# Chapter 4: Approach for Estimating Reductions for Full Attainment Scenario

## Synopsis

After applying the hypothetical modeled control strategy described in
Chapter 3, there were multiple counties that were still not projected to
attain potential new ozone standards. Because it was impossible in some
areas to meet a tighter ozone standard nationwide using only known
controls, EPA conducted a second step in the analysis and estimated the
amount of further emission reductions needed to attain an alternate
primary ozone standard. The term "extrapolated tons" will be used to
refer to these additionally needed emissions reductions. Sections 4.1
and 4.2 of this chapter present the methodology EPA developed to
determine the emissions reductions needed for full attainment of the
four alternate standards analyzed in the RIA (i.e., 0.065, 0.070, 0.075,
and 0.079 ppm) and the results of that analysis. Additionally, in other
areas, the known controls in the hypothetical strategy resulted in ozone
levels lower than one or more of the four alternate standards. Sections
4.3 and 4.4 of this chapter discuss the methodology and present the
results of the "overcontrolled" analyses.

## 4.1 Development of Full Attainment Targets for Estimate of Extrapolated Costs

As previewed in the draft RIA, we conducted additional supplemental air
quality modeling analyses for the final RIA. This was intended to
improve the estimates of extrapolated tons needed to meet various
potential standards. These additional modeling scenarios were designed
to provide more information about the response of ozone to emissions
changes in terms of non-linearities, geographic variations, the impacts
of local versus upwind emissions reductions, and the relationship
between NOx and VOC emissions changes. As a result of this additional
information, the methodology to estimate the emissions reduction targets
in the "extrapolated cost areas" has been improved.

### 4.1.1 Design of Supplemental Modeling Scenarios

There were 61 counties that did not meet the 0.070 ppm standard even
after application of the controls in the hypothetical RIA modeled
control scenario. There were 21 counties that did not meet the 0.075 ppm
standard.[^1] All 21 of these counties are in four broad geographic
regions: Houston, eastern Lake Michigan,[^2] the Northeast Corridor,[^3]
and a large part of California. Because these four areas will require
the largest emissions reductions beyond the RIA control scenario, and
therefore likely the largest extrapolated costs, we focused on these
areas within the supplemental modeling analyses. We will refer to these
four areas as "Phase 1" areas. Later, we will define a second and third
set of areas that also require extrapolated emissions reductions which
we will refer to as "Phase 2" and "Phase 3"areas. The primary
distinction between these three sets of areas is that the supplemental
modeling was done only for the Phase 1 areas.

A map of the four Phase 1 areas is shown in Figure 4.1. An approach
similar to that used to define the geographic control areas for non-EGU
point controls in the RIA control scenario (discussed in Chapter 3) was
also used to define the supplemental modeling control zones for each of
the four areas.

Figure 4.1: Counties within which Across-the-Board Emissions Reductions
were Applied in the Supplemental Modeling Analyses

![](media/image1.png){width="6.497222222222222in"
height="4.791666666666667in"}

Six supplemental modeling runs were performed as part of this analysis.
In the first three runs anthropogenic NOx emissions within the
appropriate Phase 1 areas (i.e., the red, pink, and orange counties in
Figure 4.1) were reduced across-the-board by 30, 60, and 90 percent. The
second set of runs included 30, 60, and 90 percent across-the-board
reductions to anthropogenic NOx and VOC emissions within the appropriate
Phase 1 areas (i.e., the red, pink, and orange counties for NOx; only
the red and pink counties for VOC). An estimate of the effects of VOC
controls can be determined by comparing results from the NOx and VOC
control run to the NOx only control run. In the two sets of
across-the-board supplemental modeling runs the emissions reductions
were applied on top of the controls in the hypothetical RIA control
case. As in the modeled control strategy, NOx controls were applied to
counties within a 200 km buffer and VOC controls were applied to
counties within a 100 km buffer of the starting set of counties.

