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19 CHAPTER 4 Primer on Models A primary potential application of the APEX data is to aid to compute emission factors for on-road vehicles. MOBILE compilation of airport emissions inventories. Inventories are allows the user to model emission factors for a fleet of vehicle typically compiled for criteria pollutants and their precursors types or an individual vehicle class based on the mix of vehi- (i.e., NOX, SOX , CO, VOC, and PM). Various analytical tools, cle types and age, and considers vehicle speed and ambient described in this chapter, are available to support the complex meteorological conditions as well (U.S. EPA 2007a). computations and aid in analyzing the results. 4.3 NONROAD 4.1 Emissions and Dispersion Similar to MOBILE, EPA's NONROAD model provides Modeling System emission factors for ground support equipment at airports The EDMS is a combined emissions and dispersion model that consider the rated horsepower of the engine, fuel type, for assessing air quality at civilian airports and military air and load factor. The traditional application of the model is bases. The model was developed by the FAA in cooperation to use the embedded database of county-level nonroad fleet with the USAF and is used to produce an inventory of emis- information, however, the underlying vehicle data were sions generated by sources on and around the airport or air extracted by the EPA for use in EDMS to allow the emis- base, and to calculate pollutant concentrations in these envi- sions for individual vehicles to be computed (U.S. EPA ronments (FAA Jul 2, 2007). 2007b). Altough EDMS has always computed CO, HC, NOx, and SOx emissions for all airport sources and PM emissions for 4.4 First Order Approximation 3.0 on-road vehicles, GSE, and stationary sources, Version 4.3 of the model introduced the ability to compute PM emissions The FOA3 was developed by the ICAO Committee on Avi- for aircraft main engines using the FOA. EDMS Version 5.0.2 ation Environmental Protection (CAEP) Working Group 3 applies the FOA Version 3.0a, where smoke number data are to estimate PM emissions from commercial aircraft engines available. Particulate matter emissions for on-road vehicles in the absence of acceptable data or emission factors. Data are computed using the MOBILE model, described below. from the APEX1 aircraft engine emission tests was used in its Similarly, PM emissions for GSE are computed using the development. Three components of PM are modeled by NONROAD model. EDMS also contains a database of PM FOA3, which uses the sum of three separate equations: a power emission factors for stationary sources that are commonly and polynomial function of smoke number for non-volatile found at airports. No data currently exist for modeling PM PM, a constant for SO4, and a function of HC emission indices from aircraft APU so EDMS only computes the other criteria for fuel organics. EDMS uses the FOA3a methodology for U.S. pollutants for APU. airports, which includes additional reasonable margins to accommodate uncertainties. FOA3a adapts the FOA3 equa- tions to be more conservative in the calculation of H2SO4 and 4.2 MOBILE fuel organics while keeping the equations the same for non- As mentioned above, EDMS uses the EPA-developed volatile PM and adding a term for lubrication oil (Kinsey and MOBILE model (Version 6.2 is included with EDMS 5.0.2) Wayson 2007).