Vol. 4
United States Office of Air Quality EPA-450/4-81 -026d £,1,
Environmental Protection Planning and Standards September 1981
Agency Research Triangle Park NC 27711
Air ~
Procedures for Emission
Inventory Preparation
Volume IV: Mobile Sources
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EPA-450/4-81-026d
Procedures for Emission Inventory Preparation
Volume IV: Mobile Sources
by
Monitoring and Data Analysis Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
?ftJn#5'lu£Wfy
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This document is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current EPA contractors
and grantees, and nonprofit organizations - in limited quantities - from
the Library Services Office (MD-35), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; or, for a fee, from the
National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
This report was furnished to the Environmental Protection Agency by GCA
Corporation, Bedford, Massachusetts 01730, in fulfillment of Contract
No. 68-02-3087. The contents of this report are reproduced herein as
received from GCA Corporation. The opinions, findings and conclusions
expressed are those of the author and not necessarily those of the
Environmental Protection Agency.
Publication No. EPA-450/4-81-026d
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NOTICE
The Procedures for Emission Inventory Preparation consists of these
five volumes.
Volume I - Emission Inventory Fundamentals
Volume II - Point Sources
Volume III - Area Sources
Volume IV - Mobile Sources
Volume V - Bibliography
They are intended to present emission inventory procedures and
techniques applicable in State and local air programs, and for con-
tractors and other selected users. The object is to provide the best
available and "state of the art" information. For some areas, however,
the available source information and data either may allow more precise
procedures and more accurate estimation of emissions or may not be amen-
able to the use of these procedures. Therefore, the user is asked to
share his knowledge and experience by providing comments, successfully
applied alternative methods or other emission inventory information
useful to other users of these volumes. Please forward comments to the
U.S. Environmental Protection Agency, Air Management Technology Branch,
(MD-14), Research Triangle Park, NC 27711. Such responses will provide
guidance for revisions and supplements to these volumes.
Other U.S. EPA emission inventory procedures publications:
Procedures for the Preparation of Emission Inventories for
Volatile Organic Compounds, Volume I, Second Edition,
EPA-450/2-77-028, U.S. Environmental Protection Agency,
Research Triangle Park, NC, September 1980.
Procedures for the Preparation of Emission Inventories of
Volatile Organic Compounds, Volume II; Emission Inventory
Requirements for Photochemical Air Quality Simulation Models,
EPA-450/4-79-018, U.S. Environmental Protection Agency,
Research Triangle Park, NC, September 1979.
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CONTENTS
Section Page
1.0 INTRODUCTION 1-1
2.0 OVERVIEW OF THE MOBILE SOURCE CATEGORY 2-1
2.1 Individual Mobile Source Categories 2-1
2.1.1 Off-Highway Vehicles 2-1
2.1.2 Highway Vehicles 2-2
2.1.3 Aircraft 2-2
2.1.4 Railroad Locomotives 2-3
2.1.5 Vessels 2-3
2.2 Inventory Planning 2-4
References for Chapter 2.0 2-4
3.0 EMISSIONS FROM OFF-HIGHWAY SOURCES 3-1
3.1 Inventorying Emissions from Farm Equipment 3-1
3.1.1 Derivation of an Activity Factor 3-2
3.1.2 Calculation of Emissions 3-5
3.1.3 Temporal Resolution 3-8
3.1.4 Inventory Maintenance 3-8
3.2 Inventorying Emissions from Construction Equipment 3-9
3.2.1 Derivation of an Activity Factor 3-10
3.2.2 Calculation of Emissions 3-12
3.2.3 Inventory Maintenance 3-13
3.3 Inventorying Emissions from Industrial Equipment 3-14
3.3.1 Derivation of an Activity Factor 3-14
3.3.2 Calculation of Emissions 3-16
3.3.3 Inventory Maintenance 3-16
3.4 Inventorying Off-Highway Motorcycle Emissions 3-16
3.4.1 Derivation of an Activity Factor 3-17
3.4.2 Calculation of Emissions 3-17
3.5 Inventorying Lawn and Garden Equipment Emissions 3-18
3.5.1 Derivation of an Activity Factor 3-19
3.5.2 Calculation of Emissions 3-19
3.6 Inventorying Emissions from Snowmobiles 3-20
3.6.1 Derivation of an Activity Factor 3-20
3.6.2 Calculation of Emissions 3-20
References for Chapter 3.0 3-21
4.0 EMISSIONS FROM HIGHWAY VEHICLES 4-1
4.1 General Considerations 4-1
4.2 Mobile Source Emission Factors 4-4
4.2.1 MOBILE2 Emission Factor Model 4-5
4.2.2 AP-42 4-6
4.3 Overview of Methods for Compiling Emission Estimates. . . . 4-6
4.4 Method 1—Estimating Emissions for Rural Counties
and Small Urban Areas 4-8
1X1
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CONTENTS (continued)
Section
Page
4.4.1 Data Assessment 4-9
4.4.2 Activity Factor Derivation 4-11
4.4.2.1 Apportionment of Statewide VMT 4-11
4.4.2.2 County VMT Computation 4-16
4.4.2.3 Disaggregation of VMT by Roadway Type . . . 4-16
4.4.2.4 Disaggregation of VMT by Vehicle Type . . . 4-18
4.4.2.5 Special Requirements 4-23
4.4.3 Calculation of Emissions 4-24
4.4.4 Inventory Management 4-27
4.5 Method 2—Estimating Emissions for Urban Areas Using
Manual Procedures Developed by FHWA 4-27
4.5.1 Overview and Scope 4-27
4.5.2 Totally Manual Method for Deriving Emission
Estimates 4-28
4.5.2.1 Derivation of Activity Factors 4-28
4.5.2.2 Calculation of Emissions 4-32
4.5.3 Adapting the Manual Method for Use with MOBILE2. . . 4-36
4.6 Method 3—Estimating Emissions Using Link-Based
Transportation Planning Data 4-37
4.6.1 Overview of Method 3 4-37
4.6.2 Overview of the Transportation Planning Process. . . 4-38
4.6.3 Inventory Development 4-41
4.6.3.1 HWYEMIS1 4-42
4.6.3.2 APRAC-2 4-43
4.6.3.3 Other Transportation Models 4-43
4.7 Method 4—Estimating Emissions Using a Hybrid Modeling
Approach 4-44
4.7.1 Overview of Method 4 4-45
4.7.2 Estimating Travel Related Emissions 4-45
4.7.3 Estimating Trip Related Emissions 4-46
4.7.4 Estimating Vehicle Related Emissions 4-47
4.7.5 Total Emissions . 4-47
References for Chapter 4.0 4-48
5.0 EMISSIONS FROM AIRCRAFT 5-1
5.1 Overview of Inventory Methods 5-2
5.2 Method 1—Use of a Generalized Time-in-Mode Scenario
to Estimate Emissions 5-2
5.2.1 Derivation of an Activity Factor 5-5
5.2.2 Calculation of Emissions 5-8
5.3 Method 2—Analysis of Time-in-Mode to Estimate Emissions. . 5-9
5.3.1 Derivation of an Activity Factor 5-10
5.3.2 Calculation of Emissions 5-17
5.4 Inventory Maintenance 5-18
References for Chapter 5.0 5-19
iv
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CONTENTS (continued)
Section Page
6.0 EMISSIONS FROM RAILROADS 6-1
6.1 Overview of Inventory Methods 6-1
6.2 Method 1—Emission Estimates Based on Fuel Use 6-1
6.2.1 Derivation of the Activity Factor 6-2
6.2.1.1 Apportioning State Fuel Use Data Based
on Track Mileage 6-2
6.2.1.2 Apportioning State Fuel Use Data Based on
Freight Density 6-4
6.2.1.3 Apportioning State Fuel Use Data Based
on Population 6-6
6.2.2 Derivation of Emission Estimates 6-6
6.3 Method 2—Emission Estimates Based on Work Output 6-6
6.3.1 Derivation of the Activity Factor 6-6
6.3.1.1 Data Requirements and Collection 6-7
6.3.1.2 Calculation of the Activity Factor 6-8
6.3.2 Calculation of Emissions 6-11
6.4 Temporal Distribution 6-12
6.5 Emission Forecasts 6-12
References for Chapter 6.0 6-13
7.0 EMISSIONS FROM VESSELS 7-1
7.1 Overview of Methods 7-3
7.2 Estimating Emissions from Recreational Boating Activity . . 7-3
7.2.1 Temporal Distribution of Emissions 7-7
7.3 Emissions from Commercial Vessels 7-7
7.3.1 Fuel Sales Method 7-7
7.3.2 Ship Movement Data Method 7-9
7.3.2.1 Underway Emissions 7-11
7.3.2.2 Dockside Emissions 7-13
7.3.3 Temporal Distribution of Emissions 7-14
References for Chapter 7.0 7-15
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FIGURES
Number Page
4-1 General process for developing highway source emission
estimates for rural counties or small urban areas 4-10
4-2 Link data contained in a Typical Historical Record File 4-40
5-1 Excerpt from Table 7 of Reference 3 showing airport activity
by aircraft type 5-6
5-2 Excerpt of Table 4 from Reference 2 showing airport activity
by aviation category 5-7
5-3 Isopleths (m x 10^) of mean summer morning mixing heights. . . 5-11
5-4 Isopleths (m x 10^) of mean summer afternoon mixing heights. . 5-12
5-5 Isopleths (m x 10^) of mean winter afternoon mixing heights. . 5-13
6-1 Interview record/data file for railroads 6-9
VI
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TABLES
Number Page
3-1 Data Requirements for Calculation of Emissions from Farm
Equipment 3-2
3-2 Average Annual Fuel Throughput for Agrcultural Equipment .... 3-3
3-3 National Construction Equipment Data 3-10
3-4 Annual Work Output Estimates by Type of Equipment 3-11
3-5 Distribution of Diesel-Powered and Gasoline-Powered
Construction Equipment by General Type 3-12
3-6 Annual Work Output Estimates by Type of Engine 3-14
3-7 1974 National Industrial Equipment Population Estimates 3-15
3-8 Composite Emission Factors for Motorcycles 3-18
4-1 Summary of Use and Limitations of Highway Vehicle Emission
Calculation Methods 4-7
4-2 Table VM-2 from Highway Statistics —1979 4-12
4-3 Table M-12 from Highway Statistics—1979 4-14
4-4 Vehicle Categories 4-20
4-5 Distribution of Gasoline and Diesel-Powered Heavy-Duty
Vehicles by Vehicle Configuration 4-22
5-1 Civil Aircraft Categories Used in Emission Inventory
Development 5-3
5-2 Military Aircraft Categories Used in Emission Inventory
Development 5-4
5-3 Composite LTO Cycle Emission Factors for Three General
Aircraft Categories 5-9
5-4 Time-in-Mode Data Used to Develop Generalized Emission
Factors for LTO Cycles 5-14
6-1 Switchyard Mileage Factors (f) 6-4
VII
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TABLES (continued)
Number Page
7-1 Average Emission Factors for Recreational Boats 7-7
7-2 Average Emission Factors for Commercial Motorships by
Waterway Classification 7-10
7-3 Average Emission Factors for Commercial Steamships 7-10
7-4 Fuel Consumption Rates in Gallons per Hour for Vessels
Operating in Port Areas 7-12
7-5 Emission Factors for Various General Categories of Vessels
Operating in Port Areas 7-12
7-6 Emission Factors for Vessels at Dockside 7-14
Vlll
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1.0 INTRODUCTION
A fundamental requirement in the effort to control pollution of any form
is to quantify the emissions being released. This is necessary in the context
of both understanding the relationships between emission characteristics
(rate, location, method of discharge, etc.) and resulting ambient
concentrations, and developing appropriate policies and methods to ensure that
ambient concentrations of the pollutant remain within acceptable limits. With
regard to air pollution, specific requirements are set forth in Title 40, Code
of Federal Regulations, Part 51.321 (40 CFR 51), and in the 1977 Amendments to
the Clean Air Act for the development and maintenance of ongoing programs to
inventory specific pollutant emissions. The requirements of 40 CFR 51 are for
states to prepare and submit annual reports to the U.S. Environmental
Protection Agency (EPA) regarding the emissions of particulate matter, sulfur
oxides, carbon monoxide, nitrogen oxides, and hydrocarbons from point sources
within their boundaries. The Amendments to the Clean Air Act, however,
require the development of "...comprehensive, accurate, and current..."
inventories from all sources of each pollutant for every nonattainment area,
in conjunction with the preparation of revised State Implementation Plans
(SIP). The implication, then, is that significant effort will continue to be
expended on the development and maintenance of emission inventories to meet
the requirements for both technical analysis and administrative reporting.
To assist the states in meeting the requirements for emission inventory
development, a five-volume series has been prepared that describes in detail
many of the technical aspects of the inventory process. This document is the
fourth volume in the series, and focuses on the technical aspects of
inventorying emissions from mobile sources. More specifically, this document
presents an overview of the mobile source category as a whole and identifies
specific methods that can be used to identify and inventory sources, estimate
emissions, and establish and maintain a useful, current mobile source
inventory file. In Chapter 2, the mobile source category is described in
terms of the individual sources included, the significance of each source with
respect to the mobile source category, the relative significance of the entire
mobile source category with respect to other emission sources, and a general
indication of the methods used to develop the inventory. Chapters 3 through 7
present specific methods that can be used to derive emission estimates for
each of the primary mobile source subcategories. These subcategories and the
report chapters in which they are presented are:
Off-highway Vehicles—Chapter 3
Highway Vehicles—Chapter 4
Aircraft—Chapter 5
Railroad Locomotives—Chapter 6
Vessels—Chapter 7
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The other volumes in this Procedures for Emission Inventory Preparation
series are:
Volume I—Emission Inventory Fundamentals
Volume II—Point Sources
Volume III—Area Sources
Volume V—Bibliography
Volume I is a guide to the managerial and technical aspects of the
emission inventory. It outlines the informational sources available, methods
of estimating emissions, data validation and quality assurance techniques as
well as procedures to maintain and update the inventory. Also included are a
detailed analysis of the manpower and resources required to derive each
component of an emission inventory, and a comprehensive glossary.
Volume II assists the user in the identification of point sources,
collection of data, calculation of emissions and data presentation. It
establishes standardized methods and procedures so that the user can apply
these methods to develop a point source data base.
