8-1 8.0 ALTERNATIVE MODEL APPLICATIONS

Recent model inter-comparisons between CALPUFF and full science models such as CAMx and CMAQ (Morris et al., 2003) amply demonstr ate that CALPUFF substantially overpredicts concentrations of visibility-re ducing fine particulates under va rious real-world at the larger downwind distances when compared to one-atmosphe re models. Perhaps onl y a few BART eligible sources in the CENRAP region will consider seri ously the use of alternative models to EPA’s

CALPUFF model. But for those sources whose an ticipated control costs are substantial, the application of comprehensive, full-science regional visibility assessment tools will yield more realistic BART control requirements than those genera ted by a puff model. In this chapter, the steps required to select and apply a state-of-science regiona l model and attendant data bases are presented.

While there are other alternatives to CALP UFF (i.e., PLUVUE-II, SCICHEM), only full-science models have the requisite chemistry and physics formulations to surmount the many limitations associated with CALPUFF (discussed in Chapter 3) . In addition, we briefly summarize the scope and availability of the emissions, meteorological, an d air quality modeling data bases for the CENRAP region that can be used to support alternative BART modeling.

8.1 Use of One-Atmosphere Models in Refined Assessments

States or source operato rs interested in conducting truly re fined visibility modeling of BARTeligible sources have several options for using on e-atmosphere models supported by current RPO data bases. Options available include:

> Modeling Systems : CMAQ4.5 or CAMx4.2

> Sub-Grid-Plume Treatment : CMAQ-PinG, CMAQ-APT-PM, CMAQ-MADRID-APT, CAMx PM IRON PiG, and CAMx multi-scale flexi-nesting;

> Modeling Years : 2001 (MRPO), 2002 (CENRAP, MRPO, VISTAS, WRAP), 2003 (MRPO)

> Modeling Resolutions : 12 km (VISTAS, WRAP, MP RO), 36 km (CENRAP, MPRO, VISTAS, CENRAP, WRAP)

Figures 8-1 thorough 8-6 pr esent the various grid domains used by the RPOs and the Five States Study 1 (Tesche et al., 2005b). Clearly, each CENRAP state is covered by all of the 36 km domains and by many of the higher resolution 12 km domain s as well. Depending on the source’s location and the Class I area(s) of con cern, there are likely to be several mode l/data base configurations available. All of the modeling performed on these domains has been rigorously evaluated and publicly

disseminated.

1 The Five States Study is an integrated 8-hr ozone and annual PM 2.5 modeling study in the Upper Midwest aimed at identifying effective SO 2 , NOx, and VOC controls to address the residual nonattainment beyond imposition of CAIR controls. Using augmented versions of the MRPO 2002 regional haze data sets, a suite of

nested 36/12/4 km ozone and 36/12 km annual PM 2.5 simulations are being carried out for 2002 and 2009 to

address emissions controls needed for atta inment of the 8-hr ozone and annual PM 2.5 NAAQS. These data sets will be publicly available.8-2 8.1.1 Regional Haze Modeling Data Bases

The readiness of one-atmosphere regional models for visibility impact assessment has been substantially strengthened in the past three year s as the result of the RPO efforts to address the Regional Haze Rule. CENRAP and the other four RPOs have developed and evaluated comprehensive data sets for regional haze model applications (Morris et al., 2004, 2005a,b,d; Baker, 2005a-c; Brewer and Adlhoch, 2005; Boylan and Ru ssell, 2005; Tesche et al., 2005). Over the CENRAP domain, annual fine partic ulate and visibility modeling da ta bases now exist for calendar years 2001, 2003, and 2003 (Baker, 2005c). Availability of these public data bases significantly

reduces the resource burden on that subset of states or source opera tors who may elect to carry out alternative BART modeling.

Emission Inventories . Comprehensive modeling inventories for 2002 have been developed by all of the RPOs using common national data sets (2002 NEI) together with local and state-specific emissions information. Generally, all of these inventories are consistent with on another although there are naturally some differences stemming from availabil ity of local information. The elements of the CENRAP modeling inventory we ll-characterize the work performed by all the RPOs.

