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Dispersion Modeling
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Dispersion modeling uses mathematical formulations to characterize the atmospheric
processes that disperse a pollutant emitted by a source. Based on emissions and
meteorological inputs,
a dispersion model can be used to predict
concentrations at selected downwind receptor locations.
These air quality models are used to determine
compliance with National Ambient Air Quality Standards (NAAQS), and other regulatory
requirements such as New Source Review (NSR) and Prevention of Significant Deterioration
(PSD) regulations. These models are addressed in Appendix A of EPA's
Guideline on Air Quality Models
(also published as Appendix W of 40 CFR Part 51),
which was originally published in April 1978 to
provide consistency and equity in the use of modeling within the U.S. air quality management system.
These guidelines are perodically revised to ensure that new model developments or expanded regulatory requirements are
incorporated. This site provides links for dispersion models
and other related tools and information as follows:
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Preferred/Recommended Models - Refined air
quality models
that are currently listed in Appendix W and
are required to be used for State Implementation Plan (SIP) revisions for existing sources and NSR and PSD programs.
Alternative Models - Models, not listed in
Appendix W,
that can be used
in regulatory applications with case-by-case justification to the Reviewing Authority as noted in Section 3.2, "Use of Alternative Models", in
Appendix W.
Screening Tools - Models that are often applied
before applying a refined air quality model to determine if refined modeling is needed.
Related Programs - Programs and utilities that are
used in support of some of the dispersion models listed here. Note that utilities designed for use with particular models will be found with those
models.
The EPA's Air Quality Modeling Group uses dispersion models as part of its
modeling analyses for which information can be found at
Modeling Applications & Tools
and provides guidance on the use of these models for permit modeling
available at
Modeling Guidance & Support. Additional information about dispersion models can be found at
Related Links.
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