FT'••.
January 1979
REVISIONS TO THE NATIONAL
AMBIENT AIR QUA
TANDARDS FOR
PHOTOCHEMICAL OXJDAMTS
Fedsrai Register Preamble:
Photochemical Qxiciants;
Calibration of Ozone Reference Methods;
Revisions to Implementation Procedures
R-alaiod to Phoiochsrnicai Oxidants
Final Rule
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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Title 40-Protection of Environment
CHAPTER 1 -ENVIRONMENTAL
PROTECTION AGENCY
Subchapter C-Air Programs
[FRL
PART 50-NATIONAL PRIMARY AND
SECONDARY AMBIENT AIR QUALITY
STANDARDS
Revisions to the National Ambient Air
Quality Standards for Photochemical Oxidants
AGENCY: Environmental Protection Agency.
ACTION: Final Rulemaking.
SUMMARY: In accordance with the provisions of Sections 108 and 109
of the Clean Air Act as amended, EPA has reviewed and revised the
criteria upon which the existing primary and secondary photochemical
oxidant standards are based. These standards were promulgated in
1971 (36 FR 8186) and were both set at an hourly average level of
0.08 part per million (ppm) not to be exceeded more than 1 hour per
year. On June 22, 1978, EPA proposed changes in the standard (43
FR 26962) based on the findings of the revised criteria. The pro-
posed changes included (1) raising the primary standard to 0.10 ppm,
(2) retaining the 0.08 ppm secondary standard, (3) changing the chem-
ical designation of the standard from photochemical oxidants to ozone,
and (4) changing to a standard with a statistical rather than deter-
ministic form. The final rulemaking will make three further changes""
in the standard: (1) raising the primary standard to 0.12 ppm,
(2) raising the secondary standard to 0.12 ppm, and (3) changing the
definition of the point at which the standard is attained to "when the
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expected number of days per calendar year with maximum hourly average
concentrations above 0.12 ppm is equal to or less than one."
EFFECTIVE DATE: This revision is effective immediately upon publica-
tion. The normal 30-day delay in effectiveness is not required, when,
as in this case, a restriction is eased.
FOR FURTHER INFORMATION CONTACT:
Mr. Joseph Padgett, Director (MD-12)
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Trianole Park, NC 27711
Telephone: 919-541-5204 (FTS 629-5204)
AVAILABILITY OF RELATED INFORMATION: A docket (Number OAQPS 78-8)
containing information used by EPA in revising the standards is available
for public inspection and copying between 8:00 a.m. and 4:30 p.m. Monday
Central Deckel Sacfion
through Friday, at EPA's-fairiii Iiiruilltdliun anil Referent Uiril, Room
2103
29SS, Waterside Mall, 401 M Street SW, Washington DC 20460. These
materials include the "Air Quality Criteria for Ozone and Other Photo-
chemical Oxidants" and "Control Techniques for Volatile Organic Emis-
sions from Stationary Sources," both of which were issued simultaneously
when this standard was proposed. The control techniques document and
staff papers pertaining to the form of the ozone standard, risk assess-
ment method, secondary standard, and health panel assessment are available
upon request from Mr. Joseph Padgett. Statements of the environmental,
economic, and energy impacts of implementing this standard revision are
also available upon request from Mr. Joseph Padgett, at the address
shown above. The air quality criteria document can be obtained from:
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Mr. Michael Berry (MD-52)
Environmental Criteria and Assessment Office
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Telephone: 919-541-2266 (FTS 629-2266)
This preamble describes revisions to 40 CFR Part 50, Appendix H,
"Interpretation of the National Ambient Air Quality Standards for Ozone,"
and Appendix D, "Measurement Principle and Calibration Procedure for the
Measurement of Photochemical Oxidants Corrected for Interferences Due to
Nitrogen Oxides and Sulfur Dioxide," that are related to the revision of
the air quality standard for ozone. In addition, elsewhere in this issue
of the Federal Register EPA is promulgating revisions to 40 CFR Part 50,
Appendix D, replacing (superseding) the current calibration procedure
with a new, superior calibration procedure based on ultraviolet photometry.
Revisions to 40 CFR Part 51, substituting the word "ozone" for
"photochemical oxidants" throughout that part, and to Section 51.14,
pertaining to control strategies, are being promulgated by EPA elsewhere
in this issue of the Federal Register.
SUPPLEMENTARY INFORMATION:
BACKGROUND
On April 30, 1971, the Environmental Protection Agency promul-
gated in the Federal Register (36 FR 8186) National Ambient Air
Quality Standards for photochemical oxidants. The scientific, tech-
nical, and medical bases for these standards are contained in the air
quality criteria document for photochemical oxidants, published by
the U.S. Department of Health, Education, and Welfare in March 1970.
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Both the primary and secondary standards were set at an hourly average
level of 0.08 ppm not to be exceeded more than once per year.
The asthma study cited as evidence for the original standard is based
on work by Schoettlin and Landau (1961). As discussed in the June
22, 1978, proposed revision to the original standard, EPA has re-
assessed its conclusions regarding this study. This reassessment,
plus the evaluation of medical evidence accumulated since 1970, led
EPA to propose, on June 22, 1978, a revised primary standard of 0.10
ppm (43 PR 26962). EPA did not propose £ change in the secondary
welfare standard at that time. The proposal was accompanied by pub-
lication of revised criteria and control techniques documents, as well
as various staff papers relating to the standard itself and to im-
plementation of the standard. EPA solicited written comments on the
proposed standard and, to accept oral testimony, sponsored four pub-
lic hearings (Washington, D C. -July 18; Altanta, Ga. -August 17;
Dallas, Tex. -August 22; Los Angeles, Calif. -August 24).
Oxidants are strongly oxidizing compounds, which are the pri-
mary constituents of photochemical smog. The oxidant found in larg-
est amounts is ozone (03), a very reactive form of oxygen. Oxidants
also include the group of compounds referred to collectively as peroxy-
acylnitrates (PANs) and other compounds, all produced in much
smaller quantities than ozone.
Most of these materials are not emitted directly into the at-
mosphere but result primarily from a series of chemical reactions
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between oxidant precursors (nitrogen oxides and organic compounds)
in the presence of sunlight. The principal sources of organic com-
pounds are the hydrocarbon emissions from automobile and truck ex-
hausts, gasoline vapors, paint solvent evaporation, open burning,
dry cleaning fluids, chemical plants and other industrial operations.
Nitrogen oxides are emitted primarily from combustion sources such
as electric power generation units, gas and oil-fired space heaters,
and automobile, diesel and jet engines.'
The reductions in emissions of nitrogen oxides and organic com-
pounds are achieved through Federal and State programs that have been
formalized in regulations promulgated under the Clean Air Act. The
Federal programs provide for reduction in emissions nationwide
through the Federal Motor Vehicle Control Program, the Federal
program for control of aircraft emissions, National Emission Stand-
ards for Hazardous Air Pollutants, and the development of New Source
Performance Standards. The State programs provide for additional
control measures through State Implementation Plans in those areas
of the country where the Federal programs are not sufficiently
stringent to permit attainment of air quality standards.
LEGISLATIVE REQUIREMENTS AFFECTING THIS PROMULGATION
Two sections of the Clean Air Act govern the development of a
National Ambient Air Quality Standard. Section 108 instructs EPA
to document the scientific basis (criteria) for the standard, and
Section 109 provides guidance on establishing standards and review-
ing the criteria.
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Air quality criteria are required by Section 108(a)(2) to re-
flect accurately the latest scientific information useful in indicat-
ing the kind and extent of all identifiable effects on public health
or welfare that may be expected from the presence of the pollutant in
the ambient air.
The Administrator is required to propose, simultaneously with
the issuance of these criteria, primary and secondary ambient air
quality standards based upon such criteria. The primary standard is
defined in Section 109(b)(l) as the ambient air quality standard the
attainment and maintenance of which in the Administrator's judgment,
based on such criteria and allowing an adequate margin of safety,
are requisite to protect the public health. The secondary standard
(Section 109(b)(2)) must specify a level the attainment and maintenance
of which in the Administrator's judgment, based on such criteria, are
requisite to protect the public welfare from any known or anticipated
adverse effects associated with the presence of the pollutant in the
ambient air. These adverse welfare effects, which are discussed in
Section 302(h) of the Act, include effects on soils, water, crops,
vegetation, man-made materials, animals, weather, visibility, hazards
to transportation, economic values, personal comfort and well-being,
and other factors.
The Clean Air Act specifies that primary National Ambient Air
Quality Standards are to be based on scientific criteria relating to
the level that should be attained to protect public health adequately.
Considerations of cost of achieving those standards or the
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existence of technology to bring about needed reductions of emissions
are not germane to such a determination, as the words of the Act and
its legislative history clearly indicate. Section 109(d) directs
the Administrator to complete a review of all existing standards and
criteria before the end of 1980 and at 5-year intervals thereafter
and to revise them in whatever manner that review reveals is neces-
sary. This promulgation is the result of such a review.
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Assuring attainment and maintenance of ambient air quality
standards is the responsibility of the States. Under Section 110
of the Act, they are to submit to EPA for approval State Implemen-
tation Plans (SIPs) that provide for the necessary legal requirements
for sources of the relevant pollutant so as to demonstrate attainment
and maintenance of the standards by certain deadlines. In many areas
of the country the ambient air quality standards are not being attain-
ed, despite the fact that the deadline for attainment has long since
passed. As a remedy, Part D of the Act requires states with viola-
tions of ambient air quality standards to submit revised SIPs to
ensure attainment of the standards and to meet certain new require-
ments of Part D by January 1, 1979. (Section 129(c), Pub. I. 95-95,
note under 42 U.S.C. 7502.) The Act does not authorize the Admini-
strator to extend that deadline, and consequently this revision of
the photochemical oxidant standard does not affect the deadline for
submittal of SIP revisions.
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Section 110(a)0) requires that SIP revisions be submitted
within 9 months after a standard is revised. However, this
provision refers to situations where a standard is tightened, with
the result that existing SIPs are no longer adequate to attain and
maintain the standard in question. Where a standard is relaxed,
no SIP revision is required by the law, since states may have more
stringent controls than necessary if they choose.
Furthermore, the change in the chemical species designation
of the standard from photochemical oxidants to ozone does not make
this standard subject to the provision of Section 110(a)(l) cited
above. The intent of the standard (total oxidant reduction), the
control strategies, and the index of progress toward attainment
(measured ozone levels) remain unchanged.
SUMMARY OF GENERAL FINDINGS FROM AIR QUALITY CRITERIA
FOR OZONE AND PHOTOCHEMICAL OXIDANTS
On April 20, 1977, EPA announced (42 FR 20493) that it was
reviewing and updating the 1970 criteria document for photochemical
oxidants in accordance with provisions of Section 109(d)(l) of
the Clean Air Act as amended. The notice called for information
and data that would be helpful in revising the document. In
preparing the criteria document, EPA provided a number of opportunities
for external review and comment. Two drafts of the document have been
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made available for external review, and EPA received more than 50
written comments on the first draft and approximately 20 on the
second draft. The American Petroleum Institute has submitted exten-
sive information that EPA considered in this standard review. The
criteria document was the subject of two meetings of the Subcom-
t
mittee on Scientific Criteria for Photochemical Oxidents of EPA's
Science Advisory Board. Each of these meetings was open to the
public, and a number of individuals presented both critical review
and new information for EPA's consideration. A full discussion of
comments received during the review process, as well as EPA's
disposition of these comments, can be found in the docket (OAQPS
78-8) assembled for this rulemaking.
From EPA's review of the scientific information presented in
the criteria document, several key areas with particular relevance
to setting the ozone standard have emerged:
1. Threshold concept — Although the concept of an adverse
health effect threshold has utility in setting ambient air
quality standards, the adverse health effect threshold con-
centration cannot be identified with certainty. The lowest
concentration which causes measured health effects in a
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scientific experiment depends on the particular subjects who have
been studied because sensitivity to pollutants varies among dif-
ferent members of the population. Only limited studies can be
performed on groups of unusually sensitive persons. Most experi-
mental studies of human subjects are performed on small numbers of
relatively healthy persons who do not fully reflect the range of
human sensitivity. Also, the air to which the subjects are exposed
does not include the full mix of chemicals other than the pollutant
being studied which are in the ambient air. Some of these chemicals
may be additive with the given pollutant in causing the adverse
health effeci, so that lower levels of the pollutant will result in
~he effect. Animal exposure studies cannot provide precise models
of sensitive human populations. Thus, adverse health effect thresholds
for sensitive persons are difficult or impossible to determine
experimentally, while the threshold for healthy persons or animals
is not likely to be predictive of the response of more sensitive
groups. In this notice of rulemaking EPA uses the terminology
"probable effects level" to refer to the level that in its best
judgment is most likely to be the adverse health effect threshold
concentration. It is the fact that the adverse health effect
threshold concentration is actually unknown that necessitates the
margin of safety required by the Act.
2. Ozone hea1th effects — Ozone is a pulmonary irritant that
affects the respiratory mucous membranes, other lung tissues and
respiratory functions. Clinical and epidemiological studies have
demonstrated that ozone impairs the normal mechanical function of
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the human lung and causes clinical symptoms such as chest tightness,
coughing and wheezing. These effects may occur in sensitive indi-
viduals, as well as in healthy exercising persons, at short-term
ozone concentrations between 0.15 and 0.25 ppm. The clinical
studies data base for these effects is far more extensive than that
which was available in 1970, and these effects have now been
demonstrated at lower levels than those cited in the 1970 criteria
document.
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3. Effects onasthmatics — The best available evidence suggests
that an elevated proportion of asthmatics experience attacks on
days when the peak hourly oxidant concentrations reach about
0.25 ppm. This finding is based on a revaluation of the study
by Schoettlin and Landau (1961).
4. Toxicologic findings -- The key finding from toxicologic
studies is the increased susceptibility to bacterial infection
in laboratory animals exposed to 0.10 ppm ozone and a bacterial
challenge. Infection rates are lower for animals exposed only
to the bacterial challenge. Other effects such as biochemical
changes, morphological abnormalities, and genetic changes have
i
been found in some studies of animals exposed to ozone concen-
trations as low as 0.1 to 0.3 ppm. While the data from animal
studies cannot be directly extrapolated to man, they can be
taken as indicators of the full range of effects that may
occur in humans. The epidemiology study by Durham (1974) that
reported increased rates of illness in college students following
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periods of elevated air pollution levels (with peak oxidant being
the pollution variable most strongly associated with illness)
further increases our concern regarding the implications for man of
the animal study findings.
5. Ozone effects on aging processes — A limited amount of data suggests
that ozone may accelerate the aging process in living organisms.
Exposure of rabbits to unspecified concentrations of ozone for 1
hour per week for a year has been reported to induce premature
aging symptoms such as premature cartilage calcification, severe
depletion of body fat, and general signs of aging (Stokinger, 1965).
5. Pollutant interactions — The fact that ozone exposure
is frequently accompanied by exposure to other pollutants, such
as sulfur dioxide (SO-), has prompted several investigators to
conduci laboratory evaluations of exposure of human subjects
to combinations of CL and other pollutants. Simultaneous ex-
posures to 0.37 ppm 0, and 0.37 ppm S02 were reported to pro-
duce larger changes in pulmonary function than exposure to either
pollutant alone. No obvious effects were observed in other
simultaneous exposure tests using 0.25 ppm Og and 0.3 ppm nitro-
gen dioxide (N02), as well as 03, N02> and 30 ppm carbon mono-
xide (CO). Nevertheless, the S02 - 03 synergism findings sup-
port the need for an adequate margin of safety in the ozone
standard.
7. Mortality studies — No studies have conclusively linked
exposure to ozone or photochemical oxidants with an increase in
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human mortality. A number of epidemiologic studies have been
designed and conducted to demonstrate this effect, but in each case
the results have been negative or inconclusive.
8. Welfare effects — Ozone accelerates the aging of many
materials, resulting in rubber cracking, dye fading and paint
erosion. These effects are linearly related to the total dose of
ozone and can occur at very low levels, given long-duration exposures.
Damage to vegetation, as expressed by decreased growth and yield,
is related to the long-term (growing, season) mean of the daily
maximum 6- to 8-hour-average ozone concentrations.
9. Causes and control of oxidant pollution — All presently
available evidence indicates that around urban centers with
severe oxidant problems, the major concern is the formation of
photochemical oxidants from man-made organic and nitrogen oxide
emissions. Control of these emissions will result in signifi-
cant reductions in ambient ozone, peroxyacetylnitrate (PAN),
aldehydes and photochemical aerosol.
As is the case with most standard-setting activities, the data base
on ozone will .continue to expand after the standard is set. EPA will
continue to inform itself of new research results and also will accelerate
the schedule for its own research on the health effects of ozone and other
photochemical oxidants at low exposure levels. The Agency plans to make
the results of these studies available as they are completed and to issue
an interim report on all new research results in two years.
RULEMAKING PETITIONS
The Agency was petitioned by the American Petroleum Institute
(API) and 29 member companies on December 9, 1976, and by the City
of Houston on July 11, 1977, to revise the criteria, standards and
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control strategy guidelines for photochemical oxidants. EPA had
already begun such a revision when both petitions were filed, and
the Agency responded that it was deferring decision on these peti-
tions until the rulemaking was completed. EPA considers this final
rulemaking and the accompanying one on control strategy guidelines
to be the Agency's final action on these petitions. A summary of
the two petitions and EPA's response is given below.
The API petition requested that EPA revise the air quality
criteria document for photochemical oxidants in light of new infor-
mation regarding the causes, effects, and extent of air pollution
attributed to ozone and other oxidants. EPA has published a revised
air quality criteria document for photochemical oxidants; in the
Agency's judgment, this document accurately reflects the latest
scientific information regarding the causes, effects, and extent of
air pollution attributed to ozone and other oxidants.
The second request in the API petition was that EPA establish
a national primary ambient air quality standard based on new studies
that allegedly demonstrate no significant adverse human health effects
at or below ozone levels of 0.25 ppm for 2-hour exposures. As re-
quested by API and as required under the Clean Air Act, the Agency
has considered all new studies published since 1971 that are rele-
vant to setting a revised primary standard the attainment and main-
tenance of which would, in the Administrator's judgment, protect the
public health with an adequate margin of safety. EPA disagrees with
API's conclusion that new studies conducted since 1971 demonstrate
no significant adverse human-health effects at or below 0.25 ppm.
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A more detailed discussion of EPA's judgments regarding reported or
probable health consequences at concentrations below 0.25 ppm is pre-
sented in the rationale for revising the primary standard and in the
response to comments, which appear elsewhere in this notice.
The third request by API was that the national secondary ambient
air quality standard be based on adverse effects on public welfare as
indicated by studies using ozone-specific measurement methods. In
•^
addition, API concluded that Congress intended that EPA weigh the
overall economic and social impact of a lower secondary standard against
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adverse effects of a pollutant. EPA has reviewed the data presented in
the criteria document and concluded that there is currently no evidence
of a significant decrease in yield or growth to commercially important
crops for short-term exposures to ozone concentrations below 0.12 ppm.
EPA believes a secondary standard more stringent than the primary standard
is unnecessary and that a cost-benefit analysis is not required.
In their petitions, both API and Houston requested EPA to. state
the primary and secondary standards so as to permit reliable assessments
of compliance. EPA agrees that the present deterministic form of the
oxidant standard has several limitations and has made reliable assessment
of compliance difficult. The revised ozone air quality standards
are stated in a statistical form that will more accurately reflect
the air quality problems in various regions of the country and
allow more reliable assessment of compliance with the standards.
The API and Houston petitions requested that EPA specify the
use of an appropriate measurement method for monitoring ambient
concentrations of ozone. API suggested the use of ethylene cherai-
luminescence calibrated by either gas phase titration (GPT) or ul-
traviolet (UV) photometry. As a result of EPA's continuing evaluation
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of several calibration techniques, the Agency has defined the re-
ference method to be ethylene chemiluminescence calibrated by UV
photometry. (See the amendment to Appendix D of 40 CFR Part 50
elsewhere in this edition of the Federal Register.) EPA is allow-
ing the use of a modified version of the current calibration method
(acidified KI) as an interim measure to avoid problems that would
result from immediate conversion to UV photometry.
Both the API and Houston petitions requested revision of the
State Implementation Plan (SIP) requirements (1) to delete the
assumption of no background concentration of photochemical oxidants
and (2) to specify more reliable, alternative oxidant prediction
relationships to replace Appendix J of 40 CFR Part 51 for deter-
mining the degree of necessary precursor emission reductions.
With respect to the first point, EPA recognizes that back-
ground concentrations and transport of ozone from upwind locations
can contribute to high levels of ozone in or near an urban area
during the afternoon hours. Therefore, several revisions are being
made in control strategy and implementation guidelines for ozone.
The revised guidelines set forth procedures for consideration of
both upwind transport and irreducible natural background by the
States in calculating the necessary reductions in hydrocarbon emis-
sions. In response to the second request, EPA has determined that
Appendix J of 40 CFR 51 no longer represents an acceptable analy-
tical relationship between hydrocarbons and ozone. Appendix J is,
therefore, being deleted. EPA will now allow States to use any of
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four analytical techniques to determine the amount of hydrocarbon
reduction necessary to demonstrate attainment of the national ozone
air quality standards: (1) Photochemical dispersion models, (2)
Empirical Kinetics Modeling Approach (EKMA), (3) Empirical and
statistical models, and (4) Proportional rollback. These four tech-
niques are discussed further in the revision of Part 51, which
appears elsewhere in this edition of the Federal Register.
The Houston petition requested that EPA consider information
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in their petition relative to atmospheric conditions and other
factors that affect photochemical oxidants in the Houston area. The
petition claimed that the air pollution problems in Houston warrant
special attention in standard-setting and "tailor-made" control
strategies, because the emission and meteorology situations and the
overall pollution picture in that area are "unique."
In response to the above claim, it should be noted that the ma-
jority of the data presented in the revised criteria document are
based on ozone exposure. Nearly all of the clinical and toxicological
studies are based on the effects of ozone. The biomedical data also
suggest that many of the effects observed during periods of elevated
photochemical oxidant concentrations are reasonably attributable pri-
marily to ozone in the ambient air. Since the primary and secondary
standards are based on the effects of ozone, the differences between
areas in their overall photochemical oxidant mixtures do not bear upon
the setting of national ozone air quality standards.
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EPA agrees with the Houston petition that components of the photo-
chemical oxidant mixture other than ozone may have an adverse impact on
health and/or welfare. The data base is net, however, sufficient at
this time to justify a separate standard for PAN or other non-ozone
oxidants. While EPA does not propose to establish separate standards
for the non-ozone constituents of the mixture at this time, those measures
taken to reduce ozone precursor emissions will also reduce PAN and other
non-ozone oxidant concentration levels.
In response to Houston's request for a unique standard based on their
locel situation, it must be realized that the Clean Air Act does not con-
template separate standards for different cities. Dealing in terms of
national ambient air quality standards, the Act charges EPA to identify
the air quality levels which must be attained and maintained to ensure,
with an adequate margin cf safety, that adverse health effects will not
occur.
The Houston petition also requested that EPA include realistic
requirements for the reduction of oxides of nitrogen as conditions
in the Houston area may indicate to be necessary to achieve the re-
vised standards. EPA's response is that it is the responsibility
of the State of Texas and the City of Houston to submit State Imple-
mentation Plan provisions tailored to the situation prevailing in
Houston. If the current SIP is not representative of the most
efficient means of reducing ozone in Houston, then, with Houston's
assistance, Texas should submit a revision that is consistent with
local emission and meteorological conditions.
SUMMARY OF COMMENTS RECEIVED
EPA has solicited public comment and critique on proposed re-
visions to the photochemical oxidant air quality standard during all
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phases of the standard development process. Prior to proposal (April 20,
1977), EPA announced (42 FR 20493) that it was reviewing and updating
the criteria document and called for information that might be helpful
in revising the document. Public comments were received on two drafts
of the criteria document, and the public was invited to two meetings
of the Subcommittee on Scientific Criteria for Photochemical Oxidants
of EPA's Science Advisory Board. In addition, the Agency held £ public
meeting on January 30, 1978, to receive comments from interested
parties prior to development of any formal Agency position on the initial
proposed revision of the standard. In particular, EPA actively solicited
the participation of the State and Territorial Air Pollution Program
Administrators (STAPPA) and the Association of Local Air Pollution
Control Officials (ALAPCO) in this meeting; several representatives of
these groups offered comments at the meeting. The results of this
meeting are discussed in the proposed regulation (43 FR 26970) and a
transcript of the meeting is available in docket OAQPS 78-8.
Following proposal, EPA held four public meetings to receive com-
ments on the proposed standard revisions. Meetings were held in
Washington, D. C.—Ouly 18: Atlanta, Ga.—August 17; Dallas, Tex.—
August 22; and Los Angeles, Calif.—August 24; transcripts are avail-
o
able in docket OAQPS 78-8. In addition, 16/ written comments were
received during the formal comment period, which extended through
October 16, 1978.
