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10 airport activity is responsible for the deposition of concern Beginning June 1, 2006, refiners began producing clean to the citizens. Deposition studies have been conducted near ultra-low sulfur diesel fuel, with a sulfur level at or below Los Angeles International Airport, T.F. Green Airport 15 parts per million (ppm), for use in highway diesel engines. (Providence, R.I.), Boston Logan International Airport, Low-sulfur (500 ppm) diesel fuel for nonroad diesel engines Charlotte/Douglas International Airport, Detroit Metropol- will be required in 2007, followed by ultra-low sulfur diesel itan Wayne County International Airport, John Wayne- fuel for these vehicles in 2010.12 Stringent emissions standards Orange County Airport, Seattle-Tacoma International for new GSE will be phased in between 2008 and 2014 as part Airport, Ft. Lauderdale-Hollywood International Airport, of this rule. Whether and when similar reductions in fuel and Chicago O'Hare International Airport. None of these sulfur content will occur in aviation jet fuel has yet to be studies have shown a definitive link between the airports and determined. the deposited material. These studies commonly find the deposits are typical of the material found throughout urban areas that come from diesel trucks, construction activity, What Tools are Available wind-blown dust, pollen, and mold. This is perhaps not un- for Evaluating PM Emissions expected since the PM from aircraft and APUs is comprised at Airports? of fine or ultrafine particles, which are too small to settle As noted earlier, airport emissions are analyzed by apply- gravitationally or to be deposited by impacting stationary ing emission factors (drawn from emissions testing data of surfaces and remain suspended in the atmosphere. These representative sources) to airport-specific operational data studies are not conclusive, however, since they used differ- for various emission sources. All sources are then combined ent methodologies and many only sampled dry deposition into an "emissions inventory." Inventories are usually and did not collect material deposited through rainfall, represented in mass emissions per unit of time (e.g., lbs/day which is a primary mechanism for scrubbing suspended or tons/year). Inventories are typically compiled for criteria particles from the atmosphere. Future deposition studies pollutants and their precursors (i.e., NOx, SOx, CO, VOC, will be able to build both on these findings and on new and PM). Various analytical tools are available to support information coming from aircraft PM research to improve these complex computations and aid in analyzing the our understanding of the contribution of airport emissions results. to deposited PM. As noted earlier, little was known about aircraft PM emis- sions until recently when several federally funded research Emissions and Dispersion programs were conducted. To date, a great deal is known Modeling System13 about a few engines with no testing done on most of the engine models in the fleet. The research results are still being The Emissions and Dispersion Modeling System (EDMS) analyzed to better understand PM formation in aircraft en- is used to assess air quality at civilian airports and military air gines and its evolution in the plume. Even for those engines bases. The model was developed by FAA in cooperation with studied, more testing will be required to gain the data needed the United States Air Force (USAF) and is used to produce an to develop emission factors with the same level of confidence inventory of emissions generated by sources on and around as for emission factors used for other emission sources, which the airport or air base, and to calculate pollutant concentra- can relate operating conditions to final state PM emissions. tions in these environments. With regard to GSE, EPA has taken steps to reduce PM Particulate matter emissions are computed for aircraft emissions from nonroad vehicles. In response to national main engines in EDMS version 5.0.2 by applying the First environmental regulations, refiners will begin producing low- Order Approximation version 3.0a, where smoke number sulfur diesel fuel for use in locomotives, ships, and nonroad data are available. Particulate matter emissions for on-road equipment, which includes GSE. Low-sulfur diesel fuel must vehicles are computed using the MOBILE model, described meet a 500 parts per million (ppm) sulfur maximum. This is below. Similarly, PM emissions for GSE are computed using the first step of EPA's nonroad diesel rule, with an eventual the NONROAD model. EDMS also contains a database of PM goal of reducing the sulfur level of fuel for these engines to emission factors for stationary sources that are commonly meet an ultra-low standard (15 ppm) to enable new advanced found at airports. No data currently exist for modeling PM emission-control technologies for engines used in locomo- from aircraft auxiliary power units (APU). tives, ships, and other nonroad equipment. These most recent nonroad engine and fuel regulations complement similarly 12 Environmental Protection Agency Clean Air Nonroad Diesel Tier 4 Final Rule, http://www.epa.gov/nonroad-diesel/2004fr.htm. stringent regulations for diesel highway trucks and buses and 13 Emissions and Dispersion Modeling System Homepage http://www.faa.gov/ highway diesel fuel for 2007. about/office_org/headquarters_offices/aep/models/edms_model/.
