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Good Question: Is indoor air really better on red-air days?

(KUTV) When the air is bad outside we're told to take our exercise indoors. But at gyms like Factum Mixed Martial Arts and Crossfit in Sandy, Utah, the building is not air tight. In fact, virtually zero buildings are air tight.

It’s an observation that prompted 2News viewer Jennifer to wonder, why would the air outdoors be any worse than the air indoors?

It's a good question which, for the answer, we turned to Utah division of air quality director Bryce Bird. Bird said they put a lot of work into figuring out the answer.

“We did some air sampling, where we'd set up the samplers inside buildings, especially schools," he said.

What they found is that, on the dirtiest days, the air was about twice as clean inside then it was outside.

He said there are a couple of reasons the indoor air is cleaner. For one thing, a building’s furnace filters a lot of the particulate pollution out of the air at it flows through vent.

But perhaps the biggest reason indoor air is better on inversion days has to do with the chemical reaction that makes Utah’s inversions so brutal. That pollution can't survive when it gets inside a warm room because the warm air undoes the chemical reaction.

Still, the studies didn’t find that indoor air is always better. Bird says that when the air is clean outside, it's better to be outside.

"What we found is that on the clean air days outside, the pollution levels were higher inside the building. You have the omissions that happen in the building [plus] the dust and things that get stirred up as we all move around."

And now we know why experts say workout indoors on red alert days.

Thanks, Jennifer, for the good question.

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