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The principal comments and Agency responses are summarized in
the following paragraphs (individual responses to comments are con-
tained in docket OAQPS 78-8). EPA also received comments on the pro-
posed standard after October 16. Although EPA does not have a legal
obligation to review these comments, all significant issues raised
in the post-October 16 comments have been addressed and responded
to as part of the discussion of comments in this preamble. As with
all ouher documents considered or examined by EPA as part of its
decision process, these documents have been placed in the public
docket and have become part of the administrative record of this
decision.
^ S>
The majority of comments received (13/ out of 16/) opposed EPA's
proposed standard revision, favoring either a more relaxed or a more
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stringent standard. State air pollution control agencies (and STAPPA)
generally supported a standard level of 0.12 ppm on the basis of
their assessment of an adequate margin of safety. Municipal groups
generally supported a standard level of 0.12 ppm or higher, whereas
most industrial groups supported a standard level of 0.15 ppm or
higher. Environmental groups generally encouraged EPA to retain the 0.08 ppm
standard.
Comments on the proposed revisions were received from five Federal
agencies. Three of the agencies endorsed the proposed primary standard,
but one of these agencies requested that EPA consider formulating the
standard on a daily maximum hourly average basis. Another agency
expressed concern that EPA had inadequately substantiated the rationale
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for raising the primary standard level and requested that the final
revisions provide further analysis in this regard. Finally, the
Executive Office of the President/Council on Wage and Price Stability
suggested, through the Regulatory Analysis Review Group, that the pro-
posed standard was unnecessarily stringent, recommending that EPA set
the primary standard using an alternative methodology that focuses on
the marginal costs per person-hour of ozone effects avoided.
Groups and individuals submitting comments are identified below:
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COMMENTS RECEIVED ENDORSING CURRENT PRIMARY STANDARD
LEVEL OF 0.08 pptn
Organizations and Agencies
American Lung Association of Colorado
American Lung Association of Colorado, West Region
American Lung Association cf Louisiana
American Lung Association of New Jersey
American Lung Association of New York State, Inc.
Bangor-Brewer TB and Health Association, Maine
California Lung Association
Connecticut State Department of Health
Environmental Confederation of Southwest Florida
Environmental Defense Fund
Ms. Nancy C. Fancier,, Supervisor District Two, Contra Costa County (Calif.)
Board of Supervisors
Florida Lung Association
Green!ear Nurseries, Warsaw, Indiana
Issac Walton League, Manasota Chapter
League of Women Voters of the U.S.
League of Women Voters of Dallas, Texas
Maine Health Systems Agency
Maine Lung Association
Medford-Ashland Air Quality Maintenance Advisory Committee, Oregon
Michigan Lung Association
Michigan Lung Association, Saginaw Valley Region
National Air Conservation Commission, American Lung Association
Natural Resources Advisory Committee, Cedar Grove, N.O.
New Mexico Lung Association
Oregon Environmental Council
Oregon Lung Association
Queensboro Lung Association, Jamaica, N.Y.
Sierra Club
Sierra Club, Houston Chapter
South Shore (Ohio) Christmas Seal Association
Southwestern Ohio Lung Association
U.S. Department of the Interior
Washington Air Quality Coalition
Yale Environmental Law Association
I\Jate"fense Ceu«ei\
Summary:
3/ comments from organizations, agencies or their representative and
38 comments from concerned citizens supporting the current primary
standard level of 0.08 ppm.
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COMMENTS RECEIVED ENDORSING PROPOSED PRIMARY STANDARD
LEVEL OF 0.10 ppm
Organizationsand Agencies
Air Pollution Control League of Greater Cincinnati
Air Quality Advisory Committee, California Department of Health
California Air Resources Board
Coalition of Labor and Business (COLAB), Concord, California
Colorado Department of Health
Connecticut Department of Environmental Protection
Massachusetts Department of Environmental Quality Engineering
Public Health Service, U.S. Department of HEW
Regional Planning Commission for Jefferson*, Orleans, St. Bernard and
St. Tammany Parishes, Louisiana
Rhode Island Lung Association
Southern Alameda County Board of Realtors, California
U.S. Department of Energy
U.S. Department of Transportation
Wasatch Front Regional Council, Utah
Wayne County Department of Health, Michigan
Wisconsin State Department of Natural Resources
Summary:
16 comments from organizations, agencies or their
representatives and 1 comment from a concerned citizen
endorsing the proposed primary standard level of 0.10 ppm.
23
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COMMENTS RECEIVED ENDORSING A PRIMARY STANDARD
LEVEL OF 0.12 ppm
State and Local Agencies
Alabama Air Pollution Control Coimrission
Berkeley, Charleston, and Dorchester (S.C.) Council of Governments
City of Philadelphia, Pennsylvania
Georgia Department of Natural Resources
Indiana State Board of Health
Kansas Department of Health and Environment
Kentucky Department for Natural Resources and Environmental Protection
Maryland Environmental Health Administration
Michigan Department of Natural Resources
Nebraska Department of Environmental Control
Nevada Department of Conservation and Natural Resources
New York Department of Environmental Conservation
North Carolina Department of Natural Resources and Community Development
Pennsylvania Department of Environmental Resources
Tennessee Department of Public Health
Utah Bureau of Air Quality
Virginia Air Pollution Control Board
Organizations and Companies
Area Cooperation Committee of Tidewater and Virginia Peninsula Chambers
of Commerce
Evansville, Indiana, Chamber of Commerce
Sierra Pacific Power Company
State and Territorial Air Pollution Program Administrators
Texas Oil Marketers Association
Vulcan Materials Company, Wichita, Kansas
Summary:
17 comments from State and local agencies and 6 comments from
organizations and corporations supporting a primary standard
level of 0.12 ppm.
24
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COMMENTS RECEIVED ENDORSING A PRIMARY STANDARD LEVEL HIGHER
THAN 0.12 ppm AND/OR CONTENDING PROPOSED STANDARD TOO STRINGENT
Organization or Agency
American Petroleum Institute (API)
Association of Local Air Pollution Control Officials
Associated Building Industry of Northern California
Cook County Dept. of Environmental Control, Illinois
Dow Chemical Company
Eastman Kodak -Company
General Motors Corporation
Great Plains Legal Foundation
Greater San Antonio Chamber of Commerce, Texas
Houston Chamber of Commerce, Texas
Iowa-Illinois Gas and Electric Company
Louisiana Air Control Commission
Manufacturing Chemists Association
Monsanto Chemical Intermediates Co.
Motor Vehicle Manufacturers Association
National Flexible Packaging Association
New Orleans Public Service, Inc.
Oklahoma State Dept. of Health
Owens-Illinois
Rio Blanco Oil Shale Company
St. Louis County, Missouri
San Antonio Metropolitan Health District, Texas
Shell Oil Company
Steams-Roger, Inc., Denver, Colorado
Tennessee Eastman Corp.
Texas Air Control Board
Texas Chemical Council
U.S. Council on Wage and Price Stability
Utah Manufacturers Association
Virginia Air Pollution Control Board
Western Oil and Gas Association
White River Shale Project
Endorse standard
higher than 0.12
pom
X
X
X
X
X
X
X
X
X
X
X
Proposed standard
too strinaent
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Summary:
15 comments from organizations, agencies, and companies and 4 comments from
concerned citizens supporting a primary standard level higher than 0.12 ppm,
23 comments stating the proposed standard is too stringent.
25
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The principal issues raised during the comment period relate to
the following topics:
I. HEALTH EFFECT CRITERIA AND SELECTION OF THE PRIMARY STANARD
A. Definition of an Adverse Health Effect
B. EPA's Interpretation of Cited Studies
C. Margin of Safety
D. Use of Animal Studies
E. Exposure of Sensitive Groups
F. Synergistic Effects and Chemical Species Designation of the
Standard
II. RISK ASSESSMENT METHOD
III. WELFARE EFFECTS AND THE SECONDARY STANDARD
IV. IMPLEMENTATION AND ATTAINABILITY
A. Value of Hydrocarbon Control and Timing of SIP Submissions
B. Consideration of Control Costs
C. Natural Background Concentrations
V. PROCEDURAL ISSUES
The comments received have been reviewed and a document detailing
their disposition has been placed in the rulemaking docket (OAQPS 78-8)
for public inspection. The following sections summarize the significant
comments and present the Agency's responses.
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I. HEALTH EFFECT CRITERIA AND SELECTION OF THE PRIMARY STANDARD
A. Definition of an Adverse Health Effect
Comment
The proposed standard is unsuitable because EPA has never
defined what constitutes "protection of public health." As a
specific example, EPA has not shown that pulmonary function and
ventilatory pattern changes are adverse health effects.
Agency Response
As stated in the criteria document, t«he avail able evidence
regarding pulmonary function changes observed in clinical exposures of
healthy subjects to ozone does not suggest that small changes in lung
function (unaccompanied by discomfort symptoms or impairment of oxygen
uptake) would interfere with normal activity in healthy individuals.
However, even small changes in people with underlying respiratory
disease such as asthma, chronic bronchitis, and emphysema can interfere
with normal activity and, thus, may signal impairment of public health.
Comment
EPA should identify where adverse effects begin in the
continuum of responses to pollutants.
Agency Response
In conducting a preliminary risk assessment, EPA interviewed
several biomedical experts to obtain their judgments as to the risk of
exceeding the threshold of adverse health effects in sensitive persons
for alternative standard levels. An essential feature of this risk
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assessment procedure is the utilization of the experts' judgments
as to the point in the continuum of physiological responses to
ozone that must be exceeded for an adverse health effect to occur.
As an example, discussions with several experts indicated that a
1 percent decrease in pulmonary function (e.g., forced expiratory
volume 1-second test) would be inconsequential, whereas a 50 percent
decrease would be a severe effect in sensitive persons; the experts'
judgments varied as to the point at which adverse effects would
begin, but fell within the range of a 5 to 15 percent decrease.
Comment
Quickly reversible irritation experienced for a short period
of time is a welfare effect related to personal comfort and well-being
and should therefore be considered in connection with the secondary
standard.
Agency Response
The criteria document states that physical discomfort, as
manifested by symptoms such as difficulty in breathing, chest
tightness, and pain on deep inspiration, has usually been observed
in clinical studies in conjunction with pulmonary function changes.
Even when reversible, respiratory symptoms may restrict normal
activity or limit the performance of tasks. In clinical studies,
exposure of healthy subjects to realistic levels of ozone (0.3 ppm)
has produced discomfort sufficient to prevent completion of
experimental protocols, particularly when vigorous exercise was
28
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Involved. Accordingly, the criteria document concluded that
increased rates of respiratory symptoms constitute impairment
of public health. On this topic, a physician affiliated with the
California Department of Health stated (docket OAQPS 78-8, IV-F-31)
that it was his medical opinion that symptoms such as those
described above constitute adverse health effects, inasmuch
as they signal pulmonary function decrements and an increased
t
pulmonary work load for affected individuals. He expressed his
concern for the long-term effect of repeated exposure to levels
of ozone sufficient to induce such symptoms. EPA concurs in this
view and considers such symptoms, even though transitory, to be
of concern in selecting the level of the primary standard.
B. EPA' s Interpretation of Cited Studies
1. Delucla and Adams (1977)
Comments
(a) EPA has misread the DeLucia and Adams study in claiming
significant effects have been reported at 0.15 ppm for one hour.
(b) Mouthpiece breathing may have invalidated the DeLucia
and Adams study.
(c) Since DeLucia -and Adams demonstrated effects at 0.15
ppm in healthy individuals, more susceptible populations would
be expected to sustain effects at lower levels.
29
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Agency Responses
(a) EPA acknowledges that DeLucia and Adams failed to demonstrate
any statistically significant decrements in pulmonary function resulting
from exposure to 0.15 ppm for one hour. (The investigators did observe
statistically significant decrements in pulmonary function resulting
from exposure to 0.30 ppm for one hour.) In groups as small as those
tested by Delucie and Adams (six subjects), however, tests of statisti-
cal significance are difficult to interpret. The criteria document
concluded that the study by DeLucia and Adams, although unreplicated,
has raised the question of whether 0, concentrations as low as 0.15 ppm
exert effects in a portion of healthy subjects exercising vigorously.
Indeed, DeLucie and Adams specifically state that the two most sensitive
subjects sustained markedly impaired respiratory function and exercise
ventilatory patterns during the two most stressful exercise protocols in
the four ozone-exposure experiments (i.e., both 0.15 ppm and 0.30 ppm).
Furthermore, DeLucia and Adams state that most of the subjects
experienced subjective symptoms of discomfort (e.g., congestion, chest
pain, and cough) when exposed to 0.15 ppm for one hour under the most
stressful exercise protocol (equivalent to running about 6 miles in an
hour). These symptoms occurred at a lower exercise rate when the subjects
were exposed to 0.30 ppm. DeLucia and Adams did not report the incidence
of these symptoms in a quantitative manner, but this fact does not
remove EPA's concern about the implications for healthy persons such as
those studied by DeLucia and Adams, or for more susceptible persons who
may sustain more severe reactions or who may be affected at lower
concentrations than those observed.
30
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(b) As noted in the criteria document, persons tend to breathe
through their mouths when exercising. Thus, DeLucia and Adams' utiliza-
tion of mouthpieces to dispense CL probably represents actual exposures
in persons who, in the course of their normal daily activities, are
undergoing exercise.
(c) EPA agrees with this comment, as noted above. EPA considered
the implications of this study for more susceptible members of the
population in its determination of the margin of safety for the ozone
standard.
t
2. Schoettlin and Landau (1961)
Comments
(a) There are still problems with reliance on this study because
(1) ambiguities remain in its interpretation and (2) more recent studies
of effects of ozone on asthmatics have failed to corroborate this study's
conclusions.
(b) EPA's interpretation of the concentration at which Schoettlin
and Landau correlated increased incidence of asthmatic attacks is un-
necessarily conservative. There is good reason to believe that the
0.25-ppm oxidant concentration cited by Schoettlin and Landau was a
daily peak (2-minute average) concentration rather than a daily maximum
hourly average concentration, as EPA claims. Furthermore, the level of ozone
occurring on these high oxidant days would have been less than the level
of oxidant reported.
Agency Responses
(a) The criteria document recognizes limitations that make it
difficult to interpret the Schoettlin and Landau study unequivocally.
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Nevertheless, Schoettlin and Landau did conclude that the proportion of
asthmatics having attacks was significantly greater on days when the
oxidant concentration exceeded 0.25 ppm than on days when the concen-
tration was below that level. EPA does not believe that this conclusion
has been refuted by more recent studies. The reported results of the
recent epidemic!ogical study by Kurata et al (1976) are qualitatively
similar to those of Schoettlin and Landau. EPA's analysis (docket OAQPS
78-8, IV-A-1) of the data presented in the Kurata study indicates that
a statistically significant elevation of the asthma index occurred on
days when the maximum instantaneous (2-minute average) oxidant concen-
trations exceeded 0.28 ppm. While the exact hourly average equivalent
of this value is not known, it must be less than or equal to 0.28 ppm,
and is probably in the range of 0.20 to 0.27 ppm.
(b) EPA acknowledges that it is uncertain from Schoettlin and
Landau's paper what averaging time was used in correlating oxidant
concentration and incidence of asthma attacks.. As stated in the criteria
document, however, consultations with the authors have established that
daily asthma attack rates were correlated with daily maximum hourly
average oxidant levels. EPA considers that these consultations (docket
OAQPS 78-8, IIA-C-2) have satisfactorily resolved the controversy
regarding the averaging times used by Schoettlin and Landau.
EPA agrees with the comment that ozone levels may have been lower
than the oxidant readings with which Schoettlin and Landau correlated
asthma attack incidence. Ozone levels have been shown to range from
approximately 65 percent to nearly 100 percent of the total oxidant
levels. This fact provides reason for concern that ozone in the ambient
32
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air at daily maximum hourly average concentrations less than 0.25 ppm
may adversely affect asthmatic persons.
3. Hammer et al. (1974)
Comments
(a) This study has methodological problems (such as the failure to
adjust the data for smoking habits and allergy histories) that undermine
confidence in its conclusions.
(b) It is uncertain that oxidants caused the increase in symptoms
observed in this study.
Agency Responses
(a) Hammer et al. conducted a longitudinal survey of an essentially
constant group of subjects over a period of time. Consequently, in
order for the authors' failure to adjust the data for smoking habits and
allergy histories to have biased the results, the survey response
pattern on high pollution days would had to have differed with respect
to the distribution of smokers and allergic persons as compared with the
pattern on low pollution days. Such an occurrence seems unlikely;
furthermore, the criteria document noted that the results of this epi-
demiological study are generally consistent with the results of clinical
exposure studies. This fact, along with the extensive data base evaluated
(about 53,000 person-days of observation), enhances the reliability of
Hammer's study.
(b) Hammer et al. found that symptom frequencies were more closely
correlated to photochemical oxidants than to several other environmental
parameters (e.g., carbon monoxide and nitrogen dioxide). In addition,
the criteria document noted that the oxidant levels at which cough and
33
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chest discomfort were observed to increase in the student nurse popula-
tion were quite similar to ozone concentrations that have been observed
to produce impairment of pulmonary function and respiratory irritation
in experimental exposures of healthy subjects performing intermittent
light exercise (0.27 ppm for 2 hours). Consequently, it is reasonable
to propose that photochemical oxidants—and specifically ozone in the
ambient air—contributed substantially to observed increases in rates of
cough, chest discomfort, and headache.
L. Hazucha (1973)
Comment
Results reported by Hazucha on impairment of pulmonary function at
ozone levels of 0.25 ppm for 2 hours are not statistically significant.
Agency Response
The small number of subjects (three) examined at that exposure
precludes the application of statistical methods to the results. The
absolute value of the pulmonary function decrements (about 5 percent)
is the more relevant factor in evaluating the results of this study.
As described in the criteria document, the small pulmonary function
changes observed by Hazucha in a 2-hour exposure of healthy subjects
undergoing intermittent light exercise lie along a continuum of responses
when compared with results at higher concentrations and similar exposure
regimes. There is no indication that 0.25 ppm is the threshold for
that exercise level, and indeed the study by DeLucia and Adams (1977)
has shown symptomatic effects in healthy individuals that are indicative
of pulmonary function impairment at levels as low as 0.15 ppm under a
more strenuous exercise protocol.
34
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5. Studies In which effects were not observed at levels above
0.15 pom
Comments
(a) The 1977 National Academy of Sciences (HAS) document, Ozone
and Other Photochemical Oxidants, was cited in several comments as
concluding that effects in human subjects have been observed only from
ozone exposures above 0.25 ppm.
(b) Linn et al. (1978) failed to find any significant pulmonary
effects in asthmatics exposed to 0.20 - 0.25 ppm for 2 hours under
conditions of heat and exercise.
(c) Hackney et al. (1975) observed human health effects only at
exposures above 0.25 ppm for 2 hours.
Agency Responses
(a) The NAS document states that "some limited studies show
evidence of human health effects of exposure to pure ozone at concen-
trations as low as 0.25 ppm ..." This document was prepared before
publication of the DeLucia and Adams study, which suggests effects at
lower levels. Furthermore, this NAS document in no way concludes that
effects resulting from ozone, as it occurs in the ambient photochemical
mix, do not occur at concentrations below 0.25 ppm.
(b) Although Linn et al. found statistically significant changes in
one of several measures of pulmonary function in their laboratory study,
the manner in which the investigators conducted the study (e.g., persons
with marked respiratory disability were excluded from the study) and
analyzed the data are such that the observed results probably underestimate
the effects that would occur at similar ambient exposure levels. There
was a slight increase in symptom scores during ozone exposure, and
statistically significant changes in blood biochemical factors were
35
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observed. While the clinical significance of these latter changes is
uncertain, they do represent alterations in normal body functions and
cannot be discarded in selecting a standard that protects public health
with an adequate margin of safety.
(c) Although the criteria document states that Hackney et al.
observed no lung function changes of note at 0.25 ppm for 2 hours even
among "reactive" subjects (persons giving a history of cough, chest
discomfort, or wheezing in response to allergy or air pollution exposure),
closer inspection of the Hackney et al. (1975) studies reveals that dose-
response relationships hold for sensitive subjects for lung function and
blood biochemical effects across the range of exposure from 0.20 to 0.50
ppm ozone.
6. Other Human Studies
Comments
(a) Von Nieding et al. (1975) have demonstrated effects on pul-
monary function of healthy individuals at 0.10 ppm ozone.
(b) EPA cannot justify a conclusion that Japanese epiderniological
studies indicate a risk of symptomatic effects in human beings from
ozone exposures below 0.15 ppm for one hour.
Agency Responses
(a) EPA is concerned about the findings of von Nieding et al.
showing decreased oxygen pressure in arterialized blood and increased
airway resistance after 2 hours of exposure to 0.10 ppm ozone and inter-
mittent light exercise. The criteria document points out, however,
that the investigators used non-standard physiologic measurement methods.
Thus, although von Nieding1s findings cannot be ignored in the standard-
36
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setting process, they ere unconfirmed, and must be interpreted cautiously.
(b) Makino and Mizoguchi (1975) reported an epidemiological study
of Tokyo students that showed increased rates of discomfort symptoms on
days when the oxidant level (believed to be a daily maximum hourly
average concentration) exceeded 0.15 ppm as compared with days when it
fell below 0.10 ppm. The criteria document reviewed this and several
other Japanese epidemiological studies, and concluded that the studies
were appropriately designed but that it is very difficult to interpret
their results. In setting a standard with an adequate margin of safety,
however, EPA must consider evidence such as these Japanese studies and
must evaluate the uncertainties which medical research has not yet
resolved.
7. Validity of Clinical Studies in General
Comment
At the August 22, 1978 public hearing in Dallas, testimony was
presented alleging that the ozone generators used in clinical health
studies produce other toxic materials in addition to ozone. Experi-
mental data obtained using a new total oxidant monitoring method
indicated that these additional oxidants were present in large quantities
(as high as 300 percent greater than ozone). It was hypothesized that
the adverse effects noted in clinical studies may be preponderantly
caused by the additional oxidants and not ozone.
37
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Agency Response
EPA has concluded that the experimental evidence offered to support
these findings is unconvincing and cannot be substantiated. The results
of an experimental program initiated by EPA after the Dallas hearing
indicate that the new monitoring technique which supposedly measured
ozone and any additional oxidants has a variable chemical reaction
relationsnip (stoichiometry) with ozone depending on whether or not
oxygen is present. The higher oxidant readings obtained by this tech-
nique appear to result from this variable stoichiometry rather than
representing the presence of any additional non-ozone oxidants. Further-
more, an exhaustive search for such oxidants in the output of ozone
generators operating under various conditions (using as the input stream
either dry or humidified tank air or oxygen, with very low or background
concentrations of hydrocarbons, mostly methane) failed to produce any
evidence of non-ozone oxidants. Consequently, EPA judges the hypothesis
offered by this comment to be experimentally unsupportable. A report
documenting the results of EPA's experimental program has been placed
in the docket (OAQPS 78-8, IV-A-2).
38
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C. Margin of Safety
Comment
EPA has proposed a standard with an inappropriate margin of safety.
The margin of safety was criticized as being either inadequate or too great.
Agency Response
The Clean Air Act requires that EPA set air quality standards that
are requisite to protect the public health, allowing an adequate margin
t
of safety. As stated in the legislative history of the Clean Air Act,
the standard must protect against hazards that research has not yet
identified. EPA feels that the decision regarding an adequate margin
of safety is a judgment which must be made by the Administrator after
weighing a.11 the medical evidence bearing on ozone. The factors to
be taken into account include inconclusive evidence as well as findings
from studies that are considered definitive and not subject to challenge.
For example, in selecting an adequate margin of safety, the Administrator
must consider: (1) findings from animal studies that show increased
susceptibility to infectious respiratory disease and other serious
effects at relatively low ozone levels, (2) the concern that health
studies may not always reflect the health impact in more sensitive
39
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segments of the population, and (3) studies suggesting that ozone may
produce an enhanced effect when combined with other air pollutants
commonly present in the urban atmosphere but not present in clinical
study chambers.
D- Use of Animal Studies
Comment
EPA has failed to give appropriate consideration to the results of
animal studies, especially those involving young animals and those
examining reduced resistance to infection.
Agency Response
EPA is concerned about the studies which have demonstrated fiBttaaaaa.
effects in young animals and decreased resistance to infection in animals
exposed to ozone. The infection effect has been demonstrated at exposures
as low as 0.08 ppm for 3 hours. The criteria document concluded that
these findings have definite human health implications, although different
exposure levels may be associated with such effects in humans. For this
reason, these results cannot be the sole factor used in selecting the level
of the primary standard. However, as is the case with other inconclusive
evidence, EPA must consider these studies in selecting an adequate
margin of safety.
Comment
There is no evidence of reduced resistance to infection in
epidemiologic studies in places such as Los Angeles.
40
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Agency Response
Epidemiological studies have been inconclusive in demonstrating
this effect in man. However, EPA does not agree with this comment.
