Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans (2013)

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26 This chapter offers guidance on how to prepare airport emissions inventories in support of SIPs. It is envisioned that this process can be applied by Guidebook users to all types of airports, nonattainment pollutants, and SIPs. For simplicity and ease of understanding, Figure 4-1 lists the nine recommended steps, from start to finish, for preparing an airport emissions inventory. It also serves as a guidepost for describing the individual elements of the process in the following sections. However, it is recog- nized that the applicability and sequence of each step will vary on a case-by-case basis and/or may be determined to be unnecessary altogether. 4.1 Identify Pollutants of Concern (Step 1) As described in Chapter 2, nonattainment and maintenance designations are assigned to areas that do not meet the NAAQS for any of the U.S. EPA’s criteria air pollutants (e.g., CO, NO2, etc.). It is further discussed in that section that SIPs are purposely developed to help bring these areas into attainment—focusing on those pollutants-of-concern (and their precursors) that caused or con- tributed to the violation(s). For example, SIPs for CO nonattainment or maintenance areas contain strategies for controlling emissions of this localized pollutant. By comparison, SIPs for O3 nonattainment areas are aimed at controlling emissions of NOx and volatile organic compounds (VOCs)—the two principal precur- sors to the formation of this regional pollutant. As a matter of consistency, airport emissions inventories prepared for SIPs should contain emissions data for those pollutant species for which an area is declared nonattainment or main- tenance. In other words, within CO maintenance areas, airport-related emissions of CO are the most relevant. In contrast, for O3 nonattainment areas, airport-related emissions of NOx and VOCs are the most pertinent. For ease of interpretation, Figure 4-2 provides an alphabetical listing of all six U.S. EPA criteria pollutants potentially subject to an SIP along with summary explanations of how these pollutants- of-concern (and their precursors) are typically reported as airport-related emissions. As shown, for the pollutants CO, lead, PM10 and PM2.5, the specific compound, or species, are computed; for NO2 and SO2, the broader categories of NOx and SOx are reported; and for O3, the precursor emissions of NOx and VOCs are the pollutants-of-concern and are reported. 4.2 Identify and Name Airports (Step 2) Among the most significant deficiencies uncovered in the review of existing SIPs was the inability to distinguish which airports were accounted for in the emissions inventories. As dis- cussed in Chapter 1, the majority of SIPs reviewed by the research team only identified the prin- C H A P T E R 4 How to Prepare an Airport Emissions Inventory for an SIP 5. Select Inventory Approach 6. Collect/Develop Input Data 7. Conduct Emissions Inventory 8. Conduct QA/QC 9. Report Results 1. Identify Pollutants 3. Identify Sources of Emissions 4. Identify Inventory Timeframes 2. Identify & Name Airport(s) Note: QA/QC = quality assurance/quality control. Figure 4-1. Steps to preparing an airport emissions inventory.

How to Prepare an Airport Emissions Inventory for an SIP 27 cipal airport(s) as being included or referred to airport-related emissions generically without naming any individual facilities. In other cases, the research revealed that some airports were inadvertently omitted from the inventories altogether. This oversight makes it difficult to seg- regate emissions between airports located in the same nonattainment/maintenance areas or to ensure that all airport emissions are accounted for in the SIP. Therefore, under this step, it is suggested that Guidebook users purposely identify and name the airport(s) that are to be included in the SIP and maintain this practice throughout the emis- sions inventory preparation and reporting processes. 4.3 Identify Sources of Emissions (Step 3) As shown in Figure 4-3, airports characteristically repre- sent a diverse aggregate of emissions sources: however, principal among these are aircraft, APUs, and GSE. By comparison, other, smaller sources of emissions also occur such as passenger, cargo, and employee motor vehicles; fuel storage facilities; and a wide assortment of stationary sources (e.g., back-up generators, boil- ers, etc.). Notably, construction-related emissions associated with the development of airport improvement projects are also consid- ered as an airport-related source under the CAA General Confor- mity Rule. However, as discussed in Chapter 1, this Guidebook focuses on preparing emissions inventories for aircraft, APUs, and GSE as these airport-related sources are the most significant and most commonly accounted for in SIPs. Figure 4-4 and the following sec- tions provide further details regarding these three sources of airport emissions. • Most former CO nonattainment areas are maintenance areas. • Airport-related emissions of CO are in decline. Carbon Monoxide (CO) • Nonattainment areas are localized around specific sources. • GA aircraft using leaded fuels are an important source. Lead (Pb) • SIPs address emissions of NO2 as nitrogen oxides (NOx). • By-product of high temperature/pressure aircraft engines. Nitrogen Dioxide (NO2) • Most common nonattainment pollutant across the U.S. • Airport emissions include O3-forming precursors of NOx and VOCs. Ozone (O3) • Two size ranges with NAAQS: PM10 & PM2.5 • Airport emissions include PM10/2.5 and their precursors. Particulate Matter (PM) • SIPs contain emissions of SO2 as SOx. • Airports are not considered significant sources. Sulfur Dioxide (SO2) Figure 4-2. U.S. EPA criteria pollutants. NOx Emissions VOC Emissions PM Emissions APU 3% GSE -7% Aircraft 90% APU 20% GSE-10% Aircraft 70% APU 23% GSE-13% Aircraft-64% Figure 4-3. Airport emissions sources.

