Dispersion Modeling

Dispersion modeling is generally associated with the construction permit application process and is used to predict the air quality impact of new or modified emission sources.  Other uses of dispersion modeling include: analysis of monitored violations of the National Ambient Air Quality Standards (NAAQS), assistance in planning and the development of rules.  The following information is provided as general guidance to help you through the air quality modeling process.  Although the intent is for the information to be as complete as possible, modeling methodologies and analyses can vary on a project-by-project basis.  Please work in close consultation with the Virginia DEQ modeling staff and the appropriate DEQ regional office as you develop your modeling protocol and air quality compliance demonstration. 

Air Quality Models

These refined dispersion models that are used for regulatory applications are listed in the Guideline on Air Quality Models (40 CFR 51, Appendix W) and are used for State Implementation Plan (SIP) revisions for existing sources and for the New Source Review (NSR) and Prevention of Significant Deterioration (PSD) programs.  EPA maintains the list of preferred/recommended models on the Support Center for Regulatory Modeling Applications (SCRAM) website.

EPA Preferred/Recommended Models - EPA's list of preferred/recommended dispersion models for regulatory applications. 

AERMOD - A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.

CALPUFF - A non-steady-state puff dispersion model that simulates the effects of time- and space-varying meteorological conditions on pollution transport, transformation, and removal.  CALPUFF can be applied for long-range transport and for complex terrain on a case-by-case basis.

Other Models - Other dispersion models including BLP, CALINE3, CAL3QHC/CAL3QHCR, CTDMPLUS, and OCD.

Modeling Guidance

Virginia DEQ Guidance

Virginia Modeling Guideline for Air Quality Permits (Adobe pdf) - This is Virginia's primary permit modeling guideline.  It is intended to be used along with applicable federal guidance.

Appendices - Virginia Modeling Guideline for Air Quality Permits

APPENDIX A: VADEQ Office of Air Quality Assessments, EPA Region III, and Federal Land Manager Contact Information (Adobe pdf)

APPENDIX B: PSD Modeling Protocol and Report Checklists for Class I and Class II Areas (Adobe pdf)

APPENDIX C: Virginia Toxic Air Pollutant Exemption Rates and Significant Ambient Air Concentrations (Microsoft Excel 2007)

APPENDIX D: Virginia Minor Source Baseline Dates (Adobe pdf)

APPENDIX E: Report Table Format Examples (Adobe pdf) 

Environmental Protection Agency (EPA) Guidance

EPA Support Center for Regulatory Atmospheric Modeling (SCRAM) - This website is maintained by EPA's Air Quality Modeling Group (AQMG).  The AQMG conducts modeling analyses to support policy and regulatory decisions in the Office of Air and Radiation (OAR) and provides leadership and direction on the full range of air quality models and other mathematical simulation techniques used in assessing control strategies and source impacts.  Documentation and guidance for these air quality models can be found on this website, including downloadable computer code, input data, and model processors.

Guideline on Air Quality Models (40 CFR 51, Appendix W) (Adobe pdf) - EPA’s Guideline on Air Quality Models (‘‘Guideline’’) addresses the regulatory application of air quality models for assessing criteria pollutants under the Clean Air Act.

AERMOD Implementation Guidance (Adobe pdf) - This document provides information on the recommended use of AERMOD to address specific issues and concerns related to the implementation of AERMOD for regulatory applications.  The following recommendations augment the use of experience and judgment in the proper application of dispersion models.  Advanced coordination with DEQ, including the development of modeling protocols, is recommended for regulatory applications of AERMOD.

New Source Review Workshop Manual (DRAFT, October 1990) (Adobe pdf) - This document was developed for use in conjunction with New Source Review (NSR) workshops and training, and to guide permitting officials in the implementation of the NSR program.  It is not intended to be an official statement of policy and standards and does not establish binding regulatory requirements; such requirements are contained in the regulations and approved state implementation plans.

The Office of Air Quality Planning and Standards (OAQPS) Air Quality Modeling - The mission of OAQPS is to preserve and improve the quality of our nation's air.  One facet of accomplishing this goal requires that new and existing air pollution sources be modeled for compliance with the National Ambient Air Quality Standards (NAAQS).

Atmospheric Sciences Modeling Division (ASMD) - ASMD leads the development and evaluation of predictive atmospheric models on all spatial and temporal scales for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions, and for forecasting the Nation's air quality.

Federal Land Manager's (FLM) Guidance

Federal Land Managers' (FLMs) Air Quality Related Values Work Group (FLAG) Phase 1 Report - Revised (2010) (Adobe pdf) - Guidance developed by a group consisting of the National Park Service (NPS), the U.S. Fish and Wildlife Service (FWS), and the U.S. Forest Service (USFS).  FLAG was formed to evaluate air pollution effects on air quality related values (AQRVs) primarily in Federal Class I air quality areas, but in some instances, in Class II areas; and to provide State permitting authorities and potential permit applicants consistency on how to assess the impacts of new and existing sources on AQRVs.  Based on knowledge gained and regulatory developments since the original FLAG report was completed in December 2000, the federal land managers have revised FLAG resulting in the FLAG 2010 report.  Additional information is also located on the FLAG website.

Meteorological Data and Monitoring Guidance

This section provides information about meteorological data for regulatory air quality modeling.  The OAQA has data from current and historic meteorological towers in Virginia that are suitable for use in regulatory models.  Contact the OAQA Coordinator for available data.  Approval must be obtained on a case-by-case basis before meteorological datasets are used for regulatory (e.g., air permit) modeling.

Meteorological Monitoring Guidance for Regulatory Modeling Applications (February 2000) (Adobe pdf) - This document provides guidance for the collection and processing of meteorological data for general use in air quality modeling applications.  Such applications include those required in support of air quality regulations as specified in the Guideline on Air Quality Models.

Ambient Monitoring Guidelines for Prevention of Significant Deterioration (PSD) (May 1987) (Adobe pdf) - The purpose of this guideline is to address those items or activities which are considered essential in designing PSD air quality and meteorological monitoring networks.  Operational details such as equipment specifications, sampling procedures and methods, sampling duration, and quality assurance are included in this document.

Example AERSURFACE and AERMET Stage 3 Precipitation Spreadsheet - This spreadsheet may be used to calculate AERMET Stage 3 inputs by adjusting the surface moisture obtained through multiple AERSURFACE runs (wet, dry, and average conditions).  The spreadsheet compares precipitation for the period of data to be processed to the 30-year climatological record, selecting “wet” conditions if precipitation is in the upper 30th-percentile, “dry” conditions if precipitation is in the lower 30th-percentile, and “average” conditions if precipitation is in the middle 40th-percentile.

Meteorological Data Links - The links below contain a variety of surface and upper air meteorological data that is used as input to air quality models.

Geophysical Data

Other Documents and Links

EPA Ambient Air Memoranda (Adobe pdf)

Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Revised (October 1992) (Adobe pdf)

Use of the Ambient Ratio Method for Modeling Significant Ambient Impacts of NO2 (EPA, March 15, 2002) (Adobe pdf)

Class I Area Links

Vegetation and Soils Links

Training

Air Pollution Training Institute

OS411 - Computational Atmospheric Sciences


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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000


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