Volume III outlines the methods of collecting and handling emission data
from sources too small and/or too numerous to be surveyed individually—
collectively known as area sources. Procedures are presented which will
assist the user in identifying area source categories and important reference
material which can be used to determine the activity levels associated with
area source categories. Emission factors, emission calculations, pollutant
allocation and projection techniques, and methods of data presentation are
detailed to assist in the preparation and maintenance of the emission
inventory of area source categories.
Volume V presents an extensive listing of reference material currently
available in the literature which will assist the user in the development of
the emission inventory. A concise abstract is provided for each reference
cited, outlining the pertinent emission inventory information.
1-2
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2.0 OVERVIEW OF THE MOBILE SOURCE CATEGORY
An inventory of pollutant emission sources should classify sources into
two major categories—point sources and area sources. The point source
category is described in detail in Volume II of this series.^ The area
source category is described in detail in Volume III of this series.
Mobile sources are a subcategory within the area source category of pollutant
emission sources. However, the procedures for preparing and maintaining an
inventory of emissions from mobile sources are presented herein, as a separate
document in this series, because the procedures are uniquely different from
those for other area source subcategories and because the mobile source
inventory of emissions will represent a major portion of the total emissions
of NOX, HC and CO in any comprehensive emission inventory.
The mobile sources, for which inventory and emission calculation
procedures are presented in this document, are off-highway vehicles and
equipment, highway vehicles, aircraft, railroad locomotives, and vessels. The
procedures are for calculation of tailpipe emissions and evaporative HC
emissions (from the crankcases and vehicle fuel tanks) from these five mobile
source categories. The emissions that result from tire wear, travel over
roads or other surfaces, or vehicle fueling can be calculated from the
procedures in Volume III of this series^ and are specifically excluded from
consideration in this document.
2.1 INDIVIDUAL MOBILE SOURCE CATEGORIES
The nature of mobile sources requires an understanding of the sources
themselves and their activity before any attempt is made to calculate their
emissions. The five mobile source categories are briefly characterized in
this section.
2.1.1 OFF-HIGHWAY VEHICLES
This mobile source category includes a diverse set of source types. The
movement of sources in this category occurs on surfaces other than the public
highways. The total off-highway vehicle population can be characterized by
six individual categories. They are:
(1) Farm equipment,
(2) Construction equipment,
(3) Industrial machinery,
(4) Motorcycles,
(5) Lawn and garden equipment, and
(6) Snowmobiles.
2-1
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These are difficult categories to inventory because little data are
available to determine their size or the operating characteristics of the
sources in them. Chapter 3 of this document provides procedures for
inventorying and estimating emissions from these categories.
2.1.2 HIGHWAY VEHICLES
This mobile source category includes all vehicles registered to use the
public roadways. The predominant source in this category is the automobile.
Trucks and buses are also included in this category. The total highway
vehicle population can be characterized by eight individual vehicle-type
categories. They are:
(1) Light-Duty Gasoline-Powered Vehicles (LDGV);
(2) Light-Duty Gasoline-Powered Trucks, up to 6000 Ib gross vehicle
weight (LDGT1);
(3) Light-Duty Gasoline-Powered Trucks, 6000 to 8500 Ib gross vehicle
weight (LDGT2);
(4) Heavy-Duty Gasoline-Powered Vehicles (HDGV);
(5) Light-Duty Diesel-Powered Vehicles (LDDV);
(6) Light-Duty Diesel-Powered Trucks (LDDT);
(7) Heavy-Duty Diesel-Powered Vehicles (HDDV); and
(8) Motorcycles (MC).
Automobiles will be classified into either category (1) or (5). Buses
should be classified in categories (2), (3), (4), (6) or (7) depending on
their gross vehicle weight and fuel type.
Numerous characteristics for each vehicle-type category are necessary
before emissions can be calculated. These characteristics include, among
others, vehicle, type, age distribution, annual mileage by vehicle type and
age, and average speed by vehicle type. Chapter 4 of this document presents
detailed procedures for identifying and using these and other key
characteristics to calculate emissions.
2.1.3 AIRCRAFT
This mobile source category includes all types of aircraft whether
civilian, commercial, or military. Emissions from idling, taxiing, and during
landings and takeoffs are included. Landing and takeoff cycle (LTO) emissions
are those that occur between ground level and an altitude of about 3000 feet.
The larger civil and commercial airports with continuously manned control
towers maintain records of LTO cycles by type of aircraft as part of their
2-2
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standard operating procedure. Smaller airports also maintain these records to
the extent that their control towers are manned or landing fees are recorded.
Difficulty may be encountered in obtaining data on military aircraft
operations at military airports.
The EPA has compiled a complete set of emission factors for the different
types of aircraft operating in the different modes (i.e., idle, taxi, LTO).
Chapter 5 of this document provides instruction on the methods of inventorying
and calculating emissions from this mobile source category.
2.1.4 RAILROAD LOCOMOTIVES
This mobile source category includes all fossil fuel-fired locomotive
engines operated on railways. The quantity of fuel used by locomotives and
the size, in horsepower, of the locomotives are necessary data for emission
calculations. Chapter 6 of this document provides detailed methods for
calculating emissions from this mobile source category.
2.1.5 VESSELS
This mobile source category includes all sizes of self-propelled
vessels. Two primary categories are considred—pleasure craft and commercial
vessels. The commercial category includes all military and civilian vessels.
For pleasure craft, the quantity of fuel, gasoline and diesel, used is applied
to emission factors to yield emission estimates. Two subcategories of
pleasure craft are considered—outboard and inboard. In general, direct
estimates of fuel used for pleasure boating are not available. The procedures
discussed in this document are based largely on deriving fuel use estimates as
a function of the boat population and the water facilities available for use
by these craft.
Commercial vessels include all sizes and types of boats, both military
and civilian, from small fishing vessels to the largest supertankers. Three
subcategories are considered, including:
Motorships,
Steamships, and
Others.
Motorships are powered by diesel engines and range in size from the
smallest fishing boat to the largest freighters and tankers.
Steamships are powered by steam turbines. Steam is generated in boilers
by burning any of several types of fuel. Coal is used in a few vessels while
residual and distillate fuel oils are the dominant fuels used.
Emissions from commercial vessels are computed for "in port" operations
(entering and leaving the port, docking and maneuvering) and power generation
2-3
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while the vessel is dockside. The required data for emission calculation
include the number of vessels by type entering and leaving the port, and the
average number of days that the vessel remains in port. Chapter 7 of this
document details inventory and emission calculation procedures for this mobile
source category.
2.2 INVENTORY PLANNING
Before any efforts are expended by personnel to collect the data inputs
necessary to complete an emission inventory by the methods in this document,
it is essential that the entire inventory effort be thoroughly planned. The
planning and management aspects of emission inventory preparation are
presentee! in Volume I of this series. Additional instructions on inventory
planning are contained in References 4 and 5.
References for Chapter 2.0
1. Procedures for Emission Inventory Preparation—Volume II: Point Sources,
EPA-450/4-81~026b, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, NC, September
1981.
2« Procedures for Emission Inventory Preparation—Volume III: Area Sources,
SPA-450/4-81-026c, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, NC, September
1981.
-*• Procedures for Emission Inventory Preparation—Volume I: Emission
Inventory Fundamentals, EPA-450/4-81-026a, Office of Air Quality Planning
and Standards, U.S. Environmental Protection Agency, Research Triangle
Park, NC, September 1981.
4. Procedures for the Preparation of Emission Inventories for Volatile
Organic Compounds—Volume I (Second Edition), EPA-450/2-77-028, Office of
Air Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, NC, September 1980.
5. Procedures for the Preparation of Emission Inventories for Volatile
Organic Compounds—Volume II: Emission Inventory Requirements for
Photochemical Air Quality Simulation Models, EPA-450/4-79-018, Office of
Air Quality Planing and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, NC, September 1979.
2-4
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3.0 EMISSIONS FROM OFF-HIGHWAY SOURCES
Off-highway sources include motorized equipment and vehicles that
normally are not operated on public highways to provide transportation
service. There are six categories of off-highway sources, They are:
Farm equipment,
Construction equipment,
Industrial machinery,
Motorcycles,
Lawn and garden equipment, and
Snowmobiles.
A problem inherent in preparing inventories of off-highway source
emissions is the lack of definitive data from which estimates of source
activity can be made. Generally, records are maintained at the state level of
motor fuel used by exempt vehicles, which means any vehicle (actually, any
vehicle or piece of equipment or machinery) for which fuel taxes do not
apply. Included are all types of vehicles, equipment, and machinery included
in the off-highway emissions source category, as well as many public use
vehicles (vehicles owned by state or local government agencies, etc.). Also,
reimbursements for fuel used by vehicles involved in interstate commerce are
also reflected in the figures for nontaxed fuel sales. Most state agencies
responsible for maintaining this information aggregate it so that there is no
way to separate the quantities of fuel used by individual categories of exempt
users, such as construction and agricultural applications.
An additional problem in terms of data concerns the fact that there is
very little information available regarding either the population of vehicles,
machinery or equipment, or the utilization of individual types of vehicles and
equipment contained in the off-highway category. As a result, the methods
available to develop inventories of emissions from these sources rely
extensively on assumptions and general application of a very limited amount of
empirical data.
This section presents methods for deriving an inventory of emissions
produced by sources within the off-highway vehicle category. Each of the six
source categories is presented separately.
3.1 INVENTORYING EMISSIONS FROM FARM EQUIPMENT
The two types of sources within the farm equipment category are tractors
and all other motorized equipment. Tractors account for most of the emissions
produced from farm equipment. The primary types of equipment other than
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tractors are combines, balers, harvesters, and general purpose machines. Of
interest in terms of emissions is the distribution of gasoline and diesel
equipment within each equipment category.
Data are available from the U.S. Department of Commerce, Bureau of the
Census, concerning the number of tractors and other specific types of farm
equipment in each county in the U.S. and the typical utilization rates
associated with each item of equipment. This information is reported in a
document entitled Census of Agriculture, *• which is published every 4 years.
The method presented here for inventorying emissions from farm equipment
derives an activity factor that identifies the quantity of fuel used by each
type of equipment during the inventory year and applies an emission factor
that defines the quantity of each type of pollutant produced per gallon (or
liter) of fuel burned.
Table 3-1 lists the data elements needed for the method described in this
section* Sources of these data are also included in the table. However,
should an agency have a different source that can supply the same data, that
alternative source could be used.
TABLE 3-1. DATA REQUIREMENTS FOR CALCULATION OF EMISSIONS
FROM FARM EQUIPMENT
Description
Units
Source
Identifier
Equipment population Number of each type
of equipment
Acres cultivated
Fuel usage by
equipment type
Pollutant emission
factors
Acres
Gallons/year
per piece of
equipment
Pounds/1000 gallons
of fuel
Census of
Agriculture
State or County
Agricultural
Extension Service
U.S. EPA documents2
Table 3.2.6-2, AP-423
ACR
EF
3.1.1 DERIVATION OF AN ACTIVITY FACTOR
The basic activity factor used to estimate emissions from farm equipment
is the quantity of fuel burned by tractors and other motorized equipment
during the inventory year. Separate estimates are required for diesel and
gasoline use by each type of equipment.
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Statistics concerning the county populations of various agricultural
equipment items are available in Census of Agriculture. •*• These statistics
include the number of tractors and other major items of equipment on farms in
each county in the U.S. However, the population statistics alone do not
provide an indication of the relative agricultural activity from year to year;
therefore, a procedure that will provide this information is required.
The number of acres cultivated are used to indicate agricultural
activity. These data are available from county or state agricultural
extension services. It is necessary that the farm equipment population
figures and the acres cultivated figures be for the same year.
Finally, the average annual quantity of fuel used per individual piece of
farm equipment is required. These data are available from References 2 and 4,
and are presented here as Table 3-2.
TABLE 3-2. AVERAGE ANNUAL FUEL THROUGHPUT FOR AGRICULTURAL EQUIPMENT
Equipment item
Average annual fuel use .(gallons per year)
Gasoline Diesel fuel
Combines
Balers
Harvesters
General purpose machines
Tractors
166
56
281
176
663
107
36
180
97
1460
The data presented in Table 3-2 and the study area farm equipment
population determined from Census of Agriculture^ are used to calculate an
estimate of fuel used by farm equipment during the base year represented by
the equipment census data. These fuel use estimates for the five equipment
items shown in Table 3-2 are:
and
5
£
(N.,
id
(N.
(3-1)
R. )
(3-2)
3-3
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where Qj = total annual quantity of diesel fuel used, in gallons, by all
equipment types during the base year;
N£(j = number of item i equipment in the study area that are diesel
powered;
R£,-[ = annual diesel fuel use rate, in gallons per year, for equipment
type i, from Table 3-2;
Qg = total annual gasoline use, in gallons, by all equipment types
during the base year;
N.JCT = number of item i equipment in the study area that are gasoline
powered;
R£S = annual gasoline use rate, in gallons per year, for equipment
type i, from Table 3-2.
The total base year fuel quantities are then used together with the data
on acreage of cultivated land to derive a factor describing the fuel use per
acre cultivated:
fb = [(1.4)(Qd) + (Q )] / AC (3-3)
where f^ = fuel use per cultivated acre factor for base year b;
Q^ = total diesel fuel used, in gallons, during base year b, from
Equation (3-1); and
Qg = total gasoline used, in gallons, during base year b, from
Equation (3-2);
ACRjj = total acres cultivated in the study area during base year b.
In Equation (3-3), the quantity of diesel fuel, Q^, is increased by a factor
of 1.4 to normalize the quantities of diesel and gasoline on an equivalent
energy basis. This equation is then transformed to:
[(1.4)(Q.) + (Q )] = (f, ) x ACR (3-4)
d g y b y
where [(1.4)(Q.) + (Q ) ] = the absolute value of the combined quantities of
diesel and gasoline fuel used during inventory
year y;
3-4
-------
f = fuel use per cultivated acre factor derived for
base year b, in Equation (3-3); and
ACR = total acres cultivated in the study area during
^ inventory year y.
The individual quantities Q
3-5
-------
where ftrad
Ntrad
Rid
= proportioning factor for diesel tractors;
= number of diesel tractors in the population;
= fuel use rate, in gallons per year, for diesel equipment
type i, from Table 3-2;
N£
-------
fothd
Qtragy
= proportioning factor from Equation (3-6);
= quantity of gasoline, in gallons, used by tractors during
inventory year y;
= total quantity of gasoline, in gallons, used by farm
equipment during inventory year y;
= proportioning factor from Equation (3-7);
= quantity of gasoline in gallons, used by other types of farm
equipment during inventory year y; and
= proportioning factor from Equation (3-8).