28 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans 4.3.1 Aircraft Aircraft emissions primarily consist of the fuel-based exhaust products from the aircraft’s main engines. For airport emissions inventories, these emissions are calculated throughout the landing and takeoff (LTO) cycle, which encompasses the aircraft’s final approach, landing, roll, and taxing in to the terminal area while inbound, and the engine restart, taxing out, takeoff, and climb out during the outbound segment. Within the aircraft LTO cycle, emissions are mainly a function of the number of operations (i.e., LTOs); the aircraft fleet characteristics (i.e., aircraft type, number of engines, and take-off weight); and the aircraft engine operating features (i.e., fuel flow rates and emissions factors). The effects of the individual airport operating conditions and local atmospheric mixing height on the LTO time also play a role. As discussed in Chapter 3 and restated below, the approach to preparing an airport emissions inventory (i.e., Basic, Intermediate, Advanced) determines which of these data inputs are ultimately required as well as the level of detail needed to perform the emissions calculations. 4.3.2 Ground Support Equipment (GSE) Ground support equipment (GSE) typically consists of the assortment of vehicles and equipment that service aircraft while parked at gates, in hanger areas, or on airport aprons. Represen- tative examples of GSE include aircraft pushback tractors and baggage tugs; deicing, fueling, and catering trucks; belt and cargo loaders; and passenger/employee transport vehicles operating on the airside of the airport. GSE utilization and activity levels vary by airport type (e.g., commercial versus GA), aircraft type (e.g., wide body versus nar- row body), payload (e.g., passengers versus cargo) and climatic conditions (e.g., cold versus warm). GSE emissions also vary by • Exhaust products from main engines. • Largest source of airport emissions. • Generated throughout landing/take-off cycle. • Includes commercial, cargo, military, & GA. • Exhaust products from onboard engines. • Includes tractors, tugs, loaders, deicers, etc. • Function of fuel type, engine size, & run time. • Electric alternatives gaining popularity. • Provides parked aircraft with power & AC. • Exhaust products from onboard engine. • Mostly applicable to commercial aircraft. • Gate-provided alternatives growing. Note: AC = air conditioning (heating and cooling). Figure 4-4. Aircraft, GSE, and APU emissions characteristics. Reference: ACRP Report 78: Air- port Ground Support Equipment (GSE) Emission Reduction Strate- gies, Inventory and Tutorial con- tains information and data per- taining to GSE fleet populations, emissions, and operating charac- teristics at U.S. airports.

How to Prepare an Airport Emissions Inventory for an SIP 29 fuel type (e.g., diesel, gasoline, propane, electric, etc.), model year, and horsepower rating. Again, the selected emissions inventory approach (i.e., Basic, Intermediate, Advanced) determines which GSE data are necessary to compute emissions from this source. 4.3.3 Auxiliary Power Units (APUs) Auxiliary power units (APUs) are turbine engines located onboard many commercial and cargo aircraft and are used to start the main engines and provide power to the aircraft electrical equipment (including the air conditioning systems) when air- craft are taxiing or are parked at gates or apron areas. As with the aircraft main engines, APU emissions are primarily a function of engine type and operating time. If available, aircraft can also obtain power and pre-conditioned air (PCA) from either mobile ground power units (GPU) or from hook-ups at the ter- minal gate, thereby reducing the need for APUs. 4.3.4 Other Sources of Emissions In addition to aircraft, APUs, and GSE, other emissions sources also commonly exist at airports and typically consist of motor vehicles traveling to, from, and within the site; fuel storage and transfer facilities; and a wide assortment of stationary sources, including steam boilers, emergency generators, and/or fire training facilities. Construction-related activities and equipment associated with airfield and terminal area improvement projects are also considered to be a source of airport emissions. However, motor vehicle, stationary, and construction sources of emissions are usu- ally accounted for separately in SIPs and therefore are considered outside the scope of this Guidebook. For example, emissions from off-airport motor vehicle traffic (i.e., cars, vans, and busses) are commonly accounted for in mobile source emissions inventories developed for region-wide roadway networks/systems. Many stationary sources at air- ports are individually permitted to operate by state/local agencies and thus their emis- sions are routinely documented. With a few exceptions, construction-related emissions at airports are presently not quantified or reported in SIPs. 4.4 Identify Emissions Inventory Timeframes (Step 4) As discussed in Chapter 2, SIPs incorporate specific timeframes for enacting emis- sion reduction strategies, meeting interim objectives, and demonstrating progress toward attaining the NAAQS. In support of this