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Winter leads to more air pollution in South and West Phoenix

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Columba Sainz used to spend more time outside with her two young daughters. When her husband got home from work in the evenings, the four of them would go directly to the nearby park in their neighborhood in Tempe. Sometimes they’d be there until 9 or 10 at night.

“I don’t want my children to be inside the house, watching TV all day long,” Sainz said. “I want them to be outside, to keep their minds busy.”

After about a year and a half in Tempe, Sainz was pregnant with a third child. Her husband’s commute from downtown Phoenix seemed to be getting longer. With a new baby on the way and two toddlers, she wanted the growing family to live closer to his work. 

They moved to a neighborhood south of downtown. The house seemed perfect—it was across the street from a park and near a daycare. But then Sainz’s toddler started wheezing and coughing at night. 

“It was something that we’d never seen before,” Sainz said. “We were really panicked. We took her to the hospital the next day and the first question they asked me was, 'Does she have asthma or respiratory issues?' And I said no. They never linked it to the quality of the air.” 

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South and west Phoenix have the worst air quality in the Valley. Maricopa County Air Quality Department uses monitors throughout the county to measure particulate matter, or PM, fine particles that are produced by vehicles, construction, industry, fireworks and wood burning.

PM 2.5 are airborne particles small enough to enter the lungs and can trigger asthma attacks. Young children whose lungs are still developing, and elderly people with weakened lungs, are most at risk for health problems caused by PM 2.5. This dangerous fine particle pollution tends to increase during the holiday season as more people burn wood in fireplaces and outdoor pits, and set off fireworks to celebrate the new year. 

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When her daughter started wheezing, Sainz stopped taking her to the park. After spending as many as four hours outside playing, Sainz cut the time down to a half hour, then 15 minutes. Her daughter kept wheezing. Sainz downloaded air quality apps on her phone and signed up for alerts from Maricopa County, which issues no-burn days, and the Arizona Department of Environmental Quality (ADEQ), which puts out high pollution advisories. Enforcement by the county is often lax. 

“My life just changed right there,” Sainz said, her eyes filling with tears. “How do you limit a kid from four hours to 15 minutes outside? My life depended on checking on apps before having my children go outside. The house becomes your safe zone from the outside. But at the same time, you see all these other children outside and it’s like how do you communicate to them that this could happen to them as well?”

This time of year, early morning commuters may notice the sunrise muddied by a brown haze on the horizon. That’s pollution, primarily particulate matter.

For most of the year, the sun heats the ground enough to warm the air just above it. That warm air gradually rises throughout the day, allowing pollution to disperse in a larger area.

Because the sun is weaker in the winter, cold air sits lower to the colder ground. Warmer air above it rises, but the cold air stays near the ground and doesn't mix with the rest of the atmosphere. The result is a line of brown haze trapped below the warm layer. 

Local winds are a factor too, shifting pollution to different parts of the Valley throughout the day and night, said ADEQ meteorologist Matthew Pace.

In the afternoon, the wind generally moves up the mountains surrounding Phoenix, pulling the air from the west and southwest toward the east and northeast. At night, cold air drains back to the south and southwest, eventually settling in the lowest point of the valley — near the Salt River in south and west Phoenix. 

“Any of those pollutants that you create, whether it’s PM 2.5, which is smoke, or PM 10, which is dust, that will all drain slowly down into the south part of the valley,” Pace said.

Only rain or wind can disperse the cold air layer near the ground and allow the pollution to diffuse. Christmas Eve and Christmas Day were some of the cleanest days on record because of the rain and storm system that kept smoke from building up.