Chemical & Engineering News

April 14, 1997

Copyright © 1997 by the American Chemical Society

The road to new ozone and particulate matter air quality standards is paved with good intentions, ambiguous science

Linda Ross Raber
C&EN Washington

Flowers are blooming, birds are singing, lovers walk hand-in-hand. But there's more than just spring in the air. And it's enough to make you sick - or is it?

Over the past 27 years, the U.S. has spent more than $450 billion to clean the air of life-threatening pollution. By anyone's measure, this effort has achieved tremendous success, but problems remain. The most recent report card issued by the Environmental Protection Agency indicates that pollution levels have been reduced nearly 30%, on average, over this period with even greater gains made for some of the most serious pollutants - such as lead and carbon monoxide - and in some of the most polluted cities.

Despite those achievements, EPA has proposed new regulations that suggest the U.S. has a long way to go. Last November, EPA Administrator Carol M. Browner proposed new, tighter, national ambient air quality standards for ground-level ozone and particulate matter. EPA coupled the two proposals because ozone and particulate matter come from similar sources and cause similar problems; however, Browner is under court order to come to a decision on the particulate matter standard by July 19.

Since November, an enormous public relations effort has turned up the heat on EPA, on the Clinton Administration, and on Congress to stop the agency from moving forward with the new regulations. A smaller effort, waged with fewer dollars and a fraction of the lobbying power, has supported EPA's moves and is pushing for standards even tighter than those Browner is proposing.

At issue is a fundamental policy question of whom do you protect from what and at what cost. EPA and supporters of the proposed standards point to children suffering miserably with asthma, unable to play outside in the summer, dependent on medications. It's easy to understand that from the viewpoint of anguished parents in a hospital emergency room, no cost is too high to protect their child.

Others, including most U.S. industry, say as costs go up - and these standards would cost a fortune - they have to lay off employees. They ask "Are children better served by having unemployed parents?" Numerous studies much less ambiguous than the ones cited by EPA to back its proposals show that the one condition that is clearly and consistently related to childhood asthma is poverty. How, then, should Browner play Solomon?

The Clean Air Act directs her as EPA's administrator to set air quality standards at levels that, in her judgment, protect the public health with an adequate margin of safety. That is the law and that is her job. According to the Clean Air Act, Browner must base her decision on public health considerations alone. She must not consider the cost of implementing standards. And she must use the best available science to guide her decision.

To inform the administrator's decision, the law requires EPA to convene the Clean Air Scientific Advisory Committee (CASAC). This independent scientific review committee includes at least one member of the National Academy of Sciences, one physician, and one person representing state air pollution control agencies, along with a number of other specialists. It is charged with examining the current science on criteria pollutants and advising the administrator on whether the standards should be revised.

Given the precise wording of the Clean Air Act, the inexact nature of epidemiology, and the paucity of some air quality information, Browner may be doomed to lose what she sees as a battle for children's lives.

Those for and against EPA's proposals are marshaling the large body of scientific information on the health effects of ozone and particulate matter to reinforce their positions. Opponents of the new standards have latched onto the shortcomings in the science and are exploiting every difference of opinion among CASAC members. Advocates of these standards, including EPA, point to the huge number of studies that implicate the pollutants in children's health problems.

Part of the reason that these proposed standards have been so problematic lies in the Clean Air Act itself. The national ambient air quality standards have been a cornerstone of the Clean Air Act since 1970. The law requires EPA to set standards to reduce ozone, particles 10µm or less in diameter, lead, carbon monoxide, nitrogen dioxide, and sulfur dioxide to levels that are more than adequate to protect public health. But EPA can no longer follow the letter of the law, because science, as it has evolved, does not provide clear answers about the thresholds of danger.

Since it is impossible to find a zero-risk level, it follows that it's also impossible to tack on a margin of safety. So any decision that is made to regulate criteria pollutants under the Clean Air Act is ultimately a policy call for the EPA administrator.

