USE OF AIR QUALITY MODELING AND COMPLEMENTARY ANALYSES

TO SUPPORT AIR QUALITY MANAGEMENT APPROACHES TO MEET

OZONE, PM AND RH GOALS

Strawman Draft #1

March 5, 1997

EMAD Staff

U.S. EPA

Contents

1.0 Introduction

2.0 Institutional Considerations for Modeling/Analysis

2.1 Modeling/Analysis Centers, Areas of Prime Responsibility, RAMP's and AOI

2.2 Rationale Underlying Recommended Modeling/Analysis Centers

- Air Quality Observations/Past Analyses

- Need for Expediency and Building Upon Past Experience

2.3 Scope of Modeling/Analysis Center Activities and Use of State Modeling

3.0 Use of Modeling/Analysis in Developing SIP's/TIP's

3.1 Five Step Process in SIP/TIP Development

- RAMP Formation

- Coordination/Developing Procedures

- Identification of Preliminary Areas of Influence

- Preparation of RIP's and SIP/TIP Calls

- SIP/TIP Preparation

3.2 Modeling/Analysis Tools

- MODELS3

- SAQM

- UAMV

- REMSAD

- Other Nested Models

- UAM-X Source Attribution Post Processor

- Direct Decoupled Sensitivity Method

- Individual Source Modulation Method

- MM5 Mass Tracking Approach

- Trajectory Models

- Process Analysis/Mass Tracking

- Observational Models: receptor models

- Observational Models: use of indicator species, ratios of species and chemical	lifetime data

3.3 Integrated Analyses

4.0 Steps in Performing Modeling/Analysis

4.1 Developing a Protocol

4.2 Episode Selection

4.3 Preparation of Emissions Data

4.4 Selecting Model Domains and Horizontal/Vertical Resolution

4.5 Preparation of Meteorological Inputs

4.6 Performing Diagnostic Analyses and Assessing Model Performance

4.7 Evaluating Strategies for Meeting Air Quality Goals

4.8 Reporting/Archiving Requirements

4.9 Mid-Course Reviews

5.0 Potential Issues

5.1 Managerial/Administrative Topics

5.2 Scientific/Technical Topics

6.0 Summary

7.0 References Cited

1.0 Introduction

The purpose of this paper is to outline initial thoughts on how air quality models might be appropriately used in air quality management approaches to meet proposed national ambient air quality standards (NAAQS) for ozone and fine particulate matter (PM). Use of models to help achieve goals for ameliorating regional haze (RH) is also discussed. Because we view an air quality model as one of several analytical tools potentially useful in designing effective control strategies, the paper also addresses roles for other, complementary analyses.

Modeling/analysis for helping to meet new NAAQS or RH goals is a topic which is scheduled to be addressed as part of a "phase 2 implementation" Federal Register proposal. The "phase 2 implementation" proposal is currently planned for July 1998. We are writing this strawman at an early date so that we will have an opportunity to consider suggestions from the FACA subcommittee's science/technology workgroup and STAPPA/ALAPCO's Standing Atmospheric Simulation Model Workgroup (SASWG) in preparing that part of the "phase 2" proposal which relates to modeling and analysis.

The remainder of this paper is organized as follows. In section 2.0 we discuss institutional arrangements for undertaking modeling/analysis. We recommend use of a limited number of "modeling/analysis centers", and explain how these would be related to Regional Air Management Partnerships (RAMP's) and preliminary areas of influence (AOI). We also briefly outline the rationale underlying our recommendations. In section 3.0 we go through the 5-step process leading to State implementation plan (SIP) or Tribal implementation plan (TIP) development outlined in the FACA subcommittee's National Regional Strategies Workgroup papers on AOI and institutional mechanisms. We explain our view on use of modeling and/or complementary analyses for several of the steps. We also outline our thoughts on what models are appropriate under what kinds of circumstances. Section 4.0 addresses steps in the modeling procedure in greater detail. This includes our thoughts on potential uses for various complementary analyses. In Section 5.0, we identify possible topics for issue papers which would likely be helpful in assisting us to prepare our proposal. Section 6.0 summarizes key points in the preceding sections.

2.0 Institutional Considerations for Modeling/Analysis

2.1 Modeling/Analysis Centers, Areas of Prime Responsibility, RAMP's and AOI

We recommend establishing 7 modeling/analysis centers to assist RAMP's and AOI's to develop regionally integrated plans (RIP's). Each modeling/analysis center would have an area of prime responsibility. Areas of prime responsibility are shown in Figure 1. Table 1 lists States and EPA Regional Office jurisdictions corresponding with each of the recommended areas of prime responsibility. Model applications by each modeling/analysis center would typically cover a larger geographical area than the center's area of prime responsibility. For example, it is expected that the Southeast Modeling/Analysis Center would include much of the eastern half of the U.S. in its model applications. However, episode selection would be governed by incidents which are of

Table 1. Suggested Areas of Prime Responsibility for Modeling/Analysis Centers

Modeling/Analysis Center EPA Regional Offices States Northeast I, II, III Maine New Hampshire Vermont Massachusetts Rhode Island Connecticut New York New Jersey Pennsylvania Delaware Maryland (and DC) Virginia West Virginia Midwest IV, V, VII Ohio Kentucky Indiana Michigan Wisconsin Illinois Missouri Iowa Minnesota Kansas (a) Nebraska (a) Southeast IV North Carolina South Carolina Georgia Florida Alabama Tennessee Mississippi Western Gulf/Southern Plains VI Louisiana Arkansas Oklahoma Texas New Mexico (b) Northern California IX San Joaquin Valley and points north in California, Bay Area, Coastal California south to and including San Luis Obispo County Southern California IX Santa Barbara, Ventura, South Coast Air Quality Management District, San Diego, Mohave Desert, Imperial County Western Regional VIII, IX, X South Dakota North Dakota Montana Wyoming Colorado Arizona Utah Nevada Western Regional (cont.) VIII, IX, X Idaho Oregon Washington

(a) Included in Midwest Modeling/Analysis Center to better address large cities along the Missouri River, and to reduce the number of EPA Regional Offices having jurisdictions within the Western Regional Modeling/Analysis Center.

(b) Included in Western Gulf/Southern Plains Modeling/Analysis Center, because ozone data suggest a potential regional ozone problem in the Lower Rio Grande Valley from Las Cruces to El Paso, and to reduce the number of EPA Regional Offices having jurisdictions within the Western Regional Modeling/Analysis Center.

concern to the AOI and Areas of Violation (AOV) located within its area of prime responsibility. Likewise, spatially detailed nested analyses would be confined to locations within the area of prime responsibility. We view this as essential for computational feasibility.

A modeling/analysis center is defined by its area of prime responsibility (e.g., as in Figure 1). However, it is not necessary for all analytical activities to be performed by a single State or at a single location. For example, location of air quality modeling acitivities in New York and air quality data analysis activities in Vermont for the Northeast Modeling/Analysis Center is consistent with the concept we are describing. As we describe more fully below, it is the responsibility of the appropriate RAMP and, later, the appropriate preliminary AOI to ensure coordination of these activities occurs.

