Appendix A: GSEModel Operating Instructions

APPENDIX A

GSEMODEL OPERATING 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.

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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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

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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created to store the GSEMODEL.XLS application and the 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-1 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.

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Table A-1

Summary of GSEModel Data Inputs

Scenario Inputs

IC 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.

IMPORTANT - 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 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”

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Figure 1

(indicated by a “.gse” file extension) by clicking “File” on the main menu and then

clicking “Save 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 in” 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.

IMPORTANT - 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.

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

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directly from the Windows desktop with a single mouse click. To do so, perform the

following steps:

& 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.

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Figure 2

Scenario Inputs Screen

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.

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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;

& 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

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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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 jets; 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.

Inputting Data - I-C Technology Activity & Cost Inputs Screen - Figure 3 shows the

layout of the I-C Technology Activity & Cost Inputs screen.

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Figure 3

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.

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)].

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As Figure 3 shows, check-boxes at the left of each of these activity data inputs can be

clicked to 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

documents

123456

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%.

The California Air Resources Board typically uses a HC-NOx-CO weighting scheme of 1-1-

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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Pollutant Cost-Effectiveness Weighting Scenario (optional) - Finally, using a drop-down

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 PM

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 IC 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 IC engine counterparts, with the following differences:

& Electric Use - the power consumption rate of the electric GSE equipment, in

kilowatts per operating hour; and

& 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).

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Figure 4

Electric Technology Inputs Screen

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 IC engine GSE to electric technology.

Table 3 lists these scenarios and shows the utility emission rates assumed by the model.

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.

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Table 3

Electric Utility Emission Rate Scenarios and

Power Plant Emission Factors (g/hp-hr)

Scenario HC CO NOx PM

Minimum 0.008 0.035 0.080 0.004

Typical 0.037 0.109 0.403 0.023

Maximum 0.124 0.185 2.534 1.371

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 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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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/

ear)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC 1.148 - 0.574 0.382 0.217 0.006

CO 57.648 - 36.030 36.030 0.686 0.019

NOx 0.699 - 0.525 0.525 1.842 0.068

PM 0.007 - 0.006 0.006 0.136 0.004

Emission Reductions (tons/

ear)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC n/a - 0.57 0.77 0.93 1.14

CO n/a - 21.62 21.62 56.96 57.63

NOx n/a - 0.17 0.17 -1.14 0.63

PM n/a - 0.00 0.00 -0.13 0.00

Emission Reductions (%)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC n/a - 50.0% 66.7% 81.1% 99.4%

CO n/a - 37.5% 37.5% 98.8% 100.0%

NOx n/a - 25.0% 25.0% -163.3% 90.2%

PM n/a - 16.3% 16.3% -1758.9% 46.5%

NPV Lifetime Costs ($)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

Purchase Cost $17,000 - $19,000 $21,000 $22,000 $30,000

Replacement Cost $2,568 - $2,568 $2,568 $2,568 $6,566

Fuel Cost $59,481 - $49,072 $65,058 $27,386 $5,576

Maintenance Cost $47,089 - $37,176 $37,176 $47,089 $15,614

Total Cost $126,139 - $107,816 $125,802 $99,044 $57,756

NPV Lifetime Emissions (tons)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC 10.157 - 5.079 3.381 1.924 0.056

CO 510.265 - 318.916 318.916 6.076 0.164

NOx 6.190 - 4.643 4.643 16.302 0.606

PM 0.065 - 0.054 0.054 1.201 0.035

Weighted Total: Ozone 89.243 55.281 53.584 19.094 0.685

NPV Incremental Cost Savin

s ($)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

Purchase Cost n/a - -$2,000 -$4,000 -$5,000 -$13,000

Replacement Cost n/a - $0 $0 $0 -$3,997

Fuel Cost n/a - $10,409 -$5,576 $32,095 $53,905

Maintenance Cost n/a - $9,914 $9,914 $0 $31,475

Total Cost n/a - $18,323 $337 $27,095 $68,383

NPV Emission Reductions (tons)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC n/a - 5.079 6.776 8.233 10.101

CO n/a - 191.349 191.349 504.189 510.101

NOx n/a - 1.548 1.548 -10.112 5.584

PM n/a - 0.011 0.011 -1.136 0.030

Weighted Total: Ozone n/a 33.962 35.659 70.149 88.557

Incremental Cost-Effectiveness ($/ton)

Current Alternative Technologies

Gas-4

LPG CNG Diesel Electric

HC n/a - $3,608 $50 $3,291 $6,770

CO n/a - $96 $2 $54 $134

NOx n/a - $11,839 $218 -$2,680 $12,245

PM n/a - $1,742,065 $32,057 -$23,842 $2,278,120

Weighted Total: Ozone n/a $540 $9 $386 $772

Figure 5

Sample GSEModel Results Report

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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.

4. REFERENCES