nd I immersed ourselves in ozone toxicology and epidemiology. We presented a paper titled “A Toxicological Review of the Ozone NAAQS” at various professional meetings, and are helping prepare ground-breaking analyses of the ozone data for publication in peer-reviewed journals.
Below are a few facts and simplified explanations of the TCEQ’s conclusion that a lower ozone standard is not justified.
Also see links to other references and ozone information.
Sensitivity of Asthmatics to Ozone:
- Exposure of human volunteers to ozone showed similar lung effects in asthmatics and in non-asthmatic subjects. Additionally, children are no more sensitive to ozone than are young adults.
Mortality Caused by Long-term Exposure to Ozone:
- Only 1 out of 12 studies considered by the EPA showed an association between long-term exposure to ozone and early death (after considering other pollutants). This single study is used by the EPA as evidence that long-term exposure to ozone causes mortality. Interestingly, this study did not show higher mortality in Southern California, where some of the highest ozone levels in the country are measured.
Many factors influence mortality, and the effect of an increase in ozone by 10 ppb is tiny in comparison to these other influences.
Ambient Ozone Concentrations Don’t Represent Real-world Exposure:
- Ozone is an outdoor air pollutant, because systems such as air conditioning remove it from indoor air. Since most people spend more than 90 percent of their time indoors, we (and the people in the epidemiology studies used to justify lowering the standard) are rarely exposed to significant levels of ozone.
- Even people who work outdoors are exposed to, at most, 60 percent of the ozone concentration that is measured at an ambient monitor. Additionally, there are ozone standards particularly for workers to ensure that they are protected.
- For ozone to cause a slight change in lung function in clinical studies, people need to be exposed to outdoor levels of ozone for hours while vigorously exercising (example: 6 hours of bicycling). These changes in lung function are often so small that they are within a person’s normal daily variation.
- Epidemiology studies show an association between a person’s likelihood of dying, and the outdoor concentrations of ozone in the days before (or the day of) a person’s death. However, we spend most of our time indoors (particularly people who are near death), so the people in the studies were exposed to levels of ozone that are far below those that cause any clinical effect.
Problems with Implementing a New Ozone Standard:
- Some places in the U.S. have background levels of ozone that account for up to 80 percent of total ozone. Background ozone occurs naturally, or is transported from other countries. The EPA does not take this into account when making the rule.
- Ozone is not produced directly, but instead forms when other chemicals (particularly nitrogen oxides) react with sunlight. However, ozone chemistry is complicated, and the same nitrogen oxides that produce ozone can also react with existing ozone to remove it from the air. So places that have high nitrogen oxide production (such as areas near roads), often have lower ozone levels.
- Because ozone chemistry is complex, lowering ozone-producing chemicals in the cities would decrease ozone in the suburbs, but could increase ozone in the inner-cities (because there will be a decrease in the nitrogen oxides that can remove ozone). This means that, according to EPA predictions, those living in the inner cities could bear more health burdens, while people on the outskirts enjoy the predicted benefits.
Proponents of lower ozone standards sometimes advance the argument that even if the lower standards are not scientifically justified, what is it going to hurt to have cleaner air? The answer is, why regulate something that is not really going to have a benefit? That effort should be put into regulating something that will have a benefit—perhaps air toxics—perhaps figuring out what is causing increased reported rates of ast