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22 Exhibit 2-6. Example of regional-scale model estimate of cancer risk. Source: Multiple Air Toxics Exposure Study III (MATES III), South Coast Air Quality Management District at http://www.aqmd.gov/prdas/matesIII/matesIII.html. 2.3 Project-Scale Applications impacts evaluated. Under NEPA, a project must be assessed if it involves a "major federal action significantly affecting the At the project scale, freight emissions estimates can directly quality of the human environment." (24) Every project must affect the go/no-go decision for a project, or can influence be evaluated to determine whether it meets this threshold. decisions to invest in mitigation measures. Project-scale Some federal agencies maintain lists of Categorical Exclusions applications include the comparison among project alternatives (CEs) that specify project types that the agency presumes will and assessment of air quality compliance as required by NEPA not have a significant impact. Normally, CEs do not require and similar state statutes. They can include project-scale emis- detailed emissions analysis. Projects that could have a signifi- sions estimates to satisfy the Conformity Regulations. They also cant impact require either an environmental assessment (EA) can include emissions estimates for discrete freight facilities if the agency believes the potential for significant impacts is and terminals, including railyards, seaports, and airports. low or an environmental impact statement (EIS) if the agency believes the potential for significant impacts is high. The 2.3.1 NEPA and Similar State Processes methods for estimating freight emissions are essentially the same for EA and EIS, although the level of detail may be greater Requirements for an EIS. NEPA is the foundation of environmental impact analyses Most large transportation infrastructure projects--whether in the United States and usually provides the forum in which or not dedicated to freight--fall under NEPA because they project-level emission estimates are made and air quality entail funding, permitting, or other approval by a federal

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23 agency. For many projects, the application of NEPA is clear lead agency produces a single environmental impact document because federal jurisdiction occurs directly, often with several that satisfies both NEPA and the state review process. A few agencies and actions. For example, a new interstate highway municipalities have their own environmental review processes would carry truck traffic and might involve FHWA funding, that are similar to NEPA and may require similar air quality consultation on endangered species with the U.S. Fish and analysis. Wildlife Service, and wetlands permits from the Army Corps of Engineers, among others. For other freight projects, the Types of Emissions Estimated under NEPA event that triggers NEPA may not be obvious; for example, a state DOT that is sponsoring a truck stop project may support Project-level emissions analyses under NEPA and similar part of the project from FHWA grant funds. An airport may state laws focus primarily on the criteria pollutants. However, construct a cargo facility that would not require federal involve- as concern about MSATs has mounted, FHWA and state ment but the project appears on the Airport Layout Plan, DOTs have increasingly received requests for MSAT analysis and a change to the Airport Layout Plan requires approval by in agency-funded EISs. The issue of air toxics has been raised the FAA. From the NEPA perspective, most transportation with several major highway projects around the country, infrastructure projects involve emissions from multiple vehicles resulting in lengthy deliberations and, in some cases, litigation. or sources, only a portion of which happen to be hauling freight. (2526) At the same time, the FAA has also received increasing Emissions analyses under NEPA treat freight-related emissions requests for MSAT analysis in its EISs for airport projects. in greater or lesser detail depending on the magnitude and Airport projects typically involve MSAT emissions from significance of emissions from the freight-related activities multiple source classes including aircraft, on-road vehicles, and that would be served by, or affected by, the project. The level off-road sources such as aircraft ground support equipment of rigor and detail for the freight emissions analysis is largely a (GSE) and construction equipment. Experience in the early project-specific decision. 