Denver is on a pace to eclipse the ozone-choked summer of 2003, the worst in 20 years, when the state issued 42 ozone alerts warning of unhealthy air. As of Wednesday, this summer has had 34.
Boulder and Fort Collins have unusually high ozone levels as well. Gasoline is one culprit.
Ozone is created when the sun bakes common pollutants such as engine exhaust, wildfire smoke and vapors from everything from paint cans to oil and gas wells.
There are things we can do to bring down the ozone level, or at least not make it worse:
State health officials ask people to do little things, such as not spilling gasoline at the pump, waiting to refuel until after dusk, when the vapors have less time to cook into ozone, and trading in old gasoline-powered mowers for newer models.