1

DRAFT

Memorandum

From: Brian Timin, Air Quality Modeling Group, Office of Air Quality Planning and Standards, 

EPA

To: Docket ID No. EPA-HQ-OAR-2011-0729: Regional Haze: Revisions to Provisions 

Governing Alternatives to Source-Specific Best Available Retrofit technology (BART) 

Determinations, Limited SIP Disapprovals, and Federal Implementation Plans 

Re: Sensitivity Analysis Accounting for Increases in Texas and Georgia Transport Rule State 

Budgets 

The Better than BART modeling analysis for the proposed rule and final rule was completed 

using the emissions totals from the final Transport Rule, and also assuming that the July 11, 2011

proposal regarding ozone-season NOx emissions in five states would be finalized.1 In addition to 

the changes in the July 11, 2011 supplemental notice there have been subsequent adjustments to 

state budgets. On February 21, 2012, the EPA published revisions to 2012 and 2104 state 

budgets in Arkansas, Georgia, Indiana, Kansas, Louisiana, Mississippi, Missouri, New York, 

Nebraska, Ohio, Oklahoma, South Carolina, and Texas, along with revisions to new unit setasides in Arkansas, Louisiana, and Missouri.2 In all cases, the budgets were increased. The 

analysis presented in this memorandum represents the EPA’s evaluation of the potential impact 

of the full suite of Transport Rule revisions as presented in both Transport Rule actions 

published in February 2012. Table 1 summarizes the sums of the final (77 FR 10324) and 

proposed (77 FR 10350) budget increases.

Overall, the SO2 and NOx budget increases are relatively modest compared to the total modeled 

reductions from the Transport Rule. The modeled SO2 reductions from the Transport Rule are 

~3.8 million tons per year and NOx reductions are ~125,000 tons per year. After considering the 

SO2 budget increases, the “Transport Rule +BART-elsewhere” control scenario is still projected 

to result in ~3.7 million tons per year of SO2 reductions, which is 773,000 tons more emission 

reductions than “nationwide BART”. The NOx budget increases are projected to result in the 

“nationwide BART” scenario achieving about 8,000 tons more emission reductions than the 

“Transport Rule + BART-elsewhere” control scenario. However, since the visibility 

improvements attributable to the “Transport Rule + BART-elsewhere” scenario are due primarily 

to the large emission reductions in SO2 over the Transport Rule region, the increases in SO2 

 1 The air quality modeling conducted for this analysis included in the CSAPR scenario the states addressed in the 

July 11, 2011 proposal. These states are Iowa, Kansas, Michigan, Nebraska, Minnesota, and Oklahoma. This 

supplemental notice was finalized in December 2011. 76 FR 80760. 2 77 FR 10342 and 77 FR 10350. Some of these Transport Rule revisions were published in a final rule, whereas 

others were published in a direct final rule with parallel proposal. The EPA received adverse comments on the 

parallel proposal and subsequently withdrew the direct final rule. After reviewing comments on the parallel 

proposal, the EPA plans to finalize its proposal as expeditiously as possible. The analysis in this memo confirms 

that the Transport Rule satisfies the better-than-BART test if the state-by-state budgets are no higher than would be 

the case if EPA finalizes the parallel proposal as proposed.
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emissions are most likely to affect the Transport Rule as an alternative to BART analysis. The 

SO2 increases from Georgia and Texas (shown in Table 1) make up the majority of the SO2 

increases (~70%) from the Transport Rule revision rules. Due to the dominance of sulfate 

impacts on visibility3 in both the Transport Rule and BART cases, and the relatively large SO2 

budget increases in Texas and Georgia, we completed a more detailed sensitivity analysis of the 

potential impacts from the Texas and Georgia SO2 budget increases.

Table 1. Increases in Transport Rule 2014 SO2 and NOx budgets.

State 2014 SO2

Budget 

Increase (tons)

2014 NOx 

Budget Increase 

(tons)

Louisiana N/A 4,683

Mississippi N/A 2,269

Michigan N/A 5,228

Nebraska 3,110 3,559

New Jersey N/A 679

New York 8,971 4,179

Texas 50,157 4,106

Wisconsin 7,757 2,473

South Carolina 8,013 N/A

Indiana 5,338 N/A

Ohio 5,163 2,765

Kansas 452 5,794

Georgia 40,334 13,198

Missouri N/A 26

Oklahoma N/A 859

Total Increase 129,295 49,818

Table 2 shows the Texas and Georgia SO2 emissions as modeled (i.e., with trading) in the Better 

than BART analysis and the emissions that would occur if the state budgets are increased as 

proposed assuming that all of the additional allowances are used by sources in the respective 

state (i.e., we did not re-model trading). 

