xvEPA
United States
Environmental Protection
Agency
Air and Radiation
EPA420-R-99-007
May 1999
Technical Support for
Development of Airport
Ground Support Equipment
Emission Reductions
> Printed on Recycled Paper
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EPA420-R-99-007
May 1999
for
Prepared by:
Sierra Research, Inc. for the
Office of Mobile Sources
U.S. Environmental Protection Agency
Contract No. 68-C7-0051
NOTICE
This technical report does not necessarily represent final EPA decisions or positions.
It is intended to present technical analysis of issues using data which are currently available.
The purpose in the release of such reports is to facilitate the exchange of technical information and
to inform the public of technical developments which may form the basis for
a final EPA decision, position, or regulatory action.
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Report No. SR98-12-05
Airport Ground Support
Equipment Emissions
prepared for:
U.S. Environmental Protection Agency
December 31, 1998
prepared by:
Sierra Research, Inc.
1801 J Street
Sacramento, California 95814
(916)444-6666
-------
Technical Support for Development of
Airport Ground Support Equipment Emission Reductions
prepared for
U.S. Environmental Protection Agency
Contract No. 68-C7-0051
Work Assignment No. 0-05
December 31, 1998
prepared by:
Sierra Research, Inc.
1801 J Street
Sacramento, CA 95814
(916)444-6666
-------
Disclaimer
Although the information in this report has been funded wholly or in part by the
United States Environmental Protection Agency under Contract No. 68-C7-0051, it has
not been subjected to the Agency's peer and administrative review and is being released
for information purposes only. It therefore may not necessarily reflect the views ofthe
Agency, and no official endorsement should be inferred.
-------
Technical Support for Development of
Airport Ground Support Equipment Emission Reductions
Table of Contents
Introduction
Available Information Sources
Potential Control Strategies
Basis for GSE Population Estimates
GSE Emissions and Activity Estimates
LPG and CNG Control Strategies
Electric GSE
Emissions Aftertreatment
Fixed Gate Support
GSE Control Strategy Summary
Estimating GSE Activity
Appendix A - GSE Model Instructions
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INTRODUCTION
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INTRODUCTION
Background
The significance of air pollution emissions from airports is growing as airports expand to
meet increasing demand for air travel and as the relative contribution of other sources
declines under the pressure of progressively more stringent emission control programs.
As a result, airports are being targeted for more aggressive emission control programs.
Aircraft ground support equipment (GSE) represents one of three groups of mobile
emission sources at airports. Together with aircraft and ground access vehicles, GSE
contribute a small but significant share of the hydrocarbon (HC), carbon monoxide (CO),
oxides of nitrogen (NOX), and particulate matter (PM) emitted in metropolitan areas.
Today, total emissions from these three source categories comprise on the order of 2-3
percent of total manmade emissions in a typical metropolitan area, but this share is
expected to increase as air travel continues to grow while emissions from other,
non-airport sources are subject to increasingly stringent controls.
Since airports represent a growing source of emissions, EPA issued a work assignment to
gather information and develop methodologies that can be used to develop a protocol on
how to obtain State Implementation Plan (SIP) credit for emission reductions associated
with the retrofit/replacement of airport ground support equipment by third parties, or
governmental entities. This project is in support of the U.S. EPA Office of Mobile
Sources Transportation and Market Incentives Group's (TMIG) efforts to develop
protocols for quantifying voluntary mobile source emissions programs (VMEPs).
Voluntary Measure Protocols are stand-alone guidance documents that describe the steps
and methodology necessary for states and/or third parties to quantify emission reductions
for SIP credit under EPA's Voluntary Measures Policy. Steps include requirements for
quantifying emission benefits and estimating uncertainties in emission reductions and
compliance, as well as administrative requirements for record keeping and/or SIP
submission.
Project Scope
The purpose of this work assignment was to examine the control measures available to
reduce emissions from one component of airport emissions, ground support equipment,
and to recommend methodologies to quantify the reductions associated with
implementing those control measures. This effort included the following key tasks:
DLiterature/Data Search
DList of Equipment and Control Strategies
DDescription of Individual Control Strategies
DSummary of Available Control Strategies
DMethods for Estimating Ground Support Equipment Activity
DPreparation of a Spreadsheet to Quantify Ground Support Emissions
This report presents a compendium of the work products produced under each task. To
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aid the reader in identifying products of interest, a brief summary of the contents of each
section of this report is presented below.
Literature/Data Search - An extensive review of the literature was conducted to identify
additional reports and bodies of information that provide insight into GSE emission rates,
activity levels and available technologies to reduce emissions. The results are
summarized in a series of tables addressing the following:
•General reports;
•Journal articles;
•Airport reports; and
•GSE manufacturer product information.
List of Equipment Control Strategies - Based upon a review of the available literature,
a series of tables were constructed to list the control strategies available for each category
of ground support equipment. Separate tables were prepared for each pollutant (i.e., HC,
CO, NOx, PM, and carbon dioxide [CO2]). Each table is organized by GSE type (e.g.,
airport pushback tractor, forklift, etc.), engine type, estimated U.S. population, fraction of
total GSE population, fraction of emissions, and percent emission reduction potential for
each control strategy.
Basis for GSE Population Estimates - Since there are no registration requirements for
GSE or any other national organization charged with tracking GSE activity, there is no
reliable database from which accurate GSE populations can be determined. To provide a
reliable estimate of national GSE population, a detailed statistical regression analysis of
the available data was conducted. This section presents the results of that review by
airline classification and by equipment and engine type.
GSE Emissions and Activity Estimates - Accurately characterizing the emissions
performance of a particular GSE requires detailed knowledge in two specific areas:
(1) the rate of equipment emissions per unit of activity, and (2) the amount of activity
performed during the period of interest. Generally, the unit activity emission rate can be
either measured directly or estimated from previous measurements taken for similar
equipment or engines. Because emission rates typically vary with engine speed and load
(a measure of how "hard" the engine is being worked), emission rates for GSE-type
equipment are commonly measured over a broad series of constant speed and load
operating modes that, when weighted in accordance with the amount of time the engine
spends in each mode, can describe the average emission rate of the equipment. This
section presents a methodology for estimating equipment specific activity and related
emission levels.
LPG and CNG Control Strategies - The majority of conventionally powered GSE can
be converted to either liquefied petroleum gas (LPG) or compressed natural gas (CNG)
fueling or replaced with a specially manufactured LPG- or CNG-powered counterpart.
The basic issues surrounding the use of LPG or CNG as a GSE fuel are quite similar and,
therefore, both fueling strategies can be treated together. Generally, non-methane
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hydrocarbon (NMHC), CO, NOX, PM, and CO2 emissions from LPG or CNG GSE are all
reduced relative to emissions from gasoline-powered GSE. Relative to diesel GSE,
emissions of NOX and PM are reduced, emissions of HC and CO are increased, and
emissions of CO2 can be either slightly increased or decreased depending on equipment
size. This section presents a review of important issues in determining the viability of
either conversion or replacement strategies.
Electric GSE - The majority of conventionally powered GSE can be either converted to
electric power or replaced with specially manufactured electrically powered counterparts.
Although there is an increase in offsite power generating station emissions resulting from
the increased electrical demand required to recharge electric GSE, conversion to electric
power or replacement with electric GSE can be a very effective emission reduction
strategy. Even when the increased emissions from power generating stations are
considered, electric GSE usually emit* significantly less HC, CO, NOX, PM, and CO2
emissions than their fossil-fueled (i.e., gasoline, diesel, CNG, and LPG) counterparts.
This section reviews issues for consideration in determining the viability of either
conversion or replacement strategies.
Emissions Aftertreatment - The majority of GSE continue to emit pollutants at
essentially uncontrolled rates. Certain emission species such as HC, CO, and, in some
cases, NOX can be substantially reduced by the installation of a catalytic converter in the
equipment exhaust system. Exhaust system traps (or filters) can perform similar
reduction functions for PM. Catalyst technology has been well proven in on-road vehicle
applications and paniculate trap technology has advanced considerably over the last
several years. Both systems are commercially available for equipment in the off-road
sector, but long-term reliability and effectiveness have not been proven. This section
presents a review of the systems designed for application on gasoline, diesel, CNG, and
LPG engines.
Fixed Gate Support - While the majority of conventionally powered GSE can be either
converted to or replaced by GSE powered by alternative fuels such as LPG, CNG, or
electricity, a significant fraction of GSE can be eliminated entirely by incorporating fixed
point-of-use support equipment into aircraft gate design. Such design not only eliminates
all energy demands associated with moving displaced mobile GSE between aircraft gates
and maintenance/storage facilitates, but also facilitates the use of "hard-wired" electrical
power connections, thereby eliminating the need for a recharging infrastructure and
scheduling plan. Although, as with electrically powered GSE, there is an increase in
offsite power generating station emissions due to the increased demand for electrical
power, fixed equipment is likely to consume less power than equivalent mobile GSE due
to the elimination of the motive aspect of GSE operation. Even when the increased
emissions from power generating stations are considered, fixed electrically powered
support equipment usually emit significantly less HC, CO, NOX, PM, and CO2 emissions
Technically, electrically powered GSE do not emit any pollutants. The term emit, as used here, ascribes to the
electric GSE, the offsite increase in power generating station emissions due to increased airport electrical power to
support electric GSE recharging. In essence, the electrically powered GSE are treated as if they "emitted" the
increased power generating station emissions associated with their use.
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than their mobile fossil-fueled (i.e., gasoline, diesel, CNG, and LPG) counterparts. This
section reviews issues related to the capital and operating cost and reliability of fixed
gate-based equipment.
GSE Control Strategy Summary - An evaluation of GSE and associated service
demands indicates that there are several control strategies that offer the potential to
reduce emissions over both the long and the short term. Such strategies include both
demonstrated and innovative technologies. All have associated issues that must be
considered prior to implementation, but a generalized classification includes the
following:
•The development of new engine emission standards for all currently unregulated
equipment;
•The replacement or conversion of gasoline or diesel powered GSE to LPG or CNG
fueling;
•The replacement or conversion of gasoline, diesel, LPG, or CNG powered GSE to
electric power;
•The replacement of mobile GSE with electrically powered fixed gate-based equipment;
•The retrofit of existing GSE with catalytic converters or particulate traps; and
•The preferential replacement of existing two-stroke gasoline engines.
As might be expected, both the feasibility and cost effectiveness of emission reductions
vary considerably across the potential control strategies. This section provides an
overview of the major issues associated with each strategy and, where possible, provides
an estimate of associated emissions reduction and cost effectiveness.
Estimating GSE Activity - Knowledge of the activity levels of airport GSE is critical to
accurately determining emissions performance. This is true regardless of whether one
considers the baseline emissions performance of today's GSE fleet or the potential
emission reductions that can be derived through the implementation of various control
measures. Either assessment requires the detailed characterization of equipment
population and/or usage rates to derive accurate emission or emission reduction estimates.
This section presents a review of the basic GSE emissions calculation methodology and
methods available to prepare population estimates.
GSEModel Instructions - GSEModel is a personal computer spreadsheet-based analysis
tool that has been developed to quantify emission benefits and calculate the cost-
effectiveness of converting existing airport GSE to cleaner-burning fuels and engine
technologies. The model has been developed as a planning tool for use by metropolitan
planning organizations (MPOs), airports, and other agencies interested in evaluating
potential emission benefits and cost savings resulting from available GSE emission
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control technologies. It has been designed with a mouse-enabled graphical user interface
to make it simple and easy to use.
The GSEModel tool is based upon the "best practice" methodologies and information
presented in the body of this report. It has been designed to utilize local (i.e., airport-
specific) GSE usage and cost information coupled with best-available emission factor
data to perform the following functions using a consistent methodology:
•Estimate current and alternative technology GSE emissions by individual equipment
category (e.g., aircraft pushback tractors, baggage tugs, cargo loaders, etc.);
•Compute the emission benefits of the available alternative technologies;
•Quantify the incremental capital, operating, and life-cycle costs of converting GSE units
to these alternative technologies; and
•Calculate and compare the cost-effectiveness (cost per unit emissions reduced, e.g.,
$/ton) of these alternative technologies for each equipment category under airport-specific
operating and usage conditions.
A description of the model and operating instructions are presented in this section.
This project was conducted by Sierra Research, Inc. (Sierra) and Energy &
Environmental Analysis, Inc. (EEA) under Work Assignment 0-05 of U.S.
Environmental Protection Agency (EPA) contract #68-C7-0051. Sierra served in an
oversight capacity and had primary responsibility for preparing the spreadsheet model for
quantifying GSE model and related documentation. EEA had the lead responsibility for
preparing all of the other sections presented in this report.
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AVAILABLE INFORMATION SOURCES
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TABLE 1. GENERAL REPORTS
TITLE
Airline Industry Talking Points on South
Coast/Sacramento FIPs
Manual Calculation Methods for Air Pollution
Inventories
Air Pollution Mitigation Measures for Airports and
Associated Activity
Electric Vehicles at Boston's Logan Airport (IN-
102438)
Airport Electrification Project: Consolidated
Results and Analysis (TR- 109041)
Power Quality Guidelines for Airport (TC-108418)
Document Control List
Methodology to Estimate Off-Road Equipment
Populations
Nonroad Engine and Vehicle Emission Study
Report
Airport Emission Inventories for FIP Areas
Technical Support Document Civil and Military
Aviation, California FIP NPRM
DATE
Nov-93
May-88
May-94
1994
1997
1997
not dated
May-91
Nov-91
May-93
Mar-94
SPONSOR
Air Transport Association
Guy T. Fagin, Capt, USAF, BSC, USAF
Occupational and Environmental Health
Laboratory, Human Systems Division,
Brooks AFB, Texas 78235-5501
California Air Resources Board,
Sacramento, California
Layla Sandell, Electric Power Research
Institute, Palo Alto, California
Layla Sandell, Electric Power Research
Institute, Palo Alto, California
Layla Sandell, Electric Power Research
Institute, Palo Alto, California
Environmental Protection Agency
Environmental Protection Agency,
Office of Mobile Sources, Ann Arbor,
MI
Environmental Protection Agency,
Office of Mobile Sources, Ann Arbor,
MI
Environmental Protection Agency,
Office of Mobile Sources, Ann Arbor,
MI
Environmental Protection Agency,
Office of Mobile Sources, Ann Arbor,
MI
DESCRIPTION
Presents arguments from the airline industry regarding South
Coast/Sacramento FIPs. Airlines should be able to achieve greater GSE
emission reductions than estimated by EPA.
The purpose of this report was to provide guidelines for engineers on how
to perform Air Emission Inventories. This report provided example
calculations, emission factors, and an example inventory.
Provides a reference guide to emission mitigation techniques that can be
applied to ground support equipment. Each measure is described along
with guidelines for its use and constraints that may limit its effectiveness.
No abstract available
Studied electrification opportunities at seven airports and found that 96% of
all inventoried 1C vehicles and equipment could be converted (directly or
indirectly) to similar electric powered models.
No abstract available
List of all documents used by EEA to perform tasks related to Airport
Emissions Control Regulatory Support, all work which was conducted
under an E.H. Pechan State Assistance Contract.
Discusses method used to estimate airport equipment population, based on
aircraft departures as an activity indicator. Also collected population data
from airlines to compare to estimates.
Quantifies the contribution of nonroad sources to ozone and carbon
monoxide air pollution and to other pollutants. Includes inventory and
emissions estimates of Airport Service Equipment.
Mobile source airport emissions inventory data for various nonattainment
areas in CA. Report discusses data availability, recommendations for
further data collection, a review of control strategies, and a forecast of
aircraft fleet make up and activity.
This document discusses technical information used by EPA during its
development of the proposed FIP control strategy for aircraft operations.
Includes operations and emissions data for various types of GSE.
INCLUDES
REFERENCES?
no
no
yes
no
no
yes
yes
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TABLE 1. GENERAL REPORTS (CONTINUED)
TITLE
GSE Population Data
Analysis of GSE Emissions Associated with Airport
Operations in the South Coast Air Basin
Memo - FIP Emission and Cost Forecasts for Aviation
Sources: Controlled and Uncontrolled
Memo - Refinement of FIP Ground Support
Equipment Calculations
Technical Support Document Aircraft/ Airports,
California FIP Draft IFR
Technical Data to Support FAA's Advisory Circular on
Reducing Emissions from Commercial Aviation -
Draft Final Report
Analysis of Techniques to Reduce Air Emissions at
Airports
Airport Vehicle Fleets
Flying Off Course
Airport Impact Mitigation and Management Study
DATE
Sep-93
Jul-94
May-95
Feb-95
Sep-95
Jun-97
n/a
Oct-96
Jul-90
SPONSOR
Air Transport Association
Environmental Protection Agency
Environmental Protection Agency
Environmental Protection Agency
Environmental Protection Agency, Office
of Mobile Sources, Ann Arbor, MI
Rich Wilcox - Environmental Protection
Agency; Bill Albee - Federal Aviation
Administration
Environmental Protection Agency,
Washington, DC
Gas Research Institute
National Resources Defense Council
Washington, DC 20005
South California Association of
Governments Los Angeles, California
DESCRIPTION
Individual GSE population submissions from several ATA member
airlines as part of California FIP development process
Provides explanation of the analytical methodology used by EEA to
calculate air emissions from GSE in the California South Coast area.
Describes data sources, calculations, and results.
Documents the final methodology used for evaluating the cost and
benefit of the California FIP after revisions were made. Includes a
final summary of uncontrolled and controlled emissions and cost-
impact forecasts for APUs and GSE in the FIP areas.
Summarizes the calculation methodology of the refined GSE emission
estimates presented in the previous referenced memo (May 1995).
This document discusses technical information used by EPA during its
development of the interim final FIP control strategy for aircraft
operations. Includes operations and emissions data for various types
of GSE and emission control measures.
Presents technical data to support FAA's advisory Circular on
Reducing Emissions from Commercial Aviation. Data was collected
and compiled in four main areas, including GSE.
Examines control strategies to reduce air emissions from mobile
sources at airports, as well as the potential for application of controls at
four specific airports. Detailed emission inventories are constructed
for the four airports examined.
Currently not available. According to synopsis, presents the results of
a survey of vehicle fleets at airports in the United States and Canada.
Information collected indicates a growing NGV population at some of
the busiest airports.
Determines the most important environmental issues connected with
airports and the best management techniques airports are using to
mitigate them.
Outlines possible emission control measures that could be taken at 5
airports in the Southern California area. GSEs are not explored in
depth.
INCLUDES
REFERENCES?
no
no
no
no
yes
yes
no
yes
no
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TABLE 2. JOURNAL ARTICLES
TITLE
airport rEVolution
Preparing for Takeoff Newsletter -
Volume 1, Number 2
The Evolution of Preconditioned Air
and 400 Hz Central Systems
Selecting & Paying for Fixed Ground
Support Systems
Why Use a Gas Turbine as a Main
Power Source for Air Start Units?
California Clean Air Initiatives Bog
Down
Clean Air Update: A Draft MOU for
Clean Air in California's SCAQMD
Cleared for Landing: NGVs Find a
Niche at Nation's Airports
Airports: Models of Opportunity
In Plane Sight / A Flight Plan for the
Airport Market
Ground Support Goes Electric
US Moves Closer to Towbarless
Concept
Jane's Airports, Equipmentand Services
1996-97, ATOS 3-R Towbarless Tractor
DATE
Oct-94
1997
Feb-94
Oct-96
Jun-97
Sep-97
Apr-98
Jun-95
Sep-96
Jan-98
Dec-95
Dec-96
1996-
1997
SOURCE
EPRI Journal
EPRI
GSE Today
GSE Today
GSE Today
GSE Today
GSE Today
Natural Gas Fuels
Natural Gas Fuels
Natural Gas Fuels
Jane's Airport Review
Jane's Airport Review
Jane's Internet Web Site
DESCRIPTION
Air Quality regulations are encouraging the use of electric vehicles at
urban airports across the US. Airports are ideal for EVs, given the short
distances and predictable routes that airport vehicles typically travel.
Discusses electrification projects at various airports, focusing specifically
on Southwest Airlines at Phoenix Sky Harbor Int'l airport, who is
replacing diesel-powered tugs and conveyor belt loaders with their
electric counterparts.
Discusses why usage of preconditioned air (PCA) and 400 Hz central
systems has come about. Use of PCA and 400 Hz offers the aircraft
users opportunities to reduce costs, fuel usage, noise, and air pollution.
Discusses benefits of fixed power over APUs and presents a cost
analysis.
New generation gas turbine engines are less complex than diesel engines
and more straightforward. Other benefits include lower maintenance
costs, lower fuel and oil costs, longer life span, lower emissions, and take
up less space.
Discusses California's effort to reduce airport emissions in Southern
California. Problem with figuring out what agency would have authority
for GSE. Discusses different approaches that could be taken to reduce
emissions from GSE.
Discusses draft MOU prepared by ATA to develop a system of voluntary
compliance to reduce emissions from GSE in SCAQMD. Still have to
figure outbaseline emissions, where funds should come from, and getting
an accurate GSE operations inventory.
Airports are ideal locations for NGVs due to the relatively restricted
travel range. Discusses the potential for alternative fueled vehicles at
airports with a spotlight on Denver International Airport and it's natural
gas vehicle fleet.
Discusses airports that have begun converting vehicles to natural gas as
well as funding opportunities available to airports to assist with
conversions.
Natural gas is gaining a solid reputation for its performance in airport
applications. NGVs account for the largest share of the increasing airport
AFV population. However, GSE conversions are not as popular for
several reasons.
The market potential for electric GSE depends on legislative
requirements, perceived benefits, and the feasibility of converting.
Outlines the potential advantages or disadvantages of conversion to
electric GSE.
Benefits of towbarless tractors (TLT) and possibilities of establishing a
market in the US.
The idea of using the TLT for operational or dispatch towing to save fuel
seems to have disappeared and now these tractors are used for push-back
operations. It is likely TLTs will start replacing conventional tow-tractors
at a faster rate in the future.
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TABLE 3. AIRPORT REPORTS
TITLE
Sacramento International Airport, 1995 Annual Air Quality
Report
Sacramento International Airport, Annual Air Quality Report
- Fiscal Year 1992/1993
Baltimore-Washington International (BWI) Airport, Air
Quality Plan
Final Environmental Impact Statement - San Diego
International Airport, Lindbergh Field Facilities
Improvements
Phoenix Sky Harbor International Airport, Air Pollution
Reduction Measures 1991-1994
Maricopa Association of Governments, Aviation Air Quality
Study
Washington National Airport, New Terminal and Related
Facilities Project - 400 Hertz Power System Study
San Francisco International Airport Master Plan - Final FIR
Preconditioned Air and 400 HZ Study for San Francisco
International Airport, New Concourses "A" and "G"
LAX Energy Study for Future Preconditioned Air, 400 Hz,
and Battery Powered GSE Equipment
Environmental Studies - Boston-Logan International Airport
DATE
Apr-96
Sep-93
Sept. 94
Feb-94
Aug-95
Nov-96
Oct-91
May-92
Dec-94
Aug-95
1994 and
1995
SOURCE
Jim Humphries, Air Quality Coordinator, Sacramento
International Airport, Sacramento, CA 95837
Jim Humphries, Air Quality Coordinator, Sacramento
International Airport, Sacramento, CA 95837
Barbara Grey Manager, Programming and
Environmental Services, Maryland Aviation
Administration, BWI Baltimore, MD 21240
William Johnstone, Federal Aviation Administration,
Los Angeles, CA 90009
City of Phoenix Aviation Department, Environmental
Programs
Maricopa Association of Governments, Phoenix, AZ
85007
Metropolitan Washington Airports Authority,
Washington, DC
City of San Francisco, Department of City Planning,
San Francisco, CA
Aviation Systems, Inc. for Hellmuth, Obata, and
Kassabaum
Aviation Systems, Inc. for LAX
Massport, Boston, MA
DESCRIPTION
Includes emission estimates, mitigation measures, and associated
reductions.
Includes emission estimates, mitigation measures, and associated
reductions.
Explores primary sources of air emissions, inventory methods, emissions
estimates, projections for future emissions, and possible mitigation
measures. BWI noted that GSE are a leading source of emissions and
could increase in future years.
Includes emission estimates and mitigation measures.
Overview of emission reduction measures that have been initiated at Sky
Harbor - includes conversion of airport fleet vehicles to CNG.
Purpose of this study is to develop an aviation emissions preprocessor.
Also summarizes and evaluates emissions results obtained and discusses
further enhancement recommendations.
The purpose is to compare the use of APU vs. various other methods for
providing required power, while considering installation, operating and
fuel costs to determine payback periods.
Includes emissions estimates for GSE in the aggregate.
Purpose of this study was to analyze, based on life cycle cost,
preconditioned air and 400 Hz systems using either central or point of use
systems. Includes cost analysis.
Determine the increase in electrical power as a result of adding PCA and
400 Hz systems to those gates which do not currently have them, and in
addition, the power required if all or most of the GSE was changed to
battery power
Includes emissions estimates for GSE, mitigation measures, and emission
projections.
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TABLE 4. GSE MANUFACTURER PRODUCT INFORMATION
MANUFACTURER AND
GSE TYPE
Various
Krauss-Maffei - Towbarless Tractor
Krauss-Maffei - Towbarless Tractor
Krauss-Maffei - Towbarless Tractor
Krauss-Maffei - Towbarless Tractor
FMT - Aircraft Gate Support
Equipment
FMT - Aircraft Gate Support
Equipment
Hobart - Ground Power Units
EMC Jet Way Systems - PC Air and
400 Hz
EMC Jet Way Systems - PCA, 400 Hz,
potable water
DESCRIPTION
"Advanced Transportation Vehicle Catalog" internet
web site : www. calstart. org/cgi-bin/catalog .cgi
Report - "The Super Tug Advantage"
Extract from a presentation of a paper concerning
"Towbarless Towing by Nose Gear Clamping"
Product Brochure
Product Brochure
Product Brochure
Product Presentation Material
Product Brochure
Report "400 Hz and PC Air Point of Use Systems"
Product Brochure
INFORMATION INCLUDED
The CALSTART website provides specifications for
electric and alternative fuel GSE.
Includes technology information, emissions analysis at
LAX, and environmental aspects (fuel savings, noise
reduction, and exhaust gas reduction).
Includes net fuel savings, advantages of towbarless
towing, fuel consumption comparisons, and emissions
savings.
Includes technology information.
Includes technology information, specifications, user
experience.
Technology information, time savings.
Includes advantages of vehicle free gate, products
offered by FMT, and cost comparisons.
Technology information.
Includes two case studies done by Aviation Systems,
Inc. for LAX regarding feasibility of PC Air and 400
Hz systems. Also includes customer comments,
specifications, and cost comparisons.
Capital costs, operating estimates, and approximate
payback time.
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POTENTIAL CONTROL STRATEGIES
-------
TABLE 1. POTENTIAL HC REDUCTION STRATEGIES FOR AIRPORT GSE
GSE Type
Aircraft
Pushback
Tractor
Baggage
Tug
Belt
Loader
Carts
Tool&
Lavatory
Forklift
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2113
0
489
0
63
94
2759
4399
0
4863
0
973
270
1 0505
2429
0
2317
0
314
94
5154
31
612
610
0
0
910
2163
146
0
873
0
1583
737
3339
Fraction
of All
GSE
4.7%
0.0%
1.1%
0.0%
0.1%
0.2%
6 1%
9.8%
0.0%
10.8%
0.0%
2.2%
0.6%
23.3%
5.4%
0.0%
5.1%
0.0%
0.7%
0.2%
1 1 .4%
0.1%
1.4%
1.4%
0.0%
0.0%
2.0%
4.8%
0.3%
0.0%
1.9%
0.0%
3.5%
1.6%
74%
Fraction
of Type
Specific
GSE
76.6%
0.0%
17.7%
0.0%
2.3%
3.4%
41.9%
0.0%
46.3%
0.0%
9.3%
2.6%
47.1%
0.0%
45.0%
0.0%
6.1%
1.8%
1.4%
28.3%
28.2%
0.0%
0.0%
42.1%
4.4%
0.0%
26.1%
0.0%
47.4%
22.1%
Estimated
Fraction
of All
GSEHC
3.4%
0.0%
2.2%
0.0%
0.1%
0.0%
5 8%
4.6%
0.0%
26.6%
0.0%
2.7%
0.0%
33.8%
1.7%
0.0%
6.4%
0.0%
0.4%
0.0%
8.5%
0.0%
2.0%
0.1%
0.0%
0.0%
0.0%
2.1%
0.0%
0.0%
1.5%
0.0%
1.0%
0.0%
2 5%
Potential HC Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
50
n/a
n/a
n/a
50
n/a
n/a
n/a
50
n/a
n/a
n/a
97
45
n/a
n/a
65
n/a
n/a
Convert
to CNG
Fueling
n/a
65
35
n/a
n/a
65
35
n/a
n/a
65
35
n/a
n/a
98
65
n/a
n/a
75
35
n/a
Replace
with LPG
Equipment
up 135
50
n/a
n/a
up 105
50
n/a
n/a
up 45
50
n/a
n/a
up 375
97
45
n/a
up 105
65
n/a
n/a
Replace
with CNG
Equipment
up 55
65
35
n/a
up 35
65
35
n/a
up 5
65
35
n/a
up 215
98
65
n/a
up 35
75
35
n/a
Replace2
withEV
Equipment
96
99+
98
n/a
97
99+
99
n/a
98
99+
99
n/a
98
99.9+
99+
n/a
98
99+
99
n/a
Retrofit
with Oxy
Catalyst
50
90
70
n/a
50
90
70
n/a
50
90
70
n/a
50
80
90
n/a
50
90
70
n/a
Retrofit
withPM
Trap
20
n/a
n/a
n/a
20
n/a
n/a
n/a
20
n/a
n/a
n/a
20
n/a
n/a
n/a
20
n/a
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
n/a
n/a
n/a
n/a
97
99+
99
0
98
99+
99
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
94
n/a
n/a
n/a
n/a
n/a
n/a
-1-
-------
TABLE 1. POTENTIAL HC REDUCTION STRATEGIES FOR AIRPORT GSE
(Continued)
GSE Type
Ground
Power
Unit
Service
Trucks
Fuel, Food,
Lavatory,
Water, &
Other
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2504
0
94
0
0
455
30.53
409
0
2905
0
251
0
3565
3053X
Fraction
of All
GSE
5.6%
0.0%
0.2%
0.0%
0.0%
1.0%
6.8%
0.9%
0.0%
6.4%
0.0%
0.6%
0.0%
7.9%
67. 8%
Fraction
of Type
Specific
GSE
82.0%
0.0%
3.1%
0.0%
0.0%
14.9%
11.5%
0.0%
81.5%
0.0%
7.0%
0.0%
Estimated
Fraction
of All
GSEHC
3.7%
0.0%
0.7%
0.0%
0.0%
0.0%
4.3%
0.2%
0.0%
8.4%
0.0%
0.4%
0.0%
9.0%
66. %
Potential HC Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
50
n/a
n/a
50
n/a
Convert
to CNG
Fueling
n/a
65
n/a
n/a
65
35
Replace
with LPG
Equipment
up 135
50
n/a
up 155
50
n/a
Replace
with CNG
Equipment
up 55
65
n/a
up 70
65
35
Replace2
withEV
Equipment
96
99+
n/a
96
99+
98
Retrofit
with Oxy
Catalyst
50
90
n/a
50
90
70
Retrofit
withPM
Trap
20
n/a
n/a
20
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
96
99+
0
96
99+
99
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier "up" signify emission increases (in percent).
Emission reductions due to replacement with EV equipment can vary with the emissions performance of local power generating stations. The tabulated values represent "typical" or "average"
power generating station emission rates. For HC, the range of emissions variability across U.S. power generating stations is not dramatic and the tabulated emission reduction percentages will be
affected by only a few percentage points regardless of local conditions.
In addition to the potential for direct replacement of some GSE services, fixed, gate-based systems such as electrical power and conditioned air also potentially reduce aircraft auxiliary power unit
(APU) emissions by 70-90 percent and emissions from (non-tabulated) GSE-based air conditioning service equipment by nearly 100 percent. Of the tabulated GSE, ground power unit (GPU)
replacement is most feasible, with baggage tug and belt loader replacement quite difficult in retrofit applications.
-2-
-------
TABLE 2. POTENTIAL CO REDUCTION STRATEGIES FOR AIRPORT GSE
GSE Type
Aircraft
Pushback
Tractor
Baggage
Tug
Belt
Loader
Carts
Tool&
Lavatory
Forklift
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2113
0
489
0
63
94
2759
4399
0
4863
0
973
270
1 0505
2429
0
2317
0
314
94
5154
31
612
610
0
0
910
2163
146
0
873
0
1583
737
3339
Fraction
of All
GSE
4.7%
0.0%
1.1%
0.0%
0.1%
0.2%
6 1%
9.8%
0.0%
10.8%
0.0%
2.2%
0.6%
23.3%
5.4%
0.0%
5.1%
0.0%
0.7%
0.2%
1 1 .4%
0.1%
1.4%
1.4%
0.0%
0.0%
2.0%
4.8%
0.3%
0.0%
1.9%
0.0%
3.5%
1.6%
74%
Fraction
of Type
Specific
GSE
76.6%
0.0%
17.7%
0.0%
2.3%
3.4%
41.9%
0.0%
46.3%
0.0%
9.3%
2.6%
47.1%
0.0%
45.0%
0.0%
6.1%
1.8%
1.4%
28.3%
28.2%
0.0%
0.0%
42.1%
4.4%
0.0%
26.1%
0.0%
47.4%
22.1%
Estimated
Fraction
of All
GSE CO
0.4%
0.0%
4.1%
0.0%
0.3%
0.0%
49%
0.4%
0.0%
37.9%
0.0%
4.7%
0.0%
43.0%
0.1%
0.0%
9.1%
0.0%
0.8%
0.0%
10.0%
0.0%
0.1%
0.1%
0.0%
0.0%
0.0%
0.2%
0.0%
0.0%
2.0%
0.0%
1.7%
0.0%
3 8%
Potential CO Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
40
n/a
n/a
n/a
40
n/a
n/a
n/a
40
n/a
n/a
n/a
20
40
n/a
n/a
55
n/a
n/a
Convert
to CNG
Fueling
n/a
40
0
n/a
n/a
40
0
n/a
n/a
40
0
n/a
n/a
20
40
n/a
n/a
55
0
n/a
Replace
with LPG
Equipment
up 4000
40
n/a
n/a
up 4000
40
n/a
n/a
up 3500
40
n/a
n/a
up 5000
20
40
n/a
up 4000
55
n/a
n/a
Replace
with CNG
Equipment
up 4000
40
0
n/a
up 4000
40
0
n/a
up 3500
40
0
n/a
up 5000
20
40
n/a
up 4000
55
0
n/a
Replace2
withEV
Equipment
98
99.9+
99.9+
n/a
98
99.9+
99.9+
n/a
98
99.9+
99.9+
n/a
98
99.9+
99.9+
n/a
98
99.9+
99.9+
n/a
Retrofit
with Oxy
Catalyst
90
90
90
n/a
90
90
90
n/a
90
90
90
n/a
90
90
90
n/a
90
90
90
n/a
Retrofit
withPM
Trap
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
n/a
n/a
n/a
n/a
98
99.9+
99.9+
0
98
99.9+
99.9+
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
up 30
n/a
n/a
n/a
n/a
n/a
n/a
-3-
-------
TABLE 2. POTENTIAL CO REDUCTION STRATEGIES FOR AIRPORT GSE
(Continued)
GSE Type
Ground
Power
Unit
Service
Trucks
Fuel, Food,
Lavatory,
Water, &
Other
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2504
0
94
0
0
455
3053
409
0
2905
0
251
0
3565
30538
Fraction
of All
GSE
5.6%
0.0%
0.2%
0.0%
0.0%
1.0%
6 8%
0.9%
0.0%
6.4%
0.0%
0.6%
0.0%
7.9%
67 8%
Fraction
of Type
Specific
GSE
82.0%
0.0%
3.1%
0.0%
0.0%
14.9%
11.5%
0.0%
81.5%
0.0%
7.0%
0.0%
Estimated
Fraction
of All
GSE CO
0.5%
0.0%
1.2%
0.0%
0.0%
0.0%
1 7%
0.0%
0.0%
15.3%
0.0%
1.0%
0.0%
16.4%
79 9%
Potential CO Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
40
n/a
n/a
40
n/a
Convert
to CNG
Fueling
n/a
40
n/a
n/a
40
0
Replace
with LPG
Equipment
up 4000
40
n/a
up 4500
40
n/a
Replace
with CNG
Equipment
up 4000
40
n/a
up 4500
40
0
Replace2
withEV
Equipment
98
99.9+
n/a
98
99.9+
99.9+
Retrofit
with Oxy
Catalyst
90
90
n/a
90
90
90
Retrofit
withPM
Trap
0
n/a
n/a
0
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
99.9+
0
98
99.9+
99.9+
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
1 Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier "up" signify emission increases (in percent).