Consideration of large modeling domains of the sort described above requires that the modeling/analysis centers use consistent data bases. The EPA intends to update its current 1990 emission estimates for VOC(speciated), Nox, CO, SO2, primary coarse and fine PM(speciated) and NH3 for 1996. This information will be archived so that it is accessible to each modeling center, as well as to RAMP's, AOI and individual States. One responsibility of the EPA will be to insure that revisions to the 1996 emission estimates deemed adviseable by one or more States get incorporated into the 1996 emission estimates on a periodic basis, and that all RAMP's and modeling/analysis centers are advised of the changes. A second national data base expected to be utilized by the modeling/analysis centers consists of mesoscale meteorological data. Subject to computer hardware and data base management limitations, we expect to run the MM5 model for (portions of?) each year, beginning with 1995. The goal will be to cover the contiguous 48 States, with a horizontal resolution of 36 km. This information is expected to be used by each modeling/analysis center to characterize flow outside its area of prime responsibility, as well as to serve as a starting point for each center to estimate more finely resolved meteorological fields for selected areas within its area of prime responsibility. We hope to be able to provide further insights into the necessary geographical coverage and resolution of the more finely resolved grids.

We expect modeling/analysis centers to be established within a timeframe comparable for establishing the RAMP's. Prior to identification of preliminary AOI's (anticipated via Fed.Reg. Notice in Sept. 1999), RAMP's which cover all or part of a center's area of prime responsibility are the primary clients for the modeling/analysis centers. One of centers' early responsibilities will be to perform technical analyses which assist the RAMP's to identify preliminary AOI. Once the AOI are identified, they become the centers' primary clients. The RAMP then fulfills a function of prioritizing conflicting demands of the AOI clients and facilitating communication among AOI.

2.2 Rationale Underlying Recommended Modeling/Analysis Centers

Air Quality Observations/Past Analyses. A recent review of 1993-95 AIRS air quality data indicates that the number of counties containing monitoring sites not meeting the proposed ozone NAAQS is roughly triple that for counties not meeting the current NAAQS. Further, many of the newly flagged counties are ones with small MSA's or no MSA's at all. Most of these counties are in the eastern U.S. Other analyses of eastern ozone data, such as those by Eder et al. (1993) and Cox (1997), have suggested coherant, somewhat smaller areas exist in the eastern U.S. which exhibit day to day correlations in observed daily maximum ozone levels. Perhaps more importantly, anecdotal experience gained in the Ozone Transport Assessment Group's (OTAG's) modeling efforts has shown that different episodes are of interest to different regional areas in the eastern U.S.

Ozone observations suggest different findings in the western U.S. Outside of California, there are few locations with monitored data which exceed the proposed NAAQS (i.e., El Paso, Las Cruces, Denver, Phoenix and Salt Lake City). Except for El Paso/Las Cruces, these are seperated by large geographical areas. Further, with the exception of Phoenix and El Paso, design values for all of these western cities are within 2-3 ppb of the proposed NAAQS. In California, there are two regional areas, separated by topographical features, which would appear likely to have widespread problems meeting the proposed ozone NAAQS: South Coastal/SE Desert (i.e., "Southern California") and San Joaquin Valley/Bay Area (i.e., "Northern California"). Each of these areas is characterized by several MSA's, many of which have cited regional transport as a major problem in past modeling studies.

Data for fine particulates are far less extensive than for ozone. Observations at 35 western sites in the IMPROVE network (see Table 2.5 in the STWG's Conceptual Model for Ozone, Particulate Matter and Regional Haze and Eldred (1997)) suggest that, with few exceptions, regional fine particulate matter in the western U.S. is only about 1/3 or less of the proposed annual PM NAAQS. The exceptions occur at sites in southern California likely to be influenced by urban areas and at a site on the eastern slope of the Sierra, likely to be influenced by PM levels in the San Joaquin Valley. This implies that meeting the PM NAAQS, like meeting the ozone NAAQS, is not likely to be a widespread regional problem in the western U.S.

The largest component of measured fine particulate at most rural western sites appears to be organic carbon, with sulfates a distant second (Fig.2.8, Conceptual Model). Looking at seasonal PM observations from the IMPROVE network, there does appear to be slightly higher PM in the summer at most of the Class I area IMPROVE sites, with both sulfates and organic carbon components following this general pattern. Although this seasonal pattern may coincide with patterns in regional ozone, other explanations, such as increased local biogenic emissions and increased SO2 emissions also exist for this finding. The one western urban area where we have some information on measured fine PM is perhaps atypical (i.e., South Coast Air Basin). The data there suggest a different seasonal pattern for secondary fine particulate (dominated by nitrates). The data also suggest that the South Coast Air Basin will have difficulty meeting proposed PM and ozone NAAQS unless major reductions occur in emissions.

PM measured at the Class I area IMPROVE sites is sufficient to attenuate visibility at the western IMPROVE sites. Further, recent analyses performed for the Grand Canyon Visibility Transport Commission ( Recommendations for Improving Western Vistas, June 10, 1996) suggest that there is a regional component to measured PM levels at those sites on the Colorado Plateau. The Commission's report indicates that greater effort is needed to quantify respective roles of regional vs. local (i.e., <~100 km) emissions as contributors to fine particulates measured in Class I areas.

The IMPROVE data are more limited for the eastern U.S. (12 sites). The data which do exist however, indicate PM levels in rural areas which are about 75% of the proposed annual fine PM NAAQS at sites in Arkansas, Alabama, Georgia, Tennessee, Kentucky, Virginia, West Virginia, Maryland, New Jersey and Vermont (Eldred (1997)). If these observations are generally representative of rural areas in the eastern U.S., this leaves little working margin for urban locations which may violate the PM NAAQS. The eastern observations are dominated by sulfates, with PM of unknown composition and organic carbon being the next most important contributors. There is a strong seasonal pattern in measured fine PM at eastern sites. This pattern is consistent with seasonal ozone patterns, perhaps suggesting common sets of conditions leading to high ozone and secondary PM in the East. Measured and estimated regional PM levels in the eastern U.S. are greater than those estimated in the West. This, along with other, natural factors like relative humidity, contributes to generally poorer visibility in the East. Thus, the limited information which exists at present is consistent with existence of a major regional component which could potentially contribute to violations of fine PM NAAQS and attenuate visibility in the East.

Need for Expediency and Building Upon Past Experience. Once NAAQS are promulgated, the Clean Air Act requires that State implementation plans to meet the NAAQS be prepared and executed expeditiously. Assuming the NAAQS are promulgated in July 1997, we believe it will be necessary to identify preliminary AOI by September 1999 and develop regionally integrated plans (RIP's) by January 2001 to meet a required July 2003 date for SIP and TIP submittals. Such a schedule implies that the modeling/analysis supporting SIP/TIP development will need to be completed by early in 2002.

Consideration of regional as well as local factors in identifying effective strategies to meet air quality goals is considerably more complicated than analyses which focus solely on local solutions to local problems. To perform supporting analyses within the timeframes implied by the Clean Air Act, we believe it is necessary to utilize previously formed institutions which have been engaged in regional modeling/analysis. Table 2 outlines related past experience for each of the 7 recommended Modeling/Analysis Centers.