And Browner believes that the weight of scientific evidence compels her to tighten the ambient air quality standards for ozone and particulate matter. "Hundreds of thousands of children are not protected under the current standards but would be under EPA's proposals," she says. Opponents say that the proposals are based on science that is equivocal at best - and junk at worst.

Senate Environment & Public Works Committee Chairman John H. Chafee (R-R.I.), a moderate on environmental issues, says the proposals may "push too far, too fast. ... Frankly, there is reason to be worried about the health of the Clean Air Act." And in what may be to EPA the unkindest cut of all, even other agencies within the Clinton Administration are highly critical of the standards.

But Browner has some staunch allies - for example, the American Lung Association, which sued EPA to force its review of the particulate matter standard; the Sierra Club; and the Natural Resources Defense Council. These groups support the proposed revisions to the air standards but believe they don't go far enough.

Opposing any change in the standards is a multi-million-dollar coalition of large and small businesses, major industry, electric power generators, and trade associations. The 600-member Air Quality Standards Coalition has hired the best lobbyists in Washington, D.C., to turn legislators and the public away from the proposed standards. Lobbyist C. Boyden Gray, once counsel to President George Bush, is the power behind the coalition, as well as the leader of the industry-funded group Citizens for a Sound Economy. The member companies of the coalition have each contributed between $5,000 and $100,000 for the antistandards battle.

"The current proposal reflects such little understanding that it risks complete balkanization of industrial America," says Gray. "I think it's really foolhardy. My objection is not solely, or even predominantly, on the cost side. Most of us have more problems with the fact that these standards just aren't justified. There's no need to rush. The standards may actually cause harm."

He explains: "If air conditioning is a method of screening out pollutants and neutralizing heat and humidity problems, then raising electricity costs is not a good thing to do. We know that people die because they cannot afford to keep their air conditioners going during peak periods of the summer." Gray asserts that much of the ozone precursors and particulate matter are emitted by coal-fired electric power plants. These facilities and consumers would have to bear much of the cost.

Browner may not be permitted to consider costs, but members of the Air Quality Standards Coalition certainly do. By any measure, the proposed regulations carry a big price tag.

Costs and benefits

In terms of sheer cost, the proposed standards are the largest regulatory action ever attempted by the agency. Browner estimates that the cost of implementing both standards would be approximately $6.5 billion to $8.5 billion per year with annualized benefits of $120 billion. She says that the $120 billion includes the workdays and school days that would be preserved and the reduction in hospital admissions that would be achieved. Other benefits that would accrue don't have a dollar cost associated with them. These are ecosystem protection, water quality protection, and improved visibility.

Browner says the particulate matter standard could save 15,000 lives per year by preventing premature deaths. Together, the standards would also prevent 250,000 incidences of respiratory symptoms such as aggravated coughing and difficult breathing among children annually. Although careful not to say that ozone or particulate matter causes asthma, Browner says adoption of the standards would prevent 250,000 days of aggravated asthma each year.

"Asthma among our children has increased 118% between 1980 and 1993. It is the single greatest cause of childhood hospital admissions and among the leading causes of missed days of school," Browner claims. In addition, she asserts that the standards would prevent 60,000 cases of bronchitis, 1.5 million cases of decreased lung function, and 9,000 hospital admissions annually.

EPA claims that more stringent air quality standards for ozone and ultrafine particles would produce health improvements for Americans far outweighing the costs. But even by EPA's own numbers, the health improvements realized would be slight for ozone, and the claimed benefits for ultrafine particles rest on shaky scientific assumptions.

The estimates of benefits due to reduced mortality presented in EPA's regulatory impact analysis are also controversial. Reduction in mortality contributes more than 90% to that $120 billion in benefits. EPA values reduction in mortality at $4.8 million per life regardless of how many years or days of life are lost. The benefit realized from avoidance of a case of bronchitis is $588,000. It adds up quickly.

