ASSESSMENT OF WELFARE EFFECTS AND THE SECONDARY
AIR QUALITY STANDARD
FOR OZONE
June 1978
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
U. S. Environmental Protection Agency
Research Triangle Park, NC
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Table of Contents
Section Page
I. Summary 3
II. The Need for a Secondary NAAQS for Ozone 6
III. Effects of Ozone and Other Photochemical Oxidants 7
A. Vegetation Damage 7
1. Monitoring Methods and Data Reliability 7
2. Foliar Injury 9
3. Growth and Yield Effects 13
4. Pollutant' Interactions and Ambient Exposures 16
5. Economic Assessment 17
6, Effects on the Natural Environment 18
B. Materials Damage 21
IV. Air Quality Issues 25
A. Sources and Concentrations of Oxidants in Ambient Air ... 25
1. Sources 25
2. Urban Oxidant/Ozone Levels 25
3. Rural Ozone Levels 26
4. Natural Background Levels 27
5. Levels of Non-Ozone Oxidants 31
B. Averaging Time Considerations 32
1. Discussion of Issues 32
2. Prediction of Averaging Time Distributions 33
3. Synthesis of Averaging Time and Foliar Injury Models. . 35
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• I I •
Standard Levels for
I I • • •
Standard Levels for
. . . . .
38
• 38
38
• 38
• 40
45
46
47
52
53
63
88
• • . . • . 92
• 94
Page
Section
‘I. Analysis of Alternative Secondary NAAOS
A. Pertinent Issues
B. Analysis of Options
1. Change from Deterministic to Statistical Form of
Standard
2. Analysis of the Chemical Species Designation of the’
39
/‘Standard I......
3. Analysis of Alternative
Vegetative Effects
4. Analysis of Alternative
Materials Effects •
C. Conclusion .
VI. Citations
Figurel—lO •
Tables 1 through 10 , . .
Appendix A
Appendix B
Table B—l . . . .
Table B—2
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I. Summary
The Clean Air Act mandates the setting of a national secondary ambient
air quality standard to protect the public welfare from any known or anticipated
adverse effects associated with the presence of an air pollutant in the ambient
air. Ozone and other photochemical oxidants constitute a form of air pollu-
tion that affects vegetation and materials. The resultant economic loss
has been estimated to be in the range of several hundred million dollars. per
year nationwide. Nonquantifiable losses to the natural environment occur
as well.
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 symptom of ozone
exposure and for this reason has commonly been used in attempts to
quantify damage to economic crops. Decreases in growth and yield can
occur without such visible symptoms; however, since leaf injury is the
most readily detectable and frequently reported symptom of ozone damage,
this effect provides the best available data base for evaluating alter-
native standard levels. While it is not currently possible to make
definite correlations of foliar injury with reductions in yield, several
investigators have 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.
Ozone exposures which may be reasonably expected to produce injury
ratings within this range in commercially important crops or important
indigenous flora are undesirable; therefore, the basis of the secondary National
Ambient Air Quality Standard (NAAQS) for ozone will be to protect against
such exposures.
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The effects of ozone on vegetation are not linearly dependent
on the dose (product of concentration and exposure duration) sustained
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. A mathematical
model has been used 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. Based on these results, no
commercially important crop is predicted to receive more than 3 percent
leaf injury as a result of short—term peak ozone exposures at sites where
an hourly average concentration above 0.08 ppm is expected to occur only -
once per year. Such a level of air quality should thus protect agricultural
crops from detectable effects on growth and yield due to short-term peak ozone
exposures, even after allowing for possible interaction between ozone and
other air pollutants. In addition, studies which have examined the effects
of long-term, intermittent ozone exposures.on. growth and yield of vegeta-
tion indicate that no detectable effects should occur as a result of the
long—term pattern of ozone exposures anticipated when an hourly average
concentration of 0.08 ppm is expected to be exceeded only once per year.
It should be noted that the above predictions were based on air quality
— relationships (e.g., the ratio of the 1—hour—average peak concentration to
the corresponding 8-hour-average value) which were judged to be representative
for urbanized areas where an hourly average concentration above 0.08 ppm is
expected to occur only once per year. Equivalent relationships for rural
areas have not been quantified, yet there is reason to believe that higher
8-hour-average concentrations may occur at a rural site than at an
urban site when both are attaining the same hourly average standard. EPA
has attempted to factor this uncertainty into its analysis of alternative
hourly-average standard levels, but is soliciting coments as to whether the
standard should be set for an averaging time of 8 hours rather than 1 hour in
order to insure the protection of vegetation in rural areas.
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Material damage due to ozone can be described as an acceleration of
aging processes, e.g., rubber cracking, dye fading, and paint weathering. In
contrast to the effects of ozone on vegetation, these effects appear to be
governed in a linear fashion by the ozone dose sustained by the material.
As a result, the annual average concentration will determine the rate at
which material damage occurs, and any nonzero ozone concentration (including
natural background levels) will contribute to the deterioration of sensitive
materials if the exposure is sustained long enough. In remote areas selected
to be as free from man-made influences as possible, annual average ozone
concentrations are comparable with those seen in urban areas, due to strong
nighttime scavenging of ozone in urban areas by man-made pollutants. For
the above reasons, no effect-based rationale can be offered to decide the
level of the secondary standard needed to protect materials. As a result,
EPA proposes to evaluate the level of the secondary standard principally on
the basis of the air quality required to protect vegetation from growth and
yield effects, since there is no level at which some material damage will not
occur given sufficient time.
Based on the preceding considerations, EPA proposes to set the secondary
ozone air quality standard level at an hourly average concentration of 0.08 ppm
expected to be exceeded only once per year.
A review of air quality data in remote areas indicates that ozone concentra-
tions may occasionally approach and infrequently even go above the proposed
standard level in situations when man-made influences are negligible. These
events appear more likely to occur at higher elevations during the winter and
spring months. Comparison of this data with urban and non—remote rural ozone
data indicates that the bulk of the ozone problem observed during the surmier
months in the latter areas is due to man-made influences.
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II. The Need for a Secondary NAAQS for Ozone
As the major constituent of the air pollutant category termed photo-
chemical oxidants, ozone damages vegetation and materials to an extent
that endangers the public welfare. The nationwide economic loss sustained
at the farm level due to damage of vegetation by ozone and other photochemical
oxidants has been estimated to approach $300 million annually. At least
18 different crops can no longer be grown in the Los Angeles air basin
o
due to air pollution damage, predominantly oxidant damage. Much more
difficult to quantify are the. losses resulting from oxidant damage to
natural ecosystems such as forests. For example, long-term oxidant exposure
in the San Bernardino Mountains near Los Angeles has injured conifer forests
there, reducing timber production and affecting reproduction of the conifer
population, thereby diminishing the economic, recreational, and ecological
(life-support) value of this natural resource to the residents of the region.
In addition to its effects on biological systems, ozone accelerates
the aging process of materials, with cracking of rubber products being a
major example of this effect. A 1970 study estimated nationwide losses
at the consumer level due to both air pollution (ozone) damage to rubber
products and the costs of preventive measures to be $500 million annually.4
The above summary of the detrimental effects of ozone on both economic
and aesthetic aspects of public welfare demonstrates the need for a
secondary air quality standard to protect the public welfare. The following
sections provide detailed discussions of the scientific evidence regarding
ozone effects and air quality data, and finally an analysis of alternative
standard levels.
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III. Effects of Ozone and Other Photochemical Oxidants
A. Vegetation Damage :
1. Monitoring Methods and Data Reliability : Most plant scientists
measuring the effects of controlled ozone exposures or ambient oxidant episodes
on vegetation have used wet chemical (potassium iodide, or KI) methods for
monitoring the pollutant concentrations. 5 When monitoring ambient air, KI
methods respond to other oxidants besides ozone (O3) such as nitrogen dioxide
(NO 2 ) and peroxyacetylnitrate (PAN), and their response is diminished by the
presence of reducing compounds such as sulfur dioxide (SO 2 ). Ambient air
quality measurements obtained by XI methods have been designated as 1 boxidantsu
in this document. The Federal Reference Method (FRM) for determining whether
an area is attaining the current photochemical oxidant standard is an ozone-
specific monitoring technique. Its usage for attainment purposes is based
on the premise that ozone is the major component of the photochernical oxidant
mixture and can be measured as a surrogate (substitute) for oxidants. The FRM
eliminates several problems identified in KI methods, including those involved
in correcting for the impact of other pollutants and those related to
inaccuracies and imprecisions in KI techniques. 6
Because of the inherent variability of the KI methods, these monitoring
instruments must be routinely calibrated with respect to known ozone concentra-
tions. This is true even for controlled greenhouse or field chamber studies
in which plants are exposed to purified air to which only ozone has been added.
If these procedures are not followed, actual ozone concentrations may be
50—100 percent higher than the measured values. 5 The criteria document has
reviewed several studies comparing the KI and FRM measurement techniques in
ambient 3nvironments. While recognizing the limitations placed on such studies
by the imprecisions inherent in the KI methods, the document concluded that
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properly conducted KI measurements generally indicate levels of
oxidant comparable to or slightly higher than levels of ozone as measured
by ozone—specific techniques. 7 This conclusion is compatible with the
generally established premise that photocheniical oxidant mixtures consist
predominantly of ozone and lesser amounts of other non-ozone oxidants (such
as PAN.) 8
In view of the above discussion, data obtained it i vegetation studies
examining controlled ozone exposures or ambient oxidant episodes which
stipulate the use of calibrated K! or FRM monitoring methods have for the
purposes of this document been considered to be of superior reliability.
The analysis of alternative standard levels set forth in subsequent sections
has been restricted to such data. However, such well-specified studies are
not too plentiful, so this document has for illustrative purposes presented
some data from other studies which did not meOt this criteria. Studies
meeting the superior reliability criteria have been differentiated in this
document either expressly or (for convenience) by placing the symbol h’(+)”
after the concentrations being reported.
Finally, it should be noted that the current oxidant standard and much
ambient concentration data are stated on a mass concentration basis (in
micrograms per cubic meter, or ig/m 3 ), whereas essentially all of the
effects data are identified on the basis of molar concentrations (parts
per million by volume, or ppm). The relationship between these measurement
units is a function of temperature, pressure, and chemical species, but for
the purposes of this document conversions between these units were made at
standard barometric pressure (101.3 kilopascals) and 25°C and (in the case
of ambient measurements) assuming ozone to be the only oxidant present, so
that 1 ppm of ozone equals 1960 Jg/m 3 .
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2. Foliar Injury : Both short-term and long—term controlled exposures
of vegetation to ozone have resulted in reductions of growth and yield. 9
However,mostof the data discussing vegetative response to ozone, particularly
for short-term exposures, is based on visible foliar injury as the measure-
ment of response)° Acute leaf injury may result from short-term peak ozone
exposures, with some plants developing characteristic patterns of cell
destruction (e.g., upper surface fleck in tobacco and stipple in grape).
Long-term or intermittent exposures to low ozone levels can produce chronic
leaf injury such as chiorosis (loss of chlorophyll) or premature leaf aging
(senescence). These symptoms may be confused with those caused by natural
aging or other environmental stresses. 11
The National Academy of Sciences (NAS) has compiled a list 12 classifying
some 70 species and cultivars thereof as to their susceptibility to short-
term ozone exposures. Excerpts from this list are presented in Table 1.
Several important agricultural crops listed (e.g., alfalfa, bean, corn, oats,
soybean, and tobacco) have cultivars that are sensitive to ozone damage.
The importance of considering the variation of vegetative response to
*
different ozone exposure levels in the selection of an ambient air quality
standard has been emphasized by several researchers. 13 ’ 14 For instance,
Jacobson examined this issue in a paper 13 which reviewed the scientific
literature and summarized a large amount of data relating visible foliar
injury response to short-term ozone exposure levels. These relationships
This document uses the term “exposure level” to emphasize that both
the concentration and exposure duration must be specified to adequately
describe an exposure; it has been attempted to differentiate this concept
from that of “dose”, which tern has been used to indicate the product of
concentration and exposure duration.
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were presented for two types of vegetation (woody plants and agricultural
crops) in the form of limiting values which are listed in Table 2. These
limiting values depict the range of minimum exposure levels which have
been demonstrated to produce foliar injury in a variety of plant species.
Exposure levels in excess of the upper limits are likely to injure susceptible
species, such as certain bean and tobacco cultivars, while those below the
lower limits are unlikely to cause foliar injury.
The data utilized by Jacobson in formulating these limiting values were
derived from studies which at least specified the plant species tested, the
source of the pollutant, and the concentration and duration of exposure.
While these qualifications were a less rigorous set of data reliability
criteria than might be desired, they enabled the limiting values so derived
to be based on a large amount of data obtained by many different investigators. 13
Utilizing a somewhat smaller data set than Jacobson, Larsen and Heck 14
have examined the exposure level/vegetative response issue and presented their
findings in a manner which is quite suitable for the purposes of evaluating
alternative ozone air quality standards. They have suninarized the results
obtained from experimental short-term fumigations of several species in a
mathematical model that quantitatively predicts the extent of foliar injury
in specific crops as a function of ozone concentration and exposure duration.
This model permits analysis of the standard level to be conducted without
placing undue emphasis on results obtained with convuercially unimportant
cultivars (for instance, Bel W-3 tobacco). Also, by its prediction of the
extent of foliar injury associated with a given exposure level, the model
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permits some quantitative assessment of the severity of damage
which could be expected to accompany a given air quality standard.
A further advantage of Larsen and Heck’s model for use in the analysis
of alternative standard levels is the fact that they restricted their
evaluation of the model to data of superior reliability.
This model is based on the following assumptions: (1) a constant
degree of foliar injury is produced by exposure regimes wherein the
pollutant concentration varies in inverse proportion to the exposure
duration raised to an exponent, and (2) for a given exposure duration
the degree of foliar injury varies with the pollutant concentration in
a manner producing a log-normal frequency distribution. The equation
describing this model is:
cI m 1isi t (1)
L hrJI
where c is the concentration (ppm) expected to produce a degree of foliar
injury z standard deviations from 50 percent over an exposure duration of
t hours. The other parameters are constants to be determined for a given
species and cultivar from the experimental evidence. 14
This model was evaluated using condensed data obtained from a total
of several hundred replicate ozone exposures for 15 different plant species!
cultivars which vary considerably in their susceptibility to ozone damage.
The presentation of some specific data utilized by Larsen and Heck may
be useful for illustrative purposes. Exposure of Roma tomato to 0.075 ppm (+)
ozone for 2 and 4 hours produced,respectively, 1 and 10 percent leaf injury
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as an average for 12 replicate plants) 5 The median injury ratings
for 16 replicates of Pinto bean and of BeT W-3 tobacco were 11 and 57
* 1416
percent, respectively, following exposure to-0.l ppm- for 4 hours.
