Dispersion modeling is used to assess the effects of airport-related emissions on ambient air quality. The modeling results are expressed as concentrations of the U.S. EPA criteria pollutants and are compared to the National Ambient Air Quality Standards (NAAQS). The current EPA/FAA dispersion model is the Emissions and Dispersion Modeling System (EDMS), which will be replaced by Aviation Environmental Design Tool (AEDT). The EPA recently promulgated a new, 1-hour NAAQS for nitrogen dioxide (NO₂) of 0.100 ppm. Values above this threshold are considered to be in violation of the NAAQS. As a result of the new regulations, greater attention is being paid to NO₂ concentrations, necessitating research on the accuracy of NO₂ concentrations predicted by EDMS/AEDT.The accuracy of model predictions is dependent on several factors, including emissions and chemistry, and available data can be used to evaluate the accuracy of the engine-specific NO/NO₂ emissions ratios (i.e., the Plume Volume Molar Ratio Method (PVMRM), the Ozone Limiting Method (OLM), and the Ambient Ratio Method (ARM)) in the EDMS/AEDT default values database. Further, the accuracy of NOx speciation may be improved in EDMS by explicitly calculating the NO-NO₂-ozone photostationary state. Research is needed to assess the current methods for estimating NO₂ values near airports, verify their accuracy and, if necessary, improve upon these methods.

The objectives of this research are to assess the accuracy of the NOx (NO+NO₂) emissions and speciation methods used in EDMS/AEDT (i.e., OLM, ARM, and PVMRM) to predict NO₂ concentrations, develop and assess alternative methods, and recommend a preferred method for predicting NO₂ concentrations resulting from airport emissions.