2000s with MSAT analysis for major EISs at large airports Freight railroad projects may trigger NEPA due to fund- such as Los Angeles International, (27) Chicago O'Hare (28) ing by FRA or permitting by other federal agencies as in the and Philadelphia International (29) led to FAA's issuance of highway example above. Freight railroad projects that con- interim MSAT guidance. (30) California agencies have long sist only of operational changes rather than infrastructure required MSAT analysis as well as health risk assessment in construction also may trigger NEPA if they fall under the CEQA environmental impact reports (EIRs), which are the jurisdiction of the federal Surface Transportation Board (STB). California state-level counterpart to NEPA EISs. Most projects Several types of economic actions, including certain railroad focus on priority MSATs because they represent the bulk of mergers, acquisitions, and proposals for new services over total health risk. The MATES III study identifies DPM as existing railroad lines, require STB approval and consequent the primary cancer risk factor out of all MSATs. Proximity to NEPA review. transportation facilities, typically roadways, has been estab- Several states, including Washington, Massachusetts, and lished as a primary factor leading to community exposure and California, have statutes similar to NEPA that establish state- potentially increased risk. level environmental review processes. The state-level review HAPs other than MSATs are normally not evaluated sepa- processes have various triggers that differ from state to state. rately in NEPA analyses of transportation projects. MSATs Triggers include type of project, size of project, cost of project, as a class, and priority MSATs in particular, should be good requirement for a state agency permit, and use of state funds. surrogates for all relevant HAPs because most are species of Some state processes mandate preparation of NEPA-like VOC or PM. The speciation distributions of VOC emis- documents that cover impacts to all resource areas (air quality, sions are generally similar for broad classes of transportation water quality, etc.), while other processes may include only the sources. The speciation of PM emissions differs markedly subject matter of the triggering event (e.g., a project that must between gasoline and diesel sources, but less so within the obtain an access permit for an entrance that fronts a state diesel source classes. In most cases, if emissions of priority highway might be required only to analyze traffic impacts). MSATs are insignificant, then emissions of other transporta- Projects located in California are subject to the California tion HAPs also will be insignificant and need not be analyzed Environmental Quality Act (CEQA) process. Unlike most in detail. state processes, CEQA and its implementation by California's Requests during NEPA, CEQA, and state-level scoping to air quality management districts (sub-state regional agencies include GHG emissions have become commonplace and many to which California has delegated some air quality regulatory agencies now routinely require these GHGs in project emission authority) often necessitate more complex air quality analysis estimates. The White House Council on Environmental Quality and more mitigation effort than NEPA does. In many cases, the (CEQ) issued draft NEPA guidance on climate change in 1997 state-level review proceeds concurrently with NEPA, and the that was never finalized. (31)

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24 NEPA Application: Comparison of Proposed the socioeconomic and environmental justice sections of an Project Alternatives EA/EIS, and therefore the air quality analysis would be suffi- ciently detailed to support evaluation of these resource areas. Emissions estimates are used for purposes of disclosure and Highway impacts of MSATs and PM are related mostly to agency decision making. NEPA requires that project impacts heavy-duty diesel trucks and, as a result, the freight compo- be disclosed to the public and that the sponsoring agency nent of the project emissions must be accounted for in these make a determination as to whether the impacts of the proj- analyses. ect would be "significant." Potentially, the most important Railroad projects may be entirely freight-related or may use of emission estimates is to assist the agency in selecting include passenger train movements and possibly effects on which alternative to implement from the set of project alter- highway traffic volumes due to project-induced changes in natives. In NEPA and similar processes, the alternative selec- modal shares. Port projects are usually dominated by freight tion must consider air quality impacts as well as impacts on movement and involve emissions mostly from diesel engine other resource areas. For purposes of alternative selection, the sources. For these projects, almost all of the project impact absolute magnitude of a project's air quality impact may be comes from freight. Airport emissions usually are dominated less important than the relative differences or ranking of air by emissions from passenger aircraft and GSE, followed by quality impacts among the alternatives and the directional motor vehicles accessing the airport. Air freight may be carried trend in predicted emissions over time. in dedicated cargo aircraft, which are a small proportion of Air quality impacts are characterized by emissions for the total flights at most airports, as well as "belly cargo" in overall or regional-level comparisons among alternatives and passenger aircraft. For these reasons, the emissions due to for purposes of compliance with the EPA Transportation freight as opposed to passenger operations at an airport can be Conformity and General Conformity Rules. Where localized difficult to separate within the total aircraft and GSE emissions. impacts are a concern, emissions data are used for input to The results of emissions calculations may be presented in dispersion modeling that estimates the pollutant concentra- various ways depending on the project and the intended tions at specific locations