ENVIRONMENTAL POLICY ANALYSIS

AIR QUALITY

UV-B Screening by Tropospheric Ozone: Implications for the National Ambient Air Quality Standard RANDALL LUTTER, CHRISTOPHER WOLZ U.S. Office of Management and Budget Washington, DC 20503

Tropospheric ozone reduces human exposure to harmful ultraviolet-B (UV-B) radiation. A 10-ppb decrease in seasonal average concentrations of ozone (about 20%) is estimated to lead to in­creases in cancers and cataracts valued at $0.29 billion to $1.1 billion annually. EPA in its ongoing review of the National Ambient Air Quality Standard for ozone should set a stan­dard to minimize all identifiable health effects, including UV-B radiation-related effects. If these estimates are confirmed, this approach may reduce avoidable cancers, cataracts, and deaths by leading to a different standard than that recently proposed in a program already costing more than $20 billion annually.

Tropospheric ozone, which has well-known ad­verse effects on the human respiratory system, re­duces human exposure to damaging ultraviolet-B (UV-B) radiation in a manner similar to ozone (03) in the stratosphere. Although this effect is well rec­ognized (2), EPA has not formally considered it in de­veloping its recent proposal (2) to tighten the Na­tional Ambient Air Quality Standard (NAAQS) for tropospheric 03—a standard that underlies EPA's flag­ship air pollution control program.

Under the Clean Air Act, EPA is mandated to set the health-based "primary" NAAQS to protect pub­lic health with an adequate margin of safety, based on an assessment of all identifiable healdi effects (3). The current standard-setting effort has focused ex­clusively on protection from the adverse respira­tory effects of 03. Consideration of the UV-B screen­ing effect by tropospheric 0 3 may lead to a form and level of the standard quite different from what would otherwise be set. Our preliminary analysis suggests that the value of increased UV-B-related health effects from tropospheric 03 reductions may be similar in magni­tude to the value of decreased respiratory health ef­fects In addition we find the exposure periods of con~

for respiratory effects Eire generally no more ttitin 8 h (the averaging time for EPA's proposed revised NAAQS) and are decades for most UV-B effects Con­sideration of all the effects of tropospheric O mav be necessary in setting regulatory standards that en­sure the fullest protection of public health

Ozone chemistry and federal standards Ozone is a naturally occurring reactive gas present in the troposphere (up to 10 km altitude) and in the stratosphere. In the troposphere, 0 3 occurs through downward transport from the stratosphere or by pho­tochemical production involving solar radiation, vol­atile organic compounds (both anthropogenic and biogenic), and nitrogen oxides (largely anthropo­genic) (4). Ozone varies significantly by season, lati­tude, time of day, and weather conditions. Average July daily high hourly concentrations for tropospheric 03

are 60-65 ppb in polluted areas and 50 ppb in areas that attain the current stcindcird; lows tire less man 20 ppb (5). Peak hourly urban concentrations often Tcirifife from 70 to 160 ppb (6), although because of ozone's large di­urnal variations these concentrations do not neces­sarily imply levels in excess of EPA's proposed 80-ppb standard for an 8-h average concentration

Ozone throughout the atmosphere absorbs UV-B radiation, thereby reducing risks of UV-B-induced skin cancers and cataracts (2, 7). Increases in such risks have become a concern since 1974, when chlo-rofluorocarbons (CFCs) and other manufactured chemicals were identified as likely to deplete strato­spheric 0 3 (8). Stratospheric 03 loss attributed largely

1 4 2 A • VOL. 31, NO. 3, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS 0013-936X/97/0931-142AS14.00/0 © 1997 American Chemical Society

to emissions of synthetic ozone-depleting sub­stances has been measured (9), and increases in UV-B radiation at ground level have been reported {10). EPA regulates and bans ozone-depleting chemicals at a total annual cost to the United States of more than $1.2 billion (1994 dollars) (11, 12).

Tropospheric 03 , as well as cloud cover and aero­sols such as sulfate particles, has been widely rec­ognized as playing a role in attenuating UV-B radi­ation (1, 9,13-17). This screening effect is, however, independent of any depletion of stratospheric 0 3 and exists in its absence. The only consideration of strato­spheric 0 3 relevant in assessing tropospheric 0 3

health impacts is the generally quite small effect of stratospheric 0-. depletion on the magnitude of UV-B screening by tropospheric 03 .