 3 For the 16 Class I areas examined in this analysis, the change in light extinction in the 2014 Transport Rule + 

BART elsewhere case due only to sulfate ranged from 96-121% of the total change in light extinction on the 20% 

worst days and 80-150% of total change in light extinction on the 20% best days. The fraction of visibility change 

attributable to sulfate can be greater than 100% of the total change in extinction because there is often a large 

decrease in sulfate extinction and a simultaneous increase in nitrate extinction (due to nitrate replacement). This 

shows the dominant nature of the impact of SO2 emissions reductions on the overall visibility results, especially at 

the Class I areas most affected by Texas and Georgia. 
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Table 2. Texas and Georgia 2014 SO2 emissions and decreases compared to the 2014 modeled 

base case.

2014 Base Case 

SO2 Emissions

2014 TR+ 

BARTelsewhere 

SO2

Emissions 

(estimate 

from IPM 

used in air 

quality 

modeling)

SO2

Emissions 

Decrease 

from TR 

(as 

modeled)

2014 Budget 

Increase

SO2 Emissions 

Decrease from TR 

with Increased 

Budget

Texas 453,332 266,627 -186,705 50,157 -136,548

Georgia 170,300 93,600 -76,700 40,334 - 36,366

Total 623,632 360,227 -263,405 90,491 -172,914

Table 2 shows that the modeled SO2 reductions in Texas and Georgia are ~264,000 tons per year. 

After accounting for the proposed increase in the SO2 budget for Texas and Georgia, the SO2

emissions reduction is still ~173,000 tons per year. This would reduce the total SO2 reduction 

from the Transport Rule from ~3.8 million tons per year to ~3.7 million tons per year. 

It can be seen from Table 2 that even with the increase in the SO2 budgets for Texas and Georgia 

there is still a large SO2 reduction in Texas and Georgia, compared to the 2014 base case and 

the impact on the total net SO2 reduction from the Transport Rule is minimal (~2.4% decrease in 

total Transport Rule region SO2 reductions).

Given this information, we would still expect major visibility improvements at Class I areas in 

and around Texas and Georgia from the Transport Rule. However, in order to better account for 

the potential visibility impacts from the budget revisions, we performed a very conservative 

sensitivity analysis to provide an upper estimate of the worst case impacts to visibility due to 

increases in Texas and Georgia SO2 budgets. 

Sensitivity Analysis of Better than BART with Increased Texas and Georgia SO2 Allowances 

We identified the most likely “affected” Class I areas for Texas and Georgia and then assumed 

that these areas would get less than the full modeled benefit from the Transport Rule. Table 3 

shows the nine Class I areas in and near Texas that were identified as the affected areas.4

 4 Affected Class I areas were identified by examining consultation letters from Texas to states surrounding Texas 

which were included in the Texas regional haze SIP submissions. These letters were based on the CENRAP 

analysis. The letters are included in Appendix 4-3 available here: 

We 

identified these areas by looking at the regional haze analysis conducted by the CENRAP 

regional planning organization in support of the development of regional haze SIPs in Texas and 

http://www.tceq.texas.gov/airquality/sip/bart/haze_appendices.html. We included six areas which had a > 2 Mm-1

impact from Texas. These areas had much higher visibility impacts from Texas compared to other analyzed Class I 

areas. We also included the three Class I areas that are in Texas or are represented by an IMPROVE monitor that is 

located in Texas.
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surrounding states. 

Table 3. Class I areas most affected by Texas emissions and the modeled visibility improvement 

from the Transport Rule + BART-elsewhere case.

Class I Area Name State

TR+BARTelsewhere 20% 

Best days

TR+BARTelsewhere 20% 

Worst days

Big Bend NP TX -0.2 -1.1

Caney Creek Wilderness AR -0.4 -3.2

Carlsbad Caverns NP TX -0.1 -0.9

Guadalupe Mountains NP TX -0.1 -0.9

Hercules-Glades Wilderness MO -0.6 -2.5

Salt Creek NM -0.1 -0.7

Upper Buffalo Wilderness AR -0.5 -2.5

White Mountain Wilderness NM -0.1 -0.6

Wichita Mountains OK -0.2 -1.6

Table 4 shows the seven Class I areas in and near Georgia that were identified as the affected 

areas.5 We identified these areas by looking at the regional haze analysis conducted by the 

VISTAS regional planning organization in support of the development of regional haze SIPs in 

Georgia and surrounding states. 