for comparison to the NAAQS and audience. Exhibit 2-7 presents an example of a table showing state standards for criteria pollutants. NAAQS have not been the emissions estimate for a single project alternative at an established for MSATs, although some states have established airport. Exhibit 2-8 presents an example of an EIS emissions guidelines for ambient MSAT concentrations. If significant comparison among all alternatives for a highway project. MSAT impacts are anticipated, the dispersion model results may be used as input to a human health risk assessment. NEPA Application: Ambient Air Quality Standards Most project-related health risk assessments are conducted in Compliance and Health Risk Assessment California under CEQA and agency processes for air quality permitting of stationary emission sources. Local air quality impacts in the project vicinity are evaluated No ambient standards exist for GHGs. Most analyses report using dispersion modeling that produces estimated pollutant GHG emissions by project alternative and may provide a concentrations at specific locations of interest (known as simple comparison of project GHG emissions to the total GHG receptors). Typical receptors include residences, health care emissions in the region or state. Climate change impacts of facilities, educational facilities, and recreational areas. The GHGs usually are treated as a cumulative impact under NEPA. estimated concentrations are compared to the NAAQS and Currently, the state of the practice for project-level GHG/ other applicable standards to determine compliance and the climate change analysis is evolving. significance of the impacts. Dispersion modeling typically is For many projects, especially highways, the emissions from conducted as part of project analysis under NEPA and similar project alternatives may differ very little in relative terms. For state review processes, but also may be performed for project- such projects, the influence of emissions on agency decisions level Transportation Conformity evaluations, applications for tends to be slight at most. This is true for both highway funding or air quality permits, and planning studies. Because projects in general and also for the portion of emissions from concentrations are being compared to numerical standards, the freight trucks, since most highway projects do not involve absolute levels of impact must be calculated and it is important dedicated truck facilities that would necessitate a separate to choose calculation methods that yield the greatest possible accounting of truck emissions. However, if the geographic confidence in the numerical results. variation of the project alternatives is large (multiple corridors The decision on whether to model the ambient pollutant or diverse communities), then the equity considerations of concentrations or health risks due to a project is based on an where the impacts would occur may loom larger in agency assessment of whether the project's impacts are likely to be review and public comment than considerations of the mag- significant. Under NEPA, the threshold of significance for nitude of emissions. These concerns often are addressed in concentrations is commonly taken to be the NAAQS. Under

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25 Exhibit 2-7. Example emissions estimate for a single alternative for an airport project. Projected Emissions (kg/Day) Source Categories VOCs NOx CO Aircraft Sources1 Air carriers 350 4,300 3,337 Commuter aircraft 61 459 640 Cargo aircraft 21 309 194 General aviation 304 61 499 Total aircraft sources 736 5,129 4,669 Ground Service Equipment2 234 294 5,670 Motor Vehicles Parking/curbside 16 5 112 On-airport vehicles 60 79 851 Total motor vehicle sources 76 84 963 Other Sources3 Fuel storage/handling 475 0 0 Miscellaneous sources 9 211 33 Total other sources 484 211 33 Total airport sources 1,530 5,717 11,335 Notes: 1 Calculations for 2020 are based on taxi times based on the proposed Airport Improvements Planning Project. 2 Includes vehicles and equipment converted to alternative fuels based on the 2004 fleet mix. 3 Includes the central heating and cooling plant, emergency electricity generation, and other stationary sources. NEPA and similar review processes, public or agency comments criteria pollutant impacts are modeled at "hotspots," which during project scoping may indicate sufficient concern to per- are locations at which relatively high emissions are expected form modeling even if impacts are expected to be insignificant. to occur due to traffic congestion. Hotspot modeling is used Some agencies have issued quantitative guidelines based on to assess impacts of CO, PM, and sometimes NOX. Typical traffic volumes, aircraft operations, proximity to receptors, or hotspot types include signalized intersections, roadway/rail similar criteria that determine whether dispersion modeling grade crossings, and other locations where queuing occurs such should be conducted for a project. At other agencies, the as toll plazas and freight terminal entrances. Most agency decision may be based on professional judgment informed by guidance specifies use of the EPA CAL3QHC model, or the precedent, the results of previous projects, or the current state California DOT (Caltrans) CALINE4 model in California. of modeling practice. Similar considerations apply to a decision Prior to dispersion modeling, potential hotspots normally are on whether to conduct a health risk assessment for a project. screened according to traffic volumes, level of service, and For highway projects and other projects involving highway queuing levels with the worst locations being selected for air traffic access (potentially almost any type of freight project), quality modeling. In the past, criteria pollutant impacts also Exhibit 2-8. Example EIS emissions comparison among alternatives for a highway project (tons/year). 