Improving Ground Support Equipment Operational Data for Airport Emissions Modeling (2015)

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17 C H A P T E R 3 This chapter contains an overview of airport GSE emissions inventories including what they are, how they are computed, and how the results are applied. Also discussed are suggestions for accomplishing the work based on real-world experience and practical considerations. 3.1 What Is a GSE Emissions Inventory? In general terms, an airport emissions inventory is a quantitative assessment of the types and amounts of emissions generated by the various sources of emissions associated with the airport. As discussed in Chapter 2, for airport emissions inventories, the types of emissions most often comprise the U.S. EPA criteria pollutants11 (and their precursors) but can also include hazardous air pollutants12 (HAPs) and/or greenhouse gases13 (GHGs). The outcome of an airport emissions inventory containing GSE emissions can be organized and presented in a variety of tabular and/or graphical formats depending on the application. Table 3 and Figure 2 present two typical presentation styles. The amounts of emissions are typically expressed as the mass (i.e., weight) of pollutants gener- ated over a specified timeframe (i.e., day or year) or activity level (i.e., number of aircraft opera- tions, passengers, etc.). In metric units the results are typically reported as kilograms/day (Kg/day) and expressing the individual source contributions as a percentage (%) is also common. For airports, the sources of emissions commonly include aircraft main engines, APUs, GAVs,14 fuel facilities, stationary sources (i.e., boilers, generators, live-fire training facilities), and GSE. 3.2 How Is an Airport GSE Emissions Inventory Computed? For an airport GSE emissions inventory, the results are typically based on the types (i.e., bag- gage tugs, pushback tractors, etc.) and number of GSE included in the inventory, the frequency or duration of use (i.e., minutes), their fuel types (i.e., gasoline, diesel, etc.), and the correspond- ing emission rates (i.e., CO kg/hr.) Figure 3 provides a schematic overview and further explana- tion of these components. GSE Emissions Inventories 11 The U.S. EPA “criteria” pollutants are pollutants for which there are National Ambient Air Quality Standards (NAAQS) such as carbon monoxide (CO), lead (Pb), ozone (O3), etc. In the case of O3, precursor pollutants include volatile organic compounds (VOCs) and nitrogen oxides (NOx). 12 HAPs are pollutants for which there are no NAAQS, but are regulated and of concern in connection with their potential effects on human health; HAPs comprise air pollutants such as benzene, naphthalene, toluene, etc. 13 GHGs are pollutants that are of concern because of their role in climate change and include carbon dioxide, methane, etc. 14 GAV comprise cars, trucks, vans, buses, and other motorized means of accessing/egressing the airport by patrons and employees.

18 Improving Ground Support Equipment Operational Data for Airport Emissions Modeling 3.2.1 FAA’s Aviation Environmental Design Tool (AEDT) The current, and most often used in North America, tool for computing an airport GSE emis- sions inventory is the FAA’s AEDT version 2b). Notably, AEDT replaced FAA’s Emissions & Dispersion Modeling System (EDMS) in March of 2015.15 AEDT currently computes airport GSE emissions of the following pollutants: CO, NO2, par- ticulate matter of 10 and/or 2.5 micrometers in diameter (PM10/PM2.5), SOx, and VOC. AEDT also offers two primary options for computing airport GSE emissions, described and expressed as formulas as follows: • Aircraft/gate GSE assignment option—Under this option, aircraft-specific GSE assignments (i.e., diesel aircraft tug) are made to individual aircraft types (i.e., B737-400) with correspond- ing operating times (i.e., 4 minutes) and emission factors (i.e., CO, kg/hr.) (see Equation 1). The default fleet of GSE automatically assigned to an aircraft are indicated by a checked box Table 3. Airport emissions inventory results. Table 3 Airport Emissions Inventory Results Sources Pollutants (tons/year) CO VOC NOx SOx PM10 PM2.5 Aircraft 718 146 482 59.7 7.3 7.3 APUs 22.8 1.6 12.7 2.2 2.2 2.2 GSE 81.8 6.3 51.0 0.4 5.9 5.7 Stationary sources 3.6 0.2 4.3 0.1 5.9 5.7 Motor vehicles 261 6.2 35.1 0.8 2.6 1.2 Totals 1,087 160 585 63.1 78.2 76.6 Aircra 90% APU 3% GSE 7% Figure 2. Airport NOx emissions. An equipment inventory accounts for the various types of GSE servicing an aircraft/airport, including the types of fuel or energy they use, their engine size and age, and power setting. The manner in which GSE are utilized to service aircraft or airport functions, as well as the frequency, are also important parameters. Equipment inventory, utilization, and activity information are factored against pollutant emissions rates to estimate a quantity of emissions generated from GSE operations. Emissions 1. Equipment Inventory 3. Emissions Rates 2. Utilization & Activity Figure 3. What is a GSE emissions inventory? 15 AEDT, https://www.faa.gov/about/office_org/headquarters_offices/apl/research/models/aedt/

