4.0 SCIENTIFIC SUPPORT FOR THE DEVELOPMENT OF IMPLEMENTATION STRATEGIES

Following are discussions of two key scientific documents developed by the STSWG, which offer a preliminary framework for understanding the complex scientific and technical issues associated with the revision of the ozone and PM NAAQS and the regional haze rule. The documents attempt to establish the current understanding of the present environmental condition, describe how that condition has evolved, identify tools to address the current state, and address regional transport of pollutants. The first document, described in Section 4.1, is a preliminary commentary developed by the STSWG as a result of inquiries from the BPAPWG and NRSWG on the technical basis for underlying integration of the regulatory programs for ozone, PM, and regional haze. The second document, described in Section 4.2, is a summary of the conceptual model being developed by the STSWG. When completed, the conceptual model will be comprehensive and will replace the preliminary technical document.

Section 4.3 presents the STSWG position on the two issue papers "The Regional Air Management Partnerships and Areas of Influence: A New Approach to Air Quality Control Regions" and "Framework for Areas of Influence/Areas of Violation (AOI/AOV): Responsibility for Reaching Attainment." STSWG presents nine concerns it has about aspects of these two issue papers.

4.1 Technical Discussion on the Integration of Ozone, Fine Particles and Regional Haze Air Quality Management

BPAPWG and NRSWG have asked several questions regarding the technical basis and issues underlying the integration of regulatory programs for ozone, FP, and regional haze, and the specification of geographic scales required for air quality management. The STSWG is responding to these and other inquiries by developing a conceptual model framing our current scientific understanding of ozone, FP, and haze, the associated gaps and uncertainties, and responses to questions posed by work groups. This model provides preliminary commentary on the subjects of integration and geographic scales, in advance of more comprehensive discussion on these topics being developed in the STSWG conceptual model.

Regarding the rationality of integration, the initial response of the STSWG is a qualified "yes," given the regionality, spatial patterns of air quality indices, precursors, sources, atmospheric chemistry and meteorological processes which affect more than one pollutant, and control options. However, while reading this discussion, it is important to recognize and distinguish those attributes where there is little linkage. Moreover, many examples and inferences presented here tend to reflect what is known about eastern U.S. air quality issues (e.g., ozone), with possibly little relation to western U. S. phenomena. At the risk of generalizing (and simplifying) air quality descriptions for illustrative purposes, recognition that a generalized approach cannot operate effectively everywhere must be retained. The discussion focuses on the relationships between ozone and FP, given the close linkage between FP levels and regional haze.

Some sections of this discussion are fairly technical and may only be understood by the more scientifically-inclined reader. However, a scientific background is not necessary to embrace this discussion's primary points:

Understanding the emission sources and atmospheric processes which are responsible for elevated air pollutant levels requires an examination of urban and regional geographical scales.

Ozone and FPs may exhibit similar spatial patterns, although the frequency (and importance) of co-occurring patterns is not well understood.

Many of the emission precursors (and sources of precursors) to ozone, FP, and regional haze are the same.

Many of the atmospheric processes (chemistry and meteorology) affecting ozone, FP, and regional haze are the same.

Several critically important information gaps exist which create very difficult challenges for air quality management of these pollutants.

Interacting Spatial Scales of Emissions, Atmospheric Processes, and Air Quality Indices

This chapter also includes the STSWG position on the two issue papers "The Regional Air Management Partnership (RAMP) and the Area of Influence (AOI) Process" and "A Framework for Areas of Influence/Areas of Violation (AOI/AOV): Responsibility for Reaching Attainment." STSWG presents nine concerns it has about aspects of these two issue papers.

As explained in greater detail below, a variety of emissions are precursors to elevated levels of ozone, FP, and regional haze. Historically, attempts at air quality management of these problems focused on local sources in the context of an anonymous background term quantifying imported air quality. The evolution in our understanding of the spatial and temporal scales of the effects on ozone, FP, and regional haze of the emissions from all sources has, however, spawned the recognition of the need for a larger geographical perspective. This larger geographical perspective, which considers individual sources over regional as well as local scales, is needed to support quantitative analysis of the relative contribution of the various source types and of their emission types (species) that contribute to "nonattainment" levels. The need for an altered perspective has been recognized by the establishment of Ozone Transport Commission (OTC), OTAG, and GCVTC.

Air quality management on the Metropolitan Statistical Area (MSA) or county Metropolitan Statistical Area (CMSA) has worked well historically to control the local source effect on nonattainment problems. This is evidenced by the significant decrease in the number of ozone nonattainment areas over the past decade. As these controls have reduced emissions and as modeling tools have progressed, the role of the effect of sources beyond the MSA or CMSA and the varying spatial scales of air quality indices and atmospheric processes continue to be investigated and supported by a strong body of scientific evidence:

1991 National Academy of Sciences (NAS) Report, Rethinking Ozone in Urban and Regional Scales (NRC, 1991)

1993 NAS Report, Protecting Visibility in National Parks and Wilderness Areas (NRC, 1993)

National Acid Precipitation Assessment Program (Trijonis et al., 1990)

Southern Oxidants Study (Chameides and Cowling 1995).

These studies indicate that, while sources still have their largest influence in the near field, the zones of potential influence of source regions (e.g., an urban city) can, under certain conditions, extend out hundreds of miles for ozone, FP, and regional haze. Moreover, these scales appear to be similar for ozone and FP. In other words, sources once thought to be remote with respect to nonattainment levels of ozone, FP, and regional haze are seen as potential contributors to those levels. The analyses suggest that chemical and meteorological processes which influence pollutant generation, air mass movement, and pollutant removal (e.g., clouds and precipitation) are key factors in delimiting regional zones of influence. When the various nonattainment areas of the Eastern United States are surrounded by conservative estimates of the zones of influence of these other sources, a modeling domain that may span the greater part of the Eastern United States results. Accordingly, efficient air quality management requires addressing these additional sources, atmospheric processes, and related impacts as scales of interactions over multiple spatial and temporal frames.

