The EPA issued a proposed rule on November 29, 1996, that proposes new NAAQS for ozone and particulate matter. Both standards are being lowered (i.e., made more stringent). These standards are closely linked; the same sources that emit fine particles, such as industrial and residential combustion and vehicle exhaust, can also contribute ozone precursors, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). Other sources of VOCs include chemical plants, refineries, factories, consumer and commercial products, and other industrial sources. Nitrogen oxides and volatile organic compounds react in the presence of sunlight and heat to form ground-level ozone (O3). For purposes of this assignment, only the proposed standard for ozone will be addressed.
Ground-level ozone is the chief component of smog. Numerous studies document the deleterious health and welfare effects of ozone. Even at low levels, ozone can cause acute respiratory problems, aggravate asthma, cause temporary decreases in lung capacity of 15 to 20 percent in healthy adults, cause inflammation of lung tissue, lead to hospital admissions and emergency room visits, and impair the body's immune system defenses, making people more susceptible to respiratory illnesses, including bronchitis and pneumonia. The populations most at risk include children, whose respiratory systems are still developing, the elderly, and those who are outdoors and moderately exercising during the summer months, when ozone levels are at their highest. Ozone also impacts plant health by interfering with the ability of plants to produce and store food. Weakened vegetation is more susceptible to disease, pests, and other environmental stresses. Studies have shown that ground-level ozone reduces agricultural yields for many economically important crops, such as soybeans, kidney beans, wheat, and cotton.
There is little question, therefore, that ground-level ozone is harmful to the health of humans and plants, and therefore should be regulated. There is, however, significant controversy regarding a "safe" level of ozone, that will protect human health with an adequate margin of safety. National ambient air quality standards include primary standards (i.e., those relating to protection of human health) and secondary standards (i.e., those relating to welfare-based factors, such as visibility and materials damage). The current primary ozone standard was set in 1979. The primary standard is 0.12 ppm, measured over one hour. An area is in attainment (i.e., meets the standard) when the number of days per year on which the level is exceeded is less than or equal to one (1), averaged over three (3) years. The new proposed standard is 0.08 ppm measured over 8 hours. More specifically, an area attains the standard when the third highest daily maximum 8-hour concentration, averaged over three years, is below 0.08 ppm. EPA is proposing a "concentration-based" form instead of an "expected exceedance" form because it more directly relates to ozone concentrations associated with health effects. In addition, it avoids the problem of counting all exceedances, regardless of degree, as equal. (In other words, under the current system, a value of 0.13 ppm is given the same weight as a value of 0.20; both readings are considered "exceedances").
Some of the issues on which EPA is seeking comment include:
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