The solution of Equations (3-9) through (3-12) provides the annual fuel
usage, during the inventory year, of farm tractors (diesel and gasoline) and
other farm equipment (diesel and gasoline). The annual emissions (E) are now
calculated by multiplying the annual fuel usages (Q) by the emission factors
(EF) for each pollutant and equipment type from Table 3.2.6-2 of AP-42,
according to the following equations:
rtrag
Qothgy
trady,j trady trad,j
— r\ „ "FT?
othdy,j vothdy othd,j
E_ . = Q x EF
tragy,j xtragy trag,j
E -u • = Q u x EF , .
othgy,j ^othgy othg,j
(3-13)
(3-14)
(3-15)
(3-16)
where Etracjy ; = total emissions of pollutant j, in pounds (kilograms) per
year, from diesel-powered farm tractors in inventory year
y;
Qtrady = quantity of diesel fuel used, in thousands of gallons,
during inventory year y, by diesel farm tractors, from
Equation (3-9);
EFtrad,j = emission factors, in pounds (kilograms) of pollutant j per
thousand gallons of diesel fuel used by farm tractors;
^othdy,j = total emissions of pollutant j, in pounds (kilograms) per
year, from other diesel-powered farm equipment in
inventory year y;
Qothdy = quantity of diesel fuel used, in thousands of gallons,
during inventory year y, by other diesel farm equipment,
from Equation (3-10);
3-7
-------
EFothd,j
Qtragy
EF
trag.j
= emission factors, in pounds (kilograms) of pollutant j per
thousand gallons of diesel fuel used by other farm equipment;
= total emissions of pollutant j, in pounds (kilograms) per
year, from gasoline-powered farm tractors in inventory
year y;
= quantity of gasoline used, in thousands of gallons, during
inventory year y, by gasoline farm tractors, from Equation
(3-11);
= emission factors, in pounds (kilograms) of pollutant j per
thousand gallons of gasoline used by farm tractors;
Qothgy
i = total emissions of pollutant j, in pounds (kilograms) per
year, from other gasoline-powered farm equipment in
inventory year y;
= quantity of gasoline used, in thousands of gallons, during
inventory year y, by other gasoline farm equipment, from
Equation (3-12); and
-i = emission factors, in pounds (kilograms) of pollutant j per
thousand gallons of gasoline used by other farm equipment.
3.1.3 TEMPORAL RESOLUTION
The preceeding calculations estimated the total emissions from farm
equipment for an entire year. It will frequently be necessary to determine
what fraction of the yearly emissions are actually emitted on a seasonal
basis, a daily basis, or an hourly basis. The amount of resolution (seasonal,
daily, hourly) should be decided before the data gathering is initiated.
Agricultural activity has very pronounced seasonal variations. Peaks
occur during planting and harvesting with moderate activity occurring during
interim periods. Planting activity may be concentrated during the daylight
hours while harvesting may be an around-the-clock activity. The majority of
activity could be expected to occur Monday through Saturday with minimal
activity on Sunday.
The precise variations in activity are difficult to quantify. However,
agricultural extension service and farm bureau personnel will be able to
supply information relative to when crops are planted and harvested and the
length of time these activities require. Discussions with these agencies'
personnel will supply sufficient information for a quantification of the
distribution of activity.
Temporal resolution factors are expressed as percentages of yearly
activity or emissions. When the temporal resolution factors are multiplied by
the annual emissions, the quantity of annual emissions that occur seasonally,
3-i
-------
daily, or hourly are obtained. It is assumed that activity is directly
proportional to emissions. The method for calculating temporal factors when
information is obtained from extension service or farm bureau personnel is
based on methods and assumptions available in the literature.^»^ v
Temporal allocation of annual emissions is often conducted prior to a
modeling study. The actual data elements from the procedure that would be
used by an analyst will depend on the purpose of the temporal resolution.
Information on the computerization of temporal allocation factors can be found
in The Airshed Model Data Handling System User's Guide.^
3.1.4 INVENTORY MAINTENANCE
The data required to update an inventory of farm equipment emissions are
listed in Table 3-1. The calculations necessary are those presented
previously in subsections 3.1.1 and 3.1.2.
Data on the number of cultivated acres are updated annually by
agricultural extension services. They should be contacted to determine the
latest year for which data are available. Census of Agriculture*- data are
updated every 4 years (1978 data were published in 1981). The emission
factors in AP-42-* are updated periodically as new data become available.
The Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC, or the U.S. Environmental
Protection Agency Library at Research Triangle Park, NC, can be contacted to
insure that the emission factors being used are the most current available.
As with all source categories, the analyst should properly document all
data methods and assumptions used, as well as the results of the inventory.
Reporting format and documentation should reflect the requirements specified
in either state or Federal guidance documents. Additional instruction on
reporting formats and documentation are included in Volume I of this series.^
3.2 INVENTORYING EMISSIONS FROM CONSTRUCTION EQUIPMENT
A wide variety of equipment is used in the construction industry. There
is no standard classification system by which construction equipment are
described, although the general function of the equipment and the available
horsepower are parameters used in classification structures. General
functional categories include bulldozers, power shovels, scrapers, haulers,
and motor graders. Other, more descriptive categories, such as tracked
bulldozers, wheeled dozers, and tracked power shovels can also be used.
With regard to inventorying emissions produced by construction equipment,
a primary factor involved relates to the annual hours of use of this equipment
during the inventory year. The hours of use statistic provides a basis for
deriving the activity factor, which, once determined, is applied to an
emission factor to yield emissions. The specific methodology is presented in
this section.
3-9
-------
3.2.1 DERIVATION OF AN ACTIVITY FACTOR
The activity factor used to inventory emissions from construction
equipment is the utilization, in horsepower-hours, of each piece of equipment
during the inventory year. Since direct estimates of equipment use for the
construction industry are not available, surrogate data must be used to derive
the estimates.
The surrogate data consist of national statistics concerning the
construction equipment (population by type and horsepower), and construction
industry employment statistics for both the state and nationwide. National
population data have been developed for various categories of equipment, as
shown in Table 3-3.
TABLE 3-3. NATIONAL CONSTRUCTION EQUIPMENT DATA
Type of equipment
Population Average horsepower Usage (hr/yr)
Tracklaying tractors
Tracklaying loaders
Motor graders
Scrapers
Off -highway trucks
Wheel loaders
Wheel tractors
Rollers
Wheel dozers
Miscellaneous
197,000
86,000
95,300
27,000
20,800
134,000
437,000
81,600
2,700
100,000
120
65
90
475
400
130
75
75
300
40
1050
1100
830
2000
2000
1140
740
740
2000
1200
Source: References 8 and 9.
These equipment populations are distributed to the study area on the basis of
employment and population. Specifically, the state and national employment
statistics for heavy construction [Standard Industrial Classification (SIC) 16]
are determined from References 10 and 11. Population data are required for
both the state and the study area. This information is available from a
variety of sources at both the state and county level; for example, in
planning and economic development offices, department of labor statistics
(state), etc. The entire data set is then used to estimate the total number
of each type of equipment listed in Table 3-3 used in the study area, from:
N . = (N .) x (E / E ) x (POP / POP )
ci ni cons conn c s
(3-17)
3-10
-------
where Nc£ = number of pieces of equipment type i used in the county;
Nni = number of pieces of equipment of type i in the national
inventory, from Table 3-3;
Econs = employment in construction, SIC 16, statewide;
Econn = employment in construction, SIC 16, nationally;
POPr
POPc
= county population; and
= state population.
Data presented in Reference 8 concerning average horsepower, usage, and
load cycle are multiplied together to develop an estimate of the annual work
output, in horsepower-hours, for each piece of equipment in the various
categories. These work output estimates are shown in Table 3-4.
TABLE 3-4. ANNUAL WORK OUTPUT ESTIMATES BY TYPE OF EQUIPMENT
Type of equipment
Annual work output (hp-hr)
Tracklaying tractors
Tracklaying loaders
Motor graders
Scrapers
Off-highway trucks
Wheel loaders
Wheel tractors
Rollers
Wheel dozers
Miscellaneous
84,400
21,400
22,400
617,500
480,000
96,300
27,700
16,600
390,000
14,400
Source: GCA calculations,
The data from Table 3-4 and the results of Equation (3-17) are used to derive
an estimate of horsepower-hours of utilization for each type of equipment from:
HPRS. = N . x AWO.
i ci i
(3-18)
3-11
-------
where HPRSi = horsepower-hours of utilization of type i equipment;
Nc£ = number of pieces of equipment type i used in the county, from
Equation (3-17); and
AWO£ = annual work output, in horsepower-hours, for each piece of
type i equipment, from Table 3-4.
3.2.2 CALCULATION OF EMISSIONS
Emissions are computed using the total annual work output for each type
of equipment estimated in Equation (3-18) and applying an emission factor from
AP-42.3 Prior to calculating emissions, however, the HPRSf values must be
apportioned by fuel type. Data contained in Reference 8 provide the basis for
this apportionment, as shown in Table 3-5.
TABLE 3-5. DISTRIBUTION OF DIESEL-POWERED AND GASOLINE-POWERED
CONSTRUCTION EQUIPMENT BY GENERAL TYPE
Type of equipment Percent diesel Percent gasoline
Tracklaying tractors
Tracklaying loaders
Motor graders
Scrapers
Off-highway trucks
Wheel loaders
Wheel tractors
Rollers
Wheel dozers
Miscellaneous
100
100
92.4
100
100
70.0
84.6
30.8
100
75.0
-
-
7.6
-
-
30.0
15.4
69.2
-
25.0
Source: Reference 8.
The percentages of diesel-powered and gasoline-powered equipment are applied
to HPRS£ to obtain horsepower-hours by type of equipment and by fuel type
used. These data are used with emission factors, specified in terms of grams
of pollutant per horsepower-hour, from Tables 3.2.7-1 and 3.2.7-2, in AP-42.^
Emission estimates for each type of diesel-powered and gasoline-powered
equipment are calculated from:
3-12
-------
£_,..= HPRS. x D_. x EF,. .
di,j i di di,j
E . . = HPRS. x D . x EF . .
(3-19)
(3-20)
where
HPRS
EFdi,j
Egi,j
Dgi
EF
gi.J
= annual emissions, in grams, of pollutant j from all diesel-
powered equipment type i in study area;
= horsepower-hours of utilization of type i equipment, from
Equation (3-18);
= percent of equipment type i that is diesel powered, from
Table 3-5;
= emission factor for pollutant j, in grams per
horsepower-hour, from diesel-powered equipment type i, from
Table 3.2.7-1 of AP-42;3
= annual emissions, in grams, of pollutant j from all
gasoline- powered equipment type i in study area;
= percent of equipment type i that is gasoline powered, from
Table 3-5; and
= emission factor for pollutant j, in grams per
horsepower-hour, from gasoline-powered equipment type i,
from Table 3.2.7-2 of AP-42.3
3.2.3 INVENTORY MAINTENANCE
The methodology presented in this section is based heavily on data
developed for a report published in 1973.^ That report developed its data
from a large number of different references. Information available, both then
and now, on specific construction equipment population data, horsepower, usage
or load factors is very limited. The method employed to estimate values for
these factors in the 1973 report is lengthy." Unless an agency can readily
locate more current data of this type, specific for the area under its
jurisdiction, the data presented here can be used.
The data on national and county employment and population used in
Equation (3-17) are updated periodically. The sources of these data should be
contacted to insure that the most current figures are used in updating the
emission inventory. ^>H
AP-423 emission factors are also periodically updated. Consult
subsection 3.1.4 of this chapter for a source of updated factors.
3-13
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3.3 INVENTORYING EMISSIONS FROM INDUSTRIAL EQUIPMENT
Industrial equipment includes a variety of types and sizes of machinery.
Examples of the types of equipment included in this category are forklifts,
mobile refrigeration units, auxiliary engines for hydraulic pump service on
garbage trucks and other large vehicles, generator and pump service for
utilities, airports, and state maintenance organizations, logging, mining,
quarrying, oil field operations, and portable well-drilling equipment. The
majority of these equipment types are found at companies operating in Standard
Industrial Classification (SIC) major groups 10 through 14, 20 through 39, 50
and 51.
Very few data exist regarding specific types of equipment associated with
different industries. In terras of developing emission inventories, an
assumption is made that the equipment-type distribution inherent in the
emission factor data developed by EPA is appropriate for the particular
industries in the area being inventoried. The method used for inventorying
emissions from industrial equipment involves deriving an estimate of the total
utilization in horsepower-hours of industrial equipment during the inventory
year, and applying an emission factor defined in terms of quantity of
pollutant produced per gallon of fuel consumed. This is very similar to the
method used for construction equipment.
3.3.1 DERIVATION OF AN ACTIVITY FACTOR
National statistics regarding the population of industrial equipment have
been developed indicating the total number of heavy-duty diesel, heavy-duty
gasoline, and light-duty gasoline engines used in industrial
applications. ' The average size of these three categories of engines
tends to be around 125 horsepower for diesels, 78 horsepower for heavy-duty
gasoline, and 4 horsepower for light-duty gasoline engines; and the duty cycle
(the ratio of the power actually used divided by the power available) of these
engines is, on the average, about O.3.* With this information, values of
annual work output for each of the three categories of engines have been
produced. These values are shown in Table 3-6.
TABLE 3-6. ANNUAL WORK OUTPUT ESTIMATES BY TYPE OF ENGINE
Annual work output
Engine category (hp-hr)
Heavy-duty diesel 22,500
Heavy-duty gasoline 7,000
Light-duty gasoline 360
Source: Reference 8.
3-14
-------
Engine population based on national statistics is shown in Table 3-7.
TABLE 3-7. 1974 NATIONAL INDUSTRIAL EQUIPMENT
POPULATION ESTIMATES
Engine category Estimated population
Heavy-duty diesel 417,000
Heavy-duty gasoline 990,000
Light-duty gasoline 2,105,400
Source: Reference 8.