In air quality management practice, the term "transport" has been used in a very broad context beyond the strict meteorological definition of the term. This broad context includes the (1) overall regionalization of both the scale of pollutant distributions and zone of influence of sources; (2) interaction (or effect of one area on another) among local, urban, and regional source scales; and (3) meso- and large-scale meteorological phenomena such as recirculation due to stagnant high pressure systems and land-sea interactions, "transport," which refers to large scale movement of air masses with fairly uniform motion, and other events perhaps as simple as widespread elevated temperatures. The prevalence and importance of biogenic VOC emissions (e.g., emissions from trees) in the Eastern United States is "region wide," as are many other area source emissions such as motor vehicles. All of these regional attributes are enhanced by the relatively flat and consistent terrain in the East and Midwest, contrasting the greater topographic and meteorological effects in the Western United States.

Several physical and chemical events act together in determining pollutant concentrations over multiple space and time scales. Moving air masses carry all chemical species including precursors1, fast-reacting intermediates2, and chemical sinks3, as well as the specific pollutant species of interest (e.g., FP and ozone). Removal of pollutants occurs continuously through deposition. Also, the impact of these pollutants is not simply additive. Ozone (and precursors) transported from one location can affect ozone levels downwind by indirectly accelerating atmospheric chemistry reactions through the production of chemical intermediates (e.g., hydroxyl radicals). Clouds play several roles in modifying concentrations by: (1) dissolving soluble gases (e.g., nitric acid, sulfur dioxide [SO2], hydrogen peroxide) and generating aerosols through aqueous phase reactions, (2) circulating and venting pollutants to high altitudes where strong winds promote large horizontal transport, and (3) removing pollutants through precipitation. Cloud related dissolution and transport also contributes to pollutant removal, depending on one's reference frame. Vertical air mass movements, or phenomena as basic as the daily mixed layer growth, affect air concentrations on various scales. Superimposed on these processes are a variety of emission sources with their own spatial, temporal, and component (speciation) scales. Depending on location, pollutant, and season, one particular spatial scale (e.g., urban) may or may not exert a dominating influence on air quality relative to another scale (e.g., regional). Even in cases where local and urban sources are responsible for most of the local air quality, an assessment of the contribution of distant sources to local air quality is required to reach such a conclusion. Thus, to avoid the exclusion of potentially important considerations in air quality analysis, "regionality"or "interacting scales" are more descriptive terms than "transport" that encompass the broader meaning and effects of several complex interacting phenomena operating over extensive and multiple time and space scales.

The Eastern United States differs markedly from the West, so any extension to the West based on eastern analyses or vice-versa is not appropriate (important differences exist between northern and southern regions as well). The monitoring data and modeling analyses of the GCVTC process highlight the challenge of identifying and quantifying specific sources, some at great distances, in order to estimate their effects in western national parks and wilderness areas. The variations in topography, meteorology, and source distribution across regions require that area- and case-specific differences be accounted for in any air management approach. The effects of emission reduction strategies should be viewed through multiple scales, considering regional and urban scale consequences (i.e., health and welfare protection).

A few points summarizing interacting scales and regionality should be considered in air management practices:

A.	Analyses of observations in the Eastern United States reveal the existence of very broad
multi-State regions (interacting scales approaching linear extents of 2,200 miles or more) of elevated pollutant levels and zones of source influence (Rao, 1996).

B.	Air quality modeling for the East suggests that similar regions of influence exist for
ozone and FP (Dennis, 1996), although only sparse monitoring data exist to support these similarities.

C.	Modeling analyses for the Grand Canyon National Park and other Class 1 areas show
that FP and precursors causing visibility impairment episodes are derived from both nearby (less than 120 miles) and more distant (up to 2,200 miles) regions of influence (NRC, 1993; GCVTC, 1996).

D.	Area- and case-specific analyses are required to delineate reasonable geographic areas
for air quality planning purposes because of the wide regional variations in meteorology, topography, and source distribution.

E.	The use of terms such as "transport" or "background" inadequately describes the
complex set of emissions, chemistry, and meteorological processes and interacting scales which contribute to the regionalization of air pollution.

F.	Because of broad spatial extents and gradations of interacting scales ranging from
regional down to sub-grid cell scales, an air quality assessment focusing on a particular scale (e.g., urban) must consider effects due to interactions across various space and time scales. The concept of a single MSA/CMSA nonattainment area is inconsistent with the spatial and temporal scales for ozone, FP, and haze problems.

Technical Basis and Considerations for Integrating Ozone, Fine Particles and Regional Haze Implementation Programs

The technical and scientific rationale underlying the integration of ozone, FP, and regional haze air quality management practices is based on a mix of empirical observations, atmospheric processes, and practical administrative concerns. While this discussion focuses on common attributes across pollutant groups, it is important to recognize and distinguish those attributes where there is little linkage. Many examples and inferences presented here tend to reflect what is known about Eastern United States air quality issues (e.g., ozone), with possibly little relation to Western United States phenomena. At the risk of generalizing air quality descriptions for illustrative purposes, recognition that a simplified approach cannot operate effectively everywhere must be retained. The discussion focuses on the relationships between ozone and FP4, with the implicit assumption that FP levels and chemical composition directly relate to regional visibility impairment, given the strong relationship between the constituents of FP, and the manmade portion of visibility impairment. Regional haze is a widespread impairment of visibility in every direction, mostly attributed to light scattering from FP.

