Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool (2015)

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3 Background Lead is a well-known air pollutant that can lead to a variety of adverse health impacts. Con- cerns regarding the adverse health effects of exposure to airborne lead resulted in its classification as an air pollutant pursuant to the Clean Air Act in 1976, followed by the requisite enactment of a health-based National Ambient Air Quality Standard (NAAQS) for lead in 1978—set at 1.5 micrograms per cubic meter of air based on quarterly average concentration. Thirty years later, in October 2008, the EPA promulgated a new lead NAAQS that lowered the acceptable level by an order of magnitude, to 0.15 micrograms per cubic meter based on a rolling three- month average concentration (U.S. EPA 2008). Because general aviation airports represent a significant source of lead emissions, ACRP Project 02-34 was initiated with the objective of reviewing and improving existing method- ologies to quantify and characterize aircraft-related lead emissions at airports with significant populations of aircraft that use leaded aviation gasoline. This guidebook was prepared to allow for the incorporation of key project results from ACRP 02-34 into emission inventory devel- opment for airports with significant piston-powered aircraft operations and is separate from ACRP Web-Only Document 21, the unpublished contractor’s report for ACRP Project 02-34 (Heiken et al. 2014). This guidebook and the companion Emission Inventory Analysis Tool (EIAT) on the accom- panying CD-ROM encompass a series of best practices for estimating airport lead emissions from piston-powered aircraft. The EIAT calculates annual airport lead emissions based upon user-selected options and input data sources. The guidebook and the EIAT are designed to be used concurrently. The remainder of this background chapter describes the (1) current FAA/EPA default methods, (2) inventory improvements included in the EIAT, and (3) recommended use of the EIAT. 2.1 FAA/EPA Default Methods Both the 2008 lead NAAQS and the 2010 ambient lead monitoring rulemakings declare EPA’s NEI as the default source for airport lead emission inventories. The NEI is a triennial national emissions inventory prepared by EPA; the most current published version—also known as the 2011 NEI (U.S. EPA 2013b)—is for calendar year 2011. In the 2010 rule, EPA added regulatory language stating that the facility-level lead inventory determination, which factors into the mon- itoring requirements, is “based on either the most recent [NEI] or other scientifically justifiable methods and data (such as improved emissions factors or site-specific data) taking into account logistics and the potential for population exposure” (U.S. EPA 2010). C H A P T E R 2

4 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool This guidebook supplements the existing FAA/EPA default methods for estimating airport lead emission inventories. Use of the EIAT requires familiarity with current agency methods and resources, as agency default parameters and assumptions are incorporated into the EIAT. At the most basic level, the EIAT will simulate the 2011 NEI approach, replicating the current agency default methods. Two references, described below, make up the FAA/EPA default methods that are cited in this guidebook. It is recommended that copies of these documents be obtained and used, as needed, in developing inventories using the EIAT. 1. The 2011 NEI documentation specific to lead emissions from airports (U.S. EPA 2013b) pro- vides the foundation for the default methods in this guidebook. This one document is here- inafter referred to as the “2011 NEI documentation.” The 2011 NEI documentation provides the default methods for airport operations, fuel consumption rates, determination of aircraft fleet characteristics and specification of aviation gasoline parameters. This reference is avail- able at ftp://ftp.epa.gov/EmisInventory/2011/doc/2011nei_AircraftLead_20130827.pdf. 2. The 1992 EPA emission inventory (EI) guidance document (U.S. EPA 1992)—which reflects the last time the agency issued official emission inventory guidance for the mobile source sector—remains relevant for key inventory elements. This document, referred to herein- after as the “1992 EPA EI guidance,” is directly referenced in the 2011 NEI documentation; it provides additional background and details behind specific modeling assumptions, which have been carried forward over time. Relevant to this guidebook, the 1992 EI guidance fur- ther documents the default time spent in each operating mode (termed “time in mode” or TIM) that is defined for the typical landing-takeoff (LTO) cycle. This reference is available at http://www.epa.gov/otaq/models/nonrdmdl/r92009.pdf. It should also be noted that since 1993, the FAA’s Emissions and Dispersion Modeling System (or EDMS) has been EPA’s preferred guideline model for emission inventory and air quality evaluations of airports (FAA 2013a). EDMS does not model lead emissions or report fuel consumption in a manner suitable for estimating lead inventories from piston-powered aircraft. While these limits to EDMS preclude its direct use in airport lead inventory develop- ment, the 2011 NEI documentation and this guidebook do refer to the EDMS when applicable, and the 2011 NEI methods and data input intentionally have considerable overlap with those of EDMS. The ability of the EIAT to replicate the results from the 2011 NEI is summarized in Table 1. Although the EIAT uses the same default input data, the EIAT processes the calculations at Source Fixed-Wing Fleet- Average Fuel Consumption (Gal./LTO) Fixed-Wing Fleet- Average Gasoline Lead Content (Gram/LTO) Rotorcraft Average Gasoline Lead Content (Gram/LTO) 2011 NEI Documentation 3.46 a 7.34a 6.60b EIAT Estimate Using FAA/EPA Defaultsc 3.35 7.10 6.49 % Difference vs. 2011 NEI −3% −3% −2% a U.S. EPA (2013b), p. 17. b U.S. EPA (2013b), p. 18. c LTOs are not used in EIAT; reported values are estimated by assuming 1 LTO = 2 operations in the EIAT. Table 1. Comparison of EIAT results using FAA/EPA default parameters to 2011 NEI.

