Exhibit 13
Case: 10-1252 Document: 1288492 Filed: 01/18/2011 Page: 1

ORAL ARGUMENT NOT YET SCHEDULED 

UNITED STATES COURT OF APPEALS 

FOR THE DISTRICT OF COLUMBIA CIRCUIT 

NATIONAL ENVIRONMENTAL 

DEVELOPMENT ASSOCIATION'S 

CLEAN AIR PROJECT, 

Petitioner, 

v. 

UNITED STATES ENVIRONMENTAL 

PROTECTION AGENCY, 

Respondent. 

) 

Docket No. 10-1252 

(and consolidated cases) 

DECLARATION OF ROGER W. BRODE 

1. My name is Roger W. Brode. I hold B.S. and M.S. degrees in Atmospheric Sciences and I 

am currently assigned as a physical scientist in the Air Quality Modeling Group within the 

Air Quality Assessment Division of the Office of Air and Radiation's Office of Air Quality 

Planning and Standards at the U.S. Environmental Protection Agency ("EPA"), where my 

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responsibilities include the development, evaluation and application of air quality dispersion 

models and the development of guidance associated with application of such models in 

support of EPA regulations governing the Prevention of Significant Deterioration 

("PSD")_permitting program. I have been involved in the development, evaluation, testing, 

and documentation of the American Meteorological Society EPA Regulatory Model 

("AERMOD") throughout its history. I currently serve as co-chair of the AMS/EP A 

Regulatory Model Improvement Committee (AERMIC) consisting of atmospheric scientists 

and dispersion model experts overseeing the further technical development of the model, and 

as co-chair of the AERMOD Implementation Workgroup consisting of EPA Regional Office 

and State dispersion modelers whose charge has been to indentify and assess potential issues 

with implementation of the AERMOD model as EPA's preferred model under Appendix W 

of Part 51 of the Code ofF ederal Regulations. 

2. The revised primary national ambient air quality standard for oxides of sulfur ("S02 

NAAQS") requires that the three year average ofthe annual 99111 percentile of the daily 

maximum 1-hour average concentrations ofS02 be less than or equal to 75 parts per billion. 

In addition, owners and operators of a new major stationary source or a major source 

undergoing a major modification located in areas not designated "nonattainment" for the S02 

NAAQS must obtain a PSD permit, and to do so must demonstrate (among other things) that 

the emissions increases from the new or modified source will not cause or contribute to a 

violation ofthe revised S02 NAAQS. Existing air quality models, including AERMOD, are 

readily capable of accurately predicting whether the revised primary S02 NAAQS is attained 

and whether individual sources cause or contribute to a violation of the S02 NAAQS. 

Specifically, dispersion models that are used to demonstrate compliance with the S02 (and 

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other) NAAQS, including under PSD permitting programs, use sequential hourly 

meteorological data as the basis for estimating ambient concentration levels. These data are 

combined with other inputs (chiefly source emission information, background emissions, and 

receptor information) to predict transport and dispersion of emitted pollutant plumes. Since 

the key varying inputs to these models are input on an hourly basis, all applications of these 

models under the guidance in Appendix W (40 CFR Part 51) are predicated upon the models' 

ability to predict hourly ambient concentrations. These models thus generate one-hour air 

quality distributions from which the three year average of the annual 99th percentile of daily 

maximum 1-hour average concentration of S02 can be readily calculated or otherwise 

reasonably approximated. 

3. As part ofthe basis for EPA adopting the AERMOD model as the preferred model for nearfield applications in the Guideline on Air Quality Models, Appendix W to 40 CFR Part 51, 

the performance ofthe AERMOD model was extensively evaluated based on a total of 17 

field study data bases (AERMOD: Latest Features and Evaluation Results. EPA-454/R-03-

003. U.S. Environmental Protection Agency, Research Triangle Park (2003), portions of 

which are attached to this affidavit) ("EPA 2003"). The scope of the model evaluations 

conducted for AERMOD far exceeds the scope of evaluations conducted on any other model 

that has been adopted in Appendix W to Part 51. These evaluations demonstrate the overall 

good performance of the AERMOD model based on technically sound model evaluation 

procedures, and also illustrate the significant advancement in the science of dispersion 

modeling represented by the AERMOD model as compared to other models that have been 

used in the past. In particular, adoption of the AERMOD model has significantly reduced the 

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potential for overestimation of ambient impacts from elevated sources in complex terrain 

compared to other-models. 