The study by Durham (1974) of air pollution effects on college students,
indicates that rates of new illness increase following short-term exposures
to elevated pollutant concentrations. The pollutant variable most
strongly associated with illness was peak oxtdant. Also, several
studies documenting increased levels of mucous membrane irritation
during periods of ozone exposure suggest indirectly that susceptibility
to infection may rise during these periods. Furthermore, although
animal study findings cannot be directly extrapolated to man, the criteria
document concludes that the reactions observed in mice represent
effects on basic biological responses to infectious agents, and
there is no reason to believe that the pollutant-induced alterations
of basic defense mechanisms that occur in mice could not occur in
human beings. Thus, these studies cannot be ignored in the standard-
setting process.
E. Exposure of Sensitive Gro_up_s_
Comment
EPA is being unnecessarily stringent in selecting the sensitive
population. The standard could be much less stringent without endangering
41
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the health of such persons if EPA accounted for the portion of time that
persons are indoors end, thus, not exposed to higher ambient concentraitons.
Agency Response
The legislative history of the Clean Air Act makes quite clear
Congress1 intention to protect sensitive persons (asthmatics and
emphysematous patients are cited as examples) who in the normal course
of daily activity are exposed to the ambient environment. Air quality
standards are to be established with reference to protecting the health
of c representative sample of persons comprising the sensitive group
rather than £ single person in such a group. Standards must be based
on a judgment of a safe air quality level and not on an estimate of how
many persons will intersect given concentration levels. EPA interprets
the Clean Air Act as providing citizens the opportunity to pursue their
normal activities in a healthy environment.
F. Synergistic Effects and Chemical Species Designation of Standard
Comment
There were objections to the proposed change of the chemical designa-
tion of the standard from photochemical oxidants to ozone because the
health impacts of photochemical air pollution arise not only from ozone,
but also from the spectrum of other gaseous and particulate pollutants
that co-exist with ozone. There was also concern that the change in
the chemical designation signalled a change in emphasis in oxidant control
42
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efforts that would impede progress in the reduction of non-ozone compo-
nents of the photochemical oxidant mixture such as peroxyacety]nitrate
(PAN). Specific concern was expressed regarding the eye-irritating
components of the mixture, since at ambient levels ozone clone is not
an eye irritant.
Agency Response
Certain clinical studies (such as Hazucha and Bates, 1975) have
demonstrated the potential for greater health impacts resulting from
exposure to ozone in combination with other pollutants which occur in
the ambient air than from exposure to ozone alone. The ozone standard
is not intended merely to protect against the levels of ozone that have
been demonstrated to produce effects in clinical studies where subjects
have been exposed to highly purified air to which ozone alone has been
added. Rather, setting an ozone standard with an adequate margin of
safety involves, among other considerations, evaluating the effects of
ozone as it occurs in the ambient air, in combination with other pollutants.
One reason for changing the chemical designation of the standard
from photochemical oxidants to ozone is to correct an inconsistency
between the title of the standard (photochemical oxidants) and the
chemical species (ozone) that has always been measured by the reference
method used to estimate ambient oxidant levels and determine compliance
with the standard. Consequently, no redirection of control efforts is
43
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contemplated; i.e., reductions in hydrocarbon and nitrogen oxide emissions
will continue to be required in order to reduce the levels of the
secondarily generated pollutant (ozone) measured to determine compliance
with the standard.
The criteria document examined the issue of whether or not measures
taken to reduce ozone will also Deduce other manifestations of photochemical
pollution such as eye irritation. The evidence from laboratory and
theoretical studies indicates that, for urban atmospheres, reductions in
hydrocarbon and nitrogen oxide emissions should have even greater
impacts on ambient PAN than on ambient ozone. Similarly, laboratory
data suggest a linear relation between hydrocarbon emissions and ambient
levels of photochemically produced aldehydes. Since PAN and such
aldehydes as formaldehyde and acrolein are known to be eye irritants,
the criteria document concludes that emission control measures for ozone
reduction will probably have a positive effect on reducing eye irrita-
tion in those situations where eye irritation is associated with photochemical
processes (e.g., Los Angeles).
II. RISK ASSESSMENT METHOD
Comment
The risk assessment method should not be used at this time because
it has not been reviewed adequately by the Science Advisory Board or the
scientific community.
44
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Agency Response
The risk assessment method is not being used to set the ozone
standard. In determining what ozone standard has an adequate margin of
safety, however, the findings of the initial application of the risk
assessment method to ozone have been considered. EPA agrees that the
method hss not received sufficient review. The method will be published
in the open literature and the Science Advisory Board is forming an ad-
hoc subcommittee to review the method.
Comment
EPA's risk assessment method is incomplete.
Agency Response
EPA agrees with the comment. As applied to ozone, the risk assess-
ment method assesses the risk (probability) that ozone would contribute
to health effects in some sensitive people if alternative standards were
just met. A complete risk picture would also include information on:
(a) a best point estimate of the number of people affected;
(a1) the "expected number" (in a statistical sense) of people
affected;
(a") various risks (probabilities) that the actual number of
people affected would be various amounts greater than the
expected number;
45
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(b) a best point estimate of the amount of health damage;
(b1) the "expected" health damage; and
(b") various risks (probabilities) that the actual health
damage would be various amounts greater than the expected
health damage.
As noted in the draft EPA document explaining the risk assessment method,
there are complex technical problems that must be dealt with in responsibly
developing information of this type suitable for use in setting National
Ambient Air Quality Standards. EPA is presently developing the capability
to generate this type of information and will only consider its risk
assessment method complete when the method includes this capability.
Comment
The main problem with the risk assessment method stems from its
purpose. Instead of estimating health damage, EPA provides a table of
risk numbers without providing an estimate of their health significance;
these numbers serve no function.
Agency Response
EPA agrees that the risk estimates provided do not serve the
function of estimating health damage, but the Agency does not agree
that the estimates are without value. The function of these estimates
is to indicate the varying risk (or probability) that some sensitive
people would suffer health effects in a given period of time if
alternative ozone standards were just met. For each health effect
46
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category, the response that is of sufficient concern to be deemed a
health effect has been decided upon and its seriousness described.
As EPA interprets the Clean Air Act, this detennination, which is an
important step in the process of setting National Ambient Air Quality
Standards, is a function that is to be served by a risk assessment.
There were many comments on both the procedural and the technical
aspects of the risk assessment method. EPA will consider these comments
in the detailed responses to be placed in the docket. Some of the comments
identify improvements that can be made in the risk assessment method,
while others reflect misunderstandings that will be dealt with in the
detailed docket responses. Some of the comments provide discussion and
opinions on various complex issues that arise in the conduct of a program
involving the difficult subject areas of risk assessment and standard-
setting methodology. EPA will take these comments into advisement as
it develops its risk assessment and standard-setting methodologies.
III. WELFARE EFFECTS AND THE SECONDARY STANDARD
Comment
EPA's proposal to retain the existing secondary standard is based
entirely on evidence of possible damage to extremely sensitive vegetation.
An adequate economic analysis that considers the incremental costs
and benefits of alternative secondary standard levels should be conducted.
EPA should then weigh the economic costs of pollution control measures
against the benefits of reduced damages from lower ozone concentration
levels before setting a secondary standard.
47
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Agency Response
The Clean Air Act requires EPA to set a national secondary
ambient air quality standard at a level that, in the judgment of
the Administrator, is requisite to protect the public welfare
from any known or anticipated adverse effects. The term "public
welfare," which is defined in Section 302(h) of the Clean Air Act,
includes among other things effects on crops, vegetation, wildlife,
visibility, and climate, "as well as effects on economic values and
on personal comfort and well-being."
EPA has carefully examined the data presented in the criteria
document concerning ozone-related damage to vegeiation, crops, materials,
and visibility. A staff paper, "Evaluation of Alternative Secondary
Ozone Air Quality Standards," has been placed in the docket (OAQPS 78-8,
IV-A-3).
•
With regard to damage to materials, the paper concludes that no
effect-based rationale can be offered to decide the level of the secondary
standard. Damage to materials is linearly related to the total dose
sustained by the material. As a result, the annual average concentration
will determine the rate at which material damage occurs. Current evidence
indicates that annual average concentrations for remote rural areas are
comparable to urban areas, due to strong nighttime scavenging of ozone
in urban areas by man-made pollutants. Reducing the peak 1-hour concentration
in urban areas will have virtually no impact on the annual average
concentration. Therefore, there would be no measurable reduction in
materials damage if a more stringent secondary standard level was selected.
48
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The criteria document states that there is a limited amount of data
suggesting an association between ambient ozone and visibility degradation,
particularly in the Los Angeles area. On the basis of EPA's evaluation
to date of the information presented in the criteria document, however,
EPA is unable to conclude at tnis time that a secondary ozone standard
more stringent than the primary standard is necessary to prevent visibility
deterioration. The relationship between visibility and ambienz ozone
will be considered further in the development of subsequent PSD programs
designed to protect against significant deterioration of air quality.
Finally, EPA has concluded that there is currently no evidence
indicating that a significant decrease in yield or growth of commercially
important crops or indigenous vegetation will result from the long-term
(growing season) mean of the daily maximum 7-hour-average ozone concen-
trations which is expected to occur when the primary standard is attained.
Consequently, EPA does not believe thai a secondary standard more stringent
than the primary standard is necessary to protect vegetation from ozone-
related yield reduction effects.
On the basis of these conclusions, EPA does not believe that a
detailed cost-benefit analysis of alternative standard levels is required,
since a secondary standard more stringent than the primary standard is
not necessary to protect the public welfare adequately.
Comment
The current secondary standard of 0.08 ppm should be retained to
protect vegetation and crops. There is significant reduction in growth
and yield to crops exposed to 0.10 ppm of ozone.
Agency Response
The claims that significant reduction in growth and yield occurs
49
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in crops as a result of short-term exposures to ozone at levels around
C.'O ppm are undocumented. While sensitive plants may incur foliar
injury at low ozone levels, there is currently no evidence that significant
yield or growth effects in commercially important crops or indigenous
flora are associated with the long-term (growing season) mean of the
daily maximum 7-hour-average ozone concentrations expected to occur when
the primary standard is attained. Consequently, EPA does not believe that
a secondary standard more stringent than the primary standard is necessary
tc prevent ozone-related yield reduction effects in vegetation.
IV. IMPLEMENTATION AND ATTAINABILITY
"• Velue of Hydrocarbon Control and Timing of SIP Submissions
EPA received comments on the effectiveness of hydrocarbon
controls in reducing levels of ozone.in the ambient air as well
as on the issue of whether or not the statutory deadline for
submission of revised State Implementation Plans (SIPs) for non-
atteinment areas should be postponed because of the changes in the
photochemical oxidants standard. The Agency responses to these
comments are contained in the accompanying Federal Register notice
dealing with the revision of the 40 CFR Part 51 regulations pertain-
ing to the implementation of the standard.
B. Consideration of Control Costs
Comment
Cost of control should be considered in selecting the level
of the primary standard.
Agency Response
The Agency's position with respect to control cost consideration
was stated in the preamble to the proposed regulation (43 FR 26963);
50
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this position remains unchanged. The Clean Air Act specifies that
primary National Ambient Air Quality Standards are to be based on
scientific criteria relating to the level that should be at-
tained to protect public health adequately. Considerations of
cost of achieving these standards or of the existence of tech-
nology to bring about needed reductions of emissions are not
germane to such a determination, as the words of the Act and its
legislative history clearly indicate. EPA has, however, analyzed
the cost and economic impacts of the control programs required to
attain alternative ozone standard levels in Order that the public
may be better informed of the consequences of the Agency's decision.
This analysis and the comments received in response to it are
avail able to the States for their use in developing strategies to
implement the standard.
Comment
The cost estimates presented in EPA's cost and economic impact
assessment document are understated.
Agency Response
EPA has carefully reviewed and considered these comments and is
publishing a revised economic impact assessment, which is available
from Mr. Padgett at the previously mentioned address.
C. Natural Background Concentrations
Several comments were made regarding the contribution of natural
sources to ambient ozone concentrations. These comments focus on
(1) the extent to which natural background was considered in
developing the proposed standards and related control programs and
(2) the attainability of these standards, considering the possibility
51
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that natural background may at times contravene the proposed levels.
Some of the comments suggested that EPA ignored, or did not adequately
consider, natural background in developing the proposed standards and
related control programs. While this topic was not emphasized in the
preamble to the proposed rulemaking, EPA was, and is, cognizant of the
background levels that can be attributed to natural sources. This
matter was treated extensively in the revised criteria document. Further-
more, EPA procedures for preparation of control plans recommend allowance
for natural background in developing control strategies for ozone.
For several years, EPA has been conducting an active field and
laboratory research program seeking to determine the nature and
extent of background concentrations of ozone. The results of these
studies have been widely publicized in EPA reports, scientific
literature, and public conferences. One comment suggested that
EPA had ignored evidence of natural source impacts reported in con-
tract work conducted for the Agency and that this information had
not been released for public review. Actually, all pertinent infor-
mation available to EPA was considered. However, there may have been
some contractually developed information that had not been released
or could not be specifically cited because the contract studies were
still in progress and the resulting data had not been fully validated
or analyzed. Subsequent to the comment, all information in question
were released publically or arrangements have been made to release
them as soon as possible.
EPA's review of data related to the background contri-
52
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bution leads the Agency to conclude that such levels are usually
well below the proposed levels of the standard, especially during
the season of the most active production of photochemical ozone.
It is possible, however, that natural events could occasionally
cause contravention of the promulgated standard levels. EPA policy
(see 40 CFR 51.12(d)) permits data for such occurrences to be dis-
regarded for regulatory purposes. Such events are usually dis-
tinguishable because they tend not to coincide with conditions
t
conducive to buildup of man-caused, pnotochemically produced ozone.
Field measurements at some remote sites, where man-caused ozone is
likely to be negligible, have shown low—but not insignificant-
rates of exceedances of the 0.08-ppm level originally proposed for
the secondary standard. The frequencies decrease markedly for
concentrations above 0.12 ppm} so that natural exceedances of the
standards being promulgated can be considered quite rare at
any particular location.
One comment indicated that stratospheric tracer levels measured
at surface sites increase by about 40 percent between the front and
back side of high pressure systems in the Eastern United States,
thus suggesting that stratospheric ozone, through subsidence and
horizontal circulation in highs, plays a significant role in the
widespread buildup of ozone that tends to occur in the back side of
highs in the Eastern U.S. during the photochemically active season. EPA's
estimate is that, even if commonly occurring natural ozone back-
ground were increased by 40 percent, the resulting concentration
53
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would be insufficient to exceed the standard levels being promulgated,
Also, a corresponding increase between the tracer and ozone of strato-
spheric origin would not be expected, since the tracer is chemically
stable near the surface, while ozone is rapidly depleted by reactions
with surfaces and with air contaminants.
Some comments referred to a possibly significant contribution
to ozone concentrations from reactions involving organic compounds
emitted by vegetation. Such emissions are abundant, relative to
man-made emissions, but are relatively diffuse spatially. Some of
the comments cited a recent statistical study that reported a high
correlation between vegetative growth in the Bay Area of California,
as indicated by winter rainfall, and the frequency of days with con-
.centrations above 0.08 ppm. EPA has not, however, seen sufficient
physical evidence of a relative abundance of natural organics or
associated ozone increases in ambient air to consider vegetative
sources as significant contributors to high ambient ozone levels.
The principal source of natural ozone is still considered to be the
stratosphere, with gradual transfer accounting for the more commonly
observed background levels, and sporadic intrusions being the
principal cause of anomalous high values.
more
Although research will continue to assess^definitively the
contribution of natural sources of ozone, EPA believes that adequate
54
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consideration has been given to this issue in developing control pro-
grams and implementation guideline documents.
V. Procedural Issues
Comment
EPA's use of an "Advisory Panel on Health Effects of Photo-
chemical Oxidants" was procedurally incorrect in that certain
legal requirements on establishment and use of Advisory Committees
were not met.
Agency Response
The ad hoc Advisory Panel consisted of a group of medical experts re-
tained by EPA as consultants for the purpose of obtaining their in-
terpretation of the evidence presented in a preliminary version of the
criteria document. As such, EPA did not regard the Panel as an
advisory body within the meaning of the Advisory Committee Act of 1972.
In any case, the Panel's report has been in the docket and subject to
comment since proposal, and bases for its recommendations have been
fully aired.
Comment
In revising its criteria document, EPA failed to comply with
the recommendations of the statutory scientific review body, the
Science Advisory Board (SAB), as evidenced by the SAB's refusal
to approve the criteria document.
Agency Response
The function of the Science Advisory Board subcommittee is to advise
EPA regarding the scientific and technical accuracy, the manner of pre-
sentation, and the adequacy of the criteria document. Inevitably, no
two scientists ever agree completely on the importance, accuracy and
55
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manner of presentation of data. In the final analysis the responsibility
for the criteria document rests with EPA and, therefore, the decision
regarding the content of the document must also rest with EPA.
EPA solicits the advice of its scientific advisors and has attempted
to respond to the specific comments made by members of the SAB sub-
committee established to review the criteria document by incorporating
suggested changes in the document. Following the last SAB subcommittee
meeting in February 1978, members of the subcommittee who had specific
comments were consulted by EPA personnel, and their comments and criticisms
were discussed with them prior to making the changes in the document. It
has always been Agency policy that once the EPA staff had considered the
changes suggested by the SAB and, where appropriate, incorporated them
into the criteria document, the Agency would proceed with publication.
Consequently, EPA feels that the criteria document adequately reflects
the latest scientific knowledge pertaining to the effects of ozone and
other photochemical oxidants.
Comment
EPA has failed to submit the proposed standard to the SAB for
review as required by the Environmental Research, Development, and
Demonstration Authorization Act of 1978 (Pub. L. 95-155). EPA
should do so before promulgating the standard.
Agency Response
The development of the ozone standard revision, which began in
1976, followed the procedural process in place before the enactment
of public law 95-155. Accordingly, the SAB was asked to review only
the criteria document. The independent committee established in
56
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accordance with the 1978 Act held its first session in October 1978,
when there was not adequate time for it to review the standard. The
thorough review of the technical and scientific basis for the criteria
document, which is in turn the basis for the standard, substantially
complies with the objectives of the Act.
SELECTING THE LEVEL OF THE PRIMARY STANDARD
EPA's objective in setting the standard level is to select an ozone
concentration that will reflect an accurate consideration of the existing
medical evidence and an adequate assessment of the uncertainties in this
evidence, and, thus, will protect all population groups with an adequate
margin of safety.
The criteria document supports the contention that a clear
threshold of adverse health effects cannot be identified with certainty
for ozone. Rather, there is a continuum consisting of ozone levels
at which health effects are certain, through levels at which scientists
can generally agree that health effects have been clearly demonstrated,
and down to levels at which the indications of health effects are less
certain and harder to identify. Given such a body of evidence, in
selecting a standard with an adequate margin of safety the decision-
maker is taking into account the uncertainty about whether a possible
standard will prevent adverse health effects.
This uncertainty results from several factors. First, human
susceptibility to health effects varies, and we cannot be certain that
experimental evidence has accounted for the full range of susceptibility.
57
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Second, we cannot be certain that all effects occurring at low ozone
levels have been identified and demonstrated. Third, variations in
weather create uncertainty as to the expected annual maximum ozone
concentrations.
The Clean Air Act, as the Administrator interprets it, does
not penr.it him to take factors such as cost or attainability into
account in setting the standard; it is to be a standard that will
adequately protect public health. He recognizes that controlling
czone to very low levels is a task that will have significant impact
on economic and social activities. This recognition causes him to
reject as an option the setting of e zero-level standard as an
expedient way of protecting public health without having to decide
among uncertainties. However, it is public health, and not economic
impact, thai musi be the compelling factor in the decision. Thus, the
decision as to what standard protects public health with an adequate
margin of safety is based on the uncertainty that any given level is
low enough to prevent health effects, and on the relative acceptability
of various degrees of uncertainty, given the seriousness of the effects.
In selecting the proper level fo>" the standard, EPA must make
assessments and judgments in five critical areas:
1. Reported effect levels from human studies.
2. Characterizing the sensitive population.
3. Nature and severity of effects.
4. Probable adverse health effect level in sensitive persons.
58
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5. Judgment of a standard level below the probable effect
level that provides an adequate margin of safety.
REPORTED EFFECT LEVELS
In the preamble to the proposed standard (43 FR 26965), EPA
presented a table of demonstrated effect levels in man ranging from
0.15 to 0.30 ppm. On the basis of suggestions received during the
comment period, that table has been expanded to include c greater number
of studies where effects have been reported. EPA believes that tnis is a
more'complete representation of the medical evidence since it includes
some less conclusive studies at low levels that cannot be discarded in
weighing the full body of health data. Nonetheless, the table must be
used with caution and in conjunction with qualifying statements made in
the criteria document regarding the technical merit of each study,
particularly the less conclusive studies at lower concentrations.
While this table does not provide an undisputed value for adverse
health effect levels in sensitive individuals, it does indicate that
normal body functions are most likely disrupted at relatively low ozone
concentrations. The studies also indicate that the intensity and
significance of effects increases as the pollutant level increases. The
reported findings leave open the question of increased intensity of
effects in more sensitive persons and the concern that effects reported
in some studies may occur at lower concentrations when ozone is present
in combination with other urban pollutants.
59
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~ r " ~ " " ' -RETORTED -EFFECT -L-EVELS - - - —
compilation of Results Reported in Human Studies Exaroinino Ozone or Oxidant cxoosure
Concentration,
ppre
0.01
0.3C
0.03 -
0.30
0.10
0.10 -
0.15
0.15
0.20
0.20
0.25
0.25
0.25
0.25
0.25
0.28
0.30
0.30
0.37
0.37
0.37
0.37
0.37
Exposure Duration,
hours (for clinical
studies); Averaging
time (for epidemio-
logical studies)
hourly
average
hourly
average
2
probably daily
maximum hourly
average
1
3
2
2
2 and 4
daily maximum
hourly average
0.5 - 1
dally maximum
instantaneous
(2-minute)
average
1
daily maximum
hourly average
2
2
2
2
2
Pollutant Reported
Measured Effect(s)
(0, * ozone,
OJJ * oxidant)
Oj Lung function parameters in about 25« of Japanese
school children tested were significantly corre-
lated with 0, concentrations (over the ranoe of
0.01 - 0.30 ppm) in the 2 hours prior to testing.
DX Although significant correlation was observed be-
tween decreased athletic performance and Ox con-
centrations in the ranpe of 0.03 - 0.30 ppre, the
criteria document states that inspection of the
data reveals no obvious relationship between
performance anc 0.* values below 0.10-C.1E pom.
03 Decreased 0. pressure in arterialized blood,
increased airway resistance observed using non-
standard measurement techniques.
Reference(s)
Ksgewa anc Toyams
(1S75); i-agawc e~. i',.
(1976)
Wayne et al .
(1967;
von Nieding et al.
(1976)
Ox Increased rates of respiratory symptoms and head- Makino and Mizoguchi
ache were reported by Japanese students or days when {197£j
0 concentrations exceeded 0.15 ppm as compared to
days when DX concentrations were less than C.1C ppm.
03 Subjective symptoms of discomfort were observed by
most subjects, ape discernible but not statistical-
ly significant changes in respiratory patterns oc-
curred while performing vigorous exercise.
0, Reduction in visual acuity (niaht vision) ob-
served .
0. Asthmatic patients exposed under intermittent
light exercise conditions showed no statistically
significant changes in respiratory function.
Symptom scores increased slightly during Oj ex-
posures. Small but statistically significant
blooo biochemical changes occurred.
0, Small changes in lung function were observed in 3
subjects performing intermittent light exercise.
0. No lung. function changes of note were observed in
"reactive" subjects (who had histories of cough,
chest discomfort or wheezing associated with air
pollution or allergy) while performing inter-
mittent, light exercise.
0 The average number of asthma patients having
attacks was statistically significantly elevated
on days when Ox levels exceeded 0.25 ppm.
0, Blood samples of exposed subjects had increased
3 rates of sphering of red blood cells
0 Although the reported results are inconclusive,
x EPA's examination of the evidence presented
suggests exacerbation of asthma when o levels
are above 0.28 ppm. *
0, Subjective symptoms of discomfort and statistical-
ly significant changes in pulmonary function were
observed in subjects undergoing vigorous exercise.
0 Increased rates of cough, chest discomfort, and
headache were observed in student nurses on days
when the Ox concentrations exceeded 0.30 ppm.
0, Discomfort symptoms and significant changes in
* lung function were observed in subjects undergoing"
intermittent light exercise.
0, Exposure to 0, and S0? together produced changes
SO, in lung function substantially greater than the
e -stiff) of the separate effects of the individual
pollutants.
0, The observed 0, - S07 interactive effect on lung
* function was considerably smaller than that seen
502 by Hazucha and Bates. The authors concluded that
the earlier study probably more nearly simulated
a smog episode in regions having high oxidant and
sulfur pollution.
OeLucia i Aoams
(1S77)
laoerwerff
(1963)
Linr. et al.