Background 5 a more detailed level (e.g., by individual operating mode) as necessitated by the inventory enhancements. The EIAT rounds off only at the final step, and the EIAT uses a more precise Microsoft® Excel function to convert between imperial units and metric units. The differences between the 2011 NEI and the EIAT parameter estimates are 3 percent or less for the comparable results shown in Table 1. 2.2 Inventory Enhancements Available with the EIAT The inventory methodologies available in the EIAT include several enhancements to the cur- rent FAA/EPA defaults. Before reviewing these enhancements, it should be understood that EPA acknowledges the limitations of the current default methodology; the 2011 NEI documentation includes “Section 7. Improving Airport-Specific Lead Emissions Estimates,” which outlines the following three areas for improving lead inventories: 1. Regular collection of airport-specific data on the proportion of operations by piston-engine aircraft; 2. Collection of airport-specific data on the time spent in each operation mode, and an assessment of the engine run-up procedures currently unaddressed in the default method; and 3. Determination of the airport-specific lead content in aviation gasoline dispensed, including seasonal variation. The following enhancements relate to (1) improving the fuel consumption rate method; (2) improving operating mode modeling; and (3) facilitating the incorporation of facility- specific data. 2.2.1 Fuel Consumption Rate Method The enhanced methodology makes use of the following for developing airport piston-fleet- average fuel consumption estimates: 1. An expanded database of piston-engine fuel consumption rates; 2. An improved method for fuel rate assignment based on engine efficiency (i.e., brake-specific fuel consumption, or BSFC); 3. Rotorcraft (RC, i.e., helicopter) engine load defined by operation mode; and 4. The capability to estimate activity-weighted fleet-average fuel rates for fixed-wing (FW) air- craft and RC. Lead is emitted in the exhaust from gasoline-powered piston engines, as most aviation gaso- line consumed still contains “low-level” lead (added to fuel in the form of tetraethyl lead). Given this, fuel consumption rates are obviously key to aircraft lead emission inventories, and the accuracy of the inventory method depends, in part, on the robustness of the piston-engine fuel consumption database. The default FAA/EPA lead inventory approach, which is based on fuel consumption data for 6 piston-powered aircraft engines, has been enhanced by adding fuel consumption data for 29 piston-powered aircraft. Moreover, the enhanced method also uses BSFC, an efficiency met- ric based on fuel consumed per unit of work performed instead of volume of fuel consumed at different engine power levels, as the means for developing fuel consumption rates that factor the engine size into the final result. BSFC data are also grouped by engine/fuel metering technology, such that “default” efficiencies can be used by engine technology to map to engines not covered by the database.

6 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool The enhanced method options for assessing fleet-average piston-engine fuel consumption rates are discussed in part of Chapter 4, “Aircraft Fleet Data,” of this guidebook. 2.2.2 Operating Mode Modeling The enhanced methodology makes two significant improvements in how operating modes are defined and applied in the inventory development: 1. The emissions associated with the magneto-test run-up procedures are addressed and 2. Additional modes of operation and modeling parameters are included so that “continuous” operations, as defined below, are addressed. The current FAA/EPA default includes the standard four operating modes (taxi/idle, takeoff, climb-out, approach) for FW aircraft and three modes (taxi/idle, climb-out, approach) for RC. Moreover, the FAA/EPA default assumes that every two operations consist of a standalone landing and a standalone takeoff. These two operations combined are termed a “landing-takeoff cycle,” and agency inventory methods are derived and reported on a per-LTO basis with the underlying presumption that every two operations consist of a standalone takeoff and a standalone landing. The first improvement is to address magneto-test run-up procedures, which fall outside the default modes of operation. Whereas the magneto-test run-up portion of the inventory is moderate (it adds only 5 percent more emissions to the inventory under FAA/EPA defaults), ACRP 02-34 showed that the run-up activities can result in significant airborne lead concen- trations, as the emissions occur only within prescribed areas. The second improvement addresses the finding that the standard LTO cycle approach was inadequate for evaluating the site-specific activity data collected at three airports in ACRP 02-34. A significant proportion of “continuous” operation—i.e., multiple operations executed in series such that the engine is not turned off—was observed, predominantly because of commercial flight school activity. Two distinct types of continuous operation, described below, are handled in the enhanced methodology: the “touch-and-go” and the “taxi-back.” • Touch-and-go operations for FW aircraft consist of an approach, brief ground roll (landing), an immediate takeoff, and a climb-out—all of which occur without exiting the runway. Spe- cifically, a touch-and-go operation counts as two operations in FAA procedures because both a landing and a takeoff occur. Approach and climb-out modes for the touch-and-go were handled in a manner similar to the procedure used for any standard landing and takeoff; however, the fuel rate for the ground-roll mode of the touch-and-go was handled distinctly as the average of the idling rate (typical for landing) and the takeoff rate. • Taxi-back operations for FW aircraft consist of a standard approach, landing, and taxiing off the runway, after which the aircraft taxis back to a runway and completes a takeoff and climb-out. The taxi/idle time on the ground is unique for this procedure (and accounted for separately in the methodology), and the run-up prior to takeoff is typically omitted. These two types of continuous operation represented approximately 40 to 50 percent of the piston-powered aircraft activity observed at the three airports during the field studies conducted. Correctly addressing the continuous operation was critical to the inventory development for these airports and will be equally important for any other facility with significant flight training operations. The enhanced method options for defining operating mode options are discussed in Chap- ter 5, “Operation Mode Data,” of this guidebook. Note that because the standard LTO cycle is not representative of all piston craft operations of interest in this methodology, the fuel con- sumption and emission results are not expressed on a per-LTO basis; instead, the results (when reported as per unit of activity) are expressed on a per-operation basis.

Background 7 2.2.3 Incorporation of Facility-Specific Data By design, this enhanced methodology facilitates the incorporation of facility-specific model- ing input for each of the inventory modeling parameters. Table 2 summarizes the modeling input for which facility-specific data may be used in conjunction with the inventory develop- ment. Also listed in Table 2 are the chapter of this guidebook and the worksheet of the EIAT in which the parameter enters into the analysis. While the primary recommendation of this guidance is that facility-specific data be used whenever feasible for the parameters shown in Table 2, the approach is flexible in that screen- ing values (e.g., FAA/EPA default modeling assumptions) are also included. The only modeling parameter for which no screening value is present in the enhanced methodology is airport opera- tions data, which must be supplied by the user. The approach is also flexible in that composite results from the three ACRP 02-34 airports are provided for evaluation in the EIAT for additional illustrative/screening purposes. Again, the recommended approach for inventory development is the use of locally collected, facility- specific data when feasible. 2.3 Recommended Use of the Guidebook The guidebook/EIAT encompasses a series of best practices for estimating airport lead emis- sions from piston-powered aircraft. 2.3.1 Who Should Use This Guidebook The guidebook is geared towards airport managers and air quality personnel responsible for environmental assessments. Candidate airports are any category of general aviation airports nationally, as the EIAT can perform a full range of inventory assessments from the most basic (i.e., using current FAA/EPA defaults) to the more complex (i.e., incorporating facility-specific data collection). Considerations regarding the applications of the enhanced methodology and use of the EIAT for the end-user are as follows: 1. The EIAT allows for the addition of the magneto-test run-up mode to the FAA/EPA default method without any additional user input. Modeling Input/Parameter Guidebook Chapter EIAT Worksheet Annual airport operations data Chapter 3 Worksheet 3.1 Daily airport operations data Chapter 3 Worksheet 3.1 Distribution of operations between FW and RC Chapter 4 Worksheet 4.1 Piston-engine share of FW aircraft operations Chapter 4 Worksheet 4.1 Piston-engine share of RC operations Chapter 4 Worksheet 4.1 Activity-weighted piston-engine FW aircraft fleet Chapter 4 Worksheet 4.3 Activity-weighted piston-engine RC fleet Chapter 4 Worksheet 4.4 Run-up occurrence frequency Chapter 5 Worksheet 5.1 Frequency of continuous operation modes Chapter 5 Worksheet 5.1 Time-in-mode data Chapter 5 Worksheet 5.2 Aviation gasoline parameters Chapter 6 Worksheet 6.1 Table 2. Modeling input/parameters for which facility-specific data can be used.

8 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool 2. Airports with annual lead emissions, following NEI methods, near or within the range of annual emission thresholds that trigger monitoring requirements, may apply this guidance to improve the accuracy of the inventory estimates. 3. Airports with significant flight school activities may choose to use this guidance to improve the ability to model emissions associated with continuous operations typical of training procedures. 4. Airports with lead design values close to the NAAQS may choose to apply this guidance to improve the accuracy of the inventory for air quality planning purposes. 5. The guidance may be used to evaluate the impact of modeling variables on the inventory so that the potential impact of facility data collection can be evaluated prior to developing and implementing a data collection plan. 2.3.2 How to Use This Guidebook As mentioned, the EIAT and the guidebook are designed to be used concurrently. The guidance contains two levels of pre-existing screening information for key inventory modeling parameters: FAA/EPA defaults and average site-specific results from ACRP 02-34. These screening data allow the methods to be applied with minimal user input. At a minimum, the user must supply airport-specific annual operations data in order to estimate annual lead emissions. However, it is recommended that facility-specific data be obtained and used when- ever feasible and when airport conditions warrant. Table 3 summarizes the guidebook structure and the corresponding EIAT worksheets. Chap- ters 3 through 8 of the guidebook correspond to specific EIAT worksheets as summarized in Table 3. The EIAT is designed to go through the worksheets in sequential order. The guide- book also contains two additional chapters not shown in Table 3—Chapter 9, “Implications/ Limitations,” and “References.” Further notes on the EIAT worksheet organization are provided below; these notes are also included in the “OVERVIEW” worksheet of the EIAT. 1. Worksheets of the same tab color originate from the same chapter of the guidebook. 2. The first numeric value in the worksheet name equals the chapter number of the guidebook; the second numeric value in the worksheet name is simply a sequential counter. For example, there are four worksheets related to Chapter 3 of the guidebook. These worksheets include 3.1, 3.2, 3.3, and 3.4 in the worksheet name. The worksheet title text describes the inventory element covered by the worksheet. 3. Cell A1 of each worksheet contains a comment that provides an overview of the function of the worksheet. 4. A color scheme is used to denote individual worksheet cells; the shading of specific cells is described as follows: a. Grey shading denotes areas of the worksheet in which specific inventory options are sum- marized and implemented by the user. The user is requested to select a methodological approach option from a specific list of choices. b. Green shading denotes where user input occurs. All user input will occur in green-shaded cells. c. Red shading is selectively applied to highlight cell locations that should not be modified. This color coding is applied to reference values and/or specific formula, for emphasis pur- poses. More generally, only green-shaded cells should be modified in applying this tool. d. Yellow shading is selectively used to highlight cells that include specific “comments” that provide additional information and/or clarification. Note that not all cells with comments are shaded yellow. For example, each worksheet contains a comment in Cell A1 that pro- vides an overview of that worksheet.

Background 9 Guidebook Chapter EIAT Worksheet User Input? Summary of Worksheet Function 3 – Airport Activity Data 3.1 Annual Operations Yes Airport-specific activity data input, select daily or annual input option 3.2 Temporal Profiles No Calculates normalized profiles 3.3 Day Chart No Day-of-week temporal profile chart 3.4 Month Chart No Monthly profile chart 4 – Aircraft Fleet Data 4.1 Aircraft Fleet Yes Selection of approach option for fleet apportionment data, input of fleet apportionment data 4.2 Piston Fuel Rates Yes Selection of fuel rate assignment options 4.3 FW Piston Fleet Yes Optional user input of detailed piston-engine fleet for FW aircraft 4.4 RC Piston Fleet Yes Optional user input of detailed piston-engine fleet for RC 4.5 Piston BSFC Data No BSFC database 4.6 Example Piston Aircraft No ACRP 02-34 unique set of piston-engine aircraft and BSFC assignment 5 – Operation Mode Data 5.1 Mode Definitions Yes Selection of mode options, input of mode frequency parameters 5.2 Time in Mode Yes Selection of TIM options and data input 6 – Aviation Gasoline Data 6.1 Gasoline Parameters Yes Definition of gasoline parameter assumptions 7 – Inventory Calculations 7.1 Calculations No Series of calculations to support inventory results reporting 8 – Inventory Results 8.1 Inventory Results Yes Inventory results presentation; input of inventory descriptors Table 3. Interrelation between guidebook chapters and EIAT worksheets.