approach, the emissions inventories contained in the SIP are typically computed for historic, existing, and/or future-year timeframes based upon when the nonattainment designations were originally estab- lished, the pollutant(s)-of-concern, and the degree of noncompliance. For overall consistency, ease of coordination, and aid in adoption, the airport emis- sions inventory should be computed for the same time periods identified in the SIP that serve as important benchmarks, milestones, and endpoints. Figure 4-5 broadly describes these targeted timetables. Early coordination between airport operators and SIP Time Periods Historic Characterizes conditions that existed when the nonattainment designation was originally established and serves as the baseline upon which the requisite emissions control targets and strategies to meet the NAAQS are set. Existing Corresponds to existing (or recently past) conditions in the nonattainment area and serves as a milestone toward achieving the objectives of the SIP and attaining (or maintaining) the NAAQS. Future Represents milestones and forecasted conditions when attainment of the NAAQS is expected to be achieved. Time intervals vary by original nonattainment designation date, pollutant(s)-of-concern, and the degree of nonattainment. Figure 4-5. Emissions inventory timeframes. References: ACRP Project 02-17, “Measuring PM Emissions from Aircraft Auxiliary Power Units, Tires and Brakes” and ACRP Report 64: Handbook for Evaluating Emissions and Costs of APUs and Alternative Systems both contain new data and information on APUs. Reference: ACRP Project 02-33, “Guidance for Estimating Airport Construction Emissions” provides guidance on calculating airport- related construction emissions.

30 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans air quality regulatory agencies will help ensure that airport emissions inventories are aligned with these SIP milestones. 4.5 Select an Emissions Inventory Approach (Step 5) Chapter 3 describes three alternative approaches for preparing airport emissions inventories for SIPs. As discussed, each approach reflects a number of features that are viewed as central to preparing the inventory and, when combined together, are easily defined, but also distinct from one another. Presented in increasing order of relative complexity, data needs, and relative accuracy, the three approaches (i.e., Basic, Intermediate, Advanced) are depicted in Figure 4-6 with their most prominent characteristics highlighted and further described below. • Basic Approach—This approach requires the least amount of input data but purposely pro- duces conservatively high results—making it the least accurate. This approach is best suited for non-hub commercial and GA airports with less than 100,000 annual operations and is the basis for the Airport Emissions Estimator Tool developed as a companion to this Guidebook (see Appendix C) (All Appendices, the Airport Emissions Estimator Tool, and other support- ing materials are available on the accompanying CD and online at www.trb.org, search for “Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans”). • Intermediate Approach—This approach is viewed as transitional between the Basic and Advanced approaches, producing results with a higher level of accuracy than the former while requiring less input data than the latter. Based upon airport-specific operational, aircraft fleet mix and airfield operational data, combined with an assortment of EDMS-default databases for GSE and APU usage, this approach is con- sidered suitable for large GA and small- to medium-hub commercial airports located in moderate nonattainment and maintenance areas. • Advanced Approach—This approach produces an emissions inven- tory with the highest levels of airport specificity, is the most data intensive, and is considered to be the most accurate. This approach is best suited for large-hub commercial airports and airports located in serious to severe nonattainment areas but can also be applied to small- to medium-hub and GA airports where advanced levels of precision and airport specificity are desired. Basic Approach • Requires least amount of airport-specific data. • Creates conservatively high emission estimates. • Suited for GA and non-hub airports with <100,000 operations. • Paired with the Airport Emissions Estimator Tool (see Appendix C). Intermediate Approach • Data needs are in-between the Basic and Advanced approaches. • Accounts for airport-specific operating characteristics. • Uses EDMS default data for aircraft engines, APUs & GSE. • Applicable to small- and medium-hub airports. Advanced Approach • Requires greatest amount of input data. • Produces highest level of emission inventory accuracy. • Airport operational, meteorological, APU and GSE data are airport-specific and not EDMS default values. • Recommended for large hub airports and where greater airport specificity is desired. Figure 4-6. Airport emissions inventory approaches. Reminder: When computing air- port emissions inventories, accu- rate and airport-specific results are preferred over generalized or con- servatively high estimates. How- ever, other factors and consider- ations may impede this objective.