The cost estimates are challenged by the American Petroleum Institute (API), among others, who say the annual cost of meeting EPA's proposed regulations is astronomical and would make a sizable dent in the average family's purchasing power. API claims, "The fine print reveals that [EPA's estimate] only pertains to a small portion of the total costs because the agency only estimated the costs of partial attainment and simply stopped counting when the costs began to rise exponentially." Hence, API believes the cost of reaching full compliance could be several times EPA's upper limit of $8.5 billion a year.

In fact, the President's Council of Economic Advisers estimates that the cost of fully attaining the proposed standard for ozone alone could be up to $60 billion per year - or more than the nation now spends on all air pollution abatement and control. The council's estimate indicates that an average American family of four would have its purchasing power reduced by about $900 per year to pay for the ozone standard.

Proposed standards

Although ozone in the upper atmosphere is beneficial because it shields Earth from harmful ultraviolet rays, ground-level ozone damages lung tissue, reduces lung function, and sensitizes the lungs to other irritants.

Unlike other pollutants, ground-level ozone is not emitted directly into the air by specific sources. It is formed when volatile organic compounds (VOCs) and the oxides of nitrogen (NOx) react on hot days in bright sunshine. Nitrogen oxides are produced by burning fossil fuels, mostly from highway vehicles and large industrial power plants such as those run by the electric utilities. VOCs are also produced by combustion, including burning gasoline in automobile engines, but they can come from paints and solvents. Large quantities of VOCs are produced naturally by vegetation.

The proposed rules call for replacing the standard for ozone of 0.12 ppm measured over one hour to 0.08 ppm measured over eight hours. For a locality to be in compliance, the average of the third highest reading in each year for three years cannot exceed 0.08 ppm. At this level, the proposed ozone standard is significantly more stringent than the present one-hour standard.

The chemical industry has consistently produced between 1 and 2% of nitrogen oxides and about 7% of VOCs over the past years. According to Joe J. Mayhew, assistant vice president for environmental and policy analysis at the Chemical Manufacturers Association, implementation of the proposed ozone standard would require investment in low-NOx burners. "However, indirect costs like electricity and transportation are probably bigger concerns for the chemical industry than direct costs," he says.

EPA is also seeking comment on several other options, including an ozone standard of 0.09 ppm measured over eight hours as well as a range of ozone concentrations from 0.07 ppm measured over eight hours to 0.12 ppm measured over one hour (the current standard)." EPA could adopt 0.09 with an eight-hour averaging time, and we'd be quite happy with that," says Mayhew. That eight-hour standard is roughly equivalent to the current one-hour standard.

The new standards would result in many counties being thrown into noncompliance, which can ultimately result in penalties such as state loss of federal highway funds. EPA projects that 335 counties, on the basis of their measured air quality from 1993 to 1995, would not meet the proposed ozone standard.

The other half of EPA's two-pronged proposal would set a national standard for very fine particulate matter, which comes largely from combustion sources like power plants and large incinerators. The chemical industry has consistently produced 3% of the nation's particulate matter emissions. In contrast, residential wood burning produces more than five times as much particulate matter by weight than does the chemical industry.

The proposed standard would, for the first time, regulate PM2.5 - that is, particles with diameters of 2.5 µm and smaller, in concentrations of 15 µg per cubic meter annually and 50 µg per cu m daily." This is the big-ticket item," says Mayhew. "Controlling for fine particulate matter in the chemical industry would require better electrostatic precipitators." He adds that the increased cost of electricity and fuel that would result from these standards would be the most difficult for the industry to bear.

The current particulate matter standard regulates particles 10 µm or smaller in concentrations of 50 µg per cu m annually and 150 µg per cu m daily. The 10-µm standard would remain in place under EPA's proposal because data continue to indicate that these particles are harmful.

The proposed PM2.5 standard would throw considerably more areas out of compliance than the existing PM10 standard does. Under the proposed standard for fine particulate matter, EPA projects that 167 counties would be out of compliance.

Particulates health effects

To many, the science behind the proposed standards is less than compelling - even for epidemiology - and several prominent members of CASAC do not support the standards as proposed by Browner.

