1.0	INTRODUCTION

Emerging air quality management control policies for ozone (O3), particulate matter (PM) and regional haze (RH) 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 which are designed to improve subsequent dialogues addressing program integration and the accompanying science- policy interface issues.

The Conceptual Model Document, was developed by the Federal Advisory Committee Act's (FACA) Science and Technology Support Work Group (STSWG) to address the state-of- the-science pertaining to integrated pollutant implementation. The following chapters of this document are organized by descriptions of 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 in the following chapters is reference oriented, as it covers a very broad scope of topics but provides direction and insight to the major national/regional programs and special field studies/programs which collectively form the technical foundation for ozone, particulate matter and regional haze programs.

This 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 FACA STSWG will be directed toward a full exploration of the what is known, and what is not known over the next 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 FACA Science and Technical Support Work Group. 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 conceptual models of 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. Figure 1 is a schematic diagram which outlines the major issues/topics which are covered within the Conceptual Model framework.

Consequently, the conceptual models will provide the necessary feedback mechanisms to identify additional needed information. While these will be useful to set 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 time frame 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 ambient air quality standards, e.g. 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 case of ozone, PM-fine, and regional haze, we accept that these are pollutants that have affects on humans and the environment. We accept that ambient levels of these 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 process 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 this 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.