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Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories (2009)

Chapter: Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies

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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
×
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Suggested Citation:"Chapter 3 - Emissions Calculations and Application of CO2 Equivalencies." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories. Washington, DC: The National Academies Press. doi: 10.17226/14225.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

19 This chapter provides instructions on how to calculate GHG emissions and CO2 equivalencies. The sections are arranged by source with emissions calculations followed by calcula- tion procedures for creating CO2 equivalencies. Further back- ground information on the methods used can be found in Appendices C and D. Since the majority of GHG emissions at most airports is generated by aircraft and GAVs, different methods of evalu- ation for these specific sources are provided. For aircraft and GAV, the evaluation focused mainly on three of the six Kyoto pollutants (CO2, CH4, and N2O), since these sources emit little or no amount of the other pollutants (HFC, PFC, and SF6). In large part, this is due to the lack of data for these other pol- lutants. In general, if the data are lacking (or not established) for a pollutant in each source category, that pollutant is not addressed in the respective section. The purpose of the method levels and the structure of this Guidebook is to pro- vide airport operators with evaluation methods that can be matched with the resources and data that are most com- monly available. Generally, the higher the method number, the more detailed the data that are required to undertake the analysis. Most of the emissions calculations for each source are based on estimating or obtaining fuel use (or activity) information and then multiplying by the appropriate GHG emission factor, as follows: Emission factors should be obtained from reliable sources such as IPCC, EIA, USEPA, etc. Emission factors from these different sources may vary but the differences will likely be small. For consistency, the same data sources and methods should be used, especially if tracking changes over time. Some representative emission factors are presented in the following sections, but it is the inventory developer’s responsibility to make sure all emission factors are appropriate; this includes Emissions fuel use or activity emission f= ( ) × actor( ) being up to date and specific to each fuel type. For example, emission factors for some of the lesser-used fuels (e.g., ethanol, biodiesel, etc.) can be found in the same sources that provide data for gasoline and diesel. The inventory developer is also responsible for determining when to use more appropriate (i.e., more specific, as reflected in the highest method level) data when available rather than more generalized data (as related to a lower method level). It is not the intention of this Guidebook to suggest a single set of emission factors but to allow the inventory developer to determine the most appropriate emission factors based on the needs of the emissions inventory. Although the use of continuous emissions monitoring (CEM) equipment to more accurately determine emission factors might be possible for some sources, this Guidebook does not directly address their use. CEM use is feasible for some sources (e.g., stationary sources), but the use of mea- sured data is not necessary for airport inventories because the data for significant sources (e.g., aircraft and GAVs) either are usually available or reasonable approximations of them can be made. This Guidebook identifies preferred methods for each source to prepare inventories. Recognizing that one size does not always fit all, alternate methods are also identified, especially for situations where data are not available to enable use of the preferred method. Table 3-1 summarizes the preferred and alternate methods for each source documented in the follow- C H A P T E R 3 Emissions Calculations and Application of CO2 Equivalencies Although guidance is provided on how to cal- culate GHG emissions, the inventory developer is ultimately responsible for making sure the data and methods presented herein (or referred to) are appropriate for the airport.

• Method 1: Use fuel sales data for the airport to calculate total emissions for all departure flights. Fuel sales should represent Jet A (or other jet fuels) as well as Avgas fuels. • Method 2: Use fuel sales data in combination with meth- ods or models to separately calculate LTO emissions. This method enables the emissions to be separated by those occurring from aircraft in the local environment (as defined by the LTO cycle) and those outside the local environment (referred to as cruise). These data also re- flect APU use, and, in some contexts, are referred to as residual/cruise/APU. • Method 3: Rather than using fuel sales data, this method relies on models capable of calculating fuel consumption ing sections (to point them out clearly, the preferred methods are listed in bold in the following sections). The methods overviewed in Table 3-1 correspond to the pollutants categorized under Level 2 reporting (i.e., the six Kyoto pollutants), but mainly focus on CO2, CH4, and N2O. These methods currently do not encompass life-cycle analy- sis, which is outside the scope of the Guidebook. Also, for clarity, the term method is used to refer to the hier- archy of methods adopted in this Guidebook for calculating emissions for each source. In contrast, IPCC uses the term tier to describe their hierarchy of methods. For example, Method 1 refers to a lower fidelity method (lower relative to the methods identified herein) adopted as part of this Guidebook, while Tier 1 refers to a lower fidelity method from IPCC (lower rel- ative to Tiers 2 or 3). 3.1 Aircraft The calculation of aircraft emissions closely follows, but is not identical, to the methods prescribed in IPCC. The fol- lowing methods are recommended herein: 20 Aircraft emissions calculations closely follow the tiered IPCC guidelines. FAA is expected to begin releasing Method 3 data publicly in the near fu- ture for airport operator use. Thus, it may be the preferred method for U.S. airports. Source Comments Preferred Method Alternate Method Aircraft Methods 2 or 3, depending on availability and quality of data; Method 3 is subject to FAA availability of data Method 1 APU In preparing this Guidebook, new sources were identified that may be superior to Method 2. FAA has volunteered to make these data available for public use as described under Method 3. Method 2, with APUs included as part of cruise emissions Method 1 GSE Method 2, using the noted models Method 1 GAV Need to carefully consider the utility of running models like MOBILE6.2 (USEPA 2002). If the vehicle- specific VMT data are not available, no fidelity is gained from using MOBILE6.2. Method 3 and the noted models Method 1 or 2 Stationary Sources— Combustion Activities Method 2 stationary source fuel use and specific emission factors Method 1 Stationary Sources— Facility Power (Purchased Electricity) Always falls under the Scope 2 category Power demand and local emission rate Power demand and EPA eGRID rates Stationary Sources— Waste Management Activities USEPA’s WARM with appropriate activity data NA Training Fires Fire training fuel and suppressant data NA Construction USEPA’s NONROAD or equivalent model NA Table 3-1. Summary of preferred and alternate methods by source.

