Criteria Pollutant: Ozone

Ozone is found in two different places, the stratosphere and the troposphere. The troposphere is the lowest layer of the atmosphere and contains about 95 percent of the mass of air in the Earth's atmosphere. The troposphere extends from the Earth's surface up to about 10 to 15 kilometers. All weather processes take place in the troposphere. The stratosphere is the second layer of the atmosphere, extending from about 19 to 48 kilometers (12 to 30 miles) above the earth's surface. It contains small amounts of gaseous ozone (O3 ), which filters out about 99 percent of the incoming harmful ultraviolet (UV) radiation. Ozone in this layer is considered "good ozone." It doesn't harm health.

Low-level ozone, that which forms in the troposphere, is the type that is dangerous to health. Ozone that forms in this layer makes breathing difficult for children, athletes, the elderly and those with lung disease like asthma. Ozone is generally an odorless gas. It is secondary pollutant, meaning that it is formed after other gases react with each other. In the presence of sunlight, hydrocarbons and nitrogen oxides, from burning fossil fuels, react with each other to produce ozone. Though many of ozone's sources, such as automobile exhaust, are concentrated in cities, the pollutant and its precursors are carried on air currents great distances. Even rural areas are greatly affected by ozone!

Health and Other Effects
Ninety percent of the ozone that enters the lungs is never exhaled. Ozone reacts with lung tissue to cause several health consequences. Effects vary based on duration of exposure, individual sensitivity, age, activity level, and preexisting health problems such as asthma. Negative health effects include:

• Increases susceptibility to respiratory infection and decreased immunal response.
• Impaired lung function and reduced ability to perform physical exercise.
• In severe cases, lung swelling and death
• Increased risk of respiratory disease
• Eye, nose and throat irritation

Other Effects

• Foliar damage to crops and trees
• Corrosion of materials like rubber and fabrics

Go on to the next criteria pollutant--carbon monoxide>