In the draft RIA, we used the concept of "impact ratios"[^4] to
calculate the additional tons needed to meet the air quality standard.
The updated approach uses the supplemental modeling to determine what
levels of ozone precursor reductions (NOx only or NOx plus VOC) are
expected to be sufficient to bring an area into attainment of one of the
various alternate ozone standards that were analyzed. After the
development of emission targets for the 0.070 ppm alternative standard,
we conducted a "verification" model run to assess whether our estimated
emissions reductions actually resulted in attainment of 0.070 ppm in
each area. The new estimates of extrapolated tons represent a
considerable improvement from what was done for the draft RIA.

For purposes of this analysis, we assume attainment by 2020 for all
areas except San Joaquin Valley and South Coast air basins in
California. The state has submitted plans to EPA for implementing the
current ozone standard which propose that these two areas of California
meet that standard by 2024. We have assumed for analytical purposes that
the San Joaquin Valley and South Coast air basin would attain a new
standard in 2030. There are many uncertainties associated with the year
2030 analysis. Between 2020 and 2030 several federal air quality rules
are likely to further reduce emissions of NOx and VOC, such as, but not
limited to National rules for Diesel Locomotives, Diesel Marine Vessels,
and Small Nonroad Gasoline Engines. These emission reductions should
lower ambient levels of ozone in California between 2020 and 2030.
Complete emissions inventories as well as air quality modeling were not
available for this year 2030 analysis. Due to these limitations, it is
not possible to adequately model 2030 air quality changes that are
required to develop robust controls strategies with associated costs and
benefits. In order to provide a rough approximation of the costs and
benefits of attaining 0.075 ppm and the alternate standards in San
Joaquin and South Coast air basins, we've relied on the available data.
Available data includes emission inventories, which do not include any
changes in stationary source emissions beyond 2020, and 2020
supplemental air quality modeling. This data was used to develop
extrapolated costs and benefits of 2030 attainment. To view the complete
analysis for the San Joaquin Valley and South Coast air basins see
Appendix 7b.

### 4.1.2 Results of Supplemental Modeling for Phase 1 Areas 

Figures 4.2a through 4.2d show the projected design values for
individual counties within each of the Phase 1 areas for seven modeling
cases (i.e., the RIA control scenario and each of the six supplemental
modeling runs). These figures are instructive in describing how the
extrapolated control targets were determined for these areas. For each
area, the three counties that need the most extrapolated controls were
chosen for the graphs.

Figure 4.2a indicates that the highest ozone levels in the Houston area
are projected to occur in Harris, Galveston, and Brazoria counties with
Harris being the controlling county. After application of the RIA
scenario controls, our modeling projects that the highest 2020 8-hour
ozone design value in this area will be 0.087 ppm. Thus, additional
precursor reductions are needed to reach the current standard as well as
all four of the alternate standards we are considering. Based on the NOx
plus VOC control modeling scenarios, we can see that increasing the
level of emissions reductions beyond the RIA case yields decreasing
design values. At a 30% NOx + VOC reduction, the projected design value
is 0.084 ppm. At a 60% NOx + VOC reduction, the projected design value
is 0.079 ppm. Finally at a 90% NOx + VOC reduction, the projected design
value is 0.067 ppm.

Based on these results, it is concluded that it is possible to meet the
current ozone standard with additional NOx plus VOC emissions reductions
between 0 and 30 percent. To meet an alternate NAAQS of 0.079 ppm, the
Houston area will require additional NOx plus VOC emissions of
approximately 60 percent. The 0.075 and 0.070 ppm standards will require
between an additional 60-90% NOx plus VOC reduction beyond the RIA
control case. The supplemental modeling indicates that it will take more
than 90% NOx plus VOC control (above and beyond the RIA control case) to
meet a 0.065 ppm standard. Based on these figures, one can also estimate
the levels of NOx-only controls needed to meet a particular standard. We
used linear interpolation to determine the specific percentage reduction
in cases where attainment is expected to be achieved

Figure 4.2a: Projected 2020 8-hour Ozone Design Values in the RIA
Control Scenario and Each of the Six Supplemental Modeling Scenarios for
the Highest Three Counties within the Houston Area

![](media/image2.wmf){width="6.495138888888889in"
height="2.607638888888889in"}

between the supplemental scenarios of 0, 30, 60, and 90 percent.[^5] The
specific percentage reductions for Phase 1 areas are shown in Table 4.1.