As part of the CENRAP regional haze modeling program, a gridded, hourly emissions inventory for 2002 of criteria air pollutants (CAPs) and ammonia (NH 3 ) emissions inventories for point, area, and nonroad sources has been developed (Pechan and CEP, 2005; UCR, 2005). The original Base_A 2002 inventory files completed dur ing February 2005 were updated to incorporate comments provided by the CENRAP State, Local, a nd Tribal (S/L/T) agencies and the Emissions Inventory (EI) and Modeling Workgr oups. As a result of the updates, the updated Base_B inventory was developed and is now being used in CENR AP’s 2002 and 2018 regional haze modeling. The CENRAP modeling inventorie s and supporting data prepar ed include the following:

> Comprehensive, county-level, mass emissi ons and modeling inventories for point, area,

and nonroad sources of 2002 emissions for the CAPs and NH 3 for the state, local, and tribal agencies included in the CENRAP region;

> Modeling inventory files containing 2018 projection year emissions for EGUs; and

> A modeling inventory for Ontario fires during 2002.

The mass emissions inventory files were prepared in the National Emissions Inventory (NEI) Input Format Version 3.0 (NIF 3.0) and then converted to the SMOKE/IDA format. These point, area, mobile and nonroad inventories were temporally allo cated (hourly), chemically speciated (for the CB4 mechanism) and spatially distributed (on a 36/12 km grid) over the CENRAP domain for the full calendar year 2002. The inventories include emissions rates for sulfur dioxide (SO 2 ), oxides of nitrogen (NO

x ), volatile organic compounds ( VOC), carbon monoxide (CO), NH 3 , and particles with an aerodynamic diameter less than or equal to a nominal 10 and 2.5 microm eters (i.e., primary PM 10 and PM 2.5 ). The inventories included summer day, wi nter day, and average day emissions. The temporal profiles developed by Pechan and CEP (2005) were used by the CENRAP modeling team to generate gridded, speciated, hourly emissions of photochemical, particul ate, and regional haze

precursors.

Meteorological Data Bases The MM5 model has been used excl usively by the RPOs in support of the regional haze modeling and the modeling files used in the CENRAP and MRPO haze modeling are the8-3 same ones that have been processe d to yield the CALMET fi elds discussed in Chap ter 5. In particular, the following annual MM5 simulations have been us ed to construct CAMx and CAMQ modeling data

bases over the U.S.

> 2001 MM5 data set at 36/12 km resolu tion developed for EPA by Alpine Geophysics (McNally and Tesche, 2002; McNally 2003);

> 2002 MM5 data set ad 36/12 km reso lution developed for VISTAS by Baron Advanced Meteorological Servi ces (Olerud and Sims, 2004);

> 2002 MM5 data set at 36 km resolution developed for CENRAP by Iowa DNR (Johnson, 2003a,b);

> 2003 MM5 data set at 36 km resolution developed for the Midwest RPO (Baker, 2005; Baker et al., 2004; Kembell-Cook et al., 2005); and

> 2004 MM5 data set at 36 km resolution developed for the Midwest RPO (Baker, 2005).

Each of these studies included a performance evalua tion of the MM5 against surface meteorological

observations and the results of these evaluations ar e contained in the reports or presentations cited

above.

Regional Haze Modeling Data Bases Regional modeling data base s using the emissions and MM5 fields have been developed and evaluated by VISTAS (CAMx/ CMAQ for 2002 at 36/12 km); MRPO (CAMx for 2001, 2002, 2003 at 36 km [and some 12 km]); CENRAP (CMAQ/CAMx for 2002 at 36 km [and some 12 km]). Details of these date ba se development activities and associated model performance evaluations are thoroughly de scribed in the literature references.

8.1.2 Obtaining Regional Modeling Data Bases

As discussed in Chapter 4, the aggregate file si zes of the regional haze modeling data sets are substantial, requiring several 300-500 Gbyte external di sk drives to store the information. In addition to the CENRAP CMAQ and CAMx modeling data ba ses, the MRPO and VISTAS have indicated a willingness to provide their data sets to CENRAP for use by CENRAP states or s ource operators. It is anticipated that CENRAP w ill serve as the central repository, co llecting one complete distribution of the pertinent MRPO and/or VISTAS data bases on a set of high-capacity disk drives and then making them available to the states or source operators on an as requested basis for advanced modeling.

Parallel sources of these data se ts are the modeling contractors pe rforming the regional haze modeling

for CENRAP, VISTAS, and WRAP.

8.1.3 Protocol Development

EPA’s BART guidance clearly indi cates the need for a detailed modeling protocol to support any application of alternative mode ls for BART analyses. An exampl e of the content of such a oneatmosphere modeling protocol would be the CMAQ/CAMx modeling protocols developed for CENRAP (Morris et al., 2004c) and VISTAS (Morris et al, 2004a). In addition, certain components of the screening and source-specific protocols devel oped with CALPUFF (Tables 6-1 and 7-2) would be appropriate. The alternative modeling protocol shoul d be submitted to the state, regional EPA office8-4 and FLM for review and negotiation. Note that EPA’s role in the development of the protocol is only advisory as the “states better understand the BART-eligible source conf igurations” and factors affecting their particular Class I areas (70 FR 39126).