The ozone NAAQS The Clean Air Act directs EPA to set primary ambi­ent air quality standards for certain pollutants, "the attainment and maintenance of which in the judge­ment of the Administrator, based on such criteria and allowing an adequate margin of safety, are requisite to protect the public health (3)." The act also di­rects EPA to establish a secondary standard "to pro­tect the public welfare from any known or antici­pated adverse effects associated with the presence of such air pollutant in the ambient air."

Ozone in the troposphere has been a regulatory priority of EPA because of the effect of 0 3 on hu­man respiratory function. EPA established the cur­rent 0 3 primary NAAQS in 1979 at 120 ppb, mea­sured as a daily maximum hourly average, not to be exceeded more than three times over three succes­sive years (18). EPA set that level on the basis of iden­tified effects of O. on lung function and symptoms from short-term acute exposures (1 to 3 h) at levels above 120 ppb and in consideration of effects on sen­sitive subpopulations. The effects of exposures to 0 concentrations of 80 ppb over 6 to 8 h on adults ex­ercising at moderate and heavy levels include dis­comfort coughing some loss of lung function in­creased airwav responsiveness and inflammation In healthy adults these effects are generally transient and fully reversible within 24 h Human health ef­fects from chronic exposure to elevated levels of 0 have not been documented although permanent

structural damapp to lung tissue has bppn identi-fiprl in animals siihiprt to chronic eynosurp lead-ing to concern about possible links to chronic bron-chitis and emphysema in humans (19)

About 110 million U.S. residents live in "nonat-tainment" areas that fail to meet the current 0 3

NAAQS (20). In its program to meet the NAAQS, EPA regulates emissions of 0 3 precursors from a broad range of sources such as motor vehicles, fuels, power

plants, and printing operations. Estimates of the cur­rent cost of controls to reduce 0 3 exceed $20 billion— yet these controls are not sufficient to attain the stan­dard in all areas (21, 22).

EPA's review of the NAAQS EPA has proposed a new 0 3 standard that would re­quire that the three-year average of the third high­est daily maximum 8-h reading for a year not ex­ceed 80 ppb. EPA has committed to making its final decision by June 1997 (2). EPA's proposal states that a revised standard is called for to protect against the health effects of exposures of up to 8 h and to pro­vide increased protection for sensitive subpop­ulations. EPA's analysis indicates that such a re­vised standard could increase the size and number of "nonattainment" areas to include approximately 30 million additional people (23). In its proposal EPA also asked for public comment on the adoption of a separate secondary standard based on a measure of daytime O- over three months.

An important part of EPA's decision-making record for this NAAQS review is the "Criteria Document" (CD) called for in the Clean Air Act to "accurately re­flect the latest scientific knowledge useful in indi­cating the kind and extent of all identifiable effects on public health or welfare which may be expected from the presence of such pollutant in the ambient air, in varying quantities" (24).

EPA's June 1996 "Staff Paper," based on this CD, concluded that the current NAAQS does not pro­vide adequate public health protection and recom­mended adoption of an 8-h average 0 3 NAAQS, be­tween 70 and 90 ppb, not to be exceeded more than one to five times per year on average over three suc­cessive years (25). EPA's Clean Air Scientific Advi­sory Committee (CASAC) reviewed the CD and Staff Paper and endorsed EPA staff recommendations for an 8-h, 70- to 90-ppb primary standard (26). CASAC also endorsed EPA staff recommendations for a dis­tinct secondary standard based on daytime concen­trations over three months to protect public wel­fare from known or anticipated adverse effects EPA's published proposal the CD and the Staff Paper do not discuss the health effects or welfare-related ef­fects of UV-B screening by tropospheric O

Health effects of tropospheric ozone UV-B screening by tropospheric 0 3 is generally ac­knowledged by researchers investigating the effects of stratospheric 0 3 depletion on UV-B (1,10) and has been identified by direct measurement. For exam­ple, in Los Angeles during the 1980s, UV-B absorp­tion by 03 , as well as N0 2 and S02, was estimated to have reduced erythemal irradiance for July by 6-8% of the value for "clean skies" (27). In Chicago in July un-

VOL. 31, NO. 3, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 4 3 A

der "clear skies," a 10-ppb decline in 03 was associ­ated with a 1.3±1.2% increase in (erythemal) UV-B {16).

