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LOGAN, Utah (AP) -- This mountain basin is gaining a reputation for having some of the nation's dirtiest winter air and could fall under federal regulation if things don't improve within a year.
At issue is lung-penetrating soot less than 1/40th the width of a human hair, measured as particulates up to 2.5 microns in size. Logan has recorded three of the nation's 15 most concentrated soot readings since air monitoring began here in 1999.
Once in 2002 Logan recorded 137.5 micrograms per cubic meter of particulates, more than double the Environmental Protection Agency's "unhealthy" threshold of 65 micrograms. Another bad "unattainment" day like that this year would land Cache valley on the EPA watch list and could mandate efforts at reducing air pollution.
Winter inversions put Logan air in a class with California's San Joaquin Valley, which can have some of the worst year-round air, although Logan's problem is limited to winter, primarily January and February.
At other times, "our air is really very good," said Randy Martin, an associate professor of civil and environmental engineering at Utah State University.
The problem is temperature inversions, where warm air aloft traps cold air at valley floors and prevents pollutants from dissipating. Making matters worse is Cache valley's small "mixing bowl" framed by steep Wasatch mountains, Martin said.
Rick Sprott, director of the Utah Division of Air Quality, said no "one-bullet" can solve the valley's air woes.
"You have a lot of different things going in and we don't understand exactly what the mixture is in the soup," Sprott said. "It's a puzzler, a big puzzler. What we're seeing in Cache valley is new to a lot of people in this field."
His division was building a computer model that could estimate how various steps can reduce smog, but the effort is hampered by a lack of funding.
Based on three-year averages, Cache valley would come under EPA supervision if another day this year brings concentrations of PM 2.5 that exceed 101.3 micrograms.
Or it could fall on the watch list next year with seven days of concentrations of at least 61.8 micrograms -- a threshold the basin already exceeded 17 days this year.
(Copyright 2004 by The Associated Press. All Rights Reserved.)