Table 2. Recommended Modeling/Analysis Centers and Related Experience

Modeling/Analysis Center Related Experience Northeast Ozone Transport Assessment Group (OTAG) regional modeling/analysis Midwest OTAG regional modeling/analysis Southeast OTAG regional modeling/analysis Western Gulf/Southern Plains Gulf Coast regional study Northern California San Joaquin Valley study Southern California 1985 and 1997 regional air quality studies Western Regional Modeling/analysis to support the Grand Canyon Visibility Commission

2.3 Scope of Modeling/Analysis Center Activities and Use of State Modeling

With the exception of the Western Regional Modeling/Analysis Center, it is expected that each modeling/analysis center will need to address ozone, PM and visibility attenuation within its area of prime responsibility. As noted previously, there is presently a lack of convincing evidence that meeting the proposed ozone and PM NAAQS will be a regional problem in the western U.S. (outside of California). Thus, we anticipate that the affected RAMP(s) may conclude that it is most efficient to have the Western Regional Modeling/Analysis Center focus on strategies to reduce visibility attenuation, particularly in Class I areas. Further, we recognize that individual States (particularly in the western U.S. outside of California) may conclude that a PM or ozone problem is primarily of local origin and that it is more efficient to model/analyze/develop strategies to address the problem independently of the RAMP or modeling/analysis center. Our guidance is not intended to preclude these initiatives. One function of the RAMP(s) included in the area of prime responsibility for the Western Regional Modeling/Analysis Center should be to make sure the Center takes note of strategies/assumptions in the Northern and Southern California Modeling/Analysis Centers and by individual States, so these can be considered by the Western Regional Center in analyzing strategies to improve visibility. RAMP's in other regions of the U.S. have a similar responsibility to keep the modeling/analysis centers informed of relevant independent State initiatives to reduce emissions.

3.0 Use of Modeling/Analysis in Developing SIP's/TIP's

3.1 Five Step Process in SIP/TIP Development

A five step process has been identified for developing SIP's/TIP's in a recent issue paper prepared for the FACA subcommittee. The steps are listed below. Dates in parentheses reflect our understanding of deadlines for completing each step. Dates with astericks reflect times for publication in the Federal Register. Typically, results of analyses supporting Federal Register notices should be completed about 4-6 months prior to these dates.

(1) Final identification/formation of RAMP's (January 1998);

(2) Coordination among RAMP's, modeling/analysis centers and the EPA to	identify/develop modeling/analysis procedures leading to identification of	preliminary AOI's and RIP's (~July 1998);

(3) Identification of preliminary AOI (September 1999*);

(4) Preparation of RIP's and SIP/TIP calls (July 2001*);

(5) SIP/TIP preparation (submitted to the EPA by July 2003--supporting analyses	need to be completed by early in 2002).

RAMP Formation. We anticipate that consideration of political factors and past or existing institutional arrangements will play a major role in the identification of RAMP's. Because of the short timeframe for identifying RAMP's, related modeling/analysis will likely be limited to re- interpretation of previously performed ozone modeling sensitivity analyses for the OTAG directed at 8-hour daily maxima, previously completed sensitivity tests with regional models for PM performed for a regulatory impact analyses, past statistical reviews of ozone data which identify clusters of monitoring sites exhibiting a high amount of covariance, and emission maps depicting 1990 or projected 2007 emission estimates. Whatever analysis occurs would be performed by or for the US EPA or the States. The modeling/analysis centers will not yet exist.

Coordination/Developing Procedures. These activities include setting up the apparatus for performing analyses needed later in the 5-step process. They include assigning responsibilities for communication/coordination within the RAMP, reaching agreement on the operation of the modeling/analysis centers (including who does the modeling and who does ambient analyses), agreement on which emissions data base to use, identification of appropriate models and other analysis techniques for implementing steps 3-5 of the process, and agreement on a step by step approach concerning how the modeling/analysis should proceed. This paper is intended as a very early step in the coordination/development process. We would hope that the recommendations we provide would be considered by the RAMP's so that the regional modeling/analysis centers can be formed within about 30 days of the RAMPs' formation. In section 3.2, we identify a set of modeling/analysis tools which may be of use. We anticipate refining and elaborating upon this list in dialogue with FACA participants during the coming year. In section 3.3, we present some ideas on how analyses for ozone, PM and regional haze could be integrated. In section 4.0, we identify a set of steps which we believe may be appropriate to follow in a modeling analysis.

As noted in section 1.0, we hope to get a substantial amount of feedback on both the technical and managerial aspects of performing the modeling/analysis needed to support the new NAAQS and RH rule. This is expected to culminate in a "phase 2 implementation" proposal about July 1998. We hope and expect that there will have already been a substantial amount of dialogue among the EPA, States and other FACA participants prior to January 1998, when the RAMP's are identified.

Identification of Preliminary Areas of Influence. We anticipate that the modeling/analysis centers will use tools which are less resource intensive, as well as less comprehensive, than some of those which will be used subsequently to develop RIP's. This is true for at least three reasons. First, States will likely not have had sufficient time to thoroughly review and update initial estimates of a 1996 inventory. Second, we do not believe that there will be a sufficient lead time between availability of models capable of considering ozone, PM and RH on an integrated basis and the time when preliminary AOI must be identified (September 1999). For example, an evaluated and tested version of MODELS3 is not likely until well into 1998. We foresee potential startup difficulties as the centers attempt to use this or similar tools. Third, identification of preliminary areas of influence is an intermediate goal in the process, which does not necessarily result in prescribed controls in all locations within the AOI. There is an opportunity to perform more refined analyses later in the process, prior to the time when control targets are identified for a RIP.

A number of tools which are potentially useful for identifying preliminary AOI exist. We are in the process of consulting with the scientific community concerning applicability of these for helping to identify preliminary AOI. Candidate tools include, but are not necessarily limited to, the following:

use of existing air quality models such as SAQM, UAMV and REMSAD to perform	sensitivity analyses to help establish AOI;

use of post-processor algorithms applied to past modeling results--examples	include Environ's UAM-X "source attribution approach" and Georgia Institute of	Technology's "direct decoupled sensitivity method";

direct use of mesoscale meteorological modeling outputs to track potential contributions	without chemistry;

use of back trajectories;

use of monitored indicator species and lifetime data.

Preparation of RIP's and SIP/TIP Calls. Steps in performing modeling/analysis to support development of RIP's and SIP calls are elaborated upon in section 4.0. With some exceptions (identified shortly), we expect nested regional models, which are capable of considering ozone as well as fine PM and regional haze, to be used as the primary basis for RIP's and related SIP/TIP calls. We anticipate that MODELS3 will be used as the reference procedure. Other nested regional models with similar capabilities may be used if the model/analysis center makes a convincing case for doing so. Many of the steps to be followed in the modeling procedure are amenable to considering results from other, complementary data analyses to increase the overall credibility of the end product. Some of these complementary analyses, and their role in the development of RIP's and SIP's are identified in sections 3.2 and 4.0.

Exceptions to the expected general use of nested regional models are possible under some circumstances. At least three such circumstances come to mind: (1) a case where a PM10 NAAQS is not met, but the PM2.5 NAAQS are met; (2) a case where the short-term PM2.5 NAAQS is not met in wintertime only, and the ozone NAAQS is met; (3) a case where only the ozone NAAQS is not met, and this occurs in an isolated area (e.g, as in some of the western cities noted previously). It may not be necessary to consider a model capable of considering both ozone and fine particulates in any of these cases. Further, depending on the circumstances, it may not be necessary to engage in extensive regional modeling for such cases.

