The brown cloud's time is at hand.
As winter approaches, so does the time when air inversions trap pollutants close to the ground, air-quality officials say. This phenomenon periodically produces thick layers of pollutants that can aggravate asthma, viral infections and other respiratory problems.
Here are some questions and answers about our inversions and the brown cloud:
Q. What causes temperature inversions?
A. During an inversion, cold air that usually stays above warm air in the atmosphere sinks overnight, trapping pollutants close to the ground. The warm air acts like a lid, keeping the cooler air from rising.
Q: Why are inversions more frequent and troublesome during the winter?
A: During the summer, the sun rises early, as does the sun-warmed air, carrying pollution along with it, according to the Pima County Department of Environmental Quality. But during the winter, the sun rises later in the morning, so pollutants hanging around from the night before and the early morning stay around until the surrounding air warms enough to begin rising. Because winter nights are much longer than summer nights, winter inversions are stronger and more common.
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Q. How does this make pollution worse?
A. An inversion traps pollutants from fireplaces, vehicles and industry close to the ground. They're commonly known as particulates, made up of coarse and fine particles, that can cause or aggravate lung and other respiratory problems.
Q. What can we do to reduce air pollution levels?
A. Drive less, limit idling of your car to less than a minute, keep your car well-maintained, and check your tire pressure monthly, county DEQ officials say. Also, don't light so many fires. Using a fireplace for heat is very inefficient. If you can, heat your home with electricity, natural gas or solar energy, or with an wood stove approved by the Environmental Protection Agency, DEQ says.
Contact reporter Tony Davis at tdavis@azstarnet.com or 806-7746.