2 Emission reductions due to replacement with EV equipment can vary with the emissions performance of local power generating stations. The tabulated values represent "typical" or "average"
power generating station emission rates. For CO, the range of emissions variability across U.S. power generating stations is not dramatic and the tabulated emission reduction percentages will be
affected by only a few percentage points regardless of local conditions.
3 In addition to the potential for direct replacement of some GSE services, fixed, gate-based systems such as electrical power and conditioned air also potentially reduce aircraft auxiliary power unit
(APU) emissions by 70-90 percent and emissions from (non-tabulated) GSE-based air conditioning service equipment by nearly 100 percent. Of the tabulated GSE, ground power unit (GPU)
replacement is most feasible, with baggage tug and belt loader replacement quite difficult in retrofit applications.
-4-
-------
TABLE 3. POTENTIAL N(X REDUCTION STRATEGIES FOR AIRPORT GSE
GSE Type
Aircraft
Pushback
Tractor
Baggage
Tug
Belt
Loader
Carts
Tool&
Lavatory
Forklift
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2113
0
489
0
63
94
2759
4399
0
4863
0
973
270
1 0505
2429
0
2317
0
314
94
5154
31
612
610
0
0
910
2163
146
0
873
0
1583
737
3339
Fraction
of All
GSE
4.7%
0.0%
1.1%
0.0%
0.1%
0.2%
6 1%
9.8%
0.0%
10.8%
0.0%
2.2%
0.6%
23.3%
5.4%
0.0%
5.1%
0.0%
0.7%
0.2%
1 1 .4%
0.1%
1.4%
1.4%
0.0%
0.0%
2.0%
4.8%
0.3%
0.0%
1.9%
0.0%
3.5%
1.6%
74%
Fraction
of Type
Specific
GSE
76.6%
0.0%
17.7%
0.0%
2.3%
3.4%
41.9%
0.0%
46.3%
0.0%
9.3%
2.6%
47.1%
0.0%
45.0%
0.0%
6.1%
1.8%
1.4%
28.3%
28.2%
0.0%
0.0%
42.1%
4.4%
0.0%
26.1%
0.0%
47.4%
22.1%
Estimated
Fraction
of All
GSE NOX
19.4%
0.0%
1.0%
0.0%
0.1%
0.0%
20 5%
18.8%
0.0%
7.9%
0.0%
1.2%
0.0%
28.0%
2.6%
0.0%
1.9%
0.0%
0.2%
0.0%
4.7%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.2%
0.0%
0.3%
0.0%
0.4%
0.0%
1 0%
Potential NOX Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
25
n/a
n/a
n/a
25
n/a
n/a
n/a
25
n/a
n/a
n/a
up 135
50
n/a
n/a
20
n/a
n/a
Convert
to CNG
Fueling
n/a
25
0
n/a
n/a
25
0
n/a
n/a
25
0
n/a
n/a
up 135
50
n/a
n/a
20
0
n/a
Replace
with LPG
Equipment
75
25
n/a
n/a
80
25
n/a
n/a
55
25
n/a
n/a
80
up 135
50
n/a
80
20
n/a
n/a
Replace
with CNG
Equipment
75
25
0
n/a
80
25
0
n/a
55
25
0
n/a
80
up 135
50
n/a
80
20
0
n/a
Replace2
withEV
Equipment
97
90
90
n/a
97
90
90
n/a
95
90
90
n/a
96
55
90
n/a
97
90
90
n/a
Retrofit
with Oxy
Catalyst
0
0
0
n/a
0
0
0
n/a
0
0
0
n/a
0
0
0
n/a
0
0
0
n/a
Retrofit
withPM
Trap
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
0
n/a
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
n/a
n/a
n/a
n/a
97
90
90
0
95
90
90
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
up 360
n/a
n/a
n/a
n/a
n/a
n/a
-5-
-------
TABLE 3. POTENTIAL NOX REDUCTION STRATEGIES FOR AIRPORT GSE
(Continued)
GSE Type
Ground
Power
Unit
Service
Trucks
Fuel, Food,
Lavatory,
Water, &
Other
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2504
0
94
0
0
455
3053
409
0
2905
0
251
0
3565
30538
Fraction
of All
GSE
5.6%
0.0%
0.2%
0.0%
0.0%
1.0%
6.8%
0.9%
0.0%
6.4%
0.0%
0.6%
0.0%
7.9%
67.8%
Fraction
of Type
Specific
GSE
82.0%
0.0%
3.1%
0.0%
0.0%
14.9%
11.5%
0.0%
81.5%
0.0%
7.0%
0.0%
Estimated
Fraction
of All
GSE NOV
20.9%
0.0%
0.3%
0.0%
0.0%
0.1%
21 .3%
1.4%
0.0%
3.7%
0.0%
0.3%
0.0%
5.3%
80.8%
Potential NOX Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
25
n/a
n/a
25
n/a
Convert
to CNG
Fueling
n/a
25
n/a
n/a
25
0
Replace
with LPG
Equipment
75
25
n/a
70
25
n/a
Replace
with CNG
Equipment
75
25
n/a
70
25
0
Replace'
withEV
Equipment
97
90
n/a
97
90
90
Retrofit
with Oxy
Catalyst
0
0
n/a
0
0
0
Retrofit
withPM
Trap
0
n/a
n/a
0
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
97
90
0
97
90
90
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier "up" signify emission increases (in percent).
Emission reductions due to replacement with EV equipment can vary with the emissions performance of local power generating stations. The tabulated values represent "typical" or "average"
power generating station emission rates. For NOX, the range of emissions variability across U.S. power generating stations is dramatic and emission reduction percentages can range, depending on
local conditions, from: a 182 percent increase through a 91 percent reduction relative to 2-stroke gasoline emissions; a 40-90 percent reduction relative to 4-stroke gasoline emissions; a 20-97
percent reduction relative to LPG emissions; or a 60-99+ percent reduction relative to diesel emissions.
In addition to the potential for direct replacement of some GSE services, fixed, gate-based systems such as electrical power and conditioned air also potentially reduce aircraft auxiliary power unit
(APU) emissions by 70-90 percent and emissions from (non-tabulated) GSE-based air conditioning service equipment by nearly 100 percent. Of the tabulated GSE, ground power unit (GPU)
replacement is most feasible, with baggage tug and belt loader replacement quite difficult in retrofit applications.
-6-
-------
TABLE 4. POTENTIAL PM REDUCTION STRATEGIES FOR AIRPORT GSE
GSE Type
Aircraft
Pushback
Tractor
Baggage
Tug
Belt
Loader
Carts
Tool&
Lavatory
Forklift
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2113
0
489
0
63
94
2759
4399
0
4863
0
973
270
10505
2429
0
2317
0
314
94
5154
31
612
610
0
0
910
2163
146
0
873
0
1583
737
3339
Fraction
of All
GSE
4.7%
0.0%
1.1%
0.0%
0.1%
0.2%
6 1%
9.8%
0.0%
10.8%
0.0%
2.2%
0.6%
23 3%
5.4%
0.0%
5.1%
0.0%
0.7%
0.2%
1 1 .4%
0.1%
1.4%
1.4%
0.0%
0.0%
2.0%
48%
0.3%
0.0%
1.9%
0.0%
3.5%
1.6%
74%
traction
of Type
Specific
GSE
76.6%
0.0%
17.7%
0.0%
2.3%
3.4%
41.9%
0.0%
46.3%
0.0%
9.3%
2.6%
47.1%
0.0%
45.0%
0.0%
6.1%
1.8%
1.4%
28.3%
28.2%
0.0%
0.0%
42.1%
4.4%
0.0%
26.1%
0.0%
47.4%
22.1%
Estimated
Fraction
of All
GSEPM
21.6%
0.0%
0.1%
0.0%
0.0%
0.0%
21 7%
26.8%
0.0%
1.6%
0.0%
0.3%
0.0%
28 8%
6.2%
0.0%
0.4%
0.0%
0.0%
0.0%
6.6%
0.0%
0.6%
0.0%
0.0%
0.0%
0.0%
06%
0.3%
0.0%
0.1%
0.0%
0.1%
0.0%
0 5%
Potential PM Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
15
n/a
n/a
n/a
15
n/a
n/a
n/a
15
n/a
n/a
n/a
98
35
n/a
n/a
35
n/a
n/a
Convert
to CNG
Fueling
n/a
15
0
n/a
n/a
15
0
n/a
n/a
15
0
n/a
n/a
98
35
n/a
n/a
35
0
n/a
Replace
with LPG
Equipment
97
15
n/a
n/a
96
15
n/a
n/a
96
15
n/a
n/a
85
98
35
n/a
96
35
n/a
n/a
Replace
with CNG
Equipment
97
15
0
n/a
96
15
0
n/a
96
15
0
n/a
85
98
35
n/a
96
35
0
n/a
Replace2
with EV
Equipment
97
20
5
n/a
98
45
35
n/a
97
45
35
n/a
98
99+
90
n/a
98
55
30
n/a
Retrofit
with Oxy
Catalyst
30
10
10
n/a
30
10
10
n/a
30
10
10
n/a
30
10
10
n/a
30
10
10
n/a
Retrofit
withPM
Trap
90
n/a
n/a
n/a
90
n/a
n/a
n/a
90
n/a
n/a
n/a
90
n/a
n/a
n/a
90
n/a
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
n/a
n/a
n/a
n/a
98
45
35
0
97
45
35
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
96
n/a
n/a
n/a
n/a
n/a
n/a
-7-
-------
TABLE 4. POTENTIAL PM REDUCTION STRATEGIES FOR AIRPORT GSE
(Continued)
GSE Type
Ground
Power
Unit
Service
Trucks
Fuel, Food,
Lavatory,
Water, &
Other
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2504
0
94
0
0
455
3053
409
0
2905
0
251
0
3565
30538
Fraction
of All
GSE
5.6%
0.0%
0.2%
0.0%
0.0%
1.0%
6.8%
0.9%
0.0%
6.4%
0.0%
0.6%
0.0%
7.9%
67.8%
Fraction
of Type
Specific
GSE
82.0%
0.0%
3.1%
0.0%
0.0%
14.9%
11.5%
0.0%
81.5%
0.0%
7.0%
0.0%
Estimated
Fraction
of All
GSEPM
23.0%
0.0%
0.0%
0.0%
0.0%
0.1%
23.2%
1.5%
0.0%
0.5%
0.0%
0.0%
0.0%
2.0%
83.4%
Potential PM Emission Reduction (Percent Reduction1) it:
Convert
to LPG
Fueling
n/a
15
n/a
n/a
15
n/a
Convert
to CNG
Fueling
n/a
15
n/a
n/a
15
0
Replace
with LPG
Equipment
96
15
n/a
96
15
n/a
Replace
with CNG
Equipment
96
15
n/a
96
15
0
Replace'
withEV
Equipment
97
20
n/a
97
20
5
Retrofit
with Oxy
Catalyst
30
10
n/a
30
10
10
Retrofit
withPM
Trap
90
n/a
n/a
90
n/a
n/a
Replace3
with Fixed
"At Gate"
Equipment
97
20
0
97
20
5
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier "up" signify emission increases (in percent).
Emission reductions due to replacement with EV equipment can vary with the emissions performance of local power generating stations. The tabulated values represent "typical" or "average"
power generating station emission rates. For PM, the range of emissions variability across U.S. power generating stations is dramatic and emission reduction percentages can range, depending on
local conditions, from: an 80-99+ percent reduction relative to 2-stroke gasoline emissions; a 5000 percent increase through a 98 percent reduction relative to 4-stroke gasoline emissions; a 6000
percent increase through a 98 percent reduction relative to LPG emissions; or a 100 percent increase through a 99+ percent reduction relative to diesel emissions.
In addition to the potential for direct replacement of some GSE services, fixed, gate-based systems such as electrical power and conditioned air also potentially reduce aircraft auxiliary power unit
(APU) emissions by 70-90 percent and emissions from (non-tabulated) GSE-based air conditioning service equipment by nearly 100 percent. Of the tabulated GSE, ground power unit (GPU)
replacement is most feasible, with baggage tug and belt loader replacement quite difficult in retrofit applications.
-------
TABLE 5. POTENTIAL CO2 REDUCTION STRATEGIES FOR AIRPORT GSE1
GSE Type
Aircraft
Pushback
Tractor
Baggage
Tug
Belt
Loader
Carts
Tool&
Lavatory
Forklift
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2113
0
489
0
63
94
2759
4399
0
4863
0
973
270
1 0505
2429
0
2317
0
314
94
5154
31
612
610
0
0
910
2163
146
0
873
0
1583
737
3339
Fraction
of All
GSE
4.7%
0.0%
1.1%
0.0%
0.1%
0.2%
6 1%
9.8%
0.0%
10.8%
0.0%
2.2%
0.6%
23.3%
5.4%
0.0%
5.1%
0.0%
0.7%
0.2%
1 1 .4%
0.1%
1.4%
1.4%
0.0%
0.0%
2.0%
4.8%
0.3%
0.0%
1.9%
0.0%
3.5%
1.6%
74%
Fraction
of Type
Specific
GSE
76.6%
0.0%
17.7%
0.0%
2.3%
3.4%
41.9%
0.0%
46.3%
0.0%
9.3%
2.6%
47.1%
0.0%
45.0%
0.0%
6.1%
1.8%
1.4%
28.3%
28.2%
0.0%
0.0%
42.1%
4.4%
0.0%
26.1%
0.0%
47.4%
22.1%
Estimated
Fraction
of All
GSE CO2
10.2%
0.0%
1.8%
0.0%
0.2%
0.2%
1 2 4%
9.5%
0.0%
15.2%
0.0%
2.5%
0.4%
27.6%
2.8%
0.0%
3.6%
0.0%
0.4%
0.1%
6.9%
0.0%
0.1%
0.1%
0.0%
0.0%
0.0%
0.2%
0.1%
0.0%
0.8%
0.0%
1.2%
0.2%
23%
Potential CO2 Emission Reduction (Percent Reduction2) it:
^^onv^t
to LPG
Fueling
n/a
15
n/a
n/a
n/a
15
n/a
n/a
n/a
15
n/a
n/a
n/a
40
15
n/a
n/a
15
n/a
n/a
Convert
to CNG
Fueling
n/a
20
5
n/a
n/a
20
5
n/a
n/a
20
5
n/a
n/a
45
20
n/a
n/a
20
5
n/a
Replace
with LPG
Equipment
up 5
15
n/a
n/a
5
15
n/a
n/a
up 10
15
n/a
n/a
up 15
40
15
n/a
5
15
n/a
n/a
Replace
with CNG
Equipment
0
20
5
n/a
10
20
5
n/a
up 2
20
5
n/a
up 10
45
20
n/a
10
20
5
n/a
Replace3
withEV
Equipment
45
55
50
n/a
50
55
50
n/a
55
55
50
n/a
65
80
75
n/a
50
65
60
n/a
Retrofit
with Oxy
Catalyst
up 3
up 55
up 45
n/a
up 3
up 65
up 45
n/a
up 3
up 60
up 45
n/a
up 3
up 25
up 45
n/a
up 3
up 65
up 35
n/a
Retrofit
withPM
Trap
up 2
n/a
n/a
n/a
up 2
n/a
n/a
n/a
up 2
n/a
n/a
n/a
up 2
n/a
n/a
n/a
up 2
n/a
n/a
n/a
Replace*
with Fixed
"At Gate"
Equipment
n/a
n/a
n/a
n/a
50
55
50
0
55
55
50
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
30
n/a
n/a
n/a
n/a
n/a
n/a
-9-
-------
TABLE 5. POTENTIAL CO2 REDUCTION STRATEGIES FOR AIRPORT GSE1
(Continued)
GSE Type
Ground
Power
Unit
Service
Trucks
Fuel, Food,
Lavatory,
Water, &
Other
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
2504
0
94
0
0
455
3053
409
0
2905
0
251
0
3565
30538
Fraction
of All
GSE
5.6%
0.0%
0.2%
0.0%
0.0%
1.0%
6.8%
0.9%
0.0%
6.4%
0.0%
0.6%
0.0%
7.9%
67.8%
Fraction
of Type
Specific
GSE
82.0%
0.0%
3.1%
0.0%
0.0%
14.9%
11.5%
0.0%
81.5%
0.0%
7.0%
0.0%
Estimated
Fraction
of All
GSE CO,
11.2%
0.0%
0.5%
0.0%
0.0%
1.2%
1 2.9%
0.7%
0.0%
6.8%
0.0%
0.6%
0.0%
8.1%
70.4%
Potential CO2 Emission Reduction (Percent Reduction') it:
Convert
to LPG
Fueling
n/a
15
n/a
n/a
15
n/a
Convert
to CNG
Fueling
n/a
20
n/a
n/a
20
5
Replace
with LPG
Equipment
up 5
15
n/a
up 10
15
n/a
Replace
with CNG
Equipment
2
20
n/a
up 6
20
5
Replace3
withEV
Equipment
45
55
n/a
45
55
50
Retrofit
with Oxy
Catalyst
up 3
up 55
n/a
up 3
up 55
up 45
Retrofit
withPM
Trap
up 2
n/a
n/a
up 2
n/a
n/a
Replace*
with Fixed
"At Gate"
Equipment
55
0
45
55
50
Replace
with 4-Str
Gasoline
Equipment
n/a
n/a
n/a
n/a
n/a
n/a
1 Tabulated CO2 emissions and emission reductions are based on brake-specific fuel consumption estimates and are not adjusted for the relatively high CO emission rates of engines used in GSE.
The table, therefore, reflects a scenario in which CO emissions are already controlled to a level that is minor relative to CO2. The one exception is for oxidation catalyst installation, where the
tabulated increases in CO2 are primarily associated with the oxidation of large amounts of CO to CO2 (although an increase in exhaust system backpressure also contributes a small share of the
observed CO2 increases). Adjusting baseline GSE CO2 emission rates downward due to inherently high CO would negatively influence (by a substantial margin) the CO2 impact of switching to
fuels with inherently low CO emissions. For example, correcting baseline 4-stroke gasoline CO2 emissions for high CO would alter the tabulated 15 percent CO2 emission reduction due to
conversion or replacement with LPG equipment to a 15-30 percent CO2 emissions increase.
2 Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier "up" signify emission increases (in percent).
3 Emission reductions due to replacement with EV equipment can vary with the emissions performance of local power generating stations. The tabulated values represent "typical" or "average"
power generating station emission rates. For CO2, the range of emissions variability across U.S. power generating stations is dramatic and emission reduction percentages can range, depending on
local conditions, from: a 75-90 percent reduction relative to 2-stroke gasoline emissions; a 40-85 percent reduction relative to 4-stroke gasoline emissions; a 30-85 percent reduction relative to
LPG emissions; or a 25-80 percent reduction relative to diesel emissions.
4 In addition to the potential for direct replacement of some GSE services, fixed, gate-based systems such as electrical power and conditioned air also potentially reduce aircraft auxiliary power unit
(APU) emissions by 70-90 percent and emissions from (non-tabulated) GSE-based air conditioning service equipment by nearly 100 percent. Of the tabulated GSE, ground power unit (GPU)
replacement is most feasible, with baggage tug and belt loader replacement quite difficult in retrofit applications.
-10-
-------
TABLE 6. ADDITIONAL GSE AND ASSOCIATED EMISSION IMPACT ESTIMATES
GSE Type
Conditioned
Air
Unit
Air
Start
Unit
Bobtail
Cargo
Loader
Deicer
Lift
Maintenance
Truck
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
Turbine
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
376
0
41
0
31
31
479
771
0
63
0
0
16
31
881
157
0
815
0
16
0
988
1129
0
220
0
110
0
1459
31
0
475
0
0
0
506
47
0
951
0
324
314
1636
16
0
1259
0
16
0
1291
Fraction
of All
GSE
0.8%
0.0%
0.1%
0.0%
0.1%
0.1%
1.1%
1.7%
0.0%
0.1%
0.0%
0.0%
0.0%
0.1%
20%
0.3%
0.0%
1.8%
0.0%
0.0%
0.0%
2 2%
2.5%
0.0%
0.5%
0.0%
0.2%
0.0%
3 2%
0.1%
0.0%
1.1%
0.0%
0.0%
0.0%
1 1%
0.1%
0.0%
2.1%
0.0%
0.7%
0.7%
36%
0.0%
0.0%
2.8%
0.0%
0.0%
0.0%
2 9%
Fraction
of Type
Specific
GSE
78.5%
0.0%
8.6%
0.0%
6.5%
6.5%
87.5%
0.0%
7.2%
0.0%
0.0%
1.8%
3.5%
15.9%
0.0%
82.5%
0.0%
1.6%
0.0%
77.4%
0.0%
15.1%
0.0%
7.5%
0.0%
6.1%
0.0%
93.9%
0.0%
0.0%
0.0%
2.9%
0.0%
58.1%
0.0%
19.8%
19.2%
1.2%
0.0%
97.5%
0.0%
1.2%
0.0%
Estimated
Fraction
of All
GSEHC
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
1.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0.0%
1 1%
0.2%
0.0%
4.5%
0.0%
0.0%
0.0%
47%
0.9%
0.0%
0.6%
0.0%
0.2%
0.0%
1 6%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0 1%
0.0%
0.0%
2.0%
0.0%
0.3%
0.0%
24%
0.0%
0.0%
2.9%
0.0%
0.0%
0.0%
3 0%
Estimated
Fraction
of All
GSE CO
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.1%
0.0%
0.1%
0.0%
0.0%
0.0%
0.0%
03%
0.0%
0.0%
6.3%
0.0%
0.1%
0.0%
64%
0.1%
0.0%
0.9%
0.0%
0.3%
0.0%
1 3%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0 1%
0.0%
0.0%
2.9%
0.0%
0.6%
0.0%
3 5%
0.0%
0.0%
5.4%
0.0%
0.0%
0.0%
5 4%
Estimated
Fraction
of All
GSE NOX
0.2%
0.0%
0.0%
0.0%
0.0%
0.0%
0.2%
5.6%
0.0%
0.0%
0.0%
0.0%
0.0%
0.2%
5 9%
0.9%
0.0%
1.3%
0.0%
0.0%
0.0%
2 2%
3.5%
0.0%
0.2%
0.0%
0.1%
0.0%
3 8%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
00%
0.1%
0.0%
0.6%
0.0%
0.2%
0.0%
09%
0.0%
0.0%
1.3%
0.0%
0.0%
0.0%
1 3%
Estimated
Fraction
of All
GSEPM
0.2%
0.0%
0.0%
0.0%
0.0%
0.0%
0.2%
6.3%
0.0%
0.0%
0.0%
0.0%
0.0%
0.3%
66%
1.2%
0.0%
0.3%
0.0%
0.0%
0.0%
1 5%
5.0%
0.0%
0.0%
0.0%
0.0%
0.0%
5 1%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
00%
0.1%
0.0%
0.1%
0.0%
0.0%
0.0%
03%
0.0%
0.0%
0.2%
0.0%
0.0%
0.0%
0 2%
Estimated
Fraction
of All
GSE CO2
0.1%
0.0%
0.0%
0.0%
0.0%
0.0%
0.1%
2.8%
0.0%
0.1%
0.0%
0.0%
0.0%
0.1%
3 0%
0.4%
0.0%
2.5%
0.0%
0.0%
0.0%
3 0%
1.8%
0.0%
0.4%
0.0%
0.2%
0.0%
2 3%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0 1%
0.1%
0.0%
1.2%
0.0%
0.3%
0.2%
1 7%
0.0%
0.0%
2.4%
0.0%
0.0%
0.0%
2 4%
-11-
-------
TABLE 6. ADDITIONAL GSE AND ASSOCIATED EMISSION IMPACT ESTIMATES
(Continued)
GSE Type
"Other"
GSE
Bus
Car
Pickup
Truck
Van
Apprepate
Engine
Type
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Diesel
2-str Gas
4-str Gas
CNG
LPG
Electric
All
Estimated
U.S.
Population
376
0
1195
0
141
31
1743
115
0
173
0
0
0
288
0
0
580
0
0
0
580
41
0
2595
0
141
0
mi
0
0
1842
0
63
0
1905
14533
Fraction
of All
GSE
0.8%
0.0%
2.7%
0.0%
0.3%
0.1%
3.9%
0.3%
0.0%
0.4%
0.0%
0.0%
0.0%
0.6%
0.0%
0.0%
1.3%
0.0%
0.0%
0.0%
1 .3%
0.1%
0.0%
5.8%
0.0%
0.3%
0.0%
6.2%
0.0%
0.0%
4.1%
0.0%
0.1%
0.0%
4.2%
32.2%
Fraction
of Type
Specific
GSE
21.6%
0.0%
68.6%
0.0%
8.1%
1.8%
39.9%
0.0%
60.1%
0.0%
0.0%
0.0%
0.0%
0.0%
100.0%
0.0%
0.0%
0.0%
1.5%
0.0%
93.4%
0.0%
5.1%
0.0%
0.0%
0.0%
96.7%
0.0%
3.3%
0.0%
Estimated
Fraction
of All
GSEHC
0.1%
0.0%
0.9%
0.0%
0.0%
0.0%
1 .0%
0.1%
0.0%
0.6%
0.0%
0.0%
0.0%
0.8%
0.0%
0.0%
0.6%
0.0%
0.0%
0.0%
0.6%
0.0%
0.0%
10.0%
0.0%
0.3%
0.0%
10.3%
0.0%
0.0%
8.2%
0.0%
0.1%
0.0%
8.3%
33.9%
Estimated
Fraction
of All
GSE CO
0.0%
0.0%
1.2%
0.0%
0.1%
0.0%
1 .2%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.9%
0.0%
0.0%
0.0%
0.9%
0.0%
0.0%
0.7%
0.0%
0.0%
0.0%
0.8%
20.1%
Estimated
Fraction
of All
GSE NOX
0.1%
0.0%
0.2%
0.0%
0.0%
0.0%
0.3%
0.1%
0.0%
0.1%
0.0%
0.0%
0.0%
0.3%
0.0%
0.0%
0.1%
0.0%
0.0%
0.0%
0.1%
0.0%
0.0%
2.2%
0.0%
0.1%
0.0%
2.3%
0.0%
0.0%
1.8%
0.0%
0.0%
0.0%
1 .9%
1 9.2%
Estimated
Fraction
of All
GSEPM
0.2%
0.0%
0.0%
0.0%
0.0%
0.0%
0.3%
0.6%
0.0%
0.1%
0.0%
0.0%
0.0%
0.7%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.9%
0.0%
0.0%
0.0%
1 .0%
0.0%
0.0%
0.8%
0.0%
0.0%
0.0%
0.8%
16.6%
Estimated
Fraction
of All
GSE CO2
0.1%
0.0%
0.4%
0.0%
0.0%
0.0%
0.6%
0.3%
0.0%
0.5%
0.0%
0.0%
0.0%
0.8%
0.0%
0.0%
1.8%
0.0%
0.0%
0.0%
1 .8%
0.0%
0.0%
7.8%
0.0%
0.4%
0.0%
8.2%
0.0%
0.0%
5.6%
0.0%
0.2%
0.0%
5.7%
29.6%
-12-
-------
BASIS FOR GSE POPULATION ESTIMATES
-------
BASIS FOR GSE POPULATION ESTIMATES
Background: Airport ground support equipment (GSE) comprise a diverse range of vehicles
and equipment necessary to service aircraft during passenger and cargo loading and unloading,
maintenance, and other ground-based operations. The wide range of activities associated with
aircraft ground operations lead to an equally wide ranging fleet of GSE. For example, activities
undertaken during a typical aircraft gate period include: cargo loading and unloading, passenger
loading and unloading, potable water storage, lavatory waste tank drainage, aircraft refueling,
engine and fuselage examination and maintenance, and food and beverage catering. Airlines
employ specially designed GSE to support all these operations. Moreover, electrical power and
conditioned air are generally required throughout gate operational periods for both passenger and
crew comfort and safety, and many times these services are also provided by GSE.
Emissions Impact: The majority of GSE engines continue to be "uncontrolled" from an
emissions perspective. Although an increasing number of the larger vehicles used for GSE
operations such as water, fuel, lavatory, and aircraft maintenance services are powered by
emissions-certified on-road engines, a majority of similar older GSE and nearly all
specially-designed GSE continue to utilize engines that have not been designed for low
emissions. As a result, GSE do contribute significantly to the emissions of hydrocarbons (HC),
carbon monoxide (CO), oxides of nitrogen (NOX), particulate matter (PM), and carbon dioxide
(CO2) associated with airports. A recent U.S. EPA-commissioned study of four major U.S.
airports indicates that GSE are responsible for 15-20 percent of airport-related NOX and 10-15
percent of airport-related HC. Moreover, studies have shown that the availability of alternative
fueled and electric powered GSE as well as the availability of alternative means of providing, in
some cases, equivalent aircraft support services can lead to substantial reductions in GSE
emissions from current levels. This GSE information series is designed to provide both an
overview of these available emission reduction strategies and an estimate of the magnitude of
associated emission reductions.
GSE Population: Since there are no registration requirements for GSE or any national
organization charged with tracking GSE activity, there currently is no reliable database from
which accurate GSE populations can be determined. Numerous estimates of the national GSE
population have been made over the last several years using various statistical procedures, with
total population estimates ranging from as low as 10,000 units to 100,000 units or more.*
* Examples include the following: (1) a 1994 California ARB report entitled Air Pollution Mitigation Measures for
Airports and Associated Activity estimated 2,500 GSE in California, implying a national population of about
26,000 units; (2) a 1995 ARB report entitled Documentation of Input Factors for the New Off-Road Mobile
Source Emissions Factor Model estimated 12,000 California GSE, implying a national population of about
125,000 units; (3) a 1995 U.S. EPA report entitled Technical Support Document: Aircraft/Airports estimated
2,500 GSE in California FIP areas, implying a national population of about 34,000 units; (4) a 1998 GRI report
entitled Survey of Airport Fleet Vehicles estimated a GSE population of between 24,000 and 34,000 at the top 48
airports, implying a national population of 33,000-47,000 units; (5) a 1991 U.S. EPA report entitled Nonroad
Engine and Vehicle Emissions Study - Report estimated a national GSE population of just under 85,000 units.
GSE Information Series 1 Page 1
-------
Available data on GSE is certainly sufficient to narrow this range considerably and, therefore, it
is likely that additional factors such as inconsistencies in considered equipment contribute to the
magnitude of the observed differential between previous national GSE population estimates.
Detailed data on GSE populations at specific airports were collected in support of two U.S. EPA-
and one California Air Resources Board-commissioned studies on airport emissions. As
indicated Table 1, these studies included the collection of detailed GSE inventories from 35
individual airlines at 10 U.S. airports, 6 of which are among the top 50 national airports in terms
of aircraft landing and take-off (LTO) cycles. In total, over 3,000 individual GSE were
represented in the reported inventory data and together they provide support for about 9 percent
of national annual LTO cycles. A simple extrapolation of this reported GSE population to total
national LTO activity readily indicates the inherent inaccuracy in national GSE population
estimates as low as 10,000 units and as high as 100,000 units.
Airport
Baltimore-Washington International
Boston Logan
Burbank
Long Beach
Los Angeles International
Ontario
Orange County
Palm Springs
Phoenix Sky Harbor
Sacramento
Airlines Providing Detailed GSE Data
Delta, Southwest, U.S. Airways
Business Express, Flagship, Northwest, Spirit,
U.S. Airways
Delta, Southwest, United
Delta, United
Alaska Air, American, America West,
Continental, Delta, Northwest, Skywest,
Southwest, TransWorld, United, U.S. Airways
Delta, Southwest, United
Delta, United
Delta, United
America West, Southwest
Delta, Southwest
Table 1. Airports and Airlines Providing Detailed GSE Population Data
To provide a reliable estimate of national GSE population, a detailed statistical regression
analysis of the reported data was conducted. Examinations of scatter diagrams of airline- and
airport-specific GSE population by annual airline- and airport-specific LTO cycles as well as
preliminary regression statistics reveals distinct differences in the GSE inventory characteristics
of airlines along three major classifications. First, the GSE inventories of all major airlines
except Southwest (e.g., Delta, Northwest, United) show similar characteristics. Second, regional
carriers (e.g., Business Express, Skywest) show similar characteristics amongst themselves, but
GSE Information Series 1
Page 2
-------
(not surprisingly) these characteristics are quite different than those of the major carriers.
Finally, Southwest Airlines exhibits characteristics unique from those of both the regional and
other major carriers.
Stratifying the reported GSE population data in accordance with the three-level classification
scheme (i.e., major airlines other than Southwest, Southwest, and regional airlines) and
conducting detailed classification-specific regression analysis of GSE by annual LTO cycles
yields promising statistics, but a final adjustment for the major airlines (other than Southwest) is
required to obtain optimum results. Major airlines (especially those with international service)
operate both wide- and narrow-body aircraft, which possess significantly different demands in
terms of both the number of GSE required for gate support and the length of time those GSE are
required. Therefore, major airlines with a larger wide-body aircraft fleet and more frequent
wide-body LTO cycles tend to operate more GSE than major airlines with few wide-body LTO
cycles. Once this criteria is included in the regression analysis, satisfactory GSE statistics for all
three airline classifications are obtained. Table 2 presents the applicable statistical relationships.