EPA began drafting its so-called criteria document - a collection of relevant peer-reviewed research on the health effects of particulate matter - in the middle of 1994. "Recent criteria documents have become mammoth undertakings," says CASAC Chairman George T. Wolff, an atmospheric scientist from General Motors. "The first particulate matter criteria document published in 1969 summarized the relevant science in 220 pages. The final version of the present criteria document is a three-volume set containing over 2,400 pages."

Once the criteria document is compiled, EPA then assembles its staff paper. This paper contains the agency's recommendations for the details of the standard along with justifications that are drawn from material contained in the criteria document.

CASAC reviews of both the criteria document and staff paper are iterative processes that usually involve two to three revisions to both of the documents before CASAC reaches a decision on the scientific merits of the proposals. In the past, the entire process has taken several years to complete. However, the particulate matter review was on an accelerated schedule because of the court order. CASAC members have complained about being rushed.

The evidence implicating particulate matter as a cause of death is strong but largely circumstantial. It comes mostly from epidemiological studies that looked at the rates of death and disease within specific communities and attempted to correlate that information with levels of particulates in the air. What is clear is that as levels of particles go up, so do death rates, hospital admissions, emergency room visits, and asthma attacks." As a consequence, there was a consensus among CASAC members that retaining an annual PM10 standard at the current level is reasonable at this time," says Wolff.

Two types of epidemiological studies related to particulate matter were cited by EPA and reviewed by CASAC. The first type was short-term acute mortality studies that compared daily particulate matter levels and mortality in a dozen or so locations around the U.S. "After filtering out or accounting for the effects of such things as season, day of the week, and meteorology on mortality, the remaining statistical relationship between daily particulate matter levels and daily mortality was quantified," says Wolff. "Although this relationship varied from location to location, the average value was a 4% increase in daily deaths for a 50-µg-per-cu-m increase in PM10 concentrations."

The second type of epidemiological study followed the health of certain groups of individuals for a number of years in various locations around the country. In these studies, the annual mortality rate in a given location was related to the annual average PM10 or PM2.5 concentrations after mortality rates were adjusted for smoking and other potentially confounding variables.

According to Wolff, of the three studies reported in the literature, two show a positive relationship between annual mortality and particulate matter and attribute two to three times the number of deaths to particulate matter as the short-term acute effect studies do. The third study, he says, shows no relationship between particulate matter and mortality, but EPA dismissed this study for a number of reasons, including its smaller sample size.

EPA used the higher mortality estimates from the two studies to conclude that premature deaths can result from chronic exposure to particulate matter, in addition to deaths caused by acute exposures. EPA also concluded that the mortality was due to PM2.5 rather than larger particles within the PM10 fraction of air particulates, "but the evidence for this conclusion was ambiguous," says Wolff.

Nevertheless, 19 of 21 CASAC members voted to recommend that very fine particulate matter - PM2.5 - be regulated. However, the CASAC panel could not reach consensus about an appropriate ambient level at which this ultrafine particulate matter should be regulated because, according to Wolff, "Our understanding of the health effects of particulate matter is far from complete."

EPA recommended a daily PM2.5 standard of 18 to 65 &µg per cu m and an annual standard of 12.5 to 20 µg per cu m. Four panel members supported specific ranges within or near the lower end of EPA's recommendations. Seven members supported specific ranges or levels near, at, or above the upper end of EPA's recommendations. Two members did not think a PM2.5 standard was warranted at all. The remaining eight panel members endorsed the concept of a PM2.5 standard but declined to select a specific range or level. As a result, says Wolff," only a minority of the panel members supported a range that includes the present EPA proposals."

TO SIDEBAR: Federal agencies question EPA's proposed air standards

Mary D. Nichols, EPA assistant administrator for air and radiation, believes that getting scientists to commit to a specific level of air pollution control will always be difficult. She reflects on her experience as head of the California Air Resources Board: "We set air quality standards for California that in some cases were more stringent or ahead of the federal government's, including an air quality standard for lead and a PM10 standard.

