Ozone

Ozone is a highly active form of oxygen (O₃ rather than O₂). Ozone is made when a electric spark passes through air, and this accounts for the characteristic odor give off by some electrical motors.

Ozone presents two quite different biological problems: too much at low levels of the atmosphere; too little at high altitudes.

Ozone is also produced by the reaction of sunlight, oxygen, and automobile exhaust (which contains hydrocarbons and nitrogen oxides). Ozone is largely responsible for the discomfort associated with photochemical smog. This form of smog, long familiar to people in the Los Angeles basin, is now common wherever sunlight and stagnant air occur in urban areas (Mexico City is a dramatic example). High levels of ozone during smog build-up can cause difficulty to people with respiratory ailments like emphysema and asthma. Ozone also damages plants and may be an important factor in the damage that is occurring to forests in Europe and North America.

While we often have too much ozone around us, the concentration of ozone high in the stratosphere has declined over the past two decades. This is ominous because the ozone layer up there screens out some of the ultraviolet rays reaching the earth from the sun. Ultraviolet rays can cause skin cancer. Although some of the recent depletion of ozone in the stratosphere was probably due to natural causes (volcanic eruptions, fewer sunspots), some is most likely caused by man-made chlorofluorocarbons (CFCs). These gases escape from such sources as aerosol spray cans, leaky or discarded refrigeration units, and a variety of industrial processes. The U.S., Canada, and the Scandinavian countries stopped using CFCs in aerosol cans over a decade ago, but this and other uses of CFCs have continued to grow worldwide. However, a multi-nation agreement drawn up in 1987 should lead in time to a reduction in the use of these materials.