DENVER — On a hot summer day on the Colorado Front Range, there is often a potentially hazardous air pollution , known as ground level ozone, hidden in the relatively clear air. "You’re not necessarily going to be able to see it. Ozone for the most part is invisible," said Scott Landes with the Colorado Department of Public Health and Environment (CDPHE).

"There is sometimes a little bit of a haze visible when there are very high concentrations of it." While you can't see the ozone pollution, you might be able to feel the ozone pollution in your lungs. Especially if you have sensitive lungs or a preexisting respiratory problem.

"For healthy folks, it may not affect you as much but certainly if you’re going out for an afternoon or evening run during those kind of conditions you’re going to start feeling it a little bit more," Landes said. "So we do ask people if you do have exercise planned, to have a little flexibility in your schedule." Landes said ozone pollution is created when the sun chemically alters other pollutants in the air, so outdoor activities are best in the morning hours before that process starts.

That also means the morning and early afternoon hours are the worst times to add other pollutants, like gasoline emissions, to the air which are considered precursors to ozone. So don’t fuel up the car or mow the lawn until after 5 p.m.

and put off driving early in the day if you can or carpool. "Once you get past 5 p.m.

, those precursors are not going to d.