High concentrations of ground-level ozone can cause shortness of breath, coughing, wheezing, headaches, nausea, and eye and throat irritation.¹ People who suffer from lung diseases such as emphysema, bronchitis, pneumonia, asthma and colds have even more trouble breathing when the air is polluted.² These effects can be worse in children³ , the elderly⁴ and exercising adults.⁵

Ozone is a molecule of three oxygen atoms. Ozone is formed through a chemical reaction between natural (i.e. lightning) and man-made (i.e. solvents from drying paint) emissions of VOCs and nitrogen oxides, in the presence of sunlight.⁶
Click here to view ozone creation animation.

Ozone pollution is due to an increase of ozone in the ambient air (i.e. the air that surrounds us).⁷ Ozone Pollution is mainly a daytime problem during summer months because warm temperatures play a role in formation of high ground-level ozone. For the San Antonio region, Ozone Season is April through October, when temperatures are at their highest. During these high temperatures, when the sunshine is strong and winds are weak, ozone can build up to harmful levels.

"Ground-level ozone is the most common air pollutant in Texas and the nation. Ozone is also one of several pollutants that make up "smog," which you may recognize as the reddish brown haze that forms when the air quality is poor. Since ozone itself is colorless, the air can look clear even when high ozone concentrations are present." ⁸

Ozone does occur in nature; however, many of our everyday activities produce pollution that forms ozone. The Emissions Inventory is an exhaustive list of the sources of the ozone precursors produced in a region, including everything from lawnmowers to hairspray, power plants to highway traffic. The Emissions Inventory includes the estimated rates at which the precursors are produced. The second largest single source of VOCs in Bexar County during ozone season 1999 was on-road vehicles. The pie chart below shows that, in 1999, 26% of all VOCs generated in Bexar County came from on-road vehicles. The data collection on which this pie chart is based is the 1999 Alamo Area Council of Government (AACOG) Emissions Inventory.

Similarly, according to the same Emissions Inventory, the largest single source of NOx generated in Bexar County during ozone season 1999 was on-road vehicles. This pie chart, shown below, shows that 46% of the NOx produced in Bexar County came from on-road vehicles. This helps to explain why controlling emissions from cars and trucks powered by gasoline is so effective in reducing ozone – cutting down on ozone precursors cuts down on ozone, and on-road vehicles are big contributors of ozone precursors.

1999 NOx Emissions for Bexar County

The following information is provided courtesy of the TCEQ.

Ozone Is a Health Hazard⁹

The biggest concern with high ozone concentration is the damage it causes to human health, vegetation, and to many common materials we use.

The biggest concern with high ozone concentration is the damage it causes to human health, vegetation, and to many common materials we use.

High concentrations of ozone can cause shortness of breath, coughing, wheezing, headaches, nausea, eye and throat irritation, and lung damage. People who suffer from lung diseases like bronchitis, pneumonia, emphysema, asthma, and colds have even more trouble breathing when the air is polluted. These effects can be worse in anyone who spends significant periods of time exercising or working outdoors.

Children often play outside for long periods during the summer. Their lungs are still developing, and they breathe more rapidly and inhale more air pollution per pound of body weight than adults. On days when ozone levels are high, these factors put children at increased risk for respiratory problems.

Adults breathe more than 10,000 times each day. During exercise or strenuous work, we breathe more often and draw air more deeply into the lungs. When we exercise heavily, we may increase our intake of air by as much as 10 times our level at rest. The interaction between air pollution and exercise is so strong that health scientists typically use exercising volunteers in their research.

Materials damaged by ozone include rubber, nylon, plastics, dyes, and paints. Also, many food crops are damaged by ground-level ozone each year.

Ozone levels are considered by the U.S. Environmental Protection Agency (EPA) to be "unhealthful" and exceed the National Ambient Air Quality Standard when they are measured at 125 parts per billion (ppb) or higher under the one-hour standard or at 85 ppb or higher under the eight-hour standard. When a single monitoring site has exceeded the one-hour standard on more than three days in three years, the EPA classifies the surrounding county or metropolitan area as not attaining the ozone standard, or "nonattainment" for ozone. Those areas in "attainment" of the one-hour standard are required to meet the eight-hour standard of a three-year average of the fourth-highest daily maximum eight-hour concentration measured at each site not to be at or exceed 85 ppb.

Ozone Readings in Texas¹⁰

The TCEQ collects daily ozone measurements at several monitors across the state. Peak ozone concentrations found yesterday in the state's major metropolitan areas are available, as well are daily peak ozone concentrations since January 1, 1998. Today's peak ozone concentrations are also available. These concentrations are used in determining if the National Ambient Air Quality Standard has been exceeded.

The Air Quality Index (AQI), formerly known as the Pollution Standard Index (PSI), is derived from air pollutant measurements and is used to determine an AQI rating of "Good," "Moderate," or "Unhealthy." Because ozone measurements are usually higher in Texas than those of other air pollutants, the AQI is normally based on ozone levels.

According to the EPA, work to reduce ground-level ozone concentrations has been difficult.

"In the southern and north central regions of the United states, ozone levels have actually worsened in the past 10 years ... Much of this ozone trend is due to increased emissions in nitrogen oxides (NOx), a family of chemicals that can spread hundreds of miles downwind. Between 1970 and 2000, NOx emissions in the United States have increased almost 20 percent (and 3 percent increase in the last 10 years). The majority of this increase is attributed to growth in emissions from non-road engines (like construction and recreation equipment), diesel vehicles, and power plants."¹¹

What is ozone? | Why is there a difference? | How can I help?
Back to Ozone 101: click here
Back to Learning About Air Pollution: click here
Back to Air Quality: click here

REFERENCES

For more information about AACOG's Air Quality Program contact:

Peter Bella, AACOG Natural Resources Director
8700 Tesoro Drive, Suite 700
San Antonio, TX 78217
Phone: (210) 362-5249
Fax: (210) 225-5937
E-Mail: pbella@aacog.com