GSE Emissions Inventories 19 which can be changed by unchecking/checking the box to remove or add GSE. The default GSE operating times can also be changed by clicking and overriding the given values. (Nota- bly, the horsepower and load factors are based upon the individual GSE type.) Aircraft/Gate GSE Assignment Option , , ,m E P L tp a p g g g a g g Aa ∑= ∈ Equation 1 where mp,a = the mass (in grams) of pollutant, p, emitted from all GSE assigned to aircraft Aa = the set of GSE assigned to aircraft, a Ep,g = the emission factor for pollutant, p (in grams per horsepower-hour) for GSE, g Pg = the rated power (in brake horsepower) of GSE, g Lg = the load factor (unitless) of GSE, g ta,g = for aircraft a, the number of hours GSE operates during one operation • GSE population-based option–Under this option, the airport GSE fleet is programed into AEDT by inputting the GSE type (i.e., aircraft tractor), the population (or count), the operat- ing times (annually or hourly), fuel type (i.e., gasoline, diesel), horsepower and load factor (see Equation 2). (Notably, gate assignments can also be provided for dispersion modeling purposes). GSE Population-Based Option , ,m E P L N tp g p g g g g g= Equation 2 where mp,g = the mass (in grams) of pollutant, p, emitted annually from GSE, g Ep,g = the emission factor for pollutant, p (in grams per horsepower-hour), for GSE, g Pg = the rated power (in brake horsepower) of GSE, g Lg = the load factor (unitless) of GSE, g Ng = the population of GSE, g (number of units included in the study) tg = the time (in hours) that each unit of the population of GSE, g, operates annually Importantly, airport GSE can be also added to the AEDT that presently do not exist in the model databases. This is accomplished by providing the GSE name/model (i.e., diesel fuel truck), the operating time (minutes) and the appropriate emission factors. AEDT currently incorporates emissions factor data from the U.S. EPA NONROAD model.16 NONROAD is a database of emissions factors for a wide array of nonroad vehicles and equip- ment such as construction, farm, and lawn equipment; boats and other marine vessels; and airport GSE. 3.2.2 GSE Emissions Inventory Applications For the purposes of this guidebook, there are three primary types or applications of airport GSE emission inventories that are most often prepared. The type of inventory is determined in 16 U.S. EPA NONROAD Model, http://www.epa.gov/oms/nonrdmdl.htm