and emissions associated with all modes of flight includ- ing cruise. Section 2.3 of this report discussed three levels of evaluation relative to various pollutants. For aircraft, sources of prepar- ing a Level 1 inventory (CO2 only) or Level 2 inventory (all six Kyoto pollutants) were identified. As information for many criteria pollutants is generally not available for all phases of aircraft flight, a complete Level 3 analysis is not possible. 3.1.1 Aircraft Method 1 This method relies on the use of aircraft fuel sales data with appropriate emission factors to calculate emissions. Aircraft fuel sales refers to the gallons or pounds of fuel dispensed at an airport, sometimes called aircraft fuel uplift (uplifted to aircraft). Although this is the overall method, as shown in Figure 3-1, two GHG quantification approaches are described exemplifying the use of different conversion factors. The choice of these two methods depends on how the fuel sales data are reported. These data may be obtained from several organizations, including the airport properties division, the fuel consortium, airport fixed-based operators, etc. If they cannot provide the data directly, it is likely that they will be able to specify the appropriate contact. For this calculation, the inventory developer must obtain total fuel sales data, which is typically available from the fuel providers at an airport. This information can then be con- verted to CO2 emissions using typical emission factors such as the following: • Jet A fuel = 21.095 lbs CO2 per gallon Jet A (EIA 2008) and • Avgas = 18.355 lbs CO2 per gallon of Avgas (EIA 2008). The following provides a sample calculation assuming 20,000 gallons of Jet A fuel consumption: To convert pounds to metric tons, the total pounds of CO2 should be multiplied by 0.0004536 metric tons/lb. Thus, It is important to note that some fuel sales are reported in pounds of fuel sold and not in gallons. Depending on local conditions, 1 gal of Jet A fuel generally weights 6.84 lbs, but Avgas (100LL) generally weighs 6.0 lbs/gal. These conversions are recommended to ensure calculation consistency. Similar to CO2 calculation, emissions of CH4 and N2O can be calculated using the following generic emission factors provided by the USEPA’s Climate Leaders (USEPAa 2005), which have been adopted by TCR: • Jet fuel = 0.27 g CH4/gal fuel, • Aviation gasoline = 7.04 g CH4/gal fuel, • Jet fuel = 0.21 g N2O/gal fuel, and • Aviation gasoline = 0.11 g N2O/gal fuel. Thus, for the 20,000 gal of Jet A fuel in the preceding ex- ample, 5,400 g of CH4 (20,000 gal × 0.27 g/gal = 5,400 g) and 4,200 g of N2O (20,000 gal × 0.21 g/gal = 4,200 g) would be emitted. The quantity in grams can be converted to metric tons by multiplying the grams by 0.000001 metric ton/g. Thus, in the example, 0.0054 ton of CH4 and 0.0042 ton of N2O would be emitted. The use of fuel sales data will prevent double counting at each airport since only the fuel used at an airport (i.e., for departure) will be used to represent GHG emissions at that airport. None of the methods recommended herein account for fuel tankering as such data are not publicly available. Fuel tankering is the practice of purchasing more fuel than necessary to fly an aircraft from one airport to the next. In general, it represents an economic strategy to take advantage of lower fuel costs in certain regions. Depending on where the tankering is conducted (i.e., based on fuel prices at dif- ferent locations), a GHG inventory could either under- or overestimate aircraft GHG emissions from departure flights at an airport when using fuel sales data. An issue to be considered in using fuel sales data is whether the inventory should or needs to identify the effects of vari- ous policies such as fuel taxes. For an airport located in city X (Airport X), if a notable number of flights tanker fuel, the emissions quantified using fuel sales could be understated rel- ative to the fuel required to power flight for Airport X. Thus, 421,900 lbs CO metric tons lb2 × = 0 0004536 191 . .4 metric tons CO2 CO Emissions 20,000 gal 21.095 lbs CO ga2 2= ( ) × l lbs CO2 ( ) = 421 900, 21 Airport Fuel Sales Data Emission Factors and Other Data as Necessary Calculate Total Aircraft GHG Emissions Figure 3-1. Overview of Aircraft Method 1.

fuel associated with those flights could be similarly overstated at the airports where the flights originated (Airports Y and Z). This might be illustrated when comparing the fuel or emissions re- sults of Method 3 with those of Methods 1 or 2. The leakage of emissions (i.e., the consequence of policies that result in a local decrease due to the policy but increase emissions elsewhere) caused by the fuel tax policy could only be captured through a comparison of the fuel required by actual flight (as estimated by Method 3) as compared to the fuel dispensed at an airport. 3.1.2 Aircraft Method 2 This method involves using the same fuel sales data as in Method 1, but improving the resolution of the data by calcu- lating LTO emissions separately, as shown in Figure 3-2. Fig- ure 3-2 shows the cruise derivation being performed with emissions, but it can also be conducted with fuel consump- tion before computing emissions. In air quality evaluations, flight operations in the local envi- ronment are referred to as the LTO cycle. One aircraft LTO cycle is equivalent to two aircraft operations (one landing and one takeoff). The standard LTO cycle begins when the air- craft crosses into the mixing zone (about 3,000 ft altitude) as it approaches the airport on its descent from cruising alti- tude, lands, and taxis to the gate. The cycle continues as the aircraft taxis back out to the runway for takeoff and climbs out to cross the mixing zone. The operating modes in a stan- dard LTO cycle are as follows: • Approach—portion of flight from the time the aircraft reaches the mixing height or 3,000 ft altitude and exits the runway; • Taxi/idle-in, taxi/idle-out (often combined into taxi/idle/ delay)—time aircraft is moving on the taxiway system until reaching the gate, and on departure from the gate until tax- ied on to the runway; • Takeoff—the roll down the runway through lift-off up to about 1,000 ft; and • Climbout—the departure segment from takeoff until exit- ing the mixing height or 3,000 ft. The LTO cycle has been used extensively in modeling cri- teria pollutants (e.g., CO, NOx, etc.). Therefore, the same methods for each of the pollutants apply in this method. Unless other methods are available, the FAA’s AEDT/EDMS (FAAa 2007) can be used to estimate fuel consumption dur- ing the LTO cycle, as well as to estimate the criteria pollutants emitted in this operating phase. The LTO-based fuel con- sumption information can be used with the appropriate emis- sion factors noted in Method 1 to calculate emissions for CO2, CH4, and N2O. AEDT/EDMS (on the layer titled “Aircraft by Mode”) reports the fuel burn by each aircraft type in units that can be selected by the user, ranging from grams to short tons. Thus, the fuel sales data and the LTO aircraft fuel burn from AEDT/EDMS must be converted to common units— either gallons of fuel or pounds are preferred, as noted in the Method 1 discussion. Using the LTO-based fuel consumption produced by AEDT/ EDMS (or derived LTO emissions) and the total fuel sales data (or derived total emissions), cruise fuel consumption (or the derived cruise) emissions can be determined as follows through difference: • Cruise emissions = (total emissions) – (LTO emissions) or • Cruise fuel consumption = (total fuel sales) – (LTO fuel consumption) For example, if the fuel sales data noted that 20,000 gallons of Jet A fuel were sold at the airport, and the AEDT/EDMS run for the airport indicated aircraft consumed 1,670 gal- lons (reported as 5,181 kg) in the LTO mode, this calcula- tion would indicate 18,330 gal were consumed during cruise (20,000 − 1,670 = 18,330). As a result, 175.4 metric tons of CO2 (18,330 gal × 21.095 lbs CO2/gal fuel × 0.0004536 metric ton/lb) emissions would be attributed to cruise. 22 Disaggregating the emissions into LTO and cruise allows for better tracking of emissions over time. Airport Fuel Sales Data Emission Factors and Other Data as Necessary Calculate Aircraft Cruise GHG Emissions Aircraft LTO Fuel Consumption Total Aircraft GHG Emissions AEDT/ EDMS Subtract Calculate Aircraft LTO GHG Emissions Aircraft Method 1 Figure 3-2. Overview of Aircraft Method 2.