4. Some of the field studies used to evaluate AERMOD model performance involved ambient 

sampling of S02 for a period of one year or more at several (typically about 1 0) monitors 

sited around operating power plants. Other field studies involved sampling of controlled 

releases of non-reactive tracers, typically SF6, generally over a shorter duration than the 

operational studies, but with more robust sampling to facilitate more detailed diagnosis of 

model performance. Although the long-term field studies associated with operating power 

plants included assessments of 3-hour, 24-hour and even annual average impacts from the 

model, evaluation results for 1-hour averages were routinely included for all of the field 

studies. As shown in Tables 2 and 3 of EPA 2003, modeling and monitored results for 1-

hour averages are in excellent correlation in these studies, with the ratio of predicted to 

observed performance approaching 1: 1 in most instances. Thus, in my opinion, the 

performance of the AERMOD model for estimating 1-hour ambient concentrations is welldocumented and the form of the new 1-hour S02 standard raises no questions or concerns 

regarding the appropriateness of AERMOD. 

5. The S02 NAAQS Coalition states that the revised S02 NAAQS is a "probabilistic" standard 

and asserts that this makes modeling more problematic, especially as compared to the 

previous "deterministic" standard. (Coalition p. 5.) The terms "probabilistic" and 

"deterministic" do not have an ordinarily understood meaning in this context, but it appears 

that the assertion is that predictive models like AERMOD are not suitable for a standard 

which includes a percentile-based form (where the relevant comparison is to a percentile of 

air quality from an air quality distribution), as opposed to an expected exceedance form 

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(whereby a standard may exceeded on a given number of days and compliance is assessed 

based on air quality on the designated day once the allowed exceedance days are removed 

from the distribution). I know of no reason that AERMOD and other similar types of models 

is suitable for one type of form and not the other. As just stated in paragraph 2, the models 

readily generate air quality distributions from which either percentiles (for the revised S02 

NAAQS, the 991h percentile) or exceeding days can be determined. In fact, the percentile 

form of the 1-hour S02 NAAQS is a more "stable" metric than a standard based on the 1

51-

highest or 2"d -highest concentrations, since the potential impact of "outliers" in the 

distribution is mitigated, especially when the multi-year average aspect of the S02 NAAQS 

is accounted for. 

6. Both the S02 NAAQS Coalition and their affiant Mr. Paine raise a number of points 

regarding the issue of whether allowable or actual source emissions should be modeled, 

stating that use of allowable emissions overstates sources' impacts. See, e.g. Paine Decl. at 1[ 

11-14. This issue is independent of the predictive accuracy of AERMOD or other models. 

7. EPA's rules and guidance provide significant flexibility in the choice of which models to use 

in determining if sources cause of contribute to NAAQS violations for purposes ofPSD 

permitting. EPA's rules specify that "where an air quality model specified in Appendix W of 

this part ... is inappropriate, the model may be modified or another model substituted" with 

written approval from EPA. 40 C.F.R. §51. 166 (1)(2). The rules therefore allow flexibility, 

subject to appropriate requirements, for alternative modeling techniques to be applied on a 

case-by-case basis subject to approval by appropriate reviewing authority. 