SIP/TIP Preparation. We anticipate that most of the modeling/analysis will be performed to help develop the RIP's and to help serve as a basis for the SIP/TIP calls. Identification of prospective measures in SIP's/TIP's to meet RIP targets will need to be done in just a little less than a year (mid 2001 to early 2002). Thus, it is likely that some of the previous modeling/analysis leading to SIP/TIP calls may include testing the effectiveness of various measures to meet RIP targets. During the SIP/TIP preparation step of the 5-step SIP/TIP development process, we expect modeling efforts to be limited to "confirmation runs", affirming that measures identified to meet RIP targets are likely to lead to attainment.

In discussions leading to our "phase 2 proposal", we think it may be worth considering whether to make confirmatory modeling optional in cases where a RIP is prepared. There are several reasons for this. First, there is concern that using new tools and concepts in these analyses will lead to delays in submittal of approvable SIP's/TIP's. Second, as discussed in section 4.0, in our proposal we intend to recommend that at least one mid-course review be required as part of an approvable SIP/TIP. If the initial confirmatory runs were to be made optional, we believe that, prior to the first mid-course review, the SIP/TIP would have to demonstrate steady (> proportional) progress in implementing control measures leading toward the target. Need for additional, specific (and perhaps more difficult) measures would be modeled as part of the first mid-course review. Third, we believe it will be possible to make a much stronger case for difficult, specific measures (particularly for PM) in the 2003-2005 timeframe, after monitoring data begin to become available in substantial quantities. Finally, we suspect that even if the confirmatory runs are made optional, States in most AOI will prefer to have them performed to help defend the basis for their SIP's to the public.

3.2 Modeling Tools

In this section, we identify a number of modeling and other analytical tools which we are considering for use in the 5 steps leading to SIP/TIP development. We expect the list will be refined prior to proposal. Next to each tool, we identify potential uses. In section 4.0, we discuss these uses in sequence, and cross reference the modeling tools identified in section 3.2.

MODELS3--This is a nested regional model under development by the US EPA, scheduled to undergo beta testing in 1997 and be available for use by States beginning in 1998. The initial operating version of the model will be able to consider ozone, fine PM and visibility attenuation. We see MODELS3 as the reference modeling approach for developing RIP's and SIP's.

SAQM--SARMAP Air Quality Model. This is a nested regional model used to support development of the ozone SIP to meet the current NAAQS in the San Joaquin Valley. Work is underway to develop a method for considering fine particulates and visibility attenuation in SAQM. This capability is expected by mid-1997. This model is seen as a potential alternative to MODELS3 to develop RIP's and SIP's, especially for Modeling/Analysis Centers having prior experience in its use. As discussed previously, SAQM may be used to perform sensitivity tests to help establish preliminary AOI's. The model may also be useful in weight of evidence analyses performed for attainment demonstrations with MODELS3.

UAMV--Urban Airshed Model, version V. This is a nested regional model for ozone, which has been used in the OTAG studies to help assess effects of hypothetical control strategies on regional transport of ozone and its precursors in the eastern U.S. Several States have used it to help develop SIP's to meet the current NAAQS for ozone. UAM-V is seen as a potential alternative to MODELS3 in locations where ozone NAAQS are not met. It is not applicable for PM. Sensitivity analyses performed with the model may also be useful in establishing preliminary AOI and for weight of evidence analyses in attainment demonstrations performed with MODELS3.

REMSAD--This is a nested regional model focusing primarily on primary and secondary regional fine PM concentrations. The model treats chemistry of ozone formation in an abbreviated fashion. Adequacy of this treatment is uncertain. Thus REMSAD is not recommended for development of ozone SIP's. The model is seen as being potentially useful in helping to establish preliminary AOI for fine particulate matter.

Other Nested Models--UAM-X, URM, CALGRID are examples. These are similar in concept to UAMV and SAQM (without treatment of PM). We anticipate potential uses for these approaches which are similar to those envisioned for SAQM and UAMV.

UAM-X Source Attribution Post Processor--This is an algorithm, used thus far in conjunction with the UAM-X nested regional ozone model. The algorithm describes the contribution of a subset of sources or emissions in a specific geographical area to predicted daily maximum (1-hr) ozone at a receptor site. Interface with other models and consideration of 8-hour averaging times may require further development, as may potential uses for PM-related problems. The method is seen as potentially useful in helping to identify preliminary AOI, helping to focus strategies simulated with resource-intensive nested regional models and in weight of evidence determinations used to support attainment demonstrations.

Direct Decoupled Sensitivity Method--This is an algorithm used thus far as a post-processor with Georgia Institute of Technology's Urban/Regional Model for ozone. The algorthm provides insights into the sensitivity of predicted ozone at a receptor site to changes in emissions from specified areas. Portability to other models and applicability to PM and averaging times longer than an hour may need some development. The approach is seen as potentially useful in helping to identify preliminary AOI, helping to focus strategeies simulated with nested regional models and in weight of evidence determinations used to support attainment demonstrations.

Individual Source Modulation Method--This is a method used by the US EPA to assess sensitivity of predicted sulfate concentrations to perturbations in precursor emissions. (Needs further explanation). The approach may be potentially useful for estimating preliminary AOI.

MM5 Mass Tracking Approach--This is a method developed at Penn State Univ. for utlizing wind field data developed with the MM5 meteorological model to estimate maximum potential mass contributions of emission estimates to chosen receptor sites. It may be useful for establishing preliminary AOI for ozone and PM. It may also be useful in helping to select episodes for further modeling and for helping to focus selection of control strategies to simulate with resource-intensive nested regional models..

Trajectory Models--This approach entails calculating back trajectories initiating at a receptor site at a specified time of interest. The method is subject to potential limitations due to overnight wind shear and limited ability to consider vertical mixing. However, it may be potentially useful as an upper limit in helping to identify preliminary AOI. Back trajectory analysis may also be potentially useful in helping to classify potential episodes for modeling.

Process Analysis/Mass Tracking--A method, developed at the University of North Carolina, which can be used as a post-processor for previously modeled results. The method helps explain the role of various physical/chemical phenomena leading to predicted ozone concentrations. Applicability to PM may need further development. Process analysis is seen as potentially useful in helping to evaluate model performance and for performing diagnostic analyses of model results. It may also be useful in helping to focus additional model simulations on promising strategies, and as an element in a weight of evidence analysis used to support attainment demonstrations.

Observational Models: receptor models--Receptor models use speciated air quality observations and statistical analysis to draw inferences about the relative importance of source categories of PM or VOC as contributors to monitored concentrations of these pollutants. This approach is seen as potentially useful for quality assuring emissions estimates and for prioritizing additional refinements to the inventory. It also may be useful in helping to prioritize strategies to be simulated with more resource-intensive models and in weight of evidence determinations used as part of an attainment demonstration. In some cases, such as in SIP's to meet PM10 NAAQS in a well mixed air basin or with ubiquitous sources, receptor models, used in concert with rollback procedures, may be useful for establishing control targets.