2008 2012 Existing No-Build Build Build Build Pollutant Conditions Alternative Alternative 1 Alternative 2 Alternative 3 CO 74.92 76.02 82.49 78.56 79.63 VOC 2.77 2.88 3.28 3.04 3.10 NOX 1.61 2.17 2.48 2.29 2.34 SO2 0.14 0.19 0.20 0.19 0.20 PM10 4.25 4.37 4.61 4.42 4.49 PM2.5 4.01 4.03 4.12 4.04 4.06

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26 were modeled at receptors along the highway itself. Emission conformity of an action. Because the General Conformity Rules rates from motor vehicles have decreased steadily due to EPA have absolute emissions thresholds for project-related emis- regulations under the CAAA and now are so low that, in most sion increases, it is important to estimate emissions accurately cases, agencies no longer require dispersion modeling for without excessive conservatism (overestimates) and to include locations along the highway mainline if vehicles are traveling design and operational features that will help reduce emission at cruise speeds. increases below the thresholds and avoid the need for a con- For non-highway projects, projectwide dispersion modeling formity determination. for criteria pollutants is common, and the criteria pollutant If the net emission increases due to the project are less than of greatest concern usually is PM. For large projects, and where these thresholds, then the project is presumed to conform and specified by agency guidance (primarily in California), disper- no further conformity evaluation is required. If the emission sion modeling of MSATs is used to characterize concentrations increases exceed any of these thresholds, then a conformity and (again, primarily in California) to support health risk determination is required. The conformity determination assessments. The MSAT of greatest concern usually is DPM. can entail air quality modeling studies, consultation with EPA Although the PM classes PM2.5, PM10, and DPM have unique and state air quality agencies, and commitments to revise the definitions, in practice their emission rates for freight projects SIP or to implement measures to mitigate air quality impacts. are similar in terms of mass emitted, because for most freight The conformity process is separate from NEPA and other projects the primary emissions source is diesel engines and environmental reviews but, because the required technical most DPM falls into the PM2.5 size class. The most commonly studies are very similar, a conformity evaluation usually is specified models for this application are EPA's AERMOD and conducted concurrently with other environmental review CALPUFF. In California, the Hotspots Analysis and Reporting processes. Program (HARP) model combines dispersion modeling and health risk assessment processes. The dispersion component of HARP uses the EPA's ISC3 model, which is the predecessor 2.3.3 Emissions Estimates for Linear Projects of AERMOD. Transportation infrastructure projects that are linear in nature include highways, rail lines, and some waterways. 2.3.2 Project-Level Conformity These projects may span multiple state and local jurisdictions, and federal involvement is almost assured. Emissions estimates As discussed in Section 2.2, the conformity regulations are required for NEPA, sometimes for conformity, and to prevent federal actions in nonattainment or maintenance support dispersion modeling of project impacts. In California, areas that interfere with meeting the emissions targets in the they may support health risk assessments as well. Project-level SIPs or contribute to new violations of the NAAQS. emission estimates for linear transportation projects generally Most highway projects are included in a conforming regional are used only for project approval, and are not used directly transportation plan or TIP and thus are subject to Transporta- in regional emission inventories or SIPs. Exhibit 2-9 presents tion Conformity (Section 2.2.2) as part of the entire plan. typical characteristics of emission inventories for linear freight In a few limited circumstances, a project that is located in a transportation projects. Emissions are estimated separately nonattainment or maintenance area and is subject to Trans- by type of source. portation Conformity must perform a project-level conformity determination. The project-level conformity determination can entail emissions estimates, air quality modeling studies, consul- 2.3.4 Emissions Estimates for Discrete tation with EPA and state air quality agencies, and commit- Freight Facilities/Terminals ments to revise the SIP or to implement measures to mitigate Railyard Health Risk Assessments air quality impacts. This requirement creates an incentive for agencies to have a project included in the long-range trans- Locomotive emissions estimates have been used to prepare portation plan in order to avoid