What Is Ground-Level Ozone?
Ground-level ozone is the main ingredient in urban smog. Ozone is not emitted directly into the air, but is formed when gases called nitrogen oxides (NOx) and volatile organic compounds (VOC) react in the presence of sunlight. NOx is usually a by-product of high-tem- perature combustion. Common sources are cars and power plants. VOCs include organic chemicals that vaporize easily, like gasoline.
Ground-level ozone forms readily in the atmosphere during hot and sunny times. Because people are exposed to this ground-level ozone and its harmful health effects, it is often referred to as “bad ozone.” Ozone can also form naturally in the stratosphere. Here it provides a protective layer above the earth that shields us from the sun’s harmful ultraviolet rays. Because people are not directly exposed to this ozone, and because it provides a useful purpose, it is often referred to as “good ozone.”
What Are the Health Effects of Ozone Pollution?
High concentrations of ozone can cause shortness of breath, cough- ing, wheezing, headaches, nausea, and throat and lung irritation. People who suffer from lung diseases like bronchitis, pneumonia, emphysema, asthma, and colds have even more trouble breathing when the air is pol- luted. These effects can be worse for anyone who spends significant peri- ods of time exercising or working outdoors. When we exercise heavily, we may increase our intake of air by as much as 10 times our level at rest.
Children are also at an increased risk of respiratory problems caused by ozone. Their lungs are still developing, and they breathe more rap- idly and inhale more air pollution per pound of body weight than adults.
How Can I Avoid Unhealthy Exposure to Ozone?
In general, when ozone levels are high, your chances of being af- fected by ozone increase with the amount of time you spend being active outdoors and taking part in strenuous activities. For example, walking to a nearby store is not considered a strenuous or prolonged outdoor activity, but playing soccer is. Indoor, air-conditioned areas typically have half the ozone levels that are present outdoors. So, you can avoid unhealthy expo- sure to ozone by staying indoors in these cooler areas during the day.
Another way to avoid unhealthy exposure to ozone is by limiting the time you are active outdoors or by reducing your outdoor activity level. For example, instead of running or jogging for an hour, run for just 30 minutes or take a walk. You can also plan outdoor activities for times when ozone levels are lower, usually in the early morning or evening.
Use this Air Quality Index (AQI) to plan your activities. The Envi- ronmental Protection Agency (EPA) created the index as a way to re- port daily quantities of five major pollutants. In Texas, the AQI is gen- erally a convenient measure of ground-level ozone because it is the most common air pollutant.
Where Can I Learn More About Ozone?
- Texas Natural Resource Conservation Commission, tnrcc.state.tx.us
- Clean Texas Air, www.cleantex.org
- S. Environmental Protection Agency (EPA), www.epa.gov
- American Lung Association, lungusa.org
- City, county, municipal air quality
Good (0 to 50)—Level Green
- No warning is issued at this level. No health effects are expected.
Moderate (51 to 100)—Level Yellow
- No warning is issued at this level. Concentrations of ozone at this level may cause some respiratory effects from prolonged exposure during outdoor activity in people who are unusually sensitive to ozone.
Unhealthy for Sensitive Groups (101 to 150)—Level Orange
- If you are a member of a sensitive group—children who are active outdoors, adults involved in strenuous outdoor activities, people with a respiratory disease such as asthma, and people who are unusually susceptible to ozone—exposure to concentrations of ozone at this level may causesome respiratory symptoms, such as coughing or pain when taking a deep breath. These people should limit prolonged outdoor activity.
Unhealthy (151 to 200)—Level Red
- If you are a member of a sensitive group (see description in Level Orange), exposure to concentrations of ozone at this level will increase your chances of experiencing respiratory symptoms, such as coughing or pain when taking a deep breath. These people should avoid prolonged outdoor activity. Everyone else should limit prolonged outdoor activity.
Very Unhealthy (201 to 300)—Level Purple
- If you are a member of a sensitive group (see description in Level Orange), exposure to concentrations of ozone at this level will cause severe respiratory symptoms and impaired breathing. Stay in an air-conditioned room and avoid outdoor exertion. Everyone else should limit outdoor exertion.
Hazardous (301 to 500)—Level Maroon
- If you are a member of a sensitive group (see description in Level Orange), exposure to concentrations of ozone at this level will cause severe respiratory symptoms and impaired breathing. Stay in an air-conditioned room and avoid all outdoor exertion. Level Maroon emergency conditions are extremely rare, but they are more likely to affect the entire population. Everyone should avoid all outdoor exertion.