Observational Models: use of indicator species, ratios of species and chemical lifetime data- -These approaches use chemical species or ratios of species thought to be indicative of Nox- or VOC-limited conditions for ozone formation. Use in conjunction with chemical lifetimes may provide insight into the "age" of a measured mix of chemical species. This, in turn, may be useful to help assess the role of transport vs. local sources. These approaches may be potentially useful in episode selection, model performance evaluation, diagnostic analyses, strategy selection for simulation with resource-intensive models and in weight of evidence analyses. Applicability to PM is uncertain.

3.3 Integrated Analyses

As discussed in Conceptual Model for Ozone, Particulate Matter and Regional Haze, there is reason to believe that formation of ozone, secondary particulate matter and visibility attenuation may sometimes stem from a common chemistry or from similar meteorological conditions. Further, ozone and fine PM likely share a number of common sources of precursors. This is why we expect to recommend models like MODELS3 be used to develop RIP's and SIP's in areas which appear to have a substantial regional component to pollution or in areas in which both ozone and PM NAAQS may not be met with existing measures.

It is important however, not to read too much into our expected recommendation to perform "integrated" analysis. We believe it is not realistic to expect simultaneous development of an optimal strategy to reduce ozone, fine PM and regional haze. Rather, we expect an integrated strategy to consider these pollutants will be identified in a serial manner. That is, we believe that, in most cases, the model/analysis centers will likely first focus on an effective strategy to reduce ozone. This information will then be considered in developing a strategy to reduce fine PM, where neither ozone nor fine PM NAAQS are met. In some cases, the resulting PM strategy may cause some revisions to the ozone strategy (in a midcourse review, if necessary). As a final step, the effect of the resulting PM strategy on regional haze will be assessed. It may prove necessary to delay simulation of strategies to meet fine PM NAAQS due to delays in designations resulting from lack of monitoring data. Should this happen, it would still be possible to proceed with modeling to help identify reasonable regional emission reduction goals to improve visibility.

We believe the serial approach described in the preceding paragraph is adviseable for at least three reasons. First, the short term PM and ozone NAAQS have different forms. An annual fine PM NAAQS has also been proposed. This implies that it will be necessary to consider different episodes in assessing whether strategies are likely to be successful in meeting the various NAAQS. This is consistent with a "one at a time" feature characteristic of a serial approach. Second, the ozone program is more mature than the one for fine PM, in terms of modeling capabilities, quality of emissions data and availability of monitored data. We therefore anticipate that it will be logical for the ozone analyses to proceed more rapidly than those for PM. Since regional haze depends on having prior estimates of fine PM, it is also logical to assume that analyses of strategies to meet regional haze goals will be last in the sequence (assuming there is no major delay in the PM NAAQS modeling due to delays in designation). Third, a serial approach allows greater flexibility to choose different modeling approaches for ozone and PM, should this prove desirable.

4.0 Steps in Performing Modeling/Analysis

We anticipate that guidance for applying nested models and complementary analyses to support regulatory applications for ozone and PM and visibility improvement strategies will be organized similarly to past guidance documents applicable to use of grid models for secondary pollutants. We expect to borrow some concepts similar to those in the earlier documents. These documents include Guideline for Regulatory Application of the Urban Airshed Model (US EPA 1991), Guidance on Urban Airshed Model (UAM) Reporting Requirements for Attainment Demonstration (US EPA 1994) and Guidance on Use of Modeled Results to Demonstrate Attainment of the Ozone Standard (US EPA 1996). We envision modeling/analysis to support SIP's/TIP's will reflect an eight (8) step process:

1. development of a protocol;

2. episode selection;

3. preparation of emissions data and inputs compatible with use of the air quality model;

4. selection of model domain and horizontal/vertical resolution;

5. preparation of meteorological inputs to the air quality model;

6. performing diagnostic analyses and assessing model performance;

7. evaluating strategies for meeting air quality goals;

8. archiving model-generated data, documenting procedures followed, results and means	for accessing the data.

We intend to propose a requirement for at least one reassessment of the RIP and SIP/TIP strategies in one or more mid-course reviews. It is assumed that the 8 steps will be repeated in each of the reassessments. Each of the 8 steps is discussed briefly below. The discussion is intended to highlight potential differences from past practices, as well as identify potential roles for various modeling/analysis tools identified in Secton 3.0. We conclude Section 4.0 with a short discussion of mid-course reviews.

4.1 Developing a Protocol

Unlike past protocols which have focused on a single application, the new protocols will likely be more generic. They are expected to establish means and schedules for interacting with RAMP and AOI clients. This includes identifying which issues/procedures require previous client approval and which are to be left to the discretion of the modeling/analysis center. Contact points and communication between modeling centers should be provided for. Agreement on procedures for ensuring that air quality/meteorological data analysis is coordinated with the nested modeling analyses should also be included. A work plan for performing analyses addressing each center's area of prime responsibility should be developed for review by the pertinent RAMP(s). Nature of deliverables and schedule for delivery should be agreed upon with the pertinent RAMP(s). Primacy of requests from individual States vs. those from the AOI or RAMP should be discussed and agreed upon. The extent to which confirmatory runs for RIP targets (for use in SIP's) are to be made will have to be agreed to with the RAMP's, AOI and individual States.

4.2 Episode Selection

Although we believe simulating many days is desirable, we think it likely that computer resources, and data base management difficulties will require the modeling analyses to be selective about days which are modeled. We foresee at least 3 challenges that will have to be met in developing guidance for selecting episodes. First, the proposed ozone and PM NAAQS are more robust than the previous ozone NAAQS for which past episode selection guidance has been developed. The fact that the proposed short term NAAQS for ozone and PM specify averages over a 3-year period will need to be dealt with. Second, the ozone and PM NAAQS have different forms. This means that it may not be appropriate to choose the same episodes for the two pollutants. In addition, the proposed annual PM NAAQS will likely require judgments to be made about simulating a representative sample of days during the course of a year. Third, each center's area of prime responsibility is likely to have numerous areas of violation (AOV). It will likely not be feasible to select the optimum days for each of the AOV. Thus, a procedure for prioritizing the AOVs' needs will likely need to be developed.

In general, we anticipate our guidance for the short term NAAQS will probably suggest choosing a set of diverse (meteorologically) days having observed data near the design value for ozone or PM. In the case of the annual NAAQS, we will most likely urge consideration of a diverse (meteorologically, seasonally) set of days whose observations average out to a value near the design value. It is anticipated that location of emissions within the area of prime responsibility, orientation of AOV and seriousness of violations in the AOV will be factors in prioritizing focus of the modeling among many AOV's. Modeling/analysis tools which are expected to be potentially useful in choice of episodes include emission maps, trajectory analyses, MM5 mass tracking approach, observed geographical patterns of high ozone or PM data, and consideration of ratios of indicator species.