the need for a project-level health risk assessments (HRAs) for major railyards in California. conformity evaluation. In many cases, and almost universally BNSF and UP agreed to prepare these HRAs for 17 individ- with large highway projects, the project is included in the plan's ual railyards when they signed a statewide railroad pollution travel modeling from the outset. reduction agreement with CARB in 2005. The HRAs must The General Conformity Rules apply to all other federal be prepared based on CARB's experience in preparing the actions not covered under Transportation Conformity. General Roseville Railyard Study (32) as well as CARB guidance. (33) Conformity typically applies at the project-scale for airports Emissions are estimated for all sources within the railyards, and seaports. The General Conformity Rules established emis- potentially including locomotives, on-road trucks, cargo han- sions thresholds, or de minimis levels, for use in evaluating the dling equipment, heavy equipment, transport refrigeration

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27 Exhibit 2-9. Typical characteristics of emission inventories for freight transportation projects. Project Type Regulatory Process and Use of Emissions Estimates* Major Features of Emissions Estimates NEPA State Env. Transp. General Planning/ Typical Sources Included Construction Emissions Models Used Review Conf.** Conf.** Initiatives Emissions Linear Project Highway (in some Trucks, Cars No MOBILE6.2, MOVES (draft), states) EMFAC (in CA) Railroad (in some Locomotives, Trucks (Freight For General MOBILE6.2, MOVES (draft), states) Diversion) Conformity only EMFAC (in CA), off-model databases and calculations Waterborne (e.g., (in some Ships, Dredges, Support Vessels For General Off-model databases and Canals, Channel states) Conformity only calculations Dredging) Discrete Facility Truck Stop or S S S S Trucks For General MOBILE6.2, MOVES (draft), Terminal Conformity only EMFAC (in CA) Railyard or S S S S Locomotives, Trucks (Drayage), Cargo No MOBILE6.2, MOVES (draft), Intermodal Terminal Handling Equipment EMFAC (in CA), NONROAD, OFFROAD (in CA) Seaport (in some Ocean-Going Vessels, Harbor Craft, For General MOBILE6.2, MOVES (draft), states) Cargo Handling Equipment, Conformity only EMFAC (in CA), NONROAD, Locomotives, Trucks (Drayage), OFFROAD (in CA), off-model Stationary Sources, Electric Power databases and calculations Generation Airport (in some S Aircraft, GSE, Trucks, Cars, For General EDMS, off-model databases states) Buses/Vans, Fuel Handling, Stationary Conformity only and calculations Sources, Electric Power Generation Notes: * Process: Likely; Unlikely; S Sometimes, depending on project size and federal involvement. ** Conformity rules apply in nonattainment and maintenance areas only. units (TRUs) and refrigerated rail cars, stationary sources, and dispersion model. In addition to the emissions, meteorological portable equipment. These emission inventories, conducted factors (including wind speed and wind direction) are key by the railroads and CARB, focus on emissions of TACs-- inputs to the dispersion model. CARB multiplied the resulting primarily diesel PM, but also gasoline TACs such as isopentane, concentrations by cancer risk factors to estimate cancer risk, toluene, and benzene. expressed as the chances of excess cancer risk per million The studies start with preparation of an emission inventory, people. Cancer risk is illustrated using isopleths--lines drawn which is performed by the railroads following CARB guidance. on a map through all points of equal cancer risk. Exhibit 2-11 (34) Emissions are reported by source type, as illustrated in shows an example of this presentation. Exhibit 2-10. These railyard health risk assessments are prepared under The railroads then estimated pollutant concentrations in voluntary agreements and are not directly related to any reg- the vicinity of the railyard using AERMOD, an EPA-approved ulation or government decision-making process. However, Exhibit 2-10. Example of railyard diesel PM emissions (tons/year). % of On-Site Sources Railyard 1 Railyard 2 Railyard 3 Railyard 4 Total Total Locomotives 4.9 5.9 2.3 0.6 13.6 33% On-Road Trucks 2.0 10.1 - 1.1 13.2 32% CHE 4.8 4.2 - 0.4 9.4 22% Others 0.4 3.7 0.4 1.0 5.5 13% Total 12.1 23.9 2.7 3.1 41.7 % of Total 29% 57% 7% 7% 100%

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28 Exhibit 2-11. Example of estimated potential cancer risks from railyards (chances per million people). Source: Air Resources Board, Health Risk Assessment for the Union Pacific Railroad Commerce Railyard, November 2, 2007. Available at http://www.arb.ca.gov/railyard/hra/up_com_hra.pdf. HRA reports can influence public policy decisions in a number by the seaport or airport operators. Efforts by local seaport or of ways. The cancer risk estimates provide compelling infor- airport operators to regulate emissions are constrained by mation to community and environmental groups advocating preemption of authority by the federal government or inter- for emission controls. CARB uses this information to make national agreements, and by the need to stay competitive with decisions regarding new initiatives to reduce diesel emissions. other ports. (35) Seaport or airport operators do, however, have authority to regulate the types of ground vehicles