8. The declaration of Michael E. Long voices concerns regarding the use of the AERMOD 

dispersion model to support implementation of the 1-hour S02 standard, and asserts that 

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"AERMOD significantly over predicts the actual one-hour ambient concentrations in our 

area when the available information is used in the model as directed by EPA." Long Decl. at 

8. This assertion is based on a comparison bf model-predicted ambient concentrations to 

ambient 802 concentrations reported for 2008 at local EPA monitoring stations in the 

vicinity of the ArcelorMittal facilities being modeled. Mr. Long reports that the "AERMOD 

model predicted one-hour concentrations that were higher than the monitored values 90% of 

the time and the predicted values were as much as 373,131 times higher than the actual 

monitored values." Id. Lacking any additional details regarding the model-to-monitor 

comparisons cited by Mr. Long, the response here is necessarily limited to a general 

discussion of issues involved in such comparisons. A number of factors can affect the 

comparison of a modeled concentration with a monitored concentration, including the 

accuracy of the emission rate and other source characteristics input to the model, the 

representativeness of the meteorological data input to the model, and the influence of local 

geographical features and land use characteristics on the transport and dispersion of the 

plume. Another key factor that affects comparisons of modeled vs. monitored 

concentrations, paired in time and space, is the potential error or uncertainty in the wind 

direction input to the model for that hour since the wind direction will determine the 

transport direction of the plume. Slight errors in the transport wind direction may account for 

significant differences in modeled vs. monitored concentrations for a specific hour, 

especially for elevated plumes under stable atmospheric conditions where the lateral spread 

of the plume can be very limited for relatively long transport distances, and errors of a few 

degrees in wind direction can be the difference in the plume directly impacting the monitor 

for a particular hour or the plume missing the monitor completely. In such cases, a factor of 

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3 73,131 difference between modeled and monitored concentrations could easily be 

attributable to error or uncertainty in the wind direction. Note that wind directions reported 

from routine meteorological monitoring stations located at airports, the most common source 

of meteorological data used in air quality modeling applications, are reported to the nearest 

10 degrees. In addition, the comparison may reflect issues related to use of allowable versus 

actual emissions, which is irrelevant for purposes of determining whether the AERMOD 

model itself is biased. 

9. The declaration of Robert J. Paine addresses practical issues in applying the AERMOD 

model that allegedly arise due to the form of the 1-hour S02 standard, as well as concerns 

regarding the conservatism of the assumptions on source emissions based on Appendix W 

guidance in relation to the 1-hour S02 standard. Responses to these issues are summarized 

below, numbered according to Mr. Paine's declaration, with some responses applying to 

multiple comments: 

(a) 

Paine Decl. 9. : The AERMOD model "does not yet provide results that allow permit 

applicants to follow EPA's guidance for determining whether they comply with the 1-hour S02 

NAAQS because of the unique statistical form of that NAAQS." 

Paine Decl. 11 10.: "The form ofthe 1-hour S02 NAAQS requires the applicable guideline 

dispersion model to compute the highest 1-hour concentration for each day at each modeled 

receptor point, and to keep track of this daily 1-hour maximum concentration statistic for each of 

the 365 days for each year modeled independently at each location modeled. 

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Paine Decl. 11. : "In the case for which a cumulative modeling analysis is required, this same 

procedure must be applied to the combined contributions of the individual source being 

permitted, nearby sources and regional background." 

Response: As stated in paragraph 2 above, all of these metrics are readily obtainable from model 

outputs. Although the existing version of AERMOD does not contain an algorithm from which 

these metrics emerge automatically as model outputs, this does not change the result that all of 

these metrics are obtainable. In fact, we are aware that Mr. Paine, along with other private sector 

parties, developed post-processing tools to compute the 1-hour S02 design value based on the 

form of the revised S02 NAAQS utilizing model output options available at the time. 

(b) 

Paine Decl. 'II 11. : "Furthermore, EPA in most cases requires a conservatively high regional 

background concentration to be added for all hours modeled, rather than the actual values 

measured during each hour of the modeling simulation." 