(1S78;
Hazucha (1973)
Hackney et al.
(1975)
Schoettlin and
Landau (1961)
Brinkman et al.
(1964)
Kurata et al.
(1976)
DeLucia and Adams
(1977)
Hanrner et al.
(1974)
Hazucha et al. (1973);
Folinsbee et al. (1975);
Silverman et ai. (1976)
Hazucha and Bates (1975)
Bell et al. (1977)
50
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SENSITIVE POPULATION
The legislative history of the Clean Air Act indicates that, in
setting primary ambient air quality standards, EPA is to direct its
efforts at groups of "particularly sensitive citizens such as bronchial
asthmatics and emphysematics who in the norma.1 course of daily activity
are exposed to the ambient environment." (U.S. Senate Serial No. 93-18,
93d Cong. 2d Sess. p. 410).
Clinical and epidemiological studies have shown that persons
with chronic obstructive airway disease, pa'rticularly asthmatics,
appear most sensitive to changes in ozone concentrations. This
sensitivity results from the fact that their airways are hyper-reactive
to irritants such as ozone. These people are, thus, judged to be
the principal sensitive group of concern in setting the standard.
Studies have also established -hat exercise effectively in-
creases the ozone dose delivered to the target tissues in the
respiratory tract. Thus, persons engaging in exercise are parti-
cularly vulnerable to the- acutely irritating effects of ozone. The
response of these groups to such changes in concentrations has not,
however, been systematically studied.
NATURE AND SEVERITY OF EFFECTS
Impaired Pulmonary Function and Clinical Symptoms — Ozone is a
pulmonary irritant that affects the mucous lining, other lung tissue,
and respiratory function.. Changes in lung function appear as increased
airway resistance and as reductions in vital capacity, expiratory flow
rates, and diffusion capacity. These effects are greater in exercising
individuals and individuals with hyper-reactive airways (i.e., indi-
viduals with a history of developing symptoms during light activity in
61
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smog or history of asthma). Changes in lung function are accompanied
by clinical symptoms such as coughing, chest tightness, and lower
chest soreness.
Because the human respiratory system is endowed with a large reserve,
even airway-resistance increases of 50 to 100 percent will not ordinarily
be perceived in normal individuals. As stated in the criteria document,
however, two considerations suggest that oxidant-associated changes in
lung function may signal impairment of public health. First, in people
with underlying respiratory illness such as asthma, chronic bronchitis,
and emphysema, even small decrements in lung function often interfere
with normal activity. Second, at experimental ozone concentrations as
low as 0.30 ppm, decrements in lung function have usually been accom-
panied by physical discomfort, as manifested in symptoms such as sore
throat, chest pain, cough, and headache. At times this discomfort has
been great enough to prevent the completion of experimental protocols,
particularly when subjects have been exercising vigorously. It appears
quite likely that the pulmonary irritant properties of ozone (and per-
haps other oxidants) underlie both the discomfort and the decrements in
function. Thus, at least when associated with ozone exposure, changes
in lung function often represent a level of discomfort which, even among
healthy people, may restrict normal activity or impair the performance
of tasks.
Decreased Resistance to Infection — This effect is represented by
an increased rate of mortality in laboratory animals subjected
to both a bacterial challenge and exposures to ozone. According
to some studies, the effect may be enhanced by the addition of such
62
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stresses as exercise or the addition of other pollutants in combination
with the ozone dose. Despite the uncertainties involved in predicting
human effects from animal studies, medical experts agree that decreased
resistance to infection probably does occur in man. The Durham study
(1974) reporting increased illness in college students following periods
of elevated pollution levels (with peak oxidant being the pollution
variable most strongly associated with illness) reinforces this hypothesis
and adds to EPA's concern about the relationship of ozone to the occurrence
t
of such an effect in man.
Aggravation of Chronic Respiratory Disease — Although the relation-
ship between ambient oxidant or ozone levels and chronic pulmonary
disease has not been fully assessed, available evidence suggests
that the incidence and severity of asthma attacks increase when
short-term total oxidant concentrations exceed 0.25 to 0.28 ppm.
Also, several investigators have reported a relationship between short-
term oxidant exposure and aggravation of other chronic obstructive lung
diseases. However, their reports are inconclusive since short-term
fluctuations in cigarette smoking habits were not considered in their
data analyses.
Air pollution is one of. the many stresses that can precipitate an
asthma attack or worsen the disease -state in persons with chronic
cardiopulmonary disease. Other factors that can precipitate attacks
include respiratory infections, passage of cold fronts, seasonal
pollens, extreme heat or cold, and emotional disturbances.
Eye Irn'tation — Eye irritation is associated with selected chemical
species (such as PAN) in the photochemical oxidant mix and with other
63
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organic vapors. While there is no evidence that eye irritation is pro-
duced by ozone, an ozone standard will serve to limit this effect
because control measures that reduce ozone will also reduce the eye-
irritating components in the total oxidant mix.
Biochemical Effects — Experimental exposures of human subjects to
ozone have produced changes in blood faiochemistryj such as increased
fragility of red blood cells and altered enzyme activities in the
serum. The significance of these ozone-mediated changes is not
yet known, but the criteria document states that changes of the
magnitude observed in human experimental exposures have not yet been
linked to any clinical diseases.
Carcinogenic, Mutagenic and Related Effects — Studies have been
conducted in an attempt to relate ozone to carcinogenic, mutagenic,
and related effects. Available evidence in these areas is not
particularly helpful in setting ambient ozone standards because most
of the studies have not yet been replicated (in spite of some attempts
to do so), and because some effects observed in lower life forms are
of questionable significance for man. The criteria document states that
the significance of effects such as chromosomal aberations has not
been established and that some studies have produced conflicting
results. In addition, EPA's Science Advisory Board recommended that
certain studies on the mutagenic effects of ozone, which have not
been replicated, not be emphasized in the criteria document.
64
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PRIMARY STANDARD
As illustrated in the table of reported effect levels, there is no
clear threshold air concentration of ozone indicated by the data as the
onset of adverse health effects. It is EPA's best judgment that
physiological responses probably occur in extremely sensitive persons at
very low levels. At what point these responses become an adverse health
effect and at what level they most likely occur in sensitive persons
must necessarily be an informed judgment. As stated in the proposal,
this judgment is based on (1) the Agency's understanding of the medical
evidence presented in the criteria document and in the table of reported
effect levels, (2) the findings of the advisory panel on health effects,
and (3) the judgment of medical experts as to the adverse effect level
in sensitive persons. The health experts who were consulted were asked
to focus not only on the most sensitive population group, but also on
a very sensitive portion of that group (specifically, those persons
who are more sensitive than 99 percent of the sensitive group, but less
sensitive than 1 percent of that group). The lowest adverse health effect
level estimate cited by the health panel and the median values developed
through the expert interview process are reasonably consistent, ranging
from 0.15 to 0.18 ppm. (See table below.) On the basis of the effect
levels cited in the criteria document, it is EPA's judgment that the
most probable level for adverse health effects in sensitive persons,
as well as in healthier (less sensitive.) persons who are exercising
vigorously, falls in the range of 0.15 - 0.25 ppm. While the evidence
is more convincing and the effects more pronounced at the higher end
of this range, the data shows effects of concern at the lower concentration.
65
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PROBABLE EFFECT LEVEL ESTIMATES
(Estimates for Sensitive Population Segments)
Aggravation of Asthma,
Emphysema, and Chronic
Bronchitis
Reduced Resistance to
Bacterial Infection -
(Animal Studies)
Reduction in
Pulmonary Function
Chest Discomfort -.
Irritation of t:.;
Respiratory Tract
Health panel judgment
of effect level
0.15 - 0.25 ppffi
Not available
0.15 - 0.25 ppm
OM5 - 0.25 ppm
Probable or median
effect level as esti-
mated front interviews
with health experts
(Range of estimates
given in parentheses)
0.17 ppm
(0.14 - 0.25 ppro)
0.1S ppm
(0.07 0.38 ppm)
0.15 ppm
(0.07 - 0.18 ppra)
0.15 ppm
(0.11 - 0.1E ppm)
In order to set an ambient air quality standard that protects the
public health with an adequate margin of safety, EPA must deal with the
uncertainty inherent in the judgment that the probable level for adverse
effects in sensitive persons is in the range of 0.15 - 0.25 ppm.
Because the nature and intensity of effects vary from pollu-
tant to pollutant and because medical research produces new and
different findings as science progresses, EPA does not believe that
a fixed acceptable margin of safety can be established for all
pollutants or for a single pollutant over time. Each decision on
a standard level must be made on the best evidence available at the
time and should include consideration of such factors as:
66
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1. Concern for more sensitive individuals— Sensitive persons may
respond to ozone differently from the less sensitive persons
who generally are tested in clinical studies. Individuals with
underlying respiratory illness such as asthma, chronic bronchitis,
and emphysema are particularly sensitive to even modest impairments
of pulmonary function resulting from ozone exposure. For ethical
reasons, clinical investigators normally do not expose persons
with these illnesses and thus caution that such studies may not
represent the full range of sensitivity to ozone. Also of concern
are individuals engaged in vigorous outdoor activity (construction
•r
work, tennis, jogging, etc.) where the effects of ozone are enhanced
or may occur at lower ambient concentrations.
2. Pollutant interactions — There is real concern that effects
reported in some ozone studies may occur at lower concentrations
and may be enhanced when ozone is present in combination with other
urban pollutants. Laboratory studies of a single pollutant (e.g.,
ozone in clean, filtered air), while important in elucidating
physiological effects peculiar to that pollutant, cannot be viewed
as providing definitive evidence of the minimum level at which
these effects occur when that pollutant is present as only a part
of the total insult delivered to an individual in the urban environ-
ment. Also of concern are other toxic oxidant species, such as
PAN, that are often present with ozone in the ambient photochemical
pollution mixture and cause other adverse effects such as eye
irritation. Thus, the effects of ozone must be considered in the
context of the total environment of the exposed individual; this
environment includes concentrations of other pollutants consistent
with their maximum allowable levels, high relative humidity,
high ambient temperature, and high levels of physical stress.
67
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3. Long-term deleterious effects of ozone — Unfortunately, there
are few studies that have attempted tc document the long-term
adverse effect of human exposure to repeated peaks of ozone. Some
animal studies do indicate that long-term ozone exposures act as an
inducer of biochemical or morphological changes. Some of these
changes are transient and, on a short-term basis, may have a physio-
logical significance in that they confer a resistance against
further lung injury in an oxidant environment (a similar response
has been observed in human clinical studies). Some animal studies
have indicated, however, that effects from continued exposure can
result in an emphysema-like condition (e.g., P'an et al., 1972).
4. Animal infectivity studies — Although evidence of re-
duced resistance to bacterial infection has not reached the
point where it can be meaningfully used to extrapolate concen-
trations that would similarly affect man, these studies cannot
be dismissed in selecting a standard level that provides an
adequate margin of safety. Despite the present inability to
extrapolate to an effect level in humans, most experts agree that
ozone exposures may well result in decreased resistance to
infection in humans. Further, it is the kind of effect that is
serious enough in its implications to raise a need for caution.
Thus, it is prudent public health practice to set a standard
more stringent than the probable effect level estimated from
human studies, in order to account in some measure for these
unquantified, but possibly serious, effects.
5. Inconclusive studies reporting effects at low levels —
A similar caution is suggested by both the Makino and Mizoguchi
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epidemic! ogical study and the von Nieding clinical study reporting
effects at levels around 0.10 ppm.
6. Uncertainties arising from air quality variations due
to meteorology -- Since EPA's revised standard is statistically
based and permits an expected number of allowable violations per
year, there is concern about the magnitude of these excursions and
how they might impact an exposed sensitive individual.
7. Effects of calibration procedure change — Another factor that
has been considered in establishing a,margin of safety is the
variability that exists in the measurement and calibration techniques
used in health studies and how these measurements may differ from
those made with the ultraviolet (UV) reference calibration procedure
being promulgated elsewhere in this issue of the Federal Register.
Most of the relevant clinical studies utilized monitoring instruments
calibrated with the current (NBKI colorimetric) reference calibration
procedure or modifications thereof. EPA's best judgment is that
the reference NBKI procedure shows a positive bias of about 10
percent with respect to the UV procedure when these techniques are
compared under carefully controlled experimental conditions.
However, due to the variability that can reasonably be expected in
any clinical exposure monitoring measurements, as well as the
uncertainty introduced by the modified calibration procedures, EPA
cannot determine a precise quantitative factor to adjust the findings
of these health studies. In the case of the study done by DeLucia
and Adams (1977), the authors have indicated to EPA that the reported
ozone values might be high with respect to the UV calibration
procedure. While the exact magnitude of any required adjustment in
the reported ozone values is uncertain, adjusted values could range
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from 0.12 to 0.15 ppm for the 0.15 ppm value reported by the
authors, and from 0.23 to 0.30 ppm for the 0.30 ppm concentration.
EPA will continue its evaluation of this issue through its program
of clinical exposure studies.
8. Findings from the preliminary risk assessment — The preamble to
the proposed standard described a preliminary risk assessment method
performed to aid EPA in accurately treating the uncertainties associated
with a standard decision. While this method cannot be used at this
time as the sole tool for making that decision, the Agency does believe
that the findings resulting from this initial application of the method
do not permit any relaxation of the standard above 0.12 ppm.
After reviewing the comments received from all segments of the public,
including those from the public health community, EPA remains convinced that
at levels in the range of 0.15 - 0.25 ppm, adverse health effects will almost
certainly be experienced by significant numbers of sensitive persons. Unless
the standard is set somewhat below that level, the Agency would not be ex-
ercising that degree of prudence called for by the "adequate margin of safety"
requirement of the Clean Air Act. The Administrator must exercise the in-
formed scientific judgment that Congress has authorized him to bring to bear
on these difficult problems.
There is no collection of facts or medical evidence that permits
selecting an undisputed value for the standard level. EPA proposed a
standard of 0.10 ppm, taking several factors into account in providing a
margin of safety, as discussed above. Among those were epidemiologica1
studies indicating effects below 0.15 ppm which the criteria document
did not fully endorse, but which EPA thought it unwise to disregard. (See
43 FR 26966.) Also considered were animal studies indicating reduced
resistance to bacterial infection, although extrapolation to human effects
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levels is not possible. (Id.) During the comment periods, EPA received
informed scientific opinion disputing the interpretation and application
of such studies. Based on its current understanding of these studies,
EPA has concluded that they do not dictate as wide a margin of safety
as was established in the proposal. EPA does believe, however, that these
studies do suggest the real possibility of significant human adverse health
effects below 0.15 ppm. Consequently, the Administrator has determined
that a standard of 0.12 ppm is necessary and is sufficiently prudent unless
and until further studies demonstrate reason to doubt that it adequately
protects public health.
WELFARE EFFECTS AND THE SECONDARY STANDARD
The Clean Air Act mandates the setting of a national secondary ambient
air quality standard to protect the public welfare from any known or antici-
pated adverse effects associated with an air pollutant in the ambient air.
Ozone and other photochemical oxidants constitute a form of air pollution
that has been shown to affect vegetation and materials and that may have an
impact on visibility. The economic loss resulting from current oxidant levels
has been estimated to be in the range of several hundred million dollars per
year nationwide. Non-quantifiable losses to the natural environment occur
as well. A staff paper, "Assessment of Welfare Effects and the Secondary
Air Quality Standard for Ozone," was placed in the docket at the time of
proposal. The following paragraphs summarize this report and information
received after its release.
Exposure of vegetation to harmful levels of ozone may result in
leaf injury, decreased growth and yield, or reproductive effects.
Visible leaf injury is the most readily detectable and frequently re-
ported symptom of ozone damage; however, it is not an accurate indicator
of yield or growth reduction.
In the June 22, 1978, Federal Register proposal (43 FR 26968-
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26969), it was stated that several investigators suggested that foliar
injury rates in the range of 5 to 10 percent could produce detectable
reductions in growth or yield, depending on the timing of the injury and
other environmental factors. Since proposal of the standard in June, EPA
has discussed the matter further with several experts in the field of
air pollution damage to vegetation, particularly regarding what level of
leaf injury should be of concern in protecting against significant
reductions in yield or growth in commercially important crops and
indigenous flora. These experts emphasized the uncertainty associated
with correlating yield reduction with foliar injury. Some stated that
detectable yield reductions would not occur until leaf injury reached
values as high as 10 to 20 percent, and others felt that foliar injury
was an inappropriate indicator of yield reduction.
The foliar responses o~ plants to ozone exposures are not linearly
dependent on the dose (product of concentration and exposure duration) sus-
tained by the plant. A given dose applied over a short period of time is
more damaging than if it were applied over a longer period. EPA used a
mathematical model to summarize, for several crops, the experimental results
which depict the variation in foliar response with short-term (0.5-hour to
8-hour) ozone exposures. The notice of proposed rulemaking predicted
(on the basis of the mathematical model) that a secondary ozone air
quality standard set at an hourly average concentration of 0.08 ppm,
expected to be exceeded only once per year, would prevent any important
commercial crop from receiving more than 3 percent leaf injury. On the
basis of this prediction and the aforementioned assumptions regarding
the relationship of foliar injury and yield reduction, EPA proposed to
set the secondary standard level at 0.08 ppm.
As a result of its further consultations with researchers, EPA
decided to reassess the uncertainties associated with the judgments that
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led to the proposed 0.08 ppm 1-hour average secondary standard. These
experts pointed out that there are large uncertainties in the assumptions
relating yield reduction to foliar injury. The mathematical model used
to predict foliar injury was based on chamber studies, not on studies
conducted under field conditions. The experts cautioned that these chamber
studies generally represent experimental conditions in which the most
sensitive varieties of a given species are used and in which moisture and
temperature are optimal for producing injury. In addition, a given short-
term dose of ozone, which can produce 5, 10, or even 20 percent foliar injury
in a given plant, is unlikely to have an impact on yield unless the plant is
exposed during a critical stage in the plant's life cycle.
Consequently, EPA has decided to base its decision on the secondary ozone
air quality standard on the information currently available on growth and
yielo reduction in commercially important crops and indigenous vegetation
exposed to ozone under field conditions. As discussed in a staff
paper that has been placed in the docket (OAQPS 78-8, IV-A-3), "Evaluation
of Alternative Secondary Ozone Air Quality Standards," these data indicate
that growth and yield responses are related to the long-term (growing
season) mean of the daily maximum 6- to 8-hour-average ozone concentrations.
Based on an examination of this information, and the available air
quality data, EPA concludes that there is currently no evidence indicating
that a significant decrease in growth or yield of commercially important
crops or indigenous flora will result from the long-term mean of the
daily maximum 7-hour-average ozone concentrations expected to occur when
the primary standard is attained. Consequently, EPA believes that a
secondary standard more stringent than the primary standard is not necessary
on the basis of ozone-related yield reduction effects in vegetation.
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Materials damage resulting from ozone can be described as an
acceleration of aging processes; for example, rubber cracking, dye
fading, and paint weathering. In contrast to the effects of ozone on
vegetation, these effects are linearly dependent on the total ozone dose
sustained by the material. As a result, the annual average concentration
will determine the rate at which material is damaged. Any nonzero ozone
concentration (including natural background levels) will contribute to the
deterioration of sensitive materials over a sufficient exposure duration.
While peak 1-hour ozone concentrations in urban areas tend to be considerably
higher than in rural areas remote from man-made emission sources, the annual
average concentrations observed in these areas are essentially the same. This
finding is believed to be due to the impact of very low urban-area nighttime
ozone concentrations on the annual average values; nighttime ozone levels
in remote areas are not reduced as much from the daytime levels due to
the absence of scavenging by man-made urban pollutants. As peak ozone
levels in urban areas are reduced through control of man-made pollutants,
scavenging will also be reduced resulting in little if any change in the
annual average. Consequently, no effect-based rationale can be offered
to decide the level of the secondary standard needed to protect materials.
Accordingly, EPA believes that a secondary standard more stringent than
the primary standard is not necessary on the basis of ozone damage to
materials.
The criteria document states that there is a limited amount of data
suggesting an association between ambient ozone and visibility degradation,
particularly in the Los Angeles area. On the basis of EPA's evaluation
to date of the information presented in the criteria document, however,
EPA is unable to conclude at this time that a secondary ozone standard
more stringent than the primary standard is necessary to prevent
visibility deterioration. The relationship between visibility and
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ambient ozone will be considered further in the development of sub-
sequent PSD programs designed to protect against significant deteriora-
tion of air quality.
On the basis of these conclusions with respect to ozone damage to
vegetation and materials and the association of ozone with visibility
reduction in some areas, EPA is revising the secondary ozone air quality
standard level to 0.12 ppm.
OTHER ASPECTS OF THE STANDARD
On the basis of EPA's evaluation of evidence submitted and
comments received during the public review process, no major changes
will be made in the following aspects of the proposed standard:
(1) averaging time: 1 hour, (2) chemical species: ozone, (3) form:
statistical, and (4) a separate standard for PAN is not being
promulgated. As discussed below, changes will be made in (1) the
set of hourly averages from which the number of exceedances of the
standard level is counted, ana (2) the exclusion criteria for missing
data.
Daily Maximum Hourly Average Interpretation of the Standard
The maximum ozone concentrations which will occur in any
given time period will vary from one period to the next, even
if precursor emissions remain constant. These variations are mainly
due to the random nature of meteorological factors which affect the
formation and dispersion of ozone in the atmosphere. The present
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deterministic form of the standard, which permits only a single
hourly exceedance of the standard level in any year, inadequately deals
with this situation. The risk to public health contributed to by ozone
can be managed better if the ozone standard reflects the fact that
maximum ozone concentrations are probabilistic in nature. Consequently,
EPA is changing the standard to a statistics! form that allows one
expected exceedance per year.
The proposed standard would have allowed one expected hourly
exceedance per year. EPA is further modifying the standard so that the
one expected exceedance will be given a daily interpretation; that is, a
calendar day will exceed the standard level if the maximum hourly
average concentration for the day exceeds the level of the standard.
This modification means that a day with two hourly values over the
standard level counts as one exceedance of the standard level rather
than two; similarly for days with more than two hourly values over the
standard level. As was indicated in the proposal notice, the daily
interpretation has some advantages and it is evident from the comments
received that there is considerable support for the use of this in-
terpretation.
It should be understood that the change to a daily interpre-
tation is not predicated on a reinterpretation of health data. In
making this change, EPA is not concluding that 3 hours of exposure
above a given level, for example, are no worse than 1 hour of
exposure above the same level as long as the 3 hours of exposure
occur during the same day. The impact of ozone is related to the
76
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total dose delivered to the respiratory tract, and obviously for a
given concentration a 3-hour exposure gives a greater dose than
a 1-hour exposure. In the case of ozone, the pattern of hourly
levels is mainly determined by meteorological fluctuations, and
EPA's decision to promulgate a daily standard does not affect
meteorological fluctuations. Ozone precursor emissions are not
easily manipulated on a short-term basis, so there is little
likelihood that emission sources could readily alter emission
patterns to take advantage of the daily interpretation.
The change to a daily interpretation does make the standard
slightly less stringent, and hence there is a small increase in
the risk to health. In general, the reduction in emissions of
organic compounds needed to meet the standard under the daily
interpretation will be smaller. As discussed in a report placed in
the docket (OAQPS 78-8, IV-A-4), the long-term increase in health
risk at an average geographical location is estimated to be
equivalent to the increase that would result from raising the
level of the standard to 0.123 ppm and keeping the hourly inter-
pretation of the number of exceedances.
Exclusion Criteria for Missing Data
EPA is additionally modifying the standard with respect to the
treatment of missing data. The proposed standard permitted
certain missing values to be excluded from the estimated exceedances
calculation if either of two exclusion criteria were satisfied.
The first criterion recognized the impact of short-term
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meteorological influences by allowing a missing value to be
excluded if the adjacent values were below an arbitrary limit (75
percent of the standard level). This criterion should be relatively
easy to incorporate into data-handling schemes and has been
retained, although it now applies to daily maximum hourly average
values. The second criterion dealt with comparisons with data
from the previous 3 years. The purpose of this second criterion
was to accommodate situations for which ozone data for a particular
season are not available but for which known seasonal patterns of
ozone and related meteorological factors make it unlikely that the
level of the standard would have been exceeded.
This second criterion would be more difficult to implement
because it necessitates the cross-referencing of earlier historical
date. For newly established monitors, the historical data needed
to invoke this exclusion would not be available. Thus, this second
criterion in the proposal is difficult to implement and could be
potentially burdensome in geographic areas where the climate makes
high ozone values 'during certain seasons very unlikely. It is also
possible to accomplish the intended purpose of this exclusion through
provisions of the recently proposed 40 CFR Part 58 (see 43 FR 34892)
that would grant waivers of the ozone monitoring requirements for
certain times of the year at the discretion of the appropriate
Regional Administrator. Therefore, the second exclusion criterion
has been eliminated, and the computation formulas for estimating
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the expected number of exceedances have been modified to reflect
the number of required monitoring days for the year.