Airline Classification
Major Airlines (other than Southwest)
Southwest Airlines
Regional Airlines
Regression Equation
(GSE Population = )
0.0226 (LTOwb) + 0.0054 (LTOnb)
[1=5.2] [1=4.1]
0.0022 (LTO)
[1=5.5]
0.0008 (LTO)
[1=4.0]
Correlation
Coefficient
0.79
0.83
0.75
LTO indicates the total number of annual LTO cycles, LTO^ indicates the number of annual wide-body LTO cycles, and
LTO.i, indicates the number of annual narrow-body LTO cycles.
Table 2. GSE Population Regression Statistics
As indicated by the correlation coefficients, none of the regression equations are excellent
predictors of the GSE population for a specific airline at a specific airport. However, all provide
reasonable airline- and airport-specific predictions and (since the t statistics are all significant at
over 99 percent confidence) highly significant representations of aggregate GSE population
across several airlines or several airports. Therefore, an evaluation of the three regressions using
national LTO data should provide for a good approximation of the national population of GSE.
Such an evaluation yields a population estimate of just over 45,000 pieces of equipment
(approximately the midpoint of the range of previous population estimates).
A measure of the relative GSE "demand" of the various airline classifications can also be
obtained from the derived regression coefficients. A single GSE is required for every 44
GSE Information Series 1
Page 3
-------
wide-body aircraft LTO cycles versus every 185 narrow-body LTO cycles for major airlines other
than Southwest. Southwest Airlines and regional carriers utilize substantially less GSE at the
ratio of a single GSE for every 455 and every 1,250 LTO cycles respectively. Major
narrow-body carriers utilize GSE at about 2.5 times the rate of Southwest Airlines, while
wide-body aircraft impose approximately 4 times the GSE demand of narrow-body aircraft.
GSE Population by Equipment and Engine Type: The same detailed airline- and
airport-specific data that was used to support the overall national GSE population estimate can be
used to disaggregate the estimate into its various type-specific components. As mentioned
above, over 3,000 individual GSE units are reflected in these data, representing approximately 7
percent of the estimated national GSE population. By aggregating the individual GSE
type-specific populations across the 35 airlines and 10 airports for which detailed GSE data is
available, an estimate of the national population type-specific equipment distribution can be
derived. Since the regression analysis described above indicated significant differences between
major airlines other than Southwest, Southwest, and regional airlines, this level of distinction
should be maintained in determining national GSE type distributions. The distribution of
national regional carrier GSE is developed by aggregating the data for the 5 regional carriers for
which detailed GSE population data was available. Similarly, the GSE type-specific equipment
distribution for national Southwest Airline GSE is based on the aggregation of data for the 6
airports for which detailed Southwest GSE populations were available and that of other major
airlines is based on data aggregated across the 24 available detailed populations. Table 3
presents the resulting type-specific national GSE population estimates.
Clearly, although GSE comprise myriad equipment types, several specific types are estimated to
dominate the overall population. In fact, baggage tugs and belt loaders constitute an estimated 35
percent of all GSE. Aircraft pushback tractors, forklifts, carts, ground power units, service
trucks, and pickup trucks constitute another 36 percent. Gasoline is estimated to be the dominant
engine type, powering an estimated 51 percent of GSE, while diesel engines are estimated to
power another 33 percent. The remaining 16 percent of GSE is powered in approximately equal
proportions by LPG and electricity.
References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Technical Support Document for Civil and Military Aviation, prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency in support of the
Notice of Proposed Rulemaking for the Federal Implementation Plan for California, March
1994.
4. Technical Support Document: Aircraft/Airports, prepared by Energy and Environmental
GSE Information Series 1 Page 4
-------
Analysis, Inc. for the U.S. Environmental Protection Agency in support of the Interim Final
Rulemaking for the Federal Implementation Plan for California, February 9, 1995
5. GSE population data sheets submitted by member companies of the Air Transport
Association as part of the U.S. Environmental Protection Agency's Federal Implementation
Plan development process for California, September 1993.
6. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Factor
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air
Resources Board, August 1995.
7. Survey of Airport Fleet Vehicles., Final Report, prepared by Edwards and Kelsey, Inc. for the
Gas Research Institute, April 1998.
8. Nonroad Engine and Vehicle Emissions Study - Report, 21A-2001, U. S. Environmental
Protection Agency, November 1991.
Equipment
Type
Aircraft
Pushback
Tractor
Conditioned
Air
Unit
Air
Start
Unit
Baggage
Tug
Belt
Loader
Engine
Type
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
Turbine
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Major1
Airlines
Split
4.47%
1.06%
0.22%
0.15%
5.90%
0.88%
0.07%
0.07%
0.07%
1.09%
1.72%
0.15%
0.04%
0.00%
0.07%
1.98%
9.34%
10.62%
0.59%
2.27%
22.81%
5.16%
5.09%
0.22%
0.73%
11.20%
Southwest
Airlines
Split
12.94%
2.60%
0.00%
0.00%
15.54%
0.00%
0.00%
0.00%
0.00%
0.00%
2.60%
0.00%
0.00%
0.00%
0.00%
2.60%
20.67%
11.10%
1.45%
0.00%
33.23%
16.62%
6.66%
0.00%
0.00%
23.28%
Regional
Airlines
Split
3.24%
0.00%
0.00%
0.00%
3.24%
0.00%
1.08%
0.00%
0.00%
1.08%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
13.95%
18.27%
0.00%
0.00%
32.22%
0.00%
5.41%
0.00%
0.00%
5.41%
Major1
Airlines
Population
1,914
455
94
63
2,526
376
31
31
31
469
737
63
16
0
31
847
4,000
4,549
251
973
9,773
2 212
2,180
94
314
4,800
Southwest
Airlines
Population
169
34
0
0
203
0
0
0
0
0
34
0
0
0
0
34
270
145
19
0
434
217
87
0
0
304
Regional
Airlines
Population
30
0
0
0
30
0
10
0
0
10
0
0
0
0
0
0
129
169
0
0
298
0
50
0
0
50
All Carrier
Population
2,113
489
94
63
2,759
376
41
31
31
479
771
63
16
0
31
881
4,399
4,863
270
973
10,505
2,429
2,317
94
314
5,154
All Carrier
Split
4.69%
1.08%
0.21%
0.14%
6.12%
0.83%
0.09%
0.07%
0.07%
1.06%
1.71%
0.14%
0.04%
0.00%
0.07%
1.95%
9.76%
10.79%
0.60%
2.16%
23.31%
5.39%
5.14%
0.21%
0.70%
11.44%
1 Excluding Southwest Airlines.
- continued -
Table 3a. Estimated National GSE Populations
GSE Information Series 1
Page 5
-------
Equipment
Type
Bobtail
Cargo
Loader
Cart
Deicer
Forklift
Fuel
Truck
Ground
Power
Unit
Lavatory
Cart
Lavatory
Truck
Lift
Engine
Type
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Major1
Airlines
Split
0.37%
1.87%
0.00%
0.04%
2.27%
2.64%
0.51%
0.00%
0.26%
3.41%
0.07%
2.49%
2.12%
0.00%
4.69%
0.07%
1.06%
0.00%
0.00%
1.13%
0.33%
2.01%
1.72%
3.66%
7.73%
0.18%
0.92%
0.00%
0.04%
1.13%
5.24%
0.22%
1.06%
0.00%
6.52%
0.00%
0.04%
0.00%
0.00%
0.04%
0.00%
1.58%
0.00%
0.00%
1.58%
0.11%
2.20%
0.73%
0.73%
3.77%
Southwest
Airlines
Split
0.00%
0.38%
0.00%
0.00%
0.38%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.77%
0.00%
0.00%
0.77%
0.00%
0.77%
0.00%
0.00%
0.77%
0.38%
0.77%
0.00%
1.07%
2.22%
0.00%
0.00%
0.00%
0.00%
0.00%
4.06%
0.00%
0.00%
0.00%
4.06%
0.00%
2.22%
0.00%
0.00%
2.22%
0.00%
1.84%
0.00%
0.00%
1.84%
0.00%
0.00%
0.00%
0.77%
0.77%
Regional
Airlines
Split
0.00%
1.08%
0.00%
0.00%
1.08%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
5.41%
0.00%
0.00%
5.41%
0.00%
1.08%
0.00%
0.00%
1.08%
0.00%
0.00%
0.00%
0.00%
0.00%
1.08%
0.00%
0.00%
0.00%
1.08%
22.49%
0.00%
0.00%
0.00%
22.49%
0.00%
5.41%
0.00%
0.00%
5.41%
0.00%
1.08%
0.00%
0.00%
1.08%
0.00%
1.08%
0.00%
0.00%
1.08%
Major1
Airlines
Population
157
800
0
16
973
1,129
220
0
110
1,459
31
1,067
910
0
2,008
31
455
0
0
486
141
863
737
1,569
3,310
78
392
0
16
486
2,243
94
455
0
2,792
0
16
0
0
16
0
675
0
0
675
47
941
314
314
1,616
Southwest
Airlines
Population
0
5
0
0
5
0
0
0
0
0
0
10
0
0
10
0
10
0
0
10
5
10
0
14
29
0
0
0
0
0
53
0
0
0
53
0
29
0
0
29
0
24
0
0
24
0
0
0
10
10
Regional
Airlines
Population
0
10
0
0
10
0
0
0
0
0
0
50
0
0
50
0
10
0
0
10
0
0
0
0
0
10
0
0
0
10
208
0
0
0
208
0
50
0
0
50
0
10
0
0
10
0
10
0
0
10
All Carrier
Population
157
815
0
16
988
1,129
220
0
110
1,459
31
1,127
910
0
2,068
31
475
0
0
506
146
873
737
1,583
3,339
88
392
0
16
496
2,504
94
455
0
3,053
0
95
0
0
95
0
709
0
0
709
47
951
314
324
1,636
All Carrier
Split
0.35%
1.81%
0.00%
0.04%
2.19%
2.50%
0.49%
0.00%
0.24%
3.24%
0.07%
2.50%
2.02%
0.00%
4.59%
0.07%
1.05%
0.00%
0.00%
1.12%
0.32%
1.94%
1.64%
3.51%
7.41%
0.20%
0.87%
0.00%
0.04%
1.10%
5.56%
0.21%
1.01%
0.00%
6.77%
0.00%
0.21%
0.00%
0.00%
0.21%
0.00%
1.57%
0.00%
0.00%
1.57%
0.10%
2.11%
0.70%
0.72%
3.63%
1 Excluding Southwest Airlines.
- continued -
GSE Information Series 1
Page 6
-------
Table 3b. Estimated National GSE Populations
Equipment
Type
Maintenance
Truck
Other
GSE
Service
Truck
Bus
Car
Pickup
Truck
Van
Water
Truck
All
GSE
Types
Engine
Type
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
All Engines
Diesel
Gasoline
Electric
LPG/CNG
Turbine
All Engines
Major1
Airlines
Split
0.04%
2.89%
0.00%
0.04%
2.97%
0.88%
2.71%
0.07%
0.33%
3.99%
0.66%
3.55%
0.00%
0.55%
4.76%
0.26%
0.40%
0.00%
0.00%
0.66%
0.00%
1.32%
0.00%
0.00%
1.32%
0.07%
5.93%
0.00%
0.33%
6.33%
0.00%
4.14%
0.00%
0.15%
4.29%
0.00%
0.44%
0.00%
0.00%
0.44%
32.47%
51.27%
6.85%
9.34%
0.07%
100.00%
Southwest
Airlines
Split
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
2.60%
0.00%
0.00%
2.60%
2.99%
2.99%
0.00%
0.00%
5.97%
0.38%
0.00%
0.00%
0.00%
0.38%
0.00%
0.38%
0.00%
0.00%
0.38%
0.77%
1.84%
0.00%
0.00%
2.60%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
0.38%
0.00%
0.00%
0.38%
40.76%
59.24%
0.00%
0.00%
0.00%
100.00%
Regional
Airlines
Split
0.00%
2.16%
0.00%
0.00%
2.16%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
4.32%
0.00%
0.00%
4.32%
0.00%
0.00%
0.00%
0.00%
0.00%
0.00%
1.08%
0.00%
0.00%
1.08%
0.00%
3.24%
0.00%
0.00%
3.24%
0.00%
7.46%
0.00%
0.00%
7.46%
0.00%
1.08%
0.00%
0.00%
1.08%
61.41%
35.30%
1.45%
1.84%
0.00%
100.00%
Major1
Airlines
Population
16
1,239
0
16
1,271
376
1,161
31
141
1,709
282
1,522
0
235
2,039
110
173
0
0
283
0
565
0
0
565
31
2,541
0
141
2,713
0
1,773
0
63
1,836
0
188
0
0
188
13,911
21,963
2,933
4,002
31
42,840
Southwest
Airlines
Population
0
0
0
0
0
0
34
0
0
34
39
39
0
0
78
5
0
0
0
5
0
5
0
0
5
10
24
0
0
34
0
0
0
0
0
0
5
0
0
5
377
548
0
0
0
925
Regional
Airlines
Population
0
20
0
0
20
0
0
0
0
0
0
40
0
0
40
0
0
0
0
0
0
10
0
0
10
0
30
0
0
30
0
69
0
0
69
0
10
0
0
10
802
461
19
24
0
1,306
All Carrier
Population
16
1,259
0
16
1,291
376
1,195
31
141
1,743
321
1,601
0
235
2,157
115
173
0
0
288
0
580
0
0
580
41
2,595
0
141
2,777
0
1,842
0
63
1,905
0
203
0
0
203
15,090
22,972
2,952
4,026
31
45,071
Al Carrier
Split
0.04%
2.79%
0.00%
0.04%
2.86%
0.83%
2.65%
0.07%
0.31%
3.87%
0.71%
3.55%
0.00%
0.52%
4.79%
0.26%
0.38%
0.00%
0.00%
0.64%
0.00%
1.29%
0.00%
0.00%
1.29%
0.09%
5.76%
0.00%
0.31%
6.16%
0.00%
4.09%
0.00%
0.14%
4.23%
0.00%
0.45%
0.00%
0.00%
0.45%
33.48%
50.97%
6.55%
8.93%
0.07%
100.00%
1 Excluding Southwest Airlines.
Table 3c. Estimated National GSE Populations
GSE Information Series 1
Page 7
-------
GSE EMISSIONS AND ACTIVITY ESTIMATES
-------
GSE EMISSIONS AND ACTIVITY
ESTIMATES
Background: Airport ground support equipment (GSE) comprise a diverse range of vehicles
and equipment necessary to service aircraft during passenger and cargo loading and unloading,
maintenance, and other ground-based operations. The wide range of activities associated with
aircraft ground operations lead to an equally diverse fleet of GSE, each component of which has
its own emissions performance and activity characteristics. For example, activities undertaken
during a typical aircraft gate period include: cargo loading and unloading, passenger loading and
unloading, potable water storage, lavatory waste tank drainage, aircraft refueling, engine and
fuselage examination and maintenance, and food and beverage catering. Airlines employ
specially designed GSE to support all these operations. Moreover, electrical power and
conditioned air are generally required throughout gate operational periods for both passenger
comfort and safety, and many times these services are also provided by GSE.
The Necessity for Proper Activity Characterization: Accurately characterizing the emissions
performance of a particular GSE requires detailed knowledge in two specific areas: (1) the rate of
equipment emissions per unit of activity and (2) the amount of activity performed during the
period of interest. Generally, the unit activity emission rate can be either measured directly or
estimated from previous measurements taken for similar equipment or engines. Because
emission rates typically vary with engine speed and load (a measure of how "hard" the engine is
being worked), emission rates for GSE-type equipment are commonly measured over a broad
series of constant speed and load operating modes that, when weighted in accordance with the
amount of time the engine spends in each mode, can describe the average emission rate of the
equipment.* Two standard emission tests of this type are commonly employed for GSE-type
equipment. Engines rated at 25 horsepower (hp) or less are usually tested over the Society of
Automotive Engineers' J1088 test cycle, while larger engines are tested over what is commonly
referred to as the "8 mode" test. Differences in the various test modes to which the engines are
subjected can be best defined through the amount of useful work that is performed by the engine
when operating in each mode and, therefore, emission measurements for GSE-type equipment
are usually measured in terms of grams of emissions per brake horsepower-hour of work
performed (g/bhp-hr).
Since GSE-type emission factors are measured in terms of work performed, a measurement of
the amount of work performed over the time period of interest is integral to the proper emissions
* This differs from the measurement of emissions from on-road vehicles such as passenger cars and light trucks
where the vehicle engine is exercised over a well defined, but continuously changing (or transient) driving cycle
that includes a wide range of engine speed and load conditions. Such a test is more representative of the
performance of such vehicles since they undergo a wide range of continuously varying speed and load
combinations in actual use. GSE, however, generally do not undergo either frequent speed or load changes,
instead operating within relatively narrow speed/load ranges for extended periods. Accordingly, the emissions
performance of GSE can be accurately measured by testing the equipment (or engine) over an appropriate series of
such "steady state" conditions.
GSE Information Series 2 Page 1
-------
assessment of a piece of equipment. For short, single operating mode periods, this measurement
can be derived directly from the speed and load conditions placed on the engine during the
operating mode. However, over longer periods, equipment operations usually encompass a series
of differing operating conditions (e.g., extended idle, between gate transit) and the amount of
work performed is usually defined as a fraction of total possible work that can be performed
during the period. Commonly referred to as the load factor, this fraction is equal to the ratio of
actual work performed to work which could have been performed if the engine was operated
throughout the period at its manufacturer-rated speed and horsepower (those conditions over
which engine work output is a maximum). For example, the load factor for the aggregated J1088
emissions test is 0.39 (i.e., the derived emission rate over the J1088 cycle reflects an aggregated
series of test conditions in which 39 percent of maximum engine work is performed), while that
of the "8 mode" test for larger engines is 0.56.
Once a load factor has been established for a typical operating period, emissions performance
over that or any period of similar engine operation can be calculated from measured unit-work
emission rates. The amount of work performed over the period of interest is calculated by
multiplying the engine manufacturer-rated engine output (hp) by the total number of hours of
engine operation over the period to determine maximum possible time period work, and then
multiplying this maximum possible work by the representative load factor. The product of the
unit-work emission rate and work performed over the period of interest represents the overall
emissions estimate for the period of interest. Expressed algebraically, the generalized GSE
emissions calculation methodology is:
GSE emissions g hours of operation
— :—;—— = — ;— x rated hp x — :—-—— x load factor
time period 01 interest bhp-hr time period 01 interest
While conceptually simple, each of the components of the GSE emissions calculation equation
has inherent uncertainty with the exception of the rated engine horsepower (which is an element
of engine design). The unit-work emission rate is typically based on a standardized test with a
load factor of either 0.39 (< 25 hp engines) or 0.56 (> 25 hp engines). Equipment operated at
load factors substantially different than those of the test cycle may exhibit substantially different
emission rates. Experience has shown that emission rates over a load factor range of about ±0.2
of the test cycle load factor are fairly well represented. The hours of operation for the time
period of interest is certainly conceptually simple and for a single piece of equipment, relatively
easily tracked. But defining a "typical" hours per day operating rate over extended time periods,
across multiple units, across airlines, or across airports is inherently uncertain. The load factor is
perhaps the most uncertain element of the calculation. Although GSE-specific load factors have
been developed over the last several years, there is considerable uncertainty in these estimates
across units, airlines, and airports. For example, equipment idle time can vary considerably and
in extreme cases, where idle emissions are applicable for all or most of the time period of
interest, the GSE emissions calculation methodology "falls apart" as the load factor approaches
zero while the actual emission rate per unit work performed approaches infinity. Clearly each of
the factors upon which the generalized GSE emissions calculation methodology is dependent
must be accurately quantified to determine emissions with any degree of certainty.
GSE Information Series 2 Page 2
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Emission Rate Data: Numerous studies over the last decade or so have attempted to compile
available emissions rate data on engines such as those used on GSE. Although the size of the
database continues to be relatively small, it is comprehensive in that engines of all applicable
sizes and configurations are represented. In many aspects, the state of the off-road engine
emissions database is comparable to that of on-road vehicles in the mid-1970's. Interest in
off-road engine emissions became significant only in the late-1980's and early 1990's with the
advent of U.S. Environmental Protection Agency (EPA) and California Air Resources Board
(ARB) regulatory program development efforts. Emissions data collection has accelerated in
response to these efforts, but given the wide range of engine sizes and configurations found in the
off-road sector, the number of emission tests performed on most engine categories continues to
be limited. There are some exceptions, such as small lawn mower-type utility engines which
have been the focus of early regulatory attention and are thus fairly well represented, but in
general much data collection activity remains to be performed. To date, no comprehensive,
detailed GSE-specific emissions rate data collection program has been undertaken. This is
clearly an area where the development of a structured test program could not only improve the
quantity and quality of data collected, but also provide an indication of the degree of uncertainty
associated with current GSE emissions test data.
In the mid-1990's, the ARB began development of an off-road emission factor model. A key
component of this development work was the collection and analysis of available emissions test
data for all types of off-road engines, including GSE. This emissions test data development
activity was performed at a very disaggregated level-of-detail and continues to represent the
"state-of-the-art" emissions rate "database" for GSE. Data was analyzed over relatively narrow
horsepower ranges as well as by fuel type (i.e., gasoline, diesel, etc.), valve configuration (i.e.,
overhead valve versus side valve), engine cooling design (i.e., air versus water cooled), fueling
system type (i.e., carburetion, indirect injection, direct injection), and air intake type (i.e.,
naturally aspirated versus turbocharged). In addition to emissions rate data, the ARB model
development efforts also included detailed reviews of available off-road engine (including GSE)
population (for California), load factor, and usage rate data (for California). In recognition of its
comprehensive nature, all data presented in this GSE information series, with relatively minor
exceptions where noted, are derived from the resulting model database.
Although all equipment are represented by the ARB data, it should be recognized that a targeted
GSE emissions data collection program would be invaluable in not only in augmenting and
quality assuring the existing database, but in also providing an important measure of emissions
variability. Moreover, any program based on the issuance of credits for GSE retirement or
conversion should be based on actual emission measurements for the specific equipment
involved. Only after sufficient data have been collected to provide a reasonable measure of
emissions rate uncertainty can surrogate engine data be expected to accurately represent the
emissions performance of any specific engine or equipment. The off-road emissions database,
and GSE database in particular, is not at this state of development.
Tables 1 through 11 present basic emission rate data for off-road engines by horsepower range as
extracted from the ARB off-road model. Tables 1 through 5 present new engine emission rates
for HC, CO, NOX, PM, and CO2 respectively. All emission rates, except those for CO2 are in
units of grams of emission per brake horsepower-hour of work performed (g/bhp-hr). CO2
emission rates are in grams per gallon of fuel consumed. Table 6 presents the brake-specific fuel
GSE Information Series 2 Page 3
-------
consumption (in units of pounds of fuel per brake horsepower-hour) and fuel density (in pounds
per gallon) estimates required to convert the CO2 emission rates presented in Table 5 into units of
g/bhp-hr. Specific estimates for CNG equipment are not included in the ARB model and there is
very little data available to construct detailed GSE CNG-specific emission rates. Nevertheless,
on the basis of limited data cited in previous GSE studies, CNG emission rates were estimated to
be: (1) for HC, 33 percent lower than corresponding LPG HC emissions, (2) for CO2, 8 percent
lower than corresponding LPG CO2 emissions, and (3) for CO, NOX, and PM, equivalent to
corresponding LPG emissions.
As is the case with all engines, emission rates usually increase with age due to engine and control
system deterioration, malperformances, or misadjustment. The ARB model includes estimates of
pollutant- and engine-specific emission deterioration rates, but both the magnitude and form of
these deterioration data should be viewed as even less developed than other aspects of off-road
(and specifically GSE) emission rate data since very little testing on in-use equipment has been
performed to date. As already discussed, a structured emissions testing program focused on GSE
(both new and in-use) is critical to both the validation and improvement of current emission rate
estimates. In the absence of such a test program, Tables 7 through 11 present the current best
estimates of pollutant-specific off-road engine emissions deterioration. The presented
deterioration data is expressed as the factor by which emissions increase over their full useful
life. For example, if an engine has a "when new" emission rate of X grams per brake
horsepower-hour and a full life deterioration factor of Y, its emission rate at full useful life (Z) is
equal to:
Z = X +(X)(Y) = X (1 +Y)
The emission impact estimates presented in this GSE information series are based on the
estimated emission rate at one-half of the applicable equipment's useful life. If this emission rate
is defined as Z1/2, it is algebraically defined as:
Z1/2 = X + (X)(0.5Y) + X(1 + 0.5Y)
The majority of GSE engines continue to be "uncontrolled" from an emissions perspective and
the emission rates presented in this GSE information series reflect such an assumption. Although
an increasing number of the larger vehicles used for GSE operations such as water, fuel, lavatory,
and aircraft maintenance services are powered by emissions-certified on-road engines, a number
of older GSE performing similar services and nearly all specially-designed GSE continue to
utilize engines that have not been designed for low emissions. As a result, the emission
estimates presented in this series will, in most cases, accurately reflect the potential emission
reductions due to control strategy implementation, but will in some cases, where newer GSE is
concerned, overstate potential reductions to varying extents. Actual emission reduction potential
must be based on data for the specific GSE targeted for control.
Evaporative emission estimates or evaporative emission reduction potential has not been
evaluated as part of this GSE information series. Generally, evaporative emissions are
significant
GSE Information Series 2 Page 4
-------
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
290.00
209.00
209.00
Gasoline
(4-Stroke)
26.40
7.46
7.46
5.50
4.00
4.00
4.00
LPG
4.25
3.96
3.96
2.00
2.00
2.00
Diesel
1.50
1.84
1.84
1.44
0.88
0.88
0.84
0.84
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 1. Zero Hour HC Emission Rate (grams/brake horsepower-hour)
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
840.0
311.0
311.0
Gasoline
(4-Stroke)
504.2
393.1
393.1
320.0
240.0
240.0
240.0
LPG
248.4
240.0
240.0
150.0
150.0
150.0
Diesel
5.0
5.0
5.0
4.8
4.2
4.2
4.1
4.1
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 2. Zero Hour CO Emission Rate (grams/brake horsepower-hour)
GSE Information Series 2
Page 5
-------
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.36
0.90
0.90
Gasoline
(4-Stroke)
2.12
3.48
3.48
3.75
4.00
4.00
4.00
LPG
1.99
1.77
1.77
3.00
3.00
3.00
Diesel
10.00
6.92
6.92
13.00
11.00
11.00
11.00
11.00
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 3. Zero Hour NOX Emission Rate (grams/brake horsepower-hour)
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
10.00
6.50
6.50
Gasoline
(4-Stroke)
0.74
0.14
0.14
0.05
0.042
0.032
0.032
LPG
0.49
0.09
0.09
0.032
0.042
0.022
Diesel
1.00
0.76
0.76
0.84
0.55
0.55
0.53
0.53
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
2 Values assumed to be zero in these size ranges in the ARB model, tabulated
values are based on 95 percent reduction from diesel for gasoline and 96
percent reduction from diesel for LPG.
Table 4. Zero Hour PM Emission Rate (grams/brake horsepower-hour)
GSE Information Series 2
Page 6
-------
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
8932.77
8932.77
8932.77
Gasoline
(4-Stroke)
8932.77
8932.77
8932.77
8932.77
8932.77
8932.77
8932.77
LPG
5768.71
5768.71
5768.71
5768.71
5768.71
5768.71
Diesel
9797.23
9797.23
9797.23
9797.23
9797.23
9797.23
9797.23
9797.23
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 5. Zero Hour CO2 Emission Rate (grams/gallon)
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Fuel Density (Ib/gallon)
Gasoline
(2-Stroke)
1.30
1.30
1.30
6.20
Gasoline
(4-Stroke)
1.09
0.90
0.80
0.70
0.55
0.55
0.55
6.20
LPG
0.972
0.802
0.712
0.622
0.492
0.492
4.25
Diesel
0.65
0.53
0.54
0.49
0.442
0.442
0.422
0.42
6.80
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
2 Values encoded in the ARB model are incorrect. Tabulated LPG values are set to 89 percent
of 4-stroke gasoline values; tabulated diesel values are set according to available test data.
Table 6. Brake-Specific Fuel Consumption (pounds/brake horsepower-hour)
GSE Information Series 2
Page 7
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Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.00
0.00
0.00
Gasoline
(4-Stroke)
1.09
1.59
1.59
1.38
1.38
0.37
0.37
LPG
1.09
1.59
1.59
1.38
1.38
0.37
Diesel
0.00
0.00
0.51
0.28
0.28
0.28
0.44
0.44
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 7. Full-Life HC Deterioration Factor
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.00
0.00
0.00
Gasoline
(4-Stroke)
0.32
0.09
0.09
0.83
0.83
0.56
0.56
LPG
0.32
0.09
0.09
0.83
0.83
0.56
Diesel
0.00
0.00
0.41
0.16
0.16
0.16
0.25
0.25
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 8. Full-Life CO Deterioration Factor
GSE Information Series 2
PageS
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Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.00
0.00
0.00
Gasoline
(4-Stroke)
0.04
0.38
0.38
0.06
0.06
0.14
0.14
LPG
0.04
0.38
0.38
0.06
0.06
0.14
Diesel
0.00
0.00
0.06
0.14
0.14
0.14
0.21
0.21
X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 9. Full-Life NOV Deterioration Factor
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.00
0.00
0.00
Gasoline
(4-Stroke)
1.09
1.59
1.59
0.00
0.00
0.00
0.00
LPG
1.09
1.59
1.59
0.00
0.00
0.00
Diesel
0.00
0.00
0.31
0.44
0.44
0.44
0.67
0.67
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 10. Full-Life PM Deterioration Factor
GSE Information Series 2
Page 9
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Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
750+
Gasoline
(2-Stroke)
0.00
0.00
0.00
Gasoline
(4-Stroke)
0.00
0.00
0.00
0.00
0.00
0.00
0.00
LPG
0.00
0.00
0.00
0.00
0.00
0.00
Diesel
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 11. Full-Life CO2 Deterioration Factor
Horsepower
Range
0-X1
(X+l)-15
16-25
26-50
51-120
121-175
176-250
251-500
501-750
751+
Gasoline
(2-Stroke)
Split
0.00
1.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Gasoline
(4-Stroke)
Split
0.00
0.00
0.00
0.18
0.51
0.26
0.05
0.00
0.00
0.00
Diesel
Split
0.00
0.00
0.00
0.15
0.49
0.27
0.00
0.03
0.05
0.00
Aggregate
Split
0.00
0.02
0.00
0.17
0.49
0.26
0.03
0.01
0.02
0.00
1 X equals 2 for gasoline 2-stroke; 5 for gasoline 4-stroke and diesel equipment.
Table 12. GSE Horsepower Distributions
GSE Information Series 2
Page 10
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from gasoline powered equipment and associated emission reductions would accrue through the
imposition of such control strategies as alternative fueled or electric GSE conversion or
replacement. However, the lack of evaporative emissions data for most engines and equipment
types used in the GSE sector precludes an accurate assessment of the potential significance of
such emission reductions. Experience in the on-road vehicle sector indicates that evaporative
emissions can constitute a significant fraction of total HC emissions, but this significance is
measured on the basis of over two decades of exhaust emissions control. Evaporative emissions
are likely to constitute a much smaller fraction of total HC in the GSE sector. Nevertheless, the
quantification of evaporative emission rates is an area of needed research and emission reduction
potential should be reassessed once a reasonable GSE- or off-road engine-specific database
(including engines of the size used for GSE) has evolved.
GSE Engine Size Classification: As might be expected given the diverse nature of the various
tasks required of aircraft GSE, a wide range of equipment of varying engine size and fueling type
are encountered. The information series selection entitled Basis for GSE Population Estimates
provides a detailed breakdown of the various GSE equipment by fueling type. The equipment
and fueling type population breakdowns presented in this GSE information series differ from
those of the ARB off-road model for two reasons. First, the population data encoded in the ARB
model is California-specific. Second, the methodology for estimating GSE populations has been
improved since the development of the ARB model as described in the Basis for GSE Population
Estimates information series selection. Nevertheless, the breakdown of the various engine sizes
encountered within a specific equipment type, as required to accurately estimate GSE emissions,
is best performed using engine distribution data from the ARB model. While the population of
GSE equipment should be expected to vary from that of the ARB model, there is no reason to
expect that the distribution of engine sizes encountered within a specific equipment type
(regardless of population) will vary. Moreover, since the ARB model engine size distributions
incorporate all available data on GSE engine distribution, these data represent the current state of
GSE information.
While the ARB model continues to represent the best source of horsepower distribution data, it
should be recognized that even the basis for this data is limited, consisting of GSE inventory
information collected from several airlines during the California Federal Implementation Plan
(FIP) development process of the early-1990's. There is no question that an expanded study of
GSE engine classifications is both appropriate and necessary to validate or augment existing data.
Table 12 presents the overall horsepower distribution of GSE engines. As indicated, all
two-stroke gasoline equipment is small at 15 horsepower or less. Four-stroke gasoline
equipment is found over a wide range of horsepower, ranging from 26 hp to as high as 250 hp.
Diesel equipment spans an even larger range, from 26 hp all the way up to 750 hp. Neither LPG
or CNG GSE distributions can be derived from data encoded in the ARB model since it assumes
zero GSE populations for these fuels, but the range of engine horsepower should be very similar
to that of four-stroke gasoline equipment. Table 13 presents average horsepower data for the
various GSE equipment types represented in the ARB model. The variation across types is
dramatic as is expected from the wide range of horsepower observed in the GSE sector and, as a
direct result, emissions performance across GSE types (or even across fuels within a specific
GSE type) can varies considerably. Clearly, in cases where emission credits are being
GSE Information Series 2 Page 11
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline/LPG/CNG
130
130
130
100
60
100
70
12
93
50
130
150
12
130
100
130
50
180
150
Diesel
216
300
600
78
45
100
76
12
93
52
180
145
12
130
100
130
50
170
150
Table 13. Average Horsepower by Equipment and Fuel Type
determined on the basis of equipment retirements or conversions, emission impacts should be
calculated on the basis of actual equipment horsepower.
Conspicuously absent from Table 13 and other GSE emissions-related tables in this GSE
information series are estimates for "standard" cars, pickup trucks, vans, and buses that are used
as GSE for various general services such as personnel transport. Such vehicles are
emissions-certified on-road vehicles that have simply been adapted to GSE use. As such, the
emissions performance of these vehicles is equivalent to that of other on-road vehicles and is best
determined using the U.S. EPA's MOBILE series of emission factor models developed
specifically for estimating on-road vehicle emissions. This is also the case for some unknown
fraction of the trucks used to provide fuel, food, water, and lavatory service. Generally, such
service trucks include special adaptations to facilitate use as GSE and many are of overseas
manufacture and uncertain emissions certification (since their use is restricted to off-road
applications, no specific emissions certification has historically been required). However, many
are undoubtedly certified on-road vehicles adapted for GSE use and as such, the emission
estimates presented for such vehicles in this GSE information series may be overstated.