On the basis of a preliminary estimate by EPA that a 10-ppb reduction in seasonal average tropo-spheric 0 3 (below 2 km altitude) would yield a re­duction to total column 0 3 of 1.6 Dobson units, or about 0.5% (28), Department of Energy (DOE) staff developed estimates of the health effects that would result from such a change. These include 25-50 an­nual deaths caused by melanoma skin cancers, and 13,000-28,000 cataracts per year (29) (see box). In an apparent response to these estimates, EPA stated in the regulatory impact analysis (RIA) in support of its proposal that it has conducted an analysis and re­view of the extent to which the kinds of O reduc­tions anticipated for the difference between the cur-rent 1-h and possible [8-h] standards might produce UV-B-related health effects. According to EPA's RIA "[t]he review concluded '(1) the numbers resulting from these calculations are quite small and (2) the limitations of the accuracy and reliability of the in­put to the calculations produce numbers that can­not be defended whether large or small' " (30)

DOE also noted the likelihood of "UV-B en­hanced immunosuppressive effects that activate la­tent viruses or increase incidence and/ or severity of some infectious diseases" (29, 31). DOE recom­mended that EPA give "consideration to both the ben­eficial health effects of reducing tropospheric 0 3 con­centrations and the potentially harmful effects that these reductions will have due to increased pene­tration of UV-B."

Estimates similar to DOE's are straightforward to derive using published methods. United Nations En­vironment Programme (UNEP) analysis (1) implies that a 10-ppb reduction in average July 0 3 levels at a latitude of 40° north (e.g., Philadelphia) and with a constant 0 3 mixing ratio to 10 km altitude would lead to increases in DNA-weighted dose of about 4% in July and 3% in January. (Such a dose weighs in­creases in UV of different wavelengths by effects on DNA.) This UNEP estimate is equivalent to an in­crease of 2.5% in erythemal UV-B dose, given a ra­diation amplification factor for erythemal-weighted dose of 1.2 and for DNA-weigh ted dose of 1.9 (1). This figure is roughly twice the comparable estimate in Frederick et al. (16) which is for clear skies and a higher latitude It is also larger than the 0 6% increase in erythemal UV-B dose that would result from the 0 5% decrease in total column O under­lying DOE's analysis

We estimate that the nonmelanoma skin can­

cers (NMSC) resulting from a 10-ppb decline in tro­pospheric 03, given the alternative estimated in­creases of 1.3% and 2.5% in erythemal-weighted UV-B dose, would range from 4200 to 8100 cases per year. We use biological amplification factors (BAFs) for squamous and basal skin cancer of 2.5±.7 and 1.4±.4, and a baseline of 100,000 squamous and 500,000 basal cell carcinomas annually in the United States (32), assumed to occur in 0 3 nonattainment areas in proportion to population. We assume, based on Fre­derick and Weatherhead (27), that 80% of UV-B ex­posure occurs in the warmer months when the 10-ppb reduction would result. Using lower bound BAFs and the UV-B dose increase from Frederick et al. (16) would yield 3000 NMSC cases per year; the upper bound BAFs and the UV-B dose increase from UNEP (1) would give about 10 000 cases.

Mortality incidence from NMSCs is about 0.3% (33), implying an increase of 9-30 deaths from NMSC per year. This estimate would range from 37 to 130 per year using the range of 3000-10,000 NMSCs and mortality assumptions previously used by EPA (34).

The true uncertainty in these estimates is much larger than the range presented here. For example, the lower bound of the 95% confidence interval in Fred­erick et al. (16) is about 8% of their best estimate. This uncertainty should be evaluated formally and com­pared, for example, with the uncertainty in the esti­mated risk of 03-related respiratory effects.

These preliminary estimates illustrate the risk as­sessment method and show that the UV-B-related health effects are sufficiently well documented and large to merit consideration in setting the NAAQS. Quantitative estimates of other health effects such as cataracts are not developed here but are possi­ble using existing methods (1, 34). These prelimi­nary estimates are not definitive but may help cor­roborate DOE's estimates of NMSCs.