National engine population data are then apportioned to the area being
inventoried. This is done by applying employment statistics as shown in
Equation (3-21). That equation indicates apportionment to a county by using
county employment data. Apportionment to any other geographic or political
area can be accomplished by applying employment data specific to that area
instead of county data in Equation (3-21):
N . = (N .) x (EMP. , / EMP. , ) (3-21)
ci ni indc indn
where Nc£ = number of type i engines in the county;
Nn£ = number of type i engines nationally, from Table 3-6;
EMPindc = county employment in industry, SIC codes 10-14, 20-39, and
50-51; and
EMPindn = national employment, in industry, SIC codes 10-14, 20-39,
and 50-51.
Employment data required in Equation (3-21) are obtained from References 10
and 11. The activity factor, work output, is calculated as:
HPRS. = N . x AWO. (3-22)
where HPRS^ = horsepower-hours of utilization of type i equipment;
Nci = number of pieces of equipment type i used in the county, from
Equation (3-21); and
= annual work output, in horsepower-hours, for each piece of
type i equipment, from Table 3-6.
3-15
-------
3.3.2 CALCULATION OF EMISSIONS
Emissions are computed using the total annual work output, HPRS^, for
each type of industrial engine from Equation (3-22) and applying an emission
factor from AP-42.3 When calculating emissions, the HPRS^ values for
heavy-duty and light-duty gasoline engines must be summed because the emission
factors in AP-42 do not differentiate between these engines. Emissions from
diesel and gasoline industrial equipment are calculated from:
E, . = HPRS, x
d,J d
E . = (HPRSt + HPRS, ) x EF .
g,J "8 lg g,J
(3-23)
(3-24)
where E
-------
3.4.1 DERIVATION OF AN ACTIVITY FACTOR
The activity factor for off-highway motorcycle use is vehicle-miles-
traveled (VMT). To derive an estimate of VMT by off-highway motorcycles,
several assumptions are required. Since motorcycles used primarily for
off-highway activity are not always registered, data may not exist on the
population of these vehicles. The assumption used is that the total
off-highway motorcycle VMT is a function of the total number of motorcycles
registered for on-highway use. Specifically, this relationship is:
VMTMC ,„ = MCREG x 700 miles/year (3-25)
offhwy.a a J
where VMTMCoffhWy a = off-highway vehicle-miles traveled annually in area
a, and
MCREGa = number of motorcycles registered in area a.
The usage factor of 700 miles per year in Equation (3-25) is from Reference 4.
Motorcycle registration data for the study area are obtained from the
state motor vehicle registry. If county-specific data are not available,
state level data can be apportioned based on population, as:
MCREG = (POP /POP ) x MCREG (3-26)
a a s s
where MCREGa = number of motorcycles registered in area a,
POPa = population of area a,
POPS = population of the state, and
MCREGS = number of motorcycles registered statewide.
3.4.2 CALCULATION OF EMISSIONS
Emission factors for motorcycles are provided in AP-42, Table 3.1.7-1.-*
Separate factors are provided for 2-stroke and 4-stroke engines in grams per
mile. Composite factors, based on the national distribution of 38 percent
2-stroke and 62 percent 4-stroke, are provided here in Table 3-8.
3-17
-------
TABLE 3-8. COMPOSITE EMISSION FACTORS FOR MOTORCYCLES
Composite
emission factors
Pollutant (g/mi)
Carbon monoxide
Hydrocarbons
Exhaust
Crankcase
Evaporative
Nitrogen oxides
Particulates
Sulfur oxides
Aldehydes
31
7.9
0.23
0.36
0.19
0.154
0.028
0.071
Source: GCA calculations,
Emissions are computed as:
E . = EF. x VMTMC .._ (3-27)
mc,j j offhwy,a
where E^c j = total annual emissions of pollutant j, in pounds
(kilograms) per year, from off-highway motorcycle use;
EF; = emission factor in pounds (kilograms) per mile, for
pollutant j; and
VMTMCoff].1Wy a = off-highway vehicle-miles traveled annually in
area a.
3.5 INVENTORYING LAWN AND GARDEN EQUIPMENT EMISSIONS
Included in this category are lawnmowers, lawn and garden tractors,
tillers, edgers, and snowthrowers. These machines are minor contributors to
air pollutant emissions. Emissions from lawn and garden equipment are
calculated by apportioning national fuel use to the local level and applying
emission factors from AP-42, Table 3.2.5-1.^
3-18
-------
3.5.1 DERIVATION OF AN ACTIVITY FACTOR
The activity factor used for calculating emissions from lawn and garden
equipment is the quantity of fuel used annually by this category. To do this,
the statewide total off-highway fuel use data from the National Emissions Data
System (NEDS) Fuel Use Report^ are required. The national average of
off-highway fuel used in lawn and garden equipment is 20 percent . " » ^ It
is therefore assumed that 20 percent of the statewide use is used by these
machines. Statewide fuel use is then apportioned to the county or planning
area level on the basis of housing density, as follows:
) (3-28)
where QLQ a = quantity of fuel, in gallons, used by lawn and garden
equipment in area a;
QSOH = quantity of fuel, in gallons, used for off-highway
purposes in the state;
SDUa = number of single dwelling units in area a, from
Reference 15; and
SDUS = number of single dwelling units in the state, also
from Reference 15.
3.5.2 CALCULATION OF EMISSIONS
The quantity of fuel used by lawn and garden equipment is used with an
emission factor from Table 3.2.5-1 of AP-42^ to calculate emissions. This
table lists separate emission rates for 2-cycle and 4-cycle engines. National
data-*-2 indicate that 93 percent of small engines used for lawn and garden
equipment are 4-cycle. This distribution can be applied directly to the fuel
use derived in Equation (3-28) to estimate the quantity of fuel used by
4-cycle lawn and garden equipment. Tue remainder of the total fuel is assumed
to be used by 2-cycle equipment.
Emissions are computed as:
E . = (0.93) x (Q ) x (EF .) + (0.07) x (Q ) x (EF9 .) (3-29)
i_.(j } a j LU , a 4 , j LG , a 2. , j
where ^-i,G,aj ~ total emissions, in pounds (kilograms) of pollutant j
produced by lawn and garden equipment in area a;
QLG,a = quantity of fuel, in gallons, used by lawn and garden
equipment in area a, from Equation (3-28);
3-19
-------
= emission factor, in pounds (kilograms) of pollutant j per
gallon of fuel burned, for 4-cycle lawn and garden equipment,
from Table 3.2.5-1 of AP-42;3 and
= emission factor, in pounds (kilograms) of pollutant j per
gallon of fuel burned, for 2-cycle lawn and garden equipment,
from Table 3.2.5-1 of AP-42.3
3.6 INVENTORYING EMISSIONS FROM SNOWMOBILES
Snowmobiles are a relatively minor source of emissions and are of concern
in areas such as the northeast and northern midwest portions of the U.S.
These areas account for almost 90 percent of the snowmobile use in the U.S.3
3.6.1 DERIVATION OF AN ACTIVITY FACTOR
The activity factor for snowmobiles is the number of individual
snowmobiles in use in the study area. Factors concerning the average number
of hours of use per snowmobile, the hourly fuel consumption rate, and the
emissions characteristics were used by EPA to derive a set of emission factors
based on emissions per snowmobile.
The activity factor, that is, the study area snowmobile population, is
obtained from the state agency responsible for maintaining registration
statistics. If county-specific registration data are not available, statewide
data can be apportioned from:
SNBLRG = (SNBLRG ) x (RURPOP /RURPOP ) (3-30)
a s as
where SNBLRGa = snowmobile population for area a;
SNBLRGS = statewide snowmobile population from registration data;
RURPOPa = rural population of area a, from Reference 16; and
RURPOPS = rural population of the state, from Reference 16.
3.6.2 CALCULATION OF EMISSIONS
Emissions from snowmobiles are estimated using annual per-unit emission
factors found in AP-42, Table 3.2.8-1.3 These factors are based on an
average of 60 hours of operation per year and fuel consumption of 0.94
Emissions are calculated as:
3-20
-------
E un . = (EF.) x (SNBLRG ) (3-31)
snbl,aj j a
where Esnbi ai = total emissions of pollutant j, in pounds (kilograms) per
year, produced by snowmobiles in area a;
EF; = emission factors, in pounds (kilograms) of pollutant j per
year per snowmobile; and
SNBLRGa = snowmobile population in area a, from Equation (3-30).
References for Chapter 3.0
1. 1978 Census of Agriculture, Vol. 1, Parts 1-51, C3.31-4:978, U.S.
Department of Commerce, Bureau of the Census, Washington, DC, 1981.
2. Exhaust Emissions from Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines, APTD-1430 through APTD-1496, U.S.
Environmental Protection Agency, Research Triangle Park, NC, 1972-1974.
3. Compilation of Air Pollutant Emission Factors, Third Edition (with
Supplements 1-11), AP-42, U.S. Environmental Protection Agency, Office of
Air Quality Planning and Standards, Research Triangle Park, NC, October
1980.
4. Procedures for the Preparation of Emission Inventories for Volatile
Organic Compounds—Volume I (Second Edition), EPA-450/2-77-028, U.S.
Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, NC, September 1980.
5. AEROS Manual Series, Volume II, AEROS User's Manual, EPA-450/2-76-029,
U.S. Environmental Protection Agency, Research Triangle Park, NC,
September 1980 (Update No. 3).
6. The Airshed Model Data Handling System (ASMDHS) User's Guide.
EPA-450/4-80-030, U.S. Environmental Protection Agency, Research Triangle
Park, NC, December 1980.
7. Procedures for Emission Inventory Preparation—Volume I: Emission
Inventory Fundamentals, EPA-450/4-81-026a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, September 1981.
8. Exhaust Emissions From Uncontrolled Vehicles and Related Equipment Using
fraternal Combustion Engines—Part 5, Heavy-Duty Farm, Construction, and
Industrial Engines, APTD-1494, U.S. Environmental Protection Agency,
Research Triangle Park, NC, October 1973.
9. Methodology for Estimating Emissions from Off-Highway Mobile Sources for
the RAPS Program, EPA-450/3-75-002, U.S. Environmental Protection Agency,
Research Triangle Park, NC, October 1974.
3-21
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10. County Business Patterns, U.S. Department of Commerce, Bureau of the
Census, Washington, DC, 1979 edition available during July 1981.
11. County Business Patterns, National Summary, U.S. Department of Commerce,
Bureau of the Census, Washington, DC, 1979 data available during 1981.
12. Exhaust Emissions from Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines—Part 4, Small Air-Cooled Spark Ignition
Utility Engines, APTD-1493, U.S. Environmental Protection Agency,
Research Triangle Park, NC, May 1973.
13. NEDS Fuel Use Report, U.S. Environmental Protection Agency, NADB,
Research Triangle Park, NC, 1978.
14. Highway Statistics, U.S. Department of Transportation, Federal Highway
Administration, Washington, DC, Various years.
15. Census of Housing, U.S. Department of Commerce, Bureau of the Census,
Washington, DC, Decennial publication.
16. Census of Population, U.S. Department of Commerce, Bureau of the Census,
Washington, DC, Decennial publication.
17. Exhaust Emissions from Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines—Part 7, Snowmobiles, APTD-1496, U.S.
Environmental Protection Agency, Research Triangle Park, NC, April 1974.
3-22
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4.0 EMISSIONS FROM HIGHWAY VEHICLES
In most urban areas, highway vehicles represent the largest single source
of carbon monoxide (CO) emissions and contribute significantly to the area's
total production of hydrocarbons (HC), sulfur oxides (SOX), and oxides of
nitrogen (NOX). The purposes of this section are to identify the
relationships that exist between mobile source activity and emission
production, and to present four methods for inventorying emissions from
highway vehicles.
The process of developing an inventory of emissions from highway vehicles
is complex, regardless of the method used. State, regional, and county
transportation engineering and planning agencies must be involved. The data
available from these agencies and the expertise of their personnel are
required in the methods used to inventory emissions from highway vehicles.
4.1 GENERAL CONSIDERATIONS
The quantity of emissions produced regionally from motor vehicles is a
function of the amount of travel—that is, vehicle-miles of travel (VMT)—that
occurs, of specific characteristics of the vehicles performing the travel,
travel parameters, and of certain environmental factors. The emission
inventory process must account for these factors whether explicitly as part of
the source characterization, or implicitly in the selection of emission
factors.
The most fundamental relationship between emissions and highway vehicles
as a source concerns the amount of travel that occurs within a particular
area. However, since emissions are also affected by specific characteristics
of the vehicle population and the environment, regional travel estimates must
be defined in terms of VMT by various types of vehicles operating in each of
several types of environmental settings.
Vehicle characteristics that are of interest include those that relate to
the vehicle itself, and to the operation of the vehicle. In terms of the
individual vehicle, emissions are affected by:
The type, size, and configuration of the engine;
The types of emission control devices used;
The general condition of the engine; and
The type of vehicle.
Two types of engines are currently used for highway vehicles—
gasoline engines (Otto cycle), and diesel engines. Each displays unique
emission characteristics; therefore, it is necessary to determine the relative
distribution of gasoline-powered and diesel-powered vehicle travel in the
4-1
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emission inventorying procedure. Engine size (displacement) and configuration
(block type, number of cylinders, special characteristics of the combustion
area design or type of fuel delivery system, etc.) also affect emission
characteristics of the individual vehicle. However, these are reflected in
the emission factors, which represent a composite of all engine sizes and
configurations for a particular model year, and therefore are not explicitly
considered in deriving an emission inventory.
Beginning with the 1968 model-year, vehicles manufactured in or imported
into the U.S. have had to meet emission standards that have become
increasingly stringent over time. As more stringent standards have come into
effect, the control technology applied to various model-year vehicles changed
as well. In terms of emission control technology, the particular model year
reflects both the general technology applied, and a specific level of overall
emission control. In the inventorying process, then, the distribution of VMT
by model year is required.
Regardless of the type of emission control technology applied, a certain
amount of deterioration can be expected in the effectiveness of the emission
controls as the vehicle accumulates mileage. Emission factors for motor
vehicles reflect this deterioration by assigning a higher emission rate to a
particular model year as the vehicle age represented by that model year
increases.* Again, the vehicle age distribution is required as part of
developing emission estimates.