Seven-hour exposures of 4 replicate plants of Cherry Belle radish atid
Clintland 64 oats to 0.1 ppm (+) resulted in average ‘injury ratings of
39 and 15 percent, respectively. 15
Using multiple linear regression techniques to analyze the experimental
data, Larsenand Heck evaluated the model for each of 15 species/cultivars
to determine the parameters for’ equation (1-). Their results are presented:
graphically in Figure 1 as parallel lines of constant leaf injuryon plots
of ozone concentration versus exposure duration. A reasonablygood fit’ with
the experimental data is demonstrated; each number on the ‘plot gives the
median percent injury sustained by a set of plants subjected to the ozone
exposure level given by the coordinates of the decimal point of that number) 4
The leaf injury equation parameters for the’ 15 cultivars are presented
in Table 3, along with the injury threshold concentrations (arbitrarily
defined as that concentration producing 1 percent injury) for different
exposure durations, as calculated from the equations. The column listing’
the multiple correlation coefficients for each cultivar’s injury equation
parameters indicates a reasonably good fit with the data, since all but one
coefficient is above 0.88.
* 16 17’
The principal author of the original study has recommended
that the concentrations reported be multiplied by about 1.4 to correct
them to neutral buffered KI ozone values, which would make them comparable
to the rest of the data used by Larsen and Heck.
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A preliminary statistical analysis of this model by EPA 18 on the
basis of raw data presented by Larsen and Heck’ 4 indicated that there is
considerable variability in the biological response of individual plants
to a given ozone exposure level. For this reason, the model as presented
should hot be considered sufficiently precise to distinguish between median
injury ratings that differ by five percent or less in sets of plants
subjected to different exposure levels when the sets are of sizes comparable
to those examined by Larsen and Heck. It does seem adequate to indicate
injury trends and can probably be relied upon to distinguish statistically
significant differences between the median injury ratings of exposed sets
when they differ by six to ten percent or more. The lower side of that
range would apply when absolute injury ratings are in the vicinity of 10 per-
cent, and the higher side at 30 percent. Since the purpose of this document
is to weigh the impact of alternative secondary standard levels, the sort
of relative comparison that can be obtained from this model seems adequate,
and the model will be used in subsequent sections for that purpose.
3. Growth and Yield Effects : At this point, however, some discussion
of the significance of foliar injury is warranted. An examination of
Table 1 indicates that for many sensitive crops, such as alfalfa, broccoli,
clover, coleus, petunia, spinach, and tobacco, extensive foliar injury
could result in considerable economic losses since the foliar portions are
economically important parts of these crops. Their marketability might be
reduced by the appearance of injured leaves (as, for example, with ornamentals
and tobacco), 19 or reductions in crop value might result from reduced bloinass
production (growth) associated with the leaf injury. 20 Indeed, the latter
effect has the potential for crop value reductions even in cases where the
leaves are not an economically important part of the plant, as (for example)
with beans, corn, radishes, and tomatoes. Table 4 presents data from
several studies examining the effects of controlled ozone or ambient oxidant
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exposures on leaf injury and biomass production. This summary indicates a
broad spectrum of responses: growth and yield reductions with minimal or
no foliar injury (radish and alfalfa); extensive foliar injury with no
significant effect on crop yield (tomato); and some reasonably good correla-
tions between these parameters (Pinto bean, sweet corn, soybean, and tobacco).
It may be surmised from the above discussion that foliar injury is an
imprecise measure of the effect of ozone on plant growth or yield parameters.
Nevertheless, the bulk of the data available on short-term ozone exposures
to plants presents foliar injury as the response measure. Consequently, it
is necessary to utilize this imperfect parameter to evaluate alternative levels
of the secondary standard. A question which immediately arises is the degree
of foliar injury which will be considered to be of concern. This question
has not yet been definitely answered by researchers but discussions with
investigators 21 ’ 22 ’ 23 ’ 24 1n this field have provided some enlightenment on the
issue. The consensus obtained was that for foliar injury between 5 and 10
percent there is the potential for detectable reductions in growth or yield,
depending on the timing of the injury with respect to critical stages in
the life cycle (e.g., the time when bean pods are beginning to mature) as
well as on other environmenta1 factors which might bear on the plant’s
ability to recover from the foliar injury.
Since an ozone air pollution episode might occur at any point in
a crop’s life cycle and might be randomly associated with other detrimental
factors, EPA considers foliar injury rates in the range of 5 to 10 percent to
be undesirable. Therefore, EPA proposes that the basis for the secondary NAAQS
for ozone be to protect against exDosures that may be reasonably exoected to
produce foliar injury within this range for commercially important crops or
important indigenous flora. Cultivars that were specially developed to be
sensitive to ozone, i.e., Bel W—3 tobacco, will be exempted from this analysis.
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Several investigations have examined the effect of ozone exposures
on growth and yield parameters, and the information obtained from such
studies can provide useful input to the standard-setting analysis. Table 4
presents results of a few studies relating short-term ozone exposures to
growth and yield effects, and in addition the following examples appear
notable: A 38 percent reduction in root dry weight was produced by exposure
of Cherry Belle radish to 0.25 ppm ozone for three hours. 25 Exposure to
0.1 ppm ozone for two hours produced a 9 percent reduction in the average
of three growth responses (shoot weight, flower weight, and flower number)
of Capri petunia. 26 A 16 percent reduction in leaflet area growth rate was
obtained by exposure of Pinto bean to 0.05 ppm ozone for 12 hours. 27
Long-term exposures to ozone have been experimentally demonstrated to
produce growth or yield reductions In several sensitive crops, including
radish, soybean, and corn. As noted in Table 4, measurable growth and
yield reductions in comparison to controls have been obtained from exposures
to levels as low as 0.05 ppm for 6 to 8 hours per day over several weeks.
In addition to the studies cited in Table 4, the following examples are
noteworthy: A 25 percent reduction in leaf dry weight for Pinto bean was
obtained by continuous exposure to 0.05 ppm ozone for five days. After
three days exposure, the leaves exhibited premature senescence as measured
by loss of green color. 28 Exposure of the Mesa-Sirsa cultivar of alfalfa
to 0.05 ppm (+) ozone for 7 hours per day for 68 days produced a 40 percent
decrease (average over two harvests) in forage dry weight. 29 ’ 3 ° The
criteria document assessed these long—term exposure studies by concluding
that significant growth and yield effects could occur if the average ozone
concentration exceeds 0.05 ppm beyond 15 days. 31 Based or, the evidence cited in
its support, this conclusion is for the purposes of this document interpreted
to mean 15 consecutive days with maximum 8-hour-average concentrations above
0.05 ppm.
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4. Pollutant Interactions and Ambient Exposures : Controlled
experimental studies require elimination of unmeasured environmental
factors in order to examine the effect.of the factor being evaluated
(ozone, in the above studies). However, in the ambient environment,
plants are exposed not only to ozone but also to other components
of the photochemical oxidant pollution mixture (e.g., PAN) or other
unrelated pollutants such as SO 2 . Only a. few controlled experiments have
examined the interactive effects of ozone with other pollutants, most of
these utilizing SO 2 as the co-pollutant. Mixed results have been found;
depending on the species and cultivars examined, the responses have been
observed to be additive (not significantly different from the sum of the,
effects expected from exposure to the given level of each pollutant alone),
or synergistic (greater than additive), or antagonistic (less than additive). 32
At this point a discussion of another important component of the
photocheinical oxidant mix, PAN, seems to be warranted. It has been reported
that on a molar (ppm) basis, PAN injures vegetation at lower exposure levels
than ozone does. 33 Controlled exposure of Pinto bean to PAN at 0.02 ppm for
8 hours produced 44 percent injury, and 90 percent Injury was induced at
0.04 ppm for 4 hours. 34 The characteristic injury symptoms for PAN are
glazing, silvering, or bronzing of the l wer surface of the leaves of plants
such as spinach, garden beets, Romaine lettuce, and chard. 35 PAN injury can
usually be distinguished from ozone injury by the location and type of lesions.
The information base on PAN injury to vegetation is much less extensive than
that for ozone, but the available evidence suggests that PAN can play an
important role in the effects of ambient photochemical oxidant pollution on
vegetation.
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l7.
In order to evaluate the effects of ambient mixtures of photo-
chemical oxidants and other pollutants on vegetation, several studies
have compared plants exposed to unfiltered ambient air in greenhouses
or field chambers with those grown in filtered air. In multiyear studies
of this type In California, significant reductions have been observed in
the yields of lemon (32-52 percent), 36 navel orange (54 percent), 36
Zinfandel grape (50-60 percent), 37 and Acala cotton (5-29 percent). 37
In the study of navel orange trees, oxidant concentrations were above 0.10
ppm an average of 148 hours per month from March through October during the
growing seasons studied. 36 In similar experiments conducted in Maryland,
an average of 49 percent yield reduction was obtained for two sensitive
potato cultivars (Haig and Norland) when exposed to oxidant concentrations
which were equal to or greater than 0.10 ppm for 11 hours during the growing
season. 38 In New York, ambient air field chamber exposures of Tendergreen
bean and Fireball 861 VR tomato over their growing seasons reduced the
fresh weight yields by 26 and 33 percent, respectively. The foliar injury
symptoms which occurred became more extensive and severe with time; they
closely resembled those induced by controlled ozone exposures. Hourly
average oxidant concentrations of at least 0.10 ppm (÷) occurred 125 times
during the 99-day experimental period; 0.20 ppm (+) was the maximum hourly
average concentration observed. 39
5. Economic Assessment : Several assessments of the economic losses
to agricultural and ornamental vegetation due to ozone and other oxidants
have been attempted. Notably, a study by the Stanford Research Institute (SRI)
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in 1969 developed an’empirica1 model for assessing vegetative air
pollution damage. Expected oxidant levels were evaluated for over 100
study areas across theU.S. and were used to predict foliar injury and
resultant economic damage for varioUs vegetation types. The model
estimated the national loss due to the effects of ozone and other
oxidants onvegetatión in 1969 to be$125 million at the farm level.
Due to increases in crop values-and the general lack of improvement in
ozone levels since 1969, these losses could currently approach $300 million
annually. 1
6. Effects on the Natural Environment : Finally, it must be noted
that the indigenous vegetation which constitutes the producer component
of natural ecosystems may be affected by chronic exposures to ozone and
other oxidants. Disruption of the ecosystem structure and function may
result, possibly with irreversible repercussions; For example, severe
injury has occurred to the conifer forest ecosystem of the San Bernardino
Mountains as a result of oxidant pollution transported from the
Los Angeles urban area for many years. Of the 640 square kilometers (km 2 ) in
the San Bernardino National Forest that in 1969 had ponderosa pine,.Jeffrey
pine, and/or white fir as the co-dominant (overstory) vegetation
species, 180 and 220 km 2 had sustained heavy and moderate damage,
natural ecosystem is a distinct association of plants (producers),
animals (consumers), and other biota (decomposers) with the physical environ- 40
ment (e.g., the soil, air, water, and solar energy influx) which controls them.
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respectively, in the pine species. An estimated 1.3 million trees
were affected, of which 3 percent had died. 41 A station within the heavily
damaged area recorded 100 hours in which the total oxidant concentration
equalled or exceeded 0.20 ppm (+) during the summer months of 1969, and
the air quality appears to have deteriorated further since then. 42 A 2-hectare
( 5 -acre) study plot in an area sustaining moderate damage experienced a
28 percent decrease in Jeffrey pine timber volume between 1952 and 1972.
This loss was attributed to the increased susceptibility to insect attack
In oxidant-weakened trees, and possibly also to the suppression of radial
growth due to oxidant injury. Growth suppression in pine sap1ir gs due to
ambient oxidant exposure has been demonstrated experinientally. 43 In
addition, decreased tree vigor as a result of oxidant injury has been
implicated as having detrimeritäl effects on seed production In ponderosa
pines. This effect, in conjunction with the habit of preferential seed
consumption by small vertebrates such as the gray squirrel, could seriously
reduce the reproductive capabilities of ponderosa pine. 44
Ozone injury to dominant plant species in forest ecosystems is not
restricted to California. Ozone pollution has been implicated as a
causative agent for a disease of the eastern white pine, post-emergence
tipburn, which occurs throughout the range of this species from the
Great Lake states to the Appalachian Mountains. Significantly increased
injury symptoms were observed in this species at three locales in the
Appalachian region of Virginia following a pollution episode in July 1975.
Oxidant concentrations were 0.08 ppm (+) or higher during 43 hours of this
9-day period; peak hourly values as high as 0.13 ppm (+) were recorded. 45 ’ 46
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It is very difficult to quantify adequately the impbrtance of
natural ecosystems to the public welfare and, consequently, to provide
monetary estimates of the impacts of oxidant pollution of natural ecosystems.
Timber sales from national forests are an obvious but miniscule portion of
the benefits obtained from forest ecosystems. There are other benefits
which defy monetary evaluation, benefits which relate to the life—
support roles of natural ecosystems in maintaining the quality of life
on this planet. These include free services such as the purification of
air and Water, the control of erosion, the regulation of global climate
and radiation balances, and therecreational opportunities provided by
wilderness areas.
Several impacts of oxidant pollution on natural ecosystems have been
discussed,’ such as decreased- timber production and decreased reproductive
capabilities of the dominant plants. These -impacts may be harbingers
of detrimental effects on the life-support roles of these ecosystems, and
definitely indicate the potential of oxidant pollution to diminish the
economic and recreational values of these’ natural resources as evaluated
from an anthropocentric(man-centered) point of view. Additionally, these
impacts have’ dire implications for non-human inhabitants of these eco-
systems, e.g., small vertebrates whose supply 0 f seeds and fruits are
diminished. It appears that decline of the dominant Jeff rey pine species
in portions of the San Bernardino Mountains is producing changes in eco-
system structure (such as an increase in open areas populated byozone-resistant
shrubs) 47 which may result in increased erosion and changes in the food chain that
may affect animal species. 48 It is possible that the disruption of ecosystem
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structure and function due to oxidant pollution may change the local
environmental conditions to an extent that the disruptions become
irreversible.
