1.   Ground-level ozone is formed by a combination of volatile organic compounds and nitrogen oxide emissions.

2.   Instead, they suggest, the ozone was formed by the light emitted by all the fireworks.

3.   Ozone is formed by pollutants from cars and industrial sources in the presence of sunshine.

4.   Ozone is formed by reaction between sunlight and oxygen in the presence of exhaust from engines burning fossil fuels.

5.   Separately, ozone is formed high in the stratosphere, where it shields the planet from harmful radiation.

6.   Paul Crutzen, Mario Molina and Sherwood Rowland have all made pioneering contributions to explaining how ozone is formed and decomposes through chemical processes in the atmopshere.

7.   The three scinetists have all helped explain how ozone is formed and decomposes through chemical processes in the atmosphere.