Using Method 2 would improve the Method 1 evaluation by allowing emissions to be reported in a disaggregated form (LTO and cruise). As a result, tracking of these emissions over time would be improved. 3.1.3 Aircraft Method 3 Unlike the other methods, Method 3 does not rely on the use of fuel sales information to provide (encompass) cruise fuel use. Rather, Method 3 involves the use of sophisticated methods/models to predict fuel usage for the entire flight as shown in Figure 3-3. Although some European methods/models exist, the pre- mier U.S. model that should be used is the FAA’s AEDT/ System for Assessing Aviation’s Global Emissions (SAGE) (FAAb 2005). AEDT/SAGE and other models that could be used for this Method 3 require extensive information about the aircraft fleet, flight schedules, trajectories, and aircraft performance. Note that while preparing this report, concern was expressed with the accuracy of fuel sales data to reflect fuel consumed in a flight segment because some flights may tanker fuel for use on later segments. At this time, it is not possible to estimate how fuel sales may compare to the fuel burn evaluation computed by AEDT/SAGE. Currently, AEDT/ SAGE is a research tool and is not available to the general public. However, the FAA intends to make fuel burn and CO2 data (totals for each airport) available in the following form for each U.S. airport: • Ground level (reflecting the previously defined taxi/idle mode), • Above ground to below 3,000 ft (reflecting the takeoff, climb-out, and approach modes), • Above 3,000 ft (reflecting cruise), and • Total. The FAA AEDT/SAGE-based aircraft fuel burn and CO2 data are expected to be made available on an annual basis for each U.S. airport and, as such, could be the preferred aircraft emissions method. Both fuel consumption and CO2 emis- sions data are available, and the data are expected to be fur- ther separated into domestic and international categories. The stratification by the different modes (ground, above ground, above 3,000 ft, and total) is expected to enable airport opera- tors and other parties to identify the effects of various actions on emissions on aircraft operations in these general geo- graphic areas. The fuel data can be used with appropriate emissions factors (see Section 3.1.1) to calculate emissions of CH4 and N2O. 23 The AEDT/SAGE data are 100% consistent with EDMS results for the LTO cycle (except for startup emissions) and are also consistent with the EPA’s national GHG inventory. Aircraft LTO GHG Emissions Aircraft Cruise GHG Emissions AEDT/SAGE Airport Inventories Figure 3-3. Overview of Aircraft Method 3. Due to the model integration work under the FAA’s AEDT project, both AEDT/SAGE and AEDT/EDMS use common computational components. Hence, the aircraft LTO fuel con- sumption (below 3,000 ft) computations from AEDT/SAGE are identical to those from AEDT/EDMS except for the start-up emissions, which are currently only modeled in AEDT/EDMS and not in AEDT/SAGE. Also, since AEDT/SAGE inventories are currently used by the USEPA as part of the U.S. national GHG inventory development, the AEDT/SAGE airport data promulgated as part of this method is fully consistent with the national inventory. Note the following information about backcasting and forecasting. For airports that require either a backcast or fore- cast condition, it is likely that the FAA AEDT/SAGE dataset will not include the data that the analysis may require. Thus, there may be some inconsistencies between the existing inventory (if reflecting the FAA’s Method 3 or AEDT/SAGE data), and the use of Method 1 or Method 2 for backcast or forecast con- dition. This can be handled in one of two ways. First, airport operators could note that the backcast and forecast condi- tions are prepared with differing methods, reflecting the state of available data. Alternatively, an airport could prepare its existing inventory using Method 2 and compare the results to the FAA’s Method 3 (AEDT/SAGE) dataset for the same year. One difference in the results could be due to fuel tankering (fuel transported on the aircraft that is being used for later flight segments). Another could just have to do with the pre- cision of the methods. The purpose of this comparison would be to identify any substantial variances in the fuel sales data relative to the Method 3 (AEDT/SAGE) calculation and use that information to assist with adjusting the Method 2 back- cast and forecast analysis. Using a Method 2 approach for the backcast and forecast, the results of the Method 2 data could be adjusted in a manner reflecting the variance. It needs to be

reiterated that care must be taken when backcasting and/or forecasting since the data (e.g., source activities, emission fac- tors, etc.) to support these processes may not be very accurate. 3.1.4 Other Pollutants For some of the pollutants in Level 3 (beyond the six Kyoto pollutants in Level 2), AEDT/EDMS could be used to derive inventories for many of these pollutants, but only for the LTO portion. The inventory developer will need to determine the usefulness of such data based on airport needs. IPCC pro- vides cruise-related emission factors for NOx in Volume 2, Chapter 3, Table 3.6.10 of its guidelines (IPCC 2006). Poten- tially, the fuel use derived from Method 2 could be used with these emission factors. Emissions of H2O and SOx can be esti- mated using fuel composition data with mass balance, as indi- cated in Appendix C. Emissions of fluorinated compounds (e.g., HFC and PFC) from fire extinguishers can also be taken into account. Vol- ume 3, Chapter 7 of the IPCC guidelines (IPCC 2006) and Annex 3 of the EPA inventory report (USEPAb 2008) provide methods and data for calculating emissions from fire extin- guishers. Discussions with manufacturers and airlines have indicated that no data currently exists to directly support the modeling of emissions from the Halon systems on an aircraft (Bennett 2008; Valeika 2008). 3.2 Auxiliary Power Unit At this time, APU-related GHG emissions can only be ac- counted for through Aircraft Methods 1 and 2 (fuel sales data). As discussed later in this section, a subsequent dataset is ex- pected to be released in the future, which will reflect the abil- ity to separately itemize APU emissions. The fuel used by onboard aircraft APUs is accounted for in the fuel sales data (fuel dispensed) as the main aircraft engines are powered by the same fuel that powers the APU. Therefore, both Methods 1 and 2 in Sections 3.1.1 and 3.1.2, respectively, account for APU fuel use, as shown in Figure 3-4. Although Aircraft Methods 1 and 2 account for APU emis- sions, it should be understood that the AEDT/EDMS (FAAa 2007) results for aircraft LTO fuel consumption, as shown in Figure 3-4, presently do not include APU contributions. Therefore, since the LTO emissions are subtracted from the total airport emissions to derive what is previously labeled cruise, the APU emissions would be included but as part of the cruise emissions results for Method 2. This could poten- tially be rectified as APU-specific fuel consumption and emis- sions data become available. Assuming the same combustion efficiency for jet engines, the same calculation methods from Section 3.1 can be used to convert APU fuel consumption to APU emissions. The International Coordinating Council of Aerospace Industries Association (ICCAIA) is developing an APU data- base to be managed by the Swedish Defense Research Agency (FOI). The database is expected to contain fuel consump- tion and CO2 emission factors. However, under directions from ICCAIA and the manufacturers, it is expected that the Swedish FOI will only make the database available to certain organizations (e.g., government agencies) for re- search purposes and will likely have stipulations that the data not be published in any form. Another potential source of APU data is a USEPA report entitled, “Technical Data to Support FAA’s Advisory Circular on Reducing Emissions from Commercial Aviation” (1995). Although this docu- ment appears to be publicly available, it is not recommended for use since it does not appear to have been intended for public review because it was never finalized. Therefore, unless the availability/usability of these datasets changes, airports would not be able to specifically quantify APU emissions outside of the total aircraft and cruise emissions determined from the Aircraft Methods 1 and 2, respec- tively. If Aircraft Method 3 is used, the SAGE data would not include APU emissions because it only represents air- craft emissions. The inventory documentation should clearly indicate which of these methods was used, and the reasons 24 Airport Fuel Sales Data Emission Factors and Other Data as Necessary Calculate Aircraft Cruise GHG Emissions Aircraft LTO Fuel Consumption Total Aircraft GHG Emissions EDMS Subtract Calculate Aircraft LTO GHG Emissions Aircraft Method 1 APU GH G Em issi ons APU GH G Em issi ons Figure 3-4. APU emissions accounted as part of aircraft emissions using either Aircraft Method 1 (upper box) or Aircraft Method 2 (overall figure).

