Working Draft Paper - Do not cite or quote

This is a preliminary document prepared by a subgroup of members of the
Base Programs Analyses & Policies Work Group (BPAPWG) as part of the
Federal Advisory Committee Act (FACA) subcommittee process. It is not an
EPA document. It is subject to further work group discussion. Interested
people should forward their comments to a member of the Base Programs
Analyses & Policies Work Group.

July 25, 1996

[CONTACT PERSON]{.underline}

Name: Steve Pezda/David Chock

Phone: (313) 322-9213

Fax: (313) 594-4271

E-Mail: \<usfmc3gq@ibmmail.com\>

[ISSUE TITLE]{.underline}

Implementation of a "Too Close to Call" Category As a Mechanism to
Reduce the Impact of Meteorological Fluctuations on Attainment
Designation and State Implementation Plans

[DESCRIPTION]{.underline}

[Background and Problem]{.underline}

In the closure letter on the primary standard portion of the Staff Paper
on ozone, addressed to Carol Browner, EPA Administrator, and dated
November 30, 1995, the Clean Air Scientific Advisory Committee stated:

> \"The present standard is based on an extreme value statistic which is
> significantly dependent on stochastic processes such as extreme
> meteorological conditions. The result is that areas which are near
> attainment will randomly flip in and out of compliance. A more robust,
> concentration-based form will minimize the \"flip-flops,\" and provide
> some insulation from the impacts of extreme meteorological events. The
> Panel also endorses the staff recommendation for creating a \"too
> close to call\" category.\"

Statistical studies have indicated that the current attainment test for
ozone, which immediately considers an area as noncompliance (or,
officially, as nonattainment) whenever it has four or more days in three
years with the daily maximum ozone concentration exceeding the level of
the standard, actually makes the ozone air quality standard much more
stringent than generally assumed (Refs. 1, 2, 3). This is because
meteorology fluctuates from year to year. So does the ozone (and PM)
concentration, being substantially influenced by meteorology. And in the
case of ozone, for an area to guarantee meeting the present standard at
all times, the effective design value or the annual second highest value
will have to be so low that it is within the range of the annual second
highest values observed by monitors recording background-level
concentrations. (See Figures 1 and 2.) As a result, the present ozone
air quality standard may not be achievable on a long-term basis. If the
yet-to-be-proposed ozone air quality standard is more stringent than the
present standard (and similarly for the PM case), and if the attainment
tests for the new standards continue to ignore the role of
meteorological fluctuations, then the achievability problem of the
proposed standard will be considerably more severe for a large portion
of the country.

The continuous required lowering of the design value (due to the present
attainment test) comes in the form of flip-flops in the attainment
status of many areas which may otherwise have been considered "in
attainment." The general perception to date is that once the design
value is brought down to the level of the standard, we have achieved the
standard. But actually, we are far from achieving the standard. The 1988
heat wave raised the ozone concentrations substantially across the
Eastern US. Subsequently, many theretofore attainment areas were
designated as nonattainment. But the increase in the number of
nonattainment areas was not due to the failure of the control strategy.
Rather, it was partly due to an attainment test that ignores
meteorological fluctuations. Implementation of controls in many of these
otherwise attainment areas is what drives the effective design values
downward, eventually requiring a level substantially below the level of
the standard. Furthermore, such controls are likely not cost effective
because of the increased resistance exerted by the background ozone
concentration as the ambient ozone concentration goes down. Because of
our finite resources, it may be rather impossible to demand meeting the
standard based on the current attainment test. Doing so is tantamount to
requiring building a dam that can withstand an "infinite-year" flood
which we can clearly ill afford.

Between 1983 and 1993, 49% of the counties with a continuous data base
and with a long-term mean (average of nine three-year periods) of the
annual 5th highest 8-hour values below 80 (85) ppb had at least one
violation of an annual 5th highest level of 80 (85) ppb. The highest
long-term (11 years in this case) mean without causing a violation was
73 ppb, whereas the annual 5th highest 8-hour values of the background
ozone concentrations have a range of 45 to 65 ppb. If the monitoring
period lengthens, the 73 ppb value will go down. The achievability of an
8-hour 5th highest value standard of 80 ppb will be a serious concern.