Newer on-road certified vehicles already incorporate stringent emission controls and may not be
GSE Information Series 2
Page 12
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good candidates for additional emission reduction through the imposition of the control strategies
discussed in this information series (which are slanted toward the reduction of uncontrolled
off-road engine emissions). Nevertheless, emission reduction strategies applicable to the general
on-road vehicle fleet (e.g., reformulated gasoline) are equally viable for on-road vehicles used as
GSE. Therefore, emission reductions for such vehicles should be evaluated in the same context
as that of the larger on-road vehicle fleet. The information series selection entitled Basis for GSE
Population Estimates does include an estimate of the population of on-road cars, pickup trucks,
vans, and buses in use as GSE, indicating that they may constitute as much as 12 percent of the
overall GSE fleet. The fraction of service trucks that are on-road emissions certified is less
certain and all such trucks are assumed to be uncontrolled from an emissions perspective in this
information series. Clearly, actual emissions performance should be assessed before any
emission reduction credits are granted for the imposition of emission controls on such vehicles.
GSE Load Factors: As was the case with other GSE attributes, the load factor for the various
equipment types used as GSE might be expected to vary considerably in accordance with the
range of services encountered in the sector. However, information on specific GSE load factors
is perhaps the most uncertain of all the activity indicators required to accurately estimate GSE
emissions performance. Very little detailed time-in-mode data exist and, as a result, GSE load
factors (like those for other off-road equipment types) have been estimated from actual fuel use
records and known brake-specific fuel consumption rates for GSE engines. While such an
approach is technically sound, there can be considerable uncertainty involved in associating a
specific operating time with recorded fuel use (except when concurrent equipment usage meter
readings are also available). As a result, there can also be considerable uncertainty in
determining precise load factor estimates from fuel consumption records. This uncertainty
generally increases as load factor decreases since fuel consumption rates are small relative to
rated consumption and the influence of operating time estimation errors becomes more
significant. Potential estimation errors can be reduced by increasing the size of the fuel
consumption database used to estimate the load factor, but to date the fuel consumption database
for GSE is limited and what data is available is reflected in the load factor data encoded in the
ARB off-road model. As a result, the ARB off-road model estimates have been used for the
emission estimates presented in this GSE information series. Table 14 presents a summary of the
load factor estimates by GSE type.
In reviewing the data presented in Table 14, the paucity of data on which to base GSE load
factors is obvious as several equipment types exhibit identical estimates due to the unavailability
of equipment-specific data. The 0.50 load factor estimate for small engines (i.e., carts) is
generally sufficiently close to the J1088 emissions test load factor of 0.39 so that the estimated
emission rates based on J1088 should be sufficiently representative. However, for larger
equipment (all other GSE), there are several cases where the estimated load factor is outside the
0.56 ±0.2 load factor range associated with the "8 mode" emissions test. Two (of 17) large
engine GSE exhibit estimated load factors above 0.76 and five exhibit estimated load factors
below 0.36. If these load factors are in fact accurate, then the use of "8 mode" emission test
results to accurately portray emission rates for these GSE is questionable.
GSE Information Series 2 Page 13
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline/LPG/CNG
0.80
0.75
0.90
0.55
0.50
0.55
0.50
0.50
0.95
0.30
0.25
0.75
0.50
0.25
0.50
0.50
0.50
0.20
0.20
Diesel
0.80
0.75
0.90
0.55
0.50
0.55
0.50
0.50
0.95
0.30
0.25
0.75
0.50
0.25
0.50
0.50
0.50
0.20
0.20
Table 14. Average Load Factors by Equipment and Fuel Type
Without question, additional research into GSE load factors is both appropriate and necessary.
Targeted studies using either detailed fuel consumption records and calibrated operating time
meters or automatic on-board dataloggers should be implemented at a number of airports of
varying size. These studies should include several units of each type of GSE that contributes
significantly to overall GSE emissions.
GSE Hours of Use: As indicated above, the overall emission rates for the various GSE depend
not only on emission rates, but the overall amount of time the equipment is used. However,
experience has shown that equipment usage varies considerably, not only across the various
airlines and airports, but by time-of-day, day-of-week, and season. Temporal variation is of
marginal concern in estimating long term (e.g., annual or multi-year) emission impacts, but
variation across airports is significant and prohibits the development of any generic usage rates
for GSE. For example, an airport with limited passenger service may use baggage tractors for
only a few hours per day while large, high traffic airports might use baggage tractors
continuously throughout an operating day. Based on this airport dependence, the emission
estimates presented in this GSE information series are expressed in terms of grams per operating
hour and should be equally applicable to any airport or airline employing GSE. However, due to
GSE Information Series 2
Page 14
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the uncertainties discussed above, these emission estimates should be used for "screening"
purposes only (for example, to estimate the potential emission reduction impacts due to the
replacement of conventionally fueled GSE with electrically powered equipment) and supplanted
with actual site- and application-specific emission estimates in determining actual accrued
emission impacts.
Hourly-Specific GSE Emission Rate Estimates: Tables 15-19 present the various emission
rates, in units of grams per operating hour, derived using the various GSE data discussed above.
As indicated above, these data should be used only for estimation purposes and supplanted with
actual site-specific data in determining actual emission impacts.
References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Technical Support Document for Civil and Military Aviation; prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency in support of the
Notice of Proposed Rulemaking for the Federal Implementation Plan for California, March
1994.
4. GSE population data sheets submitted by member companies of the Air Transport Association
as part of the U.S. Environmental Protection Agency's Federal Implementation Plan
development process for California, September 1993.
5. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995.
6. California Off-Road Model (June 7, 1996 version) input files EMFAC.DAT, POP.DAT, and
ACTIVITY.DAT.
GSE Information Series 2 Page 15
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline
(2-Stroke)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1,254.0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Gasoline
(4-Stroke)
493.0
462.2
554.6
371.8
202.8
371.8
236.6
80.3
597.2
139.4
154.1
533.3
80.3
154.1
338.0
308.1
232.4
170.6
142.2
LPG1
246.5
231.1
277.3
185.9
101.4
185.9
118.3
42.6
298.6
50.7
77.0
266.6
42.6
77.0
169.0
154.1
84.5
85.3
71.1
Diesel
174.6
230.6
553.4
70.4
52.0
90.3
62.4
9.0
145.0
25.6
45.1
109.1
9.0
32.6
82.1
65.2
57.7
34.1
30.1
CNG emission rate equals 0.67 times LPG emission rate.
Table 15. Equipment-Specific HC Emission Rates (grams/operating hour)
GSE Information Series 2
Page 16
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline
(2-Stroke)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1,866
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Gasoline
(4-Stroke)
31,949
29,952
35,942
18,678
10,188
18,678
11,886
2,465
30,004
6,792
9,984
34,560
2,465
9,984
16,980
19,968
11,320
11,059
9,216
LPG1
19,968
18,720
22,464
11,674
6,368
11,674
7,429
1,505
18,752
3,184
6,240
21,600
1,505
6,240
10,613
12,480
5,306
6,912
5,760
Diesel
788
1,038
2,491
222
136
285
197
30
458
81
204
493
30
147
259
295
151
154
136
CNG emission rate equals 1.00 times LPG emission rate.
Table 16. Equipment-Specific CO Emission Rates (grams/operating hour)
GSE Information Series 2
Page 17
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline
(2-Stroke)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
5.4
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Gasoline
(4-Stroke)
445.1
417.3
500.8
226.6
123.6
226.6
144.2
24.8
364.0
57.9
139.1
481.5
24.8
139.1
206.0
278.2
96.6
154.1
128.4
LPG1
333.8
313.0
375.6
170.0
92.7
170.0
108.2
12.6
273.0
46.4
104.3
361.1
12.6
104.3
154.5
208.7
77.3
115.6
96.3
Diesel
2,055.2
2,734.9
6,563.7
596.7
160.4
765.1
528.6
60.0
1,228.9
217.0
529.7
1,280.0
60.0
382.5
695.5
765.1
178.2
400.2
353.1
CNG emission rate equals 1.00 times LPG emission rate.
Table 17. Equipment-Specific NOX Emission Rates (grams/operating hour)
GSE Information Series 2
Page 18
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline
(2-Stroke)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
39.0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Gasoline
(4-Stroke)
3.1
2.9
3.5
2.2
1.2
2.2
1.4
1.5
3.5
0.8
1.0
3.4
1.5
1.0
2.0
2.0
1.3
1.1
0.9
LPG1
2.1
2.0
2.3
2.2
1.2
2.2
1.4
1.0
3.5
0.5
0.7
2.3
1.0
0.7
2.0
1.3
0.8
0.7
0.6
Diesel
117.9
159.2
382.1
44.0
19.8
56.4
38.9
6.0
90.5
16.0
30.2
73.0
6.0
21.8
51.2
43.6
21.9
22.8
20.1
CNG emission rate equals 1.00 times LPG emission rate.
Table 18. Equipment-Specific PM Emission Rates (grams/operating hour)
GSE Information Series 2
Page 19
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline
(2-Stroke)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
11,238
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Gasoline
(4-Stroke)
82,412
77,261
92,714
43,583
23,773
43,583
27,735
7,780
70,011
15,128
25,754
89,148
7,780
25,754
39,621
51,508
25,213
28,527
23,773
LPG1
69,100
64,781
77,737
36,543
19,933
36,543
23,255
6,523
58,701
12,684
21,594
74,747
6,523
21,594
33,221
43,187
21,141
23,919
19,933
Diesel
108,183
136,153
326,766
30,286
17,505
38,829
26,827
5,619
62,373
11,013
28,527
68,941
5,619
20,603
35,299
41,206
19,450
21,554
19,018
CNG emission rate equals 0.92 times LPG emission rate.
Table 19. Equipment-Specific CO2 Emission Rates (grams/operating hour)
GSE Information Series 2
Page 20
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LPG AND CNG CONTROL STRATEGIES
-------
LPG AND CNG CONTROL STRATEGIES
Basic Control Strategy Summary: The majority of conventionally powered GSE can be
converted to either liquefied petroleum gas (LPG) or compressed natural gas (CNG) fueling or
replaced with a specially-manufactured LPG- or CNG-powered counterpart. The basic issues
surrounding the use of LPG or CNG as a GSE fuel are quite similar and, therefore, both fueling
strategies can be treated together. Generally, non-methane hydrocarbon (NMHC), carbon
monoxide (CO), oxides of nitrogen (NOX), particulate matter (PM), and carbon dioxide (CO2)
emissions from LPG or CNG GSE are all reduced relative to emissions from gasoline-powered
GSE. Relative to diesel GSE, emissions of NOX and PM are reduced, emissions of HC and CO
are increased, and emissions of CO2 can be either slightly increased or decreased depending on
equipment size. Important issues for consideration in determining the viability of either
conversion or replacement strategies include: the quality of equipment conversions, the cost of
conversion or replacement equipment, and the availability (or cost) of LPG or CNG refueling
facilities.
Potential GSE Equipment Affected: Generally, there are no technical limitations to the size or
type of GSE that can be converted to LPG/CNG power or replaced with equivalent LPG/CNG
equipment. For GSE powered by gasoline engines, both conversion and replacement are
technically feasible given the spark-ignition nature of both LPG/CNG and gasoline engine
designs. However, the compression-ignition design of diesel powered GSE generally restricts the
viability of LPG/CNG conversion strategies (due to the lack of an active ignition source),
rendering equipment replacement with specially manufactured LPG or CNG counterparts as the
only realistic LPG/CNG fueling strategy for diesel powered GSE. It is recognized that there have
been demonstration projects involving the passive ignition of gaseous fuels in
compression-ignition engines through such techniques as fumigation, but in general these
technologies are not considered to be sufficiently mature for mass market penetration at this time.
LPG/CNG Conversions: Although some aspects of the conversion process for LPG and CNG
vary, in general, both involve the same elements. Conversion of a spark-ignition engine (i.e., a
gasoline engine) essentially involves the installation of a new fuel tank, a new fuel delivery
system, and a new fuel metering system. To ensure low emissions operation, most advanced
conversion kits also include closed-loop performance feedback controllers that continuously
adjust the charge air/fuel mixture to promote optimum combustion. Previous generation
open-loop (i.e., non-feedback) conversion packages were prone to frequent combustion
"detuning" and large associated increases in emissions. Complete conversion packages for
specific engines are usually sold in kits available through a number of dealers nationwide.
While, theoretically, diesel engines can also be converted to LPG or CNG fueling, the extensive
nature of the engine modifications required with current mass-market technology to turn these
compression-ignition engines into spark-ignition engines are prohibitive.
LPG/CNG Replacements: Most GSE manufacturers now sell either specially designed LPG
and CNG versions of their equipment or offer LPG and CNG fueling as an optional feature of
their gasoline-powered equipment. There are few, if any, GSE applications for which LPG- or
GSE Information Series 3 Page 1
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CNG-powered equipment cannot be purchased.
Emission Impacts: The emission impacts of replacement LPG and CNG equipment and quality
LPG and CNG conversions are fairly well characterized. However, there are two issues of
consideration relative to any assessment of these characterizations. First, the emission
relationships presented in this information series are for unregulated (from an emissions
standpoint) GSE engines and assume that replacement or converted LPG and CNG systems do
not include any emissions aftertreatment devices (for example, catalytic converters) not found on
the GSE before replacement or conversion.
To the extent that any future emissions standards are imposed that impact the engines used in
GSE (generally large industrial-type engines), the relationship between emissions from GSE
powered by gasoline, diesel, LPG, and CNG will be fundamentally altered (potentially to the
point of equivalent emission limitations). Nevertheless, the conversion of GSE to LPG/CNG
will continue to be a viable control strategy even after the imposition of emission standards due
to the lag time associated with GSE retirement and replacement, but at some point (a decade or
so after regulatory effectiveness) the emissions benefits associated with such conversion will be
eliminated.
Conversely, should replacement or converted LPG/CNG equipment include emission control
aftertreatment equipment not present on the GSE before conversion or replacement, then
LPG/CNG emission reduction benefits will be larger than indicated in this information series.
The combined emission reduction percentage (PctRedoverall) of the fundamental fueling system
replacement (generating percent emission reduction PctRedj) and the emissions aftertreatment
device (generating percent emission reduction PctRed2) can be estimated as follows:
PctRed
overall
PctRed, V PctRed,
100 A 100
xlOO
The second issue for consideration is the quality of LPG and CNG conversions. Given the nature
of current gasoline GSE engines, there is no reason that a quality, properly installed conversion
kit cannot provide for emission performance similar to factory-produced LPG and CNG
equipment. However, experience has shown that conversion kits are not always certified
(emission certifications are currently only performed by the California Air Resources Board) or,
even if certified, properly installed and calibrated and, as a result, both operating and emissions
performance can be greatly affected. Frequent detuning observed with open loop conversion kits
indicates that such packages should either be exempted from or carefully monitored to ensure
compliance with stated emission reductions. As it stands today, the current "unregulated" state
of the aftermarket conversion industry can result in after-conversion equipment that generates
emissions (of pollutants that would normally be reduced) at the same or even greater rates than
the pre-conversion equipment. Since there is no way to quantify the fraction of conversions that
are of poor quality, the emission comparisons presented in this GSE information series assume
that a proper conversion has been performed and that emissions from that conversion are
equivalent to emissions from a replacement engine. However, in practice it will be necessary to
institute some type of certification and in-use compliance procedure to ensure that any emission
GSE Information Series 3 Page 2
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reductions achieved in practice are both quantifiable and consistent with any ascribed credits.
Examples of possible conversion certification programs can be found in California, where the
State Air Resources Board (ARE) certifies aftermarket conversion kits to specific emission
standards which become enforceable under the California in-use vehicle compliance program.
Jurisdictions such as the South Coast Air Quality management District rely on these certifications
before granting emission credits under their Mobile Source Emission Reduction Credit (MSERC)
program. However, in practice these certifications are only as effective as the in-use compliance
program that ensures that installers not only adhere to kit manufacturer requirements, but actually
achieve certification level emissions performance. One possible response is to require credit
emission reduction recipients to submit associated vehicles for periodic emission inspections to
ensure performance consistent with credit assumptions. There may be other equally effective
mechanisms, but clearly an effective program will require significant oversight and enforcement.
Using data developed for the off-road emissions model recently released by the California ARB,
detailed emission estimates for LPG, CNG, gasoline, and diesel GSE have been developed as
described in the information series selection GSE Emissions and Activity Estimates. Data used in
this emissions estimation analysis include zero hour emission rates, emissions deterioration rates,
equipment horsepower, equipment load factors, and brake-specific fuel consumption. Table 1
presents a comparison of derived emission rates for baggage tractors and belt loaders, which
together constitute over a third of all GSE. Emission rates for other GSE types will vary from
those presented in Table 1 due to variations in engine size and operating characteristics, but the
relative relationships between the various fueling types remain consistent. Therefore, the data in
Table 1 can be used to assess the relative degree of emission reduction to be expected by
converting or replacing conventionally fueled GSE. Table 2 presents these emission reduction
relationships and indicates the variability across different GSE types from those included in
Table 1.
Several aspects of the tables stand out. Relative to emissions from gasoline GSE, emissions from
both LPG and CNG equipment are reduced for all five emission species examined. Similar
relationships exist for LPG and CNG NOX and PM relative to diesel GSE emissions, where the
greatest emission reductions due to equipment conversion or replacement are observed.
Although (apparently dramatic) emission increases are observed for both HC and CO relative to
diesel GSE emissions, these increases are not nearly as dramatic in absolute terms as the
percentage increase estimates imply. The large percentages simply result from the relatively low
HC and CO emission rates of diesel GSE engines. For example, while diesel baggage tractors
are estimated to emit over 200 grams of CO and about 70 grams of HC per hour, equivalent
LPG-powered equipment has estimated emission rates of over 9,000 and nearly 150 grams per
hour respectively (both well below the estimated emission rates of about 14,500 grams CO and
300 grams HC per operating hour for equivalently sized gasoline equipment (not shown in Table
1)). Finally, the variation of the estimates of LPG and CNG CO2 relative to diesel GSE around
zero are due to the sensitivity of diesel engine efficiency to engine size. However, the cases in
which diesel engine efficiency exceeds (and thus CO2 emissions are lower) than LPG and CNG
far outnumber the alternative. Finally, when considering CO2 emissions in the context of global
warming potential, it is also
GSE Information Series 3 Page 3
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Emissions from ICE-Powered Baggage Tractors of Gasoline Engine Size
Gasoline (4- Stroke)
LPG
CNG
HC
371.8
185.9
123.9
CO
18678.0
11673.8
11673.8
NOX
226.6
170.0
170.0
PM
2.2
2.2
2.2
CO2
43583.3
36543.1
33619.6
Emissions from ICE-Powered Baggage Tractors of Diesel Engine Size
Gasoline (4-Stroke)
LPG
CNG
HC
371.8
185.9
123.9
CO
18678.0
11673.8
11673.8
NOX
226.6
170.0
170.0
PM
2.2
2.2
2.2
CO2
43583.3
36543.1
33619.6
Emissions from ICE-Powered Belt Loaders of Gasoline Engine Size
Gasoline (4-Stroke)
LPG
CNG
HC
202.8
101.4
67.6
CO
10188.0
6367.5
6367.5
NOX
123.6
92.7
92.7
PM
1.2
1.2
1.2
CO2
23772.7
19932.6
18338.0
Emissions from ICE-Powered Belt Loaders of Diesel Engine Size
Gasoline (4-Stroke)
LPG
CNG
HC
52.0
101.4
67.6
CO
135.6
6367.5
6367.5
NOX
160.4
92.7
92.7
PM
19.8
1.2
1.2
CO2
17505.3
19932.6
18338.0
Table 1. Estimated Emission Rates for Baggage Tractors
HC
CO
NOX
PM
CO2
Emissions Relative to Gasoline GSE
LPG
-50% to -65%
CNG
-65% to -75%
-40% to -50%
-20% to -25%
-20%
-15%
-20%
Emissions Relative to Diesel GSE
LPG
+95% to +140%
CNG
+30% to +60%
+4000% to +5000%
-75% to -80%
-95%
-5% to +15%
-10% to +10%
Table 2. Percent Emissions Reduction Due to LPG/CNG GSE
GSE Information Series 3
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important to recognize that emission species such as methane which are not estimated here can
play a critical role in determining the overall global warming potential associated with a specific
fuel. For example, CNG equipment will emit methane at a higher rate than either gasoline, LPG,
or diesel equipment.
Costs: The incremental cost of LPG conversions has been estimated to be in the range of $1,500
to $2,000 for systems capable of storing the LPG equivalent of about 20 gallons of gasoline. For
larger GSE, costs can range as high as $3,000. High pressure fuel storage requirements push
typical conversion costs to $4,000 to $4,500 per unit for CNG, even for systems sized to store the
equivalent of only about 15 gallons of gasoline. Locating space for adequate fuel tank storage
capacity can be an issue for CNG as well as LPG conversions. Most GSE do not have significant
unused cargo volumes in which to locate additional fuel storage tanks. Since safety concerns
preclude installation in exposed areas, fuel tanks must generally replace existing conventional
fuel tanks. However, the CNG's lower fuel energy per unit volume can severely restrict
operating range, and thus conversion viability, in some applications.
For gasoline powered GSE, the incremental costs of specially designed LPG and CNG
replacement GSE equipment are similar to incremental conversion costs. However, for
replacement diesel equipment, incremental costs can be considerably higher given the generally
larger size and expected durability of diesel-type GSE. Cost premiums can be as high as 50
percent of the basic diesel GSE cost.
Some of the increased cost of equipment conversion or replacement can be offset by fuel cost
savings. Although fuel prices vary geographically, in general LPG and CNG cost from 30-50
percent less on an equivalent energy basis than retail gasoline or diesel (including the cost of
compression for CNG). However, most, and in some cases all, of this potential savings is lost in
airport applications since on-highway fuel taxes (that comprise 30-40 percent of retail fuel price)
are recouped as tax credits due to the off-road nature of GSE use. Potential fuel cost savings are
further eroded through an estimated loss in fuel efficiency of about 5 percent for LPG and 10
percent for CNG relative to gasoline GSE and losses of up to 30 percent relative to diesel GSE.
Thus fuel cost savings, if any, will be modest. LPG systems could have fuel costs about $0.10
per gasoline equivalent gallon lower than their gasoline counterparts while CNG equipment fuel
costs will be about equal to those of their gasoline counterparts and possibly somewhat higher.
Both LPG and CNG GSE could have lower routine maintenance costs than either gasoline or
diesel GSE due to reduced particulate and associated deposit formation. However, several
airlines using such equipment have reported much higher non-routine maintenance costs for LPG
and CNG equipment. This may, however, be a result of early design problems associated with
early generation LPG and CNG systems and could decline as additional experience is gained.
Table 3 presents the results of a life cycle cost comparison for a baggage tractor under a high-use
operating scenario (i.e., the GSE is generally used to service aircraft continuously throughout an
operating day as typically occurs at high traffic airports). The tabulated costs represent the net
present value of the various expenditures required over the sixteen year useful life of the tractor.
In all cases, the diesel-powered tractor exhibits the lowest life cycle costs by a substantial margin.
This is consistent with an observed movement in the GSE industry towards greater
GSE Information Series 3 Page 5
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Fuel
Type
Gasoline
Diesel
LPG
CNG
Purchase
Cost
$17,000
$22,000
$19,000
$21,000
Rebuild or
Replacement
Costs
$2,568
$1,351
$2,568
$2,568
Fuel
Costs
$59,481
$27,386
$49,072
$65,058
Reduced
LPG/CNG
Maintenance
Costs
$47,089
$47,089
$37,176
$37,176
Total Costs
if Reduced
LPG/CNG
Maintenance
$126,139
$97,826
$107,816
$125,802
Total Costs
if Same
LPG/CNG
Maintenance
$126,139
$97,826
$117,729
$135,715
Assumptions: 16 year equipment life; 6 year engine replacement interval for gasoline, LPG, and CNG; 8 year engine
rebuild interval for diesel; $2,500 unit cost for all rebuilds/replacements; equipment used 8 hours per day for 350 days per
year; gasoline use is 3.2 gallons per hour at $0.75 (after tax credits) per gallon; diesel use is 1.7 gallons per hour at $0.65
(after tax credits) per gallon; LNG use is 3.3 gallons per hour at $0.60 per gallon; CNG use is 3.5 gallons per hour at $0.75
per gallon (including the cost of refueling facility operation and amortization); maintenance costs are $1.90 per hour for
gasoline and diesel; maintenance costs are $1.50 per hour for LPG and CNG under a reduced maintenance scenario or
$1.90 per hour under a "same maintenance" scenario.
Table 3. Life Cycle Costs for Baggage Tractors
diesel utilization in large engine applications. Relative to gasoline, both LPG and CNG tractors
show reduced or similar life cycle costs if one assumes reduced maintenance requirements for
LPG and CNG engines. However, if the assumption of reduced maintenance is eliminated, the
full life cycle costs favor gasoline over CNG and the savings associated with LPG are cut in half.
Clearly, the maintenance issue is critical to the viability of LPG and CNG engines given the
current experience of many LPG- and CNG-powered GSE owners, where maintenance costs are
not only not reduced, but actually higher than those of comparable gasoline or diesel equipment.
It is also important to note that since both fuel and maintenance costs are a function of usage, the
range of life cycle costs narrows and any cost advantages of LPG and CNG engines are
diminished if GSE is used less frequently than assumed in the development of Table 3. For
example, if a baggage tractor is operated only half the time assumed (i.e., four hours per day
instead of eight), the range between diesel and gasoline life cycle costs narrows to about $12,000;
the range between gasoline and LPG narrows to about $8,000 under a reduced maintenance
scenario or $3,000 under a constant maintenance scenario; and CNG operation becomes about
$2,000 more costly than gasoline under a reduced maintenance scenario or $7,000 more costly
under a constant maintenance scenario. Clearly site- and application-specific calculations are
necessary before accurate airport and airline-specific cost relations can be determined.
Cost Effectiveness: It is difficult to provide detailed cost effectiveness estimates for either LPG
or CNG GSE because the impact of such equipment varies across the pollutants examined and
relative to whether gasoline or diesel GSE is being replaced. From the cost table presented
above, it is clear that from a simple operation and maintenance standpoint, diesel GSE are more
cost effective than gasoline, LPG, or CNG. The inclusion of an emissions valuation can shift this
relationship, but the shift is greatly dependent on the pollutants included in the valuation. Diesel
HC and CO are generally lower than those of gasoline, LPG, and CNG, so that credits assigned
to a reduction in either will continue to favor diesel GSE. Under a scenario in which only NOX
GSE Information Series 3
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reductions are assigned a marketable value, LPG becomes cost competitive with diesel at a
market value of $1,000-$2,000 per ton; CNG becomes cost competitive with diesel at a market
value of $3,000-$4,000 per ton; and gasoline becomes cost competitive with diesel at a market
value of about $3,500 per ton. A similar scenario that assigns marketable value to PM reductions
would make LPG competitive with diesel when PM is valued at $10,000-$20,000 per ton, CNG
competitive with diesel when PM is valued at $30,000-$40,000 per ton, and gasoline competitive
with diesel when PM is valued at about $30,000 per ton. The inclusion of CO2 emissions in an
evaluation program is somewhat more complex as the relationship between the various fuels
shifts slightly with engine size, but diesel engines generally emit lower CO2 than either gasoline,
LPG, or CNG so that under most scenarios in which value is granted to CO2 reductions,
diesel-powered GSE would be favored over the other three fuels.
Relative to gasoline GSE, emissions of all examined pollutants (HC, CO, NOX, PM, and CO2)
should decline through replacement with either LPG- or CNG-powered GSE. In fact, from the
table above it is clear that under a scenario in which LPG and CNG maintenance costs are
reduced relative to gasoline that these emissions reductions are derived for free (the life cycle
costs of both LPG and CNG are lower than those of gasoline) and any marketable credits
obtained through gasoline GSE replacement are essentially windfalls. (It should be noted that for
programs crediting HC, CO, or CO2, diesel GSE would also reflect a windfall status relative to
gasoline.) Even under an assumption of similar maintenance costs, LPG retains its windfall
status. However, CNG would lose its competitive edge under such an assumption unless HC
reductions are valued at about $2,000 per ton, CO reductions are valued at about $100 per ton, or
NOX reduction are valued at about $5,000 per ton (or some combination of all three).
References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995
4. Advanced Transportation Vehicle Catalog, www.calstart.org/services/catalog/, CALSTART
internet website.
5. Survey of Airport Fleet Vehicles, Final Report, GRI-98/0064, prepared by Edwards and
Kelsey, Inc. for the Gas Research Institute, April 1998.
GSE Information Series 3 Page 7
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ELECTRIC GSE
-------
ELECTRIC GSE
Basic Control Strategy Summary: The majority of conventionally powered GSE can be either
converted to electric power or replaced with specially-manufactured electrically powered
counterparts. Although there is an increase in offsite power generating station emissions
resulting from the increased electrical demand required to recharge electric GSE, conversion to
electric power or replacement with electric GSE can be a very effective emission reduction
strategy. Even when the increased emissions from power generating stations are considered,
electric GSE usually emit* significantly less hydrocarbon (HC), carbon monoxide (CO), oxides of
nitrogen (NOX), particulate matter (PM), and carbon dioxide (CO2) emissions than their fossil
fueled (i.e., gasoline, diesel, compressed natural gas (CNG), and liquefied petroleum gas (LPG))
counterparts. Important issues for consideration in determining the viability of either conversion
or replacement strategies include: the capacity of the electric equipment to handle daily GSE
scheduling and load demands, the quality of equipment conversions, the cost of conversion or
replacement equipment, the availability (or cost) of electric recharging or battery replacement
stations, and the ability to schedule recharging or battery replacement around GSE service
demands.
Potential GSE Equipment Affected: Generally, there are no technical limitations to the size or
type of GSE that can be converted to or replaced with electrically powered equipment.
Electrically powered versions of baggage tugs and belt loaders, which together account for over a
third of all GSE, are available and in use (although current usage constitutes only a minor
fraction of total activity). Additionally, electric powered versions of aircraft pushback tractors,
air start units, conditioned air units, forklifts, ground power units, lifts, general purpose vehicles
(cars, trucks, and vans), and other specialty GSE are currently available in the marketplace.
Electric carts are already fulfilling about half of overall GSE cart demand.
GSE conversion generally requires the removal of the internal combustion engine and fuel
storage tanks to obtain sufficient room to install the necessary electric motor, motor controller,
and battery pack and, therefore, is equally viable on diesel, gasoline, CNG, and LPG fueled
GSE. However, some equipment types or configurations may not be able to store sufficient
battery capacity to fulfill required service demands within existing space limitations. Therefore,
the ability to convert a specific GSE to electric power, and the specifications for conversion,
require a detailed review of the candidate equipment.
Regardless of the availability of replacement or conversion equipment, a primary issue in
evaluating the potential acceptability of electrically powered GSE is the daily usage demand
placed on the equipment. Equipment that is in continuous or near-continuous service throughout
the day will require quick turnaround battery replacement facilities, quick recharge capability, or
Technically, electrically powered GSE do not emit any pollutants. The term emit, as used here, ascribes to the
electric GSE, the offsite increase in power generating station emissions due to increased airport electrical power to
support electric GSE recharging. In essence, the electrically powered GSE are treated as if they "emitted" the
increased power generating station emissions associated with their use.
GSE Information Series 4 Page 1
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the availability of fully charged backup equipment. Most GSE will require between one and five
charging cycles per day. GSE that can operate for a full day on a single charge are candidates for
off-peak charging, but most equipment will require all-hours recharging access, at least with
current battery technology. Battery storage advances could increase the fraction of GSE that can
operate throughout the day on a single charge, but existing technology can only be extended
through an increase in battery pack size (thus imposing additional storage space considerations).
Clearly, the capability of scheduling GSE recharging within the constraints of aircraft service
demands is a key issue for those considering replacement or conversion of fossil fueled GSE.
Electric GSE Conversions: Conversion of fossil fueled GSE to electric power generally
involves the removal of the internal combustion engine and fuel tank and installation of an
electric motor, motor controller, and battery pack. Although the conversion process is generally
well established from a technical standpoint, the sizing of the electric motor, selection of an
appropriate controller, integration with (or replacement of) existing drivetrain components, and
selection and sizing of the battery pack within the volume constraints established by existing
GSE design, result in the need for a case-by-case design review. It is important to recognize that
design review and installation quality are important from a performance standpoint alone. Like
factory-designed replacement GSE, tailpipe emissions from converted electric GSE are
non-existent (unlike fossil fuel conversions such as CNG and LPG, for which emissions
performance can be quite dependent on conversion quality). Another limiting factor, in addition
to conversion design and packaging, is the location of qualified conversion facilities, which tend
to be concentrated in California.
Electric GSE Replacements: Specially designed electrically powered GSE are now available
from reputable GSE OEM s (original equipment manufacturers). The range of electric GSE now
available spans nearly the full range of aircraft service equipment. In general, the latest
generation of such equipment has attained a level of reliability equal to or better than that of
equivalent fossil fueled GSE. However, battery recharging capacity and scheduling continue to
represent major feasibility considerations given current battery technology.
Emission Impacts: The emission performance of replacement or converted electric GSE is well
understood since removal or retirement of the fossil fueled internal combustion engine (ICE)
results in zero emissions piece of equipment. Nevertheless, overall emission reduction impacts
are dependent on two key factors: (1) the emissions performance of the equipment being replaced
or converted, and (2) the specific power generating characteristics of the region in which the
airport is located.
Most GSE in operation today are unregulated from an emissions standpoint and, therefore, do not
incorporate emission reduction technology in their design. A definitive calculation of displaced
emissions due to conversion or replacement of equipment with electric GSE involves the
measurement of the average emission rate of the displaced fossil fueled GSE and the application
of the activity data associated with the displaced unit. A generalized expression of the necessary
calculation of displaced emissions takes the form:
GSE Information Series 4 Page 2
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To calculate total displaced emissions, the emission rate per unit time (e.g., pounds per year)
should be aggregated over the total time such emissions would have accrued. For example, if a
unit had an expected additional service period of four years after displacement, then emissions
throughout this four year period would be displaced. Determining the emissions performance of
units which are displaced by attrition as part of a normal replacement cycle is more complex in
that reductions will only accrue in accordance with the emission rate of the newer-design
alternative fossil fueled GSE which could (and presumably would) have been purchased in the
absence of electric GSE purchase. In addition to fossil fueled GSE emission reductions due to
technology evolution, any future emission standards imposed on GSE will reduce the emission
reduction benefits of electric GSE by reducing the emission rate of displaced fossil fueled GSE.
Under any emissions control scenario, the emission reduction benefits of switching GSE from
fossil fueling to electric power will depend on the specific fossil fuel being displaced since each
has its own emissions characteristics.