B. Materials Damage :
Ozone has been shown to accelerate aging processes for several
classes of materials,particularl.y elastomers (rubber), textile dyes and
fibers, and certain types of paints. In the case of the elastomers, ozone
accelerates the development of cracks in several commercially important
types of rubber. Several factors influence the ozone cracking phenomenon,
such as the chemical nature of the elastomer, degree of tensile stress
(strain) sustained by the elastomer, ozone concentration, exposure dura-
tion, and temperature. It has been reported that if sensitive rubber is
strained slightly (sufficiently to increase its length by 2 to 3 percent)
and exposed to concentrations of ozone as low as 0.01 ppm, cracks or cuts
will ultimately appear. 49
Several studies have shown that the cracking rate is strongly correlated
with ozone concentration, with one short—term experiment clearly demonstrating
a direct proportionality between these parameters. In this study, strips
of natural rubber were strained approximately 100 percent. On the average,
cracks were first perceived when the ozone dose reached 1.32 ppm-minutes,
with an estimated standard deviation of 0.03 ppm—minute. This study evaluated
three ozone concentrations: 0.02, 0.25, and 0.45 ppm. 5 ° The dose-dependent
behavior noted in this study implies that the average ozone concentratio;
during an exposure, without regard to the pattern of concentration varia-
tions, determines the rate of elastomer cracking. If this interpretation
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can be applied over long time scales, two sites with equal annual
average ozone concentrations would be expected to sustain equal elastorner
damage, even if one site were subject to considerably higher short-term
peak concentrations than the other.
Long-term exposure studies may be reasonably interpreted to support
the preceding conclusions, although there are considerable variations in
the data. In one such experiment, thin specimens of a sensitive synthetic
(polybutadiene) elastorner were exposed under constant strain to room air
during different seasons of the year. Average ozone concentrations were
0.048, 0.042 and 0.024 ppm in the summer, autumn, and winter, respectively.
The average dose (and estimated standard deviation thereof) required to induce
complete failure in these specimens was 16.6 ±. 4.5 ppm-hours. This dose-dependent
response indicates that elastomer cracking rates are dependent on the long-
term average ozone concentration. 51 Such a deduction is supported by theoretical
considerations of the mechanisms of ozone attack on materials. Therefore, it
is concluded that long—term (annual) average ozone concentrations determine
the extent of elastomer damage.
To protect against ozone cracking, certain substances (anti—ozonants)
are generally added to elastomer formulations, and special ozone—resistant
elastomer polymers are sometimes used. Such preventive measures are
expensive and add considerably to the total economic impact of,ozone
air pollution. In 1970 a study estimated the nationwide economic impact
at the consumer level to be $500 million annually. About $170 million
of this total was involved in preventive measures, with the remainder
due to premature failure of rubber products. 52 Such an estimate, while
demonstrating the seriousness of the problem, does not relate materials
effects to ozone exposure levels. In an attempt to provide such a relation-
ship, an equation was developed to present the optimum per capita cost of
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elastomer damage (i.e., damage prevention measures were balanced against
failure costs so as to minimize total costs) as a function of average
ozone concentration. This cost function, expressed in 1970 dollars and
given with a 25 percent error range, is:
Cost, S/year/person = (0.88) ‘(1 ± 0.25) (in g - 1) (2)
where is tne annual average ozone concentration in micrograms per cubic
meter ( jg/m 3 ). 52
The effects of ozone on textiles include deterioration of fibers
and dyes, but the fading of dyes is the more significant economic factor. 53
Three different types of textile materials have been reported to sustain
major economic losses due to ozone fading of dyes: acetate fabrics,
polyester—cotton permanent-press fabrics, and nylon carpets. 54 In 1970,
the national cost of ozone fading in these textile categories was estimated
to be $80 million per year. 55 By analogy with the above elastomer cost
function, an equation estimating the cost of ozone damage to textiles and of
damage prevention measures has been presented. 56 Expressed in 1970 dollars
and given with a 50 percent error range, this equation is:
Cost, $/year/person = (0.22)(1 ± 0.5) (in — 0.74) (3)
for values of above 5.7 .ig/m 3 .
Overall costs for paint and coatings damage by ozone have not
been estimated. Costs of additional industrial maintenance painting
and vinyl coil coating required because of ozone damage have been estimated
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in a damage function expressed in 1974 dollars. 57 Based only on these
two types of damage, the damage function is:
Cost, S/year/person = 0.0383 g + 0.00126 g
(4)
1+0.01 g 1+0.001 g
where g is defined as in equation (2).
The above cost functions for damage and preventive costs associated
with ozone effects on elastomers, fabrics, paints, and coatings have been
evaluated (at the mid—point of the error range, where applicable) for
various annual average ozone concentrations. The results are presented
in Table 5. As these cost functions indicate, there is no threshold
level for ozone damage to materials. Indeed, the experimental evidence
presented in this section regarding the dose—dependent relationship between
materials damage and ozone exposure leads one to the conclusion that any
nonzero ozone concentration will contribute to the deterioration of sensitive
materials if the exposure is sustained long enough. The ramifications of
this conclusion on the analysis of the standard level and the bearing of
natural contributions to ambient ozone levels in the issue of materials
damage will be explored in the subsequent sections of this document.
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IV. Air Quality Issues
The previous section discussing the experimental evidence of the
effects of ozone on vegetation and materials leads directly to issues
concerning current ambient levels and the contributions thereto by
natural processes (natural background), as well as the matter of which
averaging time(s) to choose for setting a secondary standard.
A. Sources and Concentrations of Oxidants in Ambient Air
1. Sources : Ozone levels in the lower atmosphere (troposphere)
essentially result from two processes: (a) tropospheric photochemical
reactions involving organic and nitrogen oxide precursors, oxygen, and
sunlight, and (b) downward transfer of ‘ozone from upper atmospheric
(stratospheric) layers into the troposphere. The latter process contributes
to the natural background of ozone, and it is possible that photochemical
reactions involving naturally emitted precursors may do so also. However,
all present evidence indicates that the severe oxidant problems occurring
in and around urban areas are preponderantly due to photochemical reactions
involving man—made •(anthropogenic) precursor emissions. 58 In areas with
lesser problems th stratqspheric source may be significant, and especially
in remote areas that may on occasions be the dominant cause of the ambient
ozone levels observed. 59
2. Urban Oxidant/Ozone Levels: . Ambient air concentrations of ozone
or oxidants were measured in 1976 at 558 monitoring sites operated by
state and local air pollution control agencies and EPA. 6 ° Table 6 presents
1976 ozone data sumaries for 100 sites in the nation’s 16 most populous
urban areas; only one valid site had its annual second—highest hourly
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* 3
concentration below the current oxid nt stand.ard ,lev 1 of 160 ig/m
(approximately 0.08 ppm). Table 7 summarizes oxidant and ozone data from
several year ’monitbr in •ih 2 3 urban a r as. “T’iie a’nnual- averagè ’côY centra—
tions for th e sit ’es”’árepf se’rited fo pat fs’dr ’with the n at’e falé ’fféc ts
Jata in Tab1e ’5.’t
‘A ‘number “of ‘thèsè’-ur-ban ‘areas ha ié ”expérienced ’ -v ’ery h’i’gh’ l él óf,
oxidant, exceedin O3 pprTi ,V Los Ang ’ ’l s,’ fór exämp 1è, ‘h as ‘i ecördëd
maximum 1-hour values j,n ‘é ces if .0.6 ’ ppn : ‘Denv.’P h ’ii de’1 ihia Hoüston,
and tI ’ie area -just’ eaT t’ of-’New York Ci -t h ’áve e pdriericéd levels. abov
0.3 ppm. Hour’lyva1ues ‘ab’ove ‘d.2 ppm have’o ccurre ’d ‘iii ’ flo t’-df thè’lnaSór
urban “areas ;)6l In addition, eg’ces’sive ione ‘concentràt’ions Oc ü
frequently in -urbanized-areas, “as’ indicated iñ -’Tab1è 6-by the f’act “ h’at
In 8 of the 16’mOst popu1o s
days in 1976 ‘had hbur-’ly va1i es above the :cLj ren tãrid rd l el.
-3; Rural ‘0zon&’Le e’ls’: ’ An-issue of ‘cdn’siderabl’e impor táncè to-getting
a secondary ozone “sta ndard “is’ the ozone ai ’r qual1t ”in rura1 áréas , si née”
the’bul’k of the veqetation is iñ’such loca1es. In recent’years’
research conducted in ‘several rural’ area i n -the e’a têrn ‘ nd’ ‘central’ part’s
of the.nation has ‘indicateththat ozone - con cèntrations abo le th current
standard ‘level can O ’ccur with a frequen y -comparáblè’to dr e eg, eatèr
than that observed in many urban areas. This is i1iustráted’-’iTa 1e’-8by
data obtained’ i’n recent EPA. Such
e’Ievated’oioñe levels in rUrã1 r’eas can be-a1 dst ’c ert-a’inl i ätl i’biItèd
largely to anthropo’géni’c ”cause : the ti-ans or ’tf-rdrT urban aré s f’o ori ’
and/or the photochemica’l reaction of récur ors generà’tédio ally
The emphasis on the second-highest values is due to the definition
of the current oxidant standard as an hour1y average concentration not to
be exceeded more than once per year. Thus the annual second-highest hourly
value determines whether the current standard is attained:
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transported from urban areas. The evidence leading to this conclusion
includes the correlation of the high ozone levels with increased concentra-
tions of such tracers of man’s activities as Freons or acetylene, as well
as wind trajectory analyses indicating the prior passage of the rural
air over urban sources. 62 The utilization of these and other techniques
has enabled researchers to substantiate such phenomena as theinterrnediate—range
transport of ozone plumes up to and exceeding 160 km downwind of urban areas,
and the synoptic-scale transport of ozone and its precursors over broad
areas (several hundred kilometers in radius) which can occur under
appropriate meteorological conditions such as stagnant high pressure
systems. The evidence for transport of ozone and other oxidants suggests
that most of the oxidant observed in rural areas is due to the influence
of upwind urban areas. 63
4. Natural Background Levels : In the assessment of the extent to
which elevated rural ozone levels are due to anthropogenic influences,
one useful technique has been to monitor ozone in remote areas in order to
determine the natural background levels. Even though remote sites are
by definition so far removed from anthropogenic pollutant sources as to
make their contamination by such pollutants unlikely, the preceeding
discussion indicates that the possibility of anthropogenic influences
cannot be suninarily discounted even’ in quite remote areas. Before ascribing
a particular ozone level observed at a remote site entirely to natural
background, it is necessary to examine the episode with respect to the
presence of tracers of man’s activities (such as Freons or acetylene)
and to conduct wind trajectory analyses to determine whether the air
parcel in question had recently passed over urban areas. Nevertheless,
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for the purposes of this report 11 remote” sites will be distinguished
from non-remote “rural” sites on the basis of the available evidence -
that anthropogenic influences play a more important role in the ozone
levels observed at rural sites (such as thpse given in Table 8) than at
remote locales.
The 1970 criteria document for photochemical oxidants reported
that oxidant concentrations at remote sites ranged from less than 0.01
to about 0.05 ppm (20, to 100 pg/rn 3 ). 64 However, a recent examination 65
of ozone and precursor air quality data at 13 monitoring stations selected
to be as remote as possible from anthropogenic sources has indicated that
ozone concentrations may occasionally approach and even go above the 0.08 ppm
standard ‘level under conditions for which anthropogenic influences are
negligible. Such events tend to occur in late winter and early spring
(February-April) when the effect of stratospheric transfer into the troposphere
is most prono,unced, and are more likely at higher elevations. These types
of excursions above the standard level were rather infrequent and in fact
none occurred at over half of the monitoring sites, with from 6 to 19 months’
data at each site. The excursions for which anthropogenic influences could
be ruled out were nearly all less than 0.10 ppm, although on one occasion a
peak hourly average concentration of 0.20 ppm was reached.
Table 9 indicates maximum hourly and long-tern average concentrations
observed and the estimated frequency of concentrations above the standard
level for the monitoring stations for which long-term data are given in
this study. Only three sites had concentrations above 0.10 ppm. Two
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29
of these (Fritz Peak, Colorado and White Face Mountain, New York)
are frequently subject to long-range transport of anthropogenic
- pollutants from urban areas despite their nominally remote locations.
The preponderance of the excursions above the standard level at these
sites can probably be attributed to ozone transport from urban areas.
At the third site (Zugspitze, West Germany), the only excursion above the
standard level was an episode in which the peak hourly ozone concentration
was 0.20 ppm. This episode was indisputably due to an unusually strong
penetration of stratospheric ozone (i.e., stratospheric intrusion) to
this mountain peak location. 65 The frequency of this type of event is
not yet known. 66 A comparison of Tables 8 and 9, particularly with regard
to frequency of concentrations above the standard level and the level of
maximum hourly average concentrations, provides further support to the
conclusion that the bulk of the ozone problem in non-remote rural areas is
due to anthropogenic influences.
A further point to be discerned from Table 9 is that the long—term
average ozone concentrations at these remote sites varied from 0.028 to
0.044 ppm. This range is somewhat higher than estimates obtained in
attempts to quantify stratospheric ozone input to the troposphere through
analyses of global circulation patterns. Annual average ground—level ozone
concentrations due to stratospheric input have been estimated by such
analyses to be in the range of 0.01 to 0.03 ppm.i Furthermore, current
understanding of the transfer of stratospheric ozone to the troposphere
indicates variations with season and latitude such that average ground-level
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ozone concentrations in the midlatitudes (e.g., the 48 contiguous states),
attributable to stratospheric input reach a peak in the winter and spring
months. Consequently, the annual average ground—level ozone concentration
due to stratospheric input should be higher than the corresponding “smog
season” average during the sumer months (when the potential for genera-
tion of anthropogenic ozone is greatest). Based on these arguments, the
criteria document estimated the contribution of stratospheric ozone to the
maximum hourly average ground-level concentration during the smog season
to be in the range of 0.015 to 0.04 ppm. 67
Comparison of Tables 7 and 9 indicates that annual average ozone
concentrations in urban areas are approximately the same as those in remote
sites, even though the maximum hourly concentrations are much higher in
urban areas. This seeming paradox can be rationally explained as resulting
from the increased rate of nighttime destruction of ozone in urban areas
by man-made pollutants such as nitric oxide (NO). 68 This process lowers the
nighttime urban ozone concentration practically to zero, whereas ozone
destruction processes in remote sites (with minimal concentrations of
anthropogenic pollutants) are much less drastic. For this reason the
annual average concentrations are comparable even though the maximum
hourly values are quite different.