How to Prepare an Airport Emissions Inventory for an SIP 31 Chapter 3 also identifies a number of important considerations, or factors, which will likely be evaluated and decided upon by the preparers of airport emissions inventories in choosing an approach. These include the expertise of the preparer; the area nonattainment designation; the airport type, function, and activity level; and the benefits/costs to conduct the analysis. The principal advantages and disadvantages of each approach are also identi- fied and discussed. Finally, a decision-tree diagram is provided to aid Guidebook users in the approach selection process. 4.6 Collect/Develop Input Data (Step 6) In the five preceding steps, Guidebook users are first advised to consider (1) the pollutant(s)- of-concern for the nonattainment/maintenance area, (2) the individual airports to be included, (3) the airport emissions sources, (4) the assessment time periods, and (5) the alternative approaches for preparing airport emissions inventories for SIPs. In this way it is expected that the subsequent steps (Steps 6 through 9), which are, by comparison, more data- and labor-intensive, can be accomplished more deliberately and effectively. Presented separately according to the three alternative approaches (e.g., Basic, Intermedi- ate, Advanced) contained in this Guidebook, this section describes the input data and sup- porting information considered necessary for preparing an airport emissions inventory. For consistency, these data needs are individually listed in Table 4-1–segregated by approach emissions source (i.e., aircraft, APUs, and GSE) and input parameter (e.g., fleet mix, operat- ing time, etc.). 4.6.1 Basic Approach Data Needs As previously discussed, the Basic Approach is the simplest approach for computing an airport emissions inventory and requires the least amount of input data. The data needs only constitute (1) the airport’s aircraft operational levels and (2) a generalized aircraft fleet mix. Conservative Data Needs Approach Basic Intermediate Advanced Aircraft • Operations □ □ □ • Fleet Mix □ □ □ • Times-In-Mode □ □ □ • Engine Type □ □ □ Auxiliary Power Units • Assignment □ □ □ • Operating Time □ □ □ Ground Support Equipment • Equipment Type □ □ □ • Fuel Type □ □ □ • Aircraft Type □ □ □ • Operating Time □ □ □ Meteorology • Mixing Height □ □ □ • Ambient Temperature □ □ □                    Table 4-1. Airport emissions inventory data needs.

32 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans assumptions regarding the aircraft engine assignments, airfield taxi/ delay times, and APU/GSE use are inherent to this approach and therefore these input data are not required. To facilitate the preparation of an airport emissions inventory using the Basic Approach, an Airport Emissions Estimator Tool has been developed as a companion to this Guidebook (see Appendix C). The sources for the input data for the Basic Approach and the Esti- mator Tool are briefly discussed below. For ease of reference, Table 4-2 provides references to Appendix B where additional details on these input data and their sources may be obtained. • Aircraft Operations—For the Basic Approach, aircraft operations input data are subdi- vided among four operational categories: (1) air carrier, (2) air taxi/commuter, (3) general aviation and (4) military. These data are most easily obtainable for those airports within the FAA’s National Plan of Integrated Airport Systems (NPIAS) that have an airport traffic control tower (ATCT). For these airports, FAA databases such as the Air Traffic Activity Data System (ATADS) and the Terminal Area Forecast (TAF) con- tain annual operational data. Other recommended data sources include a current Airport Master Plan, a Federal Aviation Regu- lations (FAR) Part 150 Noise Study, or an Environmental Impact Statement/Assessment (EIS/EA) for the airport(s) of interest, if they are up to date and available. For NPIAS airports without an ATCT, again, a recent airport-specific study or the TAF are likely sources of data, where available. For non-NPIAS airports, or in those cases where the above- mentioned data sources are unavailable for an NPIAS airport, a recent airport study, the airport’s Form 5010 Airport Master Record (AMR), or an Airport System Plan (ASP) prepared by a state/local transportation agency may contain operational data for the airport(s) of interest. For future-year operational data, Guidebook users are similarly directed to either a recent airport study or the TAF for NPIAS airports (with and without an ATCT) and to an ASP or the FAA Aerospace Forecast for all other airports. • Aircraft Fleet Mix—As discussed above, the airport operational data for the Basic Approach are segregated into (1) air carrier, (2) air taxi/commuter, (3) general aviation and (4) military cat- egories. Accordingly, the same sources identified for these air- craft operations data also provide the aircraft fleet mix. For further reference, Appendix C describes how the Estima- tor Tool was developed and provides the outcome of an analysis demonstrating the conservative nature of the tool’s results. 4.6.2 Intermediate Approach Data Needs As discussed previously, the Intermediate Approach involves direct use of the FAA’s EDMS. Input data include the level of air- craft operations and the fleet mix; however, for the Intermedi- ate Approach, the details for these two primary parameters are greater than for the Basic Approach. Again, for ease of reference, Time Period Aircraft Operations Fleet Mix Historic/ Existing Appendix B Figure B-2 & Table B-1 Same as Operations Future Appendix B Figure B-3 & Table B-2 Same as Operations Table 4-2. Basic approach input data. Reminder: When using FAA or airport-specific sources for aircraft operational and fleet mix data, it may be important to note whether the data is for the calendar- or fiscal-year time period. Reference: Appendix C describes how the Emissions Estimator Tool was developed and provides the outcome of an analysis demon- strating the conservativeness of the results. Idea: Early coordination between airport operators and air quality regulatory agencies will help ensure that airport emissions inventories are aligned with significant SIP mile- stones discussed in Chapter 2.