4.3 Preparation of Emissions Data

We intend to update national emission inventory estimates from 1990 to 1996. Emission estimates for VOC, Nox, CO, SO2, ammonia and PM10 will be made based on the projections applied to the current national emissions trends inventory (US EPA, 1995). Default speciation for VOC and PM emissions will be assumed in accordance with the VOC and PM Species Manuals (US EPA, ). PM2.5 emission estimates will be made based on what is known about size distribution of PM emissions from various source categories. We intend to provide this first cut at 1996 emission estimates for review by the States during summer 1997. The estimates, for the most part, will be based on "top-down" sorts of analyses. In the past, there has been opportunity for States to review our "top-down" estimates for VOC, Nox and CO. This led to subsequent refinements. Most sulfur dioxide emissions tend to come from a relatively small number of source categories, and these estimates have also been reviewed. Thus, we are more confident in VOC, Nox, CO and SO2 estimates than we are in the estimates for PM and ammonia. We intend to ask States to review our 1997 estimates of 1996 emissions and provide what feedback they can by July 1998. We will likely ask the States to focus on portions of the inventory in which we have the least confidence: usage factors for area source categories of primary fine and coarse particulates and for sources of ammonia.

We recognize that the period between summer 1997 and summer 1998 is not an adequate amount of time for the States to prepare comprehensive, quality assured inventories for use in developing RIP's and SIP's. This preliminary inventory would, however, need to be used to help identify preliminary AOI. As part of our July 1998 "phase 2 implementation" proposal, we intend to propose a timeframe for further quality assuring/improving emission estimates for use in developing RIP's and SIP's/TIP's. There are several tools and ambient data bases which may be helpful in quality assuring emission estimates. Chemical mass balance receptor models and multivariate analyses addressing ratios of species and covariation of species are likely to be useful for this purpose when used with measured, speciated data such as those in the PAMS or IMPROVE data sets or other data sets for PM or VOC.

Emission estimates obtained from the inventory need greater spatial and temporal refinement to be used as input to nested regional air quality models. Emission preprocessing programs are used for this purpose. We believe it is likely that we will recommend a preprocessor similar to the EMS-95-type of program used to support the OTAG analyses, and utilize BEIS2 as a means for estimating emissions of natural VOC and Nox.

4.4 Selecting Model Domains and Horizontal/Vertical Resolution

In the eastern U.S., we anticipate that the modeling domain simulated by the modeling/analysis centers will be considerably larger than the area of prime responsibility. The size may even approach that of the "SUPROXA" domain used in the OTAG studies. We expect there will be closer correspondence between the modeling domain and the area of prime responsibility in applications by the Western Regional, Western Gulf/Southern Plains, Northern and Southern California modeling/analysis centers.

As noted previously, we anticipate that it will not be necessary for a modeling/analysis center to consider horizontal grid squares more finely resolved than 36 km outside of its area of prime responsibility. Depending on results of diagnostic analyses (see also Section 4.6) it is possible that horizontal resolution as coarse as 36 km may be used for ozone analyses within large parts of the area of prime responsibility as well. It is also possible that resolution as coarse as 108 km may be acceptable outside of the area of prime responsibility. Near AOV which are the major focus of modeling analysis, we anticipate that horizontal resolution at least as fine as 12 km will be needed for ozone. For areas in complex terrain or subject to land/sea breezes, 4 km resolution may be needed for ozone. We hope to be able to establish some better guidance on the geographical extent to which fine resolution is necessary for ozone analyses as a result of MODELS3 sensitivity tests scheduled during 1997 using data from the 1995 Nashville field study, as well as other tests we hope to be able to do prior to summer 1998.

For PM analyses, we believe at present that it will not be necessary to consider horizontal resolution finer than 36 km. This less rigorous criterion results from the longer averaging times (i.e., 24 hours) inherent in the PM measurements and NAAQS, expected greater linearities between emissions and ambient PM, and data bases which are likely to be less refined (at least in the 1997-2003 timeframe) than those for ozone.

We expect that the degree of desirable vertical resolution for air quality models will be limited by computer hardware and data base management considerations. For analyses needed in the 1997- 2003 timeframe, we anticipate that there will continue to be a dichotomy between the degree of vertical resolution scientists believe is necessary to characterize vertical mixing and cloud formation (and resulting estimates of moisture and actinic flux) and the degree of vertical resolution feasible in air quality models which consider atmospheric chemistry and need to be applied over large domains for several days or more. In our guidance, we will likely recommend a maximum number of vertical layers based on practical limitations and on sensitivity tests.

The following tools/approaches may be useful in addressing domain and resolution issues:

sensitivity tests with models like SAQM, UAMV, UAM-X, URM, CALGRID,	REMSAD;

process analysis/mass tracking;

MM5 mass tracking approach;

trajectory modeling (domain size issues only);

emission maps (domain definition only).

4.5 Preparation of Meteorological Inputs

We expect to recommend that meteorological input to regional nested air quality models be generated through use of dynamic meteorological models. We anticipate that the MM5 model, developed at Penn State University, will be the reference approach. As noted in Section 4.4, we anticipate that there will be a gap between the vertical resolution needed to characterize distribution of moisture and actinic flux and limits imposed by resources needed to run air quality and meteorological models over large domains for a desirable number of days at needed horizontal resolutions. Subject to further discussion and advice, we will most likely permit use of vertical resolution which is consistent with 5-7 layers within the lowest 2000 meters of the atmosphere. This would permit a 1:1 correspondence between vertical layers in the meteorological and air quality models. If such a procedure is followed, we believe it will be necessary to supplement wind and temperature estimates obtained with the meteorological model with estimates obtained for actinic flux and moisture from measurements or by other means. We also anticipate use of methods like Newtonian nudging to take advantage of observed (urban or larger scale) wind and temperature measurements.

We expect that, in addition to observations used for Newtonian nudging or as independent means for characterizing cloud cover and moisture, observational models in concert with orientation of known sources may be useful for assessing how well winds are estimated. Review of temporal patterns of hourly air quality data like ozone, CO, Nox, and SO2 may also help assess how well the meteorological model is characterizing wind fields.

4.6 Performing Diagnostic Analyses and Assessing Model Performance

Unlike in previous guidance, we are considering combining these two steps. This reflects previous feedback that ability of a model to predict ozone may not be a sufficient measure of model performance. In addition to noting ability to replicate ozone observations, we will likely ask States or the modeling/analysis centers to document results of other tests, such as diagnostic tests, which help one to conclude that the model is furnishing plausible results. We believe a similar procedure is appropriate for PM, since compensating errors are certainly possible in producing agreement between measurements and observations over a 24-hour period. To the extent practicable (i.e., if speciated data exist and if precursor monitoring networks are sufficiently extensive to assess spatial representativeness of measurements), we will likely urge that precursor observations be considered in evaluating model performance.

Tools which may be potentially useful for performing diagnostic analyses include the following:

sensitivity tests with the models listed in Section 3.2;

comparisons with results from observational models;

process analysis/mass tracking;

use of post-processor algorithms like the UAM-X source attribution technique and the	direct decoupled sensitivity method.

4.7 Evaluating Strategies for Meeting Air Quality Goals

This step includes selecting and prioritizing strategies to consider, and comparing results with air quality goals to judge whether the selected strategy is appropriate. We expect the following tools may prove useful in selecting strategies for further study: sensitivity tests with less resource intensive models, such as REMSAD, use of post-processor algorithms (e.g., direct decoupled sensitivity method, UAM-X source attribution method, individual source modulation method) applied to base case model runs, MM5 mass tracking approach and observational models.