The preceding discussion of natural background ozone levels has
emphasized the relatively well-established fact that transfer of stratospheric
ozone to lower levels of the atmosphere does occur to an extent that can
noticeably affect tropospheric ozone air quality. Another potential source
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31
of natural background ozone that is less well defined involves the
action of photochemical processes on naturalb emitted organic compounds,
e.g., terpenes emitted from forested areas. Laboratory and field studies
of photochemical reaction processes have demonstrated that terpenes
can serve as ozone precursors under optimum conditions, that is, with
optimum ratios of the concentrations of organic and nitrogen oxide precursors.
However, these optimum ratios do not typically occur in rural areas where
the preponderance of natural organic emissions occur. Furthermore, based on
extrapolations from laboratory studies, even under optimum conditions for
ozone generation no more than 0.001 to 0.002 ppm oxidant/ozone would be
predicted to result from ambient terpene concentrations normally observed
in forested areas. Under the more typical, non-optimum conditions, the
available evidence indicates that terpenes act as ozone scavengers, reacting
with and destroying ozone and producing mainly particulate degradation
products. The criteria document reviewed the literature available on this
subject and concluded that there is no convincing reason to believe that
any known natural organic emissions (including terpenes and methane) have
an important impact on oxidant/ozone air quality. 69
5. Levels of Non-Ozone Oxidants : Some discussion of the ambient
concentrations of non-ozone oxidant species is merited. Mibient measure-
ments of such oxidants are scant and consist mostly of PAN data. PAN is
a highly reactive, unstable compound which must be treated with special
precautions, and for these reasons cannot be measured in a routine monitoring
program. 7 ° The data currently available generally indicate that in urban
areas PAN concentrations are considerably smaller than those of oxidant or
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32
ozone, but nevertheless are not negligible. 8 Levels in excess of
0.05 ppm have been observed in Los Angeles and elsewhere. 71 ’ 34 Ratios of
molar (ppm) concentrations of oxidant or ozone to PAN during midday hours
have been reported to range from, 3/1 to 80/1 in three metropolitan areas.
Measurements of ozone and PAN in rural areas near Wilmington, Ohio indicated
that absolute concentrations of PAN were lower than those observed in urban
areas, with a maximum of 0.004 ppm observed during August 1974. The ratios
of ozone to PAN varied from 10/1 to over 150/1 •7I From the wide ranges given
in the ratios of ozone to PAN it is obvious that the PAN concentration can-
not be predi,cted from the ozone concentration. These ambient data’ relation-
ships do not provide conclusive evidence that control efforts aimed at
reducing ozone levels (i.e., emission controls for organic and nitrogen oxide’
precursors) will reduce PAN levels. However, the evidence from 1aborat ry
and theoretical studies of photochemical reaction processes definitively
indicates that decreases in ‘organic and nitrogen oxide precursor emissions
should have greater impacts on ambient PAN than on ambient ozone. 72
B. Averaging Time Considerations
1. Discussion of Issues : Analysis of the variation of ambient
concentrations with averaging times is important in the standard-setting
process since effects may vary with intervals of exposure. As- has been
previously discussed, the effect of ozone on materials appears to be linearly
dependent on the dose; this implies that the annual averageozone co centra—
tion is the most appropriate indicator of materials damage. However, in the
case of vegetation the effects of ozone are not linearly dependent on’
the dose. In determining the response of vegetation to ozone or oxidants,
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concentration is more important than time. A given dose presentea
to a plant in a short period of time has a greater effect than the
same dose applied over a longer period. 73
The current photochemical oxidants standard level is specified as
a one-hour average. Rather than specify different standard levels for
different averaging times, it seems prudent from a data-handling point
of view to retain the concept of a standard specified for a single
averaging time. A one-hour averaging time is sufficiently long to
assure accuracy of measurement under conditions of fluctuating atmospheric
levels of ozone.. Accordifl l.Y. EPA proposes to retain the one-hour averaqinq
time for the standard. However, since It has been indicated that plant
response is predicated on length of exposure as well as concentration,
consideration must be given to the expected variation of ambient ozone
concentrations with averaging time in order to assure that the one-hour
average standard level is protective of undesirable effects due to
exposures sustained over longer averaging times. The following discussion
addresses this issue.
2. PredictiOn of Averaging Time DistributiOi!! The evidence obtained
from a considerable amount of air quality data indicates that the maximum
observed concentrations decrease as increasingly longer averaging times
are evaluated. This is illustrated Ifl Appendix A by plots of annual
second-highest ozone concentrations for various averaging times, as reported
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34
for 24 monitoring site-years at several urban locations in the
eastern and central parts of the nation. Each plot has been
apprc ximately fitted with a straight-line construction of an
averaging-time distribution curve. This simplified fitting
procedure is a modification of the findings presented by Larsen 74
regarding the relationship between maximum concentrations and
averaging times, and is for illustrative purposes only.
Although all the data in Appendix A show a decrease in maximum
ozone concentrations with increasing averaging time, there is con-
siderable variability in the rate of decrease. It is necessary to
develop a composite of this type of data in order to obtain useful
conclusions. Details of the analysis performed for this purpose are
given in Appendix B, and are briefly suninarized as follows: Ozone
measurements from 14 urban monitoring stations (22 site-years) were
fitted by Weibull frequency distributions and analyzed to determine
the relationships between the distribution parameters for three different
averaging times (1,3, and 8 hours). For the 3 -and 8-hour averaging times,
the data were evaluated for only the 8 and 3 time periods, respectively,
that coincide with a calendar day. None of the monitoring stations
examined were in compliance with the current oxidant standard, but
it was assumed that the relationships between the distribution parameters
for different averaging times will remain valid when the standard is
attained. These relationships were then applied to a 1—hour ozone con-
centration frequency distribution believed to describe reasonably well
an average urban area meeting the current oxidant standard. For each of
the three averaging times, this analysis produced estimates of the
concentrations which are expected to be exceeded only once per year for
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35
four alternative hourly average ozone standard levels (0.06, 0.08, 0.10,
and 0.12 ppm). These estimates are presented in Table B—i. As an example,
for an hourly average ozone standard level of 0.08 ppm (157 .ig/m 3 ), the 8-hour
average concentration expected to be exceeded only once per year is 0.052 ppm.
An estimate of the range which might be expected in this value may be obtained
by examining the data for the 5 site-years in Appendix A whose annual second-
highest hourly average concentrations were below 200 pg/rn 3 (0.1 ppm). Assuming
that a reduction in the hourly peak values to 0.08 ppm would result in a
proportional decrease in the 8-hour-average peaks, a range of annual second-
highest 8-hour—average va1ues from 0.047 to 0.064 ppm would be predicted.
3. Synthesis of Averaging Time and Foliar Injury Models : The model
proposed by Larsen and Heck 14 for analysis of foliar injury to several
plant species can now be examined in the light 0 f exposure levels expected
to accompany alternative standard levels. Table 10 presents the results
for three averaging times and four alternative hourly average ozone standard
levels. It may be readily discerned that in very many instances the 8-hour
average concentration expected to be exceeded only once per year is predicted to
produce greater foliar injury than the corresponding 1- and 3-hour concentra-
tions. At the 0.06 ppm standard level none of the 15 plant species/cultivars
examined is predicted to sustain more than 1 percent injury as a result of
short-term exposure levels expected to be exceeded only once per year. For the
0.08 ppm standard level, none of the plants tested except Bel W-3 tobacco
is predicted to receive more than 3 percent injury. However 1 at the 0.10 ppm
standard level, several comercially important cultivars (tomato, oats, and
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radish) are predicted to sustain injury within the 5 to 10 percent
range of concern due to short-term exposure levels expected to be
exceeded only once per year. At the 0.12 ppm standard level the injury is
expected to be even greater.
In addition to these short-term exposure considerations, the
evidence, previously presented on long-term ‘exposures is relevant to an
analysis of alternative standard levels. The criteria document concluded
that significant growth and yield effects could occur if the ozone 1evels are
above 0.05 ppm for 6 to ’8 hours perday for 15 èonsecutive days. 31 Since an
8-hour average concentration of 0.052 ppm is expected to be exceeded only once
per year for an hourly average ‘standard ‘level of. 0.08 ppm; it appears that
growth and yield reductions due to Iong-te in ozone exposures would be more
than adequately protected ,aga inst by that, standard, level. However,, further
discussion of this i,ssue in the next section, tempers that conclusion somewhat.
It should be noted that the analysis of, the variation of maximum
.concentrati flS with averaging times relied entirely on ozone measurements
obtained in generally urbanized areas. Sufficient data were not available
to conduct similar efforts for rural sites downwind of urban areas, but it
seems possible that the rate at which maximum ozone concentrations decline
with increasing averaging times could be lower in such areas than in
-metropolitan areas. This hypothesis is based;on the fact that, compared
with urban areas, rural sites do not have significant sources of man-made
poll ,utants (such as NO) to promote gas—phase ozone scavenging reactions.
These reactions, along with other factors such as the daily cycle of ozone
formation by photochemical processes, the temporal variations in dispersion
conditions, and the scavenging of ozone on surfaces such as soil and
vegetation, cause the peak ozone concentrations to decrease with longer
averaging times. The conclusion implied by this postulate is that of an
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37
urban area and a non-remote rural area which are both meeting a given
1-hour standard level, the rural area would sustain greater injury due
to the peak 8-hour exposure. Since the bulk of vegetation is located
in rural areas, EPA has attempted to factor the uncertainty raised by
this hypothesis into its analysis of alternative hourly average standard
levels. However, EPA is soliciting comments as to whether the standard
should be set for an averaging time of 8 hours rather than 1 hour in
order to remove the uncertainty associated with estimatinq the ratios
of 1-hour to 8-hour values in rural areas.
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V. Analysis of Alternative Secondary NAAQS
A. Pertinent Issues
A variety of factors which may be considered by the Administrator
in choosing between alternative ozone secondary NAAQS have been discussed
in earlier sections of this document, and are briefly sunvnarized as:
(1) detrImental effects of ozone on agricultural crops and the natural
environment, with repercussions on the benefits derived therefrom by man-
kind, (2) ozone damage to materials, (3) Increased effects due to interac-
tion of ozone with other pollutants, and (4) the transport of anthropogenic
photochemical pollutants (either oxidants or their precursors) from urban
areas to rural areas. An attempt has been made to weigh these factors in
the analyses of alternative ozone NAAQS presented in subsequent sections.
In addition, this document has addressed the issue of the natural
background contribution to ambient ozone concentrations. However, EPA
does not consider this issue to be relevant to the determination of the
level of air quality which is requisite to protect the public welfare from
any known or anticipated adverse effects associated with the presence of
ozone in the ambient air. 75 Consequently, although the magnitude, distribu-
tion, and variation of natural background ozone is an important issue in
developing regulatory strategies to attain the standard, it is not a
pertinent factor in the choice between alternative standard levels.
B. Analysis of Options
1. Change from Deterministic to Statistical Form of Standard : The
current standard specifies that the hourly average ozone concentration must
not exceed 160 i. g/m 3 (approximately 0.08 ppm) more than once per year. As
discussed in a companion document, 76 this deterministic form has several
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39
limitations, one of which is the fact that it does not adequately
take into account the random nature of meteorological variations.
This limitation means that compliance with the standard, and
consequently precursor emission control requirements, would be
determined on the basis of exceedingly rare adverse weather conditions.
The probability of occurrence of such rare conditions can only be
dealt with by the utilization of statistical methods. Therefore,
EPA is proposing that the standard be expressed in a statistical form.
The predictions of foliar injury due to ozone exposures expected to
accompany different standard levels given in Table 10 were performed for
standards expressed in the statistical form being proposed. Consequently,
the effect of this change is included in the analysis of alternative
standard levels.
2. Analysis of the .Chemical Spectes Designation of the Standard :
The current standard is designated as a photochemical oxidants standard,
but the FRM for determining compliance specifically measures ozone and uses
it as a surrogate for total oxidants. It is proposed to change the designa-
tion of the standard to ozone since that is the chemical species being
measured to determine compliance. The predictions of foliar injury given
in Table 10 are based on controlled exposures to ozone alone and do not
indicate the degree of foliar injury that might occur when plants are exposed
to the specified levels of ozone in the ambient air in conjunction with other
components of the photochemical oxidants category, such as PAN. Controlled
exposures of plants to PAN have indicated that it is a potent injurious agent,
and injury symptoms characteristic of PAN have been noted in ambient air
exposures, particularly in California.
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However, EPA does not propose to set a PAN secondary air quality
standard at this time for several reasons. In the first place, there
is no satisfactory technique available for use in routine PAN air monitoring
programs. Secondly, the evidence from laboratory and theoretical studies
of photochemical reaction processes definitively indicates that decreases in
organic and nitrogen oxide precursor emissions as a result of ozone control
strategies should have even greater impacts on ambient PAM levels than on
ambient ozone. 72 The possible interactive effect of ozone with residual
levels of PAN remaining after attainment of an alternative ozone standard
has been considered by EPA (along with interaction with other pollutants)
in the choice of the proposed ozone standard level, as discussed below.
3. Analysis of Alternative Standard Levels for’ Vegetative Effects :
Four alternative hourly average standard levels were selected for analysis:
0.06, 0.08, 0.10, and 0.12 ppm (approximately 120, 160, 200, and 240
The levels were ch0sen to pennit analysis of the jmpacts on the publtc
welfare from either raising or lowering the current standard level (160 pg/rn 3 ).
In each case, the standard was expressed in a statistical form such that
the standard would be attained if the expected number of hours per calendar
year with concentrations above the standard level were less than or equal
to one.
As was discussed in previous sections, EPA has concluded that protec-
tion of the public welfare requires prevention of short-tenn ozone exposures
which may be reasonably expected to ‘produce injury ratings within the
range of 5 to 10 percent in commercially important crops or important indigenous
flora. This is based on the best-judgment estimates of researchers in this field
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41
that such injury ratings could produce detectable reductions in growth
or yield, depending on the timing of the injury and other environmental
factors. Furthermore, long—term exposure patterns wherein the ozone levels
exceed 0.05 ppm for 6 to 8 hours per day for 15 consecutive days could produce
significant growth and yield effects. These two analytical criteria
provide the bases for evaluating alternative standard levels with regard
to their effects on vegetation.
With respect to the first criteria, a mathematical model was used
to summarize for several crops the experimental evidence which depicts
the foliar injury response to various short-term exposure levels. This
model facilitated the extrapolation of direct experimental results over
averaging times in the range of 0.5 to 8 hours. This permitted evaluation
of particular exposure levels for which experimental evidence was lacking
but which were critical in distinguishing between certain of the alternative
standard levels. As presented in Table 10, the model’s predictions of
the extent of foliar injury at various exposure levels were combined with
estimates of the short-term exposure levels expected to accompany alternative
hourly average standards.