How to Prepare an Airport Emissions Inventory for an SIP 33 the input data required for the Intermediate Approach are listed in Table 4-3, including refer- ences to Appendix B where the data sources are identified, and are discussed below. • Aircraft Operations—Under this approach, aircraft operations input data are the same as those identified for the Basic Approach. That is, ATADS and the TAF contain these data for NPIAS airports with an ATCT. Again, recent airport studies (e.g., Airport Master Plan, Part 150 Study, EIS/EAs) are also recommended sources for these data. However, unlike the Basic Approach, these aircraft operations input data must be segre- gated in EDMS by aircraft type (e.g., Boeing) and model (e.g., 737-700 series) under this approach. Examples of these data sets are provided in Table 4-4. • Aircraft Fleet Mix—As with the aircraft operational data discussed above, the aircraft fleet mix are also segregated by aircraft type and model. However, to achieve the fleet mix level of detail shown in Table 4-4, a variety of additional data sources may be required to obtain the engine model (explained further below). Commercial service airport data sources include (but are not limited to) a recent airport study, an Airport Noise and Operations Monitoring System (ANOMS), the U.S. Bureau of Transportation Statistic (BTS) Schedule T-100, and FAA’s Enhanced Traffic Management Sys- tem Counts (ETMSC). For future-year fleet mix data, it is suggested that Guidebook users consult a recent Master Plan Study and/or the FAA Aerospace Forecast for the airport(s). Time Period Aircraft Meteorology Operations Fleet Mix Times-In-Mode Mixing Height Historic/ Existing Appendix B Figure B-2 and Table B-1 Appendix B Figure B-4, Tables B-3 and B-5 Appendix B Table B-6 National Climatic Data Center (NCDC) or Local Agency Future Appendix B Figure B-3 and Table B-2 Appendix B Table B-4 Appendix B Table B-6 NCDC or Local Agency Table 4-3. Intermediate approach input data. Category Model Engine Operations Air Carrier Airbus A320-200 Series Boeing 727-200 Series Boeing 767-200 Series Airbus A320-200 Series V2527-A5 JT8D-15 CF6-80A V2527-A5 1,500 4,000 500 2,500 Air Taxi/ Commuter Embraer ERJ145 Saab 340-A Gulfstream G500 Bombardier CRJ-200 AE3007A1E CT7-5 BR700-710A1-10 CF34-3B 10,000 5,000 6,500 7,500 GA Bell 206 JetRanger Bombardier Learjet 45 Cessna 750 Citation X Piper PA-31 Navajo 250B17B TFE731-2-2B AE3007C Type 2 TIO-540-J2B2 1,200 2,400 500 3,600 Military Boeing F/A-18 Hornet Boeing KC-135 Stratotanker F404-GE-400 CFM56-2A series 700 2,500 Table 4-4. Example EDMS aircraft model, engine, & operations input data.