Figure 4.2b shows two other aspects of the analysis. First, in some
cases, the controlling county within an area can vary as the precursor
emissions are reduced. In the eastern Lake Michigan area, the modeling
indicates that an additional 60% NOx reduction will be sufficient to
bring two counties with high design values (Kenosha and Sheboygan WI)
into attainment of an 0.070 ppm standard. However, another county in
that area does not reach 0.070 ppm with the 60% NOx reduction. Lake IN
is still 0.077 ppm. The full attainment, extrapolated target analysis is
done on a county by county basis, and the final area target is based on
the county that requires the most additional reductions. Second, it
should be noted that in this area the addition of VOC controls can have
a significant impact on the projected design value. The 0.077 ppm value
in Lake IN is reduced to 0.073 ppm when 60% VOC controls are added to
the 60% NOx controls. Figure 4.2c is included for completeness sake and
to show the supplemental modeling results in the Northeast Corridor.

Figure 4.2b: Projected 2020 8-hour Ozone Design Values in the RIA
Control Scenario and Each of the Six Supplemental Modeling Scenarios for
the Highest Counties within the Eastern Lake Michigan Area

![](media/image3.wmf){width="6.495138888888889in"
height="2.607638888888889in"}

Figure 4.2c: Projected 2020 8-hour Ozone Design Values in the RIA
Control Scenario and Each of the Six Supplemental Modeling Scenarios for
the Highest Counties within the Northeast Corridor

![](media/image4.wmf){width="6.498611111111111in"
height="2.6034722222222224in"}

As discussed in Chapter 3 and Chapter 5, there are two areas in Southern
California that are not planning to meet the current standard by 2020
(i.e., the Los Angeles South Coast Air Basin and the San Joaquin Valley
nonattainment areas). As a result, we have not estimated extrapolated
targets that will be necessary to bring these two nonattainment areas
into attainment of the alternate standards by 2020. However, due to the
effects of ozone transport within California, we are assuming that some
extrapolated controls (beyond the RIA control case) will be needed in
these two areas to help other California nonattainment areas with
earlier attainment dates meet the standards by 2020. These additional
reductions in Los Angeles and San Joaquin Valley are considered to be
part of the controls needed to meet the current NAAQS and are therefore
not considered as part of the cost of any new alternate standard. Figure
4-2d shows the results of the supplemental modeling runs for three areas
in California.

Figure 4.2d: Projected 2020 8-hour Ozone Design Values in the RIA
Control Scenario and Each of the Six Supplemental Modeling Scenarios for
Three Specific Areas in California

![](media/image5.wmf){width="6.495138888888889in"
height="2.607638888888889in"}

Extrapolated control targets were estimated for each Phase 1 area for:
a) NOx only emissions reductions and b) NOx plus VOC emissions
reductions. The results of the analysis to estimate emissions reductions
for attainment in the Phase 1 areas are shown in Table 4.1 and Table
4.2. The amount of additional emissions reductions necessary for full
attainment ranges from zero to over 90 percent depending upon the area
and the standard.

Table 4.1: Estimated Percentage Reductions of NOx and VOC beyond the RIA
Control Scenario Necessary to Meet Various Alternate Ozone Standards in
the Phase I Areas

![](media/image6.png){width="6.183333333333334in"
height="2.911111111111111in"}

Table 4.2: Estimated Percentage Reductions of NOx beyond the RIA Control
Scenario Necessary to Meet Various Alternate Ozone Standards in the
Phase I Areas

![](media/image7.png){width="6.496527777777778in"
height="2.9319444444444445in"}

### 4.1.3 Estimating Attainment of the 0.070 and 0.065 ppm Standards in Phase 2 Areas 

As discussed above, there were 61 counties that did not reach attainment
of the 0.070 ppm standard with the controls in the hypothetical RIA
scenario. The majority of these counties are in one of the Phase 1
areas. However, there were 12 counties (9 areas) outside of the Phase 1
areas that were also not projected to meet the 0.070 NAAQS. (All
counties outside the Phase 1 areas met the 0.075 and 0.079 ppm air
quality standards.) For convenience, these nine areas will be referred
to Phase 2 areas. A two-step process was used to estimate the additional
emissions reductions necessary for full attainment in the Phase 2 areas.
Based on the Phase 1 modeling results, targets for these areas were only
generated for NOx-only control given the preponderance of cases where
the additional VOC emissions reductions did not reduce ozone enough to
consider from a cost perspective.