"In every one of these cases," Nichols recalls, "I found that the scientists were never willing to tell you that they were clear on what the exact level of the standard ought to be. They were willing to say, 'This is how far our research goes, and as a personal matter, we think you should be regulating this compound, or that this is a problem that you should be addressing.' But they understood that the setting of the standard itself is really a complex risk management decision."

Wolff believes that "the diversity of opinion expressed by the panel members reflects the many unanswered questions and large uncertainties associated with establishing the cause of the association between ultrafine particles and mortality." Most panel members were influenced, to varying degrees, by these unanswered questions and uncertainties.

One of the major uncertainties stems from the paucity of data that actually measured PM2.5 as opposed to studies that measured PM10, estimated the fraction of PM10 that is PM2.5, and extrapolated to human health effects. In addition, very tiny particles are often contaminated with other pollutants such as ozone, sulfur dioxide, or carbon monoxide. Those chemicals - not the particles - may be the real culprits.

The lack of a plausible biological mechanism for particulate matter toxicity troubled many of those presenting testimony before the Senate Committee on Environment & Public Works. And it also troubled most of the senators hearing the testimony.

Economist Anne E. Smith, vice president of Decision Focus, a Mountain View, Calif.-based risk assessment and management consulting firm, explained to the senators: "When we observe two types of data going up and down together, we should not necessarily conclude that there is a causal relationship between the two phenomena. ... When we have statistical evidence of the sort that seems to suggest that ambient particulate matter and mortality go up and down together, we also want to have scientific data about biological processes associated with particulate matter to help us explain why we should believe this is a causal relationship, and not just a statistical association."

She said that even EPA asserted in its criteria document that no credible data support particulate matter toxicity. And even when particulates were put into animals' lungs, no one could elicit consistent responses. Smith says this result is troubling, because "you might expect adverse changes to be readily observable in laboratory experiments if the health effects were as large as the statistics seem to suggest."

CASAC member Daniel B. Menzel, an environmental toxicologist who is professor and chairman of the department of community and environmental medicine at the University of California, Irvine, is skeptical because the studies show that all particles - no matter where they come from or what they're made of - have the same toxicity. Even though particles on the West Coast are mostly sulfuric acid and particles on the East Coast are mostly nitric acid, they have the same effect. "One of the basic tenets of toxicology is that toxicity occurs via chemical reaction," he says. "How then can the same effect result from very different kinds of chemistries?" According to Menzel, "We must conclude that there is no plausible mechanism ... that can account for the reported results."

Whether very fine particles are themselves the cause of death and disease isn't as much of a concern to CASAC member Morton Lippmann, professor of environmental medicine at the Institute of Environmental Medicine at New York University. Lippmann does not claim PM2.5 to be the causal agent. Rather, he says, "PM2.5 is a better measure than any alternative metric of the complex in the particulate mass that is causing excess mortality and morbidity." Excess mortality, hospital admissions for respiratory diseases, and decreased lung function are all more strongly and consistently associated with ultrafine particles rather than with the larger fraction of PM10 particles, he explains.

Protester demonstrates against proposed EPA standards outside Senate building.

Nor is Harvard University epidemiologist Joel Schwartz especially troubled by the prospect that EPA could be on the verge of regulating not the pathogen, but its harbinger. As far as he is concerned, all of the harmful particles, regardless of what they're made of, are generated by combustion. "Hence, control strategies to reduce exposure to fine particles will never focus on a specific particle, they will focus on sources," he says.

Finally, recent reanalyses of the studies cited in EPA's staff paper have included gaseous criteria pollutants in their models and have revealed that, in many cases, ozone, sulfur dioxide, or carbon monoxide can be as important as or more important than particles in describing mortality. According to Ronald E. Wyzga, senior manager for air quality and risk at the Electric Power Research Institute in Palo Alto, Calif., reanalyses do not support an association between unambiguous particulate matter and health. The results do not agree with the original investigators' conclusions of a significant association between particulate matter and health.

