According to the division, Salt Lake County has experienced 22 days this winter in which pollution levels exceeded federal air quality standards, compared with just one last year.

The air pollution has gotten so bad at times that it has prompted warnings from local doctors, spawned protests at the State Capitol and led to a variety of legislative proposals in the hopes of confronting the problem before it gets worse.

It is not that the region necessarily emits more pollution than other large metropolitan areas, or that the problem is especially new, Mr. Bird said. What makes the situation here different is the confluence of topographic and meteorological factors.

When heavy winter storms sweep through the area, they leave snow on the Salt Lake Valley floor. But intermittent warm high-pressure systems trap the cold air, creating the effect of a lid on a soup bowl and keeping dirty air from car emissions and other pollutants from escaping.

Federal safe air standards are set at 35 micrograms of particles per cubic meter of air — about the weight of a single crystal of table salt — averaged over a 24-hour period. During inversions last month, Salt Lake County reached 69 micrograms per cubic meter, while nearby Utah County got to 125 micrograms, Mr. Bird said,