For the Phase 2 areas, the first step in estimating attainment was to
consider whether the emissions reductions needed to bring the Phase 1
areas into attainment of 0.070 ppm would also reduce ozone transport
enough to bring these additional areas into attainment as well. For an
example of how this determination was made consider two counties:
Norfolk County, MA (Boston area) and Geauga County, OH (Cleveland area).

In Norfolk MA, the projected design value after the RIA control scenario
is 0.071 ppm. This county is downwind of the Northeast Corridor. The
supplemental modeling showed that if the Phase 1 areas reduced NOx
emissions by at least 30% the 2020 design value in Norfolk MA would be
reduced to 0.069 ppm (i.e., does not exceed the 0.070 standard). As part
of the Phase I analysis, we estimated that the Northeast Corridor region
would need an additional 39% NOx reduction to meet the 0.070 ppm
standard within this area. The supplemental modeling shows that the same
39% NOx reduction would enable this standard to be met in Norfolk County
as well, without any additional local controls in the Boston area.

In Geauga OH, the projected design value after the RIA control scenario
is 0.074 ppm. Thus, Cleveland will need additional local emissions
reductions to meet a revised ozone standard of 0.070 ppm. However, in
the supplemental modeling, which did not include emissions reductions in
Cleveland, the Geauga design value declined by 0.001, 0.002, and 0.003
ppm, in the 30, 60, and 90% NOx reduction runs, respectively. Given that
the Lake Michigan region is the nearest upwind Phase 1 area to Geauga
County, we believe these ozone reductions in Geauga County are
associated with the emissions reductions modeled in the Lake Michigan
region. The Lake Michigan region is estimated to need 72% additional NOx
control. Considering the projected design values with an additional
digit of precision, it is estimated that a 72% reduction in the eastern
Lake Michigan area will yield a Geauga OH design value of 0.0718
ppm.[^6]

In the second step of the process, we estimate what level of local
control is required to reach 0.070 ppm after consideration of the impact
of Phase 1 emissions reductions. For each of the Phase 2 areas that is
still nonattainment after step 1 above, we developed a site-specific
relationship between the ozone improvement in the RIA control case and
the percent reduction in local NOx emissions in the RIA control case as
compared to the baseline. This site-specific relationship was then used
to determine how much additional NOx reduction was needed to meet the
0.070 ppm goal. Continuing with the Geauga County example helps
illustrate this calculation. In this county there was a 0.0023 ppm
reduction due to the hypothetical RIA controls. The RIA scenario
represented a 17% reduction in NOx emissions within the 200 km buffer
around the Cleveland area. With the existing information it is not
possible to distinguish how much of the ozone improvement is due to
local controls (i.e., within 200 km) versus upwind controls, so we made
a simplifying assumption that all local air quality improvement for such
areas can be attributed to the controls within 200 km. Converting to
units of ppb for simplicity, dividing 2.3 ppb improvement by a 17% NOx
emissions reduction yields a Geauga-specific relationship of 0.135 ppb /
percent NOx controlled. This ratio is applied to the 71.8 ppb value from
step 1 and it is determined that an additional 7 % reduction (0.9 ppb)
would be sufficient to lower the 2020 design value in Geauga County to
70.9 ppb or 0.070 ppm, thereby attaining the standard.

The same two step methodology described above was used to estimate the
extrapolated targets for the 0.065 ppm standard in the Phase 2 areas.
Table 4.3 shows the full set of results for each of the nine Phase 2
areas. The amount of additional NOx control needed to meet the 0.070 ppm
standard in Phase 2 areas ranges from zero to 25 percent. The amount of
additional NOx control needed to meet the 0.065 ppm standard in Phase 2
areas ranges from zero to 74 percent.