Once a strategy is simulated, predictions are compared with the air quality goal to help assess adequacy of the strategy for meeting the goal. We will refer to this comparison as the modeled attainment test. The test will need to consider a number of factors implied by the definition of the air quality goal itself (e.g, site-specific requirement for ozone vs. spatially averaged requirement for PM, allowance of occasional air quality concentrations higher than the level specified in the short term NAAQS, definition of a monitored attainment criterion specifiying a 3-year average, representativeness of the episodes chosen for modeling, etc.). In addition, we acknowledge limitations in model predictions resulting from data base limitations, imperfect approximations of chemical/physical processes leading to high PM, ozone and visibility attenuation, and the necessity of making estimates for some future year in the attainment test.

Because of the uncertainties described in the preceding paragraph, we anticipate that we will propose that the modeled attainment test be made one of three required elements in an attainment demonstration. The other two elements are (1) a requirement for a weight of evidence determination, and (2) a requirement for periodic (at ~ 4-5 year intervals) re-analyses (i.e., "mid- course reviews"). For ozone, we will likely identify a number of the analyses identified in Guidance on Use of Modeled Results to Demonstrate Attainment of the Ozone NAAQS (EPA, 1996) as suitable for inclusion in a weight of evidence determination. We also intend to review a report by Demerjian et al., (1995) which addresses possible approaches for complementing or corroborating modeled estimates. Unfortunately, some of the most useful tools in a weight of evidence analysis depend on there being observed data over a long period of record. Thus, the weight of evidence analysis for PM may initially have to be more limited than that for ozone. Lack of an historical data base for fine PM is another reason (in addition to uncertainty in projecting the future) why we believe provisions for periodic reanalyses are needed as a part of the attainment demonstration.

The following tools, mentioned in Section 3.2, are expected to be potentially useful for supplementing use of a nested regional model in the attainment demonstration: reaching similar conclusions with other air quality models, use of observational models to corroborate that the simulated strategy is likely to address appropriate sources, use of post-processor source attribution algrorithms for a similar purpose, and use of process analysis to identify results which are likely to be erroneous.

4.8 Reporting/Archiving Requirements

We expect to propose similar requirements to those described in Guidance on Urban Airshed Model (UAM) Reporting Requirements for Attainment Demonstration (EPA, 1994). We also expect to review experience gained in archiving data for the OTAG studies in considering proposed archiving requirements. In addition to the RAMP or AOI clients, the modeling/analysis center will be required to provide reports/documentation to the U.S. EPA Regional Offices whose jurisdictions comprise any part of the modeling/analysis center's area of prime responsibility.

4.9 Mid-Course Reviews

We are considering proposing that periodic reanalyses be required as an integral part of an approvable attainment demonstration. We are considering a requirement for at least one such review, to be performed about 4-5 years after the initial modeling/analysis (i.e., in the 2004/2005 timeframe). We believe this is necessary for several reasons: (1) difficulty in making future projections, (2) desire to incorporate new scientific advances into the modeling/analysis tools prior to the statutory attainment date, and (3) availability of a limited data base to corroborate PM predictions in the initial analysis. We are interested in exploring what might reasonably be included in phase 2 of the proposed implementation policy to foster development of better data bases and availability of expertise to perform the reanalyses in 2004/5. In areas where air quality observations after 2005 suggest meeting the NAAQS or visibility goals may be difficult, we will likely propose to require a second reanalysis in the 2009/10 timeframe, to troubleshoot the potential problems, shortly before the NAAQS are required to be met.

5.0 Potential Issues

In this section, we go through the discussion in the preceding 3 sections to highlight areas of potential concern and issues. The purpose of this is to try to focus comments and suggestions on topics which we feel deserve greater attention. Topics are categorized as either "managerial/administrative" or "technical". For ease in relating the topics to the earlier discussion, the section where it is discussed is identified in parentheses. The lists are not intended to be exhaustive. Discussion of other topics/issues is also welcome.

5.1 Managerial/Administrative Topics

1. How would modeling/analysis centers be supported financially? (Section 2.1)

2. Would the centers be independently staffed (as in LADCO) or be drawn from an individual State's staff (as in NYDEC), or would a combination of the two be workable? (Section 2.1)

3. Is it a good idea to assign different leads for modeling and data analysis? How can we best coordinate these if there are different leads? (Section 2.1)

4. Should the centers' primary client continue to be the RAMP, even after preliminary AOI are identified? Is it a good idea to switch primary clients? (Section 2.1)

5. To what extent should modeling/analysis requirements differ for modeling/analysis center analyses vs. for analyses performed by individual States? (Section 2.3)

6. How can modeling/analysis centers be made aware of pertinent work/data bases in locations in other areas of prime responsibility (e.g., how do we ensure that the Western Regional Modeling/Analysis Center is aware of pertinent strategies and data bases in California and New Mexico)? (Section 2.3)

7. What should be a constructive role for the private sector so that their resources and expertise can be utilized in helping to identify preliminary AOI and to develop effective RIP's? (Section 3.1)

8. Should corroborative analyses performed after identification of RIP targets be made optional or mandatory? (Section 3.1)

9. Is a requirement for steady progress between initial and mid-course reviews a reasonable approach? How could it be assessed? (Section 3.1)

10. Does a serial approach meet the objectives of integrated analysis? (Section 3.3)

11. Does the mid-course review necessarily have to be as extensive as the initial analysis? What if the NAAQS are being met? (Section 3.3)

12. How "generic" can a protocol be? Are there standard requirements which should be imposed by the EPA, or is this entirely a prerogative of the RAMP's? (Section 4.1)

13. What degree of flexibility should be given to use different models for developing RIP targets? What justification for doing so should be required? (Section 4.1)

14. Who has to agree to any prioritization for dealing with the AOV? What are related consequences which the EPA should be sensitive to in reviewing subsequent SIP's/TIP's? (Section 4.2)

15. What are reasonable times for completing a quality assured 1996 inventory, which are compatible with the schedule for developing a RIP? (Section 4.3)

16. What results/data should be archived? (Section 4.8)

17. How would (should) reporting/archiving requirements differ for analyses performed by individual States vs. analyses performed by a modeling/analysis center? (Section 4.8)

18. What is reasonable to require States to include in an approvable SIP to ensure that a timely and defensible mid-course review will occur? (Section 4.9)

5.2 Scientific/Technical Topics

1. What conditions justify use of simpler modeling/analysis approaches? (Section 3.1)

2. Is demonstration of steady progress between initial and a mid-course review feasible using air quality indicators? How could this be done? (Section 3.1)

3. Are there other modeling/analysis tools which we should mention? Is there a role for UAMIV? Are any of the tools we have mentioned identified for inappropriate uses? (Section 3.2)

4. Is anything more refined than the outlined serial approach for integrated analysis likely to be feasible within the timeframe available for developing RIP's? (Section 3.3)

5. Do you agree with the proposed typical analytical sequence: ozone, PM, RH? Are there better alternatives? (Section 3.3)

6. Is it acceptable to use fidderent models for ozone and PM (e.g, UAMV for ozone, REMSAD for PM)? (Section 3.3)

7. Do you have additional suggestions for episode selection which will deal better with the more robust forms of the proposed NAAQS for ozone and PM? (Section 4.2)