These estimated UV-B-related health effects are relevant only if current and foreseeable emission con­trols adopted to attain a revised 0 3 NAAQS are ex­pected to lead to reductions in the range of 10 ppb. No direct measures of changes in seasonal average 0 3 levels resulting from emission controls exist. EPA estimated, however, that in one district in Philadel­phia summer 0 3 concentrations (90th percentile) would have to fall from 72 ppb to 54 ppb to attain an 80-ppb, 8-h, one expected violation of the stan­dard (slightly more stringent than the proposed re­vised standard) (35). Further, 0 3 reductions in this range have been observed for some areas that, de­spite still fail to meet the current NAAQS. In Chicago an annual decline of 0.5% in daily max­imum 1-h O concentrations was estimated be­tween 1981 and 1991 (36); in Los Angeles a decline over a decade in 24-h average O of 4 6± 3 ppb was measured (27); and measurements in California non-attainment areas show declines of more than 5 DDb throughout the sunniest hours of the day from 1982 to 1987 (5)

Implications for NAAQS The existence of identifiable adverse human health effects that increase as tropospheric 0 3 levels de­crease raises questions about how to set the NAAQS under the Clean Air Act. A primary standard that rec-

Health effects of a decline in tropospheric ozone The U.S. Department of Energy's Office of Health and Environmental Research has estimated that a 10-ppb reduction in seasonal average tropospheric ozone would increase the number of deaths caused by skin cancers and raise the number of cataract cases yearly (29).

Nonmelanoma skin cancers, total cases: 2000-11,000 Melanoma skin cancers

Total cases: 130-160 Fatalities: 25-50

Cataracts, total: 13,000-28,000

1 4 4 A • VOL. 31, NO. 3, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS

ognizes the tradeoff between the adverse respira­tory effects and the reductions in UV-B-related health risks may correspond best with the act's require­ment that the primary standard be set to "protect the public health." Similarly, a secondary standard set in consideration of all effects, including, for example, detrimental effects of UV-B on crop yields— analyzed by EPA for other programs {34)—may bet­ter match the statutory directive to protect "public welfare." Similar risk-risk tradeoffs in other con­texts have previously been noted and incorporated in standard-setting efforts {37).

Recognition of this tradeoff for the primary NAAQS would require EPA to develop estimates of the inci­dence of various health effects. The calculation of incidence is feasible but complex because of the variability in individual sensitivity to 0 3 and UV-B and because of the variability in exposure, which depends on atmospheric conditions and individ­ual behavior.

Even with incidence estimates in hand, the ques­tion of how to set the NAAQS remains. If such esti­mates could be aggregated, however, EPA could iden­tify a standard that would minimize all identifiable health effects of tropospheric 03.

One way to aggregate would be to use quality-adjusted life-years (38), an approach common in the medical community but rare in regulatory decision making. EPA commonly uses an alternative aggre­gation methodology based on estimates of willing­ness to pay for reductions in mortality and morbid­ity risks (and non-health risks).

Valuing changes in health risks in dollar terms is an analysis endorsed by guidance from the Office of Management and Budget {39). Indeed, EPA has an­alyzed the costs and benefits of the recent pro­posed NAAQS revision {30) so as to comply with Ex­ecutive Order No. 12866 on Regulatory Planning and Review {40), even though the Clean Air Act does not allow consideration of costs by EPA in decisions to set the health-based primary NAAQS.

An example of a health benefit valuation pre­pared by EPA in 1992, the stratospheric 0 3 program phase-out of CFCs {11), included the valuation of the average costs of NMSCs at about $4000 for a basal cell carcinoma case and $7000 for a case of squa­mous cell carcinoma. The average cost for a case of cutaneous malignant melanoma was estimated to be $15,000. EPA estimated social willingness to pay to avoid cataracts at $15,000. The value of reduced risk of mortality was estimated to be between $3 mil­lion and $12 million per statistical life, somewhat above other recommended ranges {41).

