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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 volatile organic compounds (VOCs) and nitrogen oxides, in the presence of sunlight. Ozone pollution is due to an increase of ozone in the ambient air (i.e. the air that surrounds us). 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. According to the Texas Commission on Envrionmental Quality (TCEQ), 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. There are two families, or classes, of gases that combine in the atmosphere to make ozone, and these are called ozone precursors. They are 1) oxides of nitrogen (simple combinations of oxygen and nitrogen atoms), which are called NOx, and 2) volatile organic compounds, called VOCs. When NOx and VOCs blend in the atmosphere on a hot, sunny day, they make ozone. If there isn't much wind blowing, the ozone concentrations can build up to high levels in the ambient air.  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 2002 was on-road vehicles. The pie chart below shows that, in 2002, 33% of all VOCs generated in Bexar County came from on-road vehicles. The data collection on which this pie chart is based is the 2002 Alamo Area Council of Governments (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.  The following information is provided courtesy of the TCEQ. Ozone Is a Health Hazard 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 Texas The TCEQ collects daily ozone measurements at several monitors across the state. These measurements are used in determining if the National Ambient Air Quality Standard has been exceeded. The Air Quality Index (AQI) 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. 
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Natural Resources Outreach
Brenda Williams Projects Manager Alamo Area Council of Governments 8700 Tesoro Drive, Suite 700 San Antonio, TX 78217 (210) 362-5200 |
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