Air Quality Index – What is ozone?

Ozone is a gas found in the air we breathe. Ozone can be good or bad, depending where it occurs:

• Good ozone is present naturally in the Earth’s upper atmosphere—approximately 6 to 30 miles above the Earth’s surface. This natural ozone shields us from the sun’s harmful ultraviolet rays.
• Bad ozone forms near the ground when pollutants (emitted by sources such as cars, power plants, industrial boilers, refineries, and chemical plants) react chemically in sunlight. Ozone pollution is more likely to form during warmer months. This is when the weather conditions normally needed to form ground-level ozone—lots of sun—occur.

Who is most at risk?

Several groups of people are particularly sensitive to ozone, especially when they are active outdoors. This is because ozone levels are higher outdoors, and physical activity causes faster and deeper breathing, drawing more ozone into the body.

• People with lung diseases, such as asthma, chronic bronchitis, and emphysema, can be particularly sensitive to ozone. They will generally experience more serious health effects at lower levels. Ozone can aggravate their diseases, leading to increased medication use, doctor and emergency room visits, and hospital admissions.
• Children, including teenagers, are at higher risk from ozone exposure because they often play outdoors in warmer weather when ozone levels are higher, they are more likely to have asthma (which may be aggravated by ozone exposure), and their lungs are still developing.
• Older adults may be more affected by ozone exposure, possibly because they are more likely to have pre-existing lung disease.
• Active people of all ages who exercise or work vigorously outdoors are at increased risk.
• Some healthy people are more sensitive to ozone. They may experience health effects at lower ozone levels than the average person even though they have none of the risk factors listed above. There may be a genetic basis for this increased sensitivity.

In general, as concentrations of ground-level ozone increase, more people begin to experience more serious health effects. When levels are very high, everyone should be concerned about ozone exposure.

What are the health effects?

Ozone affects the lungs and respiratory system in many ways. It can:

• Irritate the respiratory system, causing coughing, throat soreness, airway irritation, chest tightness, or chest pain when taking a deep breath.
• Reduce lung function, making it more difficult to breathe as deeply and vigorously as you normally would, especially when exercising. Breathing may start to feel uncomfortable, and you may notice that you are taking more rapid and shallow breaths than normal.

• Inflame and damage the cells that line the lungs. Within a few days, the damaged cells are replaced and the old cells are shed—much like the way your skin peels after sunburn. Studies suggest that if this type of inflammation happens repeatedly, lung tissue may become permanently scarred and lung function may be permanently reduced.
• Make the lungs more susceptible to infection. Ozone reduces the lung’s defenses by damaging the cells that move particles and bacteria out of the airways and by reducing the number and effectiveness of white blood cells in the lungs.
• Aggravate asthma. When ozone levels are unhealthy, more people with asthma have symptoms that require a doctor’s attention or the use of medication. Ozone makes people more sensitive to allergens—the most common triggers for asthma attacks. Also, asthmatics may be more severely affected by reduced lung function and airway inflammation. People with asthma should ask their doctor for an asthma action plan and follow it carefully when ozone levels are unhealthy.
• Aggravate other chronic lung diseases such as emphysema and bronchitis. As concentrations of ground-level ozone increase, more people with lung disease visit doctors or emergency rooms and are admitted to the hospital.
• Cause permanent lung damage. Repeated short-term ozone damage to children’s developing lungs may lead to reduced lung function in adulthood. In adults, ozone exposure may accelerate the natural decline in lung function that occurs with age.