Empirical Evidence for Integration

Ozone and PM-10 concentrations in the Eastern United States can exhibit similar spatial patterns during summertime episodes (NESCAUM, 1995). Analysis of particulate data consistently indicates that FP constitutes the majority mass fraction of PM-10 in the summertime East (EPA, 1996)4 . In combination, these observations qualitatively imply co-occurrence of elevated ozone and FP. However, quantification of the similarity and frequency (very common or quite unusual) of such events is severely restricted by a lack of an FP database in the East. While more data exists in certain western locations, the episodic relationships between ozone and PM appears to be more complex than in the East. For example, a major component of the FP problem in Los Angeles (as well as the San Joaquin Valley, Salt Lake City, and Denver) is wintertime formation of ammonium nitrate, which is not stable at the high temperatures associated with elevated ozone. High levels of FP in western nonattainment areas can impair visibility when high ozone concentrations are not observed. Nevertheless, smog events in Los Angeles almost always are accompanied by impaired visibility, and visibility is directly associated with FP levels. Although some limited empirical evidence is highly suggestive of area specific co-occurring events, other considerations (as described below) provide a stronger rationale for the appropriate level of integration across ozone, FP, and regional haze control programs.

Emissions and Atmospheric Process Linkages Across Ozone, Fine Particles, and Regional Haze

Several connections exist among the three pollutant categories. The linkages are based on the existence of common emission precursors, source categories, and atmospheric chemistry and meteorological processes that affect more than one pollutant. For example, emissions of NOx potentially can lead to both ozone and FP formation. A combustion source often emits both sulfur dioxide (an FP precursor) and NOx (an ozone precursor). The sequence of atmospheric chemistry reactions underlying ozone formation is in part responsible for FP formation. Similar meteorological processes affect the movement, mixing, and removal of ozone, FP, and precursors. Some of these connections are complicated and explained more completely in forthcoming FACA science documents. The following are very brief, more technical, descriptions of the connections across pollutant categories provided for those interested in more detail.

1.	Common "Direct" Precursor Emissions. Emissions of NOx, VOC, and carbon monoxide (CO) are considered precursors for ozone formation. NOx, VOC, and sulfur (SOx, mostly as SO2) emissions also can lead to FP formation through "secondary" atmospheric chemistry reactions. Both ozone and a substantial fraction of FP, which can vary greatly with season and location, are the result of secondary formation processes. The major components of secondary FP also are highly variant. They include sulfates, carbon (elemental and organic), and nitrates. The fraction of FP due to secondary processes is highly variant in space and time. During certain conditions (e.g., available ammonia, negligible sulfate, low temperatures), NOx emissions can lead to FP ammonium nitrate formation. Several directly emitted organic compounds contribute to FP organic aerosols. These organic compounds may contribute as "primary" organic aerosols, that is, they almost immediately condense to the aerosol phase during the emissions process or shortly downstream. However, certain VOC 5, (e.g., toluene) which exist as gases under most conditions, can undergo atmospheric reactions and transform into condensable "secondary" organic aerosols. Thus, a VOC like toluene can contribute to either ozone or FP formation as a precursor emission.

2.	Common Source Categories. Based on the multiple roles of precursors, a particular source (natural or anthropogenic) emitting one precursor (e.g., NOx or VOC) can affect ozone and FP, and a single source emitting multiple precursors (e.g., combustion process releasing NOx, VOC, CO, and SOx) can affect one pollutant category. In this case, integration is not dependent on atmospheric chemistry linkages. This commonality among sources should lead to a more consistent approach in estimating emissions of multiple precursors within a specific source category. For instance, a consistent approach needs to be applied for estimating and projecting both NOx and SOx emissions from a combustion source.

3.	Interaction of Atmospheric Chemistry Reaction Cycles and "Indirect" Precursors. Much of the general atmospheric chemistry involved in ozone formation can affect FP formation, as alluded to above, in certain instances. For example, ozone is the major initiator of hydroxyl radicals, a chemical intermediate that converts SO2 and NO2 to more oxidized sulfate 6 (e.g., sulfuric acid) and nitrate (nitric acid) forms. Both sulfates and nitrates can contribute to FP formation. Clearly, a linkage between ozone and FP exists through the role of ozone in generating hydroxyl radicals. Note that this linkage between ozone and FP is at the process level and does not require coexisting "high" ozone and FP levels. Many other important linkages involving oxidizing chemical species (radicals and peroxides) exist within the NOx, VOC, SOx, ozone chemistry system. A correct characterization of the basic ozone chemistry and the associated linkages among the precursors is needed to predict the effect of changing emissions on air quality indices. Consequently, the predictive air quality models used to assess ozone and FP impacts should include a basic core set of atmospheric chemistry reactions (e.g., a gas phase ozone chemistry mechanism).

Because of their common atmospheric chemistry linkages, many precursors associated with one pollutant might be considered as an "indirect" precursor for another pollutant as well. Virtually all precursor emissions (e.g., NOx, SOx, VOC, and CO) undergo initial attack by hydroxyl radicals and participate in the general cycling of various chemical intermediate species. Therefore, precursors typically not be associated with a particular secondary pollutant, such as the effect of VOC on either sulfate or nitrate, indirectly participate through their roles in atmospheric chemistry. In this general context, the term "precursor" does not imply a positive effect on an associated secondary species. The emission precursor may only share in certain atmospheric chemistry processes without leading to increases in a secondary pollutant. For example, NOx, which affects the cycling of hydroxyl radicals that convert SOx to sulfate, could act indirectly as a sulfate particle precursor. The majority of VOC species that do not transform into organic aerosols could nevertheless be FP precursors through their general role (i.e., cycling of radicals) in atmospheric chemistry. Nitrogen oxides could serve as indirect precursors for aerosol sulfate formation. This universal pool of precursors does not imply that reductions of any specific precursor leads to reductions of every pollutant. Just as reductions in NOx potentially can raise local ozone levels, a reduction of an FP precursor possibly can increase ozone or increase a different FP component (e.g., SOx reductions leading to increased ammonium nitrate or NOx reductions increasing sulfate formation). These examples are some of several conceivable indirect precursor relationships. Many other relationships with similarly unknown degrees of effect exist. Thus, integrated implementation is far from a straightforward exercise. Complex air quality simulation models, in combination with simpler models and receptor/observational methods that include approximations of these process linkages, will need to be exercised to account for the multiple nonlinearities and positive and negative feedbacks. This complexity demands high-quality emission inventories, technically credible models, and spatially and temporally representative monitoring data for use in predicting pollutant concentrations and control strategies.