Using these EPA unit values we calculate the an­nual value of adverse health effects presented ear­lier as between $0.29 billion and $1.1 billion per year (see box, "Valuation of annual UV-B-related health effects"). This estimate understates total value by ex­cluding unquantified effects and by using avoided medical costs rather than the willingness to pay. This valuation also ignores delays in changes in risk rel­ative to changes in exposure; such delays imply that these effects should be discounted.

EPA has estimated the economic value of respi­ratory health improvements that would result if air quality improved from attainment of the current stan­

dard to attainment of alternative standards that are similar to EPA's recent proposal {30). For example, an 8-h standard of 80 ppb with 4 annual violations of the standard would provide annual benefits of be­tween $5 million and $1.44 billion, with a "best" es­timate—depending on the estimation method—of $12 million or $32 million per year (figures ad­justed to 1994 dollars). Of the upper bound bene­fits estimate, $1.42 billion per year is attributable to an association with daily deaths observed by Mool-gavkar et al. {42) in Philadelphia, but not, for exam­ple, in Los Angeles, which has significantly higher 0 3

concentrations {43). Attainment of the proposed stan­dard would give slightly larger benefits.

These preliminary data suggest that the UV-B-related adverse health effects of reducing tropo­spheric 0 3 to comply with the current 0 3 NAAQS or to attain EPA's proposed more stringent NAAQS may be similar in magnitude to the respiratory-related beneficial health effects of such an 0 3 reduction. These estimated values are not entirely compara­ble, because the value of the UV-B-related effects is for a 10-ppb decline in seasonal average 03, whereas EPA's estimated benefits are for improvements in 0 3

from attainment of the current standard to attain­ment of a new standard as recently proposed. None­theless, a "health-optimal" O NAAQS might differ significantly from a NAAQS set without consider­ation of UV-B-related deaths and disease and it could even be less stringent than the current O NAAQS

Many of the beneficial effects of UV-B screening by tropospheric 0 3 appear to be related to long-term exposures, whereas the identified adverse res­piratory effects are related primarily to exposures to peak 0 3 levels over 6-8 h or less {1,19). (Some mel­anoma skin cancers and relatively poorly under­stood long-term lung damage provide the key ex­ceptions.) Thus a standard that minimizes all health effects of 0 3 could lead to the establishment of a short-term peak maximum concentration (i.e., 1 or 8 h) and a seasonal average minimum concentra­tion. Attainment of such a standard may require con­trol strategies that lower peak concentrations of 0 without lowering seasonal averages. Such "peak re­ducing" strategies may protect public health better than annual or seasonal strategies to control O EPA's ability under the Clean Air Act to such peak-reducing control strategies is uncertain (441

UV-B-related cancers and cataracts associated

Valuation of annual UV-B—related health effects By combining the Department of Energy's projections of health ef­fects (previous box) with prior EPA estimates of the cost of these health effects {11), the following calculations of the potential in­creased health costs of a 10-ppb decline in tropospheric ozone were made (in millions of 1994 dollars).

Skin cancers Nonmelanoma cases: $10-52 Melanomas

Cases: $2.0-2.5 Fatalities: $79-630

Cataracts: $210-440 Total: $290-1100

VOL. 31, NO. 3, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 4 5 A

with foreseeable reductions in tropospheric 0 3 are sufficiently understood to be considered in setting the 0 3 NAAQS. In its ongoing revision of the 0 : !

NAAQS, EPA could set a primary standard that would minimize the aggregate health effects of tropo­spheric 03 , including identifiable protective effects on UV-B-related cancers and cataracts. Such an ap­proach would be consistent with the Clean Air Act's requirement to protect the public health. Such a health-optimal standard would represent a challeng­ing departure from current practice but is feasible given current analytic techniques. This change to the standard setting may be necessary to reduce avoid­able cancers, cataracts, and deaths. In setting a sec­ondary welfare-based standard EPA could also con­sider UV-B-related effects on crops

Other regulated pollutants, such as NOx> S02, and particulate matter [also the subject of a recent NAAQS proposal (45)] have been noted as screening UV-B (i, 15), and the quantification of these UV-B-related health effects should be pursued in current standard-setting efforts.