Any number of models can be used to analyze statistical data. Hence, a researcher's choice of a model can always be criticized after the fact to call into question the results of an epidemiological study. That's the nature of epidemiology. Such statistical studies employ models that are designed to correct for so-called confounders, variables that can throw off a study's results. The myriad confounders in the particulate matter studies could include smoking, age, socioeconomic status, temperature, humidity, or other pollutants, for example.

Wyzga took aim and fired at the models used by particulate matter researchers at a Senate hearing. He said that under contract to EPA, the National Institute of Statistical Sciences, Research Triangle Park, N.C., reexamined daily mortality and particulate matter relationships in Birmingham, Ala." The reanalysis tried to ensure that the effect of hot, humid days is considered in any model trying to assess the influence of particulate matter on mortality. ... When humidity is included among the meteorological variables, the PM10 effect is not statistically significant," explained Wyzga.

Wolff and Lippmann disagree with each other on the validity of the assumption made in all of the acute studies that daily ambient particulate matter data collected from a centrally located air-monitoring site is representative of individual exposure to particulates. Wolff says the results of studies examining this assumption are ambiguous, but Lippmann says that growing evidence indicates that particles are uniformly distributed.

When experts disagree about virtually everything, it's hard to figure out what to think. Ultimately, CASAC strongly recommended that EPA immediately implement a targeted research program to address unanswered questions and uncertainties and also to get some long-term PM2.5 measurements.

Wolff believes there is plenty of time to do the research before setting standards, noting that PM10 concentrations have declined 22% from 1988 to 1995. Implementation of existing control programs required by the 1990 Clean Air Act Amendments that target PM2.5 precursors (VOCs, NOx, and SO2), diesel particulate matter emissions, and other primary emission sources are the reason for the decline.

TO SIDEBAR: Chronology of controversy over EPA's proposed standards...

"This trend will continue for the foreseeable future as additional measures required by the amendments are phased in," Wolff says. He insists that there is time to conduct the research recommended by CASAC. And once questions and uncertainties have been clarified," the appropriate PM2.5 standard could be established," says Wolff.

"EPA desperately needs to add to its understanding of how fine particulates really affect people so we can find what concentration would really protect people," says CMA's Mayhew. "Our bottom-line advice to EPA on particulate matter is to go ahead and set a fine particulate matter standard, but don't set a level now - maybe set a range. Then set up a monitoring network. This will allow EPA to go ahead and pick the level later when[ it has] more information." Mayhew believes it will take about three years to set up the monitoring network, and about three years to collect data on PM2.5.

Nichols disagrees with those who would wait. She says that, even under the most expedited view of the Clean Air Act, it will be more than a decade before any standards have to be met. And EPA is expecting litigation and possible amendments to the law by Congress to draw the process out even further. She explains that any child currently suffering under the current standards will be an adult by the time the rules go into place if EPA waits until all of the data are in before setting a standard.

Nichols explains that "setting a standard is just a starting point for a planning process. Research on control strategies, decisions on implementation, development of plans, and approval of plans all precede a final rollout of the regulatory requirement." Nichols believes it is better to use the best existing science to set a goal and then to refine that goal as more information becomes available.

Roger O. McClellan, president of the Chemical Industry Institute of Toxicology, marvels at the paradoxical situation." It appears," he says, "that the only way to get funding for more PM2.5 measurements is to get a PM2.5 standard. Thus, we are faced with the perverse situation of creating a standard to get scientific data rather than having a standard developed based on solid scientific data." Based in Research Triangle Park, N.C., the institute is a not-for-profit research organization that assesses the human health risks of exposure to chemicals.

Ozone health effects

Nichols insists that "ozone has been researched from every angle that you could research. There isn't any debate in the science community about the quality or quantity of the science on ozone. The only issue that remains on ozone is what conclusion you draw from a policy perspective from the data that exist."

CASAC looked at 185 of the latest studies of the effects of ozone on human health. All of them showed harmful effects from ozone at the current regulated level. EPA selected "outdoor children" and "outdoor workers" - particularly those with preexisting respiratory disease - as the appropriate populations to study because they would be the most vulnerable.