Integrating Control Strategy Development through an Air Quality Modeling Approach

What does integration mean from an implementation perspective? Given the complex mechanisms for and linkages between ozone and FP formation, the formulation of control strategies should acknowledge the need to optimize control options. Control of one precursor might affect both ozone and FP or might be detrimental for one or both. For example, one might start with ozone management strategies being developed as part of ongoing urban and regional study, and attempt to quantify the future impact on secondary aerosols. On the other hand, because NOx controls might increase ozone levels in certain localized urban areas or because SO2 reductions might lead increased concentrations, efficient air quality management would attempt to optimize the system in relation to VOC, NOx, and SOx emission reductions.

The real benefit of integration is the prospect of a more systematic, efficient, and comprehensive treatment of emission inventories, episode selection, and atmospheric physics and chemistry that might empower the air quality manager to characterize source to receptor effects in an orderly way. The addition of data on the costs and effectiveness of control options would enable the air quality manager to identify the cost-effective means for attaining a variety of air quality goals.

To this end, emission bases underlying most current ozone modeling efforts include most of the sources for aerosol formation, but not necessarily the aerosol specific emissions such as organic aerosols from motor vehicles. Notable exceptions include many of the fugitive primary particle sources and most sources of ammonia emissions. The result of this exercise would produce the residual aerosol and regional haze related air quality benefits from an ozone precursor control perspective. (Additional analysis directed at the specific needs for meeting FP, and visibility concerns would follow this ozone oriented approach. Ideally, an objective and likely iterative ability to assess the benefits and tradeoffs associated with managing all three pollutant categories would evolve.) Although this example does not represent full integration given the unidirectional information flow (ozone to particles), it does acknowledge similarities among programs and avoids mistakes and inefficiencies incurred from independent analyses. Aside from any direct regulatory policy, the linkages across pollutants and emissions are reasons by themselves for planning for more efficient development and use of emissions, air quality models, and monitoring networks which address sometimes confounding multiple pollutants and their related health/welfare effects and control options.

Distinctions Among Ozone, Fine Particles, and Regional Haze

Coincident ozone and FP episodes may be expected to occur given similarities in the meteorological and atmospheric chemistry processes underlying ozone and FP formation, maintenance, and destruction. As discussed above, the linkages associated with emission source categories and physical and chemical processes exist more frequently than the occurrence of co-episodic events. For example, several basic atmospheric chemistry reactions involved in ozone and FP formation occur whether or not high ozone and FP levels are generated in the atmosphere. Nevertheless, several distinctions among the pollutants persist. These differences include the contribution of primary particles to total FP, especially PM-10, and wintertime (actually non-summertime) FP events. Some primary particles are generated by strong wind conditions (e.g., soil, geologic material) and other mechanical processes (e.g., roadway fugitives). The fraction of primary PM peaks in summer in most of the western third of the country where there is little precipitation for 6 to 8 months per year, leading to dry, windy conditions for the generation and movement of geologic materials. As discussed earlier, ammonium nitrate, a significant FP component in the West, is stable at relatively low temperatures and therefore does not form significant levels during the summer. Meteorological effects that influence the creation, maintenance, or removal of high levels of ozone and FP may be significantly different among pollutants, regions of the country, and times of the year. Other specific emissions-driven events such as forest burning and wintertime wood smoke (a major wintertime source of urban PM) bear virtually no relation to ozone. Many of these PM episodes can be dominated by either primary or secondary FP components, or by primary anthropogenic coarse PM emissions. Research exploring the frequency and characterization of co-episodic and uni- episodic events would yield further insight into underlying causes of events and provide direction for integrated implementation opportunities.

Visibility protection presents several additional considerations beyond the scope of topics covered under ozone and FP. First, FP concentrations that are far below a NAAQS can adversely affect visibility in a significant manner, particularly in more pristine environments such as Class I areas in the rural West. For this reason, visibility management needs to consider the protection of "clean" days separately from assessments focusing on highly impaired days. The meteorology and emissions characteristics during clean days differs from those common during high pollution episodes. This concern raises complex technical issues related to the ability of models and monitoring instruments, which often have been designed or tested for meeting high concentration requirements, to characterize low-level conditions. Second, relative humidity plays a significant role in enhancing visibility impairment, particularly in the East. In humid conditions, particularly above 70% RH, sulfates, nitrates, and certain organics readily take on water and expand to sizes comparable to the wavelength of light. Particles in this size range (i.e., 0.1 to 1.0 micron in diameter) are efficient scatterers of light. Third, unlike the NAAQS approach of setting a national standard, the Regional Haze program under section 169A of the CAA has as its goal "the prevention of future, and the remedying of any existing, impairment of visibility in mandatory Class I Federal areas in which impairment results from manmade air pollution." States are required to make reasonable progress toward this goal. The notion of background versus manmade air pollution raises several technical and policy challenges, particularly in the protection of visibility in cleaner environments where small increases of FP can lead to significant visibility changes.

Generally, PM-10 is not considered in the integration discussions of ozone, FP, and regional haze. This is because the coarse fraction (i.e., greater than 2.5 microns) typically is derived from primary emissions such as fugitives and geologic material with little association to ozone from a process, or episodic, perspective. In addition, visibility impairment leading to regional haze is overwhelmingly associated with the FP fraction of PM-10.

