<\/a>Downtown Fairbanks is blanketed in ice fog beneath the exhaust of a coal-fired power plant in January 2012. (Photo by Ned Rozell)<\/p><\/div>\n\t\t\t\t
Benson, now an emeritus professor at the Geophysical Institute, described the mystery of ice fog in a 1969 story he wrote for his friends at the California Institute of Technology, where he had attended college.<\/p>\n\t\t\t\t
Ice fog has a magic number — minus 30 F. It does not form until air gets that cold, and it dissipates when the temperature rises above that.<\/p>\n\t\t\t\t
“Ice fog is produced when the water vapor output from urban environments meets an air mass which is too cold to dissolve it and cold enough to crystallize the condensed vapor into tiny air crystals,” Benson wrote back then for the surely baffled urban-California audience.<\/p>\n\t\t\t\t
Those ice crystals waft to the ground, latching onto air-pollution particles on the way down.<\/p>\n\t\t\t\t
Benson also explained a chemical-reaction oddity that happens as we drive. When our engines burn gasoline, “the actual mass of water ejected as vapor from the exhaust is 1.3 times greater than the mass of gasoline burned.”<\/p>\n\t\t\t\t
Though cars trailing their own cotton-candy clouds is a striking visual and is the main cause of limited driving visibility, Benson found that a major contributor of water vapor in the late 1960s was the liquid cooling water for power plants. Today, a major contributor is an open portion of the Chena River warmed by power-plant cooling water.<\/p>\n\t\t\t\t
In a paper published in fall 2023, Lea Hartl of the Alaska Climate Research Center wrote that from 1950 to 1980 Fairbanks averaged more than two weeks’ worth of days with ice fog each year.<\/p>\n\t\t\t\t
When she examined the 30 years from 1990 to 2020, she found that ice fog was in place for only about 6 days each year, on average.<\/p>\n\t\t\t\t
Why? Hartl wrote that the main reason is that — even though we get a taste of ice fog now and then — there are much fewer days in which Fairbanks experiences temperatures below that magic minus 30 F.<\/p>\n\t\t\t\t