2-1 2.0 BART MODELING REQUIREMENTS

The final version of EPA’s Regional Haze Regula tions was published in the Federal Register on 6 July 2005 (70 FR 39104). One of the provisions of the program is th e requirement that certain existing stationary sources emitting visibility-impairing air pollutants install and opera te the Best Available Retrofit Technology (BART). The regulations require case-by-case BART determination to define specific emissions limitations representing BART and schedules for compliance for each source ‘subject to BART’. These requirements would be part of the SIP revisions that each State must submit to EPA by 17 December 2007. This chapter su mmarizes the requirements of EPA’ s BART Rule, particularly with respect to the modeling analyses that are required to determine (a) if a source is ‘subject to BART’, and (b) what levels of emissions controls might be nece ssary for sources shown to cause or contribute to visibility impairment at fede rally-protected Class I areas.

2.1 Regional Haze Rule and BART Guidelines

Section 169A of the Clean Air Act (CCA) sets fo rth a national goal for vi sibility which is the “prevention of any future, and the remedying of any existing, impairment of visibility in Class I areas which impairment results from manmade air polluti on.” In 1999, EPA published a final rule to address a type of visibility impairment known as regi onal haze (64 FR 35714). The Regional Haze Rule (RHR) requires States to submit implementation plans (SIPs) to address regional haze visibility impairment in 156 federally-protected parks and wild erness areas (i.e., the Class I scenic areas identified in the Clean Air Act). The 1999 rule was issued to fulfill a long-st anding EPA commitment to address regional haze under the authority and requirements of sections 169A and 169B of the CAA. As required by the CAA, the final RHR included a requirement for Best Ava ilable Retrofit Technology (B ART) for certain large stationary sources that were put in place between 1962 and 1977. Th e regional haze rule addresses visibility impairment resulting from emissions from a multitude of sources located across a wide geographic area. Because the problem of regional h aze is believed to be caused in large measure by long-range transport of emissions from multiple sour ces, EPA adopted an approach that requires states

to look at the contribution of all BART sources to the problem of regional haze in determining both applicability and the appropriate level of control. If a source potentially subject to BART is located in an area from which pollutants may be transported to a Class I area, that source ‘‘may reasonably be anticipated to cause or contribute’’ to vi sibility impairment in the Class I area.

The BART guidelines were written primarily for th e benefit of state, local and Tribal agencies, and describe a process for making the BART determ inations and establishing the emission limitations

that must be included in their SIPs or Tribal implementation plans (T IPs). Because the individual states have the authority to require source operators to assume part of th e analytical burden in the BART analysis, there may be some differences in how the analyses are carried out across the CENRAP region. The BART guidelines also recognize that da ta collection, analysis, and rule development may be performed by Regional Planni ng Organizations, for adoption w ithin each SIP or TIP.

The BART guidelines provide a process for making BART determinations that states can use in implementing the regional haze requirements on a source-by-source basis. States must follow the guidelines in making BART determinations on a source-by-source basis for > 750 megawatt (MW) power plants but are not requir ed to use the process in the guidelines when making BART determinations for other types of sources, i.e., states retain the discretion to adopt approaches that differ from the guidelines.2-2 Sources are BART-eligible if they meet three crit eria: (a) emissions of at least 250 tons per year of a visibility-impairing pollutant, (b) in operation between 7 A ugust 1962 and 7 August 1977, and (c) one of 26 liste d source categories in the guidance. BART controls are required for any BARTeligible source which can be reasonab ly expected to cause or contribute to impairment of visibility in any of the 156 federal parks and wilderness (Class I) areas protected under the regional haze rule. Air quality modeling is an important tool available to the States in determining whether a source can be reasonably expected to contri bute to visibility impair ment in a Class I area.

In EPA’s recent 1 August 2005 proposed rulema king (70 FR 44154) entitled “Revisions to Provisions Governing Alternative to Source -Specific Best Available Retrofit Technology Determinations” the agency addressed BART for electric generating units (EGUs). Theses newlyproposed guidelines establish certain control levels or emission rates as presumptive standards for facilities of greater than 200 MW capacity at plants with total ge nerating capacity in excess of 750 MW. These presumptive levels, deve loped through a formal rulemaking process, are to be applied on a source-specific basis. EPA believe s that it appropriate to apply th em in a trading context where the burden to meet BART-equivalent reductions may be shared among non-BART eligible sources as well. Thus, when states estimate emissions reductions achievable from source-by-source BART, they must

assume that all EGUs which would otherwise be subject to BART will control at the presumptive level, unless they demonstrate such presumpti ons are not appropriate at particular units.

2.2 Role of Air Quality Models

The EPA guidelines present severa l options for assessing whether or not sources are subject to BART. The options, relying on different modeling a nd/or emissions analysis approaches, are provided as guidance and the states are entitled to use other reasonable approaches for analyzing the visibility impacts of an individual source or group of sources. The options are:

Option 1: Individual Source Attribution. States can use dispersi on modeling to determine

that an individual source cannot reasonably be anticipated to cause or contribute to visibility impairment in a Class I area and thus is not subject to BART. Under this option, states can analyze an individual source’s impact on visibi lity as a result of its emissions of SO 2 , NOx and

direct PM emissions. Because EPA’s reco mmended CALPUFF dispersion model cannot currently be used to reliably estimate the pr edicted impacts on visibilit y from an individual source’s emissions of VOC or ammonia, states may elect to use a more qualitative assessment to determine on a case-by-case basis which so urces of VOC or ammonia emissions may be likely to impair visibility and should theref ore be subject to BART review. EPA approved models should be used to predic t the visibility impacts from a single source at a Class I area.

Option 2: Use of ‘Model’ Plants. Under this option, analysis of model (or prototypical) plants could be used to exempt certain BART-eligible sources that share specific characteristics. EPA (2005) provides a model plant analysis assuming potential emissions as an example of how states might use this approa ch. The plume and stack characteristics of the model plants were developed considering a broa d range of sources, and the analysis was based on impacts at two hypothetical Class I areas. States may develop their own model plant analyses to account for the mete orology and terrain in their regi on. Alternatively, a state could determine that the assumptions in EPA’s m odel plant analyses accurately reflect the

characteristics of the sources a nd region at issue and no further analysis would be necessary. Because PM was not evaluated in EPA’s model pl ant analysis, states must determine whether PM emissions are significant enoug h to warrant further analysis.2-3 It may be most useful to use this type of anal ysis to identify the types of small sources that do not cause or contribute to visibility impairmen t for purposes of BART, and thus should not be subject to a BART review. Diffe rent Class I areas may have di fferent characteristics, however,

so care must be taken to ensure that the criter ia developed are appropria te for the applicable cases. States could use modeling analyses of re presentative plants to reflect groupings of specific sources with important common characte ristics. Based on these analyses, states may find that certain types of sources are clearly anticipated to cause or contribute to visibility impairment. States can then choose to categorica lly require those types of sources to undergo a

BART determination.

Option 3: Cumulative Modeling . States may also submit to EPA a demonstration, based on an analysis of overall visibility impacts, that emissions from BART-eligible sources in a state, considered together, are not reasonably anticipated to cause or contribute to any visibility impairment in a Class I area and thus no source should be subject to BART. States may do this on a pollutant-by-pollutant basis or for all vi sibility-impairing pollutants to determine if

emissions from these sources contri bute to visibility impairment.

While EPA identifies several options for determining whether a source is “subject to BART”, the most

credible method is the use of di spersion modeling. Air quality m odeling allows a state or source operator to analyze an individua l source’s impact on visibility as a result of its gaseous SO 2 , NOx and

direct PM emissions.

EPA assumes in the BART guidance that disp ersion modeling cannot currently be used to estimate the predicted impacts on vi sibility from an individual sour ce’s emissions of VOC or ammonia owing to uncertainties in the ammonia inventories 1 . Presumably, EPA believes that the uncertainty in current biogenic and anthropogenic ammonia inve ntories are sufficiently large that dispersion modeling of such sources would not provide meaningful results. Howe ver, this view does not comport with EPA’s CAIR modeling or ongoing RPO region al haze visibility modeling in which existing

ammonia inventories are indeed used to calculate daily and annual PM 2.5 and visibility impact assessments. EPA suggests a more qualitative asse ssment to determine on a case-by-case basis which sources of VOC or ammonia emissions may be likel y to impair visibility and should therefore be subject to BART review. CENRAP is consider ing the use of advanced one-atmosphere models (CAMx) to investigate whether VOC and ammonia emissions from BART eligible sources in the region constitute a problem. Findings from these CENRAP modeling studies ar e expected to provide information helpful to the States or source operators in deciding whether and to what extent ammonia and VOCs need to be considered in the BART modeling.

2.3 EPA Guidance on Air Quality Models

The BART determination under the Regional Haze Rule seeks to qua ntify the impact of source

emissions of SO 2 , NOx, and direct PM (PM 2.5 and/or PM 10 ) on 24-hr visibility impairment at receptors

located within downwind Cla ss I areas. Since visibility is define d in the context of light extinction, which itself is determined by atmospheric concentr ations of specific fine particulate species --

1 We believe this viewpoint is outdated, give recent improvem ents in modeling data bases and one-atmosphere models by

EPA ORD/OAQPS and others (Seigneur et al., 2000; Arnold et al., 2003; Morris et al., 2005a, b; Tesche et al, 2005).2-4 ammonium, sulfate, nitrate, organic carbonaceous matter, elemental carbon, and coarse mass – logic dictates that the modeling method(s) used must be capable of simula ting these components reliably.

EPA’s position on recommended models for fine particulate and visibility estimation from single point sources is clearly set out in the Final BART Rule and in the BART Modeling guidance document. The Final BART Rule (pg 101) stat es “Because the air quali ty model CALPUFF is currently the best application available to predict th e impact of a single source on visibility in a Class I area, we proposed that CALPUFF assessment be used as the preferred approach first, for determining

whether an individual source is subject to BART, and second, in th e BART determination process.

CALPUFF can be used to estimate not on ly the effects of directly emitted PM 2.5 emissions from a source, but also to predict the visibility impacts fro m the transport and chemical transformation of fine particle precursors.” The Rule goes on to state (pg 110) that “regional scale modeling typically involves use of a photochemical grid model that is capable of simula ting aerosol chemistry, transport, and deposition of airborne pollutant s, including particulate matter and ozone. Regional scale air quality models are generally applied for geographic scales ra nging from a multi-state to the continental scale. Because of the design and intended applications of grid models, they may not be appropriate for BART

assessments, so States should consult with the a ppropriate EPA Regional Office prior to carrying out any such modeling”.

In contrast, EPA’s “Guidance for Demonstratin g Attainment of the Air Quality Goals for PM 2.5 and Regional Haze” (EPA, 2001) sets forth the type s of models that should be used for simulating secondary fine particulate and visibility for SIPs. EPA states (pg 169): “States should use a regional scale photochemical grid model to estimate the eff ects if a control strategy on secondary components of PM. Changes in primary components may be estimated using a numerical grid model (with no chemistry), a Lagrangian model, or in some cases a receptor model”. Thus, in its Regional Haze and

PM 2.5 SIP modeling guidance, EPA indicates that CA LPUFF (a Lagrangian non- steady-state Gaussian puff model) should not be used for secondary PM and visibility impacts at Class I areas, but rather is relegated to the category of estimating primary species.

So, on the one hand, EPA maintains that CA LPUFF is the “best regulatory modeling application currently available for predicting a singl e source’s contribution to visibility impairment” and notes that “it is the only EP A-approved model for use in esti mating single source pollutant concentrations resulting from the long range transport of primary po llutants”. On th e other hand, only regional grid models with appropriate ch emistry are to be used in developing PM 2.5 and Regional Haze SIPs. EPA attempted to reconcile these two positions in the Final BART Rule by asserting that (a) regional models were not develope d to treat individual point sources and (b) CALPUFF’s secondary aerosol chemistry is adequate for estimating relative benefits of controls on BA RT sources. The first point ignores the significant amount of advanced pl ume-in-grid model development carried out at EPA and elsewhere over the past 20 years, while the second point is the focus of continuing debate in the scientific modeling community. Regardless, the BART modeling gu idance stands and CALPUFF is

the recommended model for BART determinations. EP A does allow for the use of alternative models on a case-by-case basis. Thus, th is guidance addresses both appr oaches with CALPUFF being the primary tool for most BART visibility assessments.

2.4 Steps in the BART Modeling Process

The BART guidelines identify four steps required to determine emission limitations for

affected sources.2-5 Identify BART-Eligible Sources. The first step is to identify whether a source is “BARTeligible” based on its source category, when it wa s put in service, and the magnitude of its emissions of one or more “visibility-impairin g” air pollutants. The BART guidelines list 26 source categories of stationary sources that are BART-eligible. Sources mu st have been put in service between 7 August 1962 and 7 August 177 in order to be BART-eligible. Potential emissions of 250 tons per year or more of a vi sibility-impairing air pollutant are required to make a source eligible for BART. Qualifying pollutants include primary particulate matter (PM 10 ) and gaseous precursors to secondary fine particulate matter such as SO 2 and NOx.

Whether ammonia and VOCs should be included as visibility-impairing pollutants for BART eligibility is left for the states to determine on a case-by-case ba sis. The guidance states that high molecular weight VOCs with 25 or more carbon atoms and low vapor pressure should be considered as primary PM 2.5 emissions and not VOCs for BART purposes.

Determine Sources Subject to BART

. To determine whether a source or facility is ‘subject to BART’, EPA recommends modeling all units and a ll pollutants together. This entails using plant-wide emissions and considering the effect of all pollutants combined for comparison to the visibility threshold. EGUs participating in the CAIR program may be BART-eligible for PM if plant wide potential emissions of PM are greater than de minimus. If the EGU is BARTeligible for PM and if the source emissions re sult in impairment above the state-determined threshold, the source may be deemed subject to BART.

To determine whether a BART-eligible sour ce can be excluded from BART controls, a modeling demonstration is required. EPA’s pref erred approach is an assessment with CALPUFF followed by comparison of the estimated 24-hr visibility impacts against a threshold

above estimated natural conditions to be determin ed by the states. The threshold to determine whether a single source “causes” visibility impa irment is set at 1.0 deciview change from natural conditions over a 24-hour averaging pe riod. Any exceedance of this threshold would trigger a BART review. The guidance also states that the proposed thresh old at which a source may “contribute” to visibility impairment shoul d not be higher than 0.5 deciviews, although depending on factors affecting a sp ecific Class I area, it may be se t lower than 0.5 deciviews.

EPA’s guidance builds upon the 1990 National Acid Precipitation Assessment Program (NAPAP) that found that a 5% change in light ex tinction will evoke a just noticeable change in most landscapes. Converting the 5% change in li ght extinction to a change in deciviews yields a change of approximately 0.5 deciviews. EPA believes that this is a natural breakpoint at which to set the BART exemption levels. Sin ce visibility degradat ion may begin to be recognized by a human observer at this extinction level, the guidance uses a 0.5 deciview change on a 24-hour average basis for determini ng that an individual source is causing visibility impairment at a Clas s I area. This level would be calculated by comparing the air quality model’s results for an individual source against’ natu ral visibility’ conditions. A source’s impact is asse ssed by comparing the 98 th percentile modeled value (8 th highest day annually at a receptor or 22 nd highest over 3-years) with the 0.5 deciview threshold. An impact

is declared if the source contribut es to visibility impairment. If so, it is ‘subject to BART’.

If individual BART-eligible units at a facility have impacts that are less than 0.5 dv but in aggregate with other BART eligib le sources at th e facility are greater th an 0.5 dv, the source is ‘subject to BART’. In other words, if the comb ined impact of all units is greater than the threshold for contribution determined by the st ate (such as 0.5 dv), the source is declared2-6 ‘subject to BART’. This does not imply that c ontrols are necessary for each unit; the control technology analysis, which follows the ‘subject to BART’ test, can be a unit-by-unit evaluation and a visibility analysis can be conducted for single units and individual pollutants.

Determine Appropriate Types and Levels of Control

. The third step is to determine BART for the source by considering various control opti ons and selecting the “bes t” alternative, taking into consideration: (a) any pollu tion control equipment in use at the source which affects the availability of options and thei r impacts, (b) the costs of comp liance with control options, (c) the remaining useful life of th e facility, (d) the energy a nd non air-quality environmental impacts of compliance, and (e) the degree of impr ovement in visibility that may reasonably be anticipated to result from the use of such technology.

Incorporate BART-Determinations into the State’s Regional Haze SIP. Results of the BART determinations must be incorporated into the state’s regional haze SIP which is due 17 December 2007. Instead of applying BART on a s ource-by-source basis, a state (or a group of states) has the option of impl ementing an emissions trading program designed to achieve regional haze improvements that are greater than the visibility improvements that could be expected from BART 2 alone. If the geographic distri butions of emissions under the two approaches are similar, determining whether trad ing is “better than BART” may be possible by simply comparing emissions expected under the trading program against the emissions that could be expected if BART was applied to eligib le sources. If the geographic distributions of emissions are likely to be different, however , regional air quality modeling comparing the expected improvements in visibility from th e trading program and from BART would be required.

According to the BART guidance, a modeling protocol should be submitted for all modeling demonstrations regardless of the distance from the BART-eligible source to the Class I area. EPA’s role in the development of the protocol is only advisory as the “States better understand the BARTeligible source configurations ” and factors affecting their particular Class I areas.

2.5 CALPUFF Modeling Recommendations

To evaluate the visibility impacts of a BART -eligible source at Class I areas beyond 50 km from the source, the EPA guidance recommends th e use of the CALPUFF m odel. For modeling sources closer than 50 km to a Class I area, the guidance recommends that expert modeling judgment be used “giving consideration to both CALPUFF and other methods.” While the PLUVUE-II model is mentioned as a possible tool to consider in additi on to CALPUFF within 50 km of a source, it seems unlikely this technique would be any more credible than CALPUFF. The EPA guidance notes that regional scale photochemical grid models may have merit, but such models are resource intensive relative to CALPUFF. Photochemical grid models are clearly more appropriate than CALPUFF for cumulative modeling options such as in the determin ation of the aggregate contribution of all-BARTeligible sources to visibility impairment, but such use should involve consultation with the appropriate EPA Regional Office.

2 EPA’s BART guidance suggests that CAIR would satis fy the BART requirements for affected EGUs, which could affect the modeling efforts a State would need to undertake.2-7 For both BART exemption an d BART determination modelin g with CALPUFF, emissions reflecting periods of start-up, shutdo wn and malfunction are not to be considered in determining the appropriate emission rates. The EPA recommends th at the states use the highe st 24-hour average actual emission rate for the most recent five-year peri od (excluding periods with start-up, shutdown and malfunctions). Visibility improvem ents may be evaluated on a polluta nt-specific basis. States are “encouraged to account for the magnitude, frequency, and duration of the contributions to visibility impairment caused by the source based on the natural variability of meteorology.

EPA does not recommend CALPUFF for addressing visibility impacts from VOCs because its capability to simulate secondary organic aeroso l formation from VOC emissions is deficient, especially for anthropogenic em issions. Currently, VISTAS is performing a weight-of-evidence analysis using EPA’s CMAQ regiona l air quality model to assess whether VOC emissions from all BART-eligible and non-BART point s ources in each VISTAS State cont ribute to visibility impairment. If the impact of eliminating all VOC emissions from all point sources in a VISTAS state is shown to be less than 0.5 dv, then, logically, the impact of any one BART-eligible source would be less than 0.5 dv. If the VISTAS regional modeling analysis confirms this expectation, the CENR AP States might argue similarly that VOC emissions should not be subject to BART.

EPA has given states the option to address ammonia (NH 3 ) emissions from BART-eligible sources. VISTAS weight-of-evidence modeling with CMAQ is also addressing ammonia in the same way VOCs are being examined. If the CMAQ sensitivity evaluations shows that the collective impact of all point NH 3 emissions in a state is less than 0.5 dv, th en the impact of a single BART eligible

source would be less than 0.5 dv. Should the VISTAS modeling conf irm the expected insignificant

role of direct NH 3 emissions on Class 1 area visibility, the CENRAP States might argue similarly that VOC emissions should not be subject to BART. CE NRAP is presently cons idering similar modeling

for both ammonia and VOCs. If the VISTAS mode ling demonstrates the importance of VOCs and/or

NH 3 emissions on Class I area visibility, then CENRAP will need to consider the use of advanced regional models to assist the States in establishing BART controls for these pollutants.

2.6 Alternative Models for BART Analyses

All air quality models share a common foundati on: the species-conservation (or atmospheric diffusion) equation. Source-oriented air quality models including CALPUFF derive from this equation (Tesche, 1983) which applies equally to one source or a million or more sources. The distinction lies in how the various terms are treated (CAMx, CM AQ) or neglected (CALPUFF) in the governing equations and the choice of coordi nate system (Lagrangian or Eule rian). As shown in the next Chapter, much of the simplicity of the CALPUFF m odel derives from the fact that many chemical and physical processes known to influence visibility are simply ignored. More sophisticated plume models such as SCIPUFF and SCICHEM (Karamchandani et al., 2000) rely on a second order closure treatment of turbulent mixing and detailed photoc hemical reaction schemes and to provide more realistic simulations than simpler approaches such as CALPUFF. Full-science re gional models such as CAMx and CMAQ treat the various physical and chemical processes in detail, al beit at the expense of greater computer resources. Furthermore, detailed plume-in-grid treatment is available in several regional scale models, at least in CAMx, it is now possible to perform particulate and gas-phase source apportionment within the plume-in-grid formulati on. Because EPA allows the use of alternative models on a case-by-case basis, th ese CENRAP guidelines include desc riptions of these models and how they can be used.2-8 EPA essentially dismisses the use of regional sc ale models because they are “generally applied for geographic scales ranging from a multi-state to th e continental scale and that by design they may not be appropriate for simulating in dividual point sources”. This pos ture ignores a very substantial body of research and model development carried out at the agency and elsewhere in the U.S. over the past 20 years. Modern one-atmospheric regional photochemical grid models, employing multi-scale nested grids (Kumar and Russell, 1996) and plume- in-grid techniques (Karaman chandani et al., 2002), are fully applicable to the analysis of point sour ce plumes, most especially when reactive atmospheric chemistry occurs. If they were not, then they woul d not be reliable in simulating the combined effects of the wide array of anthropogenic and biogenic emi ssions that cause gas phase, particulate, secondary aerosol, and visibility air polluti on problems—precisely the problem cu rrently being addressed by all five RPOs. Furthermore, the convergence of fast commodity-based Linux computer clusters and the recently-developed RPO regional modeling emissions, me teorological, and air quality data bases make application of these comprehensive models no longer a research or academic exercise. While regional scale modeling clearly requires expertise to perform properly, the actual program costs to conduct a CMAQ or CAMx regional modeling st udy are today quite comparable wi th and occasionally less that a traditional PSD modeling study using ISC, CALPU FF, or AERMOD. Given grid nesting and plumein-grid technology, modern regional m odels are applicable to a very broad range of scales from 10-20 km to continental scale. Regional photochemical grid models are clearly more appropriate than CALPUFF for cumulative modeling requirements such as in the de termination of the aggregate contribution of all-BART-eligible sources to visibility impairment.

States may elect to perform cumulative mode ling in order to examine the feasibility of exempting BART-eligible sources, but this is certa inly not an EPA or BART Rule requirement. The regional haze rule requires States to consider the degree of visibility improvement resulting from a source's installation and operation of retrofit tec hnology, along with the other statutory factors when making a BART determination. However, there is no longer a cumulative modeling requirement in determining the degree of visibility improvement.

For the vast majority of potential BART-eligib le sources in the CENR AP domain, application of the CALPUFF modeling sy stem will in all likelihood be sufficient to address the needs of the source operator, the state, EPA and the FLM. For those special cases where more accurate modeling results are required, appropriate full-scie nce modeling systems and supporting RP O data bases are available. Their broad use by the five RPOs in the past thre e years amply demonstrate that these comprehensive models are no longer arcane acade mic/research institution project s but applications-ready tools suitable for regulatory decision-making.