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Beat the heat of the afternoon when air quality is at its worst

On Colorado's lousy air quality days, get that jog or walk done earlier in the day.

DENVER — You've probably heard it time and time again during this run of exceptionally bad air quality in Denver and along the Front Range – get that exercise and/or outdoor activity done during the early morning hours to escape bad air quality.

But, you might not know why air quality tends to be best during the early morning – and worst during the afternoon.

Let's start with the basics: 

  • When Denver has poor air quality, it's usually because of ground ozone – though it's often mixed with or directly from wildfire smoke.

  • Ground ozone forms from a combination of car exhaust, other forms of pollution and warm temperatures.
Credit: KUSA

Because car traffic peaks in the morning and evening and temperatures usually maximize in the afternoon, that's when conditions are typically at their highest for creating ground ozone. 

That ground ozone, however, also dissipates fairly quickly after dark. Because sunlight is a critical ingredient to ozone's formation, ground ozone dissipates quickly after dark. Ground ozone levels at night are typically very low, even if they're really high during the day.

By the way, you might also notice us saying "ground ozone" as opposed to just "ozone." That's because ozone itself can be a very good thing – after all, it's what comprises the ozone layer about 20 miles above the surface. The ozone layer shields us from the majority of the sun's ultraviolet radiation. 

Ground ozone, on the other hand, creates smog and pollution at the surface.

So long story short – when you know that lousy air quality might be in the forecast, get that jog, walk or outdoor activity done during the early morning hours or at night after the sun goes down. 

These simple routine changes will spare you the worst air quality-related impacts!

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