Airports served by relatively low emitting power generation facilities will produce larger
emission reduction benefits than will accrue in areas served by older, higher emitting generating
facilities. While HC and CO emission reductions are dramatic (approaching 100 percent)
regardless of local power generation characteristics, NOX, PM, and CO2 reductions can vary
considerably. Tables 1 and 2 demonstrate this sensitivity. Table 1 presents estimated hourly
emission rates for both fossil fueled baggage tractors* and the incremental electricity generation
required to power alternative electric baggage tractors. Table 2 presents the resulting emission
reductions associated with replacement of the various fossil fueled baggage tractors under
alternative power generation scenarios. Baggage tractors alone account for just under a quarter
of all GSE and the emission impacts associated with replacement of fossil fueled baggage
tractors are consistent with the impacts associated with replacement of other fossil fueled GSE.
As indicated, the dependence of emission impacts on power generation emissions can be
dramatic. For example, NOX reductions due to the replacement of gasoline baggage tractors can
range from 40 to 99+ percent and the potential range of CO2 reductions is nearly as wide at 40 to
80 percent. PM emissions can, as indicated, increase substantially under the highest emission
power generation conditions, but can also decline by as much as 90 percent under other power
generation conditions. Both the highest and lowest power generation scenarios are equally
unlikely to be applicable to any given electric GSE replacement scenario. The highest emission
scenario represents an uncontrolled coal-fired application while the lowest emission scenario
represents a maximum controls (regardless of cost effectiveness) natural gas application.
There may be a few specific instances (e.g., California airports) where actual power generation
emissions approach those of the low emissions scenario, but generally emission reductions are
more likely to approximate those of the tabulated average scenario which is based on the
average of measured emission rates for six geographically diverse U.S. utilities. Therefore,
emissions grams , , 7 „ hours of use
= x hp x load jactor x
unit time brake hp - hr unit time
The tabulated emission rate data was developed using data from the off-road emissions model recently released by
the California Air Resources Board. Data used for this analysis included zero hour emission rates, emissions
deterioration rates, equipment horsepower, equipment load factor, and brake-specific fuel consumption. See the
information series selection entitled GSE Emission Rates and Activity for additional detail.
GSE Information Series 4 Page 3
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Emissions from ICE-Powered Baggage Tractors (grams/operating hour)
Gasoline (4- Stroke)
LPG
Diesel
HC
371.8
185.9
70.4
CO
18,678.0
11,673.8
222.4
NOX
226.6
170.0
596.7
PM
2.2
2.2
44.0
CO2
43,583.3
36,543.1
30,286.4
Incremental Utility Emissions from Electric Baggage Tractors Assuming
Utility Scenario1
Best Case
Worst Case
Average Case
HC
0.5
6.8
2.0
CO
1.9
10.2
6.0
NOX
4.4
139.4
22.2
PM
0.2
75.4
1.3
CO2
9,645.2
25,619.9
19,088.7
Incremental Utility Emissions from Electric Baggage Tractors Assuming
Utility Scenario1
Best Case
Worst Case
Average Case
HC
0.4
5.3
1.6
CO
1.5
7.9
4.7
NOX
3.4
108.7
17.3
PM
0.2
58.8
1.0
CO2
7,523.2
19,983.6
14,889.2
1 Utility (i.e., power generating station) emissions will vary in accordance with local
electricity generation practices. Major factors include boiler design, boiler fuel, and
emission controls in place. The best case scenario represents potential emissions if GSE
electrical demand is satisfied by a generating station firing natural gas and employing
maximum controls. Conversely, the worst case scenario represents potential emissions if
GSE electrical demand is satisfied by a generating station firing coal under essentially
uncontrolled (from an emissions standpoint) conditions. The average case represents a
more typical level of utility emissions and is based on actual emission rates for a
geographically diverse sample of utilities.
Table 1. Estimated Emission Rates for Baggage Tractors
GSE Information Series 4
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Percent Reduction1 from a Gasoline (4-Stroke) Baggage Tractor
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.9
98.2
99.4
CO
100.0
99.9
100.0
NOX
98.1
38.5
90.2
PM
88.9
up 3328.4
42.4
CO2
77.9
41.2
56.2
Percent Reduction1 from an LPG Baggage Tractor
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.8
96.3
98.9
CO
100.0
99.9
99.9
NOX
97.4
18.0
86.9
PM
88.9
up 3328.4
42.4
CO2
73.6
29.9
47.8
Percent Reduction1 from a Diesel Baggage Tractor
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.5
92.4
97.7
CO
99.3
96.4
97.9
NOX
99.4
81.8
97.1
PM
99.6
up 33. 8
97.8
CO2
75.2
34.0
50.8
1 Unsigned and unqualified values signify emission reductions (in percent). Values
preceded by the qualifier "up" signify emission increases (in percent)
2 Utility (i.e., power generating station) emissions will vary in accordance with local
electricity generation practices. Major factors include boiler design, boiler fuel, and
emission controls in place. The best case scenario represents potential emission
reductions if GSE electrical demand is satisfied by a generating station firing natural gas
and employing maximum controls. Conversely, the worst case scenario represents
potential emission reductions if GSE electrical demand is satisfied by a generating
station firing coal under essentially uncontrolled (from an emissions standpoint)
conditions. The average case represents a more typical level of emission reductions and
is based on actual emission rates for a geographically diverse sample of utilities.
Table 2. Estimated Emission Reductions Due to Baggage Tractor Replacement
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replacement of fossil fueled GSE will, as indicated, generate substantial emission reductions at
most U.S. airports.
Costs: Initial purchase costs for electric GSE are high relative to their fossil fueled counterparts.
The cost premium is almost entirely associated with the required battery pack and recharger.
Table 3 presents a comparison of electric baggage tractor first costs relative to those of fossil
fueled GSE. As indicated, the cost premium ranges from about $8,000 relative to a diesel
powered tractor to about $13,000 relative to a gasoline-powered tractor. These purchase price
premiums are augmented by periodic battery replacement requirements (at about $4,500 every
5-6 years) that are 2 to 4 times higher on a life cycle basis than corresponding fossil fuel engine
rebuild or replacement costs. However, these cost premiums are counterbalanced by a
substantial reduction in fuel costs. Electric GSE use no fuel during idle periods and such periods
can comprise as much as 50 percent of typical GSE operation. Using an estimated electricity
cost of $0.045 per kilowatt-hour, the overall fuel savings associated with high-use GSE
operations such as baggage tractors can range from $2,500 per year relative to diesel equipment
to over $6,000 per year relative to gasoline and CNG equipment. While lower-use GSE fuel cost
savings will be smaller, it is clear that fuel savings alone can offset the entire electric GSE
purchase price premium in 2 to 3 years. Moreover, electric GSE fuel cost savings will increase
as more efficient electric motors and motor controllers continue to evolve.
In addition to reduced fuel costs, the latest generation of electric GSE have demonstrated
significantly reduced maintenance requirements. Costs have been estimated to be reduced by as
much as two-thirds relative to gasoline and diesel powered GSE. Table 3 presents the results of a
life cycle cost comparison for a baggage tractor under a high-use operating scenario (i.e.,
generally used to service aircraft continuously throughout an operating day such as occurs at high
traffic airports). The tabulated costs represent the net present value of the various expenditures
required over the sixteen year useful life of the tractor. Regardless of whether maintenance costs
are assumed to be reduced, the electric-powered tractor consistently exhibits the lowest life cycle
costs. Life cycle costs for the electric baggage tractor are estimated to be over 40 percent lower
than the next lowest cost diesel option under a reduced maintenance scenario and still 10 percent
lower even if maintenance costs are assumed to be identical to conventional gasoline and diesel
powered GSE maintenance costs.
Cost Effectiveness: It is difficult to provide precise cost effectiveness estimates for electric GSE
because the impact of such equipment varies across the pollutants examined and relative to the
fossil fuel equipment being replaced and the emissions performance of local utilities. However,
it is clear from the data presented in Table 3 that electric GSE represent the lowest cost option
relative to all fossil fuel GSE. Therefore, if an appropriate battery recharging schedule and
infrastructure can be established, all derived emission reductions accrue for free. Assuming local
utility emissions performance is not too different from average U.S. utility emission levels,
electric GSE are cost effective from an economic standpoint alone.
GSE Information Series 4 Page 6
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Fuel
Type
Gasoline
Diesel
LPG
CNG
Electric
Purchase
Cost
$17,000
$22,000
$19,000
$21,000
$30,000
Rebuild or
Replacement
Costs
$2,568
$1,351
$2,568
$2,568
$5,147
Fuel
Costs
$59,481
$27,386
$49,072
$65,058
$5,574
Reduced
Maintenanc
e
Costs
$47,089
$47,089
$37,176
$37,176
$15,696
Total Costs
If Reduced
Maintenance
$126,139
$97,826
$107,816
$125,802
$56,418
Total Costs
If Same
Maintenance
$126,139
$97,826
$117,729
$135,715
$87,810
Assumptions: 16 year equipment life; 6 year engine replacement interval for gasoline, LPG, and CNG; 8 year engine rebuild
interval for diesel; 5 year battery life for electric; $2,500 unit cost for all rebuilds; $4,500 unit cost for all battery replacements,
equipment used 8 hours per day for 350 days per year; idle is 40 percent of operating day; gasoline use is 3.2 gallons per hour at
$0.75 (after tax credits) per gallon; diesel use is 1.7 gallons per hour at $0.65 (after tax credits) per gallon; LNGuse is 3.3 gallons
per hour at $0.60 per gallon; CNG use is 3.5 gallons per hour at $0.75 per gallon (including the cost of refueling facility operation
and amortization); electric use is 8.33 kilowatts per operating hour; maintenance costs are $1.90 per hour for gasoline and diesel;
maintenance costs are $1.50 per hour for LPG and CNG under a reduced maintenance scenario or $1.90 per hour under a "same
maintenance" scenario; maintenance costs are $0.63 per hour for electric under a reduced maintenance scenario or $1.90 per hour
under a "same maintenance" scenario.
Table 3. Life Cycle Costs for Baggage Tractors
References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995.
4. Airport Electrification Project, Consolidated Results and Analysis, EPRI TR-109041, Electric
Power Research Institute, September 1997.
5. Off-Road Electric 'Vehicle "Scoping Study, EPRI TR-101906, Electric Power Research
Institute, July 1993.
6. Electric Vehicles will Reduce Emissions at Boston s Logan Airport, Innovators with EPRI
technology, IN-102438, Electric Power Research Institute, June 1994.
7. Off-Road Electric Vehicles: An Existing Market, EPRI TR-103315, Electric Power Research
Institute, February 1994.
GSE Information Series 4
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8. Advanced Transportation Vehicle Catalog, www.calstart.org/services/catalog/, CALSTART
internet website.
9. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary
Point and Area Sources, Chapter 1 (External Combustion Sources), as downloaded on July
29, 1998 from the U.S. EPA internet website www.epa.gov/ttn/chief/ap42.html.
GSE Information Series 4 Page 8
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EMISSIONS AFTERTREATMENT
-------
EMISSIONS AFTERTREATMENT
Basic Control Strategy Summary: The majority of GSE continue to emit pollutants at
essentially uncontrolled rates. Certain emission species such as hydrocarbons (HC), carbon
monoxide (CO), and, in some cases, oxides of nitrogen (NOX) can be substantially reduced by the
installation of a catalytic converter in the equipment exhaust system. Exhaust system traps (or
filters) can perform similar reduction functions for particulate matter (PM). Catalyst technology
has been well proven in on-road vehicle applications and particulate trap technology has
advanced considerably over the last several years. Both systems are commercially available for
equipment in the off-road sector, but long term reliability and effectiveness have not been
proven. Systems designed for application on gasoline, diesel, compressed natural gas (CNG),
and liquefied petroleum gas (LPG) engines are available, but important issues for consideration
in determining the practical application of these technologies include: installation costs, costs
associated with the use of catalyst-compatible (i.e., non-poisoning) fuel blends and lubricating
oils, exhaust system space constraints, increased exhaust and exhaust system temperatures, the
compatibility of GSE operating cycles with effective conversion temperature requirements, and
impacts on equipment reliability.
Potential GSE Equipment Affected: Generally, there are no theoretical limitations to the size
or type of GSE that can be equipped with a catalytic converter or particulate trap. Effective
converters have been designed for applications as small as lawn mower engines. In terms of
practicality, however, both catalytic converters and particulate traps require sufficient exhaust
system temperatures for high conversion efficiencies and, in the case of traps, effective
regeneration. Therefore, equipment with very low load factors may experience extended periods
of comparatively low exhaust temperatures, inhibiting both and catalyst and trap performance.
Additionally, equipment that is operated only for brief periods between engine startup and
shutdown may accumulate a significant fraction of its operating time in conditions where the
catalyst has not yet attained the "light-off temperature required for significant emissions
conversion. However, the lack of actual test data for either catalyst or particulate trap
performance on GSE (or other similarly sized and utilized equipment), renders it difficult to
accurately assess the potential impacts of GSE operating cycles on exhaust aftertreatment system
performance. The effectiveness of both certainly increases with operating temperature (up to the
point where thermal degradation of catalyst materials occurs). Given the current data deficiency,
the installation of catalyst or trap technology on GSE should be treated as developmental at this
time and instances of system installation should be closely monitored until demonstrated
performance data has been collected.
Oxidation Catalysts: Oxidation catalysts function by promoting the reaction of exhaust HC and
CO with oxygen to form water and carbon dioxide. The required oxygen can be obtained by
tuning the engine air/fuel mixture to the lean side of stoichiometry (i.e., the combustion air/fuel
mixture is set so that there is excess air relative to that required for complete fuel combustion) or
by introducing air into the exhaust system upstream of the catalyst. The latter approach,
commonly referred to as secondary air injection, was widely utilized in the on-road vehicle sector
during the 1970's when oxidation catalyst technology was common. Although universally
GSE Information Series 5 Page 1
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displaced by three-way catalysts in the on-road sector, oxidation catalyst technology is well
developed and has been shown to be effective, providing appropriate operational procedures are
observed.
In the typical oxidation catalyst, the water and carbon dioxide formation reactions are usually
promoted using the noble metal platinum. Platinum effectively lowers the temperature at which
the desired reactions take place. However, platinum (as well as other catalyst metals) is easily
poisoned if proper precautions are not observed. Fuels, lubricating oils, and additives containing
lead or phosphorus compounds should be avoided. Existing regulations should serve to ensure
appropriate fuel composition, but phosphorus-containing lubricating oils are still available and
should be replaced before any catalyst is installed.
Proper engine maintenance is also important in promoting both high catalytic conversion
efficiencies and long catalyst life. Engines tuned to run overly rich, or cylinder misfire, can
result in temperatures inside the catalytic converter shell (due to the temperature increases
associated with excessive conversion reactions) which exceed the durability tolerances of both
the catalyst and the substrate onto which it is coated. Prolonged exposure to excessive
temperatures can cause the catalyst and substrate to sinter, increasing exhaust system
backpressure, in extreme cases, to the point of engine failure. Proper engine maintenance is a
critical aspect of any emission reduction strategy designed around the catalytic conversion of
engine exhaust.
As already mentioned, optimum oxidation catalyst conversion efficiency is obtained when there
is a high concentration of oxygen in the exhaust entering the catalyst. Maximum engine power,
however, is obtained with combustion mixtures that are slightly rich (i.e., that have slightly less
air than required for complete combustion) and many off-road engines are set to run in a rich
mode to obtain maximum performance. For engines that are overpowered relative to operational
demands, enleanment of the air/fuel mixture may be an acceptable means of providing required
catalyst air, but enleanment will not be a viable approach for engines requiring full power to
fulfill operational demands. For such engines, secondary air injection will be required to achieve
high catalyst conversion rates.
Space is at a premium with all types of off-road equipment, including GSE. Equipment
configuration and sizing are usually designed around a specific engine and exhaust configuration
and, therefore, there is generally not sufficient "free" space to easily accommodate modifications.
As a result, installing a catalytic converter even without an accompanying secondary air injection
system can be problematic. The requirement for secondary air simply compounds this difficulty.
Aftermarket catalyst manufacturers have responded to these space restrictions by combining
muffler and catalyst functions into a single package that can be installed in place of the standard
exhaust system muffler. Moreover, manufacturers have designed effective air breather valves
and venturi nozzles into the upstream end of the catalyst/muffler shell to provide adequate
secondary air so that compact, fully complete oxidation catalyst systems are available for most
applications. The ability of these passive secondary air systems to provide adequate air for
effective conversion on larger engines (six and eight cylinder) with lower amplitude exhaust
pressure characteristics is potentially an issue, but no definitive conclusions can be reached as
performance test data for such applications is not currently available.
GSE Information Series 5 Page 2
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Exhaust system temperatures can also be an issue of concern when considering the installation of
a catalytic converter. Catalysts produce substantial increases in exhaust system skin temperatures
and must be installed such that these increases are not a potential hazard, either through human
contact or proximity to combustible materials. Most catalyst installations require heat shielding
to ensure adequate safety, and space for such shielding can be an installation concern. Moreover,
to avoid the potential for human contact with hot catalyst surfaces, an under-body or
under-chassis installation location is generally preferred. Many currently marketed off-road
catalysts are designed to replace conventional mufflers which are already isolated for the same
heat-related concerns and, therefore, available installation locations may be acceptable (although
heat shielding may still be required given the higher skin temperatures of catalysts relative to the
mufflers they replace).
Oxidation catalysts can be purchased for gasoline, LPG, or CNG powered equipment. Specially
constructed versions can also be purchased for diesel engine application. Diesel converters are
generally larger than the mufflers they are designed to replace and, therefore, must be constructed
in recognition of the specific space allowances of the targeted equipment. HC and CO emissions
from diesel engines are generally quite low even without a catalyst. The primary diesel catalyst
design criteria is the reduction of the soluble organic portion of diesel PM. In some cases,
soluble organics can comprise up to 40 percent or more of total diesel PM.
Three-Way Catalysts: Three-way catalysts designed to promote the simultaneous oxidation of
HC and CO and reduction of NOX are also available for application in the off-road engine sector.
These catalysts effectively promote reactions which add oxygen to HC and CO to form water and
carbon dioxide and remove oxygen from NOX to form molecular nitrogen and oxygen. Issues
relating to such installations are much the same as those for oxidation catalysts, with the added
issue of a required feedback system to control engine air/fuel ratio. Three-way catalysts only
function effectively over a narrow range of air/fuel ratios (around stoichiometry), and it is critical
that an effective air/fuel mixture control system be installed in conjunction with the catalyst if
high conversion efficiencies are to be obtained. Such systems, which are commonly known as
closed loop systems and are standard equipment on all light-duty on-road vehicles, function by
monitoring the amount of oxygen in the exhaust system and adjusting the engine air/fuel mixture
to maintain stoichiometry. Off-road engines and equipment generally do not incorporate closed
loop feedback and, therefore, effective three-way converter installations must include the
installation of such a system. Open loop systems (i.e., systems which do not monitor and adjust
engine air/fuel mixtures) are available, but only effective in situations where very frequent engine
checks and adjustments are the norm. Advanced aftermarket three-way catalyst systems include
all appropriate closed loop hardware (i.e., the exhaust oxygen sensor, electronic control module,
and throttle actuator) and detailed installation instructions.
Particulate Traps: The development of traps (or filters) designed to capture and burn the solid
particulate commonly emitted by diesel engines has been advancing since the late-1980's, when
it appeared as if such devices might be required for on-road heavy duty vehicles to meet stringent
particulate standards. Although trap technology has never been required to meet PM standards in
the on-road sector (even after the imposition of two rounds of more stringent standards beyond
those originally thought to require traps for compliance - providing testament to the ingenuity of
diesel engine manufacturers), major technology advancements have continued to occur and
effective retrofit traps are available in the aftermarket. Early trap designs required an active
GSE Information Series 5 Page 3
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element to combust collected particulate and regenerate trap capacity, but current designs
function by incorporating a catalyst that effectively lowers particulate combustion temperatures
into the filter material, thereby promoting filter regeneration during high load operating periods.
As long as equipment duty cycles include periodic high load events, current generation
particulate traps can effectively reduce diesel PM emissions without need for an active filter
regeneration technology.
The issues surrounding the use of diesel PM traps on GSE are very similar to those associated
with the installation and use of catalytic converters as described above. Space limitations are
probably the most critical aspect of effective trap design because trap dimensions tend to be
substantially larger than those of gaseous catalysts, but operating cycle considerations can be as
important for some potential applications. The backpressure associated with particulate trapping
increases steadily as more particulate is collected. If equipment operating cycles do not include
sufficient periods of high load activity (promoting regeneration), this backpressure increase can
influence equipment performance. Ideal GSE applications are those with relatively high load
factors such that trap regeneration occurs routinely and backpressure is maintained at a low level.
Particulate collection and combustion efficiencies of over 90 percent are attainable in properly
designed traps applications.
Emission Impacts: No operational data is available from GSE catalyst or trap installations to
assess the actual in-use emissions performance of these devices in the aircraft support
environment. Available data is limited to catalyst and trap manufacturer test data on similar
equipment such as industrial forklifts, and although there is no reason to expect that this data is
flawed, it undoubtedly does not represent data collected under average in-use operating
conditions. Moreover, these test data reflect conversion efficiencies immediately after converter
or trap installation and do not represent measurements that might be expected after catalyst or
trap aging has occurred. Nevertheless, there is sufficient evidence from the on-road sector to
indicate that converters can maintain very high efficiencies given adherence to proper engine
maintenance routines and vehicle operating procedures. If such procedures are followed, it is not
unreasonable to expect emission reduction impacts similar to those presented in Table 1.
Oxidation catalyst HC reduction potential declines for both LPG and CNG engines due to the
increasing concentrations of short chain hydrocarbons in the exhaust of such engines. Current
catalyst technology is most effective on long chain hydrocarbons and a substantial fraction of
compounds such as methane and ethane can pass through a catalyst without undergoing further
oxidation. The substantial increase in CO2 emissions results from an assumed backpressure
increase as well as the oxidation of HC and CO, both of which are observed in high
concentrations in uncontrolled GSE engines. However, increased backpressure accounts for only
about two percentage points of the estimated increase, with CO conversion accounting for nearly
all of the remainder.
Until such time as catalyst and trap performance has been consistently demonstrated in GSE
applications and sufficient test data on in-use engines is available to confirm generalized
emission reduction impacts, exhaust aftertreatment device installation and emission credits
resulting therefrom should be treated on a case-by-case basis. Individuals applying for such
credits should
GSE Information Series 5 Page 4
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Oxidation Catalyst Installation
GSE Fuel
Gasoline
Diesel
LPG
CNG
HC
90
50
70
50
CO
90
90
90
90
NOX
0
0
0
0
PM
10
30
10
10
CO2
up 60
up 3
up 45
up 45
Three-Way Catalyst Installation
GSE Fuel
Gasoline
LPG
CNG
HC
90
70
50
CO
90
90
90
NOX
80
80
80
PM
10
10
10
CO2
up 60
up 45
up 45
Particulate Trap Installation
GSE Fuel
Diesel
HC
20
CO
0
NOX
0
PM
90
CO2
ur>2
Unsigned and unqualified values signify emission reductions (in percent). Values preceded by the qualifier
"up" signify emission increases (in percent). CO2 emission increases result from increased exhaust system
backpressure and the oxidation of HC and CO, with CO oxidation accounting for the bulk of the estimated
increase.
Table 1. Potential Emission Reduction due to Aftertreatment Device Installation (percent)
be required to perform standardized emissions testing on a representative sample of target GSE
engines, both immediately before and after aftertreatment device installation as well as
periodically thereafter. Ideally, additional concurrent emissions testing would be performed on a
sample of otherwise identical control equipment which were not targeted for aftertreatment
device installation. To defray the costs of such database development testing and encourage
early aftertreatment device trials, a limited number of credits based on emission reduction
expectations might be offered to airlines undertaking the necessary demonstration efforts to
ensure that their pioneering work is recognized. In the interim, more detailed estimates of
exhaust aftertreatment-driven emission reductions are speculative at best.
Aftertreatment Device Costs: The current aftertreatment device market for off-road engines
such as those used in GSE is based on tailored device design and construction. Each potential
application is subjected to equipment-specific design review and evaluation to determine
potential device sizing restrictions and operating constraints. Only after such review is catalyst
or trap fabrication undertaken. As a result, costs for initial equipment installations can be quite
high. Even after initial design and construction, costs remain high relative to on-road aftermarket
GSE Information Series 5
Page 5
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catalysts for two primary reasons. First, production volumes are limited due to the unique nature
of many off-road applications and limited catalyst demand (current demand results primarily
from Occupational Safety and Health Administration indoor air quality standards). Second,
catalyst loading (i.e., the amount of catalytic material present in the aftertreatment device) is
considerably higher than the typical loading for on-road catalysts. Limited catalyst size demands
increased catalyst loading for high conversion efficiency. For these reasons, off-road catalysts of
the type required in the GSE sector can cost on the order of $1,000 or more per unit (after initial
design and fabrication costs).
Cost Effectiveness: Given the current state of the off-road aftertreatment device market, it is not
possible to provide emission reduction cost effectiveness estimates. Such estimates will vary in
accordance with the pre-installation emission rates of the target equipment, the conversion
efficiency of the aftertreatment device, and the pollutants examined. Detailed cost effectiveness
calculations should be performed in conjunction with any emissions testing program
implemented to evaluate aftertreatment device potential.
References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995
4. Emission Control Products: Diesel Exhaust Purifiers, Catalytic Mufflers, Catalytic Diesel
Filters, www.nett.ca, NETT Technologies internet website.
5. Clean Cat: Diesel Engine Catalytic Converters, clean-cat.com, Applied Diesel Technology,
Inc. internet website.
6. Personal communication on off-road catalyst design constraints and cost with NETT
Technologies, Mississauga, Ontario, Canada, July 1998.
GSE Information Series 5 Page 6
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FIXED GATE SUPPORT
-------
FIXED GATE SUPPORT
Basic Control Strategy Summary: While the majority of conventionally powered GSE can be
either converted to or replaced by GSE powered by alternative fuels such as liquid petroleum gas
(LPG), compressed natural gas (CNG), or electricity, a significant fraction of GSE can be
eliminated entirely by incorporating fixed point-of-use support equipment into aircraft gate
design. Such design not only eliminates all energy demands associated with moving displaced
mobile GSE between aircraft gates and maintenance/storage facilitates, but also facilitates the use
of "hard-wired" electrical power connections thereby eliminating the need for a recharging
infrastructure and scheduling plan. Although as with electrically powered GSE, there is an
increase in offsite power generating station emissions due to the increased demand for electrical
power, fixed equipment is likely to consume less power than equivalent mobile GSE due the
elimination of the motive aspect of GSE operation. Even when the increased emissions from
power generating stations are considered, fixed electrically powered support equipment usually
emit* significantly less hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOX),
particulate matter (PM), and carbon dioxide (CO2) emissions than their mobile fossil fueled (i.e.,
gasoline, diesel, compressed natural gas (CNG), and liquefied petroleum gas (LPG))
counterparts. Important issues for consideration are essentially limited to the capital and
operating cost and reliability of fixed gate-based equipment.
Potential GSE Equipment Affected: Generally, the only technical limitations to the
replacement of mobile GSE with gate-based fixed support equipment are manifested in those
services which, by definition, require the manual movement of objects from one place to another.
Cargo and baggage loading operations and, in some cases, passenger and service personnel
transport are among the few operations which cannot be easily reduced or eliminated through the
use of fixed gate-based equipment. The use of fixed gate-based power and conditioned air
services has become quite common both in the U.S. and worldwide. Gate-based electrical
connections eliminate not only the emissions associated with ground power units (GPU), but the
majority of aircraft-based auxiliary power unit (APU) emissions** as well. Similarly, gate-based
conditioned air support eliminates the use of equivalent traditional GSE. Other GSE that can be
either eliminated or curtailed through the use of fixed gate-based equipment include: lavatory,
fuel, water, food, and air start service equipment. In the most advanced cases, even mobile
baggage tugs and belt loaders can be eliminated through the installation of a centralized conveyer
belt-driven baggage distribution and delivery system that moves baggage directly from check-in
counters to the gate. However, these systems are expensive and usually cannot be retrofitted to
* Technically, electrically powered GSE do not emit any pollutants. The term emit, as used here, ascribes to the
electric GSE, the offsite increase in power generating station emissions due to increased airport electrical power
demands to support electric GSE recharging. In essence, the electrically powered GSE are treated as if they
"emitted" the increased power generating station emissions associated with their use.
" During the period that aircraft main engines are shut down at the gate, aircraft still require power and often
conditioned air to ensure that control system operations as well as passenger and crew comfort and safety are
maintained.
GSE Information Series 6 Page 1
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existing terminal designs. Application of fixed baggage systems is really limited to new terminal
construction and is not usually a viable emission reduction option for existing airport operations.
Fixed Equipment Installation Issues: The installation of fixed airport service equipment at
new gates as well as retrofitting such equipment at existing gates is becoming more
commonplace. In the U.S., most such installations are limited to an electrical supply (which
either displaces a mobile GPU or curtails the use of an onboard aircraft APU) and possibly a
conditioned air supply for aircraft use while at the gate (which also curtails the use of an onboard
aircraft APU and displaces ground-based conditioned air GSE used in instances of
non-functional aircraft APU). However, fixed gate fuel, lavatory, food, water, and air start
services are also feasible.
Two general types of systems have been designed (and implemented) to provide fixed gate
aircraft power services. Central power systems are based on a large main electrical control center
within the airport facility that feeds individual aircraft gates through a distributed network.
Conversely, point-of-use systems incorporate essentially independent controllers at each gate,
each connected independently to the airport electrical power system. The point-of-use systems,
due to easier, less intrusive, and less costly installation, as well as a reduced demand for
preventive maintenance (in the centralized system, all gates are dependent on the functionality of
the central power unit) have become the dominant choice for fixed gate-based power. Similar
approaches have been employed for gate-based conditioned air services. Large centrally located
chillers and control units with complex piping distribution systems have been operated, but have
generally fallen into disfavor relative to independently powered and operated point-of-use
systems.
In most gate-based installations, both aircraft power and conditioned air services are offered.
However, in some cases only power services are available and, as a result, situations can arise
when aircraft APU must be operated regardless of gate power availability. If conditioned air is
demanded by weather conditions, the aircraft APU (or an on-ground, usually diesel fueled, GSE
equivalent) must be operated either in conjunction with or in place of the gate-based power
supply. Clearly, such a situation is not desirable and most airports opt to install both systems as a
package. Airports in colder climates sometimes provide both services at only a fraction of
available gates, based on the premise that conditioned air demands will be limited. However, it
is not clear whether aircraft gate routing is modified in accordance with conditioned air demands
or whether aircraft at non-equipped gates simply rely on APU usage during demanding weather
conditions.
The majority of point-of-use fixed power and air systems are installed on the underside of gate
passenger ramps and powered through electrical system cables designed to operate reliably in
conjunction with the telescoping movement of the ramp. Other systems have been installed as
"pop-up" units beneath surface of the gate apron. Either approach provides aircraft service
personnel easy access to both aircraft and service connections and allows for quick service
connection (and APU shutdown) upon aircraft arrival at the gate. APU use cannot be eliminated
completely as APU operation is required during pre-flight checks and main engine startup, but
use can be restricted to this period and APU usage for narrow body aircraft can be reduced from
40-45 minutes without fixed gate services to 5-7 minutes with fixed gate services. Wide body
GSE Information Series 6 Page 2
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aircraft APU usage reductions can be even more dramatic, with APU use declining from 60-90
minutes or more without fixed gate service to 5-7 minutes with gate service.
Fixed-gate fuel, water, and lavatory services are somewhat more complex in that each require the
availability of in-ground distribution systems or gate-based supply and storage tanks. Aircraft
refueling is already generally accomplished using an in-ground hydrant system in conjunction
with truck-mounted "hydrant-to-aircraft" equipment. This traditionally truck-mounted interface
equipment can be replaced with equivalent fixed gate equipment, with equipment storage,
reliability, and in-ground hydrant proximity being the only major technical concerns. Similar
concerns, along with the added issue of water supply connectivity, exist for gate-based potable
water service. Gate-based waste disposal concerns must be addressed in any installation of
lavatory service equipment at the gate as traditional mobile GSE will continue to be required for
any system based on simply installing gate-based transfer tanks.
Gate-based food and cabin supply service facilities can be relatively easily installed as add-on
storage rooms at existing gates. While these storage facilities will not eliminate mobile GSE
service entirely since supplies must be restocked and waste removed periodically, but gate
storage will allow for a substantial reduction in mobile GSE use as multiple aircraft can be
serviced through single re-supply and removal activities which can take place during periods of
low aircraft activity.
Emission Impacts: The emission impacts due to the installation and operation of fixed gate
services depends on three key factors: (1) the emissions performance of the equipment being
displaced or curtailed, (2) for curtailed equipment, the reduction in equipment usage, and (3) the
specific power generating characteristics of the region in which the airport is located.
Most GSE in operation today are unregulated from an emissions standpoint and, therefore, do not
incorporate emission reduction technology in their design. A definitive calculation of displaced
emissions due to equipment displacement or curtailment involves the measurement of the
average emission rate of the displaced (or curtailed) fossil fueled GSE and the application of the
activity data associated with the unit. A generalized expression of the necessary calculation of
displaced emissions takes the form:
emissions grams hours of use
:—: = -—-— — x hp x load factor x :—:
unit time brake hp-hr unit time
To calculate total displaced emissions, the emission rate per unit time (e.g., pounds per year)
should be aggregated over the total time such emissions would have accrued. For example, if a
displaced unit had an expected additional service period of four years after displacement, then
emissions throughout this four year period would be displaced. Determining the overall
longevity of emission reductions is an issue to be addressed since the emissions performance of
displaced units may have changed during normal mobile equipment replacement cycles which
are discontinued once fixed equipment is in place. In addition to emission reduction influences
due to technology evolution, any future emission standards imposed on GSE will reduce the
emission reduction benefits of fixed gate services by reducing the emission rate of displaced
mobile GSE. Under any emissions control scenario, the emissions reduction benefits of
GSE Information Series 6 Page 3
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switching from mobile GSE to fixed gate-based (electrically powered) services will depend on
the specific fossil fuel being displaced since each has its own emissions characteristics.
Without definitive knowledge of exactly which mobile GSE are being displaced or curtailed for a
given application, it is difficult to estimate the overall emission reduction potential of fixed gate
services. Moreover, experience has shown that even when fixed gate services such as aircraft
power and conditioned air are available, they are not always used. Whether such non-use is a
result of airline practice (a recent EPA study found some airlines employing APU in place of
fixed gate services about 50 percent of the time) or other factors is unclear, but the overall
emissions reduction due to the installation of fixed equipment is certainly affected. Table 1
shows the estimated hourly-specific emission rates* for the various types of GSE that can be
displaced or curtailed by the installation of fixed gate-based equipment. Operators can estimate
the impacts at their specific facilities by selecting those specific equipment affected and applying
the number of hours of curtailed use.