Table 4.3: Estimated Percentage Reductions of NOx beyond the RIA Control
Scenario Necessary to Meet the 0.070 ppm Ozone Standard in Phase 2
Areas[^7]

![](media/image8.png){width="6.495833333333334in"
height="1.7958333333333334in"}

### 4.1.4 Estimating Attainment of the 0.065 ppm Standard outside of Phase 1 and 2 Areas 

The last set of reduction targets generated are for those areas that
require additional ozone precursor controls to meet the 0.065 ppm
standard but are outside Phase 1 and 2 areas. There were 166 counties
that did not reach attainment of the 0.065 ppm standard with the
emissions reductions in the hypothetical RIA scenario. The majority of
these counties are in one of the Phase 1 or Phase 2 areas. However,
there were 46 counties (36 areas) outside of the Phase 1 and Phase 2
areas that were not projected to meet the 0.065 NAAQS. For convenience,
these areas will be referred to Phase 3 areas.

A similar methodology as described in Section 4.1.3 was used to estimate
the additional emissions reductions needed for the 0.065 ppm standard
for the Phase 3 areas, but two simplifying assumptions were made to
expedite the analysis. First, instead of explicitly accounting for the
impacts of the Phase 1 and Phase 2 upwind emissions reductions on Phase
3 areas, we assumed that the design values from the 60% NOx reduction
run were the appropriate starting point for estimating the additional
emissions reductions in the Phase 3 areas. Since the targets for the
Phase 1 areas are generally greater than 60% and since we have not
accounted for the Phase 2 reductions, these estimates should provide a
conservative estimate of the percentage emissions reductions needed for
full attainment. Secondly, we did not develop site-specific impact
ratios for the 36 Phase 3 areas. Instead, we used a standard
relationship of 0.150 ppb / 1% NOx reduction for calculating the
emissions reductions needed to attain 0.065 ppm in these areas. This
value was the average site-specific relationship calculated for the
Phase 2 areas, as described above. These assumptions are reasonable
given the available data and the relatively small role that Phase 3
areas will play in determining the full costs of meeting a 0.065 ozone
standard. However, the estimated emissions reductions needed to attain
0.065 in the Phase 3 areas are considered to be more uncertain than the
emissions reductions calculated for attaining 0.070, 0.075, and/or
0.079. The results of the Phase 3 analysis are shown in Table 4.4. The
amount of additional NOx control needed to meet the 0.065 ppm standard
in Phase 3 areas ranges from zero to 29 percent.

Table 4.4: Estimated Percentage Reductions of NOx beyond the RIA Control
Case Necessary to Meet the 0.065 ppm Ozone Standard in Phase 3 Areas

![](media/image9.png){width="6.022916666666666in"
height="5.402777777777778in"}

### 4.1.5 Aggregate Results / Verification Modeling of Extrapolated Targets 

The complete set of NOx targets are provided in Table 4.5a. As noted
earlier, a single 2020 target was determined for all of California. This
target was based on the Sacramento area which had the highest 2020
design values outside the Los Angeles and San Joaquin Valley areas. The
assumption is that if all of California reduces at that level then all
areas aside from Los Angeles and the San Joaquin Valley air basins will
attain by 2020. Areas from which reductions would be required include
the Los Angeles and San Joaquin Valley air basins, but would not
necessarily bring them into attainment. Additional reductions may be
required. Because of their later attainment date, the costs and benefits
of additional reductions for Los Angeles and San Joaquin air basins are
shown in Appendix 7b.

Table 4.5a: Complete Set of Estimated Percentage Reductions of NOx
beyond the RIA Control Scenario Necessary to Meet the Various Ozone
Standards in 2020

![](media/image10.png){width="6.5in" height="4.965972222222222in"}

In total, 33 areas were determined to need additional emissions
reductions for one or more of the alternate standards. The eastern Lake
Michigan region was the only one in which NOx plus VOC control targets
could be substantially lower than NOx only control targets. Table 4.5b
shows the NOx + VOC targets for that area.

