S C i c N l ir 1 b AND T O W M I C DILEMMA!
B Y S. K. FRIEDLANDER AND MORTON LIPPMANN .~ ~~
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ecent epidemiological studies indicate that increases in human mortality (1-9) and morbidity (10-23) have been associated with levels of particulate pollution significantly lower than those previously thought to affect human health. If the evidence withstands critical evaluation, we will probably need to revise downward the National Ambient Air Quality Standard (NAAQS) for particulate matter (PM), even though the scientific basis for making the decision is weak. Tightening the standard will have significant economic conse148 A
quences for U.S. industry and will affect air pollution standards internationally. Scientific and economic dilemmas may turn out to be minefields, unless we think the problem through carefully. Over the periods 1978-82 and 1983-87, we chaired the Clean Air Scientific Advisory Committee (CASAC) set up by Congress to advise the EPA administrator on the ambient air quality standards. Our committee met regularly to review criteria documents prepared by the EPA Office of Environmental Criteria and Assessments and staff papers prepared by the EPA Office of Air Quality Planning and Stan-
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dards. The criteria documents summarize the effects of certain pollutants on human health and welfare. (“Welfare” refers to effects other than human health, including visibility and plant damage.) The staff papers summarize the literature most directly related to the setting of the standard. The pollutants currently covered by the NAAQS are ozone, nitrogen oxides, carbon Views ore insightful commentaries on timely environmental topics. represent an author’s opinion, and do not necessarily represent a position of the society or editors. Contrasting views are invited.
0013-936X19410927-148A$04.5010 0 1994 American Chemical Society
monoxide, lead, sulfur oxides, and particulate matter. The criteria documents The criteria documents, multivolume works on each pollutant, and the staff papers were reviewed in public sessions at which environmental organizations, industry trade associations, and individual citizens made presentations. CASAC then prepared reports to the administrator, commenting on the scientific databases in the documents and papers and including the recommended concentration ranges over which the standards could reasonably be set. It was the responsibility of the administrator to make selection of.the standard. the final . .~.. ~ ~ ~ .~ ~ The Clean Air Act called for periodic reviews of the standards on a five-year cycle, but this provision has not been strictly observed (24). The standard-setting process that developed was lengthy and sometimes tedious, but the CASAC pa^ ticipation succeeded in defusin what had often been acrimonious disputes involving industry, the government, and environmental groups. These disputes had spilled over into the law courts, further delaying decisions on standards. The development of air quality standards for regulating particulate air pollution is a daunting task. The atmospheric aerosol is composed of particles ranging in size from a few nanometers to 50 pn,and each particle may consist of a mixture of chemical species. The material composing the aerosol comes from many different sources that can be identified, in part, by source attribution methods based on chemical signatures (25, 26). Much of the mass of the atmospheric aerosol, especially the submicrometer portion, is the result of gas-to-particle conversion. Even if all particulate matter were removed from emissions to the atmosphere by gas-cleaning devices, a substantial portion of the submicrometer mass would remain because of the conversion of sulfur and nitrogen oxides and organic vapors to particulate matter (27,28). ~~~~
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Nonspecificity of particulates The particulate standard is the only ambient air quality standard that is not chemically specific: one of its components, lead, is itself regulated independently of the rest of the aerosol. The concentrations of other components, such as sulfates, nitrates, and organics resulting from gas-to-particle conversion, are af-
fected by controls designed to address the NAAQS for sulfur and nitrogen oxides and ozone. Although there have been significant advances in our understanding of the dynamics of the atmospheric aerosol, the chemical and biochemical processes that underlie its effects on human health are very poorly understood; the standard is based on the total mass of the size fraction that penetrates into human lungs (< 10 pm in aerodynamic diameter). Indeed it may be that the health effects of the atmospheric aerosol do
cals and other metastable components, may be much more biochemically active t h a n t h e aerosol components measured many hours, days, or weeks later. The deposited aerosol is composed of the end products of the atmospheric chemical and physical processes that generated the short-lived components. Biochemically active components may have been present at the particle surface or inside the particles, or may originally have been present in the gas before being converted to particulate matter. Such uncertainties have long hampered efforts to develop scientifically based standards for particulate air pollution.