Definition of When the Standard is Attained -- EPA is adding
Appendix H to 40 CFR Part 50 to explain when the standard is or is
not being attained. Certain modifications to the proposal were
necessary to accommodate the daily interpretation and the previously
mentioned changes in the treatment of missing data. In order to
implement the change from an hourly to a daily interpretation, it- is
necessary to define what is meant by a valid day of ozone data. Such
a definition must ensure that a sufficient number of hours of the
day have been monitored and that the hourly values in question re-
flect the time of day when high ozone values are likely to occur.
At the same time, this criterion should be relatively easy to imple-
ment, it should allow time for routine maintenance, and yet it
should protect against high values being ignored merely because not
enough hours of the day were measured. Accordingly, a daily maximum
hourly average concentration will be considered valid if 75 percent
of the hourly values from 9:01 a.m. to 9:00 p.m. (LSI) were recorded
or if an hourly value above the level of the standard was measured.
This validity criterion is intended as a minimum requirement and not
as a recommended schedule.
The computation formula for calculating the estimated number
of exceedances per year has been modified to correspond to the daily
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interpretation of the standard. Allowance has also been made for
any situation in which the Regional Administrator has granted a
waiver of the ozone monitoring requirements under the provisions
of the recently proposed 40 CFR Part 58 and, therefore, the total
number of required monitoring days is less than a full year. The
use of the exclusion criterion may result in an underestimate of the
probability of an exceedance in some situations but is relatively
easy to implement and should suffice to account for the effect of
missing data. It should be noted that the formula given in Appendix H
is necessary to show attainment. Accounting for missing data can
never, however, decrease the number of exceedances, and thus it
is possible to establish non-attainment without the use of this
equation.
These modifications to Appendix H are intended to simplify
somewhat the calculations and to allow for more flexible monitoring
schedules. The comments received on Appendix H were varied. A few
commenters thought it was too complicated while others suggested
even more complex techniques. Most comments were, however, supportive
of (or, at least, neutral toward) the proposed approach. One
suggestion was to employ a minimum percent completeness requirement,
rather than estimating the number of exceedances. The problem with
that approach, however, is that it remains unclear as to what should
be done with data sets that fail to meet such a completeness require-
ment.
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Some comments discussed the use of 3 years of data. As
indicated in the proposal, the choice of a 3-year period
represents a compromise between added stability and reasonably
current status assessments. Even under the present deterministic
form of the standard, attainment designations (e.g., 40 CFR Part
81, Section 107) have been based on more than 1 year. Furthermore,
although 3 years are used in estimating the expected number of ex-
ceedances under the statistical form of the standard being promulgated,
it is still possible to establish non-attainment after one year if,
for example, four or more exceedances were reported. Therefore,
an upper bound to exceedances during a single year still applies
under the new form.
ECONOMIC, ENERGY, AND .ENVIRONMENTAL IMPACTS
As has been noted, the Clean Air Act specifically requires
that National Ambient Air Quality Standards be based on scientific
criteria relating to the level that should be attained to protect
public health and welfare adequately. EPA interprets the Act as
excluding any consideration of the cost of achieving such a standard
in determining the level of the primary standard. However, in
compliance with the requirements of Executive Orders 11821 and
11949 and OMB Circular A-107 and with the provisions of the recently
issued Executive Order 12044 for rulemaking proceedings that are
currently pending, EPA has prepared an analysis of economic impacts
associated with efforts to attain this standard.
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Ozone air pollution is a pervasive problem throughout the
country. Most urban and many rural areas exceed the existing
standard. Even with the less stringent standard, most of the major
urban areas are not expected to attain the standard in the near
term. Control of the organic precursor materials that generate
photochemical oxidants is a major effort in this country and a multi-
billion dollar program. The existing control program includes
measures to reduce organic emissions from automobile and truck
exhausts, production of chemical and petroleum products, the dry-
cleaning industry, most painting operations (including the automotive
industry), and other industrial operations.
Because the attainment problem in most urban areas is so severe,
the relaxation of the standard is not expected to change the level of
control requirements in the near term. The move to a 0.12 ppm standard
will, however, eliminate the theoretical need for major control programs
in many rural and wilderness areas that currently exceed the present
standard.
With the relaxation of the standard, EPA's economic impact
analysis indicates that most urban areas are expected to achieve the
standard by 1987. Even with aggressive control programs, however,
it will be very difficult for some urban areas to achieve the
standard within the next 10 years.
In addition, a document has been prepared assessing the impacts
that efforts to attain the standard may have on the nation's energy
requirements. This document examines the extent to which ozone
precursors will be controlled by recovery of organic materials
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that would otherwise be emitted to the atmosphere, with resultant
energy savings. Furthermore, an additional energy conservation should
result in those areas that utilize transportation control measures
to reduce precursor emissions by reducing the total number of vehicle-
miles travelled. Because of such energy savings, EPA believes that
ozone precursor control measures may well lessen the nation's energy
requirements.
Finally, environmental impacts associated with control of
t
oxidant precursors have been examined in a document available in
docket number OAQPS 78-8. This study indicates that modifying the
current standard should have minimal environmental impacts.
Copies of these analyses of the economic, energy, and environ-
mental impacts involved in the revised ozone standard are available
from Joseph Padgett at the address given earlier.
REVISIONS TO PART 50 REGULATIONS
In addition to the revised standard, this action necessitates
two other revisions to 40 CFR Part 50 as follows:
1. In Appendix D, as well as in the table of sections for
Part 50, the title is revised to read as follows: "Appendix
D - Measurement Principle and Calibration Procedure for the
Measurement of Ozone in the Atmosphere." The substitution of
"ozone" for "photochemical oxidants corrected for interferences
due to nitrogen oxides and sulfur dioxide" is a result of the
change in the chemical species designation of the standard.
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2. Appendix H, "Interpretation of the National Ambient
Air Quality Standard for Ozone", is added because additional
guidance is necessary to understand the statistical nature of
the revised standard.
REVISIONS TO PART 51 REGULATIONS
Elsewhere in this issue of the Federal Register, three
revisions to 40 CFR Part 51 are promulgated concurrently with
the revision to the photochemical oxidant standard. They are as
follows:
1. The term "photochemical oxidants" is changed to "ozone"
throughout Part 51.
2. Section 51.14, "Control strategy: Carbon monoxide, hydro-
carbons, photochemical oxidants, and nitrogen dioxide", is
revised to (a) allow the states to use any of four analytical
techniques in the place of Appendix J to calculate the percent
hydrocarbon reduction needed to attain the ozone standard, and
(b) require that the states consider background ozone concentrations
and ozone transport.
3. Appendix 0 is deleted from Part 51.
FEDERAL REFERENCE METHOD
The measurement principle and calibration procedure applicable
to reference methods for measuring ambient ozone concentrations to
determine compliance with the standard are not affected by this
rulemaking. Elsewhere in this issue of the Federal Register,
however, EPA is replacing (superseding) the current calibration
procedure with a new, superior calibration procedure based on ultra-
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violet photometry. The measurement principle and the current
calibration procedure are set forth in Appendix D of 40 CFR Part 50
(as amended in the February 18, 1975, issue of the Federal Register,
40 FR 7042). Reference methods — as well as equivalent methods —
for monitoring ozone are designated in accordance with 40 CFR Part 53
(40 FR 7044). A list of all methods designated by EPA as reference
or equivalent methods for measuring ozone is available from any EPA
regional office, or from EPA, Department E (MD*-76), Research
Triangle Park, NC 27711.
Date Administrator
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References
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Hyg. Assoc. J. 38: 696-706, 1977.
Brinkman, R., H. B. Lamberts, and T. S. Veninga. "Radio-
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DeLucia, A. J., and W. C. Adams. "Effects of 03 inhalation
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"A Legislative History of the Clean Air Amendments of 1970."
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EPA amends Part 50 of Chapter I, Title 40, of the Code of
Federal Regulations as follows:
1. Section 50.9 is revised to read as follows:
§50.9 National primary and secondary ambient air quality
standards for ozone.
(a) The level of the national primary and secondary ambient
air quality standards for ozone measured by a reference method
based on Appendix D to this part and designated in accordance
with Pan 53 of this chapter, or by an equivalent method
designated in accordance with Part 53 of this chapter, is 0.12
part per mi 11 ion (235 ug/m }. The standard is attained when the
expected number of days per calendar year with maximum hourly
average concentrations above 0.12 part per million (235 ug/m3)
is equal to or less than 1, as determined by Appendix H.
2. In Appendix D, as well as in the table of sections for
Part 50, the title is revised to read as follows: Appendix D -
Measurement Principle and Calibration Procedure for the Measurement
of Ozone in the Atmosphere.
3. Appendix H is added as follows:
APPENDIX H - INTERPRETATION OF THE NATIONAL AMBIENT AIR
QUALITY STANDARDS FOR OZONE
1. General
This appendix explains how to determine when the expected number
of days per calendar year with maximum hourly average concentrations
above 0.12 ppm (235 yg/nr) is equal to or less than 1. An expanded
90
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discussion of these procedures and associated examples are con-
tained in the "Guideline for Interpretation of Ozone Air Quality
Standards." For purposes of clarity in the following discussion,
it is convenient to use the term "exceedance" to describe a daily
maximum hourly average ozone measurement that is greater than the
level of the standard. Therefore, the phrase "expected number of
days with maximum hourly average ozone concentrations above the level
of the standard" may be simply stated as the "expected number of
exceedances."
The basic principle in making this determination is relatively
straightforward. Most of the complications that arise in determining
the expected number of annual exceedances relate to accounting for
incomplete sampling. In general, the average number of exceedances
per calendar year must be less than or equal to 1. In its simplest
form, the number of exceedances at a monitoring site would be recorded
for each calendar year and then averaged over the past 3 calendar
years to determine if this average is less than or equal to 1.
2. Interpretation of Expected Exceedances
The ozone standard states that the expected number of exceedances
per year must be less than or equal to 1. The statistical term
"expected number" is basically an arithmetic average. The following
example explains what it would mean for an area to be in compliance
with this type of standard. Suppose a monitoring station records a
valid daily maximum hourly average ozone value for every day of the
year during the past 3 years. At the end of each year, the number of
91
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days with maximum hourly concentrations above 0.12 ppm is
determined and this number is averaged with the results of
previous years. As long as this average remains "less than or
equal to 1," the area is in compliance.
3. Estimating the Number of Exceedances for a Year
In general, a valid daily maximum hourly average value may not
be available for each day of the year, and it will be necessary to
account for these missing values when estimating the number of ex-
ceedances for a particular calendar year. The purpose of these
computations is to determine if the expected number of exceedances per
year is less than or equal to 1. Thus, if a site has two or more
observed exceedances each year, the standard is not met and it is not
necessary to use the procedures of this section to account for in-
complete sampling.
The term "missing value" is used here in the general sense to
describe all days that do not have an associated ozone measurement.
In some cases, a measurement might actually have been missed but
in other cases no measurement may have been scheduled for that day.
A daily maximum ozone value is defined to be the highest hourly
ozone value recorded, for the day. This daily maximum value is
considered to be valid if 75 percent of the hours from 9:01 a.m. to
9:00 p.m. (1ST) were measured or if the highest hour is greater than
the level of the standard.
92
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In some areas, the seasonal pattern of ozone is so pronounced
that entire months need not be sampled because it is extremely
unlikely that the standard would be exceeded. Any such waiver of
the ozone monitoring requirement would be handled under provisions
of 40 CFR Part 58. Some allowance should also be made for days for
which valid daily maximum hourly values were not obtained but which
would quite likely have been below the standard. Such an allowance
introduces a complication in that it becomes necessary to define under
t
what conditions e missing value may be assumed to have been less than
the level of the standard. The following criterion may be used for
ozone:
A missing daily maximum ozone value may be assumed to be less
than the level of the standard if the valid daily maxima on both
the preceding day and the following day do not exceed 75 percent
of the level of the standard.
Let z denote the number of missing daily maximum values that
may be assumed to be less than the standard. Then the following
formula shall be used to estimate the expected number of exceedances
for the year:
e * v + [(v/n) * (N-n-z)] 0)
(indicates multiplication)
Where
e - the estimated number of exceedances for the year,
N = the number of required monitoring days in the year.
93
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n - the number of valid daily maxima,
v the number of daily values above the level of the
standard, and
2 - the number of days assumed to be less than the standard
level.
This estimated number of exceedances shall be rounded to
one decimal place (fractional parts equal to 0.05 round up).
It should be noted that N will be the total number of days
in the year unless the appropriate Regional Administrator has granted
a waiver under the provisions of 4-0 CFR Part 58.
The above equation may be interpreted intuitively in the follow-
ing manner. The estimated number of exceedances is equal to the
observed number of exceedances (v) plus an increment that accounts
for incomplete sampling. There were- (N-n) missing values, for the
year but a certain number of these, namely z, were assumed to be less
than the standard. Therefore, (N-n-z) missing values are considered
to include possible exceedances-. The fraction of measured values that
are above the level of the standard is v/n. It is assumed that this
same fraction applies to the (N-n-z) missing values and that (v/n)*
(N-n-z) of these values would also, have exceeded the level of the
standard.
AUTHORITY: Sections 109 and 301 of the Clean- Air Act, as amended
(42. U.S.C. 7409, 7601).
94
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Title 40 — Protection of Environment
CHAPTER ! — ENVIRONMENTAL PROTECTION AGENC
SUBCHAPTER C — AIR PROGRAMS
PART 50 — NATIONAL PRIMARY AND SECONDARY
AMBIENT AIR QUALITY STANDARDS
Calibration of Ozone Reference Methods
AGENCY: U.S. Environmental Protection Agency
ACTION: Final rule.
SUMMARY: Appendix D to 40 CFR Part 50 prescribes a measurement
principle upon which reference methods for the measurement of ozone*
in the atmosphere must be based. This appendix also specifies a
procedure to be used for calibrating those ozone reference methods.
EPA has evidence that another calibration procedure for ozone refer-
ence methods is significantly more accurate and less variable than
the procedure currently specified in Appendix D. Accordingly, EPA
is amending 40 CFR Part 50, Appendix D, to replace (supersede) the
current calibration procedure with a superior calibration procedure
based on ultraviolet photometry.
*The term "ozone" is used herein to be consistent with another EPA
action in this issue of the FEDERAL REGISTER substituting "ozone"
for "photochemical oxidants corrected for interferences due to
nitrogen oxides and sulfur dioxide," which was formerly used in
Part 50.
1
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EFFECTIVE DATE: "his action is effective immediately upon publi-
ca:-,cn c-eca^se me revise, stan<_ar_ to wnich -it ar:lies is immedi-
ately effective.
FOR FURTHER INFORMATION CONTACT: Mr. Larry J. Purdue,
Telephone 919-541-2665 (FTS: 629-2665).
ADDRESS: Department E (MD-77)
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
SUPPLEMENTARY INFORMATION:
Background
Part 50 of Title 40, Chapter I of the Code of Federal Regula-
tions specifies the National Ambient Air Quality Standards for
several air pollutants including ozone. Appendixes to Part 50
provide information concerning the reference methods which are
used to measure those pollutants. In particular, Appendix D to
Part 50 describes a measurement principle -jpon which ozone refer-
ence methods must be based, and specifies a calibration procedure
to De used for calibrating such methods. Previously, the calibra-
tion procedure specified by Appendix D was based on assay of ozone
with }% neutral buffered potassium iodide (NBKI) and was known as
the "NBKI procedure."
On June 22, 1978, EPA indicated its conclusion that another
calibration procedure was clearly superior to the NBKI procedure,
and accordingly EPA proposed an amendment to Appendix D to replace
2
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the NBKI procedure with the new procedure, based on ultraviolet (UV)
pnotometry (43 FR 26971-26984). The rationale for the proposed
amendment was discussed in the preamble to that proposal. Interested
persons and organizations were afforded an opportunity to comment on
all aspects of the proposed changes. The amendment, revised slightly
after consideration of the public comments, is being proniulgated today
in conjunction with changes in the ambient air quality standards for
photocnemical oxidants (ozone) appearing elsewhere in this issue of
the FEDERAL REGISTER.
Nature of Changes
The amendment makes three salient changes to the previous
requirements for calibration of ozone reference methods. These
are as follows:
(1) The NBKI calibration procedure is superseded by a pro-
cedure based on UV photometry for the calibration of reference
methods for ozone. Since no National Bureau of Standards (NBS)
Standard Reference Material is available for ozone, ozone standard
concentrations established via the UV procedure are tantamount to
primary ozone standards, and the UV procedure itself is thus
referred to as a "UV standard" for ozone.
(2) Independent use of a manual KI procedure known as the
"BAKI procedure" in lieu of the UV procedure is allowed for 18
months after the effective date of the amendment, with the recom-
mendation that the BAKI technique be related to a UV standard
whenever possible.
3
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(3) The use of alternative procedures as transfer standards
"s specifically allowed if they meet certain trans-er standard
performance guidelines set forth by EPA. A transfer standard is
any device or procedure which can be referenced to a UV ozone
standard and then used at another location to reproduce ozone
standards. A practical transfer standard offers some important
acvar;tages--such as lower cost, ruggedness, easier operation, or
convenience—over direct use of the UV procedure.
New UV Calibration Procedure
The new UV calibration procedure is quite simple. After
generating a stable, ozone concentration with an ozone generator,
the operator assays it by passing all 'or a portion of the gas flow
through the cell of a UV photometer. The photometer readings are
then used in a formula to calculate the ozone concentration, which
as noted earlier, is effectively a primary ozone standard. Most
commercially available photometers do the photometric calculations
automatically, and some may also make temperature and pressure
corrections automatically. The primary burden on the operator is
to insure (1) that the photometer is operating correctly, (2) that
the apparatus is set up properly and is clean and leak-free, and
(3) that the calculations are complete and accurate. While none
of these is particularly difficult, EPA has prepared a Technical
Assistance Document which explains these tasks and provides other
•detailed information about the procedure. This document, which is
4
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still in draft form to allow further incorporation of user's
comments, is available from the address soec'-iec =- -ne 3ec-"->^c
of this preamble.
The photometer is obviously of critical importance to the
procedure and must have a precision within 0.005 ppm or 3% of the
concentration, whichever is greater Hhile a calibration photom-
eter can be assembled from laboratory components, E"A recommends
the purchase of a commercial photometer which is either designed
specifically for this calibration procedure, or which can be readily
adapted to it. EPA is presently aware of 2 such commercial pho-
tometers (available from Dasibi Environmental Corp., Glendale,
California, and Science Applications, Inc., La Jolla, California)
and expects others will become available in the future.
UV photometers of the type used in ambient ozone analyzers
are likely to be suitable as calibration photometers. Conversion
of an ambient UV analyzer to a calibration photometer is covered
in the Technical Assistance Document mentioned above. However, it
is important to differentiate between the use of a UV photometer as
an ambient analyzer and its use as a calibration photometer. This
distinction is predicated more on operational differences than on
any specific physical differences. The new calibration procedure
requires that a photometer used for calibration must be dedicated
exclusively to such use, must be maintained under meticulous con-
ditions, and must be used only with clean, calibration gases. UV
analyzers used for ambient monitoring should always be calibrated
5
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with an independent calibration photometer or a certified transfer
standard. ,- :JV analyzer should not be cons leered to be "self-
calibrated" even though it contains a UV photometer which meets the
specifications of the UV calibration procedure.
New BAKI Calibration Procedure
The new BAKI calibration procedure is very similar to the pre-
viously specified NBKI procedure. Relatively Tiir.or modifications
provide somewhat less variability than the NPKI procedure. Agencies
which are familiar with the .NBKI procedure should have no difficulty
Switching to the BAKI procedure. Independent use of the BAKI pro-
cedure is allowed only for direct calibration of ozone analyzers
(not transfer standards) on a temporary basis during the 18-month
transition period to permit agencies to adopt the new, UV calibra-
tion procedure. Nevertheless, the BAKI orocedure has more varia-
bility than the UV procedure. Therefore, EPA would urge agencies
to adopt the UV procedure as soon as practical. And, when possible,
the BAKI procedure should be related to the UV procedure to imorove
the overall accuracy.
Following the 13-month period, the 3AKI procedure will not
be authorized for independent use, but can be used as a transfer
standard. As such, it must be related to the UV procedure, and its
variability and accuracy must be monitored and controlled. Thus,
agencies which find the BAKI procedure advantageous could continue
to use this orocedure as a transfer standard.
-------
Transfer Standards
EDA Is specifically allowing transfer standards *or cal •!;"=•.• rc
ozone analyzers, and has noted a number of advantages which can be
realized by their use. Transfer standards for ozone can include
procedural techniques such as BAKI and gas phase titration, as well
as devices such as ozone analyzers and stable ozone generators.
EPA recommends that agencies consider tne use of transfer stancarcs
where advantageous. But transfer standards must meet certain per-
formance specifications, and their performance must be monitored.
EPA has prepared a Technical Assistance Document on "Transfer
Standards for Calibration of Ambient Air Monitoring Analyzers rcr
Ozone," which gives the required performance specifications and
general guidance on the certification and use of any type of trans-
fer standard for ozone. This document is also still in draft form
to allow incorporation of further user's comments, and a copy of it
may be obtained from the address given at the beginning of this
preamble.
SUMMARY OF COMMENTS RECEIVED
AND CHANGES MADE TO FINAL AMENDMENT
Comments relative to the proposed amendment (43 FR 26971) were
received from 26 respondents representing EPA Regional Offices,
State and local air pollution control agencies, industrial corpora-
tions, and other organizations. Almost all of the respondents
7
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expressed general support for the proposed change to the UV photo-
netr-'c calibration procedure. Other comments ranged from issues o^
basic policy to technical aspects of the proposed amendment. After
consideration of all the comments, several minor revisions and
improvements were made to the proposed amendment, although the
basic principles and objectives have not been altered. Specific
changes to the proposed amendment are discussed briefly below.
A document containing a summary of all the comments received, the
identity of the respondents, the resulting changes made to the
amendment, and the rationale for adoption or rejection of each
comment is available from the address given at the beginning of
this preamble. This document will also be added to Docket No.
OAQPS 78-8, which is available for public inspection during normal
business hours at the USEPA, Public Information Reference Unit,
Room 2922 (EPA Library), 401 M Street, S.W., Washington, DC 20460.
Several respondents pointed to the relatively high cost of
implementing the change in calibration procedures and suggested that
EPA should either provide the necessary funds to those agencies with
nonattainment and unclassified areas, or make available, in each EPA
Region, a reference photometer that could be used to certify appro-
priate transfer standards. Other comments suggested a similar need
for such reference photometers until such time that commercial
photometers become more generally available. EPA agrees with these
general comments and intends to pursue them, but this requires no
actual change to the amendment as proposed.
8
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Many of the comments indicated a concern for a lack of relia-
bility in present commercial UV systems. Some of tnese same re-
spondents recommended revisions in the UV calibration procedure to
incorporate procedures for checking or calibrating the photometer's
wavelength, path length, and optical density (or absorbancy).
However, EPA believes that the reliability of most commercial pho-
tomete^s will be adequate. The photometer specifications require
a non-dispersive optical system which is not likely to experience
changes in the wavelength. Path length is normally fixed and
should be adequately specified by the photometer manufacturer.
Optical density checks with neutral density filters (for example)
are not practical because of the extremely small optical density
range over which the photometer normally operates. The only
practical way to check the response of the photometer is with an
absorbing gas such as ozone. The linearity test described in
Section 5.2.3 serves this purpose.
There was some concern for whether the absorption coefficient
of ozone at 254 nm (given in the procedure as 308 +_ 4 atm cm
at 0°C and 760 torr) might be different at different temperatures.
Other comments indicated that the corrections for temperature and
pressure in the UV photometeric assay procedure were not always
clear. The absorption coefficient of ozone is, in fact, quite
insensitive to temperature between 0 and 40°C—aside from the
normal effect of gas density change with temperature. For
photometers used at temperatures and pressures other than 0° and
9
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760 torr, corrections are required according to the perfect gas
laws. Efforts are being made to further clarify tnese correction
Droceaures in the ozone calibration Technical Assistance Document
mentioned earlier.
A series of comments from one respondent recommended revisions
to the proposed procedure to more clearly allow the use of other
UV photometer designs and other configurations of components
-.•/itnin the UV calibration system. It was further pointed out
that, with certain configurations, some of the components shown
in the suggested configuration might not be necessary, and some
of the procedural steps in the proposed procedure might not be
necessary or even possible. This respondent questioned whether
UV photometer linearity tests by the user are necessary if the
manufacturer of the photometer has done the tests.
Modification of the commercial photometer might be necessary to
carry out the tests and any resultant leaks in the system or
improper dilution techniques might confuse the results.
In response to these comments, EPA has revised Sections 3,
3.2, and 5.3 somewhat to more explicity allow alternate systems
or system configurations and to provide for appropriate variations
in the procedural steps to accommodate such systems. Also,
Section 5.2.3 on linearity has been changed to allow acceptance
of the manufacturer's linearity test in lieu of the user-conducted
test if the manufacturer can show that the linearity error is
less than 3*. When the user carries out the test, the error
10
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specification remains at 5% to allow for some variation in the
necessary flow measurements.