The type of vehicle refers to eight categories, including:
Light-duty, gasoline-powered vehicles (LDGV), i.e., passenger cars;
Light-duty, diesel-powered vehicles (LDDV);
Light-duty, gasoline-powered trucks, type 1 (LDGT1), i.e., pickup trucks
and vans that have a gross vehicle weight (GVW) less than 6000 pounds;
Light-duty, gasoline-powered trucks, type 2 (LDGT2), i.e., pickup trucks,
vans, and other small trucks that have a GVW between 6000 and 8500
pounds;
Light-duty, diesel-powered trucks (LDDT);
Heavy-duty, gasoline-powered vehicles (HDGV), i.e., all vehicles with a
GVW greater than 8500 pounds, powered by gasoline engines;
Heavy-duty, diesel powered vehicles (HDDV), i.e., essentially all
diesel-powered trucks; and
Motorcycles (MC).
*Mileage accumulation and vehicle age correlate very well.
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Large differences exist in the emission characteristics of vehicles
represented by these categories, therefore, regional travel estimates must
reflect the distribution of VMT by vehicle type.
In addition to being sensitive to the vehicles' physical characteristics,
emissions are also affected by the operating mode. Instantaneous emission
rates are very different for cruise, acceleration, deceleration, and idle
modes. The amount of detailed data required to perform a modal analysis
precludes using this approach for areawide inventories. The more usual
procedure is to consider travel in the context of the whole trip, whereby a
modal distribution is assumed and the average vehicle speed is used.
Another operational parameter that affects the emission characteristics
of most vehicles is the amount of travel that occurs while the vehicle is in
(1) the cold transient mode, (2) the hot stabilized mode, and (3) the hot
transient mode.* These modes reflect the impact of engine operating
temperature on the emission characteristics of gasoline powered vehicles. The
CO and HC emission rates for these vehicles are much higher during the first
few minutes of operation when the choke is closed and various engine
components (including the catalytic converter) have not yet reached their
normal operating temperatures. This transition period from a cold (ambient)
to stabilized operating temperature is referred to as the cold-start mode.
The time required for an engine and its related systems to reach a stabilized
operating temperature depends on several factors, such as the amount of time
that the engine was not run (cold soaked) prior to starting, mass of the
engine, ambient temperature, and others. In actuality, the time required for
an engine to reach the stabilized mode is a function of the initial starting
temperature and the thermodynamic properties of the engine, which represents a
fairly complex relationship. For emission estimation purposes, however, the
relationship is treated as a simple, discrete function. Specifically, the
cold-start mode is defined as the first 505 seconds of operation after the
vehicle has cold soaked for at least 1 hour, if equipped with a catalytic
converter, or 4 hours if a converter is not used. Vehicles that are restarted
after a relatively short soak period (less than 1 hour for vehicles equipped
with a catalytic converter or less that 4 hours for noncatalyst vehicles) are
considered to be operating in the hot-start mode.
Travel parameters used in the inventory must account for differences in
the emission rates associated with cold-start, hot-start, and stabilized
operating modes. This is accomplished through the analysis of the region's
travel characteristics, or, for less detailed inventories, by applying assumed
values. Details regarding these two methods and their applications are
presented in subsequent paragraphs.
*These three modes are referred to here as cold-start, stabilized, and hot-
start, respectively.
4-3
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Several other, less important factors relating to vehicle operation
exist. These concern the impact of additional engine loading on emissions.
Specifically, emission rates tend to increase when a vehicle is towing a
trailer, carrying an abnormally heavy load, or when its air conditioner is
being used. Although the impact of the additional engine loading on emission
rates is quite small, it can be accounted for where the overall inventory is
to be sufficiently detailed to warrant the extra effort involved. Information
needed to apply these factors, however, is usually difficult to obtain.
Motor vehicle emission rates are sensitive to several environmental
factors. The two most important ones are ambient temperatures and altitude.
Ambient temperature has a pronounced impact on cold mode emissions. Colder
temperatures result in lower overall combustion efficiency and require a much
richer air-fuel mixture during initial warm up, both of which increase CO and
HC emission rates. Emission rates generally increase with altitude since the
lower density of the ambient air at high altitudes effectively creates a
richer air-fuel mixture. For emission inventorying purposes, different
emission rates are used depending on whether the area is located above or
below 4000 feet elevation.
The above factors apply to tailpipe emissions, which result from the
combustion of fuel. Several other sources of emissions are associated with
motor vehicles, including evaporative and crankcase HC emissions, tire wear,
and roadway dust entrainment. Evaporative losses result from the expansion
and contraction of the air and fuel vapor mixture in the vehicle's partially
filled gasoline tank, and from hot soak losses that occur from the carburetor
areas after the engine has been shut down. Crankcase emissions occur when
pressure builds up in the oil sump and lubricating oil vapor is vented. Both
evaporative and crankcase emissions from newer vehicles are controlled as a
result of the Federal Motor Vehicle Emissions Control Program (FMVECP).
Tire wear accounts for a relatively small fraction of the particulate
emissions produced by mobile sources. The actual amount of wear, measured in
terras of grams per mile, is related to many factors, such as tire design,
wheel loading, vehicle speed, road surface abrasiveness, and the relative
amount of braking that occurs. For emission inventory development, average
wear rates are used to calculate emissions, in pounds or grams, per mile of
travel.
Entrainment of particulate matter occurs as a result of air turbulence
from moving vehicles acting on roadside deposits. The entrainment of
particulate matter from roadways is associated with the fugitive emissions
category and therefore not included as part of the mobile source inventory.
Fugitive emission quantification procedures are presented in Volume III of
this series.I
4.2 MOBILE SOURCE EMISSION FACTORS
Two sources are used to derive emission factors for highway vehicles.
The first source is a computer program entitled MOBILE2,^ which provides the
4-4
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capability of deriving CO, HC, and NOX emission factors for all vehicle
types and for a wide variety of environmental and operating conditions. The
second source is a document entitled Compilation of Air Pollutant Emission
Factors: Highway Mobile Sources,-^ which will be referred to hereafter as
AP-42. AP-42 provides the capability of deriving SOX and particulate
emission factors for highway vehicles.
4.2.1 MOBILE2 EMISSION FACTOR MODEL
The MOBILE2 emission factor program provides an integrated set of FORTRAN
routines for deriving motor vehicle emission factors that are sensitive to the
composition of vehicles in the population, the operating characteristics of
the vehicles, and the environmental conditions in which the vehicle fleet is
operated. MOBILE2 is widely used currently, thus, even local air pollution
agencies without direct access to computers are able to access the program
through their state-level agency.
The emission factors produced by the MOBILE2 model are derived from the
adjustment of a baseline composite emission factor, which reflects the
standard set of conditions used in the Federal Test Procedure (FTP). The FTP
involves the simulated operation of a vehicle over a specific driving
cycle—the Urban Driving Cycle—under controlled operating and environmental
conditions, during which emissions are measured in three sequences. The Urban
Driving Cycle represents a 7.5 mile trip over an urban highway network that
includes travel on local and arterial streets, and major arterials and
expressways. The average speed over the 7.5 mile cycle is 19.6 miles per
hour. In MOBILE2, if an input speed that is different from 19.6 miles per
hour is defined, an emission factor will be computed for a different
distribution of operating modes; if, for example, the input speed is higher,
less idling and stop and go driving will be reflected. Many different
combinations of driving modes can result in the same average speed, but
totally different emission characteristics. In spite of the potential
inaccuracy that may be introduced, uce of the Federal Test Procedure
represents the most practical method for deriving composite emission factors
for highway vehicles.
MOBILE2 is based on emission data and procedures developed by EPA and
reported in Mobile Source Emission Factors,^ which supercedes portions of
AP-42 concerning emissions of CO, HC, and NOX from highway vehicles. In
order to fully understand the process of deriving emission factors for highway
vehicles, reference should be made to AP-42, the MOBILE2 User's Guide, and
Mobile Source Emission Factors.^>3,4
In applying MOBILE2, the user specifies a number of parameters that
reflect local characteristics in terms of the vehicle fleet, the highway
network, and the environment, or he can elect to use default values that
reflect national averages for some parameters. Specific parameters that are
required as input to MOBILE2 include:
4-5
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Region for which emission factors are to be calculated (i.e., low
altitude, high altitude, or California);
Calendar year;
Vehicle speed;
Ambient temperature;
Percentage of total VMT attributable to noncatalyst vehicles operating in
the cold-start mode;
Percentage of total VMT attributable to catalyst-equipped vehicles
operating in the hot-start mode; and
Percentage of total VMT attributable to catalyst-equipped vehicles
operating in the cold-start mode.
The user has a choice of specifying local data or using default values
for the following:
Distribution of VMT by vehicle type;
Vehicle model year and accumulated mileage distributions;
Baseline emission rates; and
Factors to correct LDV emissions for air conditioner use, extra loading,
trailer towing, and humidity.
MOBILE2 also accounts for the impact of motor vehicle inspection and
maintenance (l/M) programs and is sensitive to such factors as the length of
time that the program has been in effect, the stringency or failure rate, and
the specific vehicles by type and mod^i year affected by the program.
4.2.2 AP-42
The use of AP-42 in the emission inventorying process is quite simple
since both particulates and sulfur oxides (SOX) emissions are computed as a
function of VMT by vehicle type, only. Emission factors for these two
pollutants are provided for each vehicle type in the AP-42 document. The
emission factor for SOX is based on assumed sulfur content of the fuel, and
average fuel consumption rate. If local conditions warrant different
assumptions, an adjustment to the emission factors can be easily made.
4.3 OVERVIEW OF METHODS FOR COMPILING EMISSION ESTIMATES
Four methods for developing inventories of highway vehicle emissions are
presented here. Their applicability and limitations are summarized in
Table 4.1.
4-6
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The first method is intended for use in rural or small urban areas where
Local travel estimates are not available. This method derives local travel
estimates and vehicle operation characteristics from statewide data and
general characterizations of the highway vehicle source category. The method
provides a general inventory of highway vehicle emissions. This method, while
adequate for rural areas and urban areas with populations less than 50,000,
should not be used for larger urban areas.
The second method presented here for developing a highway source emission
inventory is, like the method outlined above, a process that is intended for
use in instances where the emphasis is on expediency rather than precision.
It is different from the first method, however, in that it requires
significantly more local data and is primarily intended for use in urbanized
areas. This method also accounts for more variables than the first method.
It is intended to provide estimates of highway emissions as a function of
travel-related emissions, trip-related emissions, and vehicle-
related emissions, whereas the first method assumes that total emissions are a
function of travel only (vehicle-related and trip-related emissions are not
explicitly considered). The method was developed by the U.S. Department of
Transportation, Federal Highway Administration (FHWA), and will be referred to
here as the FHWA manual process.
The third and fourth methods are designed to integrate formal
transportation planning and air quality planning efforts by utilizing
transportaton planning data from urban area 3-C transportation planning
processes as input to an emission model to yield emission estimates. The
third method, referred to as the link-based approach, uses detailed
information developed by the transportation planning process regarding the use
and operational characteristics of individual segments (that is, links) of the
region's highway system, and a single emission factor developed for the
individual link, to estimate emissions. The fourth method, referred to as the
hybrid approach, is similar to the link-based approach with the exception that
travel-related, trip-related, and vehicle-related emission components are
derived separately. This approach provides a high degree of spatial
sensitivity to those factors that affect emissions; however, the method is
more data intensive and requires a significantly greater investment compared
to the link-based approach.
4.4 METHOD 1—ESTIMATING EMISSIONS FOR RURAL COUNTIES AND SMALL URBAN AREAS
Mobile source emissions are derived as a function of an activity
factor—vehicle-miles of travel (VMT)—and an emission factor. For many rural
and small urban areas very little data are likely to exist regarding the
amount of vehicle travel that occurs. Further, given the high cost of
developing VMT data through direct measurements, it is not likely that special
studies would be performed to derive travel data for these areas.
Notwithstanding the problem of limited or nonexistent data, it is often
necessary to develop an inventory of emissions produced by vehicular traffic
in these areas. The purpose of this section is to discuss methods that can be
applied to derive an inventory of emissions from highway vehicles in rural or
small urban areas where local tranportation data are limited.
4-8
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The general process involves the apportionment of statewide VMT to the
county (or other appropriate areas). Statewide VMT data are tabulated by all
state transportation agencies and reported to the Federal Highway
Administration (FHWA), which, in turn, publishes these and other similar data
in Highway Statistics.^ it should be noted that many states now have and
others are developing the capability of reporting county level VMT. In states
where this capability exists, the method described here for apportioning state
level VMT data to the county level would not be applicable.
Central to this overall method is the development of apportioning
factors, which, when applied to the statewide total, yield the countywide
VMT. Several bases exists for apportioning VMT, such as fuel sales,
population, motor vehicle registrations, and roadway mileage. The specific
basis selected will depend on the availability of required data. Given the
variability from state to state (and from county to county within a particular
state) of the types of transportation-related statistics maintained, it is not
possible to conclude in a general sense that one basis for developing an
apportioning factor is better (that is, more accurate, easier to use, more
cost effective to utilize, etc.) than any of the others. Selection of general
methods should be made only after carefully and thoroughly researching the
availability and quality of essential data. A key aspect of this process is
to obtain the assistance of state and county transportation engineers and
planners who should be able to provide the best assessment of both data
availability and quality. The entire data assessment phase should be
completed prior to selecting this method for conducting the inventory since
the underlying assumption is that no direct estimates of county VMT are
available.
Once the apportioning method has been developed, the resulting factors
are applied to statewide VMT to produce estimates of countywide travel. Other
data are applied to yield VMT by vehicle type and roadway classification.
This represents the activity level for the county. The remainder of the
process involves the derivation of additional data concerning county-specific
environmental characteristics, and applying these and the VMT data as input to
an emission model. Also, a common requirement among all methods and emission
source categories is the management of the inventory data. This aspect of
inventory development is discussed in a separate section. Figure 4-1 provides
an overview of the inventory method and indicates the sections of this report
where instructions can be found.
4.4.1 DATA ASSESSMENT
This is the first task undertaken after determining that there is a need
for developing an inventory of emission from highway vehicles in a rural
county or small urban area. The intent is to determine exactly what data are
available, or could be derived directly from existing data, that are relevant
to the development of the emission inventory. In order to accomplish this
step, the analyst must be familiar with the basic concepts of emission
inventory development, and have a sound understanding of factors that
influence the emission characteristics of the highway system. In this regard
4-9
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| DATA ASSESSMENT
SECTION 4.4.1
1
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1 ACTIVITY FACTOR DERIVATION
| SECTION 4.4.2
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COMPUTE EMISSIONS
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V
ENTER RESULTS ON PROPER
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^SECTION 4.4.2.1
SECTION 4.4. 2. 2
SECTION 4.4.2.3V
SECTION 4.4.2.4
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it is appropriate that the MOBILE2 User's Guide^ be reviewed prior to
beginning this task.