that may access the facility and vehicle operations while within Seaport Emission Inventories the facility. Seaports and airports have a number of similarities in Like other projects, seaports and airport projects use project activities and institutional settings that affect the estimation emissions estimates for purposes of NEPA and state-level of emissions as well as the uses of the emissions inventory. Both review, public information, and conformity. In addition, seaports and airports are characterized by intermodality: seaports and airports may develop emission inventories for passengers and goods are transported overland to the facility their entire facility. An emission inventory is necessary for port and then transferred to the vehicle (aircraft or ship) for the authorities, those doing business at ports (such as terminal longer distance portion of the trip. Most of the mass emissions operators, tenants, and shipping companies), state and local of pollutants of greatest concern for freight (NOX, PM, GHGs) entities, or other interested parties to understand and quantify occur en route from the aircraft or ship rather than from the the air quality impacts of current port operations and to facility. However, the emissions from the ground access trip assess the impacts of port expansion projects or growth in may be of greatest concern for NAAQS compliance and health port activity. Because of the wide variety of vehicles and equip- risk because of proximity of receptors to roadways and rail lines. ment that operate in or near their facilities, seaport and airport Seaport or airport operators may be state agencies, public operators may use emissions estimates to identify emission authorities, municipal departments, or private firms, and, as sources, quantify their contribution to facility-related emis- such, have varying degrees of legal authority and financial sions, and evaluate potential emission reduction strategies. capability to address emissions. Private carriers (airlines, The inventory can then be used to develop strategies to mini- shipping lines) operate in public airspace or unmanaged mize current and projected emissions and to quantify progress. international waters and are largely exempt from regulation A facility emissions inventory can inform compliance with

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29 Exhibit 2-12. Example of port emission inventory, 2005 (tons/year). Category PM10 PM2.5 DPM NOX SOX CO TOG Ocean-Going Vessels 733 586 637 6,926 6,501 603 274 Harbor Craft 30 27 30 1,004 5 237 20 Cargo Handling Equipment 56 51 56 1,737 17 450 101 Locomotives 43 40 43 1,314 76 183 74 Heavy-Duty Vehicles 243 224 243 5,607 39 1,944 433 Total 1,105 928 1,008 16,587 6,638 3,416 901 regulatory requirements such as those in SIPs for criteria calculated using the FAA's Emissions and Dispersion Modeling pollutants or city/state climate action plans for GHGs, and also System (EDMS). EDMS takes as inputs the same data for each inform voluntary initiatives such as a collaborative regional individual source type as previously discussed for highway MSAT assessment or development of a seaport/airport environ- and rail projects and port facilities. EDMS calculates emissions mental management system. (36) Exhibit 2-12 presents an from airborne aircraft only up to an altitude of approximately example summary of a facility emissions inventory prepared 3,000 ft, which corresponds with the average height of the by a large seaport. atmospheric mixing layer. Emissions above this altitude gen- erally do not disperse downward to altitudes below the mixing height and accordingly have little or no influence on ground- Airport Emission Inventories level air quality. FAA is currently developing a new model, the As noted previously, seaports and airports share many Aviation Environmental Design Tool, which is planned to operational and institutional similarities. Airports prepare eventually replace EDMS. emission inventories for the same reasons that seaports do. To date, agencies are only beginning to issue guidance on The emission inventories play equivalent roles in airport how to estimate GHG emissions associated with airports. decision making. Airport-related emissions from each type of A number of methods and assumptions have been used. The source are calculated in the same way as for seaports, with the current version (5.1) of EDMS estimates CO2, but not other exception that aircraft emissions replace vessel emissions, and GHG emissions, for aircraft only. A recent attempt to com- GSE emissions replace CHE emissions. In addition, airports pile best practices is ACRP Report 11: Guidebook on Prepar- typically have large fuel storage and handling operations with ing Airport Greenhouse Gas Emissions Inventories. (37) One associated emissions from pumps, vehicles, and fuel evapora- assumption that can have a very large effect on the results of tion. Exhibit 2-7 (presented previously) shows an example of the emissions calculations is the allocation of aircraft en route a facility emissions inventory prepared by a large airport. emissions--to the departure airport, the arrival airport, or some FAA guidance specifies that airport-related emissions of combination--because these usually are the major portion of criteria pollutants and MSATs from most sources should be aviation-related emissions.