8.2 Model Applications

Assessment of BART sources with regional models is a straightforward, albeit computationally intensive exercise. Two types of re gional model simulations are required.

8.2.1 Regional Base Case Simulation

The first step is to re-run one of the existing regional simulations for the 2002 annual basecase to establish comparability with the base case run re ported by the RPO from whom the CMAQ or CAMx modeling files were obtained. The purpose of this a nnual simulation is two-fol d. First, it establishes proper operation of the modeling system on the hos t computer via comparison with the RPO model output files. Second, it provides the gridded 24-hourly estimates of (NH 4 ) 2 SO 4 , NH 4 NO 3 , OC, EC, soil, and coarse mass needed to calculate daily extinction coefficients from the IMPROVE extinction equation for every grid cell in the domain, including the Class I areas. (Furth er discussion of natural visibility conditions is given in the following section). On a modern Linux cluster of 4-6 nodes, a 36 km simulation would require approximat ely two weeks to complete execution.

An important question to be addressed in the modeling protocol is whether one annual

simulation of 2002 would be suffici ent to provide the necessary a ssessment of a BART source’s visibility impact. Recent annual CAMx si mulations of 2001, 2002, and 2003 by the MRPO (Baker, 2005c) indicated that for these three years:

> CAMx model performance by specie was very consistent from one year to the next;

> Sulfate predictions exhibited the greatest year to year variabil ity, likely due to the interannual variability of atmospheric water content;

> CAMx performance was best for sulfate and elemental carbon; and

> Organic carbon predictions during the summer months were the poorest of the secondary particulate species; and

> Nitrate performance, a challenge in a ll regional modeling studies, needs additional improvement.

The performance levels achieved in the MRPO CAMx modeling are gene rally consistent with that of

the other RPOs. These results ar e included in Figure 4-9, presented previously. Because the regional models include all of the important known gas-pha se, aerosol, and aqueous- phase chemistry producing visibility-impairing particulates, a strong case can be made that only one year of modeling would be needed instead of the three years of CALPUFF modeling. However, if the reviewing agencies require a full three years of modeling data, a valid appr oach remains nonetheless with the 2001-2003 CAMx data sets developed by the MPRO.8-5 8.2.2 BART Source Simulati on with SGS Technology

Once the base case is established, the CMAQ or CAMx simulation is repeated with the

emissions from the BART source are included in the point source emissions file . For this application, depending upon the host model chosen, one of several pl ume-in-grid or nested grid options should be used to provide near s ource resolution of the SO 2 , NOx, NH 3 , and VOC emissions of the BART source. For most single point BART simulations conducted with a full-science photochemical grid model, the plume-in-grid technique is generally recommended over the use of multi-scale grid nesting although the latter may still be appropriate in additi on to the plume-in-grid approach for other reasons, including replication of meteorology and transport phenomena. Prescription of how the sub-grid-scale (SGS) technology is used within the regional mode l is a key point to be addressed in the modeling protocol. The use of SGS will allow the simulation of BART plume impacts down to very small scales (on the order of 1 km or less) depending upon the need.

8.2.3 Assessing Modeled BART Source Impacts

The direct impacts of the BART sources on 24-hr visibility is quantified by subtracting the 2002

Base Case simulation from the BART source simu lation and plotting the residual aerosol species concentrations and HI values in daily tile plot s. Figure 8-7 provides an example of such an incremental 24-hr average concentr ation tile plot. From the CAMx PM PinG modeling by Yarwood et al, (2005) using the 2002 MPRO data base, incremental 24-hr average SO 2 , sulfate, nitrate, and NH 4 concentration fields on 14 June 2002 are shown. This plume reveals the individual plume signatures downwind from their origin. Simila r plots of delta-deciviews can be determined using the IMPROVE extinction equation with the modeled aerosol fields from both model simulati ons. Tabular summaries of the visibility impacts in all grid cells, but especially the Class I areas are easily produced.

8.3 Estimation of Natural Visibility Conditions

8.3.1 Flexibility Suggested by EPA

Under the Regional Haze Rule, by 2008, the stat es must develop a strategy for reducing regional haze in Class I areas during the following d ecade. The rate of improvement of visibility is

intended to be at a rate sufficient to reach “natural conditions” in 2064, and thus depends on quantifying what the visibility would be under thos e conditions. The initial, “default” estimate of

natural conditions recommended by EPA (2003) – based on pre-1990 research (Trijonis, 1990) does not take into account spatial and temporal vari ability and local geogra phic and meteorological conditions. Consequently, the default natural visibili ty conditions are out-of-date and do not reflect the very substantial theoretical, observational, and modeling data bases now available for estimating natural background concentrations (Tombach and Brewer, 2005). R ecognizing that the “default” concentrations (see Table 6-3) are not appropriate fo r every Class I area, EPA allows states the option to develop "refined" estimates of natural conditions that reflects local conditions.