for use, to provide an explanation of how the APU emis- sions were handled. In the future, the FAA has indicated that they will include APU data within AEDT/EDMS to allow modeling of GHG emissions. 3.3 Ground Support Equipment Unlike criteria pollutant emissions, AEDT/EDMS (FAAa 2007) currently cannot be used to calculate GHG emissions from GSE because emission factors for those pollutants are currently not covered by this model. Therefore, a mixture of AEDT/EDMS and other methods would need to be employed. For CO2 calculations, the following two methods are suggested: • Method 1: Use fuel consumption data for GSE equipment to calculate emissions. • Method 2: Use models such as NONROAD to determine emission factors. Sections 3.3.1 and 3.3.2 discuss the calculation of CO2. Sec- tion 3.3.3 discusses the methodology for Level 2 and Level 3 pollutants. 3.3.1 GSE Method 1 If fuel-use information (e.g., fuel sales) for equipment is available, that information could be used with suitable emission factors to calculate GHG emissions as shown in Figure 3-5. For these vehicles, the airport operator would need to have records concerning the gallons of fuel that were dispensed to its vehicles, and similar records would be required for all ten- ant GSE. It is likely that most airports retain records concern- ing the fuel dispensed to their own vehicles. Fewer airports are expected to have access to the quantities of fuel consumed or dispensed by their tenants to their tenants’ vehicles. The following are some examples of fuel-based CO2 emis- sion factors: • Motor/auto gasoline = 19.564 lbs CO2/gal fuel (EIA 2008) or 8.81 kg CO2/gal fuel (USEPAa 2005), • Diesel = 22.384 lbs CO2/gal fuel (EIA 2008) or 10.15 kg CO2/gal fuel (USEPAa 2005), • Liquefied petroleum gas (LPG) = 12.805 CO2/gal fuel (EIA 2008) or 5.79 kg CO2/gal fuel (USEPAa 2005), and • Liquefied natural gas (LNG) = 4.46 kg CO2/gal fuel (USEPAa 2005). A sample calculation, assuming 150,000 gal of motor/auto gasoline was used by GSE, is as follows: When converted to metric tons, this equates to 1,331 metric tons CO2 (2,934,600 lbs × 0.00045359237 metric tons/lb). 3.3.2 GSE Method 2 At some airports, fuel use is not available, but the time that specific equipment is used is available or can be estimated. In these cases, USEPA’s NONROAD2005 (or similar models such as CARB’s OFFROAD2007, which should only be ap- plied to airports in California) could be used to determine emission factors for representative equipment, as shown in Figure 3-6. For those airports that have information concerning the use of each piece of GSE, the data would indicate category of CO emissions gal fuel lbs C2 = ( ) ×150 000 19 564, . O gal fuel lbs CO 2 2 ( ) = 2 934 600, , . 25 GSE Fuel Consumption Data Emission Factors and Other Data as Necessary Calculate GSE GHG Emissions Figure 3-5. Overview of GSE Method 1. GSE GHG Emissions NONROAD2005 or Other Models Emission Factors Airport, Airline, or EDMS Data GSE Activity and Other Data as Necessary Calculate Figure 3-6. Overview of GSE Method 2.

equipment, specific engine, date manufactured, horsepower of the equipment, and annual hours of use. Then, specific emis- sion factors can be obtained from the respective model. These data represent the GSE vehicle mix-use data. For those airports that have not conducted a GSE inventory (for either their owned equipment or their tenants’ equip- ment), estimates of such vehicle use can be prepared. For airport-owned equipment, it is best to survey the airport staff responsible for that equipment. However, in most cases, GSE Method 1 is recommended for airport-owned equipment (fuel dispensed to these vehicles). For airline GSE, AEDT/EDMS provides default GSE-use based on the aircraft fleet mix con- sidered. This information will provide types of equipment, horsepower setting, and annual hours of use. Once the GSE vehicle mix-use data are obtained, the NONROAD model can be accessed to obtain emission fac- tors that are generally representative of the vehicle mix. NONROAD can be run for the nation as a whole or for a state or county. Given the general nature of the data, it is at the discretion of the user as to whether national averages, state averages, or county local data are used. In many cases, exact vehicle matches are not possible and therefore, estimates of equipment may be made based on knowledge of the specific GSE used at the airport. Alternatively, emission factors could potentially be obtained directly from the manufacturers of the GSEs. Although this is a less likely source of information and would be time consuming, it would provide improved estimates of GSE emissions. Potentially, manufacturer spec- ification sheets (if they do not have emission factors) could also provide useful information in matching a GSE to an ap- propriate equipment type in NONROAD. The following provides a sample calculation assuming 120 annual hr of 112 hp Bobtail GSE activity, where the Bobtail generates 871.4 g/hp-hr: 3.3.3 Other Pollutants Emission factors of CH4 and N2O are provided by both the USEPA’s Climate Leaders (USEPAa 2008) and IPCC Volume 2, Chapter 3 of their guidelines (IPCC 2006) for a variety of non- highway mobile sources (e.g., small utility, large utility, etc.). Since IPCC data represent international defaults, USEPA data are preferred. It is up to the inventory developer to determine the appropriateness of this information in estimating GSE emissions for those pollutants. For GSE that has air conditioning, IPCC Volume 3, Chap- ter 7 of their guidelines (2006) provides a method to derive CO emissions h g CO h2 2= ( ) × ( ) = 120 871 4 104 568 . , g CO or 0.1046 metric tons of CO convert 2 2 ing the grams to metric tons, by multip ( lying the grams of CO by 0.000001 g metric t2 on). emissions for HFC and PFC based on default parameters related to mobile air conditioning. Designated as a screen- ing method, both the USEPA Climate Leaders and TCR have adopted this method. The inventory developer will need to determine if this method is justifiable and the corresponding data are appropriate for the airport. For the other pollutants in Level 3 (beyond the six Kyoto pol- lutants), NONROAD2005 or similar models like OFFROAD- 2007 can be used to obtain emission factors. The pollutants include various gases and PM. Emissions of H2O and SOx can potentially be estimated using fuel composition data with mass balance as indicated in Appendix C. 3.4 Ground Access Vehicles When preparing inventories of GAV, care must be exer- cised in evaluating travel for on-airport, as well as off-airport, roadways. Most airports have data concerning on-airport travel; large airports are likely to have actual vehicle count data; small airports may have more limited datasets. A review of the available inventories prepared to date indicates that the evaluation of GAV emissions may require approximations of vehicle counts and travel. Due to the scale differences between the national inventories developed under the IPCC methods and airport inventories, the calculation methods for GAVs presented herein do not correlate directly with the tiers used by IPCC. However, they share common components that are consistent. The follow- ing methods are presented in this Guidebook for GAVs: • Method 1: Use average vehicle miles traveled (VMT) es- timates with appropriate emission factors for an average vehicle. • Method 2: Use vehicle-specific VMT data with appropriate vehicle-specific emission factors. • Method 3: Use vehicle-specific VMT data with models such as MOBILE6.2 to calculate vehicle-specific emission factors. Although Method 3 is preferred, few airports have data at this level for the entire set of GAV that are suggested for in- clusion in the GHG inventory. Therefore, it may be appro- priate to use Method 3 for some subset of GAVs, such as the on-airport movement, and a lower method for the off-airport movement. It is within the GAV category of sources that data availability is likely to represent the greatest difficulty for most airports. The documentation that accompanies the inventory should clearly document the data sources and their use. Based on the availability of data, inventory developers are encouraged to use the highest method for the data available. The following three subsections discuss the calculation of 26

