What is Ozone?

Ozone is commonly known as smog at ground level. It is a gas that forms when emissions from cars, trucks, gasoline powered equipment, power plants, oil-based paints, and solvents react with heat and sunlight. It is bad because it causes health problems.

Pollution + Heat + Sunlight = Ground-Level Ozone

Ground-Level Ozone: Ozone that forms at ground-level is harmful and a public health threat. It is a result of pollution from industrial and commercial sources as well as individual activities. The Ozone Layer: Ozone is also located in the upper atmosphere 15-20 miles above the Earth's surface and is known as the "ozone layer"; it is not harmful. It forms naturally and it protects us from harmful ultraviolet rays.

Six Common Air Pollutants

Ground-level ozone is one of the six common air pollutants, or "criteria" pollutants, for which the EPA has set national air quality standards. What are the six?

• Ozone
• Particulate Matter
• Carbon Monoxide
• Nitrogen Dioxide
• Sulfur Dioxide
• Lead

Find out how each of these pollutants is formed, how they affect human health and public welfare, and what is being done to reduce them at EPA's Six Common Air Pollutants.

Ozone and Health

Ground-level ozone impairs breathing, irritates lungs, causes scar tissue in the lungs, and damages vegetation. Those most at risk are people with asthma, emphysema, heart conditions, and children, elderly, and healthy adults engaged in vigorous work or exercise outdoors. On high ozone concentration days, everyone is at risk.

The Clean Air Act requires EPA to set air quality standards to protect both public health and the public welfare (e.g. crops and vegetation). Ground-level ozone affects both.