There were several comments regarding the BAKI calibration
procedure and its use for an interim period of 18 months. One
respondent questioned the wisdom of changing from a known procedure
(NBKI) to an unknown procedure (BAKI) and then changing again to
UV photometry within 18 months. The respondent recommended that
EPA allow the continued use of the NBKI procedure on an interim
basis until the change to UV photometry can be implemented.
Another respondent questioned the necessity of allowing the con-
siderably more variable (than UV photometry) BAKI procedure for
the interim period, and recommended that comments from State and
local agencies directly affected should guide EPA in this area.
EPA agrees that the BAKI procedure is more variable than the
UV procedure but believes that some transition period is necessary
before the UV procedure is required exclusively. There were few
comments to the contrary. EPA considered allowing continued use of
the NBKI procedure during the transition period, but the BAKI pro-
cedure is really only a slightly modified version of the NBKI
procedure and is thus very similar. Since the change from NBKI to
BAKI is so easily made, and the performance of the BAKI procedure
is significantly better than the NBKI procedure, EPA feels the
interim change to BAKI is adequately justifed.
11
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A few relatively minor changes were made to the BAKI procedure
ir Sections 1, 3.S, 4.4.4, and 4 4.5 where respondents suggested
a need for clarification or where various improvements to the
method could be realized. For example, the units given as "eq"
in equation 5a of the BAKI were changed to "equivalents" in order
that they not be confused with equivalent weight. Also, the
concentration of the hydrogen peroxide added in Section 3.S has
been Increased slightly and the specification for the resulting
absorbance increase has been reduced from 0.010 to 0.008. Further-
more the calibration slope specification in Section 4.4.5 has been
changed from 25,300 +_ 600 to 26,000 +_ 780.
While several respondents endorsed the use of transfer
standards in general, one respondent questioned the advisability
of allowing the use of transfer standards based on methods known
to be highly variable even under ideal conditions. EPA still
believes that the variability of such transfer standards will be
adequately controlled by the qualification and certification
requirements on transfer standards described in the transfer
standard Technical Assistance Document mentioned previously.
Hence, EPA has made no major changes to the transfer standard
concept as originally proposed.
In regard to EPA's statement that no factor is available to
"correct" previously collected ozone measurements to make them
comparable to the new UV standard, one respondent thought that
EPA should allow individual states or Regions to make corrections
12
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to their previously obtained ozone air quality data if they have
consistent comparative data for trie NBKI and UV ohotometric
calibration techniques. EPA has re-evaluated this position, but
as noted below, still discourages such attempted corrections.
Effect on National Ambient Air Quality Standard for Ozone
Because of the substantial variability of the NBKI procedure
and the unpredictable bias results reported by various investigators,
the exact magnitude of any universal bias which may exist between
the NBKI and UV procedures cannot be determined. However, avail-
able data suggest that any such bias probably does not exceed 10:;
on the average. For this reason, EPA believes that supersession
of the NBKI calibration procedure with the UV procedure should
have no effect on the magnitude of the National Ambient Air
Quality Standard for Ozone (being revised elsewhere in this issue
of the FEDERAL REGISTER). And for the same reason, EPA discourages
any attempt to "correct" or "adjust" previously obtained oxidant
or ozone measurements to make them "comparable" to measurements
based on the new UV calibration procedure—even when individual
agencies or laboratories try to determine a more precise, laboratory-
specific bias value.
Effect on Currently Designated Reference and Equivalent Methods
As noted in the June 22 proposal, a change in the calibration
procedure specified in Appendix D of 40 CFR Part 50 does not
13
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affect the design or performance characteristics of existing
reference methods for ozone. The only effect of the chance is on
the calibration procedure described in the operation manuals
associated with the analyzers. EPA will allow a 6-month period
of time after final promulgation for manufacturers to revise
their manuals, have the revised manuals approved by EPA, and
distribute revised manuals (or manual supplements) to all analyzer
owners.
The two equivalent methods for ozone designated to date pre-
scribe the NBKI calibration procedure. Because the UV calibration
procedure and the transfer standard concept are as beneficial to
equivalent methods as they are for reference methods, EPA will
also request that the manufacturers of the two equivalent methods
revise their respective manuals to specify the UV procedure or
certified transfer standards for calibration. EPA believes that,
under the circumstances, such a modification to equivalent methods
for ozone is desirable and appropriate and should not jeopardize
their designated status. Conversly, failure to make such a
change may be considered by EPA as possible grounds for cancellation
of the equivalent method designation under 40 CFR 53.11. If all
manufacturers respond promptly to this request for appropriate
manual changes, there will be no impact (other than the change in
calibration procedure itself) to owners of designated ozone
analyzers.
14
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Revision Adopted
Accordingly, v.ith the final chances as descnoea aoove
Appendix D of 40 CFR Part 50 is revised as set forth below.
Date
nomimstrator
15
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is amended
jNments on the use of transfer standards/
j \nd or. the transfer standard guide! in*"
I aYe welcome. / I
i \ /
USE or Nr"
P?.O:.:V.CATICN
cts'j-SES ??.:OR TO-
As indicaiid .n :his prcco*;.;. ::-.e UV
calibration proceaure—ana to a lesser
extent the 3AKI procedure—axe be-
lieved \to be scientifically superior to
the currencly prescribed N^BXI cali-
bration 'procedure. And it is very likely
that the\UV procedure (and the BAKI
procedure or. a temporary basis) \v:ll
be promulgated to supersede the
NBKI procedure. Accordingly, agen-
cies which • have the capability and
desire to commence asm? these proce-
dures immediately '.vouid not be dis-
couraged :"rom coir.a so. Immediate
use of :rar.s:er s;ar.c:i:-ds couid also be
cor-siderec or. tbe s?.rr.e baj;:i.
PUBLIC PARTICIPATION
All documents and information rele-
vant 10 this ruleinaiing are being
placed :n Docket No. OAQPS 78-3. the
docket for the proposed amendments
to the standards :'or photochemical
ox;iants. That dccKc; -vul be availacie
for pub;;c :nspec::on during :r.e hours
8:00 to 4:30 at the Public Ir..'ormition
Reference Unit. Room 2922. 401 M
Street S'.V.. Washington. D.C.
Comments on any aspect of this pro-
posed amendment are solicited from
interested persons or agencies. Com-
ments shouid be submitted to Mr.
Larry J. Purdue at the address given
at the beginning of this norice. Com-
I ments should be received within 60
; days of trie date of publication-, for due
j consideration prior :o final projr.ulga-
j tion. Copies of all comments received
i will be added to trie docket. \
I In-'addition interested persons'^may
i maJte comments on :he proposal orally
! at-the public hearing on the oscne
standard scheduled for July 13, 197&
.' Dated: June 9. 1973.
DOUGLAS COSTLZ.
Administrator.
'It ia pro
tmona Part 50 of
Title 40. Code of Federal Regulations
as follows:
1. Appendix D is revised to read as
follows:
APPINSIS D— MEASUPiME.vr PsiNc:?f_r AND
CAL:SRAT:ON PSOCZBURE FOR THE MEASURE-
MENT or Ozo.tE :s THE ATMOSPHSRE
ACTHORITY: Section 109. 301 of the Cean
Air Act as amended U2 USC 57409. 7601).
MEASCREMRIT PRINCIPLE
1. Ambient air and ethylene are delivered
simultaneously to a mixing zone where the
ozone ir. '.he i:r reacis '.vitn '.he ethyier.e to
FiDEBAl SECISm. VCl.
NO. HI— THL'XSOAY. JUNS S
-------
CS;D 2ULH3
emu light, -.vhich is detected by s photomul-
tiplier '.ube. The result:-? phot ecu -rent is
a:r>-...':ed and :s e!'.hsr r?r= ::.-trr.i:. or a.s-
r^ •*,: :i s r»f?*c~r
h';s teen jesisr.atec is i r?:?r?nce rrif'./.i'j
in icTcr-ip.r,ce with Fir: 53 01 :.-.is er.ipier
ar.d caiicrated as follows:
CALIBRATION PROCESVRE
1. Principle. The calibration procedure is
based on the photometric assav of czc-e
(O,) concentrations in a dynamic ;iov.-
system. The concentration of O5 in an ab-
sorption cell is determined from a measure-
ment of the arr.eum of 25^ nrr, ligiit ac-
sorb*d bv the sample. This ceternunsticn
requires KI-.GV. :ec?» c: >1> :!-,t. -c.-crii.c.i co-
e/'::;en: t-.) o: O it 254 -T.. C :.-.* cr'.ca.
P5.1; .'.-r.rtr. ••:'. ir.roci':1. '.."".i sample iC~- ';;e
'ler.r'.r. ;. Ci-i-.m sr.c •; '.r.e isrr.y-rra.jre
(i! ar.c pressure 'P> cf the sarr.pit The-
transmiiiance :s definec as the ra:;c 1.1,.
where I :s the intensity of light, which
passes through the cell and is sensed by the
detector when the cell contains an O,
sample, and 1. is the intensity of '.,*?.: which
passes throush the ce:! and is sf:-.5ed Si the
detector v.-hcr. the eel. contains ;ero air. I: is
assumed tr.at a;i ccncit.sr.s o; u:e ."-'."err.
except fcr l".e CCI-.'IT.;; o; ::-,? as>orr-;or.
cell, ire :Jrr,:K^. t:jr.ng r-.s:-.3.:rrr;-.rii; el i
ana I.. The c..;niii,e.* ce::ric-c aiov? a.-* re-
lattG by '..-,<; Beer-Ldn-.bsrv io.sorpiicn ;it>.
(soace
3. Apparatus. A complete UV calibration
system consists of an ozone generator, an
output port or manifold, a photometer, an
appropriate source of zero air, and other
-Components as necessary. The configurator
~iust provide a stable ozone concentration
it the system output and allow the
ohotometer to accurately assay the output
concentration to the precision specified
-'or the photometer (3.1). Figure 1 shows
; commonly used configuration and serves
~o illustrate the calibration procedure
..hich follows. Other configurations may
••ecuire appropriate variations in the
procedural steps. All connections...
where:
a = absorption coefficient
nm = 308~4 atm": cm"1
of O, at 254
at O'C and 760
c = O, concentration in atmospheres
i«cpiica! path length :n cm
!n pnctice. a sta&ie O. generator is used
to produce O, concen:raticns o-er the •-*•
quir;d range. Each C. concentration is de-
terrr.iped from the measurement of the
tr?r.irr.::tance il • > of the sample at 25-i r.rn
With a photometer of p.v.fc >r.;::-. i ar.a cal-
cu:.\;cd :>om :l-.e or.un.tion,
or.
"he calculated d concentrations must be
corrected for O, losses v-'hicr; may occur in
the photometer and for '.he temperature
and pressure of the sample.
2. Applicability This procedure is applica-
ble to the calibration of a.-n&ient a:r C> ana-
lyzers, either directly or by means of a
transfer standard certified by this proce-
dure. Transfer standards must meet the re-
quirements and specifications set forth in
Reference 8.
3. Apparatus. I Tifbro 1 Illv
_ ...
[zero])
connections between
17
FfDERAl REGISTER. VOl. 43, NO. 121—THURSDAY. JUNE 22, 1978
-------
26975
glass, Teflon, or other
relatively inert materialS.T
^ev^ces C53cble o^ regulating
= if flows as necessary to
meet the outout stability
and photometer precision
recui remenzs.
components in '.he calibration system down-
stream of the Oi generator should be of
tion regarding me assembly 01 a UV photo-
metric cal:trai;cn nssaratus is yv*n in Ref-
erence D. F?r ssrti/iCatiOR o: -r?.r.s:';r st.-.r.c-
aris -va:cr. pro'.ide -.heir r.vr. so.:.-re c: O..
the :rar.s:'er star.cara .-ray replace '.r.e O,
generator ar.ci possibly other components
shown in Figure 1: see Reference 8 for guio-
ance.
3.1 UV photometer. The photometer con-
sists of 3 low-pressure mercury cischarge
lamp, (optional) collimation optics, an ab-
sorption cell, a detector, and signal-process-
ing electronics, as illustrated in Figure 1. It
must be capable of measuring the transmit-
tance. I/I., at a wavelength of 254 nm with
sufficient precision such that the standard
deviation o: the concentration measure-
ments does not exceed :h» jreater of 0.005
pp—. or 3*"- o: '.he csncer.'.raticn. 3«e?.use
the low-or»ssure mercury la.T.s radiates at
several vravejenethJ. t"S pnotorr.e'.er m':st
incorporate suitable means to assure :'..-.
no O-. a generated in :he csi: by the iarr.o.
and that at least 99.5^ of :he radiation
sensed by the detector is 254 nm raoiation.
(This can be readily achieved by prudent se-
lection of optical filter and detector re-
sponse characteristics.) The length of the
light pa:n through the absorption eeil must
be known with an accuracy of at lecit
99.5~;. In addition, the ceil and associated
piurnomg must Se des'gried :o minirjjze '.c;c
of Oj from contact witn ceil '.vails and ;as
handling components. See Reference 9 ;or
additional m:ormation.
3.2 Air flow controllers. Po'uej ;npftbi! of
3.3 Ozone genemtor. Device capable of
generating staoie levels of O> over the re-
quired concentration range.
3.4 Output manifold. The output manifold , , nn
should be constructed of glass. Teflon* or 106 I 6 L£ R
other relatively inert material, and should
be of suf'icent diameter to insure a negligi-
ble pressure drop at the photometer connec-
tion and other output ports. The sj-stem
must have a vent desisted to insure atmos-
pheric pressure in the manifold and to pre-
vent ambient air from entering the mani-
fold.
3.5 Two-way valve. Manual or automatic
valve, or otner means to switch the photom-
eter flow between zero air ana :he O, con-
centration.
3.6 Temperature indicator. Accurate to
= rc.
3." Barometer or pressure indicator. Accu-
rate to =2 torr.
4. Reagents.
4.1 Zero air. The zero air must be free of
contaminants which would cause a detect-
able response from the O< analyzer, and it
should be free o/ NO. C.H.. and other spe-
cies which react with O,. A procedure for
generating suitable zero air is a:vert-in_R.ef- , _,
erence 9. As shown in(Ju?ure~i. the zero air ( F}
supplied to the photometer ceiJ for the I.
reference measurement must be derived
from the same source as the zero air used
/or generation of the ozone concentration to
be assayed (I measurement). When using
the photometer to certify a transfer stand-
ard having its cuvn source of ozone, see Ref-
erence 3 for guidance on meeting this re-
quirement.
13
-------
26976
p-r
so '.i.'.t- as a rr...orntion stan^ara It -nou^d
s.-.vr;'. s be j.,t-d w,ih c:t-an. n'.tercd ciilibra-
lion sP-ii--- and never used for amb.en; air
iimplir.,:. Consideration should ot g:\en to
)ocn:ir.g the cilioranon phoion-.eter in a
c.rnr. i:icoratorv whore :i can ie stationary.
sroic'.tci :'rcrr. pi-.yss.-sl sr.ock. operated by
c r'.-;so:-.5-olt ar.aiy*:. ano uK-d as a common
.-/.anaard for all field ca,!brauons via trans-
icr standards.
5.2 Preparation. Proper operation of the
p!-.otomp;er ii of entics! importance 10 ihe
r-criira-". of •!;;.- c'cc-'^-re. The fo:.o«ip.5
.-•••;.>5 v..;: :.(-ip 'o 'er.:- p'.-p-.-r ip^-^.mr.
: l;h ,.;- c: v.t- p:-?:c:r.c-'.r: Vrcr. :r./:a!
.••'.;.i tr: -<-:--.-z i .; :r'-;upri::y \v.;:: r;,;
•::.^":;:'.::•.•.- rc?:::i.« or ir.aicF.: srvs recorueci
:n a c.ror.OiG^irai rc-corc either in tubuiar
form or piottec on a graphical chart.. As the
performance and stability record of the
photometer is established, the frequency of
M-.o-se r.eps raay be reauced consistent with
•nc- ,-ior-j:nenieo iias:!r.y of '.r.r shotometer.
5.2.j ;no'rv;:;:c:. rr.r-r.ua:. Cf.rrv out a'u set
•.u' 2rri ".ci.::'.:r!erit prc-rc.'.rfs or cr.eCKs .is
.-.--c: cid sr. trie oprrr.'.c-r. or ;r.s'..-jc;;cn
~ .:r.j"l ai'socia'.td \v:ch '.nf pnotorrst-ter.
5 2.; 3>.-!c-rr, check: Check, tr.t pr.o;ome:er
i.-. =•.-:-:/-. for -.r/.v^nty. icalii. c!ear.!:n«ss.
proper :lo»rates. c-:c. Service or replace fil-
ers and -e^o air scrubbers or other consum-
able rn?.:cr:als. as necessary.
5.2.3 Lir.cn.-iiv u.fu 7'.." ihc ;ho:»m-tw
for iiiiic.n:: or d.Union. Generate and assay
an O, concerstritson near the upper range
hmi; of the system <0.5 or 1.0 ppm). then ac-
curately iiiuu' that cor.cir.tration with zero
u:r anc rei.'.iav it Rt-reat at severs.! d.fler-
ens c;;ut;or. rr.::os. Co:r.par« ihe assay of
the onginai concentration \vith the assay of
t!:e dii'jtea cor.cc-ntration divided by the di-
lution ratio. 2i follows
5.2.3. Linearity: Verify that the
photometer manufacturer has adequately
established that the linearity error
of the photometer is less than 31-, or
test the linearity by dilution as
follows: Generate ...
E = :!ni?.r!tv v=rror. pc-rcent
A =;.£-:: v o! t!ie original concentration
A,= •>..-*?;.• of '.'.'.? dil',:iea cor.cer.traticn
R=diluuon ra;io = f!ow of original concen-
tration ::;vided by the total flow
T'.'.f: '.:r.e.-.r:s:- error must be less than 51-.
Since the accuracy of the measured flow-
rate? -viM affect the linearity error a? meas-
ured this w?.v. the test is not necessarily
ccr.clusr.•?. Additional information on veri-
'•• irt l;ne-rity is contained ;r. Referer.ee 9.
j.:.4 Ii:-.crccrr»par:son: V.'hen possible.
the photomeier should be occasionally in-
tercorr.pared. either directly or via transfer
standards, with calibration photometers
used by ether agencies or laboratories.
5.2.5 Ozone losses: Some portion of the
O-. may be lost upon comact with the pho-
tometer cell walls and Xas hanging c,ompo-
r.ents. The magnitude of this Joss must be
di-'.erniinec and used 10 correct the caicuiat-
ed O ror.ceritraiion. This loss must not
cxr-ed 5~:. Some guidelines for quantita-
;;•.*:;• df'rrraining this less are discussed in
Reference 9.
19
-------
PROPOSED RULSS
Insure that}"
Insure thatj-
5.3 Assay o: O. concentrations.
5.3.1 Allow the photometer system to
f.rrrs 'jp ar.d -tab'Iize
53?
a .-ej.jor.jci} sr.orV per.oc o; ::..:r 2 ..:••.'
rr.ir :s a rypica; f.ovv: The precision ci :ne
measurements is inversely reiaied ;o the
time required for Hushing, since- the pho-
tometer dnft error increases with time.
5..1.3 .rj.Hiji'ine flown-.;-.' :r.to :h-e output,
manifold ia !• -Dim at least 1 liter rr.irT
greater than the total flowrate required by
the photometer and any other flow demand
connected to the manifold.
3.3A /iajui-,;the flowrate of zero air. P,.
ir. a —>;£? at least 1 hter rr.m prpater than
thp flowrate recuired by the photometer.
5.3 5 V.'i-.h :-ro :.:: ;';e«-;r.c '•" :r:c o'.::put
r.-.nr.-ic'.c. a?"jr,;e '.'.'.? two-way i?.!v« !0
^:!v'3 the srsjtcrr.r'.er :o sirr.pie :':r;i ;he
n'.2ri;:"OiC zsro a;r. i:~.er. F. Thr t'.vo pno'vOnv
ttfr •sivlir.gs rr.js: be cs'-ai I = i, .
NOTE. In son-.e cornrr.rrc'.a^- available
photometers, the operation or :i:e two-way
valve and various other operations in sec-
tion 5.3 may be carried out automatically by
the photometer.
s.3.6 Adjust the O, generator to produce
an O'. concentration as needed.
5.3.7 Actuate '.he f.vc-wav valve :c aiii'.v
the photometer ;o sample zero air uni:i :he
iosorptior. ce'.i :s uiorouiinly :!ujhri ar.i
record in* sir.ble measured value of Ic.
5.3.3 Actuat: :he t\vo--.vay valve >o aliow
the photcm^tsr to sample the czor.e concen-
traucn until the absorption eel', is thor-
oughly flushed and rtcord the ..table meas-
ured value of I.
5.3.9 Record the temperature and pres-
sure of the sample in t::e pnoiometer ab-
sorption ceil. (See Reference 9 for guid-
ance.)
5.3.10 Calculate the O, concentration
from equation 4. An averajs of several de-
terminations will provide oetter precision.
15
where:
COJiPlT=O. concentration, pern
c»absorpt4on coeuicirnt of O-. at -:•«
?.m = 308 aim" ;rr." it 3 C a.-.i TOO lorr
• = optical path lensrth. CT.
T=sam?lc temperature. X
?* sample pressure, torr
L=correction factor Jor Oj losses from
S.:.5 = < 1-fraction O, lostQ *
.Vote.—Some commercial Bhotoir'.e'.ers_
may automatically evaluate all ^ part of
equation 4. It is tile operator's responsibility
to verify thai all of the information re-
quired for equation 4 is cbt.r.ned. either
automatically D.V the photometer or man-
ually. For "automatic" pr.ototr.eters which
evaluate the first terra of equation 4 based
on a linear approximation, t manual correc-
tion may be required, particularly at higher
O, levels. See the photometer instruction
manual and Reference 9 for guidance.
5.3.11 Obtain additional O: ccncer.tration
standards as necessary by repeating steps
5.3 6 :o 5.3.10 or by Option 1.
(or)
20
-------
more ozone stanciai"as as dcv-rr.up.^a ar'-ora-
ing to section 5.3. The exact procedure
varies dcper.cunp on ihe nr'turt and aesiirn
of the transfer standard. Consul; Reierence
8 !or guicfirice
5.5 Calibration o! ozone anai.izcrs Czone
... ^- analysers are calibrated 2- •.-"nv-.c -.;.ipf
3 Certified! , <-,7*-f s:_and.-.rds oL:.-.inL-q*T!rcr.rr.'nc •„ seC-
— ' lion 5.3 or b> means o.'^traniier s-.;:r,cr:rei.*—
5 5.1 Allo-.'. su:f:c:"rYt ::rr>p for :;>c O ar.a-
•&--. ir •;.?.?;-.;.? ;.:" • ::.:.•,;>?--
55. A:-c-.i -.:•,; O .-.-..-. -.7 ' t; s--:;5!C
;.--.^ ;_ ^^; •;•.: C .•.-.-..•.,.-•> .::: •: '-::.
-5" oi ;cn!e :< r; ,-c:r.~-r u : :_.-. ::.; ..:•„;-
otsfrvinf m-;s;".e zero cr;i. r.eccrc ;ne
stable zero air response ar. "Z".
5.5.3 Generate an O, concer.'.ralion
standard of approximate'-.- 8C-~ of the de-
sirec upper range hnv.: lURLi o:' ;!ie O. ana-
Ivser ADovv '.:ic O :•?.:•..: z-.r 'o ;a:r.; v ':;:s
spo-it" ii o^::..:.fc
5 5 •• A". • lit :r.-> O •;•::'• j.: .- -".-—. :•::••
tro; -o cj-.ii.r, a . T\ (", :-.: .-:-. •. r--- .-'••
where:
URL= upper range i:rr.:: of ihe O t.-.a:yr.-
er. ppm
Z = recorder response voth zc-ro a-.r "^ scale
Record the O> concentration and ;h^ cor-
responding ?.r.aiy;'.T rc?::-T.s« !.' safes' ?.r.':n!
.
rs-chrc:-: '.he zero and span auju.strr.i-n:* by
repeating steps 5.5. J :o 5.5.-;.
5.5.5 Generate sevc-ra! other O. concen-
tration standards «.i'. ^ea:-; 5 otnc-rs ;rc- rec-
omn-.ep.dec1 over 'h< scale rr:.-:-'1 of '.::': O
ar.alyr.er b\ ad.iu?t:r.c tr.f- O. -o-.rrre or by
Op:ior; 1. For each O cc-rjr.fntjor: ?:ir:d-
ard. ret-ord the O. cor.cs-ntrai:on and ;.he
corrcspcnc:r.c analyzer response.
5.5.6 Plot the O, ar.aiyztr re?por.><>5
\er5^j the corresponding O: conrer.tratior.s
and crr.v, ti.e O: analyzers cai:brr/ion curie
or calculate :r.r appropriate respcr.st sartor.
