Ozone air quality

What is ozone?

Ozone is an odorless, colorless gas composed of three atoms of oxygen. Ozone occurs both in the Earth's upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found:

  • Good Ozone. Ozone occurs naturally in the Earth's upper atmosphere-10 to 30 miles above the Earth's surface-where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. This beneficial ozone is gradually being destroyed by manmade chemicals. An area where ozone has been significantly depleted-for example, over the North or South pole-is sometimes called a "hole in the ozone."

  • Bad Ozone. In the Earth's lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Ozone at ground level is a harmful pollutant. Ozone pollution is a concern during the summer months, when the weather conditions needed to form it-lots of sun, hot temperatures- normally occur.

What are the health effects and who is most at risk?

Roughly one out of every three people in the United States is at a higher risk of experiencing ozone-related health effects. Sensitive people include children and adults who are active outdoors, people with respiratory disease, such as asthma, and people with unusual sensitivity to ozone.

  • One group at high risk from ozone exposure is active children because this group often spends a large part of the summer playing outdoors. However, people of all ages who are active outdoors are at increased risk because, during physical activity, ozone penetrates deeper into the parts of the lungs that are more vulnerable to injury.
  • People with respiratory diseases that make their lungs more vulnerable to ozone may experience health effects earlier and at lower ozone levels than less sensitive individuals.
  • Though scientists don't yet know why, some healthy people experience health effects at more moderate levels of outdoor exertion or at lower ozone levels than the average person.
  • Ozone can irritate the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest.
  • Ozone can reduce lung function and make it more difficult to breathe deeply and vigorously. Breathing may become more rapid and shallow than normal. This reduction in lung function may limit a person's ability to engage in vigorous outdoor activities.
  • Ozone can aggravate asthma. When ozone levels are high more people with asthma have attacks that require a doctor's attention or the use of additional medication. One reason this happens is that ozone makes people more sensitive to allergens, the most common triggers of asthma attacks.
  • Ozone can increase susceptibility to respiratory infections.
  • Ozone can inflame and damage the lining of the lungs. Within a few days, the damaged cells are shed and replaced-much like the skin peels after a sunburn. Animal studies suggest that if this type of inflammation happens repeatedly over a long time period (months, years, a lifetime), lung tissue may become permanently scarred, resulting in less lung elasticity, permanent loss of lung function, and a lower quality of life.

graphic of ozone levels by time of day

Ozone typical starts to increase in concentration at 10:00 am and peaks in late afternoon.

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