Major Technical Issues

The principal technical issues associated with integrated air quality management involve the adequacy of databases and models, including specific process formulations, on which to base credible assessments. While it is impossible to ascribe consensus opinion regarding clear acceptable limits on the available information, gradations of acceptability or comfort level can be associated with various pollutants. Generally, the tools (ambient data, models, and emissions) underlying ozone analyses are far more mature than those for FP. Major efforts in chemical mechanism development, ambient monitoring methods, and establishment of national and special study efforts for monitoring, emissions, and modeling have resulted in a wealth of information and familiarity with these tools. This relative abundance of knowledge for ozone should not be construed as a science lacking uncertainty, as significant technical issues remain (e.g., the current NARSTO effort), and even more are yet to be defined. A sampling of these issues includes the representativeness of emission inventories, particularly biogenic emissions; uncertainties in the modeling system (chemical characterizations of aromatics and biogenics, treatment of vertical mixing processes); difficulties in monitoring techniques (carbonyls, Nox, NO2, polar VOC); and lack of measurements (total reactive nitrogen, NOx upper air data). These gaps are significant and compromise our ability to perform highly credible ozone analyses and to ascribe confidence levels in our results.

Consideration of FP, and regional haze presents several additional issues, a result of: (1) a very complex multiphase, multicomponent, multiseason aerosol system, (2) the complex covariance of these data, and (3) the present PM-10 form of the NAAQS, which has resulted in few regulatory pressures to drive an improved characterization. Significant concerns include: major positive and negative measurement artifacts related to gas-particle phase changes; a simple lack of ambient data, especially urban FP measurements; poor quality assurance/control of ambient sampler data; emissions data with poor general spatial applicability; very limited availability and nearly nonexistent application and evaluation of regionally-accurate air quality models; and highly empirical treatment of organic aerosols within the available models. These gaps are interconnected in the sense that quality model evaluation and improvement rely on available quality measurements. The issue is further complicated by complexities, lack of precedence, and resource constraints in designing a data collection program to evaluate a gridded model's ability to characterize FP covering wide scales of time (annual, seasonal, daily) and spatial resolution (regional, urban, local). On the positive side, a strong history of using ambient data for PM source apportionment probably is more adaptable to FP analyses than ozone, given that the measurable components of secondary FP (e.g., sulfate) have some direct linkage to precursors, whereas an ozone measurement by itself provides no inference regarding contributing precursors.

Several interesting atmospheric chemistry questions remain to be answered. Two examples include nitrate FP formation and organic aerosols. Where and when do ammonia and sulfate become limiting factors in ammonium nitrate formation? The relatively abundant nitrate FP at sites in the urban West contrasts with abundant regional sulfate FP in the East. Substantive decreases in SO2 emissions could lead to increased nitrate FP formation in the East, if sufficient ammonia (a highly uncertain emissions category) is available. What impacts will NOx emission reductions have on FP? If nitrate is significant, one would expect a reduction in FP. However, if sufficient sulfur remains available, NOx reductions could increase or decrease sulfate formation (and therefore FP) depending on a complex cycling of oxidizing species. Reductions in NOx emissions could actually lead to sulfate increases by reducing competition between SOx and NOx for gas phase oxidizing radicals, or by increasing peroxide levels leading to greater aqueous phase sulfate production. NOx reductions could slow down sulfate formation through overall reductions in ozone and other oxidants. This relationship is very complex and we must exercise caution in associating FP benefits with NOx reductions in the Eastern United States.

What are the relative contributions of primary and secondary organic aerosols across varying spatial and time scales? The potential for large secondary organic aerosol production from biogenic sources (e.g., pinene emissions) exists throughout the East. How significant are biogenic-derived aerosols compared to local/urban contributions from primary anthropogenic organic aerosols? How different are these relative contributions across seasons, given that secondary organic aerosol formation increases during the summer? Many uncertainties underlie the integration of primary and secondary particles, aside from integrating particles and ozone. For instance, what are the interactive roles that elemental carbon emissions, other products of incomplete combustion, and geologic materials exert in both primary contribution to PM and as formation nuclei for highly complex secondary PM? On balance, the ability to perform ozone air quality assessments far exceeds that of FP. However, the infrastructure for conducting FP analyses appears to be in place as a result of progress gained from ozone and acid deposition modeling and existing monitoring programs for ozone and visibility (e.g., the IMPROVE program). Finally, although uncertainties remain in transforming particles into visibility impairment within short averaging times, the IMPROVE methodologies for particle and visibility measurements and the relationships between particles and visibility are widely accepted.

Specific issues across PM and ozone include the ability to formulate fully integrated models accounting for multidirectional effects on several pollutants. For example, the formation of secondary organic aerosols is a loss mechanism for VOC that presently is not accounted for in ozone models. Many other integration topics exist, and collectively there is uncertainty regarding the overall importance of one pollutant imparting an effect on another.

Two basic issues span the gap between science and policy: (a) the manner in which tools are applied, and (b) accommodating scientific findings and uncertainties in air quality management decision making. The first topic reflects the concerns of how one applies deterministic 7 (i.e., models that establish exact cause and effect relationships) and uncertain air quality models to probabilistic forms of the standard in ascribing rigid control requirements. The selection of severe meteorological episodes versus prototypical episodes for ozone and PM-10 modeling has been controversial and remains a difficult model application issue. Equally complicated is the emerging need to model seasonal and annual cases. The debate on the credibility of models is fueled by the manner in which they are applied as much as the valid concerns about their formulations and supporting databases. The second topic acknowledges the need for conducting policy-relevant as opposed to policy-driven research, and recognizing the different time scales operating in the research arena and the policy arena where the timeframe demands move much faster than research results. Extremely useful information emerges continuously from research programs, yet a separate, sometimes very significant, time lag occurs before information is considered in the policy setting process. Hence, opportunities must be available to incorporate the latest science into policy.

Integrating Models and Observations for Sound Air Quality Management Practice

Much emphasis has been placed on the complementary and integrated use of models and ambient data in air quality management practice (Rao et al., 1996). Several facets are associated with this topic, ranging from the need to evaluate models with sound databases to conducting fully integrated analysis optimized through the separate, strong attributes of data and models. As the technical debate on the use of models and data continues to mature, perceptions such as model or data are replaced by the intelligent and integrated use of models and data. Clearly, the demand for measurements as ground-truthing and feedback information loops initiated by the National Academy of Sciences Ozone Report (NRC 1991) has been adopted by large segments of the air quality community and reflected in major efforts such as the Photochemical Assessments Measurement Stations and NARSTO.