20 Improving Ground Support Equipment Operational Data for Airport Emissions Modeling large part on how the results are to be applied. For ease in communicating their principal char- acteristics, Figure 4 provides a synopsis of each one followed by a summary discussion. As shown on Figure 4, the intent and use of a GSE emissions inventory may differ depending on whether the application is for an airport-specific Air Quality or Sustainability Management Plan (AQMP/SMP), a NEPA or CAA document, a State Implementation Plan (SIP), or a fund- ing application. Airport AQMP and SMP efforts are underpinned by the need to establish a baseline of emissions that (1) aids in the quantification of emissions, including those related to GSE; and (2) identifies potential emissions reduction opportunities focusing on the targeted emission sources. By comparison, compliance-driven airport emissions inventories are prepared to address federal regulations such as NEPA or any equivalent state-level directives. NEPA applications include the disclosure of emissions (and potentially concentrations via atmospheric dispersion modeling), as well as adherence to mitigation measures potential resulting from the approval of an Environmental Assessment (EA) or Environmental Impact Statement (EIS). SIPs are required of state and local air quality control governance to remedy violations of the NAAQS in EPA-designated nonattainment and maintenance areas. These plans include emis- sions inventories of all emissions sources operating in EPA-designated air quality nonattain- ment areas, including GSE.17 Likewise, for airports operating in nonattainment areas, federally • Air Quality Management Plan (AQMP) / Sustainability Management Plan (SMP) - Provide for a "baseline" or future scenario of GSE emissions to the end of identifying and assessing the effects of in-place and/or alternative emissions reduction opportunities undertaken by an airport and/or its tenants. Air Quality Planning Support • NEPA & CAA Requirements - Prepared to demonstrate adherence to pertinent air quality regulations involving GSE emissions or for disclosing projects/actions that require environmental approval under NEPA or the CAA. • State Implementation Plan (SIP) - Prepared by airports or air quality agency to quantify GSE emissions for use in SIP air emission budgeting, air quality modeling, and assessment of emission control efforts required in EPA-designated nonattainment/maintenance areas. Environmental & Air Quality Compliance Support VALE Grants - Prepared by airports for submittal to the FAA for funding of alternatively fueled GSE and/or its infrastructure under the VALE program as a means of reducing GSE emissions. Funding Support Figure 4. Airport GSE emissions inventory applications. 17 ACRP Report 84: Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans, outlines best prac- tices, data sources, tools, and methodologies an airport or GSE operator can use to ensure that airport-related emissions are properly accounted in a SIP.

GSE Emissions Inventories 21 sponsored or obligated projects/actions that would effect a change in the airport’s emissions must demonstrate compliance with the SIP under the CAA General Conformity Rule. In addition, the Airports Council International (ACI) Europe has promulgated the Airport Carbon Accreditation program, which is a voluntary program that enforces the accreditation criteria for airports on an annual basis. Airports that desire to become accredited have their GHGs (i.e., carbon footprints) independently verified in accordance with ISO14064 (Greenhouse Gas Accounting). Currently, 25.9% of the global air passenger traffic has been certified under this program. 3.3 Considerations and Approaches to Preparing a GSE Emission Inventory For guidebook user convenience and to account for the range of factors that are suggested to be considered when preparing an airport GSE emissions inventory, this section describes three alternative approaches. Notably, each approach contains a common set of features that are viewed as key to preparing a GSE emissions inventory, but they are otherwise distinct from one another. Arranged in increasing order of relative complexity (i.e., from the simplest to the most complex), these strategies are briefly described here in terms of their most prominent characteristics. 3.3.1 Basic Approach The basic approach is the simplest approach and is likely to provide the most conservatively high estimate of an airport’s GSE emissions inventory. This is because the GSE data are somewhat generalized and are based upon conservative assumptions. Specifically, the basic approach relies on AEDT default values regarding the GSE fleet mix, fuel types, and use times. Requiring the least amount of input data, the basic approach is best suited for airports with small GSE fleets or applications where a high degree of accu- racy is not necessary. 3.3.2 Intermediate Approach The intermediate approach is viewed as transitional between the basic and advanced approaches by producing results with a higher level of accu- racy than the former while requiring less input data than the latter. Based on some airport-specific GSE data, this approach also relies on default databases within AEDT for GSE engine types and emission characteristics, but utilizes input data such as the GSE fleet mix to reflect actual airport conditions. The intermediate approach is generally considered suitable for larger GSE fleets and/or where more accurate results are desired when compared to the basic approach. 3.3.3 Advanced Approach Using the AEDT, the advanced approach produces an airport GSE emissions inventory with the highest level of airport specificity and is considered to be the most accurate. Rather than rely- ing on default input parameters, this approach requires the greatest levels of expertise and effort Basic Approach • Requires least amount of airport-specific data. • Relies on AEDT default data. • Creates conservatively high emission estimates. • Suitable for small GSE fleets and applications where high levels of accuracy are unnecessary. Intermediate Approach • Data needs are in-between the basic and advanced approaches. • Accounts for airport-specific GSE fleet mix. • Uses AEDT default data for GSE operating characteristics. • Applicable to larger GSE fleets and/or where more accurate results are desired.