CO2, with Section 3.4.4 discussing the methodology for the Level 2 and Level 3 pollutants for GAV. 3.4.1 GAV Method 1 Method 1 calculations involving the determination of GHG emissions from GAVs basically determine fuel consumption values for use with the appropriate emission factors. This is the general method described under both Tiers 1 and 2 of the emissions section in Volume 2, Chapter 3 (IPCC 2006). How- ever, unlike using the IPCC tiers, national fuel consumption data specific to an airport and the vehicles that use an airport are not available. Therefore data surrogates are used to pro- vide an indication of the distance that vehicles travel and the fuel economy of those vehicles. The overall method for airport GAV emissions is presented in Figure 3-7. The first step in calculating GAV emissions is to collect VMT data for all vehicles. The total origin-destination distance should be included to allow proper accounting of GHG emis- sions based on the influence of the airport. Such data could potentially be derived from passenger surveys or estimates of passenger trip distances. Although passenger vehicles will tend to account for the biggest portion of GAV emissions, other vehicles, such as those used by airport employees and shuttle buses, should also be included. Each of these vehicles should also be categorized by fuel type (e.g., gasoline, diesel, etc.). In the simplest form, the vehicles using an airport can be cat- egorized by passengers, employees, cargo, and service delivery. If specific vehicle data are not available, the inventory devel- oper will be required to estimate the number of vehicles and distance traveled of the various vehicle types. In the passen- ger category, vehicles can be further identified by the mode of travel—private vehicle, taxi, shared van, etc. For many air- ports, data of this nature are not available. Thus, sources of data that the inventory developer might consult could include: total airport activity characteristics (passenger, operations, and cargo including the FAA’s Terminal Area Forecast), air- port parking revenue (for vehicles accessing the airport park- ing lots), passenger surveys (for modes of travel and distance traveled), metropolitan planning organization (MPO is re- sponsible for regional surface traffic analysis) traffic analysis for the area, airport employee parking and badge office in- formation (concerning employees and their travel), airport master plans and environmental analysis (for ground travel information), rental car revenue data (to identify rental car companies and percentage of market shares), etc. In order to calculate GAV fuel consumption, fuel econ- omy data would need to be obtained from sources such as the USEPA (USEPAb 2005), FHWA (FHWA 2002), and DOE (DOE 2007). For national averages, some typical values are as follow: • Passenger cars = 23.9 mpg (USEPAb 2005), • Passenger cars = 22.1 mpg (FHWA 2002), and • Cars (2005) = 22.9 mpg (DOE 2007). Any of these example fuel economy values could be used since they are all from reputable sources. The inventory devel- oper needs to clearly document the sources and should consider the potential need for consistency with previous inventories when choosing which values to use. If more specific fuel economy data are available (i.e., more specific to airport GAVs), they should be used instead of the national averages. Although the data could be segregated into categories (e.g., cars and trucks), the purpose of this method is to conduct a rela- tively “simple” assessment using average values. Using these national averages, fuel consumption would be calculated as exemplified below. The following sample calculation is for one round trip: To calculate GHG emissions, emission factors can be ob- tained from the following variety of sources: • Motor gasoline = 19.564 lbs CO2/gal fuel (EIA 2008), • Diesel = 22.384 lbs CO2/gal fuel (EIA 2008), • LPG = 12.805 lbs CO2/gal fuel (EIA 2008), • Gasoline = 8.81 kg CO2/gal fuel (USEPAa 2005), • On-road diesel fuel = 10.15 kg CO2/gal fuel (USEPAa 2005), • LPG = 5.79 kg CO2/gal fuel (USEPAa 2005), • LNG = 4.46 kg CO2/gal fuel (USEPAa 2005), and • Gasoline = 19.4 lbs CO2/gal fuel (USEPAb 2005 and CFR 2003). Fuel consumption mi mpg fuel econo= ( )40 23 9. my gal fuel. ( ) = 1 67. 27 Vehicle Fuel Economy Data Calculate GAV Fuel Consumption Emission Factors Calculate GAV GHG Emissions Total VMT or by a Few Major Categories Figure 3-7. Overview of GAV Method 1.

The following is a sample calculation for one round trip: 3.4.2 GAV Method 2 Method 2 is similar to Method 1 except that the VMT data are expanded to show a range of vehicle types (e.g., cars, trucks, motorcycles, etc.) and potentially other specific categorizations including vehicle age, mileage, emissions controls, etc. This is indicated in Figure 3-8. These specific categorizations would allow better tracking of emissions over time. The inventory developer must deter- mine the range of specific categorizations that would be ap- propriate for the airport. In each of these cases, because the data are still in a general form, fuel economy data are sug- gested to quantify the fuel consumed by these vehicles. Some examples of more specific fuel economy data than that shown in Section 3.4.1 are as follows: • Light truck = 17.4 mpg (USEPAb 2005), • Light truck = 17.6 mpg (FHWA 2002), • Two-axle, four-tire truck = 16.2 mpg (DOE 2007), • Medium truck (10,000 to 26,000 lbs) = 8.0 mpg (DOE 2007), and • Heavy truck (more than 26,000 lbs) = 5.8 mpg (DOE 2007). CO emissions gal fuel lbs CO2 2= ( ) ×1 67 19 564. . gal fuel lbs CO . This equates to 02 ( ) = 32 67. .0148 metric tons which is derived using a conversion factor of 0.0004536 metric tons lb. 3.4.3 GAV Method 3 As an alternative to the use of these fuel-based emission fac- tors in Methods 1 and 2, the USEPA’s MOBILE6.2 model can be used to generate CO2 emission factors for different vehicle types (USEPA 2002). Similarly, the USEPA’s MOVES2004 (USEPAb 2004) can be used to estimate fuel consumption (and hence, CO2 emissions) as well as emissions of CH4 and N2O. These provide another option in calculating higher resolution emissions (e.g., by specific vehicle types, age, mileage, emis- sions controls, etc.) to better track emissions over time. An overview of Method 3 is provided in Figure 3-9. This method is contingent upon having the VMT data for the specific vehicle categories. If those data are not available, there would be no fidelity gained from trying to use the specific emis- sion factors from a model like MOBILE6.2. In such a situation, it would be more appropriate to simply use the MOBILE6.2 composite emission factor. In that case, the fidelity and resolu- tion would essentially be the same as Method 1, and hence, no advantage would be gained from using MOBILE6.2. 28 Vehicle Fuel Economy Data Calculate GAV Fuel Consumption Emission Factors Calculate GAV GHG Emissions VMTs for Each Specific Category of Vehicle Type, Vehicle Age, Mileage, Emissions Control, etc. Figure 3-8. Overview of GAV Method 2. Calculate GAV GHG Emissions VMTs for Each Specific Category of Vehicle Type, Vehicle Age, Mileage, Emissions Control, etc. Specific Emission Factors from MOBILE6.2 and Other Models as Necessary Figure 3-9. Overview of GAV Method 3. Method 3 for GAVs is contingent upon the availability of VMT data for specific vehicle cate- gories; no fidelity is gained from using MOBILE6.2 without such data. The following example calculation is for one round trip using an emission factor from MOBILE6.2: This example calculation would correspond to a specific cat- egory of vehicle type, age, mileage, emissions control, etc.— again, depending on the needs of the airport. CO emissions mi kg CO mi kg 2 2= ( ) × ( ) = 40 0 25 10 . CO . This equates to 0.01 metric tons CO 2 2 when using a conversion factor of 0.001 metric ton kg.