States might wish to adopt a re fined approach to es timating natural visibility conditions for

several reasons, including:

> The default estimates are shown, through mo re recent Class I area-specific observations and/or modeling analyses to be out-dated and/or incorrect;

> If the default estimates of the natural background conditi ons are close to the current8-6 visibility conditions, small uncertainties can have significant impacts on states’ ability to meet SIP goals;

> In some regions, natural sources are known to exhibit predictable seasonal influences on visibility; therefore, states might wish to use refined estimates of natural visibility

conditions to account for these influences;

> States which receive significant visibility impacts from biomass smoke might wish to distinguish more explic itly between man-made and natural sources.

EPA identifies several possible refined approach es which can be adopted for developing ore

realistic estimates of natural vi sibility conditions and states may identify others that are more appropriate for their own situations. Approach es suggested by EPA include: (a) develop refined

estimates of the constant values of one or more na tural species, (b) estimate natural visibility using species concentrations th at vary (e.g., seasonally, monthly, or climatologically ), or (c) adjust the estimated constant species to account for infrequent natural events, such as forest fires or wind-blown dust, as major influences on visibility. This latt er approach would require estimating the frequency and magnitude of the natural contribution to particle concentrations during the events. EPA encourages flexibility in these approaches so that default and refined annual average, seasonal, monthly, and event-specific species concentrations provide the best estimates of natural visibility for each of the mandatory Federal Class I areas. States wish ing to employ a refined approach should supply demonstrations that the refined approach is tec hnically sound and provides regionally representative

estimates of natural vi sibility conditions.

8.3.2 Refined Procedures for One-Atmosphere Modeling

The whole purpose of estimating natural visibility conditions is to develop a reasonable background against which a human observer might be able to discern the added presence of a BART source plume. With Lagrangian models such as CA LPUFF, this necessity arises because puff models cannot calculate the three-dimensional, hourly varyi ng gas phase and particulat e concentration fields that contain the various visibility -limiting pollutant species. Conse quently, some independent estimate of natural visibility conditions is required. Hist orical measurements of pris tine conditions measured in

the 1980s have been used to fill this void.

One-atmosphere models, by design, eliminat e the need to estimate natural background conditions against which individual plume contributions are assessed. This is done di rectly via the simulation of the hour-by-hour, day-by-day emissions (including sea salt), meteorology (rain, snow, fog), transport, chemical transf ormation and removal of gaseous a nd particulate emissions from all sources (natural and manmade) in the region of inte rest for one or more calendar years. Today, the

CENRAP, WRAP, MRPO, and VISTAS regional haze programs have all developed base year 2002 fine particulate and visibility estimates for the entir e U.S. at grid scales of 36 km and 12 km using the CMAQ and/or CAMx models (depending upon RPO). Importantly, the MRPO ha s even extended the CAMx visibility modeling to in clude the same three year peri od (2001-2003) being use in the screening and source-specific CALPUFF modeling. The 24-hour av eraged modeled ground level concentration pred ictions of (NH 4 ) 2 SO 4 , NH 4 NO 3 , OC, EC, soil, and coarse mass (i.e., all components in the IMPROVE extinction equation) from any of these regional simulati ons provide a direct quantification on a day-to-day basi s of current background visibility conditions in not only the Class I areas, but in every 12 km or 36 km grid cell in the U.S. By simply re-running one or more of these regional one-atmosphere model simulations with the BART source emissions included , and then8-7 subtracting the outputs of the two si mulations, a direct, gridded estimate is produced of the change in visibility (measured in terms of ‘delta-deciviews’) compared agai nst realistic, current background

conditions. As with the screen ing CALPUFF modeling, if the Δ dv value is greater than the 0.5 dv

threshold, the source is said to co ntribute to visibility impairment and is thus ‘subject to BART’

controls.

This approach to calculating a realistic natu ral visibility background condition departs from EPA’s suggestions in two respects. First, it is far more rigorous, and thus is more resource intensive to carry out. Second, the natural visi bility background conditions over th e Class I areas simulated by the CAMx/CMAQ models in the 2002 base cases will in all likelihood be less ‘pristin e’ then those estimated by Trijonis and others in the late 1980s. But, we maintain, they will be more representative

of the actual current co nditions in the Class I ar eas against which the BA RT plume impacts should realistically be compared.