8. Do you have suggestions for how to prioritize needs of different AOV in selecting episodes? Do you agree that this is necessary? If not, why not? (Section 4.2)

9. How can States most productively improve emission estimates from area sources of primary PM and from sources of ammonia? (Section 4.3)

10. What are reasonable times for improving the inventory? Are the needs for PM and its precursors likely to be as demanding as those for ozone's precursors? How might they differ? (Section 4.3)

11. Do emission estimates for PM and its precursors need the degree of spatial/temporal resolution required for ozone's precursors (i.e., can preprocessing these emissions be made easier)? (Section 4.3)

12. Can you offer any insights on geographical coverage needed for fine horizontal grids (ozone applications)? Do you agree with what we said about horizontal resolution adequate for PM applications? (Section 4.4)

13. Do you have any suggestions for sensitivity tests or data bases which we can use to help develop guidance on needed horizontal resolution over the next year? (Section 4.4)

14. Are there better ways for reconciling differences between preferred vertical resolution in meteorlogical models and practical limitations in air quality models than the ones we discussed? (Section 4.4)

15. Should we allow use of other meteorological models? If so, what should be the criteria for doing so? (Section 4.5)

16. What guidance is needed to limit nudging of modeled solutions? How can such guidance be developed within a year? (Section 4.5)

17. What methods might be used to identify suitable moisture/actinic flux assumptions? (Section 4.5)

18. What are appropriate measures for evaluating air quality model performance? (Section 4.6)

19. What are suitable performance criteria for the air quality model? (Section 4.6)

20. Is the outlined approach for an attainment demonstration consistent with the capabilities of the various tools identified for the process? What, if anything, would you change? (Section 4.7)

21. Do you have suggestions for additional components to include in a weight of evidence determination? Do you have any suggestions concerning criteria for weighting certain components of the weight of evidence determination more heavily than others? (Section 4.7)

22. What information do you think it is important for us to ask for so that a more sound analysis can be performed in the first mid-course review (~2004-2005)? (Section 4.9)

6.0 Summary

This paper outlines our initial thoughts on the air quality management process to implement new NAAQS and goals for ozone, PM and RH and on use of modeling/analysis tools to implement this process. The paper is intended to serve as a catalyst for comments/suggestions which will help us to prepare portions of a "phase 2 implementation policy" for proposal in the Federal Register in July 1998.

In Section 2.0, we recommend establishing 7 modeling/analysis centers. Each center would have an assigned area of prime responsibility which would be the focus of its modeling/analysis efforts. The 7 areas of prime responsibility cover the contiguous 48 States, and would be addressed by Northeast, Midwest, Southeast, Western Gulf/Southern Plains, Northern California, Southern California and Western Regional Modeling/Analysis Centers. The recommendations have been made considering air quality data reported in the AIRS data base and the IMPROVE monitoring network, past modeling analyses in which transport has been identified as a major component, distribution of emissions, presence of topographical barriers, presence of existing institutions which have demonstrated capability to address regional scale problems, and a good match with jurisdictions of U.S. EPA Regional Offices. It is anticipated that the regional modeling/analysis centers would assist RAMP's and AOI's by performing air quality and modeling analyses needed to develop defensible SIP's demonstrating attainment of air quality goals.

In Section 3.0, we discuss the role of the modeling/analysis centers in helping to implement a 5- step process for developing SIP's/TIP's which has been identified in issue papers prepared for the FACA subcommittee. In this discussion, we mention pertinent timing constraints, and identify modeling/analysis tools which are potentially useful for addressing each of the five steps in the process. We note that tools needed to identify initial areas of influence (step 3 in the process) can be less rigorous than tools used to develop regionally integrated plans and SIP's/TIP's (steps 4 and 5 in the process). We indicate that our present thinking is that the MODELS3 nested regional model will be the centerpiece for establishing emission control targets in regionally integrated plans. These control targets are then expected to serve as goals for specific control measures identified in individual SIP's or TIP's. We also recognize the possibility of using other nested regional models in place of MODELS3. Further, we recognize the need to corroborate the resulting control estimates with other types of analyses, and identify methods which might prove useful for doing so. We conclude Section 3.0 with a discussion of integrated analysis for ozone, PM and regional haze. We suggest that a serial approach might be the most suitable means for considering goals for each of these pollutants. We suggest that, ordinarily, the most appropriate sequence for considering the three pollutants is to consider ozone first, followed by PM and then regional haze.

In Section 4.0, we describe an 8-step procedure for using modeling and corroborative analyses to identify control strategies for meeting air quality goals. This is followed by a discussion of mid- course reviews, envisioned for the 2004-2005 timeframe. The 8-steps are developing a protocol, selecting episodes to model, preparing emissions data and inputs, selecting the model domain and its spatial resolution, preparing meteorological inputs, performing diagnostic studies and evaluating model performance, evaluating strategies for demonstrating attainment of goals, and reporting/archiving results. We identify analyses which could be helpful in completing several of the key steps. Our recommendation that an attainment demonstration (step 7) should consist of three components should be of particular note. These three components are: a modeled attainment test, a weight of evidence determination (of which the attainment test is one part) and inclusion of enforceable measures to facilitate a mid-course review as part of an approvable SIP.

The discussion in Sections 2.0 - 4.0 raise a number of concerns and issues which warrant further discussion and feedback. In Section 5.0, we divide some of these issues into two categories: managerial/adminstrative and scientfic/technical. Our list of topics is not necessarily exhaustive. However, it is provided to help stimulate discussion on topics for which we believe feedback is highly desirable.

7.0 References Cited

Cox, W. (1997). Personal Communication

Demerjian, K, P.Roth, C.Blanchard, (1995). A New Approach for Demonstrating Attainment of the Ambient Ozone Standard, Envair Report prepared for US EPA, ORD, Basil Dimitriades (Project Manager).

Eder, B., J.Davis, P.Bloomfield, (1993). "A Characterization of Spatiotemporal Variability of Non-Urban Ozone Concentrations Over the Eastern United States", Atmospheric Environment 27A, p.2645

Eldred, R., (1997). "Review of IMPROVE Data in Relation to Proposed PM2.5 and PM10 Standards", Univ. of California-Davis Crocker Nuclear Laboratory.

FACA, Science/Technology Work Group (1997). Conceptual Model for Ozone, Particulate Matter and Regional Haze, prepared by Science Applications International Corporation, under EPA Contract No. 68-D3-0030.

Grand Canyon Visibility Transport Commission (1996). Recommendations for Improving Western Vistas.

US EPA (1991). Guideline for Regulatory Application of the Urban Airshed Model, EPA-450/4- 91-013.

US EPA (1994). Guidance on Urban Airshed Model (UAM) Reporting "Requirements for Attainment Demonstrations, EPA-454/R-93-056.

US EPA (1995). National Air Quality and Emissions Trends Report, 1994, EPA-454/R-95-014.

US EPA ( ). Voc species manual

US EPA ( ). PM species manual

US EPA (1996). Guideline on Use of Modeled Results to Demonstrate Attainment of the Ozone Standard, EPA-454/B-95-007.