| Ozone Pollution |
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Ozone is a molecule of three oxygen atoms bound together (O3). Ozone is a pungent pollutant. It causes eye irritation and at high levels can be fatal. Plant life suffers when exposed to even relatively low concentrations of ozone, and it causes rubber to harden and turn brittle. To protect tires from ozone, manufacturers have incorporated paraffin wax, which reacts preferentially with the ozone, sparing the rubber. Ozone is found naturally in small concentrations in the Earth’s stratosphere. In this upper atmosphere, ozone is made when ultraviolet light from the sun splits an oxygen molecule (O2), forming two single oxygen atoms. If a freed atom collides with an oxygen molecule, it becomes ozone. Stratospheric ozone has been called "good" ozone because it protects the Earth's surface from dangerous ultraviolet light. |
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Although ozone pollution is formed mainly in urban and suburban areas, it ends up in rural areas as well, carried by prevailing winds or resulting from cars and trucks that travel into rural areas. Significant levels of ozone pollution can be detected in rural areas as far as 250 miles (150 km) downwind from urban industrial zones. |
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Urban concentrations of nitrogen monoxide, nitrogen dioxide, and ozone are mutually related. Early morning rush hour causes a rapid increase in nitrogen monoxide, which by midmorning has largely been converted to nitrogen dioxide. On a sunny day, following nitrogen dioxide formation, ozone levels begin to peak. In the absence of a temperature inversion, late-afternoon winds clear the pollutants away. After a night of calm, the cycle begins again. Another class of components in photochemical smog is hydrocarbons, such as those found in gasoline. In the presence of ozone, airborne hydrocarbons are transformed to aldehydes and ketones, many of which add to the foul odor of smog. Also, incomplete combustion of gasoline leads to the release of polycyclic aromatic hydrocarbons, which are known carcinogens. Significant amounts of hydrocarbons are also released each time a car is filled with gasoline. Because gasoline is a volatile liquid, any air in a closed tank of gasoline is loaded with gasoline vapors—even when the tank is near empty. Every time you fill up at the pump, these vapors, about 10 grams worth, are displaced and vented directly into the atmosphere. |
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