These air quality estimates were based on an analysis (given in Appendix B)
of the variation in short-term peak ozone concentrations with different
averaging times which was judged to be an “average” for several urban locations
approaching or attaining the current standard. Admittedly it would be more
relevant to the issue of protecting vegetation to analyze such variations
for rural locations; however, those relationships are presently not quantified.
Nevertheless, it does seem plausible that those relationships may be such
that higher 8-hour-average peak concentrations would result at a rural site
than at an urban site if both were attaining the same hourly average standard
(due to the higher urban levels of ozone-scavenging anthropogenic pollutants,
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42
such as NO). The significance of this uncertainty can be seen in the fact that
in practically each case examined in Table 10, the 8-hour exposure is predicted
to produce more injury than the shorter exposure times.
With respect to the second criteria, the analysis in Ipp n ixB
was also used to estimate long—term exposure patterns expected to accompany
alternative hourly average standard levels. This analysis contains an inherent
bias towards overestimating the long—term impacts of such standards.
The alternative standard level of 0.06 ppm is predicted to protect
all of the 15 plant species/cultivars examined in Table 10 from short—term
injury ratings above 1 percent. Appendix B indicates that the peak 8—hour
concentration is expected to be less than 0.05 ppm. This standard level
appears to be stricter than is required to protect the public welfare.
A 0.12 ppm standard level is predicted to produce short-terni injury
ratings within or exceeding the range of concern for several coninercially
important cultivars. Cherry Belle radish and Roma tomato are predicted to
sustain 12 and 19 percent injury due to the 8—hour average concentration
which is expected to be exceeded only once per year for this hourly average
standard. In addition, there are direct experimental results in the range
of exposure levels expected for this standard; these provide reasonably
good corroboration of the model’s predictions. Finally, Appendix B indicates
that the number of 8-hour average concentrations above 0.05 ppm is expected
to be 31 per year. Clearly, a 0.12 ppm standard level would not be sufficiently
protective of the public welfare, even at the “average” urban site analyzed
in Table 10 and Appendix B.
The analysis of the remaining alternatives, 0.08 and 0.10 ppm, is
somewhat more difficult than for the preceding cases. The initial evaluation
of these options with respect to the two analytical criteria presented earlier
produced conflicting results, as given below.
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43
A 0.08 ppm standard level is predicted to protect all commercially
important cultivars examined in Table 10 from short-term injury ratings
above 3 percent. Appendix B indicates that the number of 8-hour average
concentrations above 0.05 ppm is expected to be 2 per year.
Short-term ozone exposures expected to accompany a 0.10 ppm standard
level are predicted to produce injury ratings within the 5 to 10 percent
range of concern for some commercially important cultivars (specifically,
tomato, oats, and radish cultivars). Appendix B indicates that the number
of 8-hour average concentrations above 0.05 ppm is expected to be 10 per
year.
With respect to the first criteria, a 0.08 ppm standard seems to be
adequate whereas a 0.10 ppm standard does not. But applying the second
criteria indicates that both standard levels are adequate. This conflict
has been resolved in favor of the 0.08 ppm option according to the following
rationale: First, use of an “average” urban site as the basis for the
air quality estimates introduces uncertainty with respect to the possibility
that higher 8-hour-average concentrations may occur at a rural site than at
an urban site when both are attaining the same hourly average standard.
Second, another uncertainty in the air quality estimates is provided by
the fact that, for 3- and 8-hour averaging times, the data were evaluated
for only the 8 and 3 time periods, respectively, that coincide with a
calendar day. If the data were analyzed so as to examine all possible 3—
and 8-hour periods (i.e., a “running average” analysis), it seems likely
that higher 3- and especially 8—hour—average peaks would be associated with
a given hourly average standard. Third, both the foliar injury model utilized
in Table 10 and the second analytical criteria are based on studies examining
controlled exposures of plants to clean air to which only ozone had been added.
However, as discussed earlier there have been studies which have demonstrated
for some species a synergistic interaction between ozone and other pollutants.
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44
These considerations indicate that the analyses in Table 10 and Appendix B
may be underestimating the impacts of the hourly standards examined. Contravening
the above conclusion is the aforementioned bias in the analysis of iong-term
exposure patterns, so that the long-term Impacts associated with these stand rr1s
may be overestimated. Balancing the significance of these uncertainties,
EPA considers that the prudent choice for the secondary NAAQS for ozone
is an hourly average concentration of 0.08 ppm.
This document’ has cited evidence 65 that hourly average concentrations
above 0.08 ppm may occasionally occur in situations when anthropogenic
influences are negligible. In that sense, a 0.08 ppm hourly average.
standard level may be described as being within the range of’natural back-
ground’. However, these situations are ratherinfrequent and-tend to occur
in late winter and early spring (February through April) when the effect of
stratospheric transfer’ into the troposphere is most pronounced, and are
more likely to occur at higher elevations. Stratospheric ozone transfer
appears to be considerably reduced during the sununer months, which is the
time when photochemical processes for generating ozone are at a maximum (and
when vegetation is at the peak of its physiological activity). Thus the
high oxidant levels seen in the sumer months when there is greater risk
of vegetative damage appear to have their origin predominantly in photo-
chemical processes acting on anthropogenic precursor emissions.
Problems related to excursions above the standard level because of
stratospheric ozone transfer to the lower atmosphere may be satisfactorily
resolved, then, by making allowances for such occurrences in the implementa-
tion of the standard. Thus, as EPA has uggested in a recent technical
paper, 77 excursions above the standard level which can be identified with
a stratospheric intrusion should not be considered in developing regulatory
control strategies.
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45
4. Analysis of Alternative Standard Levels for Materials Effects :
As previously discussed, the rate at which ozone accelerates the aging
processes of materials depends on the annual average ozone concentration.
It seems reasonable that a lower short—term (hourly average) standard level
would result in a lower annual average concentration, but this conclusion
is brought into question by the fact that urban and remote areas have com-
parable annual average concentrations even though short-term peaks are
considerably higher in urban areas (compare Tables 7 and 9). This
anomalous situation is rationally explained as resulting from the
increased nighttime ozone destruction rates in the urban areas due
to the ability of anthropogenic pollutants (particularly No) to efficiently
scavenge ozone. 68
Despite this uncertain correlation between short-term peak and long-
term average ozone concentrations when comparing different ambient environ-
ments (that is, urban versus remote areas), it seems intuitively obvious
that for a given type of ambient environment reductions in short-term
peaks would result in lower annual averages. Therefore, it may be concluded
that ozone control measures in urban areas should reduce annual average ozone
levels, and hence reduce the costs of materials damage in a manner suggested
by Table 5. As has been noted previously, there is no threshold level below
which materials damage will not occur; exposure of sensitive materials to
any nonzero concentration of ozone (including natural background levels)
will produce effects if the exposure duration is sufficiently long. For
the above reasons, no effects-based rationale can be offered to decide the
level of the secondary standard needed to protect materials. Consequently,
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46
it is proposed that the level of the secondary standard be based on
the protection of vegetation.
C. Conclusion
EPA proposes to set the ozone secondary !h1AAQS at 0.080 ppm (157 ig/rn 3 )
for a 1—hour averaging time. This proposal involves a slight change in
the mass concentration expression of the current standard level (160 to
157 pg/rn 3 ) due to restating the standard on a molar concentration (ppm)
basis. Another proposed alteration is that the chemical designation of
the standard be changed from photochemical oxidants to ozone. Furthermore,
it is proposed that the standard be stated in a statistical format. Thus,
the proposed standard will be attained when the expected number of hours
per calendar year with concentrations above 0.080 ppm (157 pg/rn 3 ) is equal
to or less than one. EPA concludes that this secondary NAAQS is requisite to
protect the public welfare from any known or anticipated adverse effects
on vegetation due to the presence of ozone in the ambient air. This NAAQS
is believed to provide considerable protection from the effects of ozone
on materials, but no standard level (other than zero) could be said to be
completely protective. The slight acceleration in aging processes of
materials which occurs at the proposed NAAQS is judged by EPA not to be
significant or adverse.
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47
VI. Citations
1. U.S. Environmental Protection Agency (EPA), Air Quality Criteria for
Ozone and Other Photochemical Oxidants. (Referred to henceforth as
1978 Criteria Document). Publication No. EPA—600/8—78—004, April 1978
(Preprint), pp. 11-47 and 11-49.
2. Millecan, A.A. A Survey and Assessment of Air Pollution Damage of
California Vegetation, 1970 through 1974. State of California,
Department of Food and Agriculture, Sacramento, CA, 1976, p. 23.
3. 1978 Criteria Document, pp. 12—70 through 12—75.
4. Ibid., p. 13—12.
5. National Academy of Sciences (NAS). Ozone and Other Photochemical
Oxidants. NAS, Washington, oc 1977, p. 441.
6. 1978 Criteria Document, pp. 7-4 through 7-27.
7. Ibid., p. 7—17 through 7—27 and 7—43.
8. Ibid., pp. 3—7 through 3—9.
9. Ibid., pp. 11—13 through 11-33.
10. Ibid., p. 11—34.
11. NAS, op.cit. , pp. 442-443.
12. Ibid., pp. 522-529.
13. Jacobson, J.S. “The Effects of Photochemical Oxidants on Vegetation,”
from Ozon und Begleitsubstanzen imPhotochemischen.smog, in VDI
Berichte #270, VO l Verlag GMB, Dusseldorf, West Germany, 1976, pp. 163—173.
14. Larsen, R.I., and W.W. Heck. An air quality data analysis system for
interrelating effects, standards, and needed source reductions: Part 3.
Vegetation injury. J. Air Pollut. Control Assoc. 26 (4): 325—333, 1976.
15. Heck, W.W., and D.T. Tingey. Ozone. Time—concentration model to predict
acute foliar injury. In: Proceedings of the Second International Clean
Air Congress. H.M. En Tund and W.T. Beery (ed.) Academic Press, New York,
NY, 1971, p. 249.
16. Heck, W.W., J.A. Dunning, and I.J. Hindawi. Ozone: Non—linear relation
of dose and injury in plants. Science 151: 577, 1966.
17. Heck, W.W., U.S. Department of Agriculture (USDA), North Carolina State
University (NCSU), Raleigh, NC. Personal correspondence with J.O. Lokey,
U.S. i’A, March 23, 1978.
18. McMullen, 1., U.S. EPA. Interpretation of Ozone Plant Damage Data.
Memorandum to J.D. Lokey, U.S. EPA, March 24, 1978.
19. Heggestad, H.E. Ozone as a tobacco toxicant. J. Air Pollut. Control
Assoc. 11 (12): 691, 1966.
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48
20. Heagle, A.S., D.E. Body, and W.W. Heck. An open-top field chamber to
assess the impact of air pollution on plants. J. Environ. Quality 2 (3):
365, 1973.
21. Raniere, L.C., U.S. EPA, Corvallis Environmental Research Laboratory (CERL),
Corvallis, OR. Personal Comunication with J.D. Lokey, U.S. EPA, January 1978.
22. Heck, W.W., USDA, NCSU, Raleigh, NC. Personal comunication with J.D. Lokey,
U.S. EPA, February 1978.
23. Jacobson, J.S., Boyce Thompson Institute for Plant Research, Yonkers,
NY. (Temporary appointment to U.S. Department of Energy, Washington,
DC). Personal communication with J.D. Lokey, U.S. EPA, February 1978.
24. Tingey, o. i., U.S. EPA, CERL, Corvallis, OR. Personal communication
with J.D. Lokey, U.S. EPA, February 1978.
25. 1978 Criteria document, p. 11—20.
26. Adedipe, N. 0., R. E. Barrett, and 0. P. Omrod. Phytotoxicity and growth
response of ornamental bedding plants to ozone and sulfur dioxide.
J. Amer. Soc. Hort. Sd. 97(3): 341, 1972.
27. Evans, L.S. Bean leaf growth response to moderate ozone levels. Environ.
Pollut. 4: 17, 1973.
28. Engle, R. L. and W. H. Gabelman. The effect of low 1eve1s of ozone on
Pinto bean, Phaseolus vulgaris L. Proc. Amer. Soc. Hortic. Sd. 91:
304, 1967. —
29. Neely, G. E., D. T. Tingey, and R. 6. Wilhour. Effects of ozone and sulfur
dioxide singly and in combination on yield, quality, and N—fixation of
alfalfa. In: Proc. International Conf. on Photochemical Oxidant Pollut.
and Its Coi fro1. B. Dimitriades (ed.) Vol. II. Publication No. EPA-600/3—
77—OOlb, 1977, p. 663.
30. Tingey, D. 1., U.S. EPA, CERL, Corvallis, OR. Personal correspondence
with J.D. Lokey, U.S. EPA, April 14, 1978.
31. 1978 Criteria Document, p. 11-33.
32. 1978 Criteria Document, pp. ll—65’through 11—75.
33. U.S. EPA. Diagnosing Vegetation Injury Caused by Air Pollution.
Office of Air and Waste Management. Air Pollution Training Institute.
Research Triangle Park, NC, 1976, p. 3—19.
34. Taylor, O.C. Importance of peroxyacetyl nitrate (PAN) as a phytotoxic
air pollutant. J. Air Pollut. Control Assoc. 19 (5): 347, 1969.
35. 1978 Criteria Document, p. 11—12.
36. Thompson, C. R., and 0. C. Taylor. Effects of air pollutants on growth,
leaf drop, fruit drop, and yield of citrus trees. Environ. Sd. Technol.
3 (10): 934, 1969.
37. 1978 Criteria Document, pp. 11—15 through 11-18.
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49
38. Heggestad, H. E. Photochemical air pollution injury to potatoes in the
Atlantic Coastal States. Amer. Potato J. 50 (9): 315, 1973.
39. MacLean, D.C. and R. E. Schneider. Photochemical oxidants in Yonkers,
New York: Effects on yield of bean and tomato. J. Environ. Quality
5(1): 75, 1976.
40. NAS, op. cit. , p. 586.
41. 1978 Criteria Document, p. 12-46.
42. Ibid., pp. 12-27, 12—30, and 12-52.
43. Ibid., pp. 12-50 through 12—55, and 12-63.
44. Ibid., pp. 12-59 through 12—61.
45. Ibid., pp. 12—10 and 12—11.
46. Skelly, J. M., C. F. Croghan, and E. M. Hayes. Oxidant levels in remote
mountainous areas of southwestern Virginia and their effects on native
white pine ( Pinus strobus L.). In: Proc. International Conf. on
Photochemical Oxidant Po1 lut. a ff Its Control. B. Dimitriades (ed).
Vol. II. Publicatlon No. EPA — 600/3—77—OOlb. U.S. EPA, Research
Triangle Park, NCi 1977. pp. 611—620.