Not shown in Table 1 are the emission rates for aircraft APU which can also be displaced
through the installation of fixed gate services. In fact, some of the largest emission reductions
due to fixed gate services will accrue from curtailed APU usage. APU emission rates vary
considerably across aircraft, averaging about 93 grams of HC, 1,055 grams of CO, and 542 grams
of NOX per operating hour but reaching as high as 360 grams per operating hour HC, 1,978 grams
per operating hour CO, and 542 grams per operating hour NOX. As indicated above, APU
operating time can be reduced by 85-95 percent, or 35-40 minutes per narrow body gate service
and 55-85 minutes per wide body gate service. Once these parameters have been established for
a particular airport application, total APU emission reductions can be calculated as:
emissions grams operating minutes reduced aircraft service events
= x— E x
unit time operating minute aircraft service event unit time
Since fixed gate equipment uses electricity to power required pumps, compressors, etc.,
incremental power generation emissions must be subtracted from the emission reductions due to
GSE displacement to derive net emission reductions. Therefore, airports served by relatively low
emitting power generation facilities will produce larger emission reduction benefits than will
accrue in areas served by older, higher emitting generating facilities. In the absence of definitive
power consumption estimates for fixed gate-based equipment, the emissions associated with
electrically powered GSE can be used to estimate net emission reductions. While fixed electrical
equipment will likely consume less electricity per service event than mobile electric GSE due to
the elimination of motive power demands, there are likely to be offsetting consumption losses
during non-service periods. Therefore, assuming power generation emissions equivalent to those
* The tabulated emission rate data was developed using data from the off-road emissions model recently released by
the California Air Resources Board. Data used for this analysis included zero hour emission rates, emissions
deterioration rates, equipment horsepower, equipment load factor, and brake-specific fuel consumption. See the
information series selection entitled GSE Emission Rates and Activity for additional detail.
GSE Information Series 6 Page 4
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Gasoline (4-Stroke) Equipment
Type of GSE
Ground Power Units
Conditioned Air Units
Lavatory Carts
Lavatory Service Trucks
Fuel Service Trucks
Water Service Trucks
Food Service Trucks
Air Start Units
HC
533
462
80
154
154
142
171
555
CO
34,560
29,952
2,465
9,984
9,984
9,216
11,059
35,942
NOX
482
417
25
139
139
128
154
501
PM
3
3
2
1
1
1
1
4
C02
89,148
77,261
7,780
25,754
25,754
23,773
28,527
92,714
Gasoline (2-Stroke) Equipment
Type of GSE
Lavatory Carts
HC
1,254
CO
1,866
NOX
5
PM
39
CO2
11,238
LPG Equipment
Type of GSE
Ground Power Units
Conditioned Air Units
Lavatory Carts
Lavatory Service Trucks
Fuel Service Trucks
Water Service Trucks
Food Service Trucks
Air Start Units
HC
267
231
43
77
77
71
85
277
CO
21,600
18,720
1,505
6,240
6,240
5,760
6,912
22,464
NOX
361
313
13
104
104
96
116
376
PM
2
2
1
1
1
1
1
2
C02
74,747
64,781
6,523
21,594
21,594
19,933
23,919
77,737
Diesel Equipment
Type of GSE
Ground Power Units
Conditioned Air Units
Lavatory Carts
Lavatory Service Trucks
Fuel Service Trucks
Water Service Trucks
Food Service Trucks
Air Start Units
HC
109
231
9
33
45
30
34
553
CO
493
1,038
30
147
204
136
154
2,491
NOX
1,280
2,735
60
383
530
353
400
6,564
PM
73
159
6
22
30
20
23
382
CO2
68,941
136,153
5,619
20,603
28,527
19,018
21,554
326,766
Table 1. Emission Rates for Potentially Displaced GSE (grams/operating hour)
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associated with mobile electric GSE (see the information series selection entitled Electric GSE
for more information) should provide a reasonably accurate estimate of incremental utility
emissions due to the installation and operation of fixed equipment. These estimates will, of
course, need to be replaced with estimates derived from actual fixed gate-based equipment power
consumption data once fixed unit models and operating data have been established.
Regardless of the incremental power generation emissions, HC and CO emission reductions will
be dramatic (approaching 100 percent). However, NOX, PM, and CO2 reductions can vary
considerably. Table 2 presents the sensitivity of electrical equipment emission reductions to the
range of power generating facilities in operation in the U.S. As indicated, the dependence of
emission reductions on power generation practices can be dramatic. For example, NOX
reductions due to the displacement of gasoline GSE can range from 40 to 99+ percent and the
potential range of CO2 reductions is nearly as wide at 40 to 80 percent. PM emissions can, as
indicated, increase substantially under the highest emission power generation conditions, but can
also decline by as much as 90 percent under other power generation conditions. Both the highest
and lowest power generation scenarios are equally unlikely to be applicable to any given GSE
displacement scenario. The highest emission scenario represents an uncontrolled coal-fired
application while the lowest emission scenario represents a "maximum controls" (regardless of
cost effectiveness) natural gas application. There may be a few specific instances (e.g.,
California airports) where actual power generation emissions approach those of the low
emissions scenario, but generally emission reductions are more likely to approximate those of the
tabulated "average" scenario which is based on the average of measured emission rates for six
geographically diverse U.S. utilities. Therefore, installation of fixed gate-based equipment
should generate substantial emission reductions at most U.S. airports.
Costs: Several previous studies of actual fixed gate-based power and conditioned air
installations have demonstrated the economic cost effectiveness of such systems. In general,
these systems, which carry installation costs ranging from about $50,000 for narrow body aircraft
gate service to about $130,000 for wide body aircraft gate service, have been shown to
completely pay for themselves in less than one year through savings in APU fuel and
maintenance costs. Net savings are estimated to be about $200 per day for narrow body aircraft
gate service and $400 per day for wide body aircraft service. Expanding fixed gate-based
services to include water, lavatory, fuel, and catering facilities has been estimated to add another
$20,000-$50,000 to installation costs (per gate based on a complete 12 gate terminal installation).
Based on the operating and maintenance cost savings of GSE displacement alone, these services
are not as economically cost effective as gate-based power and air systems. However, additional
cost savings may accrue from reduced labor requirements for aircraft service, faster aircraft
cycling time allowing more aircraft to be serviced per gate, reduced gate congestion, and less
frequent GSE accidents.
Cost Effectiveness: It is difficult to provide precise cost effectiveness estimates for fixed
gate-based equipment because the impact of such equipment varies in accordance with the
pollutants examined, the scope of fixed services offered, the fueling characteristics of the
equipment being displaced, and the emissions performance of local utilities. However, as
discussed above, gate-based power and conditioned air systems have been demonstrated to be
costs effective on a purely economic basis and, therefore, all derived emission reductions due to
GSE Information Series 6 Page 6
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the installation of these services accrue for free. The installation of additional services may be
cost effective, but a definitive determination will require airport-specific analysis.
Percent Reduction1 from Gasoline (4-Stroke) GSE
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.9
98.2
99.4
CO
100.0
99.9
100.0
NOX
98.1
38.5
90.2
PM
88.9
up 3328.4
42.4
CO2
77.9
41.2
56.2
Percent Reduction1 from LPG GSE
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.8
96.3
98.9
CO
100.0
99.9
99.9
NOX
97.4
18.0
86.9
PM
88.9
up 3328.4
42.4
CO2
73.6
29.9
47.8
Percent Reduction1 from Diesel GSE
Utility Scenario2
Best Case
Worst Case
Average Case
HC
99.5
92.4
97.7
CO
99.3
96.4
97.9
NOX
99.4
81.8
97.1
PM
99.6
up 33. 8
97.8
CO2
75.2
34.0
50.8
1 Unsigned and unqualified values signify emission reductions (in percent). Values
preceded by the qualifier "up" signify emission increases (in percent)
2 Utility (i.e., power generating station) emissions will vary in accordance with local
electricity generation practices. Major factors include boiler design, boiler fuel, and
emission controls in place. The best case scenario represents potential emission
reductions if GSE electrical demand is satisfied by a generating station firing natural gas
and employing maximum controls. Conversely, the worst case scenario represents
potential emission reductions if GSE electrical demand is satisfied by a generating station
firing coal under essentially uncontrolled (from an emissions standpoint) conditions. The
average case represents a more typical level of emission reductions and is based on actual
emission rates for a geographically diverse sample of utilities.
Table 2. Estimated Emission Reductions Due to the Use of Electric GSE
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References:
1. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
2. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
3. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995.
4. "All the Power You Need," product literature from Hobart Ground Power, 1996.
5. "JETLINK," product literature from FMC/Jetway Systems.
6. "The Vehicle Free Ramp," product literature from FMT.
7. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary
Point and Area Sources, Chapter 1 (External Combustion Sources), as downloaded on July
29, 1998 from the U.S. EPA internet website www.epa.gov/ttn/chief/ap42.html.
GSE Information Series 6 Page 8
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GSE CONTROL STRATEGY SUMMARY
-------
GSE CONTROL STRATEGY SUMMARY
Background: Aircraft ground support equipment (GSE) represent one of three groups of
mobile emission sources at airports. Together with aircraft and ground access vehicles, GSE
contribute a small but significant share of the hydrocarbon (HC), carbon monoxide (CO), oxides
of nitrogen (NOX), and particulate matter (PM) emitted in metropolitan areas. Today, total
emissions from these three source categories comprise on the order of 2-3 percent of total
manmade emissions in a typical metropolitan area, but this share is expected to increase as air
travel continues to grow while emissions from other, non-airport sources are subject to
increasingly stringent controls. An evaluation of GSE and associated service demands indicates
that there are several control strategies that offer the potential to reduce emissions over both the
long and short terms. Such strategies include both demonstrated and innovative technologies
and all have associated issues which must be considered prior to implementation, but a
generalized classification includes:
• The development of new engine emission standards for all currently unregulated
equipment;
• The replacement or conversion of gasoline or diesel powered GSE to liquid petroleum
gas (LPG) or compressed natural gas (CNG) fueling;
• The replacement or conversion of gasoline, diesel, LPG, or CNG powered GSE to
electric power;
• The replacement of mobile GSE with electrically powered fixed gate-based
equipment;
• The retrofit of existing GSE with catalytic converters or particulate traps; and
• The preferential replacement of existing two-stroke gasoline engines.
As expected, both the feasibility and cost effectiveness of emission reductions vary considerably
across the potential control strategies. The following sections provide an overview of the major
issues associated with each strategy and, where possible, provide an estimate of associated
emissions reduction and cost effectiveness. Because all strategies will involve some application
and site specific dependencies, each ultimately needs to be evaluated in the context of the
specific conditions in place at the target airport(s). Moreover, to the extent that airlines or
airports are encouraged to undertake strategies on a voluntary basis in return for marketable
emission credits or alternative incentive rewards, the cost effectiveness of individual controls can
be greatly dependent on the (as yet undefined) value of the credit or incentive reward.
Nevertheless, a general ranking of the likelihood of implementation is possible, and the
discussions below are presented in general order of increasing to decreasing likelihood.
GSE Control Strategy Summary Page 1
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New Engine Emission Standards: The development of new engine emission standards is not a
control strategy that can feasibly be implemented on an airport-specific basis. Its inclusion here
is simply intended to place the remaining control strategies, which can be implemented locally,
in a proper context. Only the U.S. Environmental Protection Agency (EPA) and the California
Air Resources Board (CARB) have the authority to set new engine emission standards and both
have established standards, or are currently in the process of doing so, for several categories of
off-road engines used in GSE. Spark-ignition engines rated at 25 horsepower or less and
produced for California sale beginning in 1995 or national sale beginning in 1997 are subject to
CARB and EPA standards respectively. Although such engines are not found in a large fraction
of GSE, they do exist in small numbers in such applications as lavatory cart pumps. Of greater
impact on GSE are standards for off-road compression-ignition (i.e., diesel) engines. First round
standards adopted by EPA and CARB took effect in 1996 and 1995 respectively and a second set
of more stringent standards is slated to be phased in beginning in 1999. Ultimately, these
standards will affect all diesel GSE engines (currently about one-third of the total GSE engine
population), reducing emissions of HC, CO, and especially NOX and PM by substantial margins.
Currently, no emission standards have been adopted for off-road spark-ignition (e.g., gasoline)
engines rated at greater than 25 horsepower. About 60 percent of all GSE engines fall into this
category. Many such engines are derived from 1980's-era automobile engines and, in
recognition, CARB is currently in the early development stages of regulatory standards for this
engine category based on a level-of-control equivalent to that associated with the installation of
closed-loop three-way catalyst aftertreatment systems. Initial plans cite a proposed phase-in of
such standards beginning in 2001. The EPA has not yet made any formal announcements of a
planning process for emission standards applicable to this engine category (CARB standards will
only affect engines built for sale in California), but it is likely that such a process will eventually
be undertaken.
Most, and probably all, new GSE engines will ultimately be covered by stringent emission
standards. Stringent standards affecting diesel GSE engines have been formally proposed and
standards affecting larger spark-ignition (i.e., gasoline, LPG, CNG, etc.) GSE engines are
probably not far off. However, since even the already-adopted off-road engine standards have
only recently taken effect, almost all in-use GSE engines not certified for on-road use (i.e.,
between 75 and 90 percent of all GSE) are uncontrolled from an emissions standpoint.
Considering the rate of GSE engine turnover, it is likely that uncontrolled engines will continue
to dominate the GSE fleet at least through 2010. Clearly, new engine emission standards are a
longer term approach to reducing GSE emissions. To achieve short term emission reductions,
control strategies affecting the GSE engines already in use must be explored. Such short term
approaches are the focus of this summary document and the companion GSE Information Series
documents.
In considering the emission reduction and cost effectiveness estimates presented in this and
companion documents, it is critical that the reader recognize that baseline GSE emission rates are
assumed to be uncontrolled. Relative to engines certified to emission standards in effect either
now or in the future, the emissions reduction potential and cost effectiveness estimates presented
for the short term control strategies will be greatly overstated. These estimates are valid only in
the context of targeting reductions from GSE engines not certified to meet the evolving new
GSE Control Strategy Summary Page 2
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engine emission standards. Over the short term, this restriction poses few if any concerns.
However, over time, controlled engines will enter the GSE fleet and gradually (over the next 10
to 15 years) reduce or even negate the effectiveness estimates presented below. As this occurs,
revised estimates of control strategy effectiveness relative to the controlled engine emission
levels will be required.
Replacement or Conversion to LPG/CNG Power: Both LPG and CNG offer the opportunity
to reduce emissions from conventionally powered GSE. While both gasoline and diesel GSE are
candidates for replacement equipment powered by LPG or CNG, the conversion of existing
equipment is more suitable to gasoline powered GSE. For the most commonly available LPG
and CNG technologies, an active ignition system, as found on gasoline engines, is required to
initiate combustion. As a result, the conversion of compression-ignition diesel equipment is
more complicated (and expensive) than the similar conversion of gasoline equipment.
Technologies such as pilot injection/fumigation systems have demonstrated the ability to
combust gaseous fuels in diesel engines without active ignition systems, but these technologies
are generally recognized as developmental and do not reflect typical diesel conversion
technology, which includes the installation of an active ignition system.
Both CNG and LPG are currently available as factory options for most GSE. These options
generally reflect high quality design and installation and carry full manufacturers warranties.
However, conversions of existing engines can vary considerably in terms of quality and
performance. In principle, the conversion to LPG or CNG power is fairly simple, requiring in
the simplest cases only the installation of a new fuel tank and new fuel delivery and metering
systems. But achieving good performance and low emissions simultaneously can be quite
challenging and, as a result, a large percentage of conversions never achieve the emissions
reduction potential of either LPG or CNG. In some cases, emissions performance actually
declines relative to pre-conversion emissions. To aid in overcoming such problems, advanced
low emissions conversion kits include a closed-loop combustion control system capable of
continuously adjusting the combustion charge air-fuel ratio in accordance with exhaust gas
characteristics. Even so, the calibration of equipment conversions is as much art as science and
should only be performed by qualified, experienced personnel to ensure low emissions while
maintaining good engine performance. Such quality conversions can achieve emissions
performance equivalent to factory installed replacement equipment.
Under a scenario in which emission reduction credit (either marketable or State Implementation
Plan credit) is granted for GSE conversion, it will be necessary to impose certain restrictions to
ensure claimed emission reductions are actually achieved. Both the EPA and CARB have
established certification procedures for on-road engine conversion kits, but the application of
these procedures to off-road GSE engines will be difficult until such time as emission standards
for such engines are in place (generally the EPA and CARB procedures demonstrate compliance
with an emission standard not quantify a specific emission level). Nevertheless, a variation of
the on-road process designed to establish a "maximum warranted emission rate" could be adapted
to the certification of off-road engine conversion kits. Warranty requirements for kit
manufacturers and installation requirements for kit installers, as well as non-compliance
penalties, would add necessary incentives to ensure that claimed reductions are achieved.
Periodic emission testing requirements might also be imposed throughout the life of any
GSE Control Strategy Summary Page 3
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emission reduction credit. In the absence of a formal certification program, certain conversion
kit requirements might be established to provide a minimally acceptable guarantee of low
emissions. For example, kits which do not include closed-loop combustion control systems
might be excluded from any program assigning emission reduction credits. For purposes of this
document, it is assumed that an appropriate low emissions compliance program is in place and
that converted equipment emissions performance is similar to that of factory installed
replacement equipment. If such performance levels are not achieved in practice, the emission
reduction impacts presented below will be overstated.
Table 1 presents an estimate of the emission impacts associated with the replacement or
conversion of GSE to LPG or CNG power. Relative to gasoline GSE, emissions of HC, CO,
NOX, and PM as well as carbon dioxide (CO2) are all expected to decline. Relative to diesel
GSE, significant reductions in both NOX and PM are expected, while minor CO2 changes and
significant increases in both HC and CO occur. These latter increases are a function of the
inherently low HC and CO emissions associated with diesel engines. While the overall mass
emissions increase of both pollutants is modest relative to the quantity of HC and CO emitted by
gasoline GSE (as indicated, both LPG and CNG are expected to emit lower levels of HC and CO
than gasoline GSE), the percentage change as measured from a very small baseline is substantial.
For example, with new (uncontrolled) engine CO emission rates of about 5 grams per brake
horsepower-hour (g/bhp-hr) for diesel GSE, 150 g/bhp-hr for LPG GSE, and 250 g/bhp-hr for
gasoline GSE, it is easy to see that while the 145 g/bhp-hr CO increase between LPG and diesel
engines represents a 2,900 percent increase, the absolute emissions increase still places the LPG
CO emission rate at only about 60 percent of that of gasoline GSE. In-use deterioration further
expands the difference between diesel and LPG engines, but does not significantly alter the
LPG/gasoline relationship.
Therefore, relative to gasoline, a switch to LPG or CNG power will result in net emission
reductions regardless of the particular pollutant of interest. Relative to diesel, LPG and CNG are
effective emission reduction strategies for NOX and PM, but those reductions come at the cost of
increases in HC and CO.
HC
CO
NOX
PM
CO2
Emissions Relative to Gasoline GSE
LPG
-50% to -65%
CNG
-65% to -75%
-40% to -50%
-20% to -25%
-20%
-15%
-20%
Emissions Relative to Diesel GSE
LPG
+95% to +140%
CNG
+30% to +60%
+4000% to +5000%
-75% to -80%
-95%
-5% to +15%
-10% to +10%
Table 1. Emission Impacts of LPG and CNG GSE
GSE Control Strategy Summary
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The replacement cost premium for LPG GSE relative to gasoline GSE is estimated to be similar
to the cost of conversion at $2,000-$3,000 per unit. For CNG, first cost premiums are higher due
to the need for high pressure fuel storage, at $4,000-$4,500 per unit. Because off-road equipment
users are provided a one-for-one tax credit against gasoline and diesel fuel taxes, the fuel cost
savings associated with LPG and CNG usage in the on-road sector are substantially diminished.
In fact, while LPG is estimated to provide a net savings of about $0.10 per gasoline equivalent
gallons of fuel used, the cost of CNG is not expected to be significantly different than the cost of
an equivalent quantity of gasoline. Over the long term, maintenance costs for both LPG and
CNG are expected to be 20-25 percent lower than conventional fuel maintenance costs, but this
improvement has yet to be observed in-use due to a high rate of occurrence of LPG/CNG
equipment problems. This trend should disappear as experience is gained and equipment
becomes more reliable but observational support is lacking at this time.
Table 2 presents an estimate of life cycle costs for baggage tractors (which constitute up to 25
percent of all GSE) powered by the various fuel options. While absolute costs will vary
somewhat for other types of GSE, the relative relationships across fuel types will be similar.
Regardless of whether maintenance costs are reduced or not, LPG equipment is cost competitive
with gasoline GSE. Conversely, CNG is only cost competitive under a reduced maintenance,
high equipment usage scenario. In all cases, diesel GSE are estimated to be the least cost
alternative when no definitive value is assigned for emissions performance.
Although emissions valuation can alter life cycle cost relations, it is difficult to place a generic
value on emissions reduction. Emission reductions of high value in one area can be of marginal
or negative value in another. Therefore, a specific emissions valuation strategy must be
implemented before a definitive assessment of the impact on life cycle costs can be made.
Nevertheless, some
Gasoline
Diesel
LPG
CNG
High Equipment Usage Scenario (Hub-Type Airport)
Reduced Maintenance1
Same Maintenance
$126K
$126K
$98K
$98K
$107K
$118K
$126K
$136K
Average Equipment Usage Scenario (Non-Hub Airport)
Reduced Maintenance
Same Maintenance
$53K
$53K
$47K
$47K
$49K
$52K
$56K
$59K
1 The "reduced maintenance" scenario assumes LPG and CNG maintenance costs are 20
percent lower than gasoline and diesel maintenance costs. The "same maintenance" scenario
assumes all four GSE types possess similar maintenance costs.
Table 2. Life Cycle Costs for Baggage Tractors
GSE Control Strategy Summary
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general observations are possible. First, under any scenario in which a positive value is assigned
to either HC or CO reductions, the life cycle cost advantage of diesel GSE will be enhanced due
to the inherently low HC and CO emission rates of diesel engines. If NOX emission reductions
alone are valued, a value of $1,000-$2,000 per ton will render LPG life cycle costs competitive
with diesel GSE costs. A value of $3,000-$4,000 per ton of NOX will render CNG GSE cost
competitive with diesel. To achieve diesel cost competitiveness on the basis of PM reductions
alone requires a substantially higher per ton valuation, on the order of $10,000-$20,000 per ton
for LPG and $30,000-$40,000 per ton for CNG. Of course, the PM reductions are derived for
free if NOX is also valued at the rates previously indicated.
In summary, it is apparent that replacement or conversion of both gasoline and diesel GSE to
LPG or CNG can provide significant emission reductions relative to current uncontrolled
baseline emission rates and be cost competitive under reasonable emissions valuation scenarios.
In fact, LPG GSE is cost competitive with gasoline GSE regardless of emissions reduction value.
However, in cases where emissions reduction is not assigned a marketable value (as is the case
under current market conditions), diesel GSE is overwhelmingly the least cost option relative to
gasoline, LPG, and CNG. This is consistent with recent movement in the GSE sector toward a
greater utilization of diesel equipment. It is, therefore, likely that some definitive incentive will
need to be instituted before large scale shifts in the GSE fleet toward either LPG or CNG will be
observed.
Replacement or Conversion to Electric Power: Virtually all GSE, regardless of current
fueling option, are candidates for conversion to electric power or replacement with electrically
powered equipment. GSE manufacturers currently offer an electric power option on a wide
range of equipment types, while several firms (most centered in California) offer aftermarket
conversions to electric power. The issues of range and performance which continue to dampen
the acceptability of electric vehicles in the on-road sector are largely eliminated or controlled in
the operating environment of GSE. Clearly, such operations are restricted to a small geographic
area so that proximity to battery recharging or replacement centers (once in place at the airport)
is not an issue. Additionally, most GSE duty cycles consist of short periods of high load
operation followed by extended periods of idle or engine-off. Since electric GSE consume no
power under either mode, both the total time between battery discharge cycles and the amount of
time available for opportunity charging can be significant. On-road performance concerns such
as top speed and grade handling ability are usually not of concern in airport settings where grade
is limited and speed restrictions are present regardless of fuel.
The emission impacts associated with the use of electric GSE can vary with local power
generating characteristics. While electric GSE emit no pollutants in the conventional sense, they
do place an additional demand on local power generating stations and the emissions associated
with this additional demand are a direct result of electric GSE use. Table 3 presents estimates of
the emission impacts of electric GSE. To provide an indication of the dependence of emission
reductions on local power generating characteristics, Table 3 presents minimum, maximum, and
typical emission reduction estimates. The minimum reductions reflect impacts assuming
uncontrolled coal-fired power generation, while the maximum reductions reflect impacts
assuming a "maximum controls" (regardless of cost) natural gas-fired power generation scenario.
Typical
GSE Control Strategy Summary Page 6
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HC
CO
NOX
PM
CO2
Relative to Diesel
-90% to -99% (-98%)
Relative to Gasoline
-98% to -99.9% (-99%)
-96% to -99% (-98%) -99.9% to -99.9% (-99.9%)
-80% to -99% (-97%) -40% to -98% (-90%)
+30% to -99% (-98%) +3500% to -90% (-40%)
-25% to -70% (-45%) -40% to -80% (-55%)
Relative to LPG/CNG
-96% to -99.9% (-99%)
-99.9% to -99.9% (-99.9%)
-20% to -97% (-85%)
+3 500% to -90% (-40%)
-30% to -75% (-50%)
Table 3. Emission Impacts of Electric GSE
emission impacts are based on average emission rates observed across a sample of
geographically diverse power generating stations and should reflect a good estimate of the
emission impacts expected in most circumstances. Neither the minimum or maximum reductions
are reflective of likely impacts in any, except the most atypical, area. Therefore, while actual
impacts will require a local analysis for confirmation, the tabulated typical impacts should
provide a good indication of the emission reduction potential of electric GSE.
Clearly, the emission reduction potential associated with the use of electric GSE is dramatic
compared with all four internal combustion engine (ICE) fuels. Under any scenario, HC and CO
emissions are nearly eliminated. The same is typically true for NOX and PM relative to diesel
GSE. The variation in potential NOX reductions relative to gasoline, LPG, and CNG GSE is a bit
wider, but typical reductions approach 90 percent for all three fuels. Because PM emissions
from the three fuels are substantially lower than those of diesel GSE, electric vehicle PM
reductions are typically smaller than HC, CO, and NOX, but still significant. In all but the most
extreme cases, replacement or conversion of ICE-powered equipment can be expected to
generate large emission reductions for all pollutants, including CO2.
Electric GSE carry a significant purchase or conversion price premium of $10,000-$15,000
relative to gasoline GSE or $8,000-$ 10,000 relative to diesel GSE. This initial price premium is
further compounded by periodic battery replacement requirements (every five years or so) that
are twice as expensive as the alternative engine replacement or rebuild requirements associated
with ICE-powered GSE. However, electric vehicle fuel savings are significant, not only because
of lower unit fuel costs, but because no power is consumed during equipment idle periods. Fuel
savings relative to diesel GSE can reach $2,500 per year under a high equipment usage scenario
and approach $1,000 per year for average usage. Fuel savings relative to gasoline and CNG can
be twice that relative to diesel, with LPG savings between the two extremes. Electric GSE, are
expected to have reduced maintenance costs relative to ICE-powered GSE, but like CNG and
LPG equipment, first generation electric GSE were prone to high maintenance and were also
found to be inefficient and under-powered. Users of second generation electrics have reported
significant improvements in all three areas and expectations of long term maintenance cost
reductions on the order of 70 percent now appear viable. Nevertheless, electric GSE batteries
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require frequent and careful maintenance checks to ensure long battery life and keep replacement
costs to a minimum.
Life cycle cost estimates for the various ICE-powered GSE were previously presented in Table 2.
Table 4 reviews these estimates and adds similarly calculated life cycle cost estimates for electric
GSE. Once again, while the tabulated costs are specifically calculated for baggage tractors, the
relative relationships across fuels will be similar for other GSE types. Strikingly, electric GSE
possess the lowest life cycle costs under all but the same maintenance/average usage scenario
and even then electric GSE costs are competitive with the other fueling options. For a highly
trafficked airport, electric GSE are clearly the lowest cost option. This is also true for lesser
trafficked airports if electric GSE durability expectations are achieved in-use. Moreover, these
relations are based on calculations which do not include any valuation for emission reductions.
In most cases, electric GSE are cost effective on a purely economic basis alone.
Based on these relationships, a greater utilization of electric GSE is a reasonable future
expectation and any such increase will provide significant emission reductions. Nevertheless,
there are institutional barriers which must be overcome before large scale penetration can be
expected. The poor reputation inspired by inefficient, under-powered, and high maintenance first
generation electric GSE must be overcome though a demonstrated service reliability by the new
second generation equipment. If the new electric GSE can demonstrate an in-use reliability
equivalent to that of conventional GSE, greater penetrations will be observed. Additionally,
recharging infrastructure enhancements will be required at airports to support significant electric
Gasoline
Diesel
LPG
CNG
Electric
High Equipment Usage Scenario (Hub-Type Airport)
Reduced Maintenance1
Same Maintenance
$126K
$126K
$98K
$98K
$107K
$118K
$126K
$136K
$56K
$88K
Average Equipment Usage Scenario (Non-Hub Airport)
Reduced Maintenance
Same Maintenance
$53K
$53K
$47K
$47K
$49K
$52K
$56K
$59K
$42K
$52K
1 The "reduced maintenance" scenario assumes LPG and CNG maintenance costs are 20
percent lower and electric GSE maintenance costs are 70 percent lower than gasoline and
diesel maintenance costs. The "same maintenance" scenario assumes all five GSE types
possess similar maintenance costs. For electric GSE, both maintenance scenarios assume
frequent, effective battery maintenance checks to ensure long battery life.
Table 4. Life Cycle Costs for Electric Baggage Tractors
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GSE penetrations. Should these barriers be overcome, it is not unreasonable to expect significant
movement toward an electric GSE fleet. Providing additional incentive by placing a definitive
value on associated emission reductions may be sufficient to accelerate this movement.
Replacement of GSE with Electrically Powered Fixed Gate-Based Equipment: A
substantial number of the services currently provided by mobile GSE can be performed by
electrically powered equipment installed in a fixed position at each aircraft gate. Initial
movements in this direction have already taken place at many U.S. airports where fixed
gate-based equipment has been installed to handle the electrical power and conditioned air
requirements of aircraft. This equipment displaces not only GSE ground power and conditioned
air units, but high emission rate aircraft auxiliary power units (APU) as well. Additional GSE
types which are also candidates for replacement include: fuel, water, catering, and compressed air
service as well as somewhat more difficult to replace baggage and aircraft pushback tractors.
Many airports have already recognized the cost effective nature of fixed gate-based power and
conditioned air systems. Gate-based units capable of providing the 400 Hz electrical service
demanded by aircraft are being installed at an increasing number of airports. At gates without
such systems, the power necessary to operate critical aircraft systems is usually provided by an
on-board APU (a small jet engine) or, when the APU is out-of-service, a mobile GSE ground
power unit. Due to the length of time a typical aircraft spends at the gate (relative to the time
spent approaching, landing, taxiing, and taking off from an airport), APU emissions can be
responsible for 10-30 percent of the HC, 40-80 percent of the CO, and 30-60 percent of the NOX
emitted by aircraft during a typical landing and takeoff (LTO) cycle (which, from an airport
emissions standpoint, begins and ends when the aircraft enters and leaves the tropospheric
mixing zone). Although APU emissions cannot be completely eliminated due to the need for
APU operation during engine startup, overall APU emissions can be reduced by up to 90 percent.
As a result, the emission reductions derived from the installation of fixed gate-based electrical
power units far exceed those derived from the replacement of ICE-powered GSE ground power
units with mobile electric GSE.
In most cases, fixed gate-based conditioned air service is installed in conjunction with gate-based
electrical power service. These two services go hand-in-hand, because in the absence of ground
service both will be supplied using power generated by the aircraft APU. Therefore, if
climatological conditions demand conditioned air service during aircraft gate periods, the aircraft
APU (or alternative GSE conditioned air unit) will be operated even if gate-based electrical
power is available. In such situations, the emissions reduction effectiveness of gate-based
electrical power is completed negated.
As might be expected, gate-based electrical power and conditioned air service have substantial
initial costs. Such costs can range from $50,000-$130,000 per gate (for the most popular
point-of-service systems*) depending on the type of aircraft serviced (i.e., narrow body versus
Generally, two types of gate-based services are available. Point-of-use systems rely on dedicated equipment
installed at each aircraft gate. Centralized systems use large centrally located equipment, supported by a network
distribution system to transfer power and conditioned air to individual airport gates. The point-of-service systems
GSE Control Strategy Summary Page 9
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wide body), but because of the very high operating costs of aircraft APU, associated cost savings
can reach $30-$50 per hour. At highly trafficked airports, such operating cost savings result in
payback periods of less than one year. While the payback period might be several years for less
highly trafficked airports, fixed gate-based power and conditioned air systems are cost effective
from a purely economic standpoint and as recognition of this cost effectiveness continues to
increase, more and more airports are adopting fixed gate-based power and conditioned air
service. Placing a marketable value on the associated emission reductions can only serve to
accelerate a process that is already underway.
"Vehicle free" gate systems represent a longer term goal. Stationary fuel, water, and lavatory
hookups can be installed at airport gates, but each require a fairly complex distribution system to
completely eliminate the GSE currently providing these services. The installation of gate-based
food and supply storage rooms can greatly reduce GSE catering service demand. Centralized
baggage conveyors which distribute baggage from check-in points to aircraft gates can displace
GSE baggage tractors (which alone represent up to 25 percent of all GSE), but such systems are
very difficult to retrofit into existing airports. Automated aircraft pushback systems offer the
potential to displace GSE pushback tractors. All of these services are technically feasible at this
time and, in fact, have been installed at a few European airports such as Arlanda in Sweden.
However, these systems are much less cost effective than the gate-based power and air systems
described above since operating cost savings do not approach those associated with the shutting
down of aircraft APU. Nevertheless, actual cost effectiveness must be determined on the basis of
local airport conditions and the specific services targeted. Marketable emission credits may
accelerate the installation of vehicle free gate demonstration technologies, but are more likely to
influence replacement of ICE-powered mobile GSE with mobile electric alternatives due to
similar emission reductions and much lower capital cost requirements.