Health effects The recent epidemiological studies (1-23) indicating health effects at mass concentrations of particulate matter below the existing stand a d s are of two types: those that focused on the health effects of particles emitted by a steel mill operating in a valley in Utah and those I( : that focused on mortality and morbidity associated with particles in urban atmosphere. It is unlikely I that the new evidence will be the “smoking gun” that points to a “killer aerosol.” We can only speculate on what special aerosol properties, if any, caused the observed health effects. Perhaps changes in steel mill operating conditions have led to increased emissions of suhmicron aerosols, which are likely to pose a greater health risk than the .,. ’, same mass of coarse particles. Perhaps there have been changes in the composition of urban aerosols resulting from changing automotive and power plant fuels. Despite these uncertainties, the epidemiological data are sufficiently coherent to compel us to review the existing standard for particulate matter (29). A significant not depend on the specific chemical downward revision in the standard components. There have been con- will probably cost industry (and the tinuing efforts to identify the role of public) billions of dollars. Heightbiologically active chemical species ened concern about the effects of air (such as sulfuric acid) that may pollution standards on the competicause a disproportionate fraction of tiveness of US. manufacturers has been reflected in the bitter debate the health effects. In evaluating the health effects of over the environmental conseaerosol chemical components, we quences of the North American Free should not rely entirely on the Trade Agreement. Similar concerns chemical analysis of particulate appear in the 1990 Clean Air Act matter collected routinely from the (301,which calls for the “harmoniatmosphere. The chemical analysis zation” of air pollution standards is usually conducted long after the among the United States and its aerosol is sampled on filters or other trading partners. There are many sampling devices. Short-lived precedents for international cooperchemical species in the gas and/or ation on air quality. An example is aerosol phase, including free radi- the Montreal Protocol, in which the
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advanced industrial nations agreed to limit atmospheric emissions of fluorocarbons. The scale of the effects of particulate pollution extends from local to global, so international cooperation is justified for scientific and economic reasons. The harmonization of standards among nations called for in the Clean Air Act does not necessarily mean equalization. Harmonization will require some rough parity among the standards set by the participating nations. Harmonization will also stimulate development of internationally compatible monitoring and measurement networks and the regular exchange of information on pollutant concentrations. Such information will be required in tracking transfrontier air pollution, an important issue for both North America and Europe (31). In the case of particulate pollution, the experience of other nations has always influenced the U.S. criteria documents and standards. Of special importance was the London smog episode of 1952 in which 4000 excess deaths were reported. Because the biological mechanisms for the effects of the pollutants were not understood, interpreting the fragmentary data on relationships between health statistics and pollutant concentrations was very controversial. British scientists prepared a lengthy critique of the draft US. criteria document for particulate matter and sulfur oxides (32)in which they argued that the London data were used to attribute human health effects at unrealistically low particulate concentrations (33). Steps for revisions It will be in the general interest to broaden our next round of particulate standards setting to include wider international participation. This could be accomplished in a three-stage process. The first stage would involve joint workshops sponsored by the United States, the European Community, and other interested parties with the aim of reaching consensus on a common set of data on which to base the standards. Research needs for the characterization of the atmospheric aerosol and its biomedical effects should be identified. This program should be initiated in a timely fashion to help guide the standardsetting process and continued even after the standard is set until the scientific issues are resolved. In the second stage, each country or group of countries would set its 150 A
own standard and the associated air-monitoring and measurement systems. Although this stage should involve consultation among the participating nations, each country would set standards in its own way, following its own timetable. In the final stage, there should be follow-up discussions on methods of implementation and comparison of results for air quality and health and welfare effects. Broadening the standard-setting procedure to include more international participation will help us deal with an issue of enormous scientific complexity and major international economic and policy implications. It will help achieve the harmonization of standards called for by the 1990 Clean Air Act Amendments. Finally, it will help defuse contentious international issues associated with trade and competitiveness in much the same way that disputes about standards in the United States were reduced through the CASAC review processes.