Since emission factors for CH4 and N2O are highly depen- dent on vehicle type, operating conditions, control technol- ogy, etc., IPCC only allows the calculation of these emissions within its Tier 3 method. Although IPCC and other sources such as USEPA provide emission factors for these sources, there are no average values; they are provided for the specific categories. It is up to the inventory developer to properly (and reasonably) employ these specific emission factors. IPCC data for these pollutants can be found in Volume 2, Chapter 3, Tables 3.2.2 to 3.2.5 of the 2006 guidelines (IPCC 2006). The USEPA data can be found in Annex 3 Tables A-88 to 89 of the 2008 national GHG inventory report (USEPAb 2008). 3.4.4 Other Pollutants For HFC and PFC, IPCC provides methods to derive emis- sions for these pollutants based on default parameters related to mobile air conditioning. The IPCC methods can be found in Volume 3, Chapter 7 of the IPCC guidelines (IPCC 2006). Both the USEPA Climate Leaders (USEPAc 2008) and TCR (TCRa 2008) provide simplified explanations and emission factors based on the same information from IPCC. The overall method is based on material balancing of the emissions taking into account the charging, operating, and dis- posal of refrigerants. The USEPA Climate Leader’s simplified view of the emission factors and related parameters is pre- sented in Table 2 of their Refrigeration and Air Conditioning emissions guidance document (USEPAc 2008). The inventory developer will need to determine if this method is warranted and the corresponding data are appropriate for the airport. For the other pollutants in Level 3 (beyond the six Kyoto pollutants), USEPA’s MOBILE6.2 (USEPA 2002) or similar CARB’s EMFAC2007 (CARBb 2007) can be used to predict emission factors for GAV. The pollutants include various gases and PM. Emissions of other pollutants (H2O and SOx) based on fuel composition potentially can be estimated using fuel com- position data with mass balance as indicated in Appendix C. 3.5 Stationary Sources With the broad range of sources covered under this cate- gory, the methods to calculate GHG emissions from stationary sources have been grouped into the following categories: • Stationary source combustion activities, – Method 1: Use average emission factors, – Method 2: Use technology-specific emission factors, • Electricity usage. This section includes subsections devoted to CO2 emissions from the above categories. The final subsection addresses the remaining GHGs. 3.5.1 Stationary Source Combustion Activities—Method 1 Method 1 embraces both IPCC Tier 1 and 2 for emissions from stationary source combustion. Both of these IPCC tiered methods involve the use of fuel consumption data associated with these sources, coupled with emission factors to calculate GHG emissions. IPCC differentiates between these two tiers by distinguishing between the use of default IPCC emission factors in its Tier 1 method and use of country-specific data in its Tier 2 method. As such, data specific to the United States are preferred under Method 1 described herein. Method 1 involves the use of average emission factors as indicated in Figure 3-10. The stationary source fuel consumption data can be obtained from various fuel purchase or financial records and should be separated by sources owned by the airport operator versus those owned by tenants. For locations where purchased natu- ral gas or electrical records are not absolutely clear as to the quantities that are the responsibility of the airport operator versus that of the tenants, the following guidance is provided: (1.) any purchased electricity or natural gas invoices received by the airport operator, even if directly metered to a tenant, are the responsibility of the airport operator and thus their emissions should be categorized under the airport-owned category; and (2.) if invoices are received by the tenant and the airport can either gain access to them or an estimate can be made of the tenant electricity/energy usage, the associ- ated emissions should be categorized under the “tenant” category. In any case, these emissions should all be included as part of an airport GHG inventory. Airport-owned elec- tricity purchases should be classified as Scope 2 emissions whereas tenant-owned electricity purchases should be char- acterized as Scope 3 emissions. 29 Stationary Source Fuel Consumption Data Calculate Stationary Source GHG Emissions Average Emission Factors and Other Data as Necessary Figure 3-10. Overview of Stationary Source Combustion Method 1.

Appropriate conversion units may need to be applied de- pending on the units of the fuel consumption values and the emission factors used. The activity/fuel data should be mul- tiplied by an emission factor. Emission factors can be ob- tained from sources such as the USEPA and EIA. Some ex- amples of average emission factors are calculation procedures as in Method 1 but using technology- specific emission factors as indicated in Figure 3-11. The stationary source fuel consumption data can be obtained from various fuel purchase or financial records and should be separated by sources owned by the airport operator versus those owned by tenants. For locations where purchased nat- ural gas or electrical records are not absolutely clear as to the quantities that are the responsibility of the airport operator versus that of the tenants, the following guidance is provided: Any invoices for purchased electricity received by the air- port operator, even if directly metered to a tenant, are the responsibility of the airport operator and thus those emis- sions should be categorized under the airport-owned cat- egory. If invoices are received by the tenant and the airport can either gain access to tenant electrical consumption or an estimate can be made of the tenant electricity/energy usage, the associated emissions should be categorized under the “tenant- owned” category. In any case, these emissions should all be in- cluded as part of an airport GHG inventory. As noted earlier, airport-owned emissions resulting from purchased electricity should be classified as Scope 2 emissions, whereas tenant pur- chased electricity should be classified as Scope 3 emissions. Appropriate conversion units may need to be applied de- pending on the units of the fuel consumption values and the emission factors used. Emission factors can be obtained from sources such as USEPA’s Technology Transfer Network (TTN) (USEPAd 2008), Annex 2 of the USEPA’s 2008 GHG inventory report (USEPAb 2008) and IPCC Volume 2, Chapter 2 of the 2006 guidelines (IPCC 2006). The inventory developer must make sure to use the appropriate emission factors for each technology and operating condition. 3.5.3 Electricity Usage (Utility Purchases) This section covers indirect emissions (Scope 2) resulting from electricity used by the airport (electricity not generated 30 Btu—British thermal units mmBtu—Million Btu TJ—Tera joules GJ—Giga joules ft3—Cubic feet Utilities emissions are reported based on the party receiving the invoice for the utility (natu- ral gas, purchased electricity, etc.). • Natural gas (U.S. average) = 53.06 kg CO2/mmBtu fuel (TCRa 2008 and USEPAb 2008), • Natural gas (U.S. average) = 120.593 lbs CO2/1,000 ft3 fuel (EIA 2008), • Natural gas for commercial/institutional purposes = 56,100 kg CO2/TJ fuel (IPCC 2006), • Natural gas for commercial/institutional purposes = 5 g CH4/GJ fuel (USEPAb 2008), • Natural gas for commercial/institutional purposes = 0.1 g N2O/GJ fuel (USEPAb 2008), • Natural gas for commercial/institutional purposes = 5 kg CH4/TJ fuel (IPCC 2006), and • Natural gas for commercial/institutional purposes = 0.1 kg N2O/TJ fuel (IPCC 2006). The following is an example calculation using 200,000 mil- lion therms of natural gas usage: 3.5.2 Stationary Source Combustion Activities—Method 2 In keeping with the IPCC Tier 3 method for stationary combustion, the Method 2 presented herein involves the same The 200,000 million therms equates to 20,000 mmBtu using a conversion factor of 0.1 mmBtu therm Therefore, CO emissions mm2 . ,= 20 000 Btu kg CO mmBtu million kg2 ( ) × ( ) =53 06 1 061. . CO . This equates to 1,061 metric tons o 2 f CO when using a conversion factor of 0. 2 001 metric ton kg. Stationary Source Fuel Consumption Data Calculate Stationary Source GHG Emissions Technology- Specific Emission Factors and Other Data as Necessary Figure 3-11. Overview of Airport Facility Combustion Method 2.

