayor Ralph Becker to fight back. He wants to outlaw vehicle idling (beyond two minutes) as a means to cleanse the air.