34 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans For GA airports, a recent airport study, ATCT flight strips/ counters, and fixed-base operator logs may contain these aircraft fleet mix data. • Aircraft Engine Type—It is the intent of the Intermediate Approach to use the EDMS “default” engine information. For example, within EDMS the default engine for a Boeing 737-700 series is the CFM56-7B22 engine. However, not every aircraft in EDMS has a “default” engine selection available. In these instances, the Official Airline Guide (OAG) Aviation Database and the JP Airline-Fleets International Database (JP Fleets) can be consulted. • Aircraft Times-In-Mode—Airport-specific taxi-in and taxi-out times can be obtained from FAA’s Aviation System Performance Metrics (ASPM) and the BTS On-Time Statistics, if this informa- tion is available. Although EDMS offers “default” taxi times for a variety of aircraft types, the application of airport-specific taxi times by this Guidebook users can greatly improve the emissions inventory estimates. • Meteorology—Under the Intermediate Approach, EDMS is run in the “performance” mode, which automatically adjusts the aircraft times-in-modes during the approach, takeoff, and climbout periods based on other parameters defined by the user (e.g., atmospheric mixing height, temperature, relative humidity, and elevation). For the atmospheric mixing height, which defines the vertical limit of the aircraft LTO, EDMS uses a default value of 3,000 feet above ground level (AGL) if the user does not define an airport- specific value. Guidebook users can contact the state/local air agency to determine if a more appropriate mixing height should be used to develop the SIP airport emissions inventory. 4.6.3 Advanced Approach Data Needs The Advanced Approach also involves the use of the FAA’s EDMS but takes much greater advantage of the model’s ability to produce results that are airport specific. In addition to modeling the airport’s operational levels, aircraft fleet mix and airfield operating conditions in more detail than the Intermediate Approach, this approach also accounts for the airport’s unique GSE and APU fleets and operating characteristics. Again, for ease of reference, the input data required for the Advanced Approach are listed in Table 4.5, including references to Appendix B where these data sources are identified and are dis- cussed below. • Aircraft Operations—For the Advanced Approach, the sources of aircraft operations input data are essentially the same as those identified for the Intermediate Approach and include ATADS and the TAF for NPIAS airports with an ATCT. Recent airport studies (e.g., Airport Master Plan, Part 150 Study, EIS/EA’s) and airport simulation models, such as SIMMOD and TAAM, are again recommended sources of these data. Note: When using EDMS, there is no single resource of input data for computing airport emissions. Rather, several sources of data must be consulted and, in some cases, the data processed. Note: Under the Intermediate Ap- proach, Guidebook users have the option of using EDMS default data or airport-specific data for ground- based taxi times and atmospheric mixing height. Key Point: When preparing a future-year airport emissions inven- tory, the aircraft operational fore- casts are “key.” As discussed in ACRP Synthesis 2: Airport Aviation Activity Forecasting and Appendix B of this report, these forecasts are based upon parameters that are time- sensitive and subject to change. Therefore, this Guidebook suggests that these future-year forecasts be adjusted using the “TAF+10” approach, whenever justified. For example, for a 2015 emissions in- ventory, use 2025 TAF operational levels; for 2020, use 2030 opera- tional levels, etc. (see Appendix E). In this way, estimates of future- year emissions are conservatively high enough to account for the uncertainty inherent to these fore- casts but not overly conservative resulting in an emissions inventory that is entirely disproportionate or in other ways wholly misrepresen- tative of potential conditions.

How to Prepare an Airport Emissions Inventory for an SIP 35 For future-year operational levels, FAA-approved forecasts are contained in the TAF for NPIAS airports with ATCTs. Greater details are also contained in airport-specific studies where available, and may account for airport plans that are unaccounted for in the TAF. Forecast studies prepared for smaller GA airports tend to rely on trend extrapolation or market share analyses. • Aircraft Fleet Mix—Under this approach, the aircraft fleet mix data should enable the iden- tification of aircraft/engine combinations as discussed previously, as well as other parameters that reflect aircraft movement throughout the airfield (i.e., which gates, runways, and taxiways are utilized during an aircraft LTO cycle). To this end, simulation models such as SIMMOD or TAAM, supplemented with Intermediate Approach data sources including ANOMS, BTS Schedule T-100, ETMSC, and data from OAG Aviation or JP Fleets should be used. Used in conjunction, these data sources can provide insight on the level of operations by aircraft cat- egory (e.g., air carrier), airframe model (e.g., Airbus A320-200), and engine (e.g., V2527-A5), all of which are required inputs under this approach. It is also recommended that the future-year aircraft fleet mix used under the Advanced Approach should account for the future replacement of older aircraft with newer aircraft. These data can be derived using industry-wide forecasts or airport-specific studies. • Times-In-Mode—As discussed above, the Advanced Approach requires the use of EDMS in its “performance” mode. However, in addition to the ASPM or BTS for airport-specific taxi times, Guidebook users can consider using the output from airfield simulation modeling analyses (e.g., SIMMOD, TAAM, or EDMS’s Delay and Sequence Module). Under the Advanced Approach, the user can also consider adjusting aircraft takeoff and/ or approach weights in the EDMS to increase the accuracy of the emissions estimate for the takeoff, climbout, and approach modes of the aircraft LTO. • Meteorology—Users of the Advanced Approach have the option of using hourly meteoro- logical data (surface and upper air data from the NCDC) instead of “default” average weather Time Period Aircraft Meteorology Operations Fleet Mix Times-In-Mode Engine Type Mixing Height Ambient Temperature Historic/ Existing Airport Data Appx B, Fig. 2 Existing Operational Data Appx B, Fig. 4 FAA Databases or Simulation Models EDMS or OAG/JP Fleets NCDC or Local Agency NCDC Future Airport Data Appx B, Fig. 3 Future Operational Data Appx B, Fig. 3 FAA Databases or Simulation Models EDMS or OAG/JP Fleets NCDC or Local Agency NCDC Time Period Ground Support Equipment Auxiliary Power Units Equipment Type Fuel Type Aircraft Type Operating Time Assignment Operating Time Historic/ Existing Airport Data Airport Data EDMS (Default) Airport Data or EDMS Airport Data or EDMS Airport Data or EDMS Future Airport Data Airport Data EDMS (Default) Airport Data or EDMS Airport Data or EDMS Airport Data or EDMS Table 4-5. Advanced approach input data.