An appreciation of the strengths of models and observations can assist the understanding of current analyses and lead to improved techniques. A model's strength is its ability to: (1) integrate an enormous spectrum of data (e.g., emissions and meteorological variables) and process understandings (e.g., chemical mechanisms and flow phenomena), and (2) serve as an exceptional space and time mapping tool. This latter attribute reflects the model's unique ability to predict into the future and to supplement or fill in present gaps in observed data. The process formulations embedded in models enable the addressing of so many "what if" questions related to emissions control. However, models are engineering tools that invoke substantial approximations of scientific understandings of natural phenomena. Both their formulations and application methods reflect engineering principles more than fundamental science. Observations provide a basis for testing and diagnosing models, but in some instances, can capture process type relationships by themselves (e.g., the emergence of observational based models for defining NOx and VOC control preferences). However, the observations are very sparse. Hence, applied in isolation, the use of models or observations is not acceptable. Space and time constraints often bias the interpretation of observational analyses (e.g., analysis results reflect time and space of monitors which may or may not reflect the scales of concern). Models suffer from a very large spectrum of weaknesses because they attempt to portray so many phenomena. Most critical though is the risk of using a potentially biased model that is assumed bias free. The integrated use of observations and models mitigates the individual weaknesses of both approaches and produces a powerful air quality management tool, especially when applied in an iterative, even retrospective, manner to continually assess model results and related implementation strategies.

Summary

Air quality assessments for FP, ozone, and regional haze must consider emissions, meteorological processes, atmospheric chemistry, and deposition, all of which interact over multiple spatial and temporal scales. Examining in detail the sources only from the MSA/CMSA surrounding the monitor reporting nonattainment levels of air quality may need to be augmented (on a space and time basis) to responsibly allocate those levels to the sources causing them. When examining the issues on expanded time and space scales, air quality management should also take into account the similarities of these air quality indices such as their common precursor emissions (e.g., NOx, VOC), common emissions sources (e.g., mobile sources, stationary and area source combustion emissions, biogenics), and shared chemical and meteorological processes (e.g., transport, transformation, precipitation, removal).

The principal technical issues associated with integrated air quality management involve the adequacy of databases and models, including specific process formulations, on which to base credible assessments. Many of these gaps are interconnected, since model evaluations rely on available high quality measurements of emissions, atmospheric processes (such as wind fields) and ambient concentrations. On balance, the ability to perform ozone air quality assessments far exceeds that of FP, due mostly to the maturity of ozone research as well as lack of urban FP measurements and important emissions components. However, many of the components of the infrastructure for conducting FP analyses appear to be in place as a result of progress gained from ozone, acid deposition, and visibility modeling and monitoring programs.

The integrated application of models and observed data is strongly encouraged. In combination, both approaches help to mitigate the weakness of an isolated approach, producing a powerful tool for air quality management.

4.2 Conceptual Model Document Overview

Emerging air quality management control policies for ozone, PM, and regional haze rely on technical information and scientific knowledge gleaned from many diverse sources. An increasing amount of interaction among a diverse community of air quality professionals accompanies any effort toward integrating programs across pollutants and over wide geographic regions. Compounding the differences among programs and specialties is the overriding motivation to understand similarities and overlaps to optimize technical resources and identify windows of opportunity for successful integrated air quality management. The objective of the Conceptual Model document is to establish a common reference frame for the technical information and methodologies underpinning the implementation programs. These programs are designed to improve subsequent dialogues addressing program integration and accompanying science-policy interface issues.

The Conceptual Model document was developed by the STSWG to address the state-of-the-science pertaining to integrated pollutant implementation and was organized by the following topics:

Existing environmental state (through summaries of measured ambient air quality data),

Physical/chemical processes which characterize air quality, and

Scope of monitoring, modeling/analysis, and emission inventory programs to characterize and

predict air quality phenomena.

The information presented is reference oriented. It covers a very broad scope of topics, but provides direction and insight to the major national/regional programs and special field studies/programs that collectively form the technical foundation for ozone, PM, and regional haze programs.

The initial draft version of the Conceptual Model will not adequately address some of the technical issues of concern because of inherent uncertainties in the current state-of-science. To this end, much of the focus of the STSWG will be directed toward a full exploration of what is known and what is not known over the next several months, with an objective assessment of uncertainty attendant in the data and tools used for air quality analyses. Accordingly, suggestions regarding additional information sources, topics and issues requiring attention, and technical corrections are strongly encouraged and will be considered in future versions of this and other documents submitted to the docket by the STSWG. Feedback in these areas is critical for providing a meaningful and useful reference document and crediting those individuals/groups responsible for the technical and scientific work supporting national and regional air quality programs.

The Need for a Conceptual Model

To develop an adequate understanding of ozone, PM formation, and regional haze in different areas of the country, it would be very useful to develop s of Conceptual Models the processes that lead to the formation of each. Further, it would useful to develop a Conceptual Model of how monitoring, data analysis, emissions, modeling, and assessment can be used in the subsequent implementation programs. In setting out the initial model, there will be many more questions than available information to answer them.

Consequently, the Conceptual Models will provide the feedback necessary to identify additional information needs. While these models will be useful in setting research agendas, they also identify the "act as if we know how it works" assumptions that will be necessary in formulating and applying any practical computational models within a timeframe shorter than that needed to advance fundamental knowledge. The entire process of creating Conceptual Models is iterative in nature, but provides an overall framework for increasing the scientific and technical information needed to provide a basis for sound air quality planning. In addition, Conceptual Models can codify the processes independent of any air quality modeling and, thus, provide an independent mechanism to evaluate the performance of computational air quality model(s).

