Salt Lake City has been enveloped in a soup of smog for the past few days. While not uncommon there during the colder months, this "inversion" has been especially severe and prolonged; persons with chronic lung conditions are advised to remain indoors and the airport has been diverting some flights due to low visibility.
Inversions occur when a layer of cold air becomes trapped beneath warmer air, impairing the usual mixing that disperses moisture and pollutants. Salt Lake City sits in a broad valley between two mountain ranges; cold air sinks from these highlands during the night and settles in the basin. When high pressure develops over the region and winds are light, an inversion often develops. Climb a few hundred feet into the adjacent mountains and you leave the brown smog, entering clear, sunny, warmer air.
Inversions are common in many western cities, which usually sit along rivers and often have nearby mountain ranges. Before man arrived with his fireplaces, automobiles and industry, such weather conditions produced dense fog. Now, an ugly and unhealthy soup fills the valley; efforts to minimize emissions from homes, cars and factories are the only means to alleviate this growing problem.