Table 4.5b: Estimated Percentage Reductions of NOx + VOC beyond the RIA
Control Scenario Necessary to Meet the Various Ozone Standards in 2020

![](media/image11.png){width="6.491666666666666in"
height="0.6118055555555556in"}

Figures 4.3a through 4.3d show: 1) which counties are part of the 33
extrapolated cost areas and 2) the estimated percent reduction needed
beyond the RIA control case to meet each of the four alternate standards
within each of those areas. The conversion of these additional
percentage reductions to actual extrapolated tons is described in
Chapter 4.2. The calculation of the costs of these extrapolated tons is
described in Chapter 5.

Figure 4.3a: Map of Extrapolated Cost Counties for the 0.065 ppm
Alternate Standard and the Estimated Percent NOx Controls Needed to Meet
that Standard

![](media/image12.jpeg){width="4.95in" height="3.825in"}

Figure 4.3b: Map of Extrapolated Cost Counties for the 0.070 ppm
Alternate Standard and the Estimated Percent NOx Controls Needed to Meet
that Standard

![](media/image13.jpeg){width="4.95in" height="3.825in"}

Figure 4.3c: Map of Extrapolated Cost Counties for the 0.075 ppm
Alternate Standard and the Estimated Percent NOx Controls Needed to Meet
that Standard

![](media/image14.jpeg){width="4.95in" height="3.825in"}

Figure 4.3d: Map of Extrapolated Cost Counties for the 0.079 ppm
Alternate Standard and the Estimated Percent NOx Controls Needed to Meet
that Standard

![](media/image15.jpeg){width="4.95in" height="3.825in"}

As noted earlier in this section, an additional CMAQ air quality
simulation, called a "verification run," was completed after the
extrapolated percent emissions reductions were estimated. The purpose of
this run was to determine the ozone design values that would be expected
from the additional extrapolated reductions shown in Table 4.5a and
Table 4.5b. These are the reductions that were estimated to be needed
for full attainment of the 0.070 ppm standard for areas outside of Los
Angeles and San Joaquin Valley. The results of the verification modeling
were encouraging and confirmed our approach for estimating the
extrapolated reductions. For the four areas where we projected that no
additional local controls were needed and that the additional upwind
reductions would be sufficient for attainment of 0.070 (see Table 4.3),
the verification modeling indicated that all four areas had ozone design
values less than 0.070 ppm after the extrapolated reductions were
applied. Of the remaining nine areas that did not reach the 0.070 ppm
standard in the RIA control case, eight of the nine were within plus or
minus 0.002 ppm after application of the extrapolated emissions
reductions. The proximity of the verification design values to the 0.070
ppm target provides confidence that the estimates of extrapolated tons
are reasonable. Table 4.6 shows the results of the verification modeling
for the 13 areas that were included in the (0.070 ppm) extrapolated cost
analysis.

Table 4.6: Summary of the Verification Modeling Results

![](media/image16.png){width="6.49375in" height="3.1284722222222223in"}

## 4.2 Conversion of Full Attainment Percentage Targets into Extrapolated Tons

Table 4.7a provides the complete set of extrapolated tons of NOx
emissions reduction needed to satisfy the various ozone standards. These
extrapolated tons are obtained by multiplying the NOx targets in Table
4.5a by the remaining emissions for each area after the RIA control
scenario. It is important to note that the extrapolated cost areas are
potentially standard-specific because the location of counties in an
extrapolated area depends on whether the particular standard is being
violated. For example, as seen in Figures 4.3a and 4.3b, the Eastern
Lake Michigan area extends further north into Wisconsin for the 0.065
ppm standard where areas like Green Bay attained the 0.070 standard but
not 0.065 ppm standard.

Table 4.7a: Complete Set of Estimated Extrapolated Emissions Reductions
of NOx Beyond the RIA Control Scenario Necessary to Meet the Various
Ozone Standards in 2020

![](media/image17.wmf){width="6.246527777777778in" height="5.06875in"}

^a^ Jamestown is included in the Buffalo-Niagara Falls, NY cost area
because it falls within the 200km Buffalo-Niagara Falls buffer and has a
lower design value.

^b^ Erie is included in the Pittsburgh-Beaver Valley, PA cost area
because it falls within the 200km Pittsburgh-Beaver Valley buffer and
has a lower design value.

