Ozone occurs in two layers of the atmosphere. In the stratosphere, ozone protects the earth from harmful ultraviolet rays. At ground-level it is an air pollutant that can be harmful to human health and the environment. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of ozone. The Clean Air Act requires EPA, states, and cities to implement programs to further reduce emissions of ozone precursors from sources such as cars, fuels, industrial facilities and power plants. The EPA also encourages lifestyle changes such as recycling and conservation that can result in significant air quality improvements.

Recommended EPA Web pages

• Ozone: Good Up High Bad Nearby
  This brochure provides information on the differences between atmospheric ozone and ground level ozone.
• Ozone Health Effects
  Inhaling ozone can increase the susceptibility of the lungs to infections and increase responsiveness to allergens and other air pollutants.
• EPA's Draft Report on the Environment 2003: Technical Document: 1.4: Stratospheric Ozone
  Provides information about stratospheric ozone.

Air Pollutants
Aerosols, Asbestos, Carbon Monoxide, Chlorofluorocarbons (CFCs), Criteria Air Pollutants, Ground Level Ozone, Hazardous Air Pollutants (HAPs), Lead, Mercury, Methane, Nitrogen Oxides (NOx), Particulate Matter (PM), Propellants, Radon, Refrigerants, Sulfur Oxides (SOx), Volatile Organic Compounds (VOCs)

Biological Contaminants

Carcinogens

Chemicals
Benzene, Chlorofluorocarbons (CFCs), Chromated Copper Arsenate (CCA), Dichloroethylene (DCE), Dioxins, Endocrine Disruptors, Ether, Ethylbenzene, Furans, Halons, Hazardous Air Pollutants (HAPs), Heavy Metals, Hydrochlorofluorocarbons (HCFCs), Inorganic Cyanides, Ketones, Methane, Methyl Bromide, Methyl Chloride, Methyl-T-Butyl-Ether (MTBE), Nitrogen Oxides (NOx), Organic Cyanides, Particulate Matter (PM), Perchloroethylene (PCE), Phthalates, Polychlorinated Biphenyls (PCBs), Radioactive Substances, Radionuclides, Styrene, Sulfur Hexafluoride (SF6), Sulfur Oxides (SOx), Toluene, Trichloroethylene (TCE), Volatile Organic Compounds (VOCs)

Microorganisms
Coliform, Cryptosporidium, Viruses

Ozone

Radiation
Ionizing Radiation, Radiation Detection, Radiation Exposure, Radiation Protection, Radioactive Substances, Radionuclides, Radon

Soil Contaminants
Acetone, Arsenic, Barium, Benzene, Cadmium, Chloroform, Cyanide, Lead, Mercury, Polychlorinated Biphenyls (PCBs), Tetrachloroethylene, Toluene, Trichloroethylene (TCE)

Toxic Substances
Persistent Bioaccumulative Toxic Pollutants (PBTs), Persistent Organic Pollutants (POPs), Toxicological Profiles

Water Pollutants
Arsenic, Contaminated Sediment, Disinfection Byproducts, Dredged Material, Lead, Microbial Pathogens