The process of identifying and evaluating the necessary data should
include input from state and county transportation engineers and planners.
These individuals are most familar with both the data that are available and
the data required as input to the emission model, therefore, their assistance
should be solicited.
The first question to be answered during this phase is: Are direct
estimates of county VMT available? If VMT estimates are available the problem
becomes one of disaggregating it to a level that is suitable for input into an
emission model. In this instance the concern becomes how to disaggregate the
VMT data. If direct estimates of county level VMT are not available, the
immediate concern is to develop a basis for disaggregating statewide VMT
estimates obtained either from Highway Statistics-* or the state
transportation agency. During the process of answering the question
concerning the availability of VMT data, the availability and quality of other
pertinent data should be determined. The specific types of data that are of
concern are discussed in the following paragraphs.
4.4.2 ACTIVITY FACTOR DERIVATION
The preceeding step establishes whether or not direct estimates of county
VMT are available. If county estimates are not available, total statewide VMT
estimates must be obtained, from which county estimates can be derived.
Statewide VMT estimates are available directly from state transportation/
highway agencies, and from Table VM-2 in Highway Statistics^ (included here
as Table 4-2). Four methods for apportioning these statewide totals to county
or other subareas are presented below.
4.4.2.1 Apportionment of Statewide VMT
The first apportioning method is based on fuel sales data. An assumption
inherent in this method is that VMT and fuel sales are directly related. In
order for this method to be practical, county fuel sales data must be
available. If it is determined that county fuel sales data are not available,
one of the other three methods of allocating state VMT presented here should
be considered.
Since all states collect taxes on motor fuel sold within their
boundaries, formal records are maintained regarding both the fuel throughput
and the revenue derived therefrom. These statistics are usually aggregated as
state totals, therefore, special processing of the source data may be required
to identify statistics for a particular county. The data requirements should
be discussed with appropriate officials in the state taxation or revenue
agency.
As a minimum, total annual sales (gallons) of gasoline and diesel fuel in
the county and statewide are required. The monthly distribution of sales is
4-11
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also required. Note that each state reports monthly fuel sales data to the
Federal Highway Administration, which, in turn, reports various fuel use
statistics in Highway Statistics5, and in a monthly publication.6
The apportioning factor is the ratio of county motor fuel use to state
fuel use. Tables MF-25 and MF-26, respectively, in Highway Statistics5
tabulate the monthly highway use of special fuels and gasoline for each state
in the U.S. Special fuels are essentially diesel fuel and some liquified
petroleum gases. Table MF-26 indicates the actual use of gasoline and gasohol
by highway vehicles; the data shown in that table have been adjusted to
account for handling losses and exclude gasoline used for nonhighway
purposes. The VMT apportioning factor is:
f - Qc (4-1)
c _
where fc = the apportioning factor to be applied to statewide VMT to
estimate county VMT;
Qc = the total quantity (gallons) of gasoline and diesel fuel sold
in the county, obtained from the state revenue agency; and
Qs = the total quantity (gallons) of gasoline and diesel fuel sold
in the state, obtained from the state revenue agency or from
Tables MF-25 and MF-26 in Highway Statistics.5
Another method for allocating VMT to a county is to use roadway inventory
data—that is, an inventory of roadway mileage by functional category—
representing both the statewide and county highway network. The underlying
assumption in this method is that VMT is generally a function of total roadway
mileage, and that this functional relationship becomes more direct as
individual types of highways within specific areas are considered.
State transportation and highway agencies report total roadway mileage by
functional type (i.e., interstate, primary arterials, arterials, collectors,
and local streets) in both urbanized and rural areas, for both the Federal-aid
and non-Federal aid portions of the highway system. A summary of these data
is published by FHWA in Highway Statistics5 as Table M-12, which is shown
here as Table 4-3. As Tables 4-3 and 4-2 show, roadway mileage and VMT are
reported in exactly the same format—that is, by functional type on
Federal-aid and non-Federal aid highways in both urban and rural portions of
each state. One additional set of data is required—the county roadway
mileage disaggregated by the same categories as those for the statewide data.
This information should be available directly from the state transportation
agency or it can be derived based on input from both state and county
transportation agencies.
The VMT allocation factor is then derived as the ratio of county to state
roadway mileage for each category of highway in both rural or urban areas:
4-13
-------
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4-14
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f . = Mci (4-2)
C1 M—
si
where fci = the apportioning factor to be applied to statewide VMT to
estimate county VMT for roadway type i,
Mci = miles of type i roadway in the county, and
Ms£ = miles of type i roadway in the state.
The result will be as many as 13 individual allocation factors in each county,
each of which is applied to the corresponding VMT figure in Table VM-2 from
Highway Statistics^ (see Table 4-2, here).
A third method for allocating statewide VMT to the county level utilizes
motor vehicle registration data to derive an apportioning factor. The premise
here is that the amount of travel (VMT) occurring in an area is a function of
the area's vehicle population. This method assumes that travel by vehicles
registered outside the area is balanced by travel outside the area by vehicles
registered in the area and that average county travel patterns are not
significantly different from the statewide (or other) averages. Since this
overall method applies to rural counties or small urban areas, the assumption
is that travel characteristics are generally consistent within all areas of
the state regardless of the differences that may exist among the areas in
their degree of urbanization.
The allocation factor is the ratio of county registered vehicles to state
registered vehicles. Registration statistics can be obtained from the state
motor vehicle registration department for both the state and county, although
there may be a requirement for special processing of state registration files
to produce county-specific data. The factor is defined by:
f = Vc (4-3)
C '!»"
s
where fc = the allocation factor to be applied to statewide VMT to derive
county VMT,
Vc = total number of motor vehicles of all types registered in the
county, and
Vs = total number of motor vehicles of all types registered in the
state.
Finally, statewide VMT can be apportioned to the county level based on
the relative county and state population. This method has the advantage of
utilizing data that are routinely available from several sources, such as the
Bureau of Census and state and county agencies, and therefore VMT estimates
4-15
-------
can be developed with minimal effort. A disadvantage to this method is th;,t
population data may not be current. In addition, this method is perhaps the
least sensitive to variations in travel characteristics among different types
of areas and therefore may be the least accurate. The apportioning factor is:
f = Pc (4-4)
c —
s
where fc = the allocation factor to be applied to statewide VMT to derive
county VMT,
Pc = county population, and
Ps = state population.
4.4.2.2 County VMT Computation
County level VMT is estimated by applying the allocation factor, fc, to
statewide VMT statistics obtained from the state transportation agency, or
from Table VM-2 in Highway Statistics-* (see Table 4-2). Expressed as an
equation, the estimated annual VMT occurring in the county is:
VMT = f x VMT (4-5)
c c s
where VMTC = estimated annual county VMT,
VMTS = total statewide VMT, from the state transportation agency
or from Table VM-2 in Highway Statistics^, and
fc = apportioning factor derived from one of equations 4-1
through 4-4.
In all instances except where the apportioning factor is based on roadway
mileage (Equation 4-2), the value assigned to VMTg is found in the TOTAL
column for ALL HIGHWAY CLASSES in Table 4-2. If equation 4-2 is used, the
individual values of VMT for each roadway type in urban and rural areas in
Table 4-2 are used for VMTS.
4.4.2.3 Disaggregation of VMTr by Roadway Type
Emissions from motor vehicles are greatly affected by travel speed, which
in turn is directly related to the type of roadway. Defining the distribution
of VMT by roadway type enables a general distribution of VMT by roadway speed
to be derived.
The basis for deriving VMT distributions by roadway type is the relative
county and state mileage of each functional category (i.e., interstate,
4-16
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primary arterial, arterial, collector, and local street). The process is the
same one described in 4.4.2.2 for allocating statewide VMT to the county level
based on roadway mileage. The advantage to using this method of allocation is
that it provides a direct estimate of county VMT by functional category.
If some other method for allocating state VMT to the county is used, the
extra step of deriving an estimate of county VMT distribution by roadway type
is necessary. This can be done using the same method of comparing county
roadway mileage to state roadway mileage for each functional category, and
applying the resulting allocation factor to the appropriate VMT by functional
category figures found in Table 4-2. Each value thus derived is expressed as
a percentage of the total VMT computed for the county using this procedure,
and applied to the actual county VMT value. Expressed as an equation:
VMT . =
ci
f . x VMT .
Cl SI
n
1=1
(f . x VMT .)
ci si
EVMTr
(4-6)
where
VMT
ci
the derived value of VMT occurring on roadway functional
category i in the county;
fc-j = apportioning factor derived using Equation 4-2;
VMT
si
VMT,
statewide VMT on functional category i, obtained from
Table VM-2 in Highway Statistics-* (see Table 4-2); and
= total VMT derived for the county using whatever method
is deemed appropriate.
The actual purpose served by deriving VMTC by roadway functional
category is to provide a rationale for assigning travel speeds. The intent is
to assign a value to each type of roadway representing the average travel
speed over the entire network of that functional category. This may be based
on a combination of actual travel speed data and engineering judgment. States
have generally monitored speeds on the interstate system and on other
controlled access, divided highways, therefore, some speed data for these
types of highways can be expected to exist. For other types of roads data may
not exist, therefore estimates based on competent engineering judgment will be
required. The intent is to establish an estimate of the average speed over
the entire system, which is somewhat lower than the free flowing speed since
it must reflect delays, slowdowns, and normal interruptions in traffic flow.
Where no data exist, assistance should be solicited from state or county
transportation engineers to develop estimates.
Once average speed values have been assigned, VMT can be aggregated by
general functional category (i.e., limited access highways, primary arterials,
arterials, collectors, and local streets), where each category has a specific
speed associated with it.
4-17
-------
4.4.2.4 Disaggregation of VMT by Vehicle Type
Since emission rates, in grams or pounds of pollutant per vehicle-mile of
travel, are characteristically different for each of several vehicle
categories, the VMT data must be further disaggregated to reflect the relative
travel by each vehicle type. Several methods for deriving an estimate of the
relative travel by vehicle type are discussed here.
The first method is to merely accept the default distribution of VMT by
vehicle types contained in the MOBILE2. This distribution was derived by the
U.S. Environmental Protection Agency based on national statistics, and changes
slightly by calendar year to account for the apparent trend towards the use of
diesel engines for all classes of motor vehicles. In view of the general
nature of other data elements used in the inventorying process, the default
values for distributing VMT by vehicle type are appropriate. However, the
default values for rural areas in MOBILE2 may not be appropriate for those
rural areas that experience a large amount of through truck traffic. In these
cases, the actual distribution of vehicle types could be significantly
different than the default distribution values.
If it is decided that local characterization of the VMT distribution is
warranted, then one of two methods can be utilized to derive the appropriate
distributions. The first method is to obtain traffic classification data from
state, county, and local highway agencies. That data can be used to develop
representative distributions of vehicle type as a function of roadway
category. Traffic classification counts are typically made by highway
agencies as part of their ongoing traffic data collection programs, therefore,
these agencies should be considered the primary source for this information.
Classification data should be obtained for each functional category of
roadway. Although the first choice should be to obtain data for highways
located in the specific area being inventoried, data from other, similar areas
can be used.
Typical vehicle categories used in classification counts include:
Passenger cars
standard
compact
subcompact
Panel and Pickup Trucks
Single-unit Trucks
2-axle, 4-wheel
2-axle, 6 wheel
4-18
-------
3-axle
4-axle
Combinations
2-axle tractor, 1-axle trailer
2-axle tractor, 2-axle trailer
3-axle tractor, 2-axle trailer
3-axle tractor, 3-axle trailer
Buses
Commercial
Nonrevenue
Motorcycles
Miscellaneous
On the other hand, the vehicle categories that are of interest in terms of
emission inventory development are those discussed previously in Section 4.1
(e.g., LDGV, LDDV, LDGT1, etc). The relationship between the vehicle
categories used in emission inventories and those typically available from
classification counts is shown in Table 4-4.
Typically, classification counts do not distinguish diesel from
gasoline-powered vehicles as Table 4-4 shows. However, this disaggregation is
required for emission inventories, as the engine types have quite different
emission characteristics. National average values are available in MOBILE2.
They are:
Light-duty vehicles - gasoline 99.7%
- diesel 0.3%
Light-duty trucks - 1 63.6%
- 2 36.1%
- diesel 0.3%
Heavy-duty vehicles - gasoline 54.2%
- diesel 45.8%
These figures can be used unless better local data are available.
4-19
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TABLE 4-4. VEHICLE CATEGORIES
Emission
inventories
Classification counts
LDGV
LDDV
LDGTl
LDGT2
LDDT
HDGV
HDDV
MC
Passenger cars (all types)
Panel and pickup trucks
Single unit trucks, 2-axle, 4-wheel
Panel and pickup trucks
Single ur.it trucks, 2-axle, 4-wheel
Single unit trucks (all other types)
Combinations (all types)
Buses (all types)
Motorcycles
4-20
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The relative proportions of HDGV's and HDDV's can also be estimated using
data provided in the 1977 Census of Transportation—Truck Inventory and Use
Survey.^ Table 4, for example, in the U.S. report provides an indication of
the relative number of gasoline and diesel powered trucks according to 4
vehicle categories:
light;
medium;
light-heavy; and
heavy-heavy.
The "light" category includes vehicles 10,000 pounds gross vehicle weight
(GVW) or less, which are essentially panels, pickups and 2-axle, 4-wheel
trucks. For purposes here, all of these can be considered LDGTl's and
LDGT2's. The other three categories would all be heavy duty vehicles. These
categories can also be disaggregated based on the type of engine—gasoline or
diesel—also using the Census of Transportation.^ The results are shown in
Table 4-5. The TOTAL line provides a distribution of gasoline and diesel
vehicles for various subsets of single-unit and combination vehicles that can
be used with state classification counts to identify the percentage of HDGV
and HDDV for each type of roadway. Referring to the vehicle classifications
used in quantifying emissions, all vehicles represented in Table 4-5 are
either HDGV or HDDV. The same type of table can be developed from state data
contained in the individual state Truck Inventory and Use Surveys,^ although
there should not be a significant difference in the final distribution of
gasoline to diesel-powered vehicles.
The second method for deriving a distribution of VMT by vehicle type is
to assume that the distribution is a function of the number of each type of
vehicle registered in the county or the state. This method does not require
that the total county VMT be disaggregated to VMT by roadway type (see Figure
4-1). Instead, the percentage of each vehicle type is determined from
registration records and the total county VMT is disaggregated to VMT by
vehicle type with that data.
The data required consist of a detailed record of the number of motor
vehicles registered in the county, by vehicle type. The specific vehicle
categories that should be identified are those delineated here in Section 4.1,
although LDDV's and LDDT's are generally so few in number that it can be
assumed that they are respectively included with the LDGV, and LDGT1 and LDGT2
categories. Motor vehicle registration statistics routinely maintained by
many states may yield this information directly. Alternatively, special
processing may be required to tabulate the registration statistics at county
level. In lieu of county-specific data, the state vehicle population
statistics may be applied.
4-21
-------
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4-22
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The apportioning factor for each vehicle type, then, is:
N.
f . = V (4-7)
vi
n
* N.
A«^
1=1
where fv£ = apportioning factor for vehicle type i, to be applied to
VMT • pnrl
VMT ; and
c
N-; - number of type i vehicles registered in the county or state.
This method does not account for differences in the annual mileage
accrual among vehicle types. For example, some HDDV's may travel over 100,000
miles annually whereas LDG's typically travel about 10,000 miles per year.
Although statistics are available regarding the average annual mileage accrual
by various vehicle categories, these cannot be applied to travel occurring
within a relatively small area such as a county. Table 13 in Reference 7
provides information on annual mileage by truck type, by typical range of
operation. The range of operation categories include local, short-range
(generally, within 200 miles of the base of operation), and long-range (beyond
200 miles of the base of operation).* That table shows significant
differences among all categories of trucks in terms of annual mileage accrual
and range of operation. A significant portion of the mileage accrued annually
by trucks in the short-range category, and most of the mileage accrued by
vehicles in the long-range class can be expected to occur outside the general
area (county, for example) where the vehicle is registered. A VMT weighing
factor based on annual miles traveled would not be appropriate for application
at the county level. In the absence of specific data regarding the relative
amount of countywide travel by each vehicle category, it must be assumed that
the relative number of vehicles in each category provides an adequate
indication of the actual distribution of VMT, by vehicle type.
4.4.2.5 Special Requirements
It is often necessary to compute the average daily (weekday) highway
vehicle emissions during the peak ozone or carbon monoxide seasons. Daily
vehicle emissions are required for SIP revisions, for example. In these
cases, the activity factor for highway vehicles (VMT by vehicle type) must be
developed to reflect daily VMT. Total annual VMT from Table 4-2 can be
adjusted to reflect average weekday VMT during the summer months (June through
August) for ozone, and during the winter months (November through February)
for carbon monoxide by the following procedure.
*A fourth category—off the road—is included in Table 13. Vehicles in this
classification, however, are not accounted for in the on-highway emission
source category and are therefore not considered.
4-23
-------
All states maintain ongoing traffic counting programs, which can provide
information concerning daily and seasonal variations in traffic flow. The
particular seasonal pattern for an area is affected largely by the nature of
the area. Therefore, it is not possible to develop general rules that would
apply in all instances. If average daily emissions during the peak pollutant
season are to be considered, the total VMT from Table 4-2 should first be
divided by 3b5 to yield a value for the estimated average annual daily VMT,
which is similar in concept to average annual daily traffic (AADT). Average
daily traffic (ADT) patterns for each month are developed by the state highway
agencies depicting the ADT as a function of AADT. The same relationship that
exists between ADT during the peak pollutant season and the AADT can then be
assumed to exist between daily VMT and average annual daily VMT.
4.4.3 CALCULATION OF EMISSIONS
The actual calculation of emissions from highway vehicles is accomplished
using emission factors calculated from the MOBILE2 emission model, and the
activity factors. The MOBILE2 User's Guide^ must be consulted for a
detailed explanation of MOBILE2 use, as it is too lengthy for inclusion here.
This section does, however, discuss the additional requirements for local
input necessary to calculate emission factors using MOBILE2.
Input data for MOBILE2 includes a one-time data set and an emission
factor parameter data set. The first element in the one-time data set is the
VMT distribution by vehicle type (the activity factor). In developing the
activity factor, three possibilities exist:
a single distribution of VMT by vehicle-type;
a unique distribution of VMT by vehicle-type defined as a function of
roadway functional category; or
use of the default vehicle-type distributions contained as a subprogram
in MOBILE2.
The next element in the one-time data set relates to the mileage accrual by
vehicle type and age characteristics of the vehicle population. For purposes
here, the default option, which is based on national data, should be specified
unless local data are available.
Next is a data element pertaining to the baseline emission rates for the
vehicle population. The user can specify rates that are different from those
contained in the MOBILE2 program, however, for most applications the user
should specify the MOBILE2 emission rates.
Since the baseline emission rates for motor vehicles are affected by
motor vehicle inspection and maintenance (I/M) programs, the data set must
contain information on the type of I/M program, if any, in effect in the area
being inventoried. The information required include:
4-24
-------
year that the program was implemented;
stringency level;
whether or not a mechanics training program is included;
earliest and latest model year vehicles affected by the program
currently; and
vehicle types affected.
This information can be obtained from the state agency responsible for the
operation of the I/M program.
Finally, information is required concerning the average number of vehicle
trips and average length of vehicle trips, by vehicle type. Default values
are available within MOBILE2 and should be used unless local data are
available for the study area.
The second set of data contains seven parameters describing the scenarios
for which emission factors are to be calculated. The first element in this
data set is the regional designation. The options are:
low altitude (less than 4000 feet above sea level), 49-state;
low altitude, California; and
high altitude (more than 4000 feet above sea level).
The second element is the specification of the calendar year for which the
inventory is being developed. Currently, inventories must be developed to
reflect weekday emissions during the peak pollutant months for:°
base year 1980, if possible; anf
the proposed attainment year—1987.
This applies specifically to areas which are nonattainment for ozone.
Otherwise, the calendar year(s) selected should be based on the overall intent
of the inventory; if it is an annual update, the calendar year selected should
be the inventory year.
Average travel speed data are required for the highway network. As
presented in the previous section, speed data should reflect the average
travel speed over the network rather than the free-flow speed only. If VMT by
roadway functional category were developed, then separate emission factors for
each roadway type will be calculated by specifying different speeds for each
roadway type on separate MOBILE2 runs.
4-25
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An ambient temperature representative of the peak pollutant season must
also be specified. Typically, the average daily temperature during the peak
season is specified.
The percentage of VMT occurring in the cold-start and hot-start mode for
catalyst-equipped vehicles, and in the cold-start mode for non-catalyst
vehicles must be estimated. For this particular application default values
can be used in the absence of specific local data. If different roadway
categories are used, separate values for each mode may be appropriate for each
roadway category. For example, freeways may have a lower percentage of
vehicles in the cold-start mode than do local roads.
Several additional parameters can be specified that will affect the
emission factors derived by the MOBILE2 program. These involve specifying the
extent to which automobile air conditioners are used (i.e., percentage of
vehicles using air conditioners); the percentage of LDGV's, LDGTl's, and
LDGT2's carrying extra 500 pound loads; and the percentage of LDGV's, LDGTl's,
and LDGT2's that are towing trailers. In terms of air conditioner use, the
basic decision is whether or not air conditioner use should be considered
since the MOBILE2 model will compute the air conditioner useage based on the
ambient temperature. The required inputs include the dry and wet bulb
temperatures, as well as the absolute humidity in grains of water per pound of
dry air.
For vehicle loading and trailer towing, the percentage of each type of
light-duty vehicle carrying an extra load or towing a trailer must be
specified. For purposes here, these corrections can be considered
insignificant.
The data described above are then used as input to the MOBILE2 emission
model, which computes an emission rate for each vehicle type, for each type of
highway facility (actually, for each average speed value input). The emission
factors are in grams of pollutant per mile. It is important to note that
hydrocarbon emission factors can be computed as: (1) total hydrocarbons; (2)
non-methane hydrocarbons; (3) separate evaporation and crankcase emission
rates as well as the composite emission rate. In this regard the specific
type of emission factor desired should be specified. The determination of
whether total or non-methane hydrocarbon emissions should be computed ought to
be based on the overall inventory design and specifications. If there is no
real need to output evaporative and crankcase emission rates separately, only
the composite hydrocarbons (either total or nonmethane component) emission
factors should be specified.
Once the emission factors are available, they are multiplied by the
appropriate activity factor to yield the highway source emissions for the
pollutants carbon monoxide, hydrocarbons, and oxides of nitrogen.
For particulates and sulfur oxides, the emission factors are determined
directly from the MOBILE2 User's Guide^, and applied to the VMT by vehicle
type to yield the emission estimates.
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The method for developing estimates of future year emissions is
identical, except the total county VMT figure is adjusted upward or downward,
based on future year development estimates made by state or county planners.
There is no practical method that could be discussed in the context of this
document for independently projecting VMT. The process of developing an
inventory of emissions from highway vehicles requires the expertise of state,
regional, and county tranportation engineering and planning personnel.
4.4.4 INVENTORY MANAGEMENT
The basic requirements for documenting the procedures, sources of data,
results, etc. are the same for highway vehicles as for other emission
sources. The overall considerations in terms of inventory management are
presented in Volume I of this series."
4.5 METHOD 2—ESTIMATING EMISSIONS FOR URBAN AREAS USING PROCEDURES DEVELOPED
BY FHWA
4.5.1 OVERVIEW AND SCOPE
Method 1 provides a procedure for developing or updating a highway source
emission inventory for predominantly rural counties or small urban areas.
Method 2 provides a similar procedure that is intended for use in developing
and updating an inventory for those larger urbanized and standard and
metropolitan statistical areas (SMSAs), under an agency's jurisdiction.
The basis for Method 2 is a procedure developed jointly by the U.S.
Environmental Protection Agency (EPA) and the U.S. Department of
Transportation's Federal Highway Administration (FHWA). This method is
described in detail in Reference 10 and is referred to as the Manual Method
for Estimating Highway Emission Inventories.
This method follows the general process described for Method 1 (Figure
4-1). The primary differences between this method and Method 1 are in: (1)
the techniques used to derive the activity factor—that is, the distributions
of VMT by vehicle type for various highway speed categories; and (2) the
emission computations. In this method, emissions are computed manually rather
than with the MOBILE2 emissions model.
This method derives three activity factors that permit separate
computation of:
Travel-related emissions,
Trip-related emissions, and
Vehicle-related emissions.
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Travel-related emissions are a function of travel quantity (i.e., VMT) and are
computed as the product of total VMT and a baseline emission factor.
Trip-related emissions are a function of the number of vehicle trips that
occur irrespective of the VMT. Finally, vehicle-related emissions are a
function of the number of vehicles in the area and are associated with
evaporative losses from the fuel system. Total emissions from the highway
system are computed as the sum of these individual components.
The methods used for deriving activity factors for each component rely
extensively on data developed by both Federal and state agencies to define the
required travel characteristics. For example, previously established
relationships between urban population size and VMT per capita are used to
estimate total VMT based on current population. This method is not designed
for accuracy and sensitivity. It should not be applied with the intent of
using the results for detailed air quality modeling or for assessing the
impact of emission control strategies. Further, this method applies to larger
urbanized areas that usually have an ongoing regional transportation planning
program. Therefore, consideration should be given to utilizing alternative
methods, such as Methods 3 or 4 described later, that take advantage of the
much more detailed transportation data usually available from transportation
planning programs. If this general method is selected, locally developed
data, where available, should be substituted for the more general
relationships contained in Reference 10.
This method was developed for computing emission estimates manually; that
is, without the use of MOBILE2. Since this was a primary objective in
developing the method, the entire process of manually deriving emission
estimates is presented here. Following the description of this method are
instructions of how the basic elements of this method can be used to provide
appropriate input for MOBILE2.
4.5.2 TOTALLY MANUAL METHOD FOR DERIVING EMISSION ESTIMATES
The intent of this section is to summarize the methods presented in
Reference 10 for developing estimates of emissions from highway vehicles
without the use of any formal computer models. Reference 10 contains numerous
tables that are subject to periodic revision and, therefore, will not be
presented here. If this manual method for developing an inventory of
emissions from highway vehicles is to be used, the analyst should obtain a
copy of Reference 10 and a determination made as to whether the tables
contained therein are sufficiently up to date for the area being inventoried.
4.5.2.1 Derivation of Activity Factors
The first phase of the overall method is to develop activity factors,
which, when applied to appropriate emission rates, yield estimates of the
quantity of pollutant emissions produced by the region's highway network. To
develop the activity factors, five data elements must be derived:
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1. Regional or county vehicle population by vehicle type,
2. Total VMT,
3. VMT by vehicle type,
4. Speed characteristics for the highway network, and
5. Vehicle trip statistics.
Each of these is discussed below.
4.5.2.1.1 Estimating Regional Vehicle Population
Estimates of the regional auto and truck population for the study area
are developed using per capita vehicle registration statistics and growth
rates in vehicle ownership (vehicles per capita) developed by FHWA and
presented in Reference 10 in Tables 8.1 and 8.2, respectively. Per capita
auto and truck statistics for 1972 are presented for over 230 urbanized areas
while the growth rates in autos and trucks per capita are presented for each
state reflecting the period 1970 through 1975. These data, along with locally
derived estimates of the study area population, are used to estimate total
auto and truck populations, from:
AUTOS_ = [1 + (YRS)(AGR/100)] [ (APC70) (POP_) ] (4-8)
r IJ. r
and
TRUCKS.., = [1 + (YRSXTGR/100)] [ (TPC-..) (POP.,) ] (4-9)
t / / r
where AUTOS = estimated auto population in the area for the inventory
year F;
APC7 = autos per capita for 1972, from Table 8.1 in Reference 10;
TRUCKS = estimated truck population in the area for the inventory
year F;
TPC?2 = trucks per capita for 1972, from Table 8.1 in Reference 10;
YRS = number of years difference between the inventory year
and 1972;
AGR = auto growth rate, from Table 8.2 in Reference 10;
TGR = truck growth rate, from Table 8.2 in Reference 10; and
POP = estimated population for the inventory year F.
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The resulting values of AUTOSp and TRUCKSp are used to compute the
vehicle-related emission component mentioned previously, which is associated
with diurnal evaporative losses from the fuel system (for hydrocarbons only).
