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Brown Air in the Valley

Air Pollution Creates a Brown Cloud Over Phoenix


Brown Cloud Over Phoenix

Brown Cloud Over Phoenix

©Judy Hedding

January 2006

At one time, Arizona was internationally known as a respite for those suffering respiratory difficulties. With ailments ranging from allergies to asthma to tuberculosis, patients flocked to the area for relief.

The Brown Cloud

Since the early 1990s, residents of the Valley of the Sun have been looking for some relief of their own. The "Brown Cloud", as it has come to be known, shrouds the Phoenix area in pollutants nearly year-round resulting in the American Lung Association giving Maricopa County its lowest grade for air quality in both ozone and particulates in 2005.

According to the association's "State of the Air 2005" report, over 2.6 million, or 79%, of the county's residents are at high risk for respiratory complications due to air quality. Among those at risk are residents with asthma, bronchitis, cardiovascular disease, and diabetes.

What Causes Phoenix Air Quality Problems

For the most part, the Brown Cloud consists of tiny particles of carbon and nitrogen dioxide gas. These substances are deposited into the air mostly from burning fossil fuels. Cars, construction-related dust, power plants, gas powered lawn mowers, leaf blowers, and more contribute to the cloud daily.

While other areas around the country have similar fossil fuel usage without the obvious after-effects, the location, weather conditions, and rapid growth that attract residents and visitors to this area also help trap those particulates and gases.

At night, an inversion layer forms over the Valley. As with any desert, the air closer to the ground cools faster than the air above. However, unlike most other deserts, cool air then moves in on top of the warm air westward from the surrounding mountains.

As a result, the air trapped closer to the ground in the Valley, the air containing the majority of the pollutants in the area, spreads. As the desert floor heats up during the day, the particulates rise forming a visible haze that expands as the day progresses.

Throughout the day, air shifts in the Valley cause variances in the Brown Cloud. From mid-day on, the cloud is pushed to the east. With every sunset, the cycle starts all over again.

Page 1: Pollution Problems in Phoenix
Page 2: Brown Air Summit--What Must Be Done
Page 3: Is Air Quality Improving--Looking Ahead

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