In total, additional emissions reductions are provided for 31 areas. As
footnoted, Jamestown NY is included in the Buffalo-Niagara Falls NY
area. There are three reasons for this: 1) Jamestown is within the 200km
buffer for Buffalo-Niagara Falls, 2) as seen in Table 4-5a, the NOx
target is greater in Buffalo-Niagara than Jamestown for each standard,
and 3) Jamestown is in the same state. Erie is included in the
Pittsburgh-Beaver Valley PA area for the same three reasons.

As noted in Table 4.5b in Section 4.1.5, the eastern Lake Michigan area
was the only one in which NOx plus VOC additional emission reductions
could be substantially lower than NOx-only emissions reductions. Table
4.7b shows the additional NOx + VOC emission reductions for this area.

Table 4.7b: Estimated Extrapolated Emissions Reductions of NOx + VOC
Beyond the RIA Control Scenario Necessary to Meet the Various Ozone
Standards in 2020

![](media/image18.wmf){width="6.471527777777778in" height="0.88125in"}

## 4.3 Methodology Used to Estimate the Amount of "Overcontrolled" Emissions in the Modeled Control Strategy

The corollary to extrapolated tons (needed tons above and beyond the
modeled control strategy) is "overcontrolled" tons. These are emissions
reductions within the hypothetical control case that were subsequently
determined not to be needed to meet particular alternate standards. That
is, once we modeled the baseline and control strategy scenarios we found
that we had reduced ozone beyond the particular alternate standard. In
order to better estimate the costs and benefits of full attainment of
the standards, EPA has estimated the "overcontrolled" emissions
percentages within the modeled control strategy for the four alternate
standards: 079, 075, 070 & 065. These percentages are to be applied to
the tons reduced between the baseline and the control case.

The methodology for calculating the "overcontrol" percentages is based
on simple linear interpolation between the baseline scenario and the
model control strategy. These two model runs were used to estimate what
level of control was just needed to bring an area into attainment of a
standard. A caveat to this approach is that it assumes that all air
quality impacts are due to local controls; there is no consideration of
the potential impacts of ozone transport.

The details of the methodology are as follows. The first step was to
identify all counties with ozone concentrations greater than 0.070 ppm
in the base case. These 142 counties were the starting point for
designing the modeled control strategy described in Chapter 3. Because
the majority of the California controls are in the baseline and because
several CA areas continue to be nonattainment of all four alternate
standards in 2020 and beyond, we did not assess "overcontrol" in
California. The remaining counties were aggregated into 32 distinct
areas for an assessment of whether that area overcontrolled to meet an
alternate standard. Each area included the original nonattainment county
or counties, plus all counties within 200 km of that county or counties.
The "overcontrolled" analysis was done for the county with the highest
ozone levels in the control case modeling. These 32 areas comprised
1,199 counties. These are the same 1,199 non-California counties over
which NonEGU point and Area sources were controlled in the hypothetical
strategy.

A simple three-step process was used to determine the amount of
overcontrol in the hypothetical control case for each of the 32 areas.
The results are summarized in Table 4.8.

Table 4.8: Estimated Percentages of Modeled Control Strategy Emissions
Reductions not needed to Meet the Various Ozone Standards in 2020

![](media/image19.png){width="6.490972222222222in"
height="4.396527777777778in"}

a\) For each standard, we first determined if the area was below that
standard in the baseline modeled scenario. If so, then all of the
hypothetical controls should be returned from the control scenario. For
example, the highest projected design value in the Cincinnati area was
0.072 ppm in the basecase and 0.070 ppm in the baseline. Thus, that area
did not actually need any of the hypothetical controls above and beyond
the baseline to meet the 0.079, 0.075, or 0.070 standards locally.
Therefore, all of the controls in that area should be returned for those
standards.

b\) For each standard, we then determined if the area was above that
standard in the modeled control case. If so, then none of the
hypothetical controls should be given back. As an example, the Houston
area had a projected design value of 0.087 ppm in the control case.
Therefore, all of the emissions in the modeled control strategy (and
some extrapolated tons) are needed in that area.

