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Suggested Citation:"Chapter 4 - Primer on Models." National Academies of Sciences, Engineering, and Medicine. 2008. Summarizing and Interpreting Aircraft Gaseous and Particulate Emissions Data. Washington, DC: The National Academies Press. doi: 10.17226/14197.
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Page 19
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Suggested Citation:"Chapter 4 - Primer on Models." National Academies of Sciences, Engineering, and Medicine. 2008. Summarizing and Interpreting Aircraft Gaseous and Particulate Emissions Data. Washington, DC: The National Academies Press. doi: 10.17226/14197.
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Page 20

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19 A primary potential application of the APEX data is to aid compilation of airport emissions inventories. Inventories are typically compiled for criteria pollutants and their precursors (i.e., NOX, SOX , CO, VOC, and PM). Various analytical tools, described in this chapter, are available to support the complex computations and aid in analyzing the results. 4.1 Emissions and Dispersion Modeling System The EDMS is a combined emissions and dispersion model for assessing air quality at civilian airports and military air bases. The model was developed by the FAA in cooperation with the USAF and is used to produce an inventory of emis- sions generated by sources on and around the airport or air base, and to calculate pollutant concentrations in these envi- ronments (FAA Jul 2, 2007). Altough EDMS has always computed CO, HC, NOx, and SOx emissions for all airport sources and PM emissions for on-road vehicles, GSE, and stationary sources, Version 4.3 of the model introduced the ability to compute PM emissions for aircraft main engines using the FOA. EDMS Version 5.0.2 applies the FOA Version 3.0a, where smoke number data are available. Particulate matter emissions for on-road vehicles are computed using the MOBILE model, described below. Similarly, PM emissions for GSE are computed using the NONROAD model. EDMS also contains a database of PM emission factors for stationary sources that are commonly found at airports. No data currently exist for modeling PM from aircraft APU so EDMS only computes the other criteria pollutants for APU. 4.2 MOBILE As mentioned above, EDMS uses the EPA-developed MOBILE model (Version 6.2 is included with EDMS 5.0.2) to compute emission factors for on-road vehicles. MOBILE allows the user to model emission factors for a fleet of vehicle types or an individual vehicle class based on the mix of vehi- cle types and age, and considers vehicle speed and ambient meteorological conditions as well (U.S. EPA 2007a). 4.3 NONROAD Similar to MOBILE, EPA’s NONROAD model provides emission factors for ground support equipment at airports that consider the rated horsepower of the engine, fuel type, and load factor. The traditional application of the model is to use the embedded database of county-level nonroad fleet information, however, the underlying vehicle data were extracted by the EPA for use in EDMS to allow the emis- sions for individual vehicles to be computed (U.S. EPA 2007b). 4.4 First Order Approximation 3.0 The FOA3 was developed by the ICAO Committee on Avi- ation Environmental Protection (CAEP) Working Group 3 to estimate PM emissions from commercial aircraft engines in the absence of acceptable data or emission factors. Data from the APEX1 aircraft engine emission tests was used in its development. Three components of PM are modeled by FOA3, which uses the sum of three separate equations: a power and polynomial function of smoke number for non-volatile PM, a constant for SO4, and a function of HC emission indices for fuel organics. EDMS uses the FOA3a methodology for U.S. 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 fuel organics while keeping the equations the same for non- volatile PM and adding a term for lubrication oil (Kinsey and Wayson 2007). C H A P T E R 4 Primer on Models

4.5 Aviation Environmental Design Tool The Aviation Environmental Design Tool (AEDT), presently under development and testing, is designed to incorporate and harmonize the existing capabilities of the FAA to model and analyze noise and emissions. Building on current tools, including EDMS, common modules and databases will allow local and global analysis to be completed consistently and with a single tool. With this tool, users will be able to analyze both current and future scenarios to understand how aviation affects the environment through noise and emissions on a local and global scale (FAA Sep 2007). 4.6 Aviation Environmental Portfolio Management Tool The Aviation Environmental Portfolio Management Tool (APMT) is currently being developed by the FAA as a com- plement to AEDT to allow tradeoffs between noise and emissions to be better understood. The tool has three primary capabilities, cost effectiveness analysis, benefit-cost analysis, and distributional analysis, computed at a societal level by considering economic and health effects. The AEDT noise and emissions computation modules can be directly exercised by APMT over a range of scenarios to allow a statistically sig- nificant result to be produced (FAA 2006). 4.7 Community Multi-Scale Air Quality Model The Community Multi-Scale Air Quality Model (CMAQ) was developed through a NOAA-EPA partnership and permits modeling of chemistry and transport of emissions on a re- gional scale to follow a variety of air quality effects, including tropospheric ozone, toxics, acid deposition, and visibility degradation. This is accomplished by including robust mod- eling of the atmospheric physics and chemical reactions. The scale of the model is variable with grid sizes ranging from less than 4 km to over 36 km (2.5 miles to over 22.3 mi), depend- ing on the needs of the analysis (U.S. EPA Sep 19, 2008). 4.8 Microphysical Models Microphysical models refer to a class of kinetic models that follow the formation (nucleation) and evolution of par- ticles interacting with condensable gases. Microphysical models are often used to simulate atmospheric processes and are designed to predict cloud properties based on the forma- tion and size of the resulting aerosol particles. The same techniques used to predict water-based clouds in the sky can be applied to predict the formation of plumes of aerosols and PM in engine exhaust. Microphysical models have been used to simulate aviation PM evolution both at altitude and ground level. 20

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TRB’s Airport Cooperative Research Program (ACRP) Report 9: Summarizing and Interpreting Aircraft Gaseous and Particulate Emissions Data explores a series of government-sponsored aircraft emissions tests that were undertaken to gain a better understanding of gaseous and particulate emissions from aircraft engines.

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