An article in Tuesday's editions incorrectly described ozone as a chemical stew caused by pollution from various sources, including cars. Ozone is a form of oxygen with three atoms per molecule instead of the usual two. At ground level, it is a toxic pollutant formed by chemical reactions involving sunlight and oxygen in the presence of auto exhaust and other air pollutants. High in the stratosphere, ozone is created when oxygen is struck by ultraviolet radiation, blocking much of that harmful radiation from reaching the Earth's surface.
The Sun regrets the errors.