Acknowledgments Thanks to Rick Belzer, l o h n Frederick, a n d a n o n y m o u s re­

viewers. Special t hanks goes to Art Fraas for helpful s u p ­

por t . The au tho r s are with the U.S. Office of M a n a g e m e n t

a n d Budget . The views expressed in this p a p e r are entirely

the i r own a n d not necessar i ly t h o s e of a n y g o v e r n m e n t

agency. (Received for review Februa ry 15, 1996. Revised

manusc r ip t received November 19, 1996. Accepted Novem­

ber 20, 1996.)

References (1) Environmental Effects of Ozone Depletion: 1994 Assess­

men,, United Nations Environment Programme: Nairobi, Kenya, 1994.

(2) Fed. Regis.. 1996, 61, 65716. (3) "CleanAir Act"; Public Law 101-549,1970; 42 United States

Code 7409. (4) National Research Council. Rethinking the Ozone Prob­

lem in Urban and Regional Air Pollution; National Re­search Council: Washington, DC, 1991.

(5) Henderson, J. V. American Economcc Review 1996, 86(4), 789.

(6) "National Air Quality and Emissions Trends Report 1993"; Office of Air and Radiation. Office of Air Quality Plan­ning and Standards, Technical Support Division. U.S. En­vironmental Protection Agency: Research Triangle Park, NC, October 1994; No. 454/R-94-026.

(7) Setlow, R. B. Proc. Nat. Acad. Sci. USA 1974, 71 (9), 3363. (8) Molina, M. I.; Rowland, F. S. Natuee 1974, 249, 810. (9) Scientific Assessment of Ozone Depleiion: 1994; World Me­

teorological Organization, Global Ozone Research and Mon­itoring Project: Geneva, Switzerland, 1995; Report No. 37.

(10) Herman, J. R. et al. Geophys. Res. Lett. 1996, 23(16), 2117. (11) Regulatory Impatt Analysis: Compliance with Section 604

of the Clean Air Act for the Phaseout of Ozone Depleting Chemicals. Prepared by ICF Incorporated for U.S. Envi­ronmenta l Protection Agency, Office of Air and Radia­tion, Global Change Division: Washington, DC, 1992.

(12) Fed. Regist. 1993, 58, 65018. (13) "Environmental Effects of Ozone Depletion: 1991 Up­

date, Panel Report"; United Nations Environment Pro­gramme: Nairobi, Kenya, November 1991.

(14) Liu, S. C ; McKeen, J. A.; Madronich, S. Geophys. Res. Lett. 1991, 12, 2265.

(15) Seckmeyer, C ; McKenzie, R. L. Natuee 1992, 359, 135. (16) Frederick, I. E. et al. / . App.. Meteorology, 1993, 32, 1883. (17) Bruhl, C ; Crutzen, P. J. Geophys. Res. Lett. 1989, 16(7), 703. (18) Code Fed. Reg. 40, 50.9(a). (19) Air Quality Criteria for Ozone and Related Photochemi­

cal Oxidants; Office of Health and Environmental As­sessment . Environmental Criteria and Assessment Of­fice. U.S. Environmenta l Protect ion Agency: Research Triangle Park, NC, 1996; EPA/600/P-93/004aF-cF.

(20) MEMORANDUM: Distribution of Updated Condensed Nonattainment List, July 29,1996 (press release); Air Qual­ity Trends Analysis Group, Office of Air Quality Plan­n ing and S tanda rds . U.S. Env i ronmen ta l P ro tec t ion Agency: Research Triangle Park, NC, 1996.

(21) Hahn, R. Nationll Resources Journal 1994, 34(1), 312. (22) Catching Our Breath: Next Steps for Reducing Urban

Ozone, July 1989. U.S. Congress, Office of Technology As­sessment: Washington, DC, 1989; OTA-O-412.

(23) Air Quality Maps for Alternative Standards and Support­ing Materials, Aprll 25, 1994. Ozone/Carbon Monoxide Programs Branch, Air Quality Management Division, Of­fice of Air Quality Planning and Standards. U.S. Envi­ronmental Protection Agency: Research Triangle Park, NC, 1994.

(24) "Clean Air Act"; Public Law 101-549, 1970; 42 United States Code 7408.