5.5 7 Opiicn 1: T'r.e various O concentra-
tions- required in s;r?s 5.3.11 arc 5.5.5 may
be ofc:a:r.ed by dilution o: the O, concentra-
tion generated in steps 5.3.6 a-id 5 5.3. \V,:r.
tri's option, accurate flow mc.vjrorif 'its are
requirc-d. The dyr.nx.ic cai;srat;cr> sy>ttm
fi£*£!*~e modified as slio'.'.n in Ficurr ; to
aliovv for dilution a:r to be motors:! in :ov.-n-
stream of the O-. ceneraior. A mixinp cham-
ber between the O, generator and the
output manifold is also required. The flow.-
rate through the O. penorator iF.) ana the
d;:'.!t:or. air flovvrate '.F-,.1 are measured with
a rKiabie flow or volume stanoard traceable
to XES. Each O, concentration ??r.cr?.trc b'.
d:'iUt;on iscaku.ated from.
21
-------
REFERENCES
1. tT.C.T. :.-.n T.O Y. Tar.aka. "Absorption
Coe:'.'.?:sft: c? C;one :r. :.-.e Vltrav.siet and
'."j.t.i ?.tj;:cr.s . ^". O.ci. 5cc. .4.7!.. ^J. 3TO
i. A. O. H»irn. ••Ai5orr:icri of Ozo-e ir.
ihe l_";-rav.o,5: ar.S V;j;c!e Rrr:ons o: ins
>«-c:rjsi" P-3j. f''yi. Sec. (Lcndon^. /i,
PROPOSED RULSS
3 li.'.r.-r' -^; O ?..-.r-r.
.
Ciroon Mono.<:i*. and Argon '
/".-; vi.
*. ML Gnscs. -Aosorpaon Ce*ffic:er,ts of
Orone ;n the Uit.-jv.olet ind Visible Re-
ff:or.s". /. C^cn. r*.yj.. VS. 85T • l°63>.
5. K. K. Becbcer. U. Schurain. and H. S*$.tz.
"Osene O:-:-f-.r. Reic::cns in th? C-w ?\:^e.
/r.:l Jour, o.' CTiLvn. .f:n#i;i-s, "I. 705 • 197-1;.
5. M. A. A. C'.yn» ana J. A Coxcm. • Kinsr-
ic S'.uciss of O>:--:-.i:ocen Radical S.'sirrr.s '.
/"roc. .Ecy. .Voe.. .4J-/0 20T < ISrtSi.
26977
Uelets "in
draft form'}
-.. R. J. ?;;;.-. H. A. V. -3.r = r.
_..
?-:siica::or. availasie
?A. 2-?r.r:-?r.: £ •
r.r.i.* ?a.-,:. X C. J771'
I Calibration of Ambient Ozone
UJonitors",
(77)
22
-------
2'59T8
PROPOSED RULES
JCON7ROU-R T
I 11 OVV
COMROUEP
r
: «LOi'.
' CO'.TP.OUiF
F.ours 2 Scrt-i-5iic any*1* o- * I,P-«! '-'• f-'-c-n-r- c :. : -.v-v— ;-.
FtDiRAL REGISTiR, VOL 43, NO. 121-THURSOAY, JUNE 22. 1978
23
-------
-cr.:hs i::er '.he Sate o.' i':r.a: ?ro:rtui«a-
'.:or-.; .\:~.r '.'.-.:.: ::~? tr.is procfi-j.-i car. be
.-..•-.= . rr C:. '.-•".•'. :: .-—.;.or.: Air Mm:-
: ?r-.r.r-:.» Tr..3 r?.:.i.-a!.5- prseesure •. 1)
.3 taiss jpor. '.-.e reaction ;e:-.veen oior.e
• O-- a" pjt.Yiiiusr. .o-iise (XI! to release
ioc:r.£ «. acrorsir.g :o ;h* itoicmornetnc
equ.it.OR: .I;
The s:o:c:::o:r.etry .s sucr. i!-.at the air.cunt
of I; re:-?2.*ea :s ecuivalertt is the amour.: of
O. absorbea. Ctone a absori»d in a 0.1M I
^* • >.K^I^. VT^a. ^^^u.tc id U'J^W* wTU 111 a U.1**L I K
tone i..i H3D; sc:u-..o^ c2.r.:A»-:-5_Lri« reacts with excess iodide ion (I ) to form triiodide
.^..•^-.^-."•V. ion (IZ) which . .'
•i.:sra::ir. ir.c --::ftoc: physical movesient.
and :: is recai::raico pr.or to each use. Al-
t«rr.i::ve'..- -.he O aaalj-sr say be calibrat-
es =v assay.nr :hs O, .ror-centritions using
r. :_i.:- -:•. ^.--.-.r.r T.e rorr->5por.K:r.i? Oi
''L~z'.'^~ rr'.' • -o j- .•^".-•"•'o'" ov •>- op-
•::r.i. :.-_:.:_:": •-:-..;.:?. '.V :-.:-." :h;s ;pc;cr..
?.ci'-:;r.i. .. --r.:;r.:rr.:.cn siansa.'Ss re-
;=..:.-.2 :>..-•' :-.:- -:.:-.-.!r.s«: :y :i:u:;cn.
2. Apparatus. Fir-res i and i illustrate a
;"E;cit 3.-.i-" O, .-a^sraf.or. >ys;em and
csjr.ioRST.ts ..it-.'s c=;ott'. Ail connections be-
f.v»eri ccrr.por.er.ts downstream of ;r>.e Oi . , _
i-.T.erst;.' 5r.5u:d be of s'.iss. TsilonA^o? (delete "R )
:.: .-^r :'.)••.' .•;r"t.-oi:«"i:ev.ce capicle o:
2.2 Air :".c-'v:nc'.sr. Calibrated floxvmeter
cr.psc.t- j:' — 2ijiir:r.z ar.d norutjr.n? the
'.'.J O^cr" -."-.era'cr ^'. ?s capribie of
:r- •.-::.-.. ••.,-.i lc.r:3 •:; O; o'.?r ".i-.; re-
...r. j . rr.i'Cr.:r-'.;cr. r^..-.?-;.
•(delete "R")
;.U:# ;-r;-j^r? 2.-oa i: ;r.e -.-aiynr ccr.r.ec-
v. :r. T:;; .> jrsrr. ;r/:.-.; ;-.2'.c- a ven: des;zr.e
-------
500, ]-.-
e>. c.' -'3 is reco-r.mended The orifice should
".- rro'rctea '.ri.rut —.?•; ^r? -.re -v ••:.;•
'.'."r -•.•;. > ••*•-.-.:;?*• '-• . -..
it*.-. '.• 5-'iT -t~cspri*"es across t:\r ;rr.::i!
3r.;.cc AUer.-.a-:i-»!y. a needle valve couii
be used with '.he pump :o acjust the flow
th.-c.ugs the irr.p:.-.£ers A fiowmerer is then
recommended to monitor the i'io\v The
neec.e vaive-flov.-meier combir.a^or. :hould
'oe protected ajair.it moisture ?.nd par'.icu-
iate matter »ith a membrane ii.ter or mois-
ture trap.
2.7 Thermometer. Accurate to =1"C.
2.8 Bc,rcr.-,?-.s-r. Accurate to =2 tcrr.
1.5 Volumetric ilasxs 'Class A>. 25. ICO.
_S-!V-""-"-T-- ,^_, ~
!. 2. /. 5. 10.
rary cf r ! ~- ar.a l.r.eir reipor.s^r over we
rar.gs oi 0-1.0 absorbar.ce un.is. Tr.e pr.oio-
metric accuracy may be cheesed using opti-
cal glass filters ivhich have certified absor-
oar.ce values at specified wavelengths.
Ma'-cned 1-crr. cr 2-crn cells should be used
;or n.: 2fcsorcar.ce se;errr.ir.a:ioni
3 I Zero ?.:.- T.-e ne.-c a:- rr.::s: be frp-s cf
r*-. O'jrt.^c or. '.r.v O- .".r.ar2:v ~r ".r.icr. ,T..Vr.t
rcici »•.•.:; 1~ 3AKI. .-.:r -r.~*':r.s this re-
ciuirtrr.tnc T.S*- C6 ODvSir. ?ii ov } ? csssins ,t
;hr;uT-h 5:1. ca ?el :or c.-"T.?; (2! trea'ins ;t
v.'sih O- to con'.er; any nitric oxide (NO) r.o
nitrogen dioxide filter to remo1 1 ar.y paniculate
3.2 3or;c acid -K.BO.V ACS rr-.jf.-.t zrade.
3.3 Pctaisiuir. .ocilJe iKI/. ACS reagent
grade.
3.4 Kydrccer. peroxide iK,O,). ACS rea-
gent praai. J~- or iO~.
i.5 Pociss-j.-T: ii'C-.-ti .KlO.i. ACS reajer.t
greet certifies O.l.N"
3.c SuiiuriC acid -K.SO.). ACS reagent
grade. 9i~: to i3~-.
3.7 Distiiied v.-ater. Ui-,-ci :or preparation
of Mi rcseents.
3.S Absorbing re??'?r.t. Dissolve 6.2 ? of
boric acici :H,BO,) in approximate.1:,- 750 mi
of distilled water in r ii.]nfni-.-..-.r.>r-no 1000-
ml volumetric flask. The flask may be
heated gently to speed absolution of the
H,3Oi. but the solution must then be cooled
to rcor.i temperature or below before pro-
cftii.-g w:'h •:•.£ reagent preparation.
.'.'^i.c" the H 3O; solution ,s c-^clir.?. t.c-
p?.:'? t \c }•' cic^en peroxic-e 'H.O.. solution
according 'o :r.e directions m 3.9.) When
'.he H.BO- 3Olut.cn has cooled, add 10 g of
poiassium iodide >KI> to the H,3O, solution
and dissolve. Add 1 ml of.*) j_o:o~ HrQ; solu-
tion isee 3.9) ar.d mix thoroughly. Within 5
minutes after adding the peroxide, dilute to
volume .'/nil ais;iilcd water, mix. and deter-
.T.II'.T ;r.o absorbar.ce of tnis 3AKI solution
a; 352 r.m a.ainst ci:.;;.llrd ^n^cr as tne reT-
fr-i-cv Tl-.e pH of 'he BAK! jolu'-icn m*trt
_ ,^ n ^^^^^^^^^
Set the absorbing .solution aside for 2
hours ar.'i :her. rec:i.'terrriin
-------
25979
aSscri?.r.ce unit: cm rr?at?r :han the first
Using a
graduated
Dioet, add f
:•. 7
a" -•.:::: :t aisccrsic. '-.i th.j ever.:, pre-
pare :resr. absorbing reagent jsir.j a i.;'.'er-
er.: r.umcerec iot si Kl. It unacceptable ab-
sorcmg reagent results from c.f'jron: '.ots
01 Kl. :est tne poss;bi!;;y 01' cor.:a.T.;r.a:io-
in -.he KJJOi by usir.g a different numbered
lot o: H,3C,.
3.9 Hydrogen peroxide 5oiu::ar.V7 ."i? ,
JPm.^cJ cf 30- Cfa» ml of 3y
peroxioe 'K.-O;) >»;o apprcxirr.ito'v :oo ml
cf dist:!!ec wateriil
r.isic. dilute to "oiurr.f
and m:x :.-icrc-'.:«'ii:' To
- * • --••!. -.-^.
c:::.:ied v.-^te.-. a.-.d rr.::: :.-.orcu;r..y. T'r.;i
J;O, iolu::cn rr.us: be prepares
fresr. each time a fresh batch c' ibsorsi.-.g;
reagent a prepared. Therefore, the remain-
ing contents of both volumetric ilasxs
ihcuii be discardec after :rsatrser:t c-f ::-.e
;.' pc:a«:urr. :or.?.;e KIC hi.-.r.s 2 CST::-
f:eo r.crr-.al:::--.
3.1! Sul.'uric ac:d I**'. ~i:'j:-.- -2 —.. o;
to volime .n a liCO-rr.i vo: j~.*;r:t :".ssct.
4. Prccscu.-e.
4.i Asserr.ale an ozone cai:bra:;;n »;.';;em
sucn as shown in F:7U-"e 1.
•i.2 Assemble the Kl js.m5r.-g :.":.-. such
as shown in Figure :. Ail conr.sctiorj 'ce-
weer. the various components must :e '.eaK
fjc:.-?, or 7e:':or.? . '
F.« f.O'.vrace correc:rd to r<»fer»r.e» cor.ai-
P.»barorr.(f'.r.c pressure at -amsUr.x con-
ditions. :orr
P1M»vapor pressure ot' Ki it T,. ;orr 'For
•vet volume standard. For a cry stand-
ard. P,,::.-O>
T, = temp. :r":i"
'.vhen ne"ueo. as foilo'-vs:
A. Accurately pioi". 10 mi of •) IN s'ar.cri.'d
potaiiium lOdu'.c K'.O-- »oiut.or. ir.to i :JO-
ml •.oiumetr.c :!a»': :cr.;ai:u;;2 iscrox:.T.air-
!y 50 ml 3! aiatilicd .vater. And ; j si potas-
sium .odiie .KI ir.d 5 rr.: of ;N sui.'ur::
i^^.-^- [c.008
[0.002 IS
7.0
1500
.(delete "in")
[5
--(delete "R")
-------
26980
see- «• into a U.o-rr.! \ok::r.?tr!C flask and
Chute :o • o.ume v.i;.n absorbing reagent.
Then fur-.h-r diiute t.-.is ?o:-j;:on by pspet-
ting 10 ml of it into a 200-ml volumetric
lias* and diluting it to \olume with absorb-
:r.p reiser,;.
C. In '..,;-n, picet 5. 10. 15. 20. and 25 ml
aliquots o.' the linai 1- so:ut:on prepared ;n
step B above i.-v.o a ser-es o' "5-mi x-olumst-
ric I!.-:.--;' Diiu'.e each to volume w:th ab-
sorb:!-.; r-r-aent and mix thoroughly. To
;•'- '-P.: i. losses ov '.o.;r ,i:za;ion. tne "i.a^s
•i 4 _ D t.rr.-.'rv. tr.f a"»cro"nce of esch
1 sttrscarc ^t 2i: .-..-n Also measure the ao-
sorcunce of i sampie of unexposed absorb-
ing reagent. Determine the net abscrbance
o: each 1; standard as:
-. -. 3 Tor -:•.••: 1. v.i.-.dsrd. ?:.!:•„, -,e '.he
b = ;.Tu:op. :r. ;-.••„.; .::..•:• as:
C3..1 «concen:rKi:cn of f?.cn I, standard.
'
>.. -r.ar-.al:-.;. c: KIO. (from
V=\ oluwe of I.- solution tfrom step
4.4.1.Ci = 5. 10. !5. CO. or 25 ml
1 equivalent I
1 mole !,
KI03 1 equivalent KI03 2 equivalent I2
10
Vi
2T
(5a)
-[equ-j va] ent
•S.J.3 P!ot net abfcrbnr.ce cm (y-axis)
versus ;he rr.ole I; :::sr .>:-axiS' for each I,
s:;./.dsrd ano crs'.v :he KI caj;orai;on curve.
C.-..; j..-.:j i:-.r slop:- ci ;;-.e curve in iiter
mo.e' cm" and rs-rord as £.. The value of
the siope should betfsa»fe«§^If JLURjiLofift... ..[26,000
is not tt-.lhm lh:s range, and the photomet- L '
ric accuracy of the spectrophoiometer
meets th? specifications given in 2.11. repeat
the procedure using freshly prepared I,
standards. !f :he slope is still not within the
sp?cii':s-n ranee, repeat ;hi? procedure using
A d:'.:cn ~T.: ic; of ci?rt:f;<.s 0.1N KIO, to pre-
780
27
-------
PROPOSED P.UIS3
4 5.1 .A:; ... • .:'.- a:r ".-••-'• '.:::. :-:: :.:* O
ifr-jr.v.cr :o :.-.e -j*i..-ti f.cv.rats a.-.a r-cc.-i:
.-.s F. A: a.J t.mes fr.? a.r f.c'.v thrcu,.;: '.-.e
generator rr.-st ce treat*.- -han the lots!
flow requires by '.he sampling systems, to
aisure exhaus: .".cu a: the vent.
4.5.0 With the O-. zer.era.tor off. flush the
sysierr. -.vith zero nr for at Ir-ast 15 minutes
to remove residual O>. P'.pet 10 m! of absorc-
ins reagent :sto each of : impir.jrers and
connect them into the sampling train i£
shown in Figure 2. Dra-;.v? ':M- ., c: O aciC'C-"-' as'
ic::-.r.cD5 c: •..-.:- :v>o sc.jnons :o obta:rs :ne
tctai net absircar.is. Calculate the indicat-
ed Oj concentrator, (system blaniG as ecuiv-
alent O. concentration according to 4.5.4. If
the system blank ;s greater thar. 0.005 ppm
O,. continue fiusr.ine tne Os ftST.sration
c?t?rrr..n* the «y:tjrr. ::ir.k. I/ tr.e syst?m
t:i::.-, .; £::.• ^r;i;j-r '..t:r. 0.005 cpm O.. the
r.^r-> a;r proja.i.y cc-.iains traces o: an oxi-
c.::-; rcr..irr.ir-ar.:. .•..-.: .;\* r.ctivatec cnar-
coa; ar.s ,T.i.;i:u.ar ;u'.e 'see 3.1: snou:a oe
4.5.3 Ac.ust the d s,-?nerator to generate
r»n p. ccn:sr.:ra;.ir. sr. ths rants ef ir.tsrest
ana aiioxv im syjteni to eauiii'cra:3 for
about 15 rr.:r.u:is. Ths .ir.cahiratsc O, ana-
lyzer to be cal.irated can conveniently be
-ised to imitate tne sta.bK.ty of tne O, gen-
erator cutset, 'when t:-.s O. generator
cu;pu: has Swir:l.zc2. ;.?tr-. 10 rr.l of abiorb-
from t.-.2 output mar...';.a of :.-.s O, calibra-
tion systsir. i.-.rcush tr.s siir.pung train it
0.4-0.6 ii.er ;r.:n. Use a sarr.pie time of be-
twsen 10 ar.i 30 rr..r.u:es sum that a total
n?t aiscrbases cst-.ve?r. O.l ara 1.0 ibsor-
cr.r.:e -r.;.s u c=;a:r.?s. A: ar. O concentra-
-,.z- c; O.l ppm ar.a a sa.— p.:ne rate of 0.5
:::e" r.ir.. a total r.?: assorpar.ce ifl.l aosor-
bar.rr v.r.i:s ir.3.:= :e -;-ainsi if a sa—.pl.n?
::r.-.? cf CD rr..r.i::r.= ar.c l-crr. 3-e;:rop.-.oto-
m?:?r cjlls ar? us?2. lrr.rr.*C'.2ts:y after col-
!e:".:3n. :ran?fsr :he expcssd soluiior^ to
c.iir. rpsctroihsiometir ?»i:s Determine
•.::? net sosoriar.cs -aamp.e abssrbar.ce—'.in-
rxposei rvag?n: ao.ssrbance• of each solu-
tion at 352 nm a-.thin il'.ree minutss. Add
the net aosorbances of the f.vo solutions to
obtain the ;cta: rset absorbance.
4.5.4 Calculation of ozone concentration.
4.5 4.1 Calculate the '.ota: volume of air
s.-mp:ed. corrected to re.'erer.ce cor.ou.ons
of 25 C ifia T'60 torr zs:
V,.?,xt,
where:
", = volume of air farr.pied. corrected to
reference cononisr.s. liter
F^s.-arr.pi.rc flowrate -orrected to refer-
or.
^; O, = mole L.\24.47x10*
4.5.4.4 Calculate the O- concentration ;n
ppm as:
4.5.5 Hr?#.\t :t#5S -1 ; 3
cr.t mor? :.m* r.t ::-.r <:i:-.;r
i:ng. Averace i..e tv>o •:.-
f.ons and r-£:o.-i: ::'.e a^cra
C; generator set:.:n?.
4.5.S Adjust :he O. j
other Ci concjr.trationi
range. Determine each
us;n< :.x.e procedure -rive
more Oi concentrations a
?'.ot trir C. cor.cer.i ri; .;r.s
spcr.din? O, ser.entcr =..-:t
O: gsr.sraior cajitra;.o
oration of :.he ozone ar.aiy
4.5.1 Allow su;:ic:sr.t ti
lyzer to .varrr.-up and i:a::
r.t:-a:cr :o ooia;r.
ever :.-,e z?s:Tf.~
Oi concrr.'..-:u!or.
r, above. FY. e or
re rerom.v.er.aed.
Ai:;-v '.h
'.he O- a:-.
zer1: air ur.::! a s:a:u' r?s
a-i aci;uat t::e O- ir.aiyx
Offsetting the ar.a:y;..*i j
-5-~ of :ca:e .s reccrr.m-.
obssr-.r.g nryatsvs :=-ro
itaole zsrc a;r respor.i-' ?.s
4 6.3 Vs:r.s T.? O. : .-.— --.<
?ro ac.i':s;m-. ".'. '.o
centrat-.or. near 80'" of
rinse limit 'URL) of .he
4.6.4 Ai!o-.v the O- .ir.
this O- concentration ant:
:s obtairrd. Adjust the :r.
-.ro! '.c ostain a conven
spor^e ij ;nc:cate-: soiow:
"r;;t. P.ecora ;r.e
"Z"
ra-.cr ?..- cr.;-crnt--j
r.**rdtr ?.r. 0 *on-
-..-,•; Ss.'s-.r'-d -pper
- analyzer.
.r.lvur to 'ample
?. stabse response
.al\-s?r's -car. con-
ior.-. rc-ccrcer re-
:0i3r<.- * * concentration at the output mani-
fold. PPT. URL m upper ranze :srs:t of
the O- anaivrer. :om. Z = recoraer re-
spor.se '.x-jth zero ».r. ~< icale
28
-------
PRC?O2cD 3UIES
tra:
0'. '-•
ac
6.5 Ge:
lions (at
.- trie ic.
•.e.-aie
.i/as; 5
severa
others
I other O, concen-
; are recommenced)
irte O, ar.aiyier by
quired. The flowrate chrough
ator
-------
25961
O, concentn::ons us-.n? -.he Procter.-* :n -i.i
•A'tuje simultaneously measuring Che corre
spending O, analyzer responses as specified
IT. 4.5,
RETTRENCES
1. D I_ Hamm. "Analysis of Ozon? at Low
Concentration -A-itri 3or:c Ac:c 3-.::fereo
KI." £.Ti-tron. S«. recAnoi.. ;.'. 973US77..
2. 3. E. Sa!i:s»ar. and N Gilb-rr. ••lodorne-
:ric Micrpdeternur.ation of Orjar.ic Os1-
oanis iso Ozone." And Chen., 3i. 19M
(195S).
3. J. ?. Lodge. Jr.. J. 3. Pa-.e. 3. E.
Ammons. and O. A. Siranson. "The Use of
HypooersHC Needles « Cntieai Or.fices in
Air Sampling." J. Air Poll Control Assoc.,
:S, 197 (1966).
v
4. "Transfer Standards for Calibration of
Ambient Air Monitoring Analysers for ,
Ozone." EPA P-jbiicitson avaUasie *y.-.rru; > , . -(delete "in drart T
t*nx- from EPA. Department E MD-X).
Research Triangle Park. N.C. 2'~li. -ft
30
-------
PROPOSES R'JuiS
n "
\j
ZERO
AIR
FLOW
CONTROLLER
F0
03
r.E'.EF.ATOR
!
!
, t N T
V.-'.'rDLO
EXTRA OJTLETSCAPPEO
:.HE\ r.QT l\ USE
TO I'.LET OF
TO T.LET Of A
31
FEDERAL REGISTER, VOL 43, NO. 171-THURSDAY, JUNE 22, 1978
-------
•V c : 0 LI
30 ml ."l.i
10 ml . j ...
30ml
~Tt*
20 mi _fU
10 ml .1 U
'L'BSiS
SEPTUM
MEMBRANE
FILTER
CRITICAL ORlFICt FLOW CONTROL
I.V.?iS'GE'.S
:SEH 5ELOVYJ
10 mm O.D.
? 2- 40 CO.'.'CE'.'TRiC'.MTH
O'Jli?. ?l£C2 A?JD WITH
NOZZLE
GRADUATIONS AT 5-ml
INTERVALS. ALL THE
WAY AROUND
GLASS ,' *- \
~
WOOL/,/^Vv\ {
TR-P
1 5
Jt, • J -
t ' ' ^ s-v?
i fi££3L2 VALVE
FLO'.V.VETE?.
3 "0 5 Tin
0 D
NOZZLE ID.EXACTLY
1mm: PASSES 0.09 TO 0.11
cfmAT12m H?0 VACUUM.
