Left by itself oxygen prefers to exist as a two atom molecule, O2. However, electrical discharge such as a lightning strike or ultraviolet light from the sun can cause O2 to become three atoms of oxygen or O3. This is an allotrope of oxygen that we call ozone. Ozone has a sharp sweet odor, yet oxygen is odorless. We live on oxygen but ozone is toxic.
Scientists are worried about depleting the ozone layer in the upper atmosphere.
Yet in a city, ozone is considered a pollutant. Answers to these questions can form the foundation for a significant Science Fair Project. Fifty experiments explore life and physical sciences, astronomy, mathematics, and engineering. Many of the experiments appear in VanCleave's single-discipline books, but this offers the convenience of one volume.