(25) Review of National Ambient Air Quality Standards for Ozone, Assessment of Scientific and Technical Informa­tion, OAQPS Staff Paper. Office of Air Quality Planning and Standards. U.S. Environmental Protection Agency: Research Triangle Park, NC, 1996; EPA-452/R-96-007.

(26) Wolff, G. T. Letter(s) to Honorable Carol Browner, Ad­ministrator, U.S. Environmental Protection Agency; EPA-SAB-CASAC-LTR-96-(002, 006). Appendix G of EPA-452/ R-96-007.

(27) Frederick, J.; Weatherhead, E. "Regional Variations in Sur­face Ultraviolet Irradiance: An Analysis Based on Gas­eous Air Pollutants"; final report to the Alternative Flu-o r o c a r b o n s E n v i r o n m e n t a l Accep tab i l i t y S tudy on Contract CTR90-12/P90-031; Depa r tmen t of the Geo­physical Sciences, The University of Chicago; Chicago, IL, 1992.

(28) Impatt of Changes in Tropospheric Ozone on UV-B Flux: Preliminary Calculations by EPA Staff, Novembrr 15,1994. Submitted with DOE remarks at March 21, 1995, Public Meeting of Clean Air Scientific Advisory Committee, Re­view of Criteria Document for Ozone and Related Pho­tochemical Oxidants, Chapel Hill, NC; U.S. Environmen­tal Protect ion Agency Science Advisory Board Public Meet ing File; Wash ing ton DC 1995; ECAO-CD-92-0746

(29) U.S. Depar tmen t of Energy, Office of Health and Envi­ronmen ta l Research; remarks presen ted at March 21, 1995, Public Meeting of Clean Air Scientific Advisory Com­mittee; U.S. Environmental Protection Agency Science Advisory Board Public Meeting File; Washington, DC, 1995; ECAO-CD-92-0746.

(30) Regulatory Impatt Analysis for Proposed Ozone Na­tional Ambient Air Quality Standard, Ch. IV; U.S. Envi­ronmental Protection Agency: Research Triangle Park, NC, Dec. 1996.

(31) Science 1992, 257, 1211. (32) Grant-Kels, J. Pediatric Dermatology 1993, 10, 1. (33) Wingo, R A. et al. Ca Cancer J. Clin. 1995, 45, 8. (34) Regulatory Impatt Analysis: Protection of Stratospheric

Ozone Volume I, Ch. 2; Office of Air and Radiation. U.S. Environmental Protection Agency: Washington, DC, Dec. 1987.

(35) Johnson, T. et al. "Estimation of Ozone Exposures Expe­rienced by Outdoor Workers in Nine Urban Areas Using a Probabil ist ic Version of NEM," Cont rac t No. 63-D-30094; p r e p a r e d for U.S. E n v i r o n m e n t a l P ro tec t ion Agency, Office of Air Quality Planning and Standards; Re­search Triangle Park, NC, 1996.

(36) Cox, W; Chu, S. Atmo.. Environ. 1993, 278(4), 425. (37) Graham, J.; Weiner, J. Risks versus Risks, Tradeoffs in Pro­

tecting Heatth and the Environment; Harvard Univer­sity Press: Cambridge, MA, 1995.

(38) Tolley, G.; Kenkel, D.; Fabian, R. Valuing Health for Pol­icy: An Economcc Approach; University of Chicago Press: Chicago, IL, 1994.

(39) Economcc Analysis of Federal Regulations Under Execu­tive Order 12866; U.S. Office of Management and Bud­get: Washing ton , DC, January 1996. At: h t t p : / / w w w . whi tehouse .gov/WH/EOP/OMB/html /miscdoc .

(40) Fed. Regist. 58, 51735, Oct. 4, 1993. (41) Viscusi, W. K. Journal of Economcc Literature 1993, 31 (4),

1912. (42) Moolgavkar, S. et al. Epidemiol. 1995, 6(5), 476. (43) Kinney, P. L.; Ozkaynak, J. Environ. Res. 1991, 54, 99. (44) "Clean Air Act"; Public Law 101-549, 1970; 42 United States

Code 7602. (45) Fed. Regis.. 1996, 61, 65638.

1 4 6 A • VOL. 31, NO. 3. 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS