Problems with Ozone.

When three atoms of oxygen bond they form a molecule of ozone (O3 ). Ozone is both much rarer and much more chemically active than O2 molecules — the common form of oxygen found on earth. Nevertheless, ozone posed two significant health risks during the 1980s. The first problem was that there was too much of it in urban areas near the planet's surface. The second problem was that there was not enough of it at high altitudes. Both problems were "man-made."

Ozone as an Urban Problem.

At low altitudes, in the earth's troposphere, automobiles and factories poured tons of organic gases into the atmosphere. When these chemicals mix with nitrogen oxides they form smog — one ingredient of which is the highly poisonous ozone. During the 1980s the government issued "ozone alerts" — cautioning citizens to stay indoors or curtail vigorous outdoor...