Ground-level ozone is formed when the sun makes certain emissions turn into ozone—over time—usually one or several hours of time. Putting your ozone-forming emissions into the air in the early hours before daybreak, (by filling your gas tank or mowing the lawn in the early morning) means those emissions will be prime several hours later for making ozone in the sunlight! In the evening when the sun starts to set, less solar energy and less time is available make ozone. Also, evening winds often increase to help dissipate emissions overnight even more. Often, evening winds may increase as well, allowing emissions to somewhat dissipate overnight.