.PIECES SHOULD 3E INTER-
CHANGEABLE MASNTAI.NINC
NOZZLE CE^JTERi'JG A;iO
CLEARANCE TO BOTTOM
I.'JSIOE SURFACE
ALL GLiSS VlOGET !.V,P!.';G£5 THIS :S A COV.VS
STOCKED IT£V.!.
32
KOIUAl R8GIS7E8, VOL. 43. NO. 121—THU«SOAY, JUN6 22, 1978
-------
26934
FLOW
CONTROLLER
FIOV.V.ETER
F0
*
03
GENERATOR
i \>T -*
I <
f '!
CXTRi
iVHir. \CT i;. USE
OUTPUT
V.ANIFOLO
TQIfJLtT OF
HI SAMrLIXG TRAIN
TO ir.'LET of A:;ALVZER
U'.'OEH CALIBRATION
[FR Coc 7S-lTi54 F'.'ifc 6-21-TE. £:45 am)
33
FEDERAL REGISTER, VOL 43. NO. 121-THURSDAY, JUNE JZ 1978
-------
Title
-------
EFFECTIVE DATE: This rulemaking is effective upon publication oecause
the revision of the national standard to which it relates is effective
inrediately.
ADDRESSES: U.S. Environmental Protection Agency, Office of Air Quality
Planning and Standards, Control Programs Development Division (MD 15),
Research Triangle Park, North Carolina 27711.
FOR FURTHER INFORMATION CONTACT: Joseph Sableski, Chief, Plans Guidelines
Section, at the above address or.at 919-5^1-5^37 (commercial) or
529-5^37 ;F~S).
SUPPLEMENTARY INFORMATION
1. BACKGROUND
On June 22, 1978, at 43 FR 26985, EPA proposed certain revisions to
40 CFR Part 51 concerning the procedures for preparation of State Imple-
mentation Plans for photochemical oxidants. This proposed action was
taken simultaneously with related EPA proposals in the same issue of the
FEDERAL REGISTER to numerically revise the primary photochemical oxidant
standard, to redesignate the primary and secondary standards as ozone
standards, and to chance to standards with a statistical form rather
than a deterministic form (43 FR 26962); and to replace the existing
calibration procedure for the ozone reference methods (^3 FR 26971).
A total of four public hearings were held during July and August to
receive comments on all the actions being taken relative to photochemical
oxidants (ozone). In addition, written comments were received through
October 16. EPA received comments on the proposed revisions to the
-------
-implementation requirements from 27 commenters, including 12
representatives from industry, 10 from State and local governmental
agencies, and 5 rrom citizens' organizations and crivate citizens.
2. SUMMARY OF COMMENTS AND RESPONSES
The following discussion summarizes the comments received on the
proposal to amend 40 CFR Part 51. In some cases, similar comments are
considered together in order to prepare a common response where appro-
priate. Where an interested person wishes to identify individual
consents. a summary of all comments received, including those cc~r,en.ts
pertaining to the other related actions, and EPA's responses is available
for public inspection in Docket No. OAQPS-78-8 on file in EPA's Central
Docket Section, Room 2903-B, 401 M Street, S.W., Washington, D.C. 20460.
2.1 CONTROL STRATEGY
Two regulatory changes are being made with regard to the development
of control strategies for ozone. First, Appendix J is being replaced
by four analytical techniques. States must use one of the four technicues
to determine the amount of hydrocarbon reductions necessary to demonstrate
attainment of the national ozone standard. The four techniques include:
(1) Photochemical dispersion models, (2) Empirical Kinetics Modeling
Approach (EKMA), (3) Empirical and Statistical Models, and (4) Propor-
.tional Rollback. EPA received several comments related to these analytical
techniques. These comments and EPA's responses are presented in this
section.
-------
The second chance provides that States must consider beckgrounc
ozone concentrations and ozone transported into an area in the develop-
"•ent of their control strategies. Previously. Ststes were allowed to
assume that there were no background ozone concentrations. The considera-
tion of ozone background and transport may significantly affect the
calculated control requirements under certain circumstances; in some
cases, however, the net impact on control requirements is relatively
insignificant. A discussion of these effects and procedures ~or taking
background and transport into account is provided in the EPA document
entitled Uses, Limitations and Technical Basis of Procedures for Quantifying
Relationships Between Photochemical Oxidants and Precursors (EPA-450/2-
77-021a). EPA did not receive any comments expressing opposition to
this particular change; however, a number of comments were made concerning
the contribution of both natural background and ozone transport to
ambient ozone concentrations. Comments concerning transport are handled
in this section. Some of the comments concerning natural background
levels are discussed in the preamble to the 40 CFR Part 50 notice promul-
gating the new ozone standard which appears elsewhere in this issue of
the ^EDERAL REGISTER. Other comments on natural background are contained
in the docket (No. OAQPS-73-3) containing information used by EPA in
revising the ozone standard.
Several commenters criticized the analytical technioues proposed to
replace Aopendix J, citing various shortcomings of the techniques! Some
commenters pointed to the failure of the EKMA and rollback techniques to
account for temporal and spatial distributions of sources in the design
-------
o' control strategies and pointed out that, since control of in
sources will be extremely costly, the most effective models should be
used in strategy develooment. One conimenter indicated that the level CT"
control necessary to achieve the standard coulc not be predicted v.ith a
satisfactory level of confidence since the various techniques produced
different results. EPA acknowledges the fact that the various techniques
do produce different results since different assumptions and different
data bases are required for each specific node!. Also, EFA agrees that
centre! strategies should be based on the nest effective models. However.
effectiveness is in part determined by the cost of gathering input data
and running a model. If simple models, such as rollback, indicate the
need for extensive controls, EPA feels it may not be necessary to expend
additional time and resources to gather the information needed to run a
more sophisticated model which would reach the same general conclusion.
A sophisticated model, i.e., a photochemical dispersion model, would
appear to be most warranted in cases where there is some doubt whether
extensive controls are needed to attain the standard. EPA requires that
States attempting to demonstrate attainment and maintenance of the
revised ozone standard by 1982 without adopting reasonably available
control technology (RACT) regulations for large hydrocarbon sources rcust
employ photochemical dispersion modeling. The use of other less rigorous
analytical techniques are only acceptable in areas where RACT measures
are also scheduled for implementation. Where States are unable to
demonstrate attainment by 1982, EPA believes any of the models are
-------
•jse~ul for indicating the magnitude of the ozone problem and for identi-
fying the need for major control programs to be implemented over the
next several years. As these control programs are implemented and the
State moves closer to attainment, it is likely that sufficient information
will be acquired to use dispersion models to adjust the control strategy.
Additionally, it should be noted that the city-specific version of EKMA
can account, to a limited extent, for temporal and spatial distribution
of sources.
Another concenter stated that the annual emission inventory -.ay not
be readily adaptable to the models and to refine the inventory into
hourly segments may be very costly, time-consuming, and inaccurate. In
response, EPA points out that of the techniques specified, only photo-
chemical dispersion models require a detailed emission inventory to
arrive at their predictions (with the exception of the more sophisticated
city-specific version of EKMA which can consider emission data). The
other techniques primarily utilize ambient air quality data. At the
same time, EPA recognizes the importance of an accurate emission inventory
in translating the requirements forecast by these simple models into
actual control programs. For example, suppose EKMA predicts that a 70
percent control requirement is needed to meet the standard. If the
emission inventory only includes 50 percent of the emissions, a 70
percent reduction in the inventory would only result in a 35 percent
reduction in actual emissions. Photochemical dispersion models, on t^he
other hand, do require explicit information concerning hourly emissions.
It would obviously be impractical to make hourly measurements for every
-------
source. However, hourly rates can be estimated by suoeriirposirc observec
diurnal emission patterns on annual average emissions. Such patterns
have been observed i^ several cities so that it ,/ould be possible zc
utilize annual emissions data.
Several persons commented that there is an inadequate understanding
of the relationsnip between hydrocarbons and ozone, and that controlling
hydrocarbon emissions may or may not be effective in reducing maximum
ozone concentrations. This particular issue was addressed in a recent
published report for the "Manufacturing Chemists Association (!-:CA)" .-.-hicr,
c
noted a lack of any clear downward trend in Houston's ozone levels
despite control measures to reduce hydrocarbons. This report concluded
that existing ambient air quality data do not necessarily support the
hypothesis that reducing hydrocarbon emissions reduces ambient ozone
levels. At least two difficulties exist which prevent straightforward
-interpretation of the study's findings. First, the period of record was
relatively short (two to three years of data) and no attempt has been
made to normalize the trends for meteorological differences. It is
generally believed by EPA that at least a five year period of record may
be needed to discern a trend in air quality attributable to changes in
emissions. A recent review of ozone trend data conducted for EP- in
areas having long periods of records suggests that periods as long as
eight years may be required.3 Thus, while efforts are underway within
EPA to develop procedures for "normalizing" trends for differing mete-
orology during short periods of record, at the present time trend analyses
are useful in only a limited number of areas. The second difficulty in
-------
using the conclusions drawn from the study is that it appears as though
some of the controls may have been initiated prior to any substantial
air quality measurement programs.
EPA believes that convincing evidence exists to say that reducing
hydrocarbons will reduce ambient concentrations of ozone. This position
4-15
rests primarily upon experimental and theoretical studies which have
clearly established a physical cause-effect relationship between organic
ocllutants and ozone in the presence of oxides of nitrogen. Snog chamber
studies nave shown that maximum ozone concentrations are particularly
sensitive to hydrocarbon controls when the ratio of non-methane hydro-
carbons (NMHC) to nitrogen oxides (N0x) is lower than 15-20:1. In fact,
the lower the ratio the more effective the hydrocarbon strategy is
likely to be. Examination of available NMHC and N0x data suggests that
most U.S. cities experience ratios in the order of 5-12:1. Also, there
is a limited number of areas having ambient air quality data and emission
estimates over sufficiently long periods of record that tands to confirm
the theory of smog formation. '
Two commenters indicated that a consequence of relaxing the standard
could be the change of some urban areas from nonattainment to attainment
status, thus, permitting greater hydrocarbon emissions than allowed by
their fcroer status. In one case the commenter argued that prior to
revising the standard EPA should ascertain that existing downwind viola-
tions would not be further aggravated. The other commenter opposed the
revision because, when coupled with current EPA control strategy policy,
more of the burden of control would be shifted to the States where ozone
-------
is measured end away from States where emissions originate. E?~ does
not believe that consideration of such arguments is appropriate in
setting the national oriirary ambient air cuality standard, "re C",ear.
Air Act requires that primary standards be based solely upon effects on
public health. However, the consequences indicated by the commenters
are appropriate for consideration in the formulation of policy and
guidance to assist States in developing a control strategy to meet the
standards. EDA does not believe that either concern is warrantee for
areas that could be classified as'attainment based on the new ozone
standard. Two basic reasons exist for this EPA position: first, the
potential increase in the transported levels of ozone, which may occur
as a result of the greater emissions permitted by the new standard, will
be offset by the equally increased allowable level of ozone in the
downwind areas. Second, it should be noted that future levels of ozone
being transported from attainment areas will tend to be reduced as a
result of the Federal Motor Vehicle Control Program which requires
reductions in the emissions of hydrocarbons and nitrogen oxides from new
motor vehicles, and control requirements applicable to new stationary
sources which will, in some instances, replace existing sources having
fewer, less effective controls.
-------
E-A is concerned, however, that the transport of ozone ~ey be a
problem when it originates in areas for which insufficient monitoring
data orec'ude classifying the area as either attainment or nonattainment.
EPA is now taking steps to identify areas which are currently unclassified
but which have a high potential for exceeding the national ozone standard.
Within such areas, States will be urged to require controls on existing
large stationary sources. If controls are not subsequently adopted, the
States will be required to monitor for ozone, whereupon, the area in
question will be classified ncnattainment if violations are identified.
These areas would then be subject to the requirements to control hydro-
carbon emission's from existing stationary sources as in other nonattain-
ment areas. EPA believes that the present policy focuses the limited
resources of air pollution control agencies and industry on the areas
(i.e., nonattainment areas) where the controls will be most effective.
One commenter suggested that the chemical diethylhydroxylamir,e
(DEHA) be dispersed in the atmosphere to scavenge free radicals as an
effective means of controlling ambient concentrations of photochemical
oxidarts. The use of various free radical scavenger compounds has been
suggested in the past as a means of reducing pollutant concentrations;
however, no compound has yet been demonstrated to be completely accsotable.
Sefore this approach to controlling air pollution can be seriously
considered, comprehensive studies must show not only that the chemical
employed is effective in laboratory studies, but also that the results
can be extrapolated to actual ambient atmospheres. Such concerns'as
how, when and where to introduce the chemical to the atmosphere-constitute
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problems whose solutions can be extremely difficult to derive, -ur-e-cre
thorough consideration must be given to the potential hazards of exposing
a Dooulat^on to a s:-oc-inhibiting cherrical or to any of its reaction
products. One of the earliest suggestions for using DEHA carne as a
result of its ability to inhibit conversion of NO to N02. Consequently,
various tests of DEHA's smog-inhibiting ability have been performed over
the past several years. Recently, irradiation of mixtures of NO , HC
and DEHA was carried out in a large srr.og chamber at E^A.'s Research
Triangle Park, ;iorth Carolina, facility. Test results incicatec zhat
while the initial effect of adding DEHA is an immediate suppression of
ozone formation, consumption of the chemical ultimately causes increased
formation of ozone and ozone producing chemicals. The studies pointed
to possible adverse impacts on rural areas downwind from the urban
center as well. Further problems raised by the studies included, among
others, the danger of exceeding the odor threshold of DEHA at certain
"effective" atmospheric doses, and population exposure to an unknown N'O
A
on
product being formed by the DEHA reactions. Obviously, EPA cannot at
this time accept or encourage the use of DEHA as an effective control
strategy for ozone. Instead, EPA believes that direct control of precursor
emissions will result, in greater and more certain improvements in air
quality.
Several commenters claimed that the ozone problem is an urban
problem and EPA requirements for control strategies should concentrate
on the urban area while paying special attention to the present levels
of NO and the NMHC/NO ratio. EPA agrees that the ozone attainment
X A
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orobler. is primarily an urban problem. Consaauently, the most stringent
requirements are imposed in the urbanized nonatiainment areas with a
DCDolc-ion greater than 200,000. Low NMHC/MO ratios primarily occur in
me urbanized areas, thus the required controls would be effective 'in
controlling ozone levels. However, EPA does not feel it is appropriate
to completely ignore hydrocarbon emissions outside the urbanized nonattain-
ment areas because these emissions may contribute to the overall ozone
nonattainment problem, particularly during adverse meteorological conditions,
Er.- "nerefore believes it is justified in requiring that large hydrocarbon
sources (more than 100 ton/year potential emissions) in rural nonattain-
ment areas implement reasonably available control techniques (RACT) to
reduce their organic emissions.
One commenter claimed that EPA failed to issue timely guidance on
control techniques as required by the Clean Air Act and as needed by
States in revising their implementation plans. The commenter's argument
is based on Section 108(b)(l) of the Clean Air Act which requires control
technique information to be issued simultaneously with the issuance of
health and welfare related air quality criteria. EPA did issue the
control technique information required by the Act in a document entitled
''Control Techniques for Volatile Organic Emissions from Stationary
Sources (EPA-450/2-72-C22, May, 1978). However, this was not the infor-
mation which EPA intended States to use to develop and enforce regulations
for implementation plans. In addition to the document described above,
EPA has published a series of Control Technique Guidelines (CTGs)'which
/
define reasonably available control technology (RACT) for stationary
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sources of hydrocarbons. These CTGs are sceci-ically designed tc assist
States and local agencies in the development of air pollution control
•'eculations for volatile'organic emissions. The ozone SI-s sue on
uanuary 1. 1S79 are to reflect the application of RACT to the stationary
sources for which EPA has published CTGs by January, 1978. Additional
CTGs are planned for future publication such that States will be required
to adopt and submit additional RACT regulations on an annual basis
beginning in January, 1980, for those CTGs that have been published by
January cf tne rrecesdinc year.
One commenter inquired as to why the proposal did not retain the
original statement contained in Section 51.14(c)(4) which allowed States
to assume that the hydrocarbon emission reductions necessary to attain
the ozone standard would also be adequate to attain the national hydro-
carbon standard. EPA's response is that this statement was uninten-
tionally omitted from the June 22 proposal, and this omission is being
corrected in today's action. Previously, statements concerning the
attainment of the ozone standard and the hydrocarbon standard were both
contained in Section 51.14(c)(4). To take the actions described herein,
EPA is deleting (and reserving) paragraph (c)(4) of Section 51.H and
establishing three new paragraphs (c)(7), (c)(8), and (c)(9). Paragrach
(c}(7) is to be used to set forth the four analytical techniques for
determining the amount of hydrocarbon reduction necessary to demonstrate
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attainment of the ozone standard; paragraph \c}(B] describes specific
considerations to be made in developing the ozone control strategy; and
oaragraph (c)(9- addresses attainment of the hydrocarbon standard.
2.2 SUSf-'ITTAL OF SI? REVISIONS
Several industrial and governmental agency spokesmen expressed the
opinion that EPA should grant States extensions of up to nine months to
correct their SIPs to be consistent with the revision of the ozone
standard. EPA's response to this request is provided in detail in the
"rea-cle to the revision of the ozone standard aopearing elsewhere in
today's FEDERAL REGISTER. In summary, States are still expected to
submit their plan revisions to EPA on January 1, 1979, as required by
the Clean Air Act. These plans will most likely be based upon the old
standard of 0.08 p.p.m. However, once submitted, any State is free to
n^a.ke the additional revisions necessary to account for the revised
standard, if they so desire. Thus, the time schedule for submitting the
latter revisions is to be determined by each State.
3. OTHER CHANGES FROM PROPOSAL
In reviewing the June 22 proposed rule, EPA. has determined that two
changes from the proposal are necessary even though no comments addressing
these particular matters v/ere received. With regard to the first cnange,
EPA originally proposed to change the terrcs "photochemical oxidants" and
•'oxidants" to "ozone" in 40 CFR Parts 51 and 52 to be consistent with
the proposed redesignation of the photochemical oxidant standard to an
ozone standard. EPA has decided not to proceed with the proposed nomen-
clature changes in Part 52 at this time. The reason for this decision
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is that in numerous places throughout Part 52 the terms "photochemical
oxidants" and "oxidants" are used either as part of the title of a State
Implementation Plan or to denote use of the terms within the plan
itself. EPA therefore, feels that it would be proper to wait until
States made the appropriate nomenclature changes in their plans prior to
enacting any changes to Part 52.
The second change concerns EPA's proposal to allow States to use
photochemical orjd models as one of four analytical techniques for
r
determining the needed hydrocarbon emission reductions. The intended
terminology for such models should have been photochemical dispersion
models. There are two major types of dispersion models grid (or
Eulerian) and Lagrangian. EPA intends to allow either type model to be
used where appropriate. Thus, the more inclusive terminology (i.e.,
photochemical dispersion models) will appear in Section 51.14(c)(7)(i).
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4. REFERENCES
1. Uses, Limitations and Technical Basis of Procedures for
Ci.ar.fi "yinc Relationships Between Photochemical Cxidants and -recursors,
'„.$. EDA, Research Triangle Park, N.C. 27711, EPA 450/2-77-021a,
November, 1977, p. 31.
2. Examination of Ozone Levels and Hydrocarbon Emissions
Reduction, Final Report, OCN 77-100-151-04. Prepared by the Radian
Corporation, Austin, Texas, for the Manufacturing Chemists Association,
Washington, D.C., November, 1977.
3. l-.'ayne, 1., et el., Detection and Interpretation of Trends
-in Oxiaant Air Quality, Prepared for U.S. EPA by -acific Environmental
Services, Santa '-Icnica, Calif., E?A -5C/3-75-034 (October, 1975).
4. U.S. Department of Health, Education and Welfare, Air
Quality Criteria for Photochemical Qxidants, AP-63, (March, 1970),
Ch. 2.
5. Altshuller, A.P., and J.J. Bufalini, "Photochemical Aspects
of Air Pollution: A Review," Environmental Science and Technology,
5, 39 (January, 1971).
6. Dimitriades, 3., Photochemical Oxidar.ts in the Ambient
Air of the-United States, U.S. EPA, Research Triangle Park, N.C. 27711,
EPA 500/3-76-017, \February, 1976), Ch. 3.
7. Air Quality Criteria for Ozone and Other Photochemical
Oxidants, volume I, U.S. EPA, Washington, O.C., EPA 6QO/3-73-C04,
(April, 1973), Ch. 4.
3. Dimitriades, 8., "Effects of Hydrocarbon and Nitrogen
Oxides in Photochemical Smog Formation," Environmental Sciences
and Technology, 6, 253 (1972).
S. McCracken, M.C., et al., Development of an Air Pollution
Model for the San Francisco Say Area. Volume I, .'IT'S Ho. -JCP.L-31920,
(October, 1975).
10. Dodge, M.C., Combined Use of Modeling Techniques and Smog
Chamber Data to Derive Ozone-Precursor Relationships, U.S. EPA,
Research Triangle Park, N.C. 27711, EPA 60C/3-77-001b, p. SSI,
(January, 1977).
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11. Dimitriades, B., "Oxidant Control Strategies, Part 1: An
Urban Oxidant Control Strategy Derived from Existing Smog Chamber
Data," Environmental Science and Technology, 11, p/80 (1977).
12. Anderson, G.E., et al., Air Qua!ity in the Denver ''etro-
colitan Region 197^-2000, Prepared for U.S. EPA by Systems Aoplicetions,
Inc., San Rafael, Calif., EPA 908/1-77-002, (Kay, 1977), Ch. 2.
13. Seinfeld, J.H., and K.R. Wilson, International Conference
on Oxldants, 1976 - Analysis of Evidence and Viewpoints. Part VI,
The Issue of Air Quality Simulation Model Utility, EPA 600/3-77-118,
(November 1977).
14. Air Quality Criteria for Ozone and Other Photochemical
Oxidents. Volume I, U.S. EPA, l-.'ashinoton, D.C.. EPA 600/8-78-OC^,
(April. 1978), Ch. 6.
t
"'5• Guideline for the Evaluation of Air Quality Trends,
Guideline Series OAQPS No. 1.2-014, U.S. EPA, Research Triangle
Park, N.C. 27711, (February 1974).
16. Altshuller, A.P., "Evaluation of Oxidant Results at CAMP
Sites in the United States," Air Pollution Control Association Journal,
25, 19 (January 1975).
17. Trijonis, J.C., et al., Emissions and Air Quality Trends
in the South Coast Air Basin, EQL Memo No. 16, Environmental Quality
Laboratory, California Institute of Technology, Pasadena, CA 91125.
18. Gise, J.P., Recent Ozone Trends in Texas, AICHE, 83rd
National Meeting, Houston, Texas, (March 1977).
19. Trijonis, J., et al., Verification of the Isopleth Method
for Relating Photochemical Oxidant to Precursors, Prepared for U.S.
EPA by Technology Services Cooperation, Santa Monica, Calif., EPA
600/3-78-019, Ch. 2-3, (February 1978).
20 Cupitt, L.T., and E.W. Corse, Status Report and DEHA
Experiments, Technical Report Prepared for U.S. EPA by Northrup
Services, Inc., Research Triangle Park, ri.C. 27711, ESG-TR-78-17,
Section 3, (December 1978).
Administrator
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The Code of Federal Regulations, Title 4C, Chapter I, Dart 51. is
amended as follows:
1. Wherever the terms "ohotocheniicai oxidant(s):i or ''oxidant(s)"
appear in Part 51, they are changed to read "ozone."
2. Appendix J is deleted and reserved.
3. Section 51.14(c) is amended by deleting and reserving paragraph (4)
and by adding new paragraphs (7), (8) and (9) as follows:
§ 51.14 Control strategy: Carbon monoxide, hydrocarbons, ozone,
and rntrcgen dioxide.
* * * * *
(c)
(4) [Reserved].
* * * * *
(7) In selecting an appropriate model to determine the amount of
hydrocarbon reductions necessary to demonstrate attainment of the ozone
standard, one of the following techniques must be applied:
(i) Photochemical dispersion models - These models are based on
the most accurate available physical and chemical principles underlying
the formation of ozone.
(ii) Empirical Kinetics Modeling Approach (EKMA) - This .Tiodel
represents a compromise between rigorous treatment of chemical and
physical principles underlying ozone formation and dispersion and the
extensive data requirement that would be necessitated by such an approach,
/ i
(iii) Empirical and statistical models - These models reflect
observed relationships between ozone and other variables.
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(iv) Proportional rollback This model assumes a linear relation-
ship between hydrocarbon emissions and ambient concentrations of ozone.
(2) In developing an ozone control strategy for a particular area,
background ozone concentrations and ozone transported into an area must
be considered. States may assume that the ozone standard will be attained
in upwind areas.
(9) The degree of total hydrocarbon emission reduction necessary
for attainment of the national standard for ozone will also be adequate
for attainment of the national standard for hydrocarbons.
AUTHORITY: Sections 110 and 301(a), Clean Air Act, as amended (42
U.S.C. 7410, 7601).
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