Source: Environmental Protection Agency
Ozone is a major element of urban smog. Ozone can limit the ability to take a deep breath, and it can cause coughing, throat irritation, and breathing discomfort.
There is also evidence that ozone can lower resistance to respiratory disease (such as pneumonia), damage lung tissue, and aggravate chronic lung disease (such as asthma or bronchitis).
Children and those with pre-existing lung problems (such as asthma) are sensitive to the health effects of ozone.
Even healthy adults involved in moderate or strenuous outdoor activities can e xperience the unhealthy effects of ozone.
What is ozone?
Ozone is a colorless gas that can be found in the air we breathe. Each molecule of ozone is composed of three atoms of oxygen, one more than the oxygen molecule we need to breathe to sustain life. The additional oxygen atom makes ozone extremely reactive. Ozone exists naturally in the Earth's upper atmosphere, known as the stratosphere, where it shields the Earth from the sun's ultraviolet rays. However, ozone is also found close to the Earth's surface. This ground-level ozone is a harmful air pollutant.
Where does ground-level ozone come from?
Ground-level ozone is formed by a chemical reaction between volatile organic compounds (VOCs) and oxides of nitrogen in the presence of sunlight. Sources of VOCs and oxides of nitrogen include:
Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds.
How does ozone affect human health?
Even at relatively low levels, ozone may cause inflammation and irritation of the respiratory tract, particularly during physical activity. The resulting symptoms can include breathing difficulty, coughing, and throat irritation. Breathing ozone can affect lung function and worsen asthma attacks. Ozone can increase the susceptibility of the lungs to infections, allergens, and other air pollutants. Medical studies have shown that ozone damages lung tissue and complete recovery may take several days after exposure has ended.
Who is sensitive to ozone?
Groups that are sensitive to ozone include children and adults who are active outdoors, and people with respiratory disease, such as asthma. Sensitive people who experience effects at lower ozone concentrations are likely to experience more serious effects at higher concentrations.
What is an Ozone Action Day?
An Ozone Action Day may be called by your State or local air quality agency when ozone levels are forecast to reach unhealthy levels. These programs, often in partnership with local businesses, encourage voluntary actions to reduce emissions of pollutants that contribute to ground-level ozone formation.