47. 1978 Criteria Document, p. 12-46.
48. Westman, W.E. How much are naturess services worth? Science 197: 960, 1977.
49. Crabtree, J. and F. S. Malm. Deterioration of rubber from use and with
age. In: Engineering Uses of Rubber. A. 1. McPherson and A. Kiemin (eds.).
New VoW, Reinhold Publishing Corp. 1956, pp. 140-170.
50. 1978 Criteria Document, pp. 13-7 and 13-8.
51. Ibid., p. 13—7.
52. Ibid., pp. 13—12 and 13—13.
53. Ibid., p. 13—14.
54. Ibid., pp. 13-14 through 13-18.
55. Ibid., p. 13—25.
56. Ibid., pp. 13—25 and 13—26.
57. Ibid., pp. 13—30 through 13—32.
58. Ibid., p. 1—2.
59. Ibid., p. 4-1.
60. U.S. EPA. Air Quality Data - 1976 Annual Statistics. Publication
No. EPA—450/2/78-009, January 1978 (In press).
61. 1978 Criteria Document, p. 3-7.
62. Ibid., p. 3—11.
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50
63. Ibid., pp. 1—4, and 4—38 through 4—40.
64. U.s. Department of Health, Education, and Welfare (U.S. DHEW). Air
Quality Criteria for Photochemical Oxidants. U.S. DHEW, Washington, DC,
1970, P. 4-2.
65. Singh, H. B., F. L. Ludwig, and W. B. Johnson. Ozone in Clean Remote
Atmospheres: Concentrations and Vartabilities. Stanford Research
Institute, Menlo Park, CA, June 1977.
66. 1978 Criteria Document, p. 4-53.
67. Ibid., pp. 4—47 through 4—62.
68. Iverach, D., U.S. EPA. Some General Comments on the Occurrence of
Short-term NO 2 . Memorandum to E.L. Meyer and S. Coerr, U.S. EPA,
January 1978.
69. 1978 Criteria Document, pp. 4—62 through 4—69.
70. Ibid., p. 7—29.
71. Lonneman, W. A., J. J. Bufalini, and R. L. Seila. PAN and oxidant
measurement in ambient atmospheres. Environ. Sd. Technol. 10 (4):
374, 1976.
72. Dimitriades, B. On the function of hydrocarbon and nitrogen oxides in
photochemical—smog formation. Bureau of Mines, U.S. Dept. of the Interior,
Report of Investigation, RI 7433, Washington, DC, September 1970.
73. 1978 Criteria Document, p. 11-87.
74. Larsen, R. I. A new mathematical model of air pollutant concentration
averaging time and frequency. J. Air Pollut. Control Assoc. 19 (1):
24, 1969.
75. The Clean Air Act as amended August 1977, Section 109(b)(2).
76. U.S. EPA, Alternative Forms of the Ambient Air Quality Standard for
Photochemical Oxidants. U.S. EPA Staff Paper, May 1978.
77. U.S. EPA. Procedures for Quantifying Relationships between Photochemical
Oxidants and Precursors: Supporting Documentation. Publication No.
EPA—450/2-77—021b, February 1978, p. 2—8.
78. PEDC0 Environmental, Inc. The Validity of the Weibull Distribution as a
Model for the Analysis of Ambient Ozone Data. Draft report to the U.S.
Environmental Protection Agency, November 1977.
79. Tingey, 0.1., and R. A. Reinert. The effect of ozone and sulphur dioxide
singly and in combination on plant growth. Environ. Pollut. 9: 117, 1975.
80. 1978 Criteria Document, p. l1 30.
81. Maas, E. V., G. J. Hoffman, S. L.Rawlins; and,6.’ qgata.Sa1 it ity.pzone
interactions on Pinto bean: Integrated response to ozone cdncentra ion and
duration. J. Environ. Quality 2 (3): 400, 1973...
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51
82. Omrod, 0. P. , N. 0. Adedipe, and G. Hofstra. Responses of cucumber, onion,
and potato cultivars to ozone, Can. J. Plant Sci. 51: 283, 1971.
83. Tingey, 0. 1., W. W. Heck, and R. A. Reinert. Effect of low concentrations
of ozone and sulfur dioxide on foliage, growth and yield of radish. J.
Amer. Soc. Hort. Sci. 96 (3): 369, 1971.
84. Tingey, D. 1., R, A. Reinert, C. Wickliff, and W. W. Heck. Chronic ozone
or sulfur dioxide exposures, or both, affect the early vegetative growth
of soybean. Can. J. Plant Sd. 53: 875, 1973.
85. Heagle, A. S., D. E. Body, and 6. E. Neely. Injury and yield responses of
soybean to chronic doses of ozone and sulfur dioxide in the field.
Phytopathology 64: 132, 1974.
86. Heagle, A. S., 0. E. Body, and E. K. Pounds. Effect of ozone on yield
of sweet corn. Phytopathology 62: 683, 1972.
87. 1978 Criteria Document, p. 11—31.
88. Oshima, R. J., 0. C. Taylor, P. K. Braegelmann, and D. W. Baldwin.
Effect of ozone of the yield and plant biomass of a corniiercial variety
of tomato. J. Environ. Quality 4 (4): 463, 1975.
89. U.S. EPA. National Aerometric Data Bank (NADB), maintained by Office of
Air Quality Planning and Standards (OAQPS), Research Triangle Park, NC.
Data printouts obtained April 12, 1978 and April 14, 1978.
90. u.s. EPA, NADB, maintained by OAQPS, Research Triangle Park, NC. Data
printouts obtained June through August, 1977, and December 19, 1977.
91. U.S. EPA. Photochemical Oxidants in the Ambient Air of the United States.
Publication No. EPA—600/3—76-017, 1976, p. 8.
92. U.S. EPA. Investigation of Ozone and Ozone Precursor Concentrations at
Nonurban Locations in the Eastern United States. Publication No. EPA—
450/3—74—034, May 1974, pp. 1-38, 1—39, and 1—46.
93. U.S. EPA. Investigation of Rural Oxidant Levels as Related to Urban
Hydrocarbon Control Strategies. Publication No. EPA-450/3—75-036, March
1975, pp. 56—57.
94. U.S. EPA. Formation and Transport of Oxidants along Gulf Coast and in
Northern U.S. Publication No. EPA—45O/3—76—033, August 1976, pp. 92—93.
95. Singh, H.B., Stanford Research Institute, Menlo Park, CA. Personal
communication with J.D. Lokey, U.S. EPA, January 1978.
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52
90 O• Summer Squash
5 .
s ft
I I
0.1 1 10 1 10 1 10 100
Exposure duration, hou,
FIgur. 1. Percent leaf injixy In fifteen plain species exposed to various ozone ooncenfrations for venous
dwations
Reprinted with permission from Larsen and Heck 14
*The concentration axes for these two cultivars should be
multiplied by 1.4 per the recomendation of W. W. Heck. 17
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53
Table 1 Selected Vegetation Genera and Species Grouped by
Sc nsitivity to Ozone 12
Sensitive
(total 28 species)
Intermediate
(total 41 species)
Resistant
(total 42 species)
Alfalfa ( 6 )a
Bean (4)
Broccoli (1)
Chrysanthemum
Clover (1)
Coleus (1)
Corn (1)
Grass (6)
Oats (6)
Petunia (2)
Radish (5)
Soybean (14)
Spinach (4)
Tobacco (35)
Tomato (7)
Alfalfa (9)
Bean (5)
Beet (1)
Cabbage (1)
Chrysanthemuni (13)
Clover (4)
Coleus (1)
Corn (2)
Grass (10)
Lettuce (1)
Oats (5)
Onion (1)
Petunia (1)
Radish (6)
Soybean (19)
Spinach (3)
lobacco (12)
lomato (6)
Wheat (1)
Alfalfa (3)
Bean (5)
Chrysanthemum (39)
Clover (1)
Corn (1)
Cotton (2)
Grass (3)
Lettuce (8)
Oats (1)
Onion (1)
Petunia (16)
Soybean (6)
Spinach (1)
Tobacco (1)
Iomato (3)
(6)
aNumbers in parentheses C ) are the numbers of varieties_of the species
for which reports of ozone response were reviewed in the 4AS report. 12
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54
Table 2 Limiting Values for Foliar Injury by Ozone’ 3
Ozone Concentration, pg/rn 3 (ppm)
Averaging Time, Agricultural Crops Trees and Shrubs
Hours Lower Limits Upper Limits Lower Limits Upper Limits
0.5
400 (0.20)
800 (0.41)
1
200 (0.10’)
500
(0.26)
400
(0.20)
1000 (0.51)
2
140 (0.07)
300
(0.15)
200
(0.10)
500(0.26)
4
75*(004)
180
(0.09)
120
(0.06)
340 (0.17)
8
40*(O.02)
100
(0.05)
80*(O.04)
200 (0.10)
*Although these values appear in figures depictinq limiting values for
foliar injury, the au thor stated that limiting values at concentrations
of 03 below 100 ug/m (0.05 ppm) are not useful because of inaccuracies
in measurements. He further stated that much of the data utilized in
formulating these limiting values was derived from KI monitoring methods
that if uncalibrated would tend to underestimate the actual concentrations
by as much as 50 percent. For many of the studies utilized, calibration
procedures were not specified.
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TABLE 3 Calculated Injury Parameters for Plants Exposed to Ozone
The injurythreshold is arbitrarilydefined here as 1% lealmjury In the median plantofan exposed set.
— m 2
*The concentrations given as injury thresholds for these
multiplied by 1.4 per the recommendation of Heck. 17
Calculated Injury
Threshold’, ppm.
for Exposure of
Leaf Injury
Equatton
Parameters
Multiple
Correl.
Injury Conc
Ratio, median!
Pollutant and Plant
1 hr 3 hr
8 hr
en 9
s
P
Coeff
threshold
OLone *
a. Bean, Pinto
0.13 0.07
0.04
0.31
1.44
—0.57
0.98
2.3
b Tomato, Roma
0.09 0 06
0.04
0.24
1.53
—0.35
0.98
2.7
c. Clover, Penscott Red
0.20 0 12
0.08
0.65
1.68
—0.43
089
3.3
d. Tobacco. Sd W.3*
0.11 0.05
0.03
0.34
1.60
—0.68
093
3 0
e Spinach. Northland
0.24 0.13
0.08
0.72
1.60
—0.55
089
3.0
f Chrysanthemum, Oregon
0.36 0 26
0.20
1.79
2.00
—0.27
076
5.0
g. Begonia, Thous. Wonders
0.18 013
0.10
0.76
1.85
—0.31
090
4.2
h Corn, Pioneer 509
0.18 0.10
0.05
0.80
1.91
—0.57
0.94
45
i. Corn, Golden Cross
0 15 0.09
0.06
0.83
2.11
—0.44
0.99
5 7
j. Bromegrass, Sac Smooth
0.16 0.11
0.07
0.64
1.80
—0.38
095
3.9
k Oats. aintland 64
009 006
0 04
0.47
2.02
—0.41
0.91
5 1
1. Radish. Cherry Belle
0.08 0.06
0.04
0.29
1.72
—0.32
0.93
3.5
in. Periwinkle. Bright Eyes
048 031
0.21
1.37
1.57
—040
0.94
2.8
ii. Wheat, Wells
0.39 0 23
0.14
0.83
1.3
—04
094
2 2
o. Squash, Summer
0.17 0 17
0.17
0.70
1.83
—0.01
0.96
4.1
Reprinted with permiision from Larsen
and Heck
U,
U,
cultivars should be
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56
Table 4
Growth and Yield Responses of Plants to Ozone Exposures,
Compared with Foliar Injury Response
Plant species 0 concentration. Exposure pattern Plant growth or yield Foliar injury Reference
& cultivar (cv.) ppnia Number of hours(h), response, % reduction response, % increase
days(d), & weeks(w) from control over control
Alfalfa, 0.05 (+) 8h/d, 5d/w, 12w 1211, foliage dry wt; 0 30.79.80
cv. Vernal 2211, root dry wt;
Bean,
cv. Pinto 0.30 O.5h/d, 14d 119, leaf dry wt; 22 b 81
141, stem dry wt;
231, root dry wt.
0.30 lh/d, 14d 401, leaf dry wt; 82 b
571, stem dry wt;
651, root dry wt;
0.30 2h/d, 14d 701. leaf-dry wt; b
801. stein dry wt;
831, root dry wt;
0.30 3h/d, 14d 761, leaf dry wt;
859, stem dry wt;
889, root dry wt;
Cucumber, 1.0 lh 199, top dry wt; 1* 82
cv. Ohio Kosiac 1.0 4h 379. top dry wt; 181
Onion, 1.0 lh 211. plant dry wt; 2* 82
cv. Spartan Era 1.0 41i 484, plant dry wt; 6*
Radish,
cv. Cherry Belle 0.05(+) 8h/d, Sd/w. 5w 10##, leaf dry wt; 1 83
I 5041, root dry wt;
Radish, o.is( ) 4h No significant effect 13
cv. Cherry Belle
045(e) 4h 3391. foliage dry wt: 80 30,19
7799, root dry wt;
Soybean o.o5() 8h/d, 5d/w ,3w 2*, top fresh wt; 81
cv. Hood 3* root fresh wt;
and I re o.lo(+) 8 hId. 5dfw, 3 211, top fresh vt; 199
241, root freshwt;
Soybean. -
cv. Dare O.05( ’) 6h/d, 133d 3*, seed yield; 191 86
22*, plant fresh wt;
0.10 ( ) 6h/d, 133d 554, seed yield; 371
651. plant fresh wt;
Sweet corn.
cv. Golden Midget O.05(+) 6h/d, 64d 9*, kernel dry wt; 141 86,87
0.10(1-) 6h/d, 64d 454, kernel dry wt; 259
Tobacco, ambient: often
cv. Bel W—3 >O.O5ppin(+) 48d 229, leaf fresh wt; 171 17,20
Tobacco.
cv. Bel W—3 O.05(+) 8h/d. 5d/w, 4w 1*, leaf dry wt. 8 30 79
- 3099, stem dry wt;
4299, root dry wt;
Tobacco,
cv. Burley-2l 0.05(+) 8h/d, 5d/w, 4w No significant reductions trace 30,79
Tomato, 0.20(f) 2.5h/d, 3d/w, 15w l**, fruit yield; extensive, considerable as
cv. H-li 3211. top dry wt; amount of defoliation
il**. root dry wt;
0.35(f) 2.5 h/d, 3dfw, 15w 45’#, fruit yield; extensive, almost
7291, top dry wt; cmnp etely defoliated
5994, root dry wt;
*I statistically significant difference from controls, at the 5% confidence level
** statistically significant difference from controls, at the 1% confidence level
fStatistically significant difference from controls, at the 5% confidence level
‘Statistically significant difference from controls, at the 1% confidence level.
aThe symbol (+) indicates that the reference specified both the monitoring method
and the calibration technique.
binese data are not presented in reference 81, bit were derived froe infor’ratio—
contained therei-.
