Smog and haze obscure the Phoenix skyline in this view from Piestewa Peak on Dec. 21, last year, the second-worst day of 2005 for particulate pollution in the area. Weather forecasters are predicting a return of the dry, stagnant conditions this winter that cause air pollution.

DEIRDRE HAMILL / Arizona REpublic

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PHOENIX — The dry, stagnant conditions that contributed last year to some of the worst air quality in Phoenix in recent memory could return this year, meaning the metro area could be in for another winter of pollution records.

It's too early to say for sure what this winter's air conditions will be.

Forecasters this month were predicting below-normal rainfall. Dry conditions, such as the 143 days the Phoenix area went without rain last winter, allow dirty air to accumulate.

Tony Haffer, who runs the National Oceanic and Atmospheric Administration forecast office in Phoenix, said a developing El Niño could change the dry forecasts, however.

Rain mixes with the atmosphere and dilutes pollution.

But even if El Niño does bring rain, it won't entirely sweep away the area's air pollution. "We will have days with the brown cloud, for sure," Haffer said.

The brown cloud, which at its worst can obscure the Phoenix skyline, usually makes its appearance in early October but was visible last year by late September.

The cloud is a haze of dust, nitrogen oxides and exhaust from cars and other combustible elements.

The ingredients are present year-round. During the winter months, however, the air near the ground cools faster after sunset than the air above it, trapping the particles and gases. There's also less wind to disperse pollution.

The cloud contains particles of grime that can travel inside the lungs and cause wheezing, coughing and shortness of breath and aggravate respiratory conditions. Studies have linked these particles to lung damage and premature death.

A 2001 report from the Governor's Office said brown-cloud pollution was responsible for an additional 250 to 1,000 deaths a year in the Phoenix area.

The American Lung Association of Arizona routinely ranks Maricopa County the worst place for air pollution in the state, giving the area failing grades in its annual air-quality report cards.

Eva Willis, 59, said she has noticed more pollution in the past few years than in the 46 previous years she has lived in the area. Her father has emphysema, and they pay close attention to the pollution warnings.

"It just seems that people are not in general feeling as well as they were when the air was cleaner," Willis said.