Health 1991,46, 135. 011 Pope, C. A. ; Kanner, R. E. Am. Rev. Respir. Dis. 1993, 147. 1336. References 22, 23 concern chmnic respiratory disease (221 Schwartz. J. Environ. Res. 1993,62. 7. (23) Abbey, D. E. et al. I. Expos. Anal. Environ. Epidemiol. 1993, 3, 99. (24) Lippmann, M. Aerosol Sci. Technol. 1987, 6, 93. 1251
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nol. 1973. 7.235. (26)Gordon, G. E. Environ. Sci. Technol. 1988,22,1132.
Hering. S. V.; Friedlander, S. K. Atmos. Environ. 1982. 16.2647. (28)Seinfeld, J. H. Atmospheric Chemistry a n d Phvsics of Air Pollution; Wile": New Ydrk. 1986. (29) Bates, D. V. Environ. Res. 1992. 59, (27)
336.
Clean Air Act, Public Law 101-549. Nov. 15, 1990. Section 811. (31) Rand Corporation Workshop o n Transfrontier Air Pollution and the Law of the Atmosphere, May 1993. Delft, The Netherlands. I321 . . "US. EPA Air Oualitv Criteria for Particulate Matter and'sulfur Dioxides"; U.S. Environmental Protection Agency: Washington. DC, Dec. 1982; EPA-600/8-82-029a,h.c. (33) Holland, W. W. et al. Am. I. Epidemiol. 1979, 110. (30)
References Ozkaynak. H.; Thurston, G. D. Risk Anal. 1987, 7, 449. (2) Archer, V. E. Arch. Environ. 1990,45, (1)
325. (3)
Fairley, D. Envimn. Health Perspect. 1990, 89, 159.
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Kinney. P. L.; Ozkaynak. H. Environ.
Res. 1991, 54, 99. (5) Dockery, D. W.; Schwartz, 1.; Spengler. J. D.Envimn. Res. 1992, 59, 326. (6) Schwartz. 1.; Dockery. D. W. Am. Rev. Respir. Dis. 1992, 145. 600.
Schwarlz, J.; Dockery. D. W. Am. I. Epidemiol. 1992, 135, 12. (8) 110. K.;Thurston.G. D.; Lippmann. M. Arch. Environ. Health. 1993. 48. 213. (9) Dockery. D W et al. N h g l / Med (7)
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References 10-14 concern hospital admissions and emergency mom visits (101 Bates, C. V.; Sizto, R. Environ. Res. 1987, 43, 317. (11)
Pope, C. A. Alch. Environ. Health
1991, 46, 90. I121 Thurston. G. D. el al. I. Expos. Anal. Environ. Epidemiol. 1992,Z. 429. 113) Sunyer. 1. et al. Am. I. Epidemiol. 1993,137,701. (14) Schwartz. J. et al. Am. Rev. Respir. Dis. 1993, 147, 826. References 15-18 concern symptoms and
restricted activities I151 Ostro. B. D. Risk Anal. 1990.. 10.. 421. Pope.'C. A. et al. Am. Rev. Respir. Dis. 1991,144,668,
Ransom, M. R..; Pope, C. A. Environ. Res. 1992, 58, 204. Ostro. B. D. et al. Am. 1. Epidemiol., 1993,137,691.
References 19-21 concern pulmonary function I191 Schwartz. J. Environ. Res. 1989. 50. 309.
(20) Chestnut, L. G. et al. Arch. Environ.
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S. K. Friedlander is Parsons Professor of Chemical Engineering a n d director of t h e Aerosol Technology Laboratory a t the University of California-Los Angeles. H e h a s worked on aerosol size distrihuliuii dynamics, discovering that v e T small particles in gases tend to approach osymptotic size distributions independent of their initial properties. He also i n t r o d u c e d t h e widely used method of receptor modeling for relating air quality to emissions sources. He is currently working on the processes controlling the formation of nanophase particles a n d their ossembly into agglomerate structures.
Morton L i p p m a n n is a professor a t the Nelson Institute of Environmental M e d i c i n e of t h e N e w York University Medical Center. His research h a s been focused on particle deposition and clearonce m B lunes. on the use of inert tracer aeros, i as probes in in vivo airway dimensio and lung function. and on identifving ond characterizing the responses of h u m a n populations in natural setting to exposures to particulate and vopor-phase pollutants.
