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Cold temperatures bring haze to desert

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Cold temperatures bring haze to desert

Pollutants become trapped in chilly air

  • Air appears hazy near the Rincon Mountains in December 2010.
    grant_loy/FlickrAir appears hazy near the Rincon Mountains in December 2010.

Early risers may have wondered why the sky appears hazy in the mornings now that temperatures are dropping.

This effect is called temperature inversion, and is caused by falling temperatures, which trap pollutants in the chilly air, while the warm air above traps the cool air down below. When the sun comes up the chilly air warms, and rises, taking the pollutants with it, and therefore clearing up visibility.

Temperature inversions are even more enhanced by the mountains surrounding the city, which create a downward flow of the cold air onto the desert floor, according to a Pima County Department of Environmental Quality press release.

This additional cold air can increase the strength and duration of the hazy morning weather.

Although the pollution is visible, the levels of pollutants in the air are not high enough to impact health, said Beth Gorman of the Pima County Department of Environmental Quality.

Light scattering and the angle of the sun in the morning make the haze even more visible, she said.

To reduce pollutants in the air, the county advises Tucsonans to minimize their time on the road and to car pool.

Fireplaces also add more pollutants to the air and are actually an inefficient source of heat, according to the press release. Natural gas and electric solar-powered heat or a wood stove certified by the Environmental Protection Agency, are better options for heat, the press release said.

Daily information on local pollution levels, including particulates, ozone and carbon monoxide readings can be found at

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