22 Improving Ground Support Equipment Operational Data for Airport Emissions Modeling by the preparer and is the most data intensive. Data requirements include (but are not limited to) the GSE fleet mix model and fuel types and operating times. This approach is best suited for large-hub commercial airports but can also be applied to small-to-medium hub and general aviation (GA) airports where advanced levels of accuracy and airport specificity are desired. 3.3.4 Factors to Consider When Choosing an Approach To aid the preparers of airport GSE emissions inventories in evaluating and choosing an approach, this section discusses several of the most impor- tant factors, or issues, that will likely be encountered, weighed, and decided upon by the users of this guidebook. For ease of reference, Figure 5 also pro- vides a simple matrix that couples these considerations with the alternative approaches described earlier. • Preparer expertise—The chosen approach to conducting an airport GSE emissions inventory will likely depend in large part on the expertise of the preparer. In some cases, it is expected that the preparer will possess a high level of knowledge and experience related to computing emissions for airport sources (e.g., aircraft, GSE, APUs). In other cases, it is assumed that the users may only have a general understanding of airports (and GSE) and be comparatively less accomplished conducting an emissions inventory. Importantly, this three-level characterization should not be misconstrued to mean that those with low levels of expertise only use the basic approach and those with high level expertise only use the advanced approach. Rather, it is intended to serve as a signal to the preparer of the airport GSE emissions inventory that their expertise should correspond as closely as pos- sible to the level of the analysis, particularly in those cases that are data intensive and a high level of accuracy is required. • Accuracy—By general definition, accuracy is a function of how close the computed results are to actual values. Therefore, it is the quality of the input data that determines the level of accuracy of the airport GSE emissions inventory (i.e., the quality data in, quality data out analogy). In other words, the use of airport-specific GSE data that are up-to-date and suf- ficiently detailed is expected to produce results that are more accurate than an assessment that relies on a set of generalized assumptions. Again, the data inputs to the GSE emissions inventory such as equipment type, fuel use, and operating time are all important variables in this regard. Advanced Approach • Requires greatest amount of input data. • Produces highest level of GSE emissions inventory accuracy. • Uses airport-specific GSE fleet mix and operational data. • Suggested for large GSE fleets and/or airports when greater specificity and accuracy are desired in the results. Figure 5. Airport GSE emissions inventory approach factors.

GSE Emissions Inventories 23 • Data needs and availability—Of the factors and considerations given to preparing an airport GSE emissions inventory, the availability of input data and supporting information is poten- tially one of the most meaningful and limiting. For example, aircraft and GSE fleet data (e.g., fleet mix, utilization times, etc.) can vary widely between airports of similar size and func- tion. Likewise, among airports of comparable size, the GSE fleet mix can also differ markedly according to the principal air and cargo carriers serving the airport. The fleet mix and operat- ing parameters will also change over time due to technological advancements and/or varying market conditions. To further demonstrate the significance of this consideration, Table 4 provides a partial listing of the data expected to be required when preparing an airport GSE emissions in- ventory using this guidebook. As shown, these data mainly reflect the AEDT GSE inventory options (see Section 3.2.1), the GSE fleet mix, and other operational conditions. • Preparation time and costs—The preparation time and financial costs for preparing an airport GSE emissions inventory are determined in large degree by the approach selected to complete the work. Therefore, it follows that under the basic approach where the input data needs are comparatively limited, the preparation time and costs are expected to be lower when con- trasted against the advanced approach, which involves an array of additional input data. Among the other variables that can potentially affect the preparation time and costs for conducting the analyses is the availability of the required input data. In other words, the collec- tion, development, and preparation of the input data for the GSE emissions inventory require research and analyses that are additive to computing the results. For example, airport-specific GSE fleet mix, fuel type, and operating time data are typically collected from the equipment owners or developed from field surveys. In other cases, the fore- casting of airport operational levels, predicting aircraft fleet mix data, or foreseeing APU/GSE utilization under future-year conditions involves additional research and development time, also adding to the overall costs. Data Needs Description Approach Basic Inter. Advanced Aircraft/Gate GSE Assignment Option Aircraft type Aircraft types by model (i.e., B777, A380, etc.) GSE type GSE types by model (i.e., baggage tug, etc.). Fuel type GSE engine fuel type (gasoline, diesel) Operating times Engine-on times (i.e., minutes) Horsepower Brake horsepower Load factor 0 to 100% Age Date of manufacture GSE Population Option GSE type GSE types by model (i.e., baggage tug, etc.). GSE count No. of GSE by type (i.e., 3 baggage tugs) Fuel type GSE engine fuel type (i.e., gasoline, diesel) Operating times Engine-on times (i.e., hours) Horsepower Brake horsepower Load factor 0 to 100% Age Date of manufacture Table 4. Airport GSE emissions inventory data needs.