Installation of On-Road Type Emissions Aftertreatment Devices: As discussed above, many
current GSE engines are similar to those used in 1980's-era automobiles. In recognition of this,
CARB is in the early stages of proposing new engine emission standards equivalent to the
level-of-control possible through the use of three-way catalytic converters. Catalysts have been
in use in the on-road vehicle sector for 25 years and have demonstrated the capability to maintain
high emissions conversion efficiencies throughout the useful lives of passenger cars and light
trucks. However, it must be recognized that one reason catalyst effectiveness and durability have
advanced to their current state in the on-road sector is that vehicle manufacturers have designed
complete combustion control systems around the aftertreatment equipment. Unleaded gasoline,
highly effective stoichiometric air-fuel mixture control systems, and current discussions to limit
fuel sulfur content are but examples of the advances made (or proposed) to accommodate
emissions aftertreatment. Notwithstanding the fact that current GSE engines and engine controls
are not manufactured to support today's sophisticated automotive aftertreatment devices, retrofit
of devices such devices or their less sophisticated predecessors is possible. For gasoline, LPG,
and CNG GSE, potential aftertreatment devices include both three-way and oxidation catalysts
while diesel aftertreatment, due to excess air combustion characteristics, are limited to oxidation
catalysts and particulate traps
generally have lower capital costs and can be installed with less service disruption.
GSE Control Strategy Summary Page 10
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While there are no theoretical limitations to the retrofit of catalyst or particulate trap technology
on GSE, there are several practical issues regarding both installation and operation. Off-road
engine powered GSE are open-loop systems in that they do not have combustion control
feedback systems to adjust combustion air-fuel mixture as necessary to promote aftretreatment
efficiency. Therefore, the simplest catalyst installations will be limited to oxidation-only
catalysts which do not require near-stoichiometric combustion for effective operation. However,
most spark-ignition GSE are tuned rich, at least under high load conditions, necessitating the use
of secondary air injection to promote effective oxidation. Closed-loop combustion control
systems could be included as an integral component of the retrofit, thereby opening the
possibility for the use of three-way oxidation/reduction catalysts, but a switch to stoichiometric
operation may limit critical maximum power for some GSE. Perhaps most importantly, most
GSE have operating cycles that consist of short engine-on periods interrupted by extended
engine-off periods. Therefore, a substantial portion of GSE operation may occur before exhaust
catalysts have reached effective conversion temperatures (i.e., light-off) or paniculate traps have
reached effective regeneration temperatures. Finally, installation location and space will be
restricted on most GSE so that aftertreatment packages designed to replace stock mufflers are
likely to be the most feasible approach. Neither the durability or effectiveness of such units have
yet been demonstrated over extended usage periods.
Table 5 presents the potential emission reduction effectiveness of exhaust aftertreatment devices.
It is critical to recognize that these estimates are not based on any demonstrated experience in the
GSE sector, but instead rely on performance observed for on-road vehicles. Until such time as
the appropriate demonstrations have been made on off-road equipment such as GSE, the
reduction estimates presented in Table 5 should be interpreted as upper-bound reduction
potentials. Catalytic HC reduction potential declines for both LPG and CNG engines due to the
increasing concentrations of short chain hydrocarbons in the exhaust of such engines. Current
catalyst technology is most effective on long chain hydrocarbons and a substantial fraction of
compounds such as methane and ethane can pass through a catalyst without undergoing
oxidation. The substantial increase in CO2 emissions results from an assumed backpressure
increase as well as the oxidation of HC and CO, both of which are observed in high
concentrations in uncontrolled GSE engines. Increased backpressure accounts for only about two
percentage points of the estimated increase, with CO conversion accounting for nearly all of the
remainder.
Until such time as catalyst and particulate trap performance has been consistently demonstrated
in GSE applications and sufficient test data on in-use engines is available to confirm generalized
emission reduction impacts, exhaust aftertreatment device installation and any emission credits
granted for such installation should be treated on a case-by-case basis, supported by on-going
emissions testing. Given catalyst and trap sizing and design limitations, costs for aftertreatment
device installation will be substantially higher than the cost of similar devices for on-road
equipment. Initial catalyst costs of $1,000 or more per unit are likely. Given the lack of
practical experience, it is not possible to accurately estimate cost effectiveness at this time, but
clearly emissions reduction potential is significant and the institution of marketable emission
credits may be sufficient incentive to undertake at least the necessary demonstration programs.
GSE Control Strategy Summary Page 11
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Oxidation Catalyst Installation
GSE Fuel
Gasoline
Diesel
LPG
CNG
HC
-90%
-50%
-70%
-50%
CO
-90%
-90%
-90%
-90%
NOX
0%
0%
0%
0%
PM
-10%
-30%
-10%
-10%
CO2J
+60%
+3%
+45%
+45%
Three-Way Catalyst Installation
GSE Fuel
Gasoline
LPG
CNG
HC
-90%
-70%
-50%
CO
-90%
-90%
-90%
NOX
-80%
-80%
-80%
PM
-10%
-10%
-10%
CO2
+60%
+45%
+45%
Particulate Trap Installation
GSE Fuel
Diesel
HC
-20%
CO
0%
NOX
0%
PM
-90%
CO2
+2%
1 CO2 emission increases result from increased exhaust system backpressure and the oxidation
of HC and CO, with CO oxidation accounting for the bulk of the estimated increase.
Table 5. Potential Emission Impacts of Exhaust Aftertreatment
Preferential Replacement of Two-Stroke Gasoline Engines: Uncontrolled two-stroke
gasoline engines emit about 7 times the HC, 1.5 times the CO, and 10 times the PM of similarly
sized uncontrolled four-stroke engines, while two-stroke NOX is only about 20 percent of that of
four-stroke engines. While the population of two-stroke GSE is declining, there remains a
number of such units in use in applications such as pumps on lavatory carts. In general, all such
equipment is rated at less than 25 horsepower and, therefore, subject to recent new engine
emission standards established by both the EPA and CARB. Since both two-stroke and
four-stroke engine standards are identical under the EPA and CARB programs, high emission
rate two-stroke engines will disappear from the GSE fleet over time. Nevertheless, near term
preferential replacement of existing two-stroke engines can generate significant reductions in HC
and PM. While, because of relative low two-stroke engine populations, these reductions are not
of the magnitude possible through the previously discussed control strategies, they can be cost
effective as the cost and reliability of small four-stroke engines become competitive with
similarly sized two-strokes.
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References:
1. Basis for GSE Population Estimates, GSE Information Series 1, prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency, September
1998.
2. GSE Emissions and Activity Estimates, GSE Information Series 2, prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency, September
1998.
3. LPG and CNG Control Strategies, GSE Information Series 3, prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency, September
1998.
4. Electric GSE, GSE Information Series 4, prepared by Energy and Environmental Analysis,
Inc. for the U.S. Environmental Protection Agency, September 1998.
5. Emissions Aftertreatment, GSE Information Series 5, prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency, September
1998.
6. Fixed Gate Support, GSE Information Series 6, prepared by Energy and Environmental
Analysis, Inc. for the U.S. Environmental Protection Agency, September 1998.
7. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
8. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
9. Technical Support Document for Civil and Military Aviation; prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency in support of
the Notice of Proposed Rulemaking for the Federal Implementation Plan for California,
March 1994.
10. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air
Resources Board, August 1995.
11. Airport Electrification Project, Consolidated Results and Analysis, EPRI TR-109041,
Electric Power Research Institute, September 1997.
GSE Control Strategy Summary Page 13
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12. Off-Road Electric "Vehicle" Scoping Study, EPRI TR-101906, Electric Power Research
Institute, July 1993.
13. "Electric Vehicles will Reduce Emissions at Boston's Logan Airport," Innovators with EPRI
technology, IN-102438, Electric Power Research Institute, June 1994.
14. Off-Road Electric Vehicles: An Existing Market, EPRI TR-103315, Electric Power Research
Institute, February 1994.
15. Advanced Transportation Vehicle Catalog, www.calstart.org/services/catalog/, CALSTART
internet website.
16. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: Stationary
Point and Area Sources, Chapter 1 (External Combustion Sources), as downloaded on July
29, 1998 from the U.S. EPA internet website www.epa.gov/ttn/chief/ap42.html.
17. "All the Power You Need," product literature from Hobart Ground Power, 1996.
18. "JETLINK," product literature from FMC/Jetway Systems.
19. "The Vehicle Free Ramp," product literature from FMT.
20. Emission Control Products: Diesel Exhaust Purifiers, Catalytic Mufflers, Catalytic Diesel
Filters, www.nett.ca, NETT Technologies internet website.
21. Clean Cat: Diesel Engine Catalytic Converters, clean-cat.com, Applied Diesel Technology,
Inc. internet website.
22. Personal communication on off-road catalyst design constraints and cost with NETT
Technologies, Mississauga, Ontario, Canada, July 1998.
GSE Control Strategy Summary Page 14
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ESTIMATING GSE ACTIVITY
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ESTIMATING GSE ACTIVITY
Knowledge of the activity levels of airport ground support equipment (GSE) is critical to
accurately determining emissions performance. This is true regardless of whether one considers
the baseline emissions performance of today's GSE fleet or the potential emission reductions that
can be derived through the implementation of various control measures. Either assessment
requires the detailed characterization of equipment population and/or usage rates to derive
accurate emission or emission reduction estimates.
The basic GSE emissions calculation methodology for a particular piece of equipment can be
summarized algebraically as:
unit GSE emissions g hours of operation
— :—;—— = — ;—x rated hp x— :—-—— x load factor
time period 01 interest bhp - hr time period 01 interest
where: g/bhp-hr" represents an equipment-specific emission factor expressed in grams of emissions
per brake horsepower-hour of work,
"rated hp " indicates the maximum power output of the equipment expressed in horsepower,
"hours of operation/time period of interest" indicates the total accumulated time (expressed in
hours) the equipment's engine is in operation during any particular period of interest, and
"load factor" indicates the ratio of actual expended work to maximum possible work during the
same time period.
Both the "g/bhp-hr" and "rated hp" parameters are elements of engine design. However, the
former is generally dependent on the latter (at least across discrete power ranges) and, therefore,
the specific horsepower demands of a given airline's or airport's support services can influence
the emission rates of its GSE. In this context, the horsepower distribution of GSE can be viewed
as an indicator of GSE activity (i.e., is the activity being conducted by large, high-powered GSE
or smaller, lower-powered counterparts). The remaining two parameters, "hours of
operation/time period of interest," and "load factor" are obviously indicators of GSE activity and
can vary with both GSE application and airport design.
While the four parameters defined above are sufficient to determine emission rates for a
particular equipment type, total GSE emissions can only be determined once the overall
distribution and population of GSE is known. Expressed algebraically, aggregate GSE emissions
are calculated as:
Estimating GSE Activity Page 1
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aggregate GSE emissions GSEtypes
time period of interest
•= Z
unit GSE emissions |
time period of interest J.
x GSE population;
where: "unit GSE emissions/time period of interest" are calculated as above,
"GSE population " indicates the number of individual units of a particular equipment type in
operation, and
"GSE types " indicates the total number of different types of equipment in operation.
Both the population of individual equipment and the number of equipment types in service will
vary across airlines and airports. Therefore, even given a detailed database of GSE-specific
emission factors, it is still necessary to accurately define at least five specific GSE activity
parameters (rated horsepower, load factor, usage rate, equipment-specific population, and
number of specific GSE types in use) to estimate overall GSE emissions. Unfortunately, detailed
knowledge of each of these parameters is complicated by several factors. First, GSE includes a
diverse range of vehicles and equipment of differing sizes, usage rates, and load factors. Second,
usage rates and load factors can vary substantially across time so that GSE activity, and therefore
emissions, can be temporally dependent. Third, GSE demands can vary substantially across
airports in accordance with (among other factors) airport design and aircraft activity. For
example, a busy airport may require dedicated GSE for each gate to meet service demands while
a low volume airport may be able to use the same equipment to service multiple gates. Fourth,
and perhaps most importantly, very little information has been collected on any of these
parameters so that databases sufficient to distinguish temporal and airport- or airline-specific
influences remain to be developed.
Given this situation, GSE emissions estimation must be considered as a developing exercise at
this time. Initial estimates for all the parameters required to calculate emissions have been
developed, but the uncertainties inherent in these parameter estimates are unknown as the robust
databases necessary to evaluate such uncertainty are non-existent. An overview of current GSE
emissions estimation parameter values as well as important associated background information is
presented in the GSE Information Series 1 and 2 selections, entitled Basis for GSE Population
Estimates and GSE Emissions and Activity Estimates respectively. This abbreviated document
serves to both bring together these parametric values in a single document and provide an initial
assessment of some of the uncertainty inherent in key GSE emissions estimation parameters.
Before presenting current "best estimates" for each of the required GSE activity parameters, it is
important to place the limitations imposed by the relative infancy of the GSE emissions
estimation field in a proper perspective. Basically, such perspective involves the recognition that
the majority of emissions estimation uncertainty comes into play only when aggregated estimates
are required, be they across equipment types, airlines, or airports. Emissions estimation
parameters for specific GSE units can be readily determined from site-specific analysis.
Population estimation methods become irrelevant when treating individual units and equipment
horsepower, usage rates, and load factors can be readily determined either through direct
Estimating GSE Activity
Page 2
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observation or analysis of associated data such as fuel use records. Therefore, in instances where
emission reduction estimates due to such control measures as fueling system conversion are
required, most of the emissions estimation uncertainty can be controlled simply by replacing the
"average" parametric estimates used for aggregate GSE emissions estimation with site-specific
equivalent estimates derived specifically for the affected equipment.
GSE Population Estimates: Ideally, GSE population data by equipment type would be
compiled and maintained through a national database so that accurate population estimates for
any given airport, airline, or equipment type could be readily developed. However, no such
database exists and no standard GSE tracking procedures have been developed across airports.
Therefore, alternative mechanisms for estimating GSE population must be derived. Two
possible approaches involve so-called "top-down" and "bottom-up" estimation. Under the
top-down approach, aggregate (i.e., national or state-specific) GSE populations are estimated and
allocated to individual airports on the basis of some activity indicator. For example, scrappage
algorithms can be applied to annual GSE sales data to estimate aggregate GSE populations.
These GSE can then allocated to individual airports through the use of an activity indicator such
as the number of aircraft landing and take-off (LTO) cycles. Such an approach was employed in
the U.S. Environmental Protection Agency's (EPA's) 1991 Nonroad Engine and Vehicle
Emissions Study (NEVES). Alternatively, under a bottom-up approach, GSE populations are
estimated for individual airports and aggregated as necessary. In the absence of comprehensive
airport-specific data, such an approach typically involves the statistical analysis of known GSE
population data for a given sample of airports in order to relate observed GSE populations to one
or more explanatory parameters that are readily available for all airports (e.g., LTO cycles).
Once such a relationship has been defined, it is a relatively simple matter to apply the regression
equation to other airports and develop airport-specific GSE population estimates.
Both approaches are theoretically sound, but both also have inherent weakness and potentially
large uncertainties. Generally, however, the bottom-up approach tends to more readily
incorporate airport-specific information into the derived population estimates. Moreover,
uncertainties with potential top-down approach sources of error, such as the use of standard
scrappage algorithms, are inherently addressed in the derived bottom-up regression relations. For
these reasons and given that a small sample of airport-specific GSE population data are available
to undertake the necessary regression analysis, the bottom-up approach generally reflects a more
robust GSE population estimation approach. The current best estimate bottom-up regression
equation approach is presented in GSE Information Series 1 selection entitled Basis for GSE
Population Estimates. Basically, the approach is based on aircraft LTO cycles as the predictive
GSE population parameter and the resulting regression equation is expressed algebraically as
follows:
GSE = 0.0226 (LTOnswwb) + 0.0054 (LTOnswnb) + 0.0022 (LTOSW) + 0.0008 (LTOprop)
Estimating GSE Activity Page 3
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where: "GSE" represents the calculated GSEpopulation,
"LTOn!smllb" indicates the number airport LTO cycles accumulated by wide-body jets, exclusive
of those operated by Southwest Airlines,
"LTOnsmlb" indicates the number airport LTO cycles accumulated by narrow-body jets,
exclusive of those operated by Southwest Airlines,
"LTO^" indicates the number airport LTO cycles accumulated by all jets operated by
Southwest Airlines, and
"LTO " indicates the number airport LTO cycles accumulated by non-jet aircraft.
As described in GSE Information Series 1, the regression equation yields a national GSE
population estimate of about 45,000 units. This estimate is consistent with several estimates
derived over the last several years using alternative approaches, but considerably lower than the
estimate derived using the top-down approach employed for the NEVES (about 85,000 units).
Although the regression equation is based on a significant sample of observed GSE population*
and the relationships with the selected predictive parameters (i.e., the various LTO cycle
parameters) are significant at over 99 percent confidence, the variability observed across airlines
and airports is, nevertheless, significant (correlation coefficients for component regressions are
generally around 0.80). Therefore, a review of the ability of the regression equation to accurately
forecast individual airport GSE populations is important in assessing the absolute utility of the
population predictions.
Airlines at several airports were contacted directly to obtain comparative GSE inventory
information, but unfortunately this survey was not successful as airline and airport managers at
airports including Atlanta's Hartsfield International, Indianapolis International, Norfolk
Regional, Albuquerque International, and Portland (Oregon) International declined to provide the
requested information. Of the airports surveyed, only Sacramento Metropolitan and Madison
County Airport in Huntsville, Alabama provided comprehensive GSE population data which can
be compared with regression predictions. As a alternative source of comparative data, survey
responses included in Appendix A of the Gas Research Institute's (GRI's) 1998 "Survey of
Airport Vehicle Fleets: Final Report" were examined and those that included sufficient data to
estimate airport GSE populations were identified. Of the 38 survey responses included in the
GRI report, the 12 airports presented in Table 1 included sufficient information to estimate
airport GSE populations (note, Table 1 also includes statistics for the Huntsville and Sacramento
airports which provided GSE population data in response to direct requests).
* In total, GSE populations for 35 individual airlines at 10 airports, comprising nearly 2,500 GSE, are incorporated
in the regression analysis. Together, these airline/airport combinations account for about 9 percent of national
LTO cycles.
Estimating GSE Activity Page 4
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Airport
Huntsville
Orange County
Sacramento
San Antonio
Kansas City
Baltimore
San Diego
Salt Lake City
Miami
Detroit Metro
St. Louis
Los Angeles
Dallas/Ft. Worth
O'Hare
1996
LTO's
5,792
40,628
42,778
45,301
66,243
73,917
77,447
100,029
127,880
170,980
229,259
247,388
373,263
377,096
NSWWB
LTO's
0
709
437
317
78
161
1,511
9,527
27,265
9,767
6,221
40,005
14,070
22,825
NSWNB
LTO's
5,792
34,964
20,349
27,410
48,152
56,092
43,835
72,969
92,336
151,640
142,626
139,292
262,531
300,658
SW
LTO's
0
4,955
18,366
15,142
17,082
10,873
27,069
15,408
1
6,163
31,022
38,047
1
1
PROP
LTO's
0
0
3,626
2,432
931
6,791
5,032
2,125
8,278
3,410
49,390
30,044
96,661
53,612
Observed
GSE
37
66
128
112
169
325
356
554
2,819
661
1,196
2,200
600
2,894
Predicted
GSE
31
216
163
191
300
336
335
645
1,121
1,055
1,019
1,764
1,812
2,181
Percent
Error
-16%
227%
28%
70%
78%
3%
-6%
16%
-60%
60%
-15%
-20%
202%
-25%
Aggregate Data
1,978,001
132,893
1,398,646
184,130
262,332
12,117
11,169
-8%
Aggregate Data Exclusive of Miami and Dallas/Ft. Worth
1,476,858
91,558
1,043,779
184,128
157,393
8,698
8,236
-5%
Table 1. Predicted Versus Observed GSE Populations
LTO cycle data, as required to evaluate the GSE population regression equation, was extracted
from the U.S. Department of Transportation, Bureau of Transportation Statistics' (BTS') report
entitled "Airport Activity Statistics of Certificated Air Carriers" for the calendar year 1996.
LTO cycle data for each airport was disaggregated into the four required predictive parameters
(i.e., wide-body jet LTO's exclusive of Southwest Airlines, narrow-body jet LTO's exclusive of
Southwest Airlines, Southwest Airlines LTO's, and non-jet LTO's) using the aircraft type- and
airline-specific LTO data published in the BTS report. The single limitation associated with the
use of the BTS report data is that it does not include LTO cycles accumulated by foreign air
carriers. As a result, airports at which foreign carrier LTO's comprise a significant fraction of
total LTO cycles can be expected to exhibit some under-prediction of GSE population.
Foreign carrier LTO data can be requested from the FAA, but requires special processing by
agency staff and, therefore, such data were not requested for this basic analysis. Previous
analyses of aircraft operations have, however, demonstrated that foreign carriers can comprise as
much as 15 percent of LTO cycles at high traffic international airports such as Los Angeles
International, with smaller contributions of 0-5 percent at non-hub international airports such as
Estimating GSE Activity
Page 5
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Boston Logan and Baltimore/Washington International. Since foreign carrier LTO's tend to be
more heavily weighted toward wide-body aircraft, which (as indicated by regression coefficients)
carry about 2.5 times the GSE demand of narrow-body aircraft, GSE under-prediction due to
non-consideration of foreign carrier LTO's can reach 25 percent or more at foreign hub airports
such as Los Angeles International, Chicago O'Hare, and Miami International. Lesser
under-predictions of 0-10 percent would be expected at foreign carrier non-hubs such as St.
Louis Lambert, Detroit Wayne, and Kansas City International.
Table 1 indicates observed (domestic carrier) LTO cycles, observed GSE population, the
regression-predicted GSE population, and the percent error of prediction for each of the 14
airports at which observed GSE population data was available for comparison. Figure 1 presents
a corresponding graphical illustration of the observed and predicted GSE populations. As
indicated, the error of prediction ranges from -60 to +227 percent, with an aggregate error over
all 14 airports (representing about 25 percent of all domestic carrier LTO's) of about -8 percent.
Unfortunately, due to the third-party nature of 12 of the 14 observed GSE populations, it is not
possible be certain that all of the indicated error is, in fact, associated with the regression
predictions. For example, as shown in Figure 1, Miami and Dallas/Ft. Worth exhibit observed
GSE populations that are vastly out-of-line with other airports of similar LTO activity. Miami
exhibits an "observed" GSE population as large as airports with three times as many LTO cycles,
whereas Dallas/Ft. Worth exhibits a population that is as small as airports with two to three times
less LTO activity. Clearly, it is possible that the GSE populations reported in the GRI survey for
these airports are not correct. In fact, if these two airports are eliminated from the analysis, the
regression predictions are within about ±25 percent of observed for eight of the twelve airports
investigated, with an aggregate error of -5 percent.
The largest band of prediction error appears to fall in the 40,000-70,000 LTO range, where the
regression equation appears to over-predict GSE populations by a substantial margin. Three of
the four airports with errors of prediction outside the ±25 percent range (excluding Miami and
Dallas/Ft. Worth) fall within this LTO region. Conversely, for those seven airports with greater
than 70,000 LTO cycles (again, excluding Miami and Dallas/Ft. Worth), four: San Diego, St.
Louis, Los Angeles, and O'Hare, all exhibit under-predictions right-in-line with expectations
given the exclusion of foreign carrier LTO's and two: Salt Lake City and Baltimore, are only
slightly over-predicted. Only Detroit's Wayne County Airport shows evidence of substantial
over-prediction.
Given the estimated prediction errors, several conclusions can be drawn regarding the use of the
GSE population regression*. First, additional regression development may improve predictions.
* Although the reliability of "observed" GSE populations (on which the regression prediction error is based) is not
assured given the simple extraction of such populations from published surveys of uncertain consistency and
quality, the general magnitude of most such "observations" appears reasonable. Therefore, while additional
efforts to collect and validate accurate GSE population data will be beneficial, it is quite probable that the
extracted observations provide a good assessment of regression accuracy, especially in terms of differences across
airports.
Estimating GSE Activity Page 6
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,uuu
2,500 -
S 2,000 -
o
•-P
§• 1,500 -
0.
O 1,000 -
500 -
* Observed
o Predicted
111
-------
used to support various service demands and not all airlines address the same service
requirements with the same equipment. Certain units such as aircraft pushback tractors, baggage
tugs, and belt loaders are fairly common across carriers and airports, but others such as forklifts,
carts, and ground power units vary considerably in usage rates and population, depending on both
airline and airport practices. Even developing a specific list of GSE types that apply at all
airports is not straight-forward. However, over the last several years, a somewhat "standard" list
of 23 GSE types has been in-use in the airport analysis community and, in the absence of
alternatives or obvious deficiencies, this list represents a convenient GSE categorization scheme.
These 23 equipment types, as listed in Table 2, provide an adequate level-of-detail to characterize
the important differences in design and usage of component GSE.
Given the current paucity of detailed GSE population data, there is little alternative at this time
but to base estimates of specific equipment type populations on the aggregate equipment
distributions for those carriers which have provided detailed GSE data. As described in GSE
Information Series 1, such data consist of detailed population distributions for 35 airlines at 10
U.S. airports. Table 2 presents the equipment type distributions derived from this data, at both
the level-of-classification associated with the overall GSE population regression parameters (i.e.,
jet aircraft exclusive of Southwest Airlines, Southwest Airlines, and non-jet aircraft) and at an
aggregate level for all observed sample distributions.
At this point in the development of GSE databases, the equipment type-specific distributions
presented in Table 2 reflect the "best methodology" for estimating specific equipment
populations at airports for which site-specific data is unavailable. GSE population estimates for
any selected airport can be developed by applying tabulated distribution data to aggregate
population estimates predicted using the GSE population regression described above. While this
approach inherently incorporates all of the uncertainty already described for regression-predicted
aggregate GSE populations, as well as any additional uncertainty inherent in the equipment
type-specific distributions, it nevertheless incorporates the most complete data currently
available.
Figures 2 and 3 present a comparison of equipment type distributions estimated using the "best
methodology" regression/disaggregation approach to distributions derived from data for GSE at
two airports not reflected in the database used to develop the underlying estimation statistics.
The data for St. Louis was extracted from the GRI airport fleet vehicle survey already described,
while that for Sacramento was provided directly by airport personnel. Note, the comparisons
presented focus solely on error in the equipment type-specific distributions and ignore any
aggregate GSE population prediction error (due to the use of the GSE/LTO regression equation)
which has already been discussed above. Also, the default (or predicted) GSE distributions were
developed by applying the aircraft-specific GSE distributions presented in Tables 2a-2c to
airport-specific LTO data for 1996. The aggregate GSE distributions presented in Table 2d are
not considered in these comparisons, but would deviate substantially from those indicated. As
expected, the "best methodology" approach to determining individual equipment subpopulations
includes substantial error when applied to any given airport. Nevertheless, in the absence of
alternative site-specific data, the default (i.e., predicted) equipment type-specific distributions do
provide a reasonably accurate means of estimating of equipment populations. In most cases, the
Estimating GSE Activity Page 8
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Equipment
Type
Aircraft Pushback Tractor
Conditioning Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other GSE
Service Truck
Bus
Car
Pickup Truck
Van
Water Truck
All Equipment
Population
Fraction
0.0590
0.0109
0.0198
0.2281
0.1120
0.0227
0.0341
0.0469
0.0113
0.0773
0.0113
0.0652
0.0004
0.0158
0.0377
0.0297
0.0399
0.0476
0.0066
0.0132
0.0633
0.0429
0.0044
1.0000
Diesel
Share
0.7577
0.8017
0.8701
0.4093
0.4608
0.1614
0.7738
0.0154
0.0638
0.0426
0.1605
0.8034
0.0000
0.0000
0.0291
0.0126
0.2200
0.1383
0.3887
0.0000
0.0114
0.0000
0.0000
0.3247
Gasoline
Share
0.1801
0.0661
0.0744
0.4655
0.4542
0.8222
0.1508
0.5314
0.9362
0.2607
0.8066
0.0337
1.0000
1.0000
0.5823
0.9748
0.6793
0.7464
0.6113
1.0000
0.9366
0.9657
1.0000
0.5127
Electric
Share
0.0372
0.0661
0.0189
0.0257
0.0196
0.0000
0.0000
0.4532
0.0000
0.2227
0.0000
0.1630
0.0000
0.0000
0.1943
0.0000
0.0181
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0685
LPG/CNG
Share
0.0249
0.0661
0.0000
0.0996
0.0654
0.0164
0.0754
0.0000
0.0000
0.4740
0.0329
0.0000
0.0000
0.0000
0.1943
0.0126
0.0825
0.1153
0.0000
0.0000
0.0520
0.0343
0.0000
0.0934
Turbine
Share
0.0000
0.0000
0.0366
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0007
Table 2a. Jet Aircraft GSE Distribution, Exclusive of Southwest Airlines
Estimating GSE Activity
Page 9
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Equipment
Type
Aircraft Pushback Tractor
Conditioning Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other GSE
Service Truck
Bus
Car
Pickup Truck
Van
Water Truck
All Equipment
Population
Fraction
0.0324
0.0108
0.0000
0.3222
0.0541
0.0108
0.0000
0.0541
0.0108
0.0000
0.0108
0.2249
0.0541
0.0108
0.0108
0.0216
0.0000
0.0432
0.0000
0.0108
0.0324
0.0746
0.0108
1.0000
Diesel
Share
1.0000
0.0000
n/a
0.4329
0.0000
0.0000
n/a
0.0000
0.0000
n/a
1.0000
1.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.4076
Gasoline
Share
0.0000
1.0000
n/a
0.5671
1.0000
1.0000
n/a
1.0000
1.0000
n/a
0.0000
0.0000
1.0000
1.0000
1.0000
1.0000
n/a
1.0000
n/a
1.0000
1.0000
1.0000
1.0000
0.5924
Electric
Share
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
LPG/CNG
Share
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
Turbine
Share
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
Table 2b. Southwest Airlines GSE Distribution
Estimating GSE Activity
Page 10
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Equipment
Type
Aircraft Pushback
Tractor
Conditioning Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other GSE
Service Truck
Bus
Car
Pickup Truck
Van
Water Truck
All Equipment
Population
Fraction
0.1554
0.0000
0.0260
0.3323
0.2328
0.0038
0.0000
0.0077
0.0077
0.0222
0.0000
0.0406
0.0222
0.0184
0.0077
0.0000
0.0260
0.0597
0.0038
0.0038
0.0260
0.0000
0.0038
1.0000
Diesel
Share
0.8325
n/a
1.0000
0.6221
0.7138
0.0000
n/a
0.0000
0.0000
0.1724
n/a
1.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.5000
1.0000
0.0000
0.2941
n/a
0.0000
0.6141
Gasoline
Share
0.1675
n/a
0.0000
0.3341
0.2862
1.0000
n/a
1.0000
1.0000
0.3448
n/a
0.0000
1.0000
1.0000
0.0000
n/a
1.0000
0.5000
0.0000
1.0000
0.7059
n/a
1.0000
0.3530
Electric
Share
0.0000
n/a
0.0000
0.0438
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0145
LPG/CNG
Share
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.4828
n/a
0.0000
0.0000
0.0000
1.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0184
Turbine
Share
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
0.0000
0.0000
0.0000
n/a
0.0000
0.0000
Table 2c. Non-Jet Aircraft GSE Distribution
Estimating GSE Activity
Page 11
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Equipment
Type
Aircraft Pushback Tractor
Conditioning Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other GSE
Service Truck
Bus
Car
Pickup Truck
Van
Water Truck
All Equipment
Population
Fraction
0.0612
0.0106
0.0195
0.2331
0.1144
0.0219
0.0324
0.0459
0.0112
0.0741
0.0110
0.0677
0.0021
0.0157
0.0363
0.0286
0.0387
0.0479
0.0064
0.0129
0.0616
0.0423
0.0045
1.0000
Diesel
Share
0.7659
0.7850
0.8751
0.4188
0.4713
0.1589
0.7738
0.0150
0.0613
0.0437
0.1774
0.8202
0.0000
0.0000
0.0287
0.0124
0.2157
0.1488
0.3993
0.0000
0.0148
0.0000
0.0000
0.3348
Gasoline
Share
0.1772
0.0856
0.0715
0.4629
0.4496
0.8249
0.1508
0.5450
0.9387
0.2615
0.7903
0.0308
1.0000
1.0000
0.5813
0.9752
0.6856
0.7422
0.6007
1.0000
0.9345
0.9669
1.0000
0.5097
Electric
Share
0.0341
0.0647
0.0182
0.0257
0.0182
0.0000
0.0000
0.4400
0.0000
0.2207
0.0000
0.1490
0.0000
0.0000
0.1919
0.0000
0.0178
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0655
LPG/CNG
Share
0.0228
0.0647
0.0000
0.0926
0.0609
0.0162
0.0754
0.0000
0.0000
0.4741
0.0323
0.0000
0.0000
0.0000
0.1980
0.0124
0.0809
0.1089
0.0000
0.0000
0.0508
0.0331
0.0000
0.0893
Turbine
Share
0.0000
0.0000
0.0352
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0007
Table 2d. Sample Aggregate GSE Distribution
Estimating GSE Activity
Page 12
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default distributions are able to identify both the type and relative presence of the various
equipment types in-use at each airport. Most importantly, estimates for aircraft tugs (pushback
tractors), baggage tugs, belt loaders, and on-road vehicles, which together comprise 60-75
percent of observed equipment populations, are generally accurate. While the comparative data
used to generate Figures 2 and 3 does not include the fuel-type statistics, one can reasonably
expect substantial error in fuel-specific equipment population predictions given individual air
carrier and airport practices regarding alternative fuel use, etc.
Given airline- and airport-specific influences on equipment type distributions, error in the use of
default GSE distributional data is not unexpected. As indicated above in the discussion of
aggregate population predictions, the default distributional data should only be used for screening
purposes only. Default distributions can provide a reasonable first estimate of potential emission
loads associated with GSE or potential emission reductions due to GSE controls, but detailed
"official" emission estimates should be reserved until actual site-specific GSE counts are
available. For determining the emission reduction associated with control measures which focus
on one or several specific pieces of equipment, all default distribution uncertainty becomes
irrelevant as data specific to the targeted equipment must be known and can easily displace
default statistics.
GSE Horsepower Classification: As described in the GSE Information Series 2 selection
entitled GSE Emissions and Activity Estimates, the basis for current "best estimates" of GSE
horsepower, load factor, and usage rates all derive from data developed for the California Air
Resources Boards' (ARB's) off-road emission factor model. The aggregate data presented below
differs somewhat from that of the ARE model only because the California-specific equipment
population data included in the ARB model has been replaced with more robust national data to
develop aggregate individual equipment data. Extractions from the ARB model remains the
"best estimate" methodology for determining GSE horsepower for several reasons. The model
continues to incorporate all GSE horsepower data currently available. Moreover, the model
treats the horsepower data in very disaggregated format so that subsequent aggregations using
alternative population data are quite easy. However, while the ARB model continues to represent
the best source of horsepower distribution data, it should be recognized that the basis for this data
continues to be limited, consisting of GSE inventory information collected from only a handful
of airlines during the California Federal Implementation Plan (FIP) development process of the
early-1990's. There is no question that an expanded study of GSE engine horsepower
distribution is both appropriate and necessary to validate and augment existing data.
