## 7. Conducting Dispersion Modeling for Criteria Air Pollutants 

This section addresses two t ypes of atmospheric dispersion modeling conducted in support of FAA projects/actions: (i) atmospheric dispersion for airports and (ii) dispersion modeling. 

## 7.1. Atmospheric Dispersion Modeling for Airports 

This section discusses the recommended guidance and approaches for conducting and reporting atmospheric dispersion modeling of aviation-related emissions in connection with FAA projects/actions. Appendix D ( Atmospheric Dispersion Modeling ) provides additional information on dispersion modeling methods, data requirements, and other supporting materials. 

## 7.1.1. Introduction & Background 

In general terms, dispersion modeling is the process by which the dispersal of atmospheric pollutants are simulated and assessed under effects of meteorological, terrain and other influencing factors. Computer models such as the American Meteorological Society/ EPA Regulatory Model (AERMOD) have been developed and used for this purpose. The results of this modeling allow for the prediction of pollutant concentrations at or near an source(s) and enable the comparison of these results to the NAAQS. 

## 7.1.2. EPA Guidance 

EPA’s principal guidance of conducting dispersion modeling and assessing the air impacts on nearby receptors is entitled and described as follows: 

• Appendix W to Part 51 - Guideline on Air Quality Models 70 

This guidance contains recommendations and supporting information on the selection and applications of air quality models, determining background concentrations and the use of meteorological data. This guidance also specifies dispersion models required to be used for SIPs revisions and for New Source Review (NSR) and Prevention of Significant Deterioration (PSD) programs. 

Notably, dispersion modeling requirements and methodologies may vary by purpose and/or locale, thus state and regional air quality regulatory agencies should be consulted on methodology, assumptions, and data sources utilized. 

However, as discussed previously in Section 5 ( Air Quality Assessment Models ), the FAA’s EDMS is the required model for performing air quality assessments of aviation-related sources in support of FAA projects/actions until EDMS is replaced by AEDT2b. 71 Coupled with 