The Formulation of a Conceptual Model

In formulating a Conceptual Model, we accept the following: (1) that there are in the environment pollutants which are harmful to human health and welfare, (2) that there are acceptably safe levels of these pollutants (codified as NAAQS), and (3) that human and civilized activities do influence or even create the harmful levels. The social goal desired is to modify human activities so as to reach safe levels of these pollutants. We accept that some form of regulation will be necessary to achieve this modification of human activities. In the specific cases of ozone, PM-fine, and regional haze, we accept that these are pollutants that have effects on humans and the environment. We accept that ambient levels of these pollutants need to be maintained below specific air quality standards and that the magnitude and form of these standards are outside the scope of this work group's activities. While there are specific emissions, transport, and transformation processes that are unique to ozone, PM and regional haze, we accept that there are also common processes that link the three. That is, ozone, PM-fine and regional haze have a sufficiently common origin that it makes sense to seek an integrated set of modified human activities that will achieve reduction and maintenance of ambient concentrations of these pollutants.

In the following chapters of the Conceptual Model document, detailed information is contained on the following:

Chapter 2:	The Current Environmental State

Chapter 3:	Processes: How the State is Created, Sustained and Maintained

Chapter 4:	Current Tools to Address and Implement the Current State of Knowledge

Chapter 5:	Time-Distance Considerations Relevant to Transport and Regions of Influence

It is through the compilation of these chapters that we attempt to form a conceptual framework for our understanding of the pertinent scientific issues surrounding the revision of the ozone and particulate matter NAAQS and the regional haze/visibility rule.

1.	Precursors are compounds that contribute or lead to the formation of a secondary pollutant. For example, NOx and VOC are ozone precursors.

2.	Intermediates include the short-lived radicals (hydroxyl, hydro-, and organic-peroxy) that perform many of the important atmospheric oxidation reactions.

3.	Chemical sinks are termination compounds that essentially remove other compounds (e.g., nitric acid, hydrogen, organic peroxides). Some sinks can eventually break down and reform precursor compounds (e.g., peroxy acetyl nitrate).

4.	Most of the chemical component analyses are based on samples derived from rural networks like IMPROVE.

5.	Most low molecular weight VOC species (which are most prevalent in ambient air) are not expected to contribute significantly to secondary aerosol formation. Certain aromatics, and higher molecular weight alkanes and alkenes (>6 carbons) are believed to be the major contributors to secondary organic aerosol formation.

6.	Although significant gas phase transformation of SO2, aqueous phase oxidation is believed to be responsible for the majority of annual sulfate conversion in the Eastern United States.

7.	The use of a deterministic model to simulate naturally occurring stochastic processes is a separate technical issue.

4.3 Science and Technical Support Work Group's Position on AOI/AOV Issue Papers

The STSWG has provided technical approaches to be used for implementing the new standards. This body of work has been presented in the Conceptual Model report and in numerous issue papers that STSWG developed in response to questions from other work groups.

The STSWG recommends using scientific methods to establish cause and effect relationships to solve the ozone and PM problems. It is recommended that the problem area be identified as the area of violation (AOV). It is realized that all or part of the cause of the problem may come from outside the AOV. Thus, it is recommended that appropriate technical approaches be used to identify the cause of the problem, and then establish the area of influence (AOI). Then the planning would continue by developing a set of appropriate and effective control measures that would eliminate the cause of the problem. This process provides decision makers with a greater degree of confidence that the controls that are implemented will be successful in eliminating the fundamental cause of the problem. STSWG recognizes that planning will always have inherent uncertainties, and has recommended the use of an iterative process which links observed data to the predicted changes in air quality.

Previous efforts have developed the concept of a Regional Air Management Partnership (RAMP) that would be responsible for the technical work to identify the AOVs and AOIs and, in some cases, recommend control measures that would be effective. This concept was followed to a certain extent by the Ozone Transport Assessment Group (OTAG). Previously ozone nonattainment areas have been identified and various States and combinations of States attempted to develop control plans to solve the problem. Some of these areas could be considered technical RAMPs (e.g., Lake Michigan Air Directors). In other areas the modeling process identified areas outside the modeled area that potentially contributed to the ozone problem. OTAG was formed (and functioned as an expanded RAMP that was both technical and political) to address these problems of transport across a large portion of the country. The OTAG process identified regional controls that would decrease regional ozone concentrations and assist in solving the ozone problems in the previously identified nonattainment areas.

Two recent non-STSWG issue papers have appeared that recommend mechanisms by which the EPA could move forward to address both ozone and PM nonattainment issues. STSWG believes that these papers do not fully reflect the technical processes that STSWG has suggested.

The first of these papers is from the EPA and is titled "The Regional Air Management Partnership (RAMP) and the Area of Influence (AOI) Process." The paper suggests that no RAMPS are needed for ozone and PM issues should be addressed with two RAMPs nationwide.

The second paper, "A Framework for Areas of Influence/Areas of Violation (AOI/AOV): Responsibility for Reaching Attainment," is a product of a small ad hoc group trying to resolve the problem of the present approach to nonattainment for the new ozone standard and for assumed nonattainment for the then yet-to-be finalized PM-fine standard. The Framework paper recommends that those areas that would be classified as nonattainment under the new standards make early reductions to improve air quality or even reach attainment prior to implementing a major SIP process. Among the assumptions in this Framework paper is the desirability of developing a presumptive list of control measures that should be implemented by the AOV in the years preceding the SIP process. The paper assumes that the AOV can be exempted from some control measures by using a set of simple criteria and will not need a rigorous SIP analysis to determine what measures are necessary.

The following nine points represent the STSWG concerns with the concepts outlined in these two papers:

1.	STSWG felt that neither paper supports the idea that the underlying foundation
beneath EPA's air management process should be the use of adequate tools and	databases (both modeling and economic) to establish the cause and effect relationship needed to solve the ozone and PM-fine problems. STSWG has consistently recommended that there is a need to improve air quality models, economic models, databases, and data analysis techniques to ensure that planning decisions are effective.