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11 MOBILE14 model and analyze noise and emissions. Building on current tools, including EDMS, common modules and databases will As mentioned above, EDMS uses the EPA-developed allow local and global analyses to be completed consistently MOBILE model (version 6.2 is included with EDMS 5.0.2) to and with a single tool. With this tool, users will be able to ana- compute emission factors for on-road vehicles. MOBILE lyze both current and future scenarios to understand how avi- allows the user to model emission factors for a fleet of vehicle ation effects the environment through noise and emissions on types or an individual vehicle class based on the mix of vehi- a local and global scale. cle types and age, and considers vehicle speed and ambient meteorological conditions as well. Aviation Environmental Portfolio NONROAD15 Management Tool18 The Aviation Environmental Portfolio Management Tool Similar to MOBILE, EPA's NONROAD model provides (APMT) is currently being developed by the FAA as a compo- emission factors for ground support equipment at airports nent of AEDT to allow tradeoffs between noise and emissions that consider the rated horsepower of the engine, fuel type, to be better understood. The tool has three primary capabili- and the load factor. The traditional application of the model ties: (1) cost-effectiveness analysis, (2) benefit cost analysis, is to use the embedded database of county-level nonroad fleet and (3) distributional analysis. The "costs" and "benefits" are information; however, the EPA extracted the underlying computed at a societal level by considering economic and vehicle data for use in EDMS to allow the emissions for indi- health effects. vidual vehicles to be computed. First Order Approximation 3.0a16 Community Multiscale Air Quality Model19 First Order Approximation 3.0 (FOA3) is being developed by The Community Multiscale Air Quality Model (CMAQ) the ICAO Committee for Aviation Environmental Protection was developed through a NOAA-EPA partnership and (CAEP) Working Group 3 to estimate PM emissions from com- allows the analyst to model a variety of air quality effects, mercial aircraft engines in the absence of acceptable data or emis- including: tropospheric ozone, toxics, acid deposition, and sion factors. Data from the APEX aircraft engine emission tests visibility degradation. This is accomplished by including are being used in its development. FOA3 models three compo- robust modeling of the atmospheric physics and chemical re- nents of PM using the sum of three separate equations: a power actions. The scale of the model is variable with grid sizes and polynomial function of smoke number for nonvolatile PM, ranging from less than 4 km to over 36 km depending on the a constant for SO4, and a function of HC emission indices for fuel needs of the analysis. organics. EDMS uses the FOA3a methodology for U.S airports, which includes additional reasonable margins to accommodate Microphysical Models uncertainties. FOA3a adapts the FOA3 equations to be more conservative in the calculation of SO4 and fuel organics while Microphysical models refer to a class of atmospheric mod- keeping the equations the same for nonvolatile PM. els intended to predict cloud formations based on the forma- tion and size of droplets and the nucleation of particles. The same techniques used to predict water-based clouds in the sky Aviation Environmental Design Tool17 can be applied toward predicting the formation of plumes of The Aviation Environmental Design Tool (AEDT), aerosols and particulate matter. Microphysical modeling has presently under development and testing, is designed to incor- been used to model aviation PM evolution both at altitude porate and harmonize the existing capabilities of the FAA to and at ground level. 14 MOBILE 6 Homepage http://www.epa.gov/otaq/m6.htm. 15 18 Aviation Environmental Portfolio Management Tool (APMT) Prototype http:// NONROAD Homepage http://www.epa.gov/otaq/nonrdmdl.htm. 16 Kinsey, J., Wayson, R.L, EPAct PM Methodology Discussion Paper (2007). www.faa.gov/about/office_org/headquarters_offices/aep/models/ 17 Federal Aviation Administration, Office of the Environment and Energy AEDT history/media/2006-02_CAEP7-WG2-TG2-6_IP02_APMT_Prototype.pdf . News, (1:1), September 2007. 19 CMAQ Homepage http://www.epa.gov/asmdnerl/CMAQ/cmaq_model.html.