-------
Table 5 Approximate Annual Per-Capita Materials Damage Costs
For Various Annual Average Ozone Concentrations
Costs,
$/year/persOfl
nnual Average Ozone Concentration Elastomers Fabrics Paints and Coatings
g/m 3 (ppm) ___ 4
10 (0.005) 1.15 0.34 0.36
20 (0.010) 1.76 0.50 0.66
30 (0.015) 2.11 0.59 0.92
40 (0.020) 2.37 0.65 1.14
50 - (0.026) 2.56 0.70 1.34
60 (0.031) 2.72 0.74 1.51
70 (0.036) 2.86 0.77 1.66
80 (0.041) 2.98 0.80 1.80
90 (0.046) 3.08 0.83 1.92
100 (0.051) 3.17 0.85 2.03
-------
58
Table 6. Ozone Data from Air Quality Control Regions (AQCR)
Containing the 16 Most Populous Urbanized Areas of the U.S., 197689
ACQR Total Number Number of sites Range of % days with hourly
of valid with 2nd max. 2nd max. values above
sitesa hourly value hourly standard level
above standard values, at the worst site C
levelb
(ppm)
New Jersey — New York - 2 2 447—470 29
Connecticut (0.23-0.24)
Metropolitan 21 20 137—706 55
Los Angeles (0.07-0.36)
Metropolitan 11 11 186—529 10
Chicago (0.09-0.27)
Metropolitan 10 10 294-412
Philadelphia (0.15—0.21)
Metropolitan 2 2 347—367 10
Detroit—Port Huron (0.18—0.19)
San FranciscO 14 14 196—333 24
Bay Area (0.10-0.17)
Metropolitan 2 2 314-345 23
Boston (0.16—0.18)
National Capital 11 11 284—539 17
(0.14—0.27)
Greater Metropolitan 4 4 222-345 28
Cleveland (0.1 1-0.18)
Metropolitan 8 8 198-418
St. Louis (0.10-0.21)
Southwest 0
Pennsylvania
Minneapolis — 0
St. Paul
Metropolitan 4 4 365—523 34
Houston—Galveston (0.19—0.27)
Metropolitan 2 2 314—353 9
Baltimore (0.16—0.18)
Metropolitan 2 2 321—353 20
Dallas — Fort North (0.16—0.18)
Southeastern 7 7 - 198—504 - 25
Wisconsin (0.10—0.26)
aOnly sites having a minimum of 4000 hourly observations were included in this sumary.
bThe photochenical oxidant standard is a one-hour average of 160 ug/rn 3 (0.082 ppm) of
ozone not to be exceeded more than once per year.
CThe worst site is defined as the site having the highest percentage of days with
hourly values above the standard level.
-------
59
Table 7 Oxidant Levels in 23 Urban Areas
a 90,91
of the U.S.. 1954-1976
Location Year
Data
Collected
Annual Second
Highest l- our
Value, pg/n t (ppm)
Annual Averaqe
Con 9 ntration
pg/rn (ppm)
Camden, NJ
1973
1974
1975
68
90
63
I
376 ‘(0.19) 44 (0.022)
366 (0.19) 40 (0.020)
505 1(0.26) 38 (0.019)
Corpus Christi, TX
1974
1975
80
70
241 1(0.12) 41 (0.021)
241 (0.12) 44 (0.022)
Des Moines, IA
1975
1976
90
72
192 (0.10) 47 (0.024)
199 (0.10) 66 (0.034)
Louisville, KY
1973
1974
1975
89
97
99
362 (0.18) 18 (0.009)
186 (0.09) 18 (0.009)
352 1(0.18) 23 (0.012)
Mamaroneck, NY
1973
1974
1975
64
94
84
309 0.16) 26 (0.013)
313 (0.16) 27(0.014)
258 0.13) 23 (0.012)
Memphis, TN
197(
1975
95
91
2251 (0.11) 38 (0.019)
254(0.13) 47 (0.024)
Newport, KY
1973
1974
1975
77
95
92
305 (o.16 ‘ 41 (0.021)
297(0.15) 30 (0.015)
321 (0.16) 34 (0.017)
naha, NE
1974
1975
90
83
166(0.08) \ 32 (0.016)
225 (0.11) I 53 (0.027)
Racine, WI
1974
95
562 1(0.29)1 50 (0.026)
‘
Richland\Co. . Sc
1973
1974
1975
65
94
98
155 (0.08) 30 (0.015)
270 (0.14) 41 (0.021)
245 (0.13) 40 (0.020)
Kansas City, KS
1973
1975
97
95
130 (0.07) 24 (0.012)
160 (0.08) 19 (0.010)
Pasadena, CA
Los Angeles,-CA
San Diego, CA
1964-65 NIAb
‘ N/A
“ N/A
950 (O 48)* 1 82 (O.042 I
840J0.43 * - 71 (0.0361 1
Denver, Co
St. Louis, MO
Philadelphia, PA
1964-65
‘
‘
N/A
NIA
N/A
440 (0.22)* 71(O.0 6)
360 (0.18)* 61 (0.031)
570 (O.29)* 51 (0.026)
.
i r iientd, CA
Cincinnati, OH
Santa Barbara, CA
1964-65
“
“
N/A
N/A
N/A
400 (0.20)* 59 (0.030)
280 (0.14)* 59 (0.030)
310 (0.16)* 71 (0.036)
,
Washington, DC
San Francisco, CA
Chicago, IL
1964-65
‘
“
N/A
N/A
N/A
310 (O.16)* 57 (0.029) *
220 (0.11)* 37(0.019)
250 (0.13)* 55(0.028)
AA11 data in this table obtained after
1970 were measured by ozone—specific
techniques. Earlier data measured total oxidants. Also, post-1970 data were
obtained from sites having valid data for at least 60 percent of the hours in the
year; consequently, the sites presented in this table may not have recorded the
maximum annual second—highest hourly values for their respective cities.
bNOt available
*Estimated from frequency distribution analyses.
-------
60
Table 8. Summary of Ozone Data for Rural and
Urban Sites in the Eastern and Central U.S., l973_l97592 93 94
Location Maximum Avg. Concen. % Days with Hours % Hours
Hourly Avg. over Period ‘Hourly Values Above Above
Con 9 ntration , Exant ned, Above Level Standard Standard
jig/rn (ppm) 1.tg/nv’ (ppm) of Standard Level Level
June 26 — September 30, 1973: Rural Sites
McHenry, MD 360 (0.18) 149 (0.076) 78 599 37
Kane, PA, 310 (0.16) 130 (0.066) 65 635 30
Coshoctan OH 350 (0.18) 112 0.057) 46 350 20
Lewisburg WV 280 (0.14) 105 (0.054) 39 253 15
June 14 — August 31, 1974: Rural Sites
Wilmington, OH 370 (0.19) 103 (O.O 58 259 14.9
McConnelsviIle, OH 330 (0.17) 102 (1)052) 56 239 13.3
Wooster, OH 330 (0.17) 94 O.O48) 55 262 14.0
McHenry, MD 330 (0.17) 113 [ 0.058) 43 262 13.0
DuBois, PA 400 (0.20) 112(0.057). 54 341 20.5
June 14 — August 31, 1974: Urban Sites
Canton, OH 280 (0.14) 71 (0.036) 44 148 8.0
Cincinnati, OH 360 (0.18) 49 (0.025) 20 54 3.5
Cleveland, OH 270 (0.14) 62 (0.032) 26 51 3.0
Columbus, OH 340 (0.17) 65 (0.033) 27 113 5.8
Dayton, OH 260 (0.13) 71 (0.036) 35 114 7.2
Pittsburgh, PA 300 (0.15) 56 (0.029) 37 106 6.5
June 27 — September 30, J975: Rural Sit s -
Bradford, PA 248 (O.f3) 1 81 iQ.O41) 18.5 100 4.3
Lewi sburg, WV 225 (0.11) 76 (O’ .039)i 11 .1 59 2.5
Cresthn IA 245 (0.12) 70 (Q,036J 7.9 17 0.8
DeRidder, LAa 256 (0.13) 61 (0.031) 8.0 38 1.3
Poynette, WI 243 (0.12) 76 (0J1391. 21.7 121 5.0
Port O’Connor, TX 259 (0.13) 55 (0.028) 12.4 99 3.4
June 1 - September 30, 1975: Urban Sites
Pittsburgh, PA 490 (0.25) 60(0.031) 34.6 227 8.0
Columbus, OH 196 (0.10) 44 (0.022) 11.6 43 1.5
Cedar Rapids, IA 180 (0.09) 50 (0.026) 0.9 6 0.2
Des Moines, IA 196 (0.10) 73 (0.037) 20.9 124 4 9
Omaha, NE 216 (0.11) 71 (0.036) 20.1 64 3.6
Nederland, TX 380 (0.19) 55 (0.028) 33.6 138 5.1
Austin, TX 206 (QJ1) 49 (0.025) 9.6 19 0.8
Houston, TX 629 (0.32) 51 (0.026) 37.6 141 6.7
a- -
Data obtained for this site through October 31, 1975.
-------
TABLE 9
Ozone Air Quality In Remote Locations — 65 —
Station Location Elevation Extent of Avg. Concen. Maximum Month in Number of Estimated
Number Above Mean -- Data ,Months over Period 1—hour which Max. flays with S Days with
Sea Level. (Years of - Examined, Average Ozone 1-hr. Value Hours above Hours above
m Observation). lag/rn 3 (ppm)a Conc ntration, Occurred Standard Stand rd
ug/m (ppm) Level Level
I Qulllayute, WA 62 19 (1974-75) 55 (0.028) 120 (0.063) Apr11 0 0
2 McRae, MT 975 15 (1974-75) 77 (0.039) 160 (0.080) March, June 0 0
3 BN Site, MT 1082 10 (1975-76) 86 (0.044) 180 (0.093) April 5 <1.9
4a White River, UT 1590-1625 16 (l974-76 __75 (0.038) 190 (0.096) May N/I” N/A
4b 16 (1974-76) 7J (0.036) 150 (0.076) May 0 0
4c 18 (1974-76) 67 (0.034) 150 (0.076) March 0 0
5a Rio Blanco, CO 1900 19 (1974-76) 55 (0.028) 160 (0.080) June 0 0
Sb 2100 19 (1974-76) 55 (0.028) 150 (0.078) June 0 0
6 Fritz Peak, COC 2730 9 (1975) 73 (0.037) 228 (0.116) August 7 3
7 Converse Co., WY N/A 6 (1974) (0.043) 150 (0.076) June 0 0
8 White Face Mtn., NYC 1510 23 (1974-76) 61 (0.031) 212 (0.108) May 19 3
9 Mauna Loa, HI 3400 24 (1974-75) 67 (0.034) 190 (0.095) July 6 1
10 Zugspitze, 3000 21 (1974-76) 59 (0.030) 385 (0.196) January 2 0.4
West Germany
dThese data are not p sented in the reference; they were derived from data in the reference after consultation with
one of the authors
bNot available
C -
These sites, although nominally remote, are frequently subject to contamination due to long-range transport from
urban areas.
-------
Table 10
Predicted Median Foliar Injury (Percent) due to Ozone Exposures Expected o be Exceeded Only Once per Year for
Different Standard Levels. After Larsen and Heck l’+
Plant species.
ultivar
Hourly average standard level, ppm (Wg/m 3 )
0.06 (118) 0.08 (157) 0.10 (196) 0.12 (235)
Exposure levels expected to be exceeded only once/year, ppm x hr - - -
0.060
x
1
0.052
x
3
0.039
x
8
0.080
x
1
0.069
x
3
0.052
x
8
0.100
x
1
- 0.086
x
3
.O.065
x
8
0.120
x
1
0.104
x
3
0.078
x
8
Bean, pi t 0 a
0
0
0
0
0
1
0
0
3
0
1
7
romato, Rome
0
0
1
0
2
3
2
7
9
5
15
19
Clov ,Penscott Red
0
0
0
0
0
0
0
0
0
0
0
1
Tobacco. Bel W-3
0
0
1
0
1
4
0
2
11
0
5
20
Spinach. Northland
0
0
0
0
0
0
0
0
0
0
0
1
Chrysanthemum. Oregon
0
0
0
0
0
0
0
0
0
0
U
U
Begonia. Thous. Wonders
0
0
0
0
U
U
Corn. Pioneer 509
0
0
0
0
0
1
0
1
2
0
i
4
Corn. Golden Cross
0
0
0
0
0
1
0
1
1
0
2
Bromegrass. Sac Smooth
0
0
0
0
0
0
0
0
1
0
1
1
Oats. Cllntland 64
0
1
1
1
2
3
1
4
5
3
7
g
Radish, Cherry Belle
I )
1
1
1
2
3
2
6
6
11
12
Periwinkle, Bright Eyes
0
0
0
0
0
0
0
0
0
0
0
0
Wheat. Wells
0
0
0
0
0
0
0
0
0
0
0
0
Cr ia h, Sj’r ’r
0
0
0
0
0
0
0
0
0
0
0
0
a
T ie concentrations given In the column headings were divided by 1.4 in order to conver+ them into
values equivalent, to those used In generating the follar Injury equations for these cultivars. 17
-------
63
APPENDIX A
Annual Second—Highest Ozone Concentrations
versus Averaging Times for
Twenty-four Site-Years of Data
-------
a
:r
J :E
r
r
Ti:
: :
4 56 1891
I;
I. :,
:
I! Il ’ 1i
:
r
f
—
LL_.
—r -
,
‘
——
- —
- — .—
-
-r-r-r
- ti
r
-
J I
-
7
L
..LLL.
i11
7
L”I:fT HT:T1
WI
r
4
r
4 567891 2 3 4 5 61891 3 4 5 G789 1
r
LL
- -±
LE
U
7
E’
,
i1
:, 1
ft
T T _..l T:f1U TJ _i ,
rr
:1
1 Ce
7;
II
. ,-
I
-- :-- -. ..
;
T
Li i i
L
i U
—• i -
i
: U
..
:
L
I.
1
H
.4;:
-_ -
L.
-
Tr:.