The recently released Advance Notice of Proposed Rulemaking by EPA did
not contain sufficient specifics to define the proposed new ozone and PM
air quality standards. For the ozone standard, there was an unofficial
version that considered an area to be "in attainment" if its 3-year
averaged annual 2nd highest value of the daily maximum 8-hour
concentrations did not exceed 80 ppb, or "not in attainment" if its
averaged annual 5th highest value exceeded 80 ppb. Based on the present
attainment test, for the 1991-1993 period, 17% and 32% of counties with
data do not attain the current and the 8-h/5th highest/80 ppb standards,
respectively; 83% and 41% attain the current and the 8-h/2nd highest/80
ppb standards, respectively. For the 1986-1988 period, 50% and 67% of
counties with data did not meet the current and the 8-h/5th highest/80
ppb standards, respectively; 50% and only 15% attained the current and
the 8-h/2nd highest/80 ppb standards, respectively. This unofficial
standard is considerably more stringent than the present standard even
if we consider only the 5th highest value part of the unofficial
standard. Presumably, the region in between is considered "within the
range of attainment." This region could be assumed to be intended to
absorb the fuzziness in health effects. However, it does not cushion the
impact of meteorological fluctuations. Much more importantly, the ranges
of the year-to-year fluctuations (described as within one standard
deviation of the three-year means) of the annual second and fifth
highest values are considerably greater than the difference between
them. And if we continue to apply the current attainment test to both
the 2nd high and the 5th high parts of the unofficial standard, then one
does not remove the achievability problem.

[OPTIONS]{.underline}

The options below have been proposed by members of the BPAPWG. The
purpose of the options is designed to alleviate, but not eliminate, the
problem of achievability. Their relative advantages and disadvantages
are described based on their technical merits and practical
implications.

[Option #1 - No change from present methodology]{.underline}

This option will continue to use the current attainment test which
requires a zero-percent chance of violation of the standard. An
advantage of this approach is that there is no need to introduce any new
measure. However, a serious consequence is that the impact of
uncontrollable year-to-year meteorological fluctuations will continue to
be ignored, leading to a situation where, for the present ozone air
quality standard, the effective annual second highest value will have to
be within the range of the annual second highest values of the
background ozone concentrations to assure long-term compliance of the
standard. Consequently, the problem of achievability arises. If the
standards are to become more stringent still, then the achievability
problem (at least for ozone and possibly for PM as well) will be even
more severe. The control will be much more costly and much less
effective as the background ozone concentrations are being approached,
while the benefit of public health improvement is likely to be minimal
at best.

[Option #2 - Implement a new attainment test to determine if an
attainment area that briefly exceeds the level of the standard should be
classified as "Too Close To Call" (TCTC) or reclassified as
"nonattainment"]{.underline}

This approach is designed for an area that has been designated "in
attainment" previously. A meaningful TCTC assignment requires a
characterization of the year-to-year fluctuation of the ozone (or PM)
concentrations. The standard error of the (3-year) average of the annual
*m*th highest values is a logical choice. This quantity varies according
to the year-to-year concentration fluctuation over a 3-year period. A
simple statistical attainment test can then be designed that, in
essence, says that our level of confidence on the average annual *m*th
highest value increases or decreases according as the year-to-year
concentration fluctuation decreases or increases. Under this condition,
an area that is previously designated as in attainment may be
temporarily considered a TCTC area if it only briefly exceeds the level
of the standard due to unusual meteorology. A more detailed description
of this option is presented in the Appendix.

This option helps reduce (but far from eliminate) the mismatch between
the perceived and actual stringency of the standard. It also helps
reduce costly and ineffective control requirements that produce very
little health benefits in areas that effectively attain the standard. It
also slightly improves the long-term achievability of the standard. Of
course, the achievability issue is very much dictated by the form and
level of the standard relative to the behavior of the background
pollutant concentrations.

The unofficial new ozone standard contains an interval dubbed "within
the range of attainment." The question is whether this interval could
play the role suggested by the present option even though the interval
was designed to absorb the fuzziness in health effects. However,
meteorological fluctuations are independent of uncertainties in the
health effects. And both boundaries of the standard are subject to the
impact of meteorological fluctuations. In fact, this option should be
applied to both boundaries. The truly relevant boundary of this standard
is that for the annual 5th highest value. The present option can be
applied to this boundary alone.

A disadvantage of this option is the need for a paradigm shift and the
need for a better appreciation of the statistical behavior of ozone
concentrations. An outreach effort may be necessary to educate the
public at large.

[Option #3 - Implement a TCTC approach as in Option #2 but apply it
equally to both attainment and nonattainment areas]{.underline}

In this option, the TCTC interval will cover both sides of the level of
the standard. This option reflects a concern that Option #2 does not
consider the nonattainment areas that may temporarily indicate
attainment due to unusual meteorology. This concern was actually
considered in a Monte Carlo simulation of the attainment process (Ref.
1). The only sensible outcome of classifying a nonattainment area as
TCTC when its design value moves below the level of the standard is not
to impose more control because its design value is already below the
level of the standard. As a result, the area effectively attains the
standard. Therefore, this option is essentially the same as Option #2.
However, this option may continue to impose any remnant control that was
introduced when the area was not in attainment.