36 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans data contained in EDMS. The atmospheric mixing height can also be determined from NCDC databases or by consulting the state/local agency preparing the SIP. • Ground Support Equipment—Airport-specific GSE fleet data can be obtained from in-the- field surveys and/or equipment inventories compiled by the airport operator, airlines, cargo carriers, and GSE providers. Information pertaining to the GSE type (e.g., baggage tractor, deicer, belt loader, etc.); horsepower; manu- facturer, model, and year; and fuel type are useful inputs for users adhering to the Advanced Approach. GSE utilization data by aircraft size/type (e.g., narrow body, wide body, and commuter) and operat- ing time are also desirable. Terminal area gate infrastructure such as hydrant systems or pre- conditioned air (PCA) units should be noted during the field surveys, as these devices typically reduce the usage and operating conditions of some GSE such as fuel trucks and portable air conditioners. Finally, cargo, GA, and military GSE usage should also be surveyed if these types of opera- tions represent a large proportion of the total aircraft operations at the airport. • Auxiliary Power Units—For aircraft that use APUs (i.e., commercial and commuter), EDMS automatically assigns an APU make and model and by default assigns the APU an operating time of 13 minutes on arrival and 13 minutes on departure—for a total of 26 minutes per LTO cycle. However, under the Advanced Approach, airport-specific APU operating times should be considered. If in-the-field surveys reveal ground power/gate power and PCA are available at the airport, the assumed APU operating times and their emissions can be reduced significantly. For some nonattainment SIPs, air quality agencies will use the airport emissions inventory results as input data to atmospheric dispersion models such as the Urban Airshed Model. In these instances, additional data describing the temporal and spatial characteristics of the airport- related emissions are called for, as follows: • Temporal Profiles—Temporal profiles describe how aircraft operations vary over time (e.g., monthly, daily, hourly, etc.). These data can be obtained or developed from sources such as the FAA Operations Network (OPSNET) database, ANOMS data, and/or ATCT counts. • Spatial Data—The spatial data describe the geographic and/or vertical locations of the air- port-related emissions sources relative to common reference points (e.g., airport centroid or distance above sea level). These data can be obtained from ALPs and/or the Universal Trans- verse Mercator (UTM) system. This Guidebook is aimed principally at producing airport emissions inventories and, therefore, the additional data requirements for dispersion modeling need to be obtained elsewhere. 4.7 Conduct Emissions Inventory (Step 7) Upon the completion of the input data development and collection process described above, the airport emissions inventory should be computed. The appropriate method for conducting the inventory is dictated by the selected approach. • Basic Approach—To facilitate the preparation of an airport emissions inventory using the Basic Approach, the Airport Emissions Estimator Tool has been developed as a companion to this Guidebook (see Appen- dix C). Therefore, it is suggested that Guidebook users utilize this Tool for computing the airport emissions inventory under this approach. Idea: Airport-specific data collected on GSE and APU use can improve emissions estimates from these sources significantly. Idea: While the nonattainment pol- lutants (and their precursors) are of primary importance for the SIP, other criteria pollutants can be computed using the Emissions Esti- mator Tool or EDMS with no addi- tional effort.