by the airport). Any emissions from electricity generated by the airport through combustion of fuel should be categorized under Section 3.5.1 or 3.5.2. As shown in Figure 3-12, the method for calculating emissions from non-airport-generated electricity involves using electricity consumption (energy con- sumption) information with the appropriate emission factor. With electricity usage generally reported in kilowatt hours (kWh), emission factors from local utility providers or from USEPA’s eGRID system are recommended (USEPAf 2007). Airports are suggested to use local factors if available to ensure consistency of local inventories. In lieu of local factors, the USEPA’s model should be used. The eGRID emission factors are typically in lbs CO2 per MWh (megawatt hours). The following is an example calculation with 300,000 kWh of electricity use: Emission factors for CH4 and N2O are also available from the USEPA’s Climate Leaders in Appendix B of their Indirect Emissions from Purchased/Sold Electricity guidance docu- ment (USEPAa 2004). Based on fuel use data from eGRID, the USEPA developed emission factors for these pollutants. 3.5.4 Other Pollutants For HFC and PFC, IPCC provides methods to derive emis- sions for these pollutants based on default parameters related to air conditioning and refrigeration. The IPCC methods can be found in Volume 3, Chapter 7 of the IPCC 2006 guidelines (IPCC 2006). Both the USEPA Climate Leaders (USEPAc 2008) and TCR (TCRa 2008) provide simplified explanations and emission factors based on the same information from IPCC. CO emissions kWh lbs CO MWh2 2= ( ) ×300 000 1 388, , for Georgia 2004 MWh 1,000 kWh 416,4 ( ) × ( ) = 1 00 lbs CO This equates to 188.9 metric t2. ons when using a conversion factor of 0.0004536 metric ton lb. The overall method is based on material balancing of the emissions taking into account the charging, operating, and disposal of refrigerants. The USEPA Climate Leader’s simpli- fied view of the emission factors and related parameters is pre- sented in Table 2 of their Refrigeration and Air Conditioning emissions guidance document (USEPAc 2008). The inventory developer will need to determine if this method is warranted and the corresponding data are appropriate for the airport. Although IPCC (2006) provides methods to predict emis- sions of SF6 from industrial-type activities such as electronics etching, cleaning, and temperature control applications, these are not typical activities at an airport. The methods and data necessary for predicting emissions of SF6 from these types of activities can be found in Volume 3 (Industrial Processes and Product Use) from the IPCC 2006 guidelines (IPCC 2006). The inventory developer needs to determine if any of these activities occur at the airport, and if so, use the appropriate methods and data to determine the associated SF6 emissions. Also, IPCC provides a mass balance method to account for SF6 emissions from electricity transmission that is consistent with the method from the USEPA’s Emission Reduction Partner- ship for Electric Power Systems. However, this method is not intended for use by an entity that uses the electricity; rather, it is intended for the entity that owns the transmission lines. Hence, no SF6 emissions from electricity transmission lines can feasibly be allocated to airports at this time. For the other pollutants in Level 3 (beyond the six Kyoto pollutants), AEDT/EDMS (FAAa 2007) provides coverage of a wide range of pollutants (e.g., CO, NOx, VOC, etc.) for var- ious stationary sources. The USEPA’s eGRID also provides emission factors for SO2 and NOx. In addition, if the fuel com- position is known or estimated, a mass balance could be con- ducted to derive emission factors for H2O and SOx (modeled as SO2) as indicated in Appendix C. 3.6 Waste Management Activities Most airports have implemented waste management activ- ities designed to recycle various forms of waste. These activi- ties produce GHG emission reductions when contrasted with activities that do not recycle. The emissions associated with waste reduction-related equipment owned and operated by airport operators should be captured in the stationary source methodologies discussed previously (see Section 3.5). This section discusses capturing the GHG emission reduction as- sociated with lifecycle-related waste management activities. Few methodologies exist to capture the lifecycle emissions benefits associated with waste management activities. It is recommended that airport inventories not attempt to capture the full lifecycle emissions benefits associated with waste management activity, especially reduction-related activities. Rather, only the direct emissions from energy necessary to 31 Electricity Use (e.g., kWh) Calculate GHG Emissions from Indirect Electricity Use Emission Factor from EPA’s eGRID or Local Source Figure 3-12. Overview of indirect GHG emissions calculations from airport electricity use.

handle waste (e.g., incineration, disposal, etc.) can be reflected. The Guidebook does not address upstream and downstream emissions at this time. For airports that are required for local reasons to consider the GHG consequence of various waste management strate- gies, the USEPA’s Waste Reduction Model (WARM) (USEPAb 2007) is recommended as indicated in Figure 3-13. However, the USEPA’s website specifically notes the following re- garding this model, which reflects a lifecycle approach to considering such emissions: “This lifecycle approach is not appropriate for use in inventories because of the diffuse na- ture of the emissions and emission reductions contained in a single emission factor.” As indicated by USEPA, WARM models source reduction, recycling, combustion, composting, and landfilling. Some ex- amples of materials covered by the model include aluminum cans, glass, plastic, and paper. WARM also provides several options for landfill emissions modeling, including whether or not landfill gases are recovered. WARM uses national average emission factors. Modeled results are provided in metric tons of carbon equivalent (MTCE) and metric tons of CO2 equiv- alent (MTCO2E). Because few airport inventories would in- clude waste management emissions, such users are referred to the USEPA website for information about this model, data requirements, and reporting (USEPAb 2007). 3.7 Training Fires GHG emissions can be calculated from a training fire using the fuel usage information and an appropriate emission fac- tor as indicated in Figure 3-14. The fuel-use data for fire training activities (to the degree training occurs at an airport) are typically maintained by air- port operations or the fire department. Fuels used in creating live fires are typically reported in gallons. Fire suppressants should also be reviewed to determine the GHG consequence of the materials. The GHG emission factors depend on the fuel and may be obtained from sources such as EIA (2008); exam- ples of emission factors for some different types of fuel were in- dicated in Section 3.1.1. Alternatively, for fuels specifically geared toward training exercises, such as Tekflame, emission factors could potentially be obtained from manufacturers. The following is an example calculation assuming a hypo- thetical 10 gal of fuel and 20 lbs/gal emission factor for CO2: If the CO2 emission factor is not directly available, but the fuel composition data are (or can be estimated), the emission factor can be derived using mass balance and assuming com- plete combustion as indicated in Appendix C. Emissions of fluorinated compounds (e.g., HFC and PFC) from fire extinguishers also need to be taken into account. Volume 3, Chapter 7 of the IPCC guidelines (IPCC 2006) and Annex 3 of the EPA inventory report (USEPAb 2008) provide methods and data for calculating emissions from fire extinguishers. Emissions of various other pollutants (e.g., CO, NOx, VOC, etc.) are also generated during combustion of the fuel. These can also be predicted by AEDT/EDMS (FAAa 2007) using the stationary source definitions within the model. 3.8 Construction Activities The calculation of construction activity emissions for cri- teria pollutants is a well-established and understood process. The evaluation of construction emissions for GHG emissions CO emissions gal fuel lbs CO gal fuel2 2= ( ) × ( )10 20 = 200 lbs CO This equates to 0.09072 metric t 2. on when using a conversion factor of 0.0004536 metric ton lb. 32 Quantity of Materials Recycled, Landfilled, etc. WARM GHG Emissions from Waste Management Activities Figure 3-13. Overview of using USEPA’s WARM to calculate GHG emissions. Fuel-Use Data Calculate GHG Emissions from a Training Fire Appropriate Emission Factor Figure 3-14. Overview of GHG emissions calculations from training fires.