[Option #4 - Use a "Weight of Evidence" approach in the attainment
test]{.underline}

This option addresses mostly the ozone attainment test. The option
allows two acceptable tests, one statistical and the other
deterministic. Failing either test, an area can use a "weight of
evidence" determination to reassess its attainment status. The
statistical test allows up to 3 exceedances of the level of the present
standard (124 ppb) at every location on severe episode days. The
magnitude of each allowed exceedance will be limited to be consistent
with observed ozone patterns at sites currently attaining the standard.
For a new concentration-based standard, this statistical test will have
to be modified, perhaps using the annual 7th or 8th highest value in
place of the 3 exceedances if the standard is to be based on the annual
5th highest value. The deterministic test requires the daily maximum
concentrations in every surface grid cell to be below the level of the
standard for all primary episode days. A primary episode day is every
modeled day except the first day of each episode. Clearly, the
deterministic test is more stringent than the statistical test.
Accordingly, the burden of proof required from corroborative analyses is
less for a weight of evidence determination to amend the conclusion of
the deterministic test.

The weight of evidence determination may consist of several
corroborative analyses: (1) grid model performance and degree of
confidence in model input database and predictions, length of projection
period, etc.; (2) trend analysis based on the extent of the monitoring
network, quality of the statistical model for trend predictions, the
length, persistence and significance of a downward trend, etc.; (3)
consistency in direction of control between observation-based model
results and grid model predictions; (4) severity of episodes selected
for modeling; (5) incremental cost/benefit analyses addressing potential
lack of alternatives for reducing emissions, lack of model
responsiveness for variety of strategies as the level of the standard is
approached, etc. The weight given to each corroborative analysis
presented will depend on the degree of confidence one has on the result
of the analysis.

This option shows a genuine attempt to take all factors into
consideration in determining the attainment status and control
implementation. It contains flexibility on a case-by-case basis. It also
reflects the complexity of the ozone (and, likely, PM as well) problem.
Of course, an obvious disadvantage is that it may be too complex. Also,
since the weight of evidence determination relies heavily on the
richness of data and model applications, this option is suitable
primarily to major urban areas.

[Option #5 - Use five years of data and ignore the highest and the
lowest values to calculate the three-year mean]{.underline}

After removing the highest and the lowest values, the mean from the
three, not necessarily consecutive, years is compared with the level of
the standard to determine compliance. This option does not address the
"too close to call" situation in the context presented here because this
is a method to reduce the fluctuation of the mean whereas we are
addressing how to take this fluctuation into consideration in the
attainment test. The two processes are distinct and independent. In
fact, they can be coupled together in actual applications. This option
provides an alternative to EPA's approach of estimating the mean using
three years of data. While the resulting mean is more stable, the
fluctuation about this mean can remain large and should still be
considered in a rational attainment test.

The approach requires five years of data instead of three. Consequently,
long-term trends may wind up playing an important role in attainment
designation, which may not be desirable. EPA's choice of three years for
attainment designation is a good balance between the need to use a large
database and the need to avoid long-term trends.

[OTHER ISSUES]{.underline}

• If an area is shown to contribute to or cause the nonattainment status
of a downwind area, then regardless of its own status, control ought to
be implemented to help assure the downwind area to attain the standard.

• The approach of S. T. Rao was raised in the TCTC discussions. This
approach attempts to use the normal conditions as the basis of control.
S. T. Rao's approach is not a TCTC approach. It does not address the
attainment designation issue. It emphasizes the control in the mean
daily-maximum concentrations but continues to require the control to be
applicable to the extreme meteorological conditions.

[RECOMMENDATIONS]{.underline}

The Base Programs Analyses and Policies Work Group referred these issues
to the Science and Technical Support Work Group for their consideration.
The Science and Technical Support Work Group discussed these issues. The
Science and Technical Support Work Group recognized the issue of coming
in and out of attainment due to the variability in meteorology (and the
related issue of the achievability of the standards), and that a
statistical test may mitigate, but not eliminate the problems. Based
upon this recognition, their recommendation was to acknowledge the
existence of this problem. However, since no scientific technique can
completely eliminate this problem, it was their judgement that this is a
policy question of how to implement air quality standards in areas
subject to these changes in attainment status.

Independent of these recommendations from the Science and Technical
Support Work Group, the Base Programs Analyses and Policies Work Group
recognized that one of the potential forms of a revised ozone standard
raises similar questions regarding the implementation implications for
areas which are not clearly attaining the NAAQS and yet are not clearly
violating the standards. The Base Programs Analyses and Policies Work
Group will be developing this policy issue and appropriate
recommendations for addressing these problems in a subsequent issue
paper.

