But over all, the danger was no greater than that on a smoggy day, some officials said.

Children are sensitive to ozone, as are people who exercise outdoors on smoggy days, drawing air deeply into their lungs.

You're in the heart of Los Angeles on a miserably smoggy day and decide to do your bit to clean up the air.

Something a little more than a smoggy day with heat lightning.

"This smog patrol is a good idea," said Thomas Massarotti, whose cement mixer was stopped by Officer Gibson one recent smoggy day.

A hiker following the length of the Appalachian Trail this summer, therefore, is likely to encounter some pretty smoggy days.

People who exercise outdoors on hot, smoggy days, for example, increase their exposure to pollutants in the air.

After four years in Beijing, I've learned how to gauge the pollution before I open the curtains; by dawn on the smoggiest days, the lungs ache.

This reduction in temperature would reduce peak ozone levels by as much as 7% and smoggy days by 50%.

Volvo estimates that on particularly hot, smoggy days, PremAir could actually consume more ozone than the car generates.