Table 4. Class I areas most affected by Georgia emissions and the modeled visibility 

improvement from the Transport Rule + BART-elsewhere case.

Class I Area Name State

TR+BARTelsewhere 

20% Best 

days

TR+BARTelsewhere 20% 

Worst days

Cohutta Wilderness GA -0.8 -3.8

Great Smoky Mountains NP TN -0.8 -3.7

Joyce-Kilmer-Slickrock Wilderness TN -0.8 -3.7

Okefenokee GA -0.9 -2.5

Shining Rock Wilderness NC -0.7 -3.8

Sipsey Wilderness AL -0.9 -3.7

Wolf Island GA -0.9 -2.5

 5 Affected Class I areas were identified by reviewing the results of the VISTAS consultation process. This process is 

summarized in Chapter 10 of the Georgia SIP, which is available at 

http://www.gaepd.org/Files_PDF/plans/sip/Narr_061009.pdf (accessed May 2, 2012). We included four areas 

outside of Georgia where EGUs whose allocation increased was identified as contributing more than 0.5% to 

visibility impairment. We also included the three Class I areas that are in Georgia. 
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For this analysis, we assumed that the visibility benefits shown in Tables 3 and 4 would be 

proportionally reduced as a result of the allowance adjustments for SO2 in Texas and Georgia. 

The SO2 allowance increases in Georgia cause a 52% reduction in the number of SO2 tons 

reduced compared to the proposal modeling, therefore we multiplied the visibility improvement 

at the Class I areas affected by Georgia by a factor of 0.48. The SO2 allowance increases in 

Texas cause a 27% reduction in the number of SO2 tons reduced compared to the proposal 

modeling. Therefore we multiplied the visibility improvement at the Class I areas affected by 

Texas by a factor of 0.73. This assumes that the 52% and 27% reduction in SO2 emissions 

reductions in Georgia and Texas respectively will linearly reduce the visibility benefits in nearby 

Class I areas by 52% and 27%.

The methodology employed is very conservative because we assume that all of the visibility 

improvement from the Class I areas affected by Texas and Georgia are solely due to emissions 

from Texas and Georgia respectively. This is an especially conservative assumption for the Class 

I areas affected by Georgia because there are over 1 million tons of SO2 reductions from the 

Transport Rule in the nearby states of Alabama, North Carolina, South Carolina, Tennessee, 

Virginia, and Kentucky. Emissions reductions from these states would also affect the Class I 

areas identified as being affected by Georgia. But in this analysis we assume that only Georgia 

impacts these areas. 

As shown in Table 1 there are additional states that have smaller SO2 and NOx allowance 

increases. However we believe the conservative nature of this analysis more than offsets any 

small impact from other states. We therefore believe it is appropriate to limit the analysis to 

Texas and Georgia.

Sensitivity Analysis Results

We recalculated the average visibility changes at the 60 Eastern and 140 nationwide Class I areas 

in the Better than BART analysis, using the adjusted visibility change at the 16 Class I areas in 

Tables 3 and 4. The first prong of the Better than BART test is still passed because there will be 

no degradation in visibility at any Class I areas on either the 20% best or 20% worst days. Table 

5 below shows the average visibility results and the re-calculated average visibility results for the 

sensitivity case. 
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Table 5. Average visibility improvement on the 20% best and 20% worst days in the Better than 

BART analysis and the Texas and Georgia sensitivity analysis.

“Transport Rule + 

BARTelsewhere”

“Transport Rule + 

BART-elsewhere” 

Texas/Georgia 

Sensitivity Case

“Nationwide BART”

60 Class I Areas in the Eastern 

Transport Rule Modeling 

Domain

20 percent Worst Days 1.6 1.3 1.0

20 percent Best Days 0.3 0.2 0.2

140 Class I Areas in the Western 

and Eastern Transport Rule 

Modeling Domains

20 percent Worst Days 0.7 0.6 0.5

20 percent Best Days 0.1 0.1 0.1

Table 5 shows that the even with the conservative assumptions in this analysis, the Transport 

Rule+ BART-elsewhere case is still, on average, better than (or equal to) nationwide BART on 

both the 20% best and 20% worst days at the 60 Eastern Class I areas and at the 140 nationwide 

Class I areas.