Only two basic vehicle categories are of interest since Reference 10 provides
evaporative emission factors that reflect a composite of the specific vehicle
types included in the general auto and truck categories.
Alternative sources of regional auto and truck registration data should
be considered. Stete motor vehicle registration agencies, for example, may be
able to provide statistics on the regional vehicle population. Also, regional
planning agencies may have more current information on per capita vehicle
population than is presented in Reference 10.
4.5.2.1.2 Estimating Total Travel
Four methods are presented in Reference 10 for estimating total regional
VMT. Prior to selecting a particular method, the availability and reliability
of the data required for each method (and for alternative methods, such as
those described in Method 1) should be assessed.
The first method presented in Reference 10 is to develop VMT estimates
based on traffic counts taken in the region. It is very unlikely that
sufficient counts would exist to develop VMT estimates for most areas.
Therefore, special traffic counting studies would be required. In view of the
overall scope and intent of Method 2, special data collection efforts
(particularly of the type needed to develop estimates of regional VMT) are not
recommended.
The second method presented in Reference 10 for estimating regional VMT
is through the use of output data from travel simulation models. Most urban
areas have continuing transportation planning programs that are responsible
for assessing current and future transportation needs. These assessments are
made with the aid of travel demand models that simulate various transportation
parameters including current and future highway utilization. An output from
these models is the total VMT accommodated by the existing or proposed
regional highway system. The type of data available from the planning program
varies from planning agency to planning agency, but, as a minimum, a base year
VMT estimate for the planning network is typically available. It is important
to recognize, however, that the transportaton planning base year may not be
the same as the inventory base year, therefore the VMT estimates may require
some adjustment. Also, the VMT estimates may only reflect interzonal travel,
therefore a significant amount of local travel may not be included. In any
case, if VMT estimates are developed from transportation planning data, the
analyst must be certain that he/she is aware of exactly what the data
represent. If adjustments are required, the transportation planning agency
that developed the data should perform the adjustments.
The third method for estimating regional VMT involves the use of data
compiled by FHWA regarding daily VMT per capita as a function of urban area
population. Figure 8.1 in Reference 10 shows this relationship for the years
1977, 1982, and 1987. Population data must be derived locally.
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The fourth method described in Reference 10 for estimating regional VMT
is to use data compiled by individual state transportation departments and
reported by FHWA in National Functional System Mileage and Travel Summary. *
The data tabulated in this document represent daily VMT for each urbanized
area in the U.S., estimated during 1975. The specific urban area boundaries
assumed for these estimates may not be the actual ones that currently exist;
therefore, some adjustment may be required. Also, basic travel patterns and
trends may be somewhat different from those assumed when the VMT projections
were made. The VMT data obtained from Reference 11 should, therefore, be
reviewed and validated by the regional transportation agency prior to being
used in the development of the emission inventory.
Finally, alternative methods for estimating regional VMT should be
considered. The procedure described in Method 1 that uses VMT estimates from
Highway Statistics^ and an inventory of regional highway mileage by
functional type would provide a good basis for assessing the reasonableness of
VMT estimated using any of the four methods described above.
4.5.2.1.3 Distribution of VMT by Vehicle Type
The requirement as specified in Reference 10 is to disaggregate total VMT
into two components—auto VMT and truck VMT. To accomplish this, Reference 10
provides a table (Table 8.4) indicating the percentages of total regional VMT
performed by trucks for 34 different urban areas in the U.S. The percentages
range from 10 to 21 percent and are based on several studies performed during
the late 1960's and early 1970's. The recommended procedure is to select from
the table one of the urban areas that is considered similar (population,
geographic location, etc.) to the area being inventoried and use the
corresponding truck factor. VMT by vehicle type is derived from:
VMTA - VMT - VMT (4-11)
< ft (4-10)
and
where VMT = truck VMT,
VMT = auto VMT,
A
VMTTQT = total regional VMT, and
f = truck factor, from Table 8.4 in Reference 10.
4.5.2.1.4 Estimating Travel Speed
Since emission rates are a function of travel speed, estimates must be of
the speed characteristics of the highway system must be developed. The
guidance provided in Reference 10 is to use local data where they exist;
otherwise use an average speed value of from 25 miles per hour for older, more
densely developed urban areas to 35 miles per hour for more modern and smaller
cities that have extensive freeway systems.
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A more appropriate approach may be to disaggregate total VMT by
functional roadway class and use actual speed study data, if available, or
engineering estimates to characterize speed. This approach is explained in
part of Method 1.
4.5.2.1.5 Estimating Trips
One component of the total emissions produced by highway vehicles is
associated directly with the number of individual vehicle trips that occur.
The procedures established in Reference 10 require that only auto trips be
considered, since trip-related emissions have been incorporated into the truck
emission rates applied to truck VMT.
The most appropriate method for determining the number of auto trips
occurring in the study area is to use trip generation data, if available, from
the regional transportation planning agency. If direct estimates of trips are
not available, Reference 10 recommends the use of a set of curves that
presents the relationship between average trip distance and the urban
population for 1982 and 1987, and the application of the appropriate average
trip distance to the auto VMT value derived in the previous step to yield
total auto trips. The curves are presented in Figure 8.2 of Reference 10.
The estimated number of auto trips occurring in the study area, then, is:
(4-12)
t\JLLi
where N = number of auto trips;
VMT = auto VMT, calculated from equation (4-11); and
A
ATD = average trip distance, derived from Figure 8.2 in Reference 10.
4.5.2.2 Calculation of Emissions
The data derived provide the basis for estimating total emissions from
highway vehicles using emission factors from Reference 4. The procedures
contained in Reference 10 for calculating each emission component - that is,
vehicle-related, trip-related, and travel-related emissions are discussed
below.
4.5.2.2.1 Calculating Vehicle-Related Emissions
Vehicle-related emissions are associated with evaporative losses from the
fuel system and involve hydrocarbons only. They are calculated as the product
of the regional vehicle population and an emission factor, which is presented
in Reference 10 for calendar years 1977, 1982, and 1987. Evaporative losses
are calculated separately for autos and trucks, as:
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EVAP = AUTOS x EF A (4-13)
A evapA
and
EVAP^ = TRUCKS x EF _ (4-14)
T evapT
where EVAP = evaporative emissions from autos;
A
EVAP = evaporative emissions from trucks;
AUTOS = number of autos in the study region, from equation (4-8);
TRUCKS = number of trucks in the study region, from equation (4-9);
EF = evaporative emission factor, in grams HC/day, for autos;
evapA c T, c i n j
from Reference 10; and
EF = evaporative emission factor, in grams HC/day, for trucks,
from Reference 10.
4.5.2.2.2 Calculating Trip-Related Emissions
Trip-related emissions are calculated for autos only. These emissions
are associated with the cold-start and hot-start conditions when the exhaust
emissions rate is temporarily much higher than after the vehicle has been
operated for a few minutes. Startup emissions are determined by the total
number of auto trips, the percentage of those trips that start with the engine
fully cooled, and the ambient temperature.
The first step in calculating trip-related emissions is to determine the
number of trips that begin with the engine fully cooled to ambient
temperature. Reference 10 provides two methods that require the use of
regional parking duration data, and also provides a set of default values that
can be applied in the absence of specific parking information. These default
values are:
53 percent for calendar year 1977,
64 percent for calendar year 1982, and
67 percent for calendar year 1987.
The number of cold-start trips, then, is:
N = N x P (4-15)
CS CS
where N = number of trips in the cold-start mode;
N = total number of trips, from equation (4-12); and
PCS = percentage of trips beginning in the cold-start mode, based on
the percentages provided above, or local data.
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Cold-start emissions of hydrocarbons, carbon monoxide, and oxides of
nitrogen are calculated separately as the product of the number of trips
beginning in the cold-start mode and an emission factor provided from Table
8.6, 8.7, or 8.8 in Reference 10:
ECS. = N x EF . (4-16)
A cs csA
where ECS = cold start emissions from auto trips;
A
N = number of trips beginning in the cold-start mode, from
equation (4-15); and
EF . = cold-start emission factor, in grams/trip, from Reference 10,
CS Tables 8.6, 8.7, and 8.8, respectively for HC, CO, and NO
emissions.
It should be noted that the cold-start emission factors for HC and CO are
temperature dependent; therefore, these emission components are derived for a
particular month or season. Again, the intent is generally to develop an
inventory reflecting the critical season for the pollutant of interest. This
usually means that HC inventories reflect summer conditions, while CO
inventories are based on winter conditions. For NOX emissions, a humidity
correction factor incorporating ambient temperature, barometric pressure, and
relative humidity must be applied. This correction factor is based on
prevailing conditions during the morning hours (0700 to 0900 hours) during the
critical NOX season, and is computed as:
CF = 1.353 -
f R (T + 459.4)
(6.449 x 104)P - (4.887 x 10~2) f R (T + 459.4)
(4-17)
where CF = NOX correction factor for humidity;
f = relative humidity expressed as a percent;
R = water vapor capacity in g/nr, from Table 8.11 in Reference 10;
T = temperature in degrees F; and
P = barometric pressure in inches of Hg.
Compute CF and multiply the total NOX emissions from all sources by CF to
obtain the total NOX corrected for humidity.
The second element of the trip-related emissions component concerns hot
soak emissions. These are additional evaporative losses of HC that result
from high engine temperatures at the end of a trip. Hot soak emissions are
computed for autos only, from:
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EHSA = N x EF, . (4-18)
A hsA
where EHS = hot soak emissions from auto trips, HC only;
A
N = number of auto trips, from equation (4-12); and
EF, = hot soak emission factor, in grams EC/trip, from page A8-18
of Reference 10.
4.5.2.2.3 Calculating Travel-Related Emissions
Travel-related emissions are computed as the product of VMT and an
emission factor in grams of pollutant per VMT. Reference 10 provides emission
factors for both autos and trucks, respectively, for HC, CO, and NOX, as a
function of average travel speed and calendar year, in Tables 8.8 and 8.9.
Travel emissions for autos and trucks are computed from:
n
ETRAA = vMTA. x EF .. (4-19)
A *— ' Ai traAi
ETRAT = T. x EF (4-20)
where ETRA = travel emissions from autos;
A
VMT . = VMT by autos at speed i;
Al
EF . = Emission factor, in giams of pollutant/VMT, at speed i,
from Table 8.9 in Reference 10;
ETRA = travel emissions from trucks;
VMT . = VMT by trucks at speed i; and
EF . = emission factor, in grams of pollutant/VMT, at speed i,
from Table 8.10 in Reference 10.
4.5.2.2.4 Calculation of Total Emissions
Total emissions from highway vehicles in the inventory area are computed
as the sum of the individual components:
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For HC:
EHC = EVAP + EVAP + ECS + EHS + ETRA + ETRA (4-21)
A i A A A i
For CO:
ECO = ECS. + ETRA. + ETRAT (4-22)
A
And, for NO :
x
ENO = (CF) x (ECSA + ETRAA + ETRA,,,) (4-23)
x A A T
where EHC = total HC emissions from highway vehicles,
ECO = total CO emissions from highway vehicles,
ENO = total NO emissions from highway vehicles, and
x x
all other terms are as defined previously.
4.5.3 ADAPTING THE MANUAL METHOD FOR USE WITH MOBILE2
The methods described above for deriving activity factors can also be
applied where emission calculations are to be performed using MOBILE2 rather
than a manual procedure. The activity factors are derived exactly as
indicated in Section 4.5.2.1, with the exception that vehicle population and
vehicle trip statistics do not have to be calculated. Otherwise, total VMT
for the region is estimated as described in Section 4.5.2.1.2, and the
distribution of the VMT by vehicle type is determined as in Section 4.5.2.1.3.
Finally, the distribution of VMT by speed category is determined using the
procedure discussed in Section 4.5.2.1.4, which completes the minimum
requirements for activity factor specification.
Further disaggregation of VMT by vehicle categories—model year and type
distributions—can be accomplished using default values in MOBILE2, as
described in Section 4.4.2.4. Cold and hot start percentages should be
obtained from the default values in the emission model (MOBILE2), rather than
from the procedure described in Section 4.5.2.2.2 Other input, such as
calendar year, meteorological parameters, etc., can be specified on the same
basis as for the manual method of calculating emissions.
The manual method described in Reference 10 for calculating emissions is
based on the MOBILE1 emission factors—MOBILE1 is the predecessor of MOBILE2.
Thus, it is more appropriate to apply Method 2 herein (Section 4.5.2) whereby
only the activity factors are derived using the procedures contained in
Reference 10, and the emission computations are then performed using MOBILE2
emission factors.
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4.6 METHOD 3—ESTIMATING EMISSIONS USING LINK-BASED TRANSPORTATION PLANNING
DATA
Since the early 1960 "s, urban areas with populations over 50,000 have
maintained formal transportation planning programs in order to meet Federal
requirements for securing certain transportation funds. These programs are
intended to establish the means for identifying both current and future
transportation needs and for planning for the implementation of projects that
will fulfill the defined needs. An important aspect of this process concerns
the regional highway network. In order to assess the adequacy of the highway
system, extensive effort is expended on carrying out detailed analyses of how
the existing highway systems are utilized, and how they will be utilized in
the future, given various scenarios for regional development. These analyses
produce detailed quantitative characterizations of the highway network that
allow the transportation analyst to determine what improvements are needed and
how they should be sequenced. Of significance here is that these analyses
also provide much of the information required for the derivation of emission
estimates for the regional highway system. The objective of this section is
to discuss how the data routinely developed by transportation planning
agencies can be utilized to construct and maintain inventories of highway
source emissions.
The method presented in this section and Method 2 presented in Section
4.5 are intended for use in estimating emissions from highway vehicles in the
larger urbanized areas under an agency's jurisdiction (see Table 4-1). These
emission estimates are then combined with estimates of rural areas to provide
an inventory of highway vehicle emissions for the entire area under an
agency's jurisdiction. However, if the data necessary for this method are
available, this method can be used to estimate emissions from all areas (rural
and urban) under the agency's jurisdiction.
4.6.1 OVERVIEW OF METHOD 3
Method 3 is referred to as a link-based approach since the primary focus
is to define all vehicular activity in terms of travel over a system of
individual highway links and calculate emissions based on the VMT and
operating characteristics of traffic on each link. In this method, each
vehicular emission component - that is