Clearly, the acceptability of this refined one -atmosphere modeling procedure for calculating natural visibility background conditions in the Class I areas will need to be disc ussed with state, EPA,

and FLM staff in order to reach consensus on the merits and acceptability of the approach. The fallback is to use the default (EPA, 2003) numbers.

8.4 Cumulative Impact Assessments

While the use of regional models incorporating plume-in-grid or multi-scale nesting allow for rigorous assessment of 24-hr average point source a nnual visibility impacts over one or more years, where one-atmosphere models are most useful is in cumulative impact assessments. The example shown in Figure 8-7 is one such application. The modeling perf ormed by Yarwood et al., (2005) treated several dozen point sources with plume- in-grid technology allowing for the opportunity to assess the cumulative impact of all of these sources in the context of all anthropogenic and biogenic

sources in the central U.S.

As noted in Chapter 1, each CENRAP state is re quired to carry out four types of visibility modeling under the Regional Haze Rule: (a) single-source mode ling to determine which BARTeligible sources are ‘subject to BART’, (b) single-s ource modeling to determine the degree of visibility improvement attributable to proposed BART controls for each source subject to BART, (c) cumulative modeling to determine the co mbined effect of proposed BART contro ls for sources subj ect to BART in each CENRAP state; and (d) regional-scale modeling to determine if the combined effect of proposed BART controls for all CENRAP states ultimately satisfy the RHR visibility improvement goals. The third responsibility, cumulative impact assessment of all state sources subject to BART, is best addressed through the use of regional models.

8.5 Concluding Remarks

Only a few states and/or BART eligible source s are expected to seriously examine the merits of using full-science models as an alternative CALPUFF. But fo r those who do, the review of oneatmosphere modeling capabilities (Chapter 4) and the procedures one would follow in their application to BART sources (this chapter) will hopefully provide useful information to inform decision-making. Fortuitously, the recent work by the various RPOs and model developers has produced a suite of state-of-science models and asso ciated data bases that are ideally suited to rigorous BART visibility impact modeling. While the resource re quirements of an alternative modeling study – using existing models and data bases-- exceed those of a typical CALPUFF8-8 analysis, the potential to devel op more reasonable control limits on certain BART sources may easily eclipse the additional cost s of full-science modeling.

-2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 -2000 -1500 -1000

-500 0 500 1000 1500

12 km Domain 36 km Domain

Figure 8-1. CENRAP 36/12 km CMAQ/ CAMx Domain Used for 2002 Annual OneAtmosphere Regional Haze Simulations. 36 km domain is outer grid; 12 km domain is colored red. (Note: Model Si mulations on 12 km domain may not be performed for full annual cycle). (Source: Morris et al., 2005d).8-9 

## MM5 CAMx

Figure 8-2. MRPO 36 km CAMx Domain Us ed for 2001, 2002, 2003 Annual One-Atmosphere Regional Haze Simulations (Source: Baker, 2005c).8-10 \

Figure 8-3. MRPO 36/12 km CAMx Domain Used for 2002 Annual One-Atmosphere Regional

Haze Simulations. 36 km domain is oute r grid; 12 km domain is colored green (Source: Koerber, 2005).8-11 Figure 8-4. VISTAS 36/12 km CMAQ/CAMx Do main Used for 2002 Annual One-Atmosphere Regional Haze Simulations. 36 km domain is outer grid; 12 km domain is colored green (Source: Tesche et al., 2005).8-12 Figure 8-5. WRAP 36 km CMAQ/CAMx Doma in Used for 2002 Annual One-Atmosphere Regional Haze Simulations. (Source: Morris et al., 2004b).8-13 Figure 8-6. Five States Study 36/12/4 km PM2.5/8-hr Oz one Study Using CAMx for the 2002 Annual Period. (Source: Tesche, et al., 2005b).8-14 24-hr SO 2 Concentrations 24-hr SO 4 Concentrations

24-hr NO 3 Concentrations 24-hr NH 4 Concentrations

Figure 8-7. Incremental 24-hr Average SO 2 , Sulfate, Nitrate, and NH 4 Concentrations Fields on

14 June 2002 from the CAMx PM PiG Si mulation Over the Upper Midwest. Apparent in this figure are the individual plume footprints downwind from their origin. The modeled plumes result from full chemistry interaction between the background regional atmosphere and the chemical and physical dynamics of the individual plumes. (Adapted from Yarwood et al., 2005).