How to Prepare an Airport Emissions Inventory for an SIP 37 • Intermediate Approach—The Intermediate Approach involves use of the FAA’s EDMS. Therefore, it is suggested that Guidebook users utilize EDMS for computing the airport emissions inven- tory under this approach. • Advanced Approach—The Advanced Approach also involves direct use of the FAA’s EDMS and it is again suggested that Guidebook users utilize EDMS for computing the airport emis- sions inventory under this approach. In all three cases, the emissions inventory should be computed for the individual airport(s), time period(s), emissions sources, and pollutant(s)-of-concern identified in Steps 1 through 4 described above. (Note: Air emissions included in the EDMS output but generally not addressed in SIP emissions budgets include carbon dioxide (CO2), total hydrocarbons (THC), non-methane hydrocarbons (NMHC), and total organic gases (TOG).) 4.8 Conduct QA/QC of Input and Output Data (Step 8) Because the preparation of an airport emissions inventory involves the development and pro- cessing of input data, selecting among alternative choices or commands and interpreting results, unforeseen errors can occur. Failure to identify and correct these errors will result in an over- or underestimation of emissions from airport-related sources. Therefore, it is suggested that Guidebook users perform QA/QC procedures on both the input data and the results prior to incorporating the airport emissions inventory into SIPs. Table 4.6 provides a listing of some of the most common errors that are expected to occur when preparing airport emissions inventories. Also shown are the resultant consequences and the remedies to these errors. Note: EDMS will be replaced by the Airport Environmental Design Tool (AEDT) in 2013. However, this will not change the application of the Guidebook. Error Consequence Remedy Airport Operational Levels Operations are not converted to LTO cycles or vice versa. Emissions are over- or under- estimated. Make proper conversions. (2 operations = 1 LTO) Aircraft Fleet Mix Incorrect aircraft/aircraft engine combination selected (Advanced) Aircraft emissions are over- or underestimated. Check and correct input data, if necessary. Atmospheric Mixing Height Default value of 3,000 feet is used when another value is more appropriate (Inter./Adv.) Aircraft emissions are over- or underestimated. Coordinate with state/local agency for correct mixing height values. GSE & APU Input Default GSE fleet mix selected for one or more aircraft types (Adv.) GSE emissions are over- estimated. Check and correct input data, if necessary. Default APU assignments selected for aircraft types (Adv.) APU emissions overestimated. Check and correct input data, if necessary. EDMS Set Up Metric units are selected instead of English units (Inter./Adv.) Resulting emissions computed as metric- instead of short-tons. Check and correct input data, if necessary. Incorrect analysis year selected in EDMS (Inter./Adv.) GSE emissions are overestimated since emission factors for GSE are based on NONROAD modeling for specific years. Check and correct input data, if necessary. Note: Inter. = Intermediate, Adv. = Advanced. Table 4-6. Common errors when preparing airport emission inventories.

38 Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans 4.9 Document and Report Results (Step 9) Once the Guidebook user has prepared an airport emissions inventory using one of the three recommended approaches (i.e., Basic, Intermediate, Advanced), the results should be tabulated, documented, and prepared for inclusion in the SIP. However, because air quality regulatory agencies use a variety of means for recording airport-related emissions in SIPs, airport/agency coordination on this matter is suggested as discussed in Chapter 5. As a means of harmonizing the documentation and reporting methods, Table 4-7 provides a simplified example format for compiling the emissions inventory data. This format can be modi- fied and/or expanded upon as necessary to meet the needs of the stakeholders. Nevertheless, the emphasis should be placed on identifying the airport(s), pollutant type(s), emissions sources, and time period(s) that the emissions inventory results represent. For clarification, the terms used in Table 4.7 are defined as follows: • Emissions “X”—These are the pollutant(s)-of-concern for the nonattainment/maintenance area for which the SIP applies (see Section 4.1). These consist of the U.S. EPA criteria pollut- ants and/or their precursors: “X” = CO, NOx, VOCs, etc. • Airport “Y”—This is the name of the airport for which the airport emissions are computed (see Section 4.2): “Y” = airport name. • Source Category—These are the emissions sources that are included in the airport emissions inventory (see Section 4.3). These sources consist of aircraft, APUs, and GSE. • Year—This is the historic, existing, and/or future year for which the airport emissions are computed (see Section 4.4). As discussed, the airport emissions inventory should coincide with the same time periods identified in the SIP that serve as important benchmarks, milestones, and endpoints. Years “1,” “2,” and “3” represent the years of the emissions inventory (e.g., 2012, 2015, etc.). • Totals—These values represent the subtotals and totals of the emis- sions inventory by source category, pollutant type, and year. For SIP purposes, the reporting units are typically in tons per year but can vary (e.g., metric tons per year, pounds per day, kilograms/day, etc.). Supporting documentation for the airport emissions inventory is recommended and should include a listing or description of the overall approach, data sources, and assumptions that were relied upon to complete the analysis. This information and data can be summarized in a brief technical memorandum or as a detailed technical report. Airport “Y” Emissions “X” Year “1” Year “2” Year “3” Source Category Aircraft • Aircraft Engines - - - • Auxiliary Power Units (APUs) - - - Aircraft Totals -- -- -- • Ground Support Equipment (GSE) - - - Airport Totals --- --- --- Table 4-7. Example airport emissions inventory reporting format. Idea: As discussed in Chapter 5, coordination between airport operators and air quality regula- tory agencies will help ensure that airport emissions inventories are properly documented and recorded in the SIP.