24 Improving Ground Support Equipment Operational Data for Airport Emissions Modeling • Other factors—As discussed above, SIPs are prepared to help guide areas with unacceptable air quality into compliance with the NAAQS. Because airport emission inventories (including GSE emissions) are included in SIPs, the airport area’s attainment/nonattainment/maintenance classification and degree of nonattainment are important considerations when selecting an approach. Emissions inventories and control measures are incremen- tally more rigorous in SIPs prepared for nonattainment areas with more severe nonattainment designations compared to those with lower classifi- cations. As a result, preparers of emissions inventories for airports located within severe and extreme nonattainment areas should consider using the approaches that produce the most accurate results. 3.3.5 GSE Emissions Inventory by Fuel Consumption GSE emissions inventory can be estimated by the total volume of fuel consumed by GSE. Using the EPA’s NONROAD model, the fuel flow in grams per horsepower-hour can be obtained. An appropriate fuel flow can be identified for each GSE by using the type of fuel and horsepower rating of the engine and converting into gallons per horsepower-hour. The total volume of fuel consumption can be calculated as a product of total hours of operation of each GSE and fuel flow. The total fuel flow can then be used to calculate GHG emissions. However, drawbacks to this method include difficulty in obtaining fuel consumption information from airports. 3.4 Selecting an Approach Section 3.3 introduced the three suggested approaches to preparing an airport GSE emissions inventory and briefly discussed their most prominent characteristics. Based on this information, this section is intended to aid guidebook users in choosing the most appropriate approach for their airport(s). 3.4.1 Benefits versus Costs Ultimately, the process of formulating and selecting an approach for preparing an airport emissions inventory becomes a compromise, or balance, as shown in Figure 6, between the ben- efits of obtaining results that are as accurate and as airport-specific as possible while considering the overall costs in terms of the input data, manpower and time required to complete the work. In some cases, this benefit/cost decision is also a function of who is preparing the inventory and for what purpose. For example, preparers of an airport GSE emissions inventory for large-hub commercial air- ports located in severe O3 nonattainment areas are more incentivized and enabled to conduct a higher level (i.e., more detailed) analysis commensurate with the need for accurate and defensible results. By comparison, preparers of GSE emissions inventories for small/medium hub airports located in attainment areas may possess less incentive and have fewer resources to conduct such detailed analysis. In other instances, airport staff may have multiple airports or an array of other non-GSE emissions sources to quantify but limited resources and time to complete the work. Finding the suitable balance and selecting the appropriate approach to preparing an airport emissions inventory is typically achieved by evaluating the array of factors discussed in Section 3.3.4 and weighing the benefits and costs of each one individually, then as a group. However, because there is no one approach that fits all for preparing airport emissions inventories, the decision is usually made on a case-by-case (i.e., airport-by-airport) basis. Note—Nonattainments are listed in the USEPA Green Book of Non- attainment Areas by pollutant, state, and county, http://www.epa. gov/airquality/greenbook/ Figure 6. Balancing benefits and costs of approach selection.

GSE Emissions Inventories 25 3.4.2 Making a Selection As above in Section 3.3, there are a number of factors to consider when formulating an approach to preparing an airport emissions inventory, and in Section 3.3.4 the pros and cons of each approach are identified. This section serves as a final distillation of the decision-making process to aid guidebook users in the selection process. Using two important variables, Figure 7 comprises a simple decision-tree diagram to further assist in the selection process. As shown, guidebook users are first urged to take into account the airport size and function (e.g., small, medium, large-hub or GA) and then the assessment’s required level of accuracy. Following this course, the scale of the airport’s GSE emissions are appropriately matched to the tiered approach and the user is able to determine the desired accu- racy of the emission inventory results. Start Small Airport or Aainment Area Large to Med. Airport in Nonaainment Area Large Airport in Nonaainment Area Most Accurate Results Desired Advanced Approach Moderately Accurate Results Acceptable Intermediate Approach Conservavely High Results Acceptable Basic Approach Or Yes Or Yes Or Yes NoNo NoNo Figure 7. Airport GSE emissions inventory approach selection decision-tree diagram.