CASAC concurred that "ozone may elicit a continuum of biological responses down to background [which is about 0.04 ppm]," says Wolff. So, CASAC concluded that there is no "bright line" that distinguishes any of EPA's proposed standards as significantly more protective of public health. "For example," says Wolff," the differences in the proportion of outdoor children responding [to levels] between the present standard and the most stringent EPA proposal were small, and their ranges overlapped for all health endpoints." Consequently, CASAC reports, "the selection of a specific level and number of allowable exceedances is a policy judgment."

So why did EPA, as a matter of policy, propose to tighten the standard when even its advisory committee could see no difference in the health effects resulting from exposure to ozone at the current standard level and to exposure to ozone at the tightest standard proposed?

Nichols says Browner gave more weight to the opinions of those CASAC members who were health scientists, like physicians and epidemiologists, than she did to the opinions of those whose expertise was in areas like atmospheric chemistry or control technologies. Browner says EPA decided to propose the 0.08-ppm level because it was the lowest level recommended by individual CASAC panel members and because it was the lowest level tested and shown to cause effects in controlled human-exposure health studies.

"Given the uncertainties associated with this kind of complex health decision, we believe that an appropriate goal is to reduce the number of people exposed to ozone concentrations that are above the highest level recommended by any of the members of the CASAC panel," Browner explains.

Wolff describes controlled human-exposure studies reviewed by CASAC. In these, individuals were exposed to ozone concentrations slightly above, at, or below the present standard, usually for six hours, while engaged in light to heavy exercise. Before, during, and after the exposure, the individuals' lung functions were monitored, and any symptoms, including coughing, shortness of breath, or chest pain, for example, were recorded.

"These studies have produced two important results," says Wolff. First, no decreases in lung function were observed for people exposed for one or two hours while resting until ozone concentrations were greater than three times the present standard. But after people had been exercising for many hours, their lung function decreased even at concentrations below the present standard.

"This evidence suggests that an eight-hour standard is a better measure of response than a one-hour standard," Wolff says. All CASAC members voted to recommend that EPA propose an eight-hour standard instead of a one-hour standard.

The hospital admission studies for ozone examined the relationships between daily ozone concentrations and daily hospital admissions for respiratory problems. "These studies have consistently shown an apparent linear relationship in various North American locations between ozone and the admissions, and EPA has assumed that this relationship is cause and effect," says Wolff. The relationship held even for exposures to ozone at concentrations below the present standard. "There is no evidence of a threshold concentration, and this reinforces the conclusion from the field studies," Wolff says.

According to George D. Thurston, associate professor of environmental medicine at New York University's School of Medicine, "Studies have shown compelling and consistent evidence of adverse effects by ozone below the current U.S. standard."

Both population-based epidemiologic studies, in which an entire city's population might be considered in the analysis, and cohort studies, in which selected individuals - such as a group of asthmatics - are considered, have confirmed the association between exposure to ozone air pollution and increasing numbers of adverse impacts, Thurston explains.

One of the field studies Thurston offers as evidence that ozone is harmful to human health is his own study, which is quite controversial. In summer camps, asthmatic children, engaged in the normal physical activities that occur at these camps, participated in lung function testing, and the results were compared to the ambient ozone concentrations.

"This study of a group of moderately to severely asthmatic children shows that these children experience diminished lung function, increased asthma symptoms, and increased use of unscheduled asthma medications as ozone pollution levels rise," says Thurston. "On the highest ozone days, the risk of a child having an asthma attack was found to be approximately 40% greater than on an average study day, with these adverse effects extending to below 120 ppb ozone," he says.

Thurston based his conclusion on a study of 166 children (ages seven to 13) attending an "asthma camp" downwind of New York City during the last week of June 1991 (52 children ), 1992 (58 children), and 1993 (56 children). He found that there were, on average, 20 unscheduled uses of medication each day among each group of children. On the day with the highest level of air pollution, there were 28 unscheduled uses. Thurston attributes this entire increase in unscheduled medication use to air pollution.

