• What is ozone?
• O3
• Properties: blue color, characteristic smell (a little like chlorine) , UV adsorption
• highly reactive compound
• discovered by Schoenbein, 1940
• There are two problems associated with ozone, 'good' and 'bad' ozone (Fig)
• Stratospheric ozone
• 85 to 90% of ozone found in the stratosphere
• UV produces Ozone in stratosphere, maximum at about 30 km height
• vertical concentration distribution (Fig)
• Typical maximum concentration: 12 ppm
• ozone hole, caused by CFC's -> increase in UV -> skin cancer (Ozone hole 1980)
• Dobson Unit: the unit of measure for total ozone. If you were to take all the ozone in a column of air stretching from the surface of the earth to space, and bring all that ozone to standard temperature (0 Celsius) and pressure (1013.25 millibars, or one atmosphere, or "atm"), the column would be about 0.3 centimeters thick. Thus, the total ozone would be 0.3 atm-cm. To make the units easier to work with, the "Dobson Unit" is defined to be 0.001 atm-cm. Our 0.3 atm-cm would be 300 Dobson Units (DU).
• Tropospheric ozone
• Troposheric, or ground-level ozone, is the major ingredient in smog and continues to pose a health risk to many Americans
  • ozone attacks cells and breaks down tissue
  • decreased ability to breathe, coughing, increased susceptibility to respiratory diseases such as pneumonia and bronchitis
  • increased sensitivity to allergens
  • long-term exposure may result in permanent lung damage
  • Risk groups: sensitive healthy adults (5-25%), children, individuals with respiratory disease, exercising individuals
• ozone is a plant toxin, enforced by presence of SO2 and NOx
• ozone also damages materials such as nylons, rubber, and certain fabrics
• economic impacts
  • damage of agricultural crops, forests, and wilderness areas
  • lowering of ozone levels by 25% may increase US crop yield by $0.5 to #1.0 billion per year (mainly soybeans, corn, and tobacco;Office of Technology Assessment)
• natural tropospheric ozone concentration: 10ppb
• National Ambient Air Quality Standards (NAAQS) established under the Clean Air Act: : 0.12ppm or 120ppb (maximum hourly average).
• EPA introduced a 'Pollution Standard Index' (PSI), 0.12ppm = PSI of 100
• Nearly 100 major cities in the United States are periodically exposed to concentrations of ozone that exceed health-based air-quality standards.
• According to the U.S. EPA, 80 million people lived in areas designated "non-attainment" for ozone in 1991.
• Trends in tropospheric ozone
• Urbanization is increasing and air pollution will worsen
• Ozone on northern hemisphere is increasing 1-2%/y
• Ozone as a greenhouse gas (Hansen and Lebedeff, 1988)
• Formation of tropospheric ozone
• series of reactions involving
  • VOCs: volatile organic compounds: mostly emitted by motor vehicles, vegetation, industrial, and commercial, dry cleaners, paints
  • NOx: nitrogen oxides,motor vehicles, power plants, industrial facilities, biomass burning, lightning
  • sunlight
  • heat
  • first two: PRECURSERS
• chemistry of ozone formation (Ozone cycle)
  • complex
  • involved are: VOC (RH), OH (hydroxyl radical) M (inert body, N2, or O2); O3 can be dissociated by UV and will form two OH -> chain process
  • VOC and NOx concentrtaions control ozone concentrations in a complicated way (Fig)
  • meteorology is also influencing ozone concentrations (Fig)
• National emissions inventory (1985)
  • NOx, 5.67 Teragrams nitrogen/y (Fig)
  • VOC's, 20.02 Teragrams/year (Fig)

WHO/UNEP (1994) Air pollution in the World's Megacities. Environment, 36, 2.

National Research Council (1992) Rethinking the ozone problem in urban and regional air pollution. National Academy Press, Washington, D.C., 500pp.

Search with web engines for "ozone pollution"

Commonly asked questions about Ozone, NOAA

EPA, Office of Air Quality Planning and Standards

The TOMS home page, NASA

Atmsopheric Chemistry and Resources, NASA

Pennsylvania DEP ozone information

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