c\) For each standard, and for all other areas that were above the
standard in the baseline and below in the control case, we used linear
interpolation to estimate what percentage of the emissions reductions in
the modeled control strategy could be returned and still allow the
standard to be met. For example, the maximum projected design value in
the Cleveland area was 0.0795 ppm in the basecase, 0.0765 ppm in the
baseline, and 0.0742 ppm in the control case. Linear interpolation[^8]
between the baseline and the control case indicates that 74% of the
controls in the Cleveland area, including counties within a 200km
buffer, could be given back and still just meet the 0.075 ppm target.
All of the control strategy reductions would be given back for the
less-stringent 0.079 ppm standard and none of the reductions would be
given back for the more-stringent 0.070 ppm standard.

## 4.4 Conversion of Estimated Percentages of Unnecessary Emission Reductions into "Overcontrolled" Tons

The percentages of modeled control strategy emissions reductions not
needed to meet the various ozone standards in 2020 shown in Table 4.8
were applied to the control case reductions in Table 4.9. In areas and
targets where the percentages in Table 4.8 were "ALL," the unnecessary
emissions reductions in Table 4.9 are equal to the baseline minus
control case emissions seen in the same table. Similarly, in areas and
targets where there was no "over-control" ("NONE" in Table 4.8),
emission reductions not needed for alternative standards in Table 4.9
are zero; that is, the control scenario did not "over-control" emissions
for that area and target. As seen in Table 4.8, ozone concentration
estimates are greater than 0.0795 ppm in both Houston and Eastern Lake
Michigan; therefore there was no over-control and no unnecessary
emission reductions.

Table 4.9: Estimated 2020 Control Case Emission Reductions not needed to
Meet the Various Ozone Standards in 2020

![](media/image20.wmf){width="6.493055555555555in"
height="5.191666666666666in"}

[^1]: 10 counties did not meet the 0.079 ppm standard. 166 counties did
    not meet the 0.065 ppm standard.

[^2]: This geographic area is an aggregate of five existing
    nonattainment or maintenance areas: a) Chicago-Gary-Lake County,
    IL-IN; b) Milwaukee-Racine, WI; c) Sheboygan WI; d) La Porte IN; and
    e) South Bend-Elkhart IN.

[^3]: This geographic area is an aggregate of six existing nonattainment
    or maintenance areas: a) Philadelphia-Wilmington-Atlantic City,
    PA-NJ-MD-DE; b) New York-Northern New Jersey-Long Island, NY-NJ-CT;
    c) Greater Connecticut, CT; d) Baltimore MD; e) Kent and Queen Anne
    counties MD; and f) Poughkeepsie NY.

[^4]: The units for impact ratios are ppb/kton. In the draft RIA we used
    a single, national impact ratio that assumed that 10,000 tons of NOx
    control would yield 0.001 ppm of ozone improvement.

[^5]: To add precision to this process, we based these calculations on
    projected design values that contained data four places to the right
    of the decimal (e.g., 0.0755 ppm). In the last step of the process
    however, EPA truncates all decimal places beyond the third decimal.
    This is consistent with past policy on ozone design values.

[^6]: The full step 1 calculation for the Geauga OH example is as
    follows. A 60 percent reduction yields a design value of 0.0722 ppm.
    A 90 percent reduction yields a design value of 0.0710 ppm. The
    estimated Phase 1 target for eastern Lake Michigan is 72%, or
    four-tenths of the "distance" between 60 and 90% control. Forty
    percent of the 0.0012 ppm difference between the two runs is 0.00048
    ppm. Subtracting that from 0.0722 ppm, yields the
    transport-considered design value of 0.0717 ppm which would be
    truncated to 0.071 ppm.

[^7]: The entry "will attain" in Tables 4.3 and 4.4 signifies that this
    area will come into attainment of the standard due to reduced ozone
    transport resulting from upwind controls.

[^8]: The calculation used to determine the 74% target for the 0.075 ppm
    targets is as follows:

    1.0-\[(0.0765-0.0759)/(0.0765-0.0742)\], where 0.0759 ppm represents
    the highest ozone level that still attains a 0.075 ppm standard, due
    to the usual truncation of the fourth decimal place.