2.	STSWG believes that a model's greatest strength is in evaluating past episodes and not in making future predictions of pollution events. This reality will always introduce
uncertainty into the planning process, and it is important that model limitations must be	recognized in any planning exercise.

3.	STSWG supports the idea that an iterative process be utilized so that a midcourse
correction may be made if necessary. Because of the uncertainties in the planning process, model predictions should be compared with ambient air quality measurements at some point in the future (e.g., five or six years after the adoption of the plan), and the effectiveness of the model and the control measures should be re-evaluated. This concept is also embedded in the Reasonable Further Progress issue paper.

4.	Use of presumptive controls for secondary pollutants without sufficient scientific
evidence may not effectively ameliorate air quality. STSWG questions the recommendation that an AOV should implement a presumptive set of controls to address air quality issues for secondary pollutants without scientific or anecdotal evidence. A method of presumptive controls may be adequate (but not necessarily cost- effective) in some cases for controlling primary pollutants and preclude the necessity for detailed modeling. Without understanding the complex non-linear chemistry producing ozone or secondary aerosols, no simple mechanism exists to judge if presumptive controls will benefit air quality or provide cost-effective solutions. Controls which reduce ozone in one area may not be effective in another region and they may not reduce PM-fine. For PM- fine, specific scientific areas requiring more study include the collection of speciated monitoring data, the development of modeling techniques, and the development of appropriate emissions inventories (for primary PM-fine, organic aerosols, and ammonia).

5.	STSWG believes that continued technical analyses will be necessary to determine which control strategy choices are appropriate for the control of ozone. From a technical
perspective, there is a continued need to obtain more air quality, emissions and meteorological data and carry out further data analyses to better understand the local and regional scale formation of ozone. STSWG has recently stressed the need to consider the concept of a linkage between air quality models and economic models, such as the one developed by the Cornell Institute of Social and Economic Research in conjunction with the Department of Atmospheric Sciences at SUNY. STSWG believes that the economic models also need to undergo a rigorous evaluation of their underlying assumptions.

6.	STSWG believes that the results from a linked approach would be negated by the adoption of the recommendations in the RAMP/AOI and Framework papers. The concern is that there may be differences in the ranking of control measures (including the spatial nature of the measure) when considering strategies to maximize pollution reduction and minimize cost for the one- and 8-hour standards. Pursuit of a strategy that moves to meet the one-hour standard may be likely to show improvements in air quality with respect to the corresponding 8-hour standard. However, these controls may not be optimal for meeting the 8-hour standard. The implementation of a control program for the one-hour standard could adversely affect the liquidity of the market needed to devise a least-cost program for the 8-hour standard. The adoption of a set of presumptive controls would also have a negative impact by including options which would not be used in a least-cost approach.

7.	The definitions and roles of RAMPs, AOVs, AOIs, and modeling centers should be
stated explicitly in such a way that political entities will support rather than hinder the work of the scientific community. STSWG views RAMPs as political entities which	identify technical people, establish the funding sources for the modeling centers, and approve the scientific findings. The decisions about where RAMP boundaries are established should not interfere with scientific investigations.

8.	STSWG believes that the OTAG process showed that multi-State planning can work, but OTAG did not operate as the type of RAMP described in the RAMP/AOI paper. The OTAG process was driven by an arbitrary time line which resulted in compromises when developing the underlying database and in planning the ultimate strategies. To deal with the increasingly complex issues associated with the new PM and ozone standards, a cooperative process will be necessary that involves all stakeholders. OTAG and other groups, such as GCVTC and NARSTO, laid the foundation for future multi-state planning efforts.

Some members of STSWG felt that the RAMP process might be more successful if two	levels of RAMPs are recognized. The first RAMP could be large and political in nature with the goal of directing the initial analyses and defining the AOIs and AOVs. The AOI and	AOV boundaries would then define the second set of RAMPs, and each technical RAMP (or technical/political RAMP) could proceed with the technical development and the assessment of planning tools and control strategies.

9.	STSWG believes that the automatic assumption that there is no need for ozone RAMPs is an oversimplification. The formation of exactly two RAMPS for PM issues is also	questionable. These decisions should be made with a more complete scientific record.

Summary

In conclusion, the issues highlighted above illustrate STSWG's position that there is a continued need to obtain air quality, emissions and meteorological data and to carry out sufficient data analyses. The data analyses must at least be standardized on a regional scale. Whether mandated by the EPA, by scientists from groups of agencies and organizations with similar regional air quality issues, or by decentralized individual interests based on national/regional/peer-reviewed data collection/analysis, these data are needed in the near-term future. The FACA Subcommittee should explicitly state the need and importance of these data for future policy decisions.

References:

Appleton, E.L., 1995, "A Cross-Media Approach to Saving the Chesapeake Bay," Environmental Science Technology, 29, 550A-555A.

Dennis, R.L., 1996, Personal Communication.

NESCAUM, 1995, "Preview of 1994 Ozone Precursor Concentrations in the Northeastern U.S.," Northeast States for Coordinated Air Use Management, Boston, MA.

NRC, 1991, "Rethinking the Ozone Problem in Urban and Regional Air Pollution," National Academy Press.

NRC, 1993, "Protecting Visibility in National Parks and Wilderness Areas," National Academy Press.

Rao, S.T., E. Zalewsky, and I.G. Zurbenko, 1995, "Determining Temporal and Spatial Variations in Ozone Air Quality," J. Air & Waste Management Association, 45, 57-61.

Rao, S.T. et al., 1996, "Dealing with the Ozone Nonattainment Problem in the Eastern United States."

Rao, S.T., 1996, Personal Communication.

Trijonis, J. et al, 1990, "Report 24 - Visibility: Existing and Historical Conditions - Causes and Effects," from Acidic Deposition: State of Science and Technology, Volume III, National Acid Precipitation Assessment Program.

U.S. EPA, 1996, "PM Criteria Document."