H-t
iUi
r
1 .L 1
‘p
1000
1 10 100
Averaging Time, Hours
Figure A-i
Camden, NJ, 1973 (68 percent data)
1
0001 ‘_
9
4 56 7b9
-1 -
1.1. —, -.
H—
t
71
—
I I
CQ 1
I,,
Tr
E
C
0
4 )
L
4)
c
Q)
U
C
0
c i)
C
0
NJ
f
1i
II.
• : : ••. : I I
II.:..’
II’
1
8
b
2
100
9
a
7
6
S
4
2
10,
9
8
7
6
S
4
2
II
4
IjJ
H
I i
II .
III
t
II
t Hj
•1
-------
I :• : :
rr r • • •
FJ fl4
T : ‘ J
:1L
r T
—J-—
1
4 -1
-
r
EE
TL
:
. * 4
Hi
y 1
t1 ± * !
1-
1 f llhi1i i 1 H
j! ‘Ii I r
t { Ii 1k
=-::: ‘
l ±4
—
t, Tt
1
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T # ’
L
I _ HH
t t
1lf
4_Jj
$1 LIt1fl II11LhL
r; L ••?
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-—:
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I
II
—
t:
—
1
it ——
H4f
!
ia i Ti I.
I
: 1 rn fm
Figure \—2
Averaging Tir e, Hours
Camden, NJ, 1974 (90 percent data)
3 4 5 6 7891
:;
2 3 4 5 6 7891
.t :T T 7
i— H -
I’
J :l:i Ij f ,j . . . .
3 4 5 67891
I ‘ . ‘. :1 ; . ;:.
I ! • • 1 :
i 1!
I ! lI , .
! I
: :
I !
Im
1 1
‘1 F
2 3 4 5 67891
1
: I
N
.
. ; i’_ ‘_ U iI •
r i
1
i ‘:l i I : , 1 L
1 ‘ • ‘ e ,,
El
I . .III I. ..
1
. . .,
.
I : . ; :i
ht
-
4 5 t 7 B 1
c
. . .!:I
, II , .I
H: 9if9fiT r T if 1 !
I1
•1’•
0001
9
8
7
6
5
4
:
2
1 OQ
9
a
7
6
5
4
3
1Q
9
8
7
6
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T .
:
.11
;j ji [
! !t
100 1000
. . . .li I I . :
, 1i , I4,I I
-------
Averaging Time, Hours
Figure A-3
Camden, NJ, 1975 (63 percent data)
4 5 6 ? 9
——,-, . .i-
. . • —t—’ r
-h -I-
-:--—7 [ -TT-tT •- 1
T •
L’ • r; .
. •i: :
4 5 6 7891
I— --,—-
-. - -
9
8
7
6
S
4
2
9
8
7
6
3 4 S 67891
I : [ :
ii :
:... :i
. Ii •i
1000
c .)
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c i)
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0
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0
r’4
10
: :• 1 : 1
H•
3 4 5 6 7891
I’
A
8
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:4
3 4 5 C.7 i
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t i
4
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ti
H
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4 t-— H -- r--’ -- - --- -- - -‘- - +- -—- — I
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-ri-i—T - - — — .. — — ifi iii (1”; •• • 4 -r iirnn ”ir ‘i
- -I— 4 — — — — — — J4 w •_ _ — — . $1 .4 —i £F
3t PH__ : f :: I
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i iii i ii _ _
t , ;
1Jili I Ti I Tn
1 10 100 1000
-------
Averaging Time, Hours
Figure A-4 Corpus Christi, TX, 1974 (80 percent data)
4 5 67b91
3 4 5 6 7091
I.
I : . i ; H ‘i ,:
1000
9
8
7
6
S
4
3
I
, : .‘
3 4 5 67691
1
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Figure A-5
Corpus Christi, TX, 1975 (70 percent data)
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Figure A-6
Des Moines, IA, 1975 (90 percent data)
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Figure A.-7
Des Moines, IA, 1976 (72 percent data)
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Averaging Time, Hours
Figure A-8
Louisville, KY, 1973 (89 percent data)
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Figure
Averaging Time, Hours
A-9 Louisville, KY, 1974 (97 percent data)
10001
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Figure A-b
Louisville, KY, 1975 (99 percent data)
4 b 6 7891
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Averaging Time, Hours
Figure A-li
Mamaroneck, NY, 1973 (64 percent data)
2 3 4567891
I
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Figure A-12 Mamaroneck, NY, 1974 (94 percent data)
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Averaging Time, Hours
Figure A-13 Mamaroneck, NY, 1975 (84 percent data)
-
3 4 S 67891
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Averaging Time, Hours
Figure A.-14 Memphis, TN, 1974 (95 percent data)
1
H
4 S 6 7891 3 4 S 6 1091
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88
Appendix B
Calculation of Exposures Expected
to Accompany Alternative Standard Levels
-------
89
This appendix explains the computation for different short-term
averaging times of the maximum exposure levels which are expected to
accompany alternative hourly average standards, and estimates lona—
term exposure patterns expected to accompany such standards.
1. Weibull Frequency Distribution
For the purposes of this document, the Weibull frequency distribu-
tion was assumed to provide a reasonably good description of the frequencies
at which ambient ozone concentrations occur in urban areas. This assump-
tion was based on an analysis of ozone data collected during 22 site-years
in 14 urban areas across the nation, as presented in a draft report 78
prepared for EPA by PEDCo Environmental, Inc. (referred to henceforth as
the PEDCo report).
A useful form of the Weibull frequency distribution equation is:
G(x) = exp (B-i)
where G(x) is the fraction of the total members of a population having a
value greater than x, and k and .5 are two parameters of the frequency
distribution. The Weibull distribution is readily adapted for analysis of
an air quality standard expressed in a statistical form. Such a standard
level , Cstd, is expected to be exceeded no more than E times per year. If the
standard level is based on an averaging time such that there can be a total
of n measurements in a year, one has:
Ic 1k
G’ _E .. I std l
- — exp - L j B-2
Rearranging this equation enables one to define the parameter .5 in terms of
-------
90
the standard specifications, like so:
(B-3)
Uk
[ ln )
There will be different frequency distributions for different averaging times, and
the parameters for these are designated in this appendix by subscripts, e.g., klhr
and 3hr
2. Short—term Exposure Levels
This section will for illustrative purposes examine an hourly average
standard of 0.08 ppm (157 i.’g/m 3 ) for which E equals one in order to evaluate
the 3- and 8—hour—average concentrations idesignated as C3hr and C8hrI
respectively) which may be expected to be exceeded only once per year.
To begin this analysis, one must choose a value of the parameter klhr
suitable for an area attaining a 0.08 ppm hourly average standard level. The
average klhr for the 22 urban site—years listed in Table 5-1 of the PEDCo
report is 1.05. None of these sites attained the current standard; several
had more than 200 hours above 160 ig/m 3 (as indicated in Table 6—1 of the
PEDCo report). However, an examination of those sites with relatively few
hours (less than 60) above the standard level along with other data from
two site-years at Kansas City, Kansas which did’attain the standard indicates
that a klhr value of about 1.25 provides a reasonably good estimate of what
might be expected for an average klhr value in urban areas attaining a 0.08 ppm
hourly average standard.
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91
Having selected an average k1hr one can use equations B-4 and B-5
(which were obtained by linear regression analyses of the k values in Table
5—1 of the PEDCo report) to determine k3hr and k8hr• It is assumed that the
relationship between the k parameters for different averaging times which is
indicated by Table 5—1 is valid when a 0.08 ppm standard level is attained.
k3hr = 1.02 klhr + 0.014 = 1.289 (B—4)
k8hr = 1.23 klhr — 0.043 ]..495 (B—5)
The correlation coefficients (R 2 ) for equations B-4 and B—5 are 0.98
and 0.92, respectively, indicating a reasonably good fit with the data.
Using the selected kihr one can determine lhr from equation B-3:
Cstd = 157 1g/m 3
____________ _______________ = 26.9 i g/m 3 (B-6)
6 lhr = l/klhr 876011/1.25
[ in ]
For given lhr and k1hr Figure 2—I in the PEDCo report permits calculation
of the annual average concentration, g, as follows:
For klhr = 1.25, ihr = 0.938, so = 25.2 i.ig/m 3 (B-7)
The annual average concentration is the same regardless of whether data expressed
in 1-, 3—, or 8-hour averaging times are used to compute . This fact enables one
to calculate 6 3hr and 8hr using Figure 2—1:
For k3hr = 1.289, .4— 0.931, so 3hr = 27.1 hg/rn 3
3hr
For k8hr = 1.495, 4— = 0.903, so 6 8hr = 27.9 iig/rn 3
8hr
Fin l1y, one may detr rmine the concentration c which is expect to be
exceeded E times per year for 3-hour or 8-hour averaging times by returning to
the Weibull frequency distribution equation:
G(c) = = exp
(B—i)
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92
Rearranging the above equation yields
1/k
c = 6 (in ) (B—b)
Thus,
C hr = 6 3hr [ in 1.0 ] 136 Mg/rn 3 (0.069 ppm) (B-li)
CBhr = 6 8hr In lOg 5 l/k8hr 103 g/m 3 (0.052 ppm) (8-12)
Those are the concentrations expected to be exceeded only once per year for
each averaging time in an urban area just attaining a 0.08 ppm hourly average
standard level. These values are presented in the table below,
along with corresponding values derived for alternative standard levels.
Table B—i
Short—Term Ozone Exposures Expected to Accompany Alternative Standard Levels
Cstd
ppm ( ig/m )
c , concentration expected to be exc eded only once per year
for given averaging times, ppm ( ig/m )
1 hour
3 hour
8 hour
0.06 (118)
0.08 (157)
0.10 (196)
0.12 (235)
0.060 (118)
0.080 (157)
0.100 (196)
0.120 (235)
0.052 (102)
0.069 (136)
0.086 (169)
0.104 (203)
0.039 (77)
0.052 (103)
0.065 (l2 )
0.078 (154)
Excerpts from this table are presented as column headings in Table 10
for use in the foliar injury analysis.
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93
3. Long—term Exposure Patterns
The preceding computational technique may be used to obtain an estimate
of the long-term exposure patterns that are expected to accompany alternative
short—term standard levels. In this regard, the criteria document concluded
that significant growth and yield effects could occur if the average ozone
concentration exceeds 0.05 ppm (98 .ig/m 3 ) beyond 15 days. 3 ’Based on the evidence
cited in its support, this conclusion is for the purposes of this document
interpreted to mean 15 consecutive days with maximum 3—hour-average concentra-
tions above 0.05 ppm. The analytical criteria indicated by this conclusion
provides the basis for evaluating alternative standards levels with respect
to their long-term impacts on vegetation. - ________________
Unfortunately, this criteria cannot be rigorously evaluated using the
computational methods presented in this appendix. These procedures can only
predict the number of times a given exposure level will be exceeded in a year,
and do not address the probability that such exceedances will occur on
consecutive days. This means that using these methods to analyze alternative
standard levels with regard to the above criteria inherently introduces a
bias towards overestimating their long-term impacts on vegetation.
The existence of this bias indicates the need for caution in interpreting
the results obtained by these procedures. Nevertheless, EPA has judged that
these methods are the. best analytical techniques currently available to
evaluate the long-term impacts on vegetation for alternative standard levels,
and —— recognizing their limitations —— has used them accordingly. The
results are indicated in the table below. For several alternative hourly
average standards, the 8—hour frequency distribution was analyzed in the same
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94
manner as in the previous section. In this case, the quantity being
evaluated was E, the expected number of 8—hour average concentrations
per year above 0.05 ppm (98 pg/rn 3 ). This was obtained from the following
modification of the Weibull frequency distribution equation:
E = n exp —1-i-. 1 k8hr (B-13)
8hrJ
Table B-2
Long-Term Ozone Exposure Patterns Expected
to Accompany Alternative Hourly Average Standards
cS d E, expected number of 8-hour—average
ppm (pg/rn 3 ) concentrations per year above 0.05 ppm (98 pg/rn 3 )
0.06
(118)
0
0.08
(157)
2
0.10
(196)
10
0.12
(235)
31
Contravening the aforementioned bias toward overestimating the long-term
impacts on vegetation for a given standard level, other uncertainties involved
in this analysis tend to underestimate the impacts. For example, the analysis
does not examine the possibility that in rural areas the rate of decrease of
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95
peak concentrations with increasing averaging times may be lower than
in the urban areas for which there are sufficient data to assess such
rates of decrease. In other words, it is uncertain what relationships
might be valid between the k parameters for different averaging times
at representative rural sites. It seems plausible that these relation-
ships would be such that higher 8-hour—average peak concentrations would
result at a rural site than at an urban site if both were meeting the same
hourly average standard, due to the higher levels of ozone—scavenging
anthropogenic pollutants (such as NO) at the urban sites. Nevertheless,
it was necessary to use urban relationships to conduct the foregoing analysis
because the rural relationships (which are admittedly more pertinent to the
issue of a secondary standard) have not been quantified.
Another uncertainty in the air quality estimates is provided by the
fact that, for 3- and 8—hour averaging times, the data were evaluated
for only the 8 and 3 time periods, respectively, that coincide with a calendar
day. If the data were analyzed so as to examine all possible 3- and 8-hour
periods (i.e., a “running average” analysis), it seems likely that higher 3-
and especially 8—hour—average peaks would be associated with a given hourly
average standard. This is because the maximum ozone levels tend to occur in
the afternoon hours (approximately 12 p.m. through 8 p.m.), which period is
split by examining the three 8—hour periods that coincide with a calendar day
(12 a.m. — 8 a.m., 8 a.m. — 4 p.m., and 4 p.m.- 12 a.m.). Unfortunately,
the analysis of air quality data that was performed in this appendix was not
capable of evaluating “running averages”, so this uncertainty must be weighed
into the examination of alternative standard levels.
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A further uncertainty involved in interpreting Table B—2 with
respect to the adequacy of a particular standard level lies in the
possible interactive effects of ozone with other pollutants. The
conclusion of the criteria document that significant growth and yield
effects could occur if the (8-hour) average concentration exceeded 0.05 ppm
beyond 15 days was based On studies examining controlled exposures of plants
to filtered air to which only ozone had been added. The simultaneous
presence of non—ozone oxidants (such as PAN) or other pollutants such as
SO 2 in the ambient air could produce synergistic effects if the specified
ozone concentration were exceeded for fewer than 15 days.
Because of the uncertainties discussed above, it is concluded that
a 0.10 ppm standard level may not in fact be sufficiently stringent to
protect against significant growth and yield effects due to the long-term
exposure patterns expected to accompany that standard. It does appear that
a 0.08 ppm standard level would be adequate for this purpose.
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