March 16, 1997
Triatomic oxygen, O3, is most commonly known as ozone. It has a resonance structure, and can be drawn in two different ways: O=O- O-O=O It is a bluish, explosive gas at room temperature, and has a boiling point of -119°C. It has a melting point of -193°C, and is a blue liquid. It 's critical temperature and pressure are -12.1°C and 53.8 atm, respectively. It has a pleasant odor in concentrations of less than 2 ppm, and is irritating and injurious in higher concentrations. The density of ozone gas is 2.144 g/L, and the density of ozone as a liquid is 1.614 g/mL. It is extremely unstable, and solutions containing ozone explode upon warming. It is found in varying proportions on Earth, but it is about 0.05 ppm at sea level. Ozone absorbs harmful ultraviolet radiation in the upper atmosphere, and protects humans from skin cancer. But ozone is also the main ingredient of smog, and causes serious health effects and forest and crop damage in the lower atmosphere. Ozone is formed through the chemical reaction of volatile organic compounds and nitrogen dioxide, in the atmosphere, in the presence of sunlight.
This reaction is called a photochemical reaction, because sunlight is required.
The product is known as smog. The notorious brownish color of smog is due to nitrogen dioxide of the mixture. Increased temperature stimulate the reaction, which is why ozone conditions are worse in the summer. It is an oxidant, meaning it takes electrons away from other molecules, and disrupts key structures in cells by starting chain reactions. Ozone is a serious national problem. Half of the largest urban areas in the United States exceed the ozone standards. The worst regions in the US include California and the Texas Gulf coast, and the northeast and the Chicago-
Milwaukee area during the summer. The ozone condition varies from year to year, as the temperature and weather fluctuate. This fluctuation also occurs
Bibliography: Harte, John, and Cheryl Holdre, Richard Schneider, and Christine Shirley. Toxics A to Z. pp 372-74. University of California Press: Los Angeles, 1991. "Ozone Most Harmful to Trees" USA Today Magazine. June 1992. pp 9-10 Scott, Geoff. "The Two Faces of Ozone," Current Health. September 1992. pp 24- -25.