In terms of health effects, this would mean that on the day with the most air pollution, one in seven moderately to severely asthmatic children would use their medication one extra time per day, and one in five moderately to severely asthmatic children would have one additional respiratory symptom per day. Thurston and EPA find this information compelling. But others don't.

"On their face, these results demonstrate that air pollution is not the severe health threat that EPA and the American Lung Association would have us believe," says Steven J. Milloy, who is an attorney, health scientist, biostatistician, crusader against "junk science," and a consultant on environmental risk management. "But do they establish that air pollution caused even the effects observed?"

Milloy points out that Thurston collected data on relative humidity and pollen and found that neither significantly correlated with adverse health effects. "However, changes in temperature, atmospheric pressure, dust, fumes, and food preservatives may also exacerbate asthma," he says. "But the researchers did not consider any of these risk factors."

Milloy says asthma is "easily and commonly exacerbated by anxiety ... but these researchers ignored this potentially important confounding risk factor." He illustrates: "Imagine being a 10-year-old at 'asthma camp' where 'the buzz' around camp is about the latest pollution readings. Pollution levels increase. Kids get anxious. Airways constrict. Unscheduled medication use increases."

Other studies have analyzed summertime daily hospital admissions of patients with respiratory symptoms. These studies show a positive relationship with ambient levels of ozone. Some studies suggest that these associations remain even after controlling for temperature, allergens, and other pollutants.

Research conducted by Thurston and reviewed by CASAC projected increases in hospital admissions of asthmatics in the New York City area for various ozone air quality standards. The research projected that there would be 100 fewer potential hospital admissions for respiratory symptoms attributable to ozone in excess of background levels if the current standard were tightened to a standard very close to EPA's proposal. However, the 100 fewer admissions are a tiny fraction of the 28,195 asthma admissions in New York City each year. Whether this is an important benefit depends on whether you're one of those 100 people.

"Based on the available health evidence, the vast majority of the public is not in danger of noticeable health effects from current air quality in most U.S. cities," says Kenneth W. Chilton, director of the Center for the Study of American Business in St. Louis. "Certainly, it is not clear at this time that a new, more stringent ozone standard is needed."

Nevertheless, Nichols maintains, "the data are absolutely clear that ozone causes cellular damage in humans. They are absolutely clear that there are short-term effects on lung function, on people's ability to breathe. It affects people's ability to do work; it affects people's susceptibility to colds, respiratory infections, and coughs; and it triggers asthma attacks in people who have asthma."

"There's no dispute about cause and effect," Nichols says. "We know it's ozone. We measure the ozone; we measure the people or the [test] animals. The only dispute is about whether we ought to care as a country. And we think the Clean Air Act tells us, yes, we care."

Nichols insists that the decision on whether to revise the standards has not been made and probably will not be made until very close to the court-imposed deadline of July 19. "It is important for people to understand that, in putting out the proposals, the agency used CASAC and relied on review by CASAC of a variety of peer-reviewed scientific documents," she says. "CASAC, by overwhelming consensus, did tell us to set standards, even if it didn't tell EPA precisely where to set the standards." Nichols says EPA has proposed the rationale that it believes is the most convincing for where those standards should be set.

"We are compelled to review the standards; we are not compelled to change them, except if the evidence is convincing," Nichols explains. The scientific evidence that was available when the standards were proposed convinced EPA that there was a good reason to change them. "Those who are trying to create an impression that EPA is out there on its own trying to ratchet up standards so it can justify increasing its budget are really doing the whole debate a disservice," she says.

"Why are they rushing to do something when they could easily take three to five years to do some research, which they say they badly need to resolve the great uncertainties?" asks Gray. "EPA being sued by the Lung Association gives the agency the excuse to do this now, but the only thing the lawsuit says is that you have to make a decision one way or the other. The lawsuit doesn't require EPA to implement the standards," he adds.

"I'm really not a zealot," says Nichols." And I'm not a person who believes in jumping off of cliffs. I think we have the weight of the facts on our side, and we have the overall public interest on our side. And if at the end of the day the proposal is modified slightly, it's not a defeat and it's not the end of the world."

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