Response: EPA issued guidance on a range of issues related to the new 1-hour S02 standard on 

August 23,2010, including a recommendation that the overall highest 1-hour monitored S02 

concentration from a representative monitor could be used to account for the monitored 

background component in a cumulative impact assessment "without further justification." We 

recognize that use of the overall highest 1-hour monitored value may entail a degree of 

conservatism that could prevent a source from demonstrating compliance with NAAQS; 

however, that conservatism forms the basis for allowing the approach to be used without further 

justification. The August 23 memorandum further stated that "Additional refinements to this 

'first tier' approach based on some level of temporal pairing of modeled and monitored values 

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may be considered on a case-by-case basis, subject to approval by the reviewing authority, with 

adequate justification and documentation." However, we also note that Appendix W explicitly 

makes "no attempt" to "comprehensively define" the criteria involved in determining which 

nearby sources to include in an analysis "owing to both the uniqueness of each modeling 

situation and the large number of variables involved in identifying nearby sources." See 

Appendix W section 8.2.3.b. 

(c) 

Paine Decl. 1! 12.: "Following EPA's regulatory requirements for PSD modeling, the modeled 

predictions of hourly concentrations of a probabilistic standard such as the 99th percentile daily 

maximum hourly S02 concentrations produced by a single source for which a permit is sought 

can be much higher than concentrations that actually occur in the ambient air." 

Response: As noted in paragraph 6 above, the issue of allowable versus actual emissions is 

independent to the question of the accuracy of AERMOD or other models. Also, as stated in 

paragraph 5 aboYe, there is no reason that AERMOD (or other similar models) is not equally 

accurate in predicting percentile air quality distributions or expected exceedances on a given day. 

The underlying data which are input to the model generate air quality distributions which are 

equally suitable for either type of form. 

(d) 

Paine Decl. 12. : "Modeling of peak S02 emissions as if they occur continuously is a 

distortion of reality and will overestimate the ambient air concentrations. This is especially true 

for 1-hour averages, since the variation of emissions for such a short averaging period is 

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potentially much higher than that for the other S02 NAAQS averaging periods. This makes the 

assumption of constant peak emissions a critical issue for this new standard." 

Response: The purpose of dispersion modeling in the context of the PSD permitting program is 

to demonstrate that the proposed new or modified emissions will not cause or contribute to 

violations of the standard if the permit is granted. This is inherently a predictive exercise since it 

entails an assessment of proposed future emissions. EPA's guidance for conducting such 

analyses is dictated by and consistent with that purpose. Mr. Paine's statement that 1-hour 

averages are more variable than longer averaging periods again does not relate to potential model 

bias and in any case makes a sweeping generalization for situations that differ case-by-case. The 

statement that peak S02 emissions should not be modeled is a restatement of the dispute as to 

use of allowable or actual emissions, and does not relate to the issue of model bias. 

(e) 

Paine Decl. , 13. : "The model overprediction tendency is even more likely to be a problem in a 

cumulative impact analysis because numerous sources (i.e., the source being permitted and 

potentially thousands of other nearby sources) are all modeled at peak emissions at all times and 

added to a regional background level of S02 ... leading to unrealistic predictions that the 1-hour 

S02 NAAQS will be exceeded." 

Response: As noted, the issue of allowable versus actual emissions is independent ofthe issue of 

models' predictive accuracy. However, EPA's August 23,2010 clarification memo regarding 

the applicability of Appendix W guidance for the 1-hour S02 NAAQS cautioned "against the 

literal and uncritical application of very prescriptive procedures for identifying which 

background sources should be included in the modeled emission inventory for NAAQS 

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compliance demonstrations, including those described in Chapter C, Section IV. C.l of the draft 

New Source Review Workshop Manual (EPA, 1990), noting [again] that Appendix W 

emphasizes the importance of professional judgment in this process." One motivation for that 

caution was a concern that application of such procedures could lead to an overly conservative 

result by including too many background sources in the cumulative impact assessment. As noted 

elsewhere, Section 8.2.3.b of Appendix W suggests that "the number of such sources is expected 

to be small except in unusual situations." 

(f) 

Paine Decl. 13. : "Moreover, since the nearby sources will be modeled individually (but their 

emissions are already accounted for in the regional monitoring), there will inevitably be doublecounting of the background impacts between the components of the "nearby sources" and the 

"regional background", especially for the common situation of the state requiring a single peak 

regional background value to be used for all modeled hours." 

