This guidance is a living document and may be revised periodically. Updates, revisions,

and additional documentation will be provided at Any mention

of trade names or commercial products in this document is not intended to constitute

endorsement or recommendation for use. Users are cautioned not to regard statements

recommending the use of certain procedures or defaults as either precluding other procedures or

information, or providing guarantees that using these procedures or defaults will result in actions

that are fully approvable. As noted above, EPA cannot assure that actions based upon this

guidance will be fully approvable in all instances, and all final actions will only be taken

following notice and opportunity for public comment. The EPA welcomes public comments on

this document and will consider those comments in any future revisions of this guidance

document, providing such approaches comply with all applicable statutory and regulatory


1.0 Introduction

This document describes how to estimate if an emissions control strategy will lead to

attainment of annual and 24-hour national ambient air quality standards (NAAQS) for particles

smaller than 2.5 :m in diameter (PM2.5) and the 8-hour NAAQS for ozone. We also describe

how to use modeled and monitored data to estimate the visibility improvement in Class I areas

(e.g., national parks, wilderness areas) as part of a uniform rate of progress analysis1.

The document describes how to apply air quality models to generate the predictions later

used to evaluate attainment and/or uniform rate of progress assessments. Modeling to show

attainment of the NAAQS primarily applies to nonattainment areas2 for which modeling is

needed, or desired. Modeling to assess uniform rate of progress for regional haze applies to all


The guidance consists of two major parts. Part I addresses the question, “how should I

use the results of models and other analyses to help demonstrate attainment and/or assess

uniform rate of progress?” We begin by describing a modeled attainment test for the 8-hour

ozone NAAQS, the annual PM2.5 NAAQS, and the 24-hour PM2.5 NAAQS. We also recommend

a modeled test to assess uniform rate of progress goals to reduce regional haze. We explain

what is meant by a modeled attainment demonstration, a modeled attainment test, and a weight

of evidence determination. We also identify additional data which, if available, can enhance the

credibility of model results. Part I concludes by identifying what documentation States/Tribes

should include as part of an attainment demonstration.

Part II of the guidance describes how to apply air quality




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