Table 3 presents average horsepower data for the various GSE equipment types. As expected,
the variation across equipment types is dramatic, in accordance with the wide range of engine
power demands in the GSE sector. As a result, the emissions performance of specific GSE types
(or even across fuels within a specific GSE type) can vary considerably. As described above for
GSE population estimation, these data should only be used for emissions screening purposes and
should be displaced with actual equipment horsepower in all instances of emission reduction
estimates for specific equipment controls. Note also that Table 3 does not include estimates for
on-road vehicles used in GSE applications since emission estimates for such equipment should
be derived using the appropriate on-road emission factor model (i.e., MOBILEx, PARTx, or
EMFACx). It should similarly be recognized that an unknown fraction of the trucks used to
Estimating GSE Activity Page 13
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0.35
—*— St. Louis Actual Population Fractions
--o---- st. Louis Default Population Fractions
GSE Type
Figure 2. Comparative Equipment Type Distributions for St. Louis
0.35
0.30 --
0.25 --
—*— Sacramento Actual Population Fractions
--o---- Sacramento Default Population Fractions
GSE Type
Figure 3. Comparative Equipment Type Distributions for Sacramento
Estimating GSE Activity
Page 14
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Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline/LPG/CNG
130
130
130
100
60
100
70
12
93
50
130
150
12
130
100
130
50
180
150
Diesel
216
300
600
78
45
100
76
12
93
52
180
145
12
130
100
130
50
170
150
Table 3. Average Horsepower by Equipment and Fuel Type
provide fuel, food, water, and lavatory service are also on-road certified vehicles. Generally,
such service trucks do include special adaptations to facilitate use as GSE and many are of
overseas manufacture and uncertain emissions certification (since their use is restricted to
off-road applications, no specific emissions certification has historically been required).
However, many are undoubtedly certified on-road vehicles adapted for GSE use and as such,
associated emission estimates should also be determined using on-road emission factor models.
GSE Load Factors. As described above for GSE horsepower, the basis for current "best
estimates" of GSE load factors derives from data developed for the ARB's off-road emission
factor model. As was the case for GSE horsepower data, the aggregate data presented below
differs somewhat from that of the ARE model because California-specific equipment population
data has been replaced with more robust national data to aggregate individual equipment
estimates. Nevertheless, extractions from the ARE model continue to incorporate all GSE load
factor data currently available. Like horsepower, the model treats load factor data in a very
disaggregated format so that subsequent aggregations using alternative population data are quite
Estimating GSE Activity
Page 15
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easy to accomplish. However, it must be recognized that the basic data used to develop the ARB
model continues to be limited in scope, consisting primarily of GSE inventory information
collected from only a handful of airlines during the California Federal Implementation Plan (FIP)
development process of the early-1990's. An expanded study of GSE load factors is both
appropriate and necessary to validate and augment existing data.
Table 4 presents a summary of current "best estimate" GSE load factors by equipment type. As
was the case with GSE horsepower, on-road equipment types have been excluded from Table 4
as associated emissions estimation should be conducted using the appropriate on-road emission
factor models. Again, some fraction of service trucks will also be on-road certified vehicles and
should also be modeled as such.
Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other
Service Truck
Water Truck
Gasoline/LPG/CNG
0.80
0.75
0.90
0.55
0.50
0.55
0.50
0.50
0.95
0.30
0.25
0.75
0.50
0.25
0.50
0.50
0.50
0.20
0.20
Diesel
0.80
0.75
0.90
0.55
0.50
0.55
0.50
0.50
0.95
0.30
0.25
0.75
0.50
0.25
0.50
0.50
0.50
0.20
0.20
Table 4. Average Load Factors by Equipment and Fuel Type
Estimating GSE Activity
Page 16
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GSE Hours of Use: Like all GSE emissions estimation parameters, equipment usage rates vary
considerably from airport to airport. Moreover, use hours even at a single airport can vary
considerably by time-of-day, day-of-week, and season. Little investigation into such variation
has been undertaken for GSE and, therefore, usage rates have generally focused on long term
(e.g., annual) activity. Even so, variation across airports (e.g., due to variations in aircraft LTO
cycles) is significant and limits the utility of generic usage rates for GSE. Nevertheless,
estimates of annual equipment usage have been developed for such applications as the ARB
off-road model. Like other estimates extracted from the ARB model, usage rates are based on
limited data, consisting primarily of GSE information collected from only a handful of airlines
during the California Federal Implementation Plan (FIP) development process of the
early-1990's. An expanded study of GSE activity (and its variability across airports) is both
appropriate and necessary to validate and augment existing data.
Table 5 presents the average annual GSE usage rates derived from the ARB off-road model. As
with all other GSE activity parameters, the use hour estimates should be supplanted with actual
site-specific data whenever possible. For use hours, this caution is amplified. Large,
highly-trafficked airports may experience GSE usage rates much higher than those presented.
For example, baggage tugs might operate as much as eight hours per day for 350 days or more
per year, yielding an annual usage rate of 2,800 hours or more. This is over three times the usage
rate indicated in Table 5. Similar, but opposite, errors can be evidenced at very low-traffic
airports. Since emission estimates are directly proportional to usage rate and airport-specific
differences can be large, substantial emissions estimation errors can accrue due to a failure to
account for airport-specific usage rates. As with all other GSE activity estimation parameters,
"default" usage rates should be limited to emissions screening analysis only.
Equipment Type
Aircraft Pushback Tractor
Conditioned Air Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Use Hours/Year
551
22
135
876
810
876
719
150
22
726
22
796
183
1212
Estimating GSE Activity
Page 17
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Lift
Maintenance Truck
Other
Service Truck
Water Truck
376
449
183
1299
310
Table 5. Average Annual Hours-of-Use by Equipment Type
References:
1. Survey of Airport Vehicle Fleets, Final Report, prepared by Edwards and Kelsey, Inc. for the
Gas Research Institute, April 1998.
2. Airport Activity Statistics of Certificated Air Carriers for twelve months ending December
31, 1996, U.S. Department of Transportation, Bureau of Transportation Statistics.
3. Breakdown of GSE Equipment for Sacramento Metropolitan Airport, provided by Jim
Humphries to Bob Dulla of Sierra Research via fax, August, 1998.
4. Analysis of Techniques to Reduce Air Emissions at Airports, Draft Final Report, prepared by
Energy and Environmental Analysis, Inc. for the U.S. Environmental Protection Agency,
September 1997.
5. Air Pollution Mitigation Measures for Airports and Associated Activity, prepared by Energy
and Environmental Analysis, Inc. for the California Air Resources Board, May 1994.
6. Technical Support Document for Civil and Military Aviation; prepared by Energy and
Environmental Analysis, Inc. for the U.S. Environmental Protection Agency in support of the
Notice of Proposed Rulemaking for the Federal Implementation Plan for California, March 1994.
7. GSE population data sheets submitted by member companies of the Air Transport
Association as part of the U.S. Environmental Protection Agency's Federal Implementation Plan
development process for California, September 1993.
8. Documentation of Input Factors for the New Off-Road Mobile Source Emissions Inventory
Model, prepared by Energy and Environmental Analysis, Inc. for the California Air Resources
Board, August 1995.
9. California Off-Road Model (June 7, 1996 version) input files EMFAC.DAT, POP.DAT, and
ACTIVITY.DAT.
Estimating GSE Activity
Page 18
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APPENDIX A
GSE MODEL INSTRUCTIONS
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GSEMODEL OPERATING INSTRUCTIONS
Introduction
GSEModel is a personal computer spreadsheet-based analysis tool that has been developed to
quantify emission benefits and calculate the cost-effectiveness of converting existing airport
ground support equipment (GSE) to cleaner-burning fuels and engine technologies. The model
has been developed as a planning tool for use by metropolitan planning organizations (MPOs),
airports, and other agencies interested in evaluating potential emission benefits and cost savings
resulting from available GSE emission control technologies. It has been designed with a mouse-
enabled graphical user interface to make it simple and easy to use.
The GSEModel tool is based upon the "best practice" methodologies and information presented
earlier in the body of this report. It has been designed to utilize local (i.e., airport-specific) GSE
usage and cost information coupled with best-available emission factor data to perform the
following functions using a consistent methodology:
• Estimate current and alternative technology GSE emissions by individual equipment
category (e.g., aircraft pushback tractors, baggage tugs, cargo loaders, etc.);
• Compute the emission benefits of the available alternative technologies;
• Quantify the incremental capital, operating, and life-cycle costs of converting GSE units
to these alternative technologies; and
• Calculate and compare the cost-effectiveness (cost per unit emissions reduced, e.g.,
$/ton) of these alternative technologies for each equipment category under airport-
specific operating and usage conditions.
Nevertheless, as with any analysis tool, the results computed by the model retain the inherent
uncertainties of the data and estimates upon which they are based. As described in the operating
instructions that follow, the model provides "default" values for a number of inputs to enable the
user to quickly develop GSE emission reduction and cost-effectiveness estimates associated with
alternative technologies. Where actual local data are available, the user is encouraged to utilize
them to provide more accurate results.
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Following this introduction, the remaining sections of the GSEModel documentation are
organized as follows:
• Required Operating Environment - describes the software and hardware needed to run
the GSEModel application;
• Quick-Start Installation and Instructions - provides an overview on installing and
executing GSEModel to get started quickly; and
• Detailed Operating Instructions and Guidance - contains step-by-step instructions for
operating the application and basic guidance for inputting data and interpreting the
results.
Required Operating Environment
Software Requirements - GSEModel is a spreadsheet-based application that runs on personal
computers using Microsoft's Windows 95 or Windows 98 operating systems.* The model was
written in Microsoft Excel Visual Basic for Applications (VBA), an extension of the Visual
Basic programming language that allows applications to be designed with a user-friendly
interface around a series of Excel spreadsheet calculations. As a result, users must have
Microsoft Excel 95 (i.e., Excel 7.0) or Excel 97 installed on their computer in order for the
GSEModel application to run.
Hardware Requirements - The minimum hardware requirements listed by Microsoft to run
Windows 95 and Excel 7.0 are sufficient to use the GSEModel program. The application has
been satisfactorily tested at 640 x 480, 800 x 600, and 1,024 x 768 display resolutions, at both
256-color and 16-bit (HiColor) depths, and should run at any available video display setting.
The GSEModel program requires 500 KB of disk capacity. Each saved scenario file (described
later) occupies 14 KB of disk space.
"Quick-Start" Installation and Operating Instructions
Installation of the application simply consists of downloading or copying the GSEMODEL.XLS
file to any valid directory chosen by the user. However, it is suggested that a separate, initially
empty directory be created for the GSEModel application (e.g., C:\GSEMODEL) and the
GSEMODEL.XLS file copied into it. As explained later in more detail, a key ease-of-use feature
of the application is its ability to save and re-load "input scenario" files. Thus, it is
recommended that a new directory be created to store the GSEMODEL.XLS application and the
* The GSEModel application should theoretically also be able to run under Windows NT 4.0, but
it has not been tested under that operating system.
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user-created scenario files (suffixed ".gse") that it uses in order to separate them from other files
on your computer.
Running the Program - From Windows 95 or Windows 98, the GSEModel application can be
executed in several ways familiar to Windows users:
• Create and launch a shortcut to the application (creating a shortcut is discussed in the
next section);
• Double-click* the GSEMODEL.XLS file from within the Windows Explorer or Internet
Explorer window (assuming Excel has been installed and associated with .XLS file
types);
• Right-click the GSEMODEL.XLS file, then click "Open" from the pop-up menu; or
• Click the Start button at the bottom left of Windows 95 and Windows 98 desktop,
select "Documents" from the pop-up menu, and then click the GSEMODEL.XLS file
from the pop-up list of documents.
(Note that this latter method works only when the GSEMODEL.XLS file has been recently
opened and appears in the "Recent Documents" list.)
Inputting Data - Once the program finishes loading (signaled by a "Ready" indicator at the
bottom left of the application window), the user is placed at the top of the first of three data input
screens, the SCENARIO INPUTS screen. Using the graphical "point-and-click" interface, much
of the input data required by the application can be easily entered by clicking drop-down lists and
selecting specific items or clicking various check-boxes to utilize default information supplied by
the model. Table A-l provides a brief summary of the data inputs required by the application.
The buttons near the bottom of each input screen allow the user to navigate from screen to
screen.
Viewing Results - After entering all required inputs (or selecting default values), GSEModel
automatically performs the alternative technology emission reduction and cost-effectiveness
calculations. To view the results, simply click the "View Results" button (the right button at the
bottom of each input screen). The user can scroll down the tabular summary to examine the
calculated results.
* If the Windows Explorer has been replaced by Internet Explorer (e.g., in Windows 98), Internet
Explorer can be configured to launch programs with a single mouse click instead of a double-
click.
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Table A-l
Summary of GSEModel Data Inputs
Scenario Inputs
1C Technology Activity
& Costs Inputs
Electric Technology Inputs
A scenario title (optional)
The GSE equipment category
being evaluated
The "base" or current
technology used in that type of
equipment
The number of units of that
type and technology being
considered for conversion
The alternative technologies to
be assessed
Annual hours of operation (of
the selected equipment type)
Expected equipment and
engine life
Purchase, replacement,
operating and maintenance
costs
Discount rate assumed (for Net
Present Value cost analysis)
The weighting scheme
(optional) used to combine
pollutant emission reductions
in calculating cost-
effectiveness
The amount of time (in %) that
the current technology GSE
equipment being evaluated is
operated at idle
Expected electric GSE
equipment life and battery life
Electric GSE purchase,
replacement, operating and
maintenance costs
Power-generation utility
emission rates reflective of
local conditions
(Note that if complete input data have not been entered, when the View Results button is clicked
an "Incomplete Input" message box is displayed that indicates which data must still be entered.)
To return to the input screen after viewing the results calculated by GSEModel, click the "Edit"
item on the main menu near the top of the application window. Then click either of the three
"Return to ..." items to go back to one of the input entry screens.
IMPOR TANT - Other than exiting the program, this is the only way to navigate out of
the Results screen!
Printing Inputs and Results - To print both the input data and the tabulated emission reductions
and cost-effectiveness results for the current scenario being evaluated, click the "Print" item on
the main menu bar, then click the "Print Scenario" item on the drop-down menu. A two-page
report is then printed on the current "default" printer selected from Windows. The first page
shows a summary of the data inputs; results are displayed on the second page.
Saving and Loading Scenario Files - To make repeated use of the GSEModel tool quicker and
easier, the application includes the capability to save a complete set of analysis inputs and re-use
them later as a modifiable template for evaluating other GSE scenarios. (This avoids having to
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type in complete data from scratch for each analysis.) After inputting data for a specific analysis
case, the information can be saved to a "scenario file" (indicated by a ".gse" file extension) by
clicking "File" on the main menu and then clicking "£ave Scenario." A dialog box is then
displayed, allowing the file to be saved to disk for later use. Click the arrow to the right of the
"Save m" box to select the destination directory, then type a file name for the scenario to be
saved in the "File name"box, using the .GSE suffix. (It is suggested that the ".gse" scenario files
be saved to the same directory where the application program was stored, e.g., C:\GSEMODEL.)
Similarly, to load and re-use a saved scenario file, click "File" on the main menu, then click
"Load Scenario." Select the directory and file to be loaded into the application.
Exiting the Program - To exit the GSEModel application, click "File" on the main menu, then
click "Exit GSEModel." The application will then close and exit. Remember to save the current
inputs in a scenario file as described above if you plan to re-use them later.
IMPOR TANT - Do not close the GSEModel application using the Close Box in the
upper right-hand corner of the application window such as the one shown.
If this happens inadvertently, you may be prompted as shown below in Figure 1 to save
changes to the GSEMODEL.XLS file.
Figure 1
Microsoft Excel
S ave changes in 'G S E M odel. His'?
Yes I No I Cancel!
ANSWER "NO" TO THIS PROMPT, OR ELSE YOU MAY CORRUPT THE
PROGRAM!
Detailed Operating Instructions and Guidance
This section of the documentation provides step-by-step descriptions and guidance for operating
and inputting data to the GSEModel application and understanding the calculated results.
Creating a Shortcut to Launch GSEModel - Prior to running the application for the first time, the
user may want to create a shortcut to the application, enabling it to be launched directly from the
Windows desktop with a single mouse click. To do so, perform the following steps:
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• Open the Windows Explorer and locate the GSEMODEL.XLS file in the
folder/directory it was installed into;
Right-click the GSEMODEL.XLS file and click "Copy"on the pop-up menu;
• If necessary, size the Explorer window so that part of the desktop is visible, then right-
click the mouse on any visible portion of the desktop and click "Paste Shortcut" from
the pop-up menu.
Windows then places a shortcut to the application on the desktop called "Shortcut to
GSEMODEL.XLS." To rename the shortcut (e.g., to simply "GSEModel"), select the shortcut
icon, right-click and select "Rename" from the pop-up menu. Type in the new name and hit the
Enter key on the keyboard when finished.
Inputting Data - Scenario Inputs Screen - After being launched, the GSEModel program takes
several seconds to load. When loading is finishing (denoted by a "Ready" indicator in the lower
left corner of the application window), the user is placed at the first of three inputs screens, the
Scenario screen, shown in Figure 2. The user can navigate from screen to screen using the
buttons located toward the bottom of each input screen.
Figure 2
Scenario Inputs Screen
X! Airport GSE Emissions fc Cost Model
file Edit Print
SCENARIO INPUTS
ENTER SCENARIO TITLE BELOW (optional!
SELECT EQUIPMENT CATEGORY SELECT CURRENT TECHNOLOGY HOW WILL YOU INPUT NO. OF UNITS TO BE EVALUATED?
_3 I _E] O Enter it myself
v> Have program calculate it from LTO's
SELECT ALTERNATIVE
TECHNOLOGIES
l~~ Gasoline 4-Stroke
r LPG
r CNG
r Diesel
l~~ Electric
r All Above
Ready
Carrier Type
Jet, Non-SW- Wide Body
Jet, Non-SW- Narrow Body
Jet, SouthWest
Regional
Annual
LTO's
Total GSE Units:
GSE
Units
ACTIVITY 8, COST
INPUTS
ELECTRIC TECH.
INPUTS
VIEW RESULTS
Sum=D
MUM
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On the Scenario screen, basic information about the analysis case being evaluated are entered,
including the GSE equipment category and the current and alternative emission control
technologies being considered. White-colored areas indicate where user inputs are provided.
Each of the inputs on this screen is discussed below.
Scenario Title (optional) - If desired, the user can enter a specific title for the scenario being
evaluated.
Equipment Category - Using a drop-down list, accessed by clicking the down arrow to the right
of this input box, one of 19 available GSE equipment categories must be selected for analysis.
(As stated earlier, the GSEModel application is set up to analyze emission reductions and cost-
effectiveness for one category at a time.) Table 2 lists the available GSE equipment categories.
Table 2
GSE Equipment Categories
Aircraft Pushback Tractor
Air Conditioning Unit
Air Start Unit
Baggage Tug
Belt Loader
Bobtail
Cargo Loader
Cart
Deicer
Forklift
Fuel Truck
Ground Power Unit
Lavatory Cart
Lavatory Truck
Lift
Maintenance Truck
Other GSE
Service Truck
Water Truck
Current Technology - A similar drop-down list feature is used to select the technology currently
used in the GSE equipment being evaluated. The following choices are available:
• Gas-2 - Two-stroke gasoline engines;
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Gas-4 - Four-stroke gasoline engines;
LPG - Liquid Petroleum gas-fueled engines;
CNG - Compressed natural gas-fueled engines;
Diesel - Diesel-designed and fueled engines; and
Electric - Electrically powered equipment.
Note that for a given GSE equipment category, any one of these options can be selected. The
GSEModel program does not include logic to identify "valid" choices for each individual
equipment category. That responsibility is left up to the user.
Input Units Method/Number of Units - By clicking either of the two radio buttons, the user
indicates which of two methods will be used to input the number of GSE units (for the selected
category and current technology) to be evaluated:
1. Direct Entry - The user simply enters the number of units being considered in the cell
below (e.g., 30 baggage tractors); or
2. Calculate from LTOs - If the number of units of a particular equipment category is
unknown, annual LTO (landing and takeoff operation) information can be entered and
the GSEModel program will estimate the number of units of the equipment type and
current technology selected.
If option 2 is selected, annual LTO data for four commercial air carrier categories are required:*
• Wide-body jets from all carriers except Southwest Airlines;
• Narrow-body jets from all carriers except Southwest Airlines;
• Southwest Airlines j ets; and
• Non-jet regional/commuter aircraft (e.g., turboprops).
Alternative Technologies - Using a group of check-boxes, the user can select alternative
technology categories to be evaluated by the program as indicated. (Depending upon the current
technology selected earlier, one of the alternative technology check-boxes may be disabled and
shaded out.) The "All Above" check-box can be used to select or de-select all available
technologies.
*The GSE Information Series 1 (Basis for GSE Population Estimates) document also prepared
under this EPA Work Assignment provides a detailed discussion of how GSE equipment unit
counts can be derived from air carrier LTO data.
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Inputting Data - I-C Technology Activity & Cost Inputs Screen - Figure 3 shows the layout of the
I-C Technology Activity & Cost Inputs screen.
This screen is used to enter activity and cost data for the current and alternative technologies for
the GSE equipment category selected earlier. (Information for all internal combustion (I-C)
technologies is entered on this screen. Electric technology-specific data are entered on the next
screen.) Each input area is discussed below.
Activity Inputs - Three "activity"-related data elements are entered in this table for both the
current and alternative technologies being modeled:
• Annual Usage - the number of hours per year that the equipment is operated (for I-C
engines, this consists of the entire time the engine is on and running, including idling);
• Equipment Life - the expected useful life, in years, of the GSE equipment (typically 16
years); and
• Engine Life - the estimated interval, in years, before an engine replacement or rebuild
is needed.
As Figure 3 shows, check-boxes at the left of each of these activity data inputs can be clicked to
Figure 3
I-C Technology Activity & Cost Inputs Screen
X Airport GSE Emissions & Cost Model
j File Edit Print
I-C TECHNOLOGY ACTIVITY & COST INPUTS
CHECK
TO USE
DEFAULT
VALUES
r
r
r
ACTIVITY INPUTS
ANNUAL USAGE (hrs/year)
EQUIPMENT LIFE (years)
ENGINE LIFE (years)
COST INPUTS
PURCHASE PRICE (S)
REPLACEMENT/REBUILD COST ($)
FUEL USE (GGEgal/hr)
UNIT FUEL COST ($/gal)
UNIT MAINTENANCE COST (S/hr in use)
DISCOUNT RATE (%)
CURRENT
ALTERNATIVE I-C TECHNOLOGIES
CURRENT
ALTERNATIVE I-C TECHNOLOGIES
POLLUTANT COST-EFFECTIVENESS WEIGHTING SCENARIO
(produces
SCENARIO ELECTRIC TECH.
INPUTS INPUTS
multi-pollutant CE estima e, optional)
VIEW RESULTS
(none) f\
Ready
Sum=0
MUM
-------
have the program supply default values for each element. However, the user is encouraged to
utilize actual data for the specific airport being modeled, especially for the annual usage inputs.
Also note that depending upon which current and alternative technologies have been selected
earlier, one or more of the columns in this table (and the Cost Inputs table discussed below) will
be disabled and shaded out.*
Cost Inputs - A similarly displayed table is used to enter required cost information as follows:
• Purchase Price - the initial purchase cost of that equipment category and technology, in
dollars;
• Replacement/Rebuild Cost - the cost of rebuilding or replacing the engine of the
equipment category and technology being evaluated at each interval specified above in
the Engine Life inputs, in dollars;
• Fuel Use - the estimated amount of fuel used for each specific technology, in Gasoline
Gallon Equivalent (GGE) gallons per hour of operation:
• Unit Fuel Cost - the cost of each technology-specific fuel, in dollars per gallon; and
• Unit Maintenance Cost - the maintenance-related costs of each equipment/technology
combination, in dollars per hour of equipment use.**
Reliable, verified data for these costs are not currently available. Therefore, no defaults have
been set up within GSEModel for these inputs. The GSE Information Series documents123456 also
compiled under this Work Assignment provide rough estimates for these inputs.
Discount Rate - Below these tables is a cell to enter the discount rate (in percent) to be used in
the Net Present Value (NPV) cost calculations (discussed in detail later). A typical discount rate
used in NPV analysis is 6%.
Pollutant Cost-Effectiveness Weighting Scenario (optional) - Finally, using a drop-down
*This is normal. The GSEModel program uses logic that fixes the columns in these tables to
specific technologies. Depending on which technology has been selected as the current
technology and the alternative technologies chosen, the columns in these tables corresponding to
non-selected technologies will be deactivated.
"Most maintenance cost data are reported in these units. If only annual costs are available for a
number of GSE units, simply divide these costs by the product of the number of units and their
annual usage level, i.e., Unit Maint. Cost ($/hr) = Annual Maint. Cost for Multiple GSE Units /
[# Units x Usage (hrs/year)].
-------
list, the user can optionally select a weighting scheme to calculate combined-pollutant cost-
effectiveness in addition to the simple, individual pollutant cost-effectiveness estimates always
produced by the program. For example, for ozone-related control-strategy analysis, planning
agencies often calculate cost-effectiveness by combining HC, NOx, and CO reductions, where
CO is discounted relative to the ozone-formation potential of HC and NOx.* In addition to
ozone, default weighting schemes have been set up for PM10 and CO-only control strategy cost-
effectiveness calculations. (To bypass this option, simply leave the "(none)" item selected in the
drop-down list.)
Inputting Data - Electric Technology Inputs Screen - If the electrically powered GSE alternative
technology was selected for evaluation in the Scenario Screen described earlier, additional
electric technology-specific inputs must be entered on this screen, shown in Figure 4. The inputs
required in this screen are defined below.
Activity Inputs - The activity-related data required for electric technology is similar but not
identical to 1C engine inputs. These input distinctions are as follows:
• Base Tech. Operation at Idle - the frequency at which the "base" or current technology
engine being modeled operates at idle when turned on**, in percent;
• Battery Life - the expected life of the battery as regularly charged and used to power
electric GSE, in years.
The model provides default battery life estimates by GSE category if the check-box to the left of
the table is clicked.
Cost Inputs - As with the activity data, electric GSE cost inputs required by the model are similar
to their 1C engine counterparts, with the following differences:
• Electric Use - the power consumption rate of the electric GSE equipment, in kilowatts
per operating hour; and
*The California Air Resources Board typically uses a HC-NOx-CO weighting scheme of 1-1 -V7,
respectively to assess ozone-related control strategies for which multi-pollutant reductions are
anticipated.
"This input is used by the model to account for the fact that many I-C engine-powered GSE are
left on for prolonged periods and continue to idle without being used. Conversely, it assumes
that electric GSE are shut off when not actually in use.
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Figure 4
Electric Technology Inputs Screen
X Airport GSE Emissions & Cost Model
I Re Edit Print
ELECTRIC TECHNOLOGY INPUTS
CHECK
TO USE
DEFAULT
VALUES
ACTIVITY INPUTS
BASE TECH. OPERATION AT IDLE (%)
EQUIPMENT LIFE (years)
BATTERY LIFE (years)
COST INPUTS
PURCHASE PRICE ($)
REPLACEMENT/REBUILD COST ($)
ELECTRIC USE (kw/operating hr)
UNIT ELECTRICITY COST ($/kw-hr)
UNIT MAINTENANCE COST ($/hr in use)
SELECT UTILITY EMISSION RATES SCENARIO
SCENARIO
INPUTS
ACTIVITY!, COST
INPUTS
VIEW RESULTS
Ready
Sum=0
MUM
Unit Electricity Cost - the energy rate charged by the local electric utility, in dollars per
kilowatt-hour (airports are typically charged an industrial rate that is cheaper than
residential rates).
The program contains default values for both of these inputs based on data contained in the GSE
Information Series 4 - Electric GSE guidance cited earlier. That guidance also includes estimates
for the other electric technology cost data required by the program for selected equipment
categories.
Utility Emission Rates Scenario - Finally, using a drop-down list, the user must select one of
three utility emission rate scenarios contained in the program. This input is used to account for
the emissions generated at the utility power plant due to the incremental power demand that
results from converting 1C engine GSE to electric technology. Table 3 lists these scenarios and
shows the utility emission rates assumed by the model.
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Table 3
Electric Utility Emission Rate Scenarios and
Power Plant Emission Factors (g/hp-hr)
Scenario
Minimum
Typical
Maximum
HC
0.008
0.037
0.124
CO
0.035
0.109
0.185
NOx
0.080
0.403
2.534
PM
0.004
0.023
1.371
Once all of the inputs required in each of the screens described above are entered (or default
values are selected), the GSEModel program automatically performs emission reductions and
cost-effectiveness calculations. The "View Results" button located at the bottom of each of these
screen can then be clicked to examine the results, or the "Print" item on the main menu can be
clicked to print them.
Output Results - Emissions and Cost-Effectiveness Calculations - This final sub-section of the
GSEModel documentation briefly discusses how the emission reduction and cost calculations are
performed and presents results from a sample calculation. The methodologies (and default data)
used by the program are based entirely upon the GSE Information Series guidance that is
summarized in the body of the report to which this documentation is appended.
Using equipment category-specific "average life" emission factors contained in that guidance
multiplied by the annual usage inputs described in the preceding sub-sections, GSE emissions (in
tons/day) are estimated for current and alternative technologies selected.
Emission reductions (from the current technology emission levels) are then computed on both an
absolute (tons/day) and relative (%) basis.
Lifetime costs (based on the equipment useful life, not the engine replacement interval) are then
forecasted for engine/battery replacement, operation (i.e., fuel or electricity use), and
maintenance by combining the various cost inputs with the equipment usage inputs, and the
initial capital cost.
A Net Present Value (NPV) calculation is then performed on these cash flows, using the input
discount rate, to compute NPV life-cycle costs for each cost component (initial, replacement,
operating and maintenance), and in total under each technology evaluated. The NPV
methodology provides a basis to compare a series of uneven future cash flows for difference
scenarios (i.e., GSE technologies as used in this application) on an equivalent present value basis,
given an assumed discount rate.
Once the NPV costs are computed, individual pollutant cost-effectiveness ($/ton) is computed by
dividing incremental NPV costs (alternative technology costs relative to the current technology)
by incremental emission reductions for each alternative technology, where the emission
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reductions are also expressed on an NPV basis. If selected by the user, combined pollutant cost-
effectiveness is similarly calculated by dividing incremental NPV costs by the summed
weighted-pollutant reductions.
A sample GSEModel Results report showing these outputs is provided in Figure 5.
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Figure 5
Sample GSEModel Results Report
GSE MODEL RESULTS
SCENARIO TITLE: Cost-Effectiveness Calculation Example (Baggage Tug)
EQUIPMENT CATEGORY: Baggage Tug
CURRENT TECHNOLOGY: Gas-4
NUMBER OF UNITS: 1
Emissions (tons/Year}
HC
CO
NOx
PM
Emission Reductions (tons/vear't
HC
CO
NOx
PM
Emission Reductions (°/n\
NPV
NPV
NPV
NPV
HC
CO
NOx
PM
Lifetime Costs (&)
Purchase Cost
Replacement Cost
Fuel Cost
Maintenance Cost
Total Cost
Lifetime Emissions (tons'*
HC
CO
NOx
PM
Weighted Total: Ozone
Incremental Cost Savings ($}
Purchase Cost
Replacement Cost
Fuel Cost
Maintenance Cost
Total Cost
Emission Reductions (tons'*
HC
CO
NOx
PM
Weighted Total: Ozone
Incremental Cost-Effectiveness (S/ton't
HC
CO
NOx
PM
Weighted Total: Ozone
Current
Gas-4
1.148
57.648
0.699
0.007
Current
Gas-4
n/a
n/a
n/a
n/a
Current
Gas-4
n/a
n/a
n/a
n/a
Current
Gas-4
$17,000
$2,568
$59,481
$47,089
$126,139
Current
Gas-4
10.157
510.265
6.190
0.065
89.243
Current
Gas-4
n/a
n/a
n/a
n/a
n/a
Current
Gas-4
n/a
n/a
n/a
n/a
n/a
Current
Gas-4
n/a
n/a
n/a
n/a
n/a
Alternative Technologies
LPG
0.574
36.030
0.525
0.006
CNG
0.382
36.030
0.525
0.006
Diesel
0.217
0.686
1.842
0.136
Electric
0.006
0.019
0.068
0.004
Alternative Technologies
LPG
0.57
21.62
0.17
0.00
CNG
0.77
21.62
0.17
0.00
Diesel
0.93
56.96
-1.14
-0.13
Electric
1.14
57.63
0.63
0.00
Alternative Technologies
LPG
50.0%
37.5%
25.0%
16.3%
CNG
66.7%
37.5%
25.0%
16.3%
Diesel
81.1%
98.8%
-163.3%
-1758.9%
Electric
99.4%
100.0%
90.2%
46.5%
Alternative Technologies
LPG
$19,000
$2,568
$49,072
$37,176
$107,816
CNG
$21,000
$2,568
$65,058
$37,176
$125,802
Diesel
$22,000
$2,568
$27,386
$47,089
$99,044
Electric
$30,000
$6,566
$5,576
$15,614
$57,756
Alternative Technologies
LPG
5.079
318.916
4.643
0.054
55.281
CNG
3.381
318.916
4.643
0.054
53.584
Diesel
1.924
6.076
16.302
1.201
19.094
Electric
0.056
0.164
0.606
0.035
0.685
Alternative Technologies
LPG
-$2,000
$0
$10,409
$9,914
$18,323
CNG
-$4,000
$0
-$5,576
$9,914
$337
Diesel
-$5,000
$0
$32,095
$0
$27,095
Electric
-$13,000
-$3,997
$53,905
$31,475
$68,383
Alternative Technologies
LPG
5.079
191.349
1.548
0.011
33.962
CNG
6.776
191.349
1.548
0.011
35.659
Diesel
8.233
504.189
-10.112
-1.136
70.149
Electric
10.101
510.101
5.584
0.030
88.557
Alternative Technologies
LPG
$3,608
$96
$11,839
$1,742,065
$540
CNG
$50
$2
$218
$32,057
$9
Diesel
$3,291
$54
-$2,680
-$23,842
$386
Electric
$6,770
$134
$12,245
$2,278,120
$772
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4. REFERENCES
1. GSE Information Series 1, "Basis for GSE Population Estimates," Energy and
Environmental Analysis, Inc., September 1998.
2. GSE Information Series 2, "GSE Emissions and Activity Estimates," Energy and
Environmental Analysis, Inc., September 1998.
3. GSE Information Series 3, "LPG and CNG Control Strategies," Energy and Environmental
Analysis, Inc., September 1998.
4. A. "GSE Control Strategy Summary," Energy and Environmental Analysis, Inc., September
1998.
B. "Estimating GSE Activity," Energy and Environmental Analysis, Inc., September 1998.
5. GSE Information Series 5, "Emissions Aftertreatment," Energy and Environmental
Analysis, Inc., September 1998.
6. GSE Information Series 6, "Fixed Gate Support," Energy and Environmental Analysis, Inc.,
September 1998.
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