emissions may indicate a problem with the magnitude and/or the speciation of the emissions

sources. If discrepancies are found, those implementing the modeling protocol (see section 12)

should consult with the appropriate U.S. EPA regional office to reach agreement on what, if any,

adjustments should be made to the emissions estimates for the identified sources.

It is also important to quality assure the model outputs. Modeling each species of

primary PM2.5 separately within the dispersion model should aid in this analysis, especially if the

selected control strategies applied in the future year do not control each primary species to the

same degree. If a speciation monitor exists, the speciated data from the monitor may also help

quality assure the dispersion model results. However, the relative application of the dispersion

model results will help to reduce the impact of possible over- or under-estimations by the

dispersion model due to emissions, meteorology, or general selection of other model input


6.0 What Is The Recommended Modeling Analysis for Regional Haze?

In this section, we describe the recommended modeled test to assess visibility

improvement. The visibility analysis has many similarities to the attainment tests described in

Section 5. The recommended visibility analysis and the attainment tests both use monitored data

to define current air quality. They divide PM2.5 into major species, and component-specific

relative response factors are multiplied by current monitored values to estimate future


Section 6.1 provides background information on the requirements of the Regional Haze

rule and defines the components of a reasonable progress analysis. The rest of the section

describes the recommended modeling analysis which supports the regional haze rule.

6.1 Regional Haze Rule Background

Section 169A of the Clean Air Act states “Congress hereby declares as a national goal

the prevention of any future, and the remedying of any existing, impairment of visibility in

mandatory class I Federal areas which impairment results from manmade air pollution.” Section

169B calls for EPA to “carry out the Administrator's regulatory responsibilities under [section

169A], including criteria for measuring ‘reasonable progress’ toward the national goal.”


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