uses the same models and data. Therefore, it is recommended that USEPA’s NONROAD2005 (or CARB’s OFFROAD2007 for airports in California) be used to determine emission fac- tors for representative equipment as shown in Figure 3-15 (USEPAc 2005 and CARBa 2007). To use emission factors from this model, the airport oper- ator is required to identify the specific construction vehicles that would be deployed on the construction, as well as the an- nual hours of use, equipment horsepower, and load factor. This information is further described in the user’s manuals for the models. In modeling these emission factors, reasonable approxi- mations may need to be made based on the data available in NONROAD and knowledge of the local construction vehicle mix. The inventory developer needs to make this determina- tion based on knowledge of the specific equipment used at the airport. Alternatively, emission factors could potentially be obtained directly from the manufacturers. Although this would be a time-consuming effort, it would provide im- proved emissions estimates. Potentially, manufacturer spec- ification sheets could also provide useful information in matching a construction vehicle to an appropriate equipment type in NONROAD. Once the emission factors are known, activity information needs to be estimated. Since emission factors from NON- ROAD are provided in grams per break horsepower-hour, suitable load factors would need to be used. If the loading data are not available, assumptions could be made based on the inventory developer’s experience. The following provides an example calculation assuming 1 h activity for one piece of construction equipment: Emission factors for CH4 and N2O are provided by both the USEPA’s Climate Leaders and IPCC for various non-highway mobile sources (e.g., small utility, large utility, etc.). The emission factors can be found in the Climate Leaders mobile source inventory guidance document (USEPAa 2008) and Volume 2, Chapter 3 of the IPCC 2006 inventory guidance (IPCC 2006). Since the IPCC data represent international de- faults, the USEPA’s data are preferred. It is up to the inventory developer to determine the appropriateness of this informa- tion in estimating emissions for construction equipment. For construction equipment that has air conditioning, the IPCC provides a method to derive emissions for HFC and PFC based on default parameters related to mobile air condi- tioning. The IPCC methods can be found in Volume 3, Chap- ter 7 of the IPCC 2006 guidelines (IPCC 2006). Both the USEPA Climate Leaders (USEPAc 2008) and TCR (TCRa 2008) provide simplified explanations and emission factors based on the same information from IPCC. The overall method is based on material balancing of the emissions, taking into account the charging, operating, and disposal of refrigerants. The USEPA Climate Leader’s simpli- fied view of the emission factors and related parameters is pre- sented in Table 2 of their Refrigeration and Air Conditioning emissions guidance document (USEPAc 2008). The inventory developer will need to determine if this method is warranted and the corresponding data are appropriate for the airport. For the other pollutants in Level 3 (beyond the six Kyoto pollutants), NONROAD2005 (USEPAc 2005) or similar mod- els like OFFROAD2007 (CARBa 2007) can be used to predict emission factors. The pollutants include various gases and PM. Emissions of H2O and SOx can potentially be estimated using fuel composition data with mass balance as indicated in Appendix C. 3.9 Other Airport Sources The preceding sections identify the common sources of GHG emissions at an airport. Since every airport is different, it is likely that there are unique sources operating at an airport that are not captured in the preceding sections. Therefore, the Guidebook recommends that the inventory developer con- sider the principles noted in the previous sections in devel- oping a methodology to capture the emissions from other sources (i.e., making logical choices of using appropriate emission factors and applying them to the associated activity data for each source). The methodology should be clearly doc- umented in the text that accompanies the resulting inventory. CO emissions h g CO h g CO 2 2 2 = ( ) × ( ) = 1 10 000 10 000 , , . This equates to 0.01 metric ton when using a conversion factor of 0.000001 metric ton g. 33 Construction Activity GHG Emissions NONROAD2005 or Other Models Emission Factors Construction Equipment Activity Data Calculate Figure 3-15. Overview of GHG emissions calculations for construction activities.

The 100-year notation in Table 3-2 refers to the corre- sponding time horizon for the GWP values. In keeping with the general protocols of both IPCC and USEPA, the GWP100 values should always be used. Whether the GWPs for other time horizons should be used (i.e., in addition to GWP100) will depend on the needs of the airport and/or the purpose of the inventory. The following is an example calculation for 10 metric tons of CH4: The recommended format for reporting CO2e is exempli- fied in Table 3-3. As indicated in the table, the mass emissions of each pollu- tant are reported along with CO2e values. This is recom- mended as it would enable swift updates to the CO2e should new and improved GWPs be developed in the future. Further information on CO2e can be found in Appendix D. CO emissions metric tons CH GWP f2e 4 100= ( ) ×10 25 or CH metric tons CO 4 2e ( ) = 250 3.10 Calculation of CO2 Equivalencies After each applicable source has been addressed and the emissions of each pollutant have been calculated, CO2 equiv- alencies need to be developed as indicated in Figure 3-16. The GWPs from the IPCC’s fourth and most recent assess- ment report (IPCC 2007) should be used, and this source needs to be clearly cited. However, based on the needs of the airport (e.g., comparisons to older inventories), GWPs from other reports could potentially be used as long as the sources are clearly stated. GWPs from the IPCC Fourth Assessment Report are reproduced in Table 3-2 for some pollutants. for any of these other pollutants reported in the inventory, no CO2 equivalent (CO2e) emissions can be developed. Even if GWPs are available for a pollutant, the original mass emis- sions for that pollutant should still be reported in addition to the CO2e emissions. 34 Non-CO2 Emissions Calculate CO2 Equivalent Emissions for Non- CO2 Pollutant Appropriate GWP Figure 3-16. Overview of CO2 equivalency calculations. Pollutant GWP100 CO2 1 CH4 25 N2O 298 SF6 22,800 Table 3-2. 100-year GWPs from IPCC Fourth Assessment Report. Annual Metric Tons Metrics CO2 CH4 N2O SF6 Others Source X Emissions 1,000 4 2 0.01 Not Assessed GWP100 1 25 298 22,800 CO2e 1,000 100 596 228 NotAssessed Total CO2e 1,924 Note: The above GWP100 factors represent emissions from IPCC’s Fourth Assessment Report. Table 3-3. Example format for reporting equivalencies (CO2e). Sources of GWP factors should be clearly identi- fied, as well as the emissions of individual pollu- tants prior to the application of the GWP. Both the mass emissions of each of the non- CO2 pollutants and its CO2e emissions should be reported. GWPs for HFC and PFC depend on the specific fluorinated species. Values for some other pollutants can be found in the IPCC report. However, most of the pollutants outside of the six Kyoto pollutants (e.g., precursors) will not have GWPs. So,

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Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories Get This Book
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TRB’s Airport Cooperative Research Program (ACRP) Report 11: Guidebook on Preparing Airport Greenhouse Gas Emissions Inventories explores a framework for identifying and quantifying specific components of airport contributions to greenhouse gas emissions (GHG). The report is designed to help airport operators and others to prepare an airport-specific inventory of greenhouse gas emissions.

Appendices A through F to ACRP Report 11 were published online as ACRP Web-Only Document 2. The appendices titles are as follows:

Appendix A-Reasons for Developing GHG Inventories

Appendix B-Emissions and Sources

Appendix C-Methods for Calculating GHG Emissions

Appendix D-Methods for Calculating CO2 Equivalencies

Appendix E-Inventory Development Protocols

Appendix F-Approaches Used in Airport Inventories Prepared to Date

An ACRP Impacts on Practice related to ACRP Report 11 is available.

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