Response: As noted in several responses above, there are many application-specific factors that 

need to be considered in determining how to conduct an adequate assessment of cumulative 

impacts, accounting for contributions from nearby backgroun-d sources explicitly in the model as 

well as a monitored contribution, while avoiding or minimizing the potential for double-counting 

of modeled and monitored impacts. 

(g) 

Paine Decl. 14. : "The distribution of total peak daily emissions over the three-year period of 

2000-2002 [from major S02 sources in central North Dakota] was found to overpredict the 

second-highest monitored 24-hour concentrations by roughly a factor of2 because the emissions 

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on average are lower than peak values assumed in the modeling. For the probabilistic 1-hour 

standard . . . and for closer receptors, the overprediction ratio would likely be even higher than 

for a 24-hour average, causing extensive areas of fictitious modeled NAAQS violations." 

Response: The first statement in this comment merely confirms what was indicated in an earlier 

response, namely that modeled impacts based on maximum allowable emissions should not be 

expected to accurately predict ambient monitored concentrations in most cases, since monitored 

concentrations can only reflect impacts from actual emissions. Overprediction by a factor of 2 

does not suggest a significant degree of conservatism given that modeled emissions reflected 

peak emissions. No rationale is offered to support the assertion that the overprediction ratio 

would likely be even higher for the 1-hour standard, and we see no reason to expect that 

necessarily to be the case. 

(h) 

Paine Decl., 14. : "Based on my experience with modeling the 1-hour NAAQS for nitrogen 

dioxide - a NAAQS that is .similar in form to the 1-hour S02 NAAQS - this overprediction ratio 

could approach a factor of 10 in areas with numerous sources modeled together." 

Response: Although the form of the 1-hour N02 standard is very similar to the form of the 1-

hour S02 standard, the role ofNOx chemistry in modeling ambient N02 impacts associated with 

NOx emissions makes it difficult to draw comparisons between the two standards in terms of the 

potential for the model to overestimate ambient impacts as compared to monitored 

concentrations. The comment does not indicate what assumptions were made in the N02 

modeling analyses regarding the conversion ofNO emissions to ambient N02. An overly 

conservative assumption in relation to that conversion could introduce a significant bias in the 

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modeled concentrations relative to monitored concentrations ofN02 that would have no 

relevance to modeling 1-hour 802 impacts. 

(i) 

Paine Decl. 15. : "If a cumulative modeling assessment shows violations of the NAAQS, then 

the PSD permit applicant can still obtain a permit for its source by showing that the proposed 

source does not contribute significantly to the modeled violation. EPA, however, has not yet 

defined a procedure for determining whether a proposed source that conducts a cumulative 

modeling analysis and finds modeled violations due to other sources is by itself causing or 

contributing to these predicted (and possibly false) 1-hour 802 NAAQS violations. This "safety 

valve" thus does not yet exist for applicants trying to demonstrate that their proposed 802-

emitting sources will not cause or contribute to any modeled violations of the.l-hour 802 

NAAQS." 

Response: Recognizing the importance of the significant contribution test within the PSD 

permitting program, EPA recommended an interim Significant Impact Level (SIL) in its August 

23 guidance memorandum regarding the 1-hour 802 NAAQS. This interim SIL provides the 

"safety valve" that may allow a permit applicant to obtain a permit in cases where the cumulative 

impact assessment shows modeled violations of the 1-hour 802 NAAQ8, if it can be 

demonstrated that the proposed emission increases do not contribute significantly to those 

modeled violations, paired in time and space. Although the form of the 1-hour 802 standard 

may complicate the "bookkeeping" needed to make such a demonstration, the principle of the 

significant contribution test based on the SIL has not changed under the 1-hour 802 NAAQS. 

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Pursuant to 28 U.S.C. § 1746, and under penalty of perjury, I declare the foregoing is 

true and correct to the best of my knowledge. 

Date Roger W. Brode 

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