What time of day are ground-level ozone levels the highest?
[Back to Top] Ozone begins forming in the morning and formation increases as temperatures increase during the day. Ozone accumulates through the day, especially when winds are calm. In most areas of North Carolina, ozone levels peak during mid-afternoon through early evening, when temperatures are hottest. Ozone levels decrease as the sun sets, drop at night and are lowest around dawn. However, at high elevations (above 4,000 feet) in the mountains, ozone levels can remain high throughout the day and actually reach their highest values overnight.