[REFERENCES]{.underline}

1.  Chock, D.P. and B. Nance, "A Monte-Carlo Simulation of the Ozone
    Attainment Process," *J. Air Waste Manage. Assoc.* **43:**995,
    (1993).

2.  Chock, D.P., "The Need for a More Robust Ozone Air Quality
    Standard," *JAPCA* **39:**1063, (1989).

3.  Fairley, D. and C.L. Blanchard, "Rethinking the Ozone Standard," *J.
    Air Waste Manage. Assoc.* **41:**928, (1991).

[APPENDIX: A Statistical Attainment Test Useful for Constructing the
TCTC Interval]{.underline}

A rational, simple, and statistically valid choice for the attainment
test to establish the TCTC category is the *t* test. The test basically
says that if the fluctuation associated with a mean is large, then we
have less confidence on the precise location of the mean. In our
application, a very important but often not well appreciated point about
this test is that the test only measures the size of the fluctuation
against the difference between the three-year mean of the annual *m*th
highest value (may be population weighted) and the level of the
standard. It is highly discriminating if the year-to-year pollutant
concentration fluctuation is small and less discriminating if the
fluctuation is large (relative to this difference) ***regardless of
whether the unusual years may become more common in the future**.*

For a given MSA, the TCTC test can be done by comparing a concentration
fluctuation interval, let us call it the TCTC interval, defined as 0.617
x (standard deviation of the annual *m*th highest value in three years)
/(square root of 3), to the difference between the three-year mean (of
the annual *m*th highest value) and the level of the standard. If the
TCTC interval is greater than the difference, then the TCTC designation
may be considered. (See below for the TCTC designation protocol.)
Otherwise, the nonattainment designation applies.

For example, if a previously designated attainment area has the
following annual 5th highest values: 90, 83, 85 ppb (The standard is
assumed to be 85 ppb), then the three-year mean and the standard
deviation are 86 ppb and 3.60 ppb, respectively. The TCTC interval is
0.617 x 3.60/1.732 = 1.28 ppb. The difference from the standard is 1.0
ppb. Since the interval is greater than the difference, TCTC designation
should be considered.

On the other hand, if the three 5th highest values are 88, 84, 85 ppb,
the mean is still the same, at 86 ppb, but the standard deviation is now
2.12 ppb. The TCTC interval is now 0,76 ppb, less than the difference of
1.0 ppb. The nonattainment designation should be considered.

The fluctuation interval formula comes from assuming an alpha of 0.3 and
a sample size of 3 for three-year averaging. Alpha is the probability of
misclassifying an attainment area as nonattainment. The larger the
alpha, the more we ignore the meteorological fluctuation. The present
attainment test, in effect, uses an alpha of = 0.5 which gives a TCTC
interval of 0 ppb. In other words, the information on fluctuation has
been ignored. The smaller the alpha, the wider the TCTC interval. An
alpha of between 0.2 and 0.3 is recommended.

A possible protocol for TCTC classification is described as follows.

1.  A TCTC region is defined only for MSAs that have already acquired
    the attainment status based initially on a three-year mean (of the
    annual *m*th highest value) that is lower than the level of the
    standard.

2.  If in the ensuing year since acquiring the attainment status, a MSA
    registers a three-year mean that is greater than the level of the
    standard, then a TCTC test is required: If the MSA has a TCTC
    interval (see above) that is greater than the difference between the
    three-year mean and the standard level, it is considered a
    nonattainment area; otherwise, it is in a TCTC category.

3.  A MSA with a TCTC classification can retain its existing control
    options. However, it can retain this classification for no more than
    three consecutive years at a time. In the fourth year, it will be
    classified as nonattainment. The three-year allowance is consistent
    with the three-year averaging. It allows an area to wait out the
    impact of an unusual year.

The 1988 heat wave pushed many otherwise attainment areas into
nonattainment. If the TCTC classification as described above had been
invoked, roughly ten percent of all nonattainment areas in the 1986-1988
period would have been classified as TCTC. On the other hand, there were
very limited year-to-year ozone concentration fluctuations for the
period of 1989-1991. Consequently, only about one percent of the
nonattainment areas would be classified as TCTC.

There is some concern that the *t* test is too complex for the general
public to understand. This concern can be mitigated if a tabular form is
provided to calculate the TCTC interval and an intuitive explanation is
provided to educate the public. This step is necessary if science is to
serve as a rational guide in the implementation step.

One may also consider a fixed concentration interval as the TCTC
interval. However, this interval cannot adjust itself with the
year-to-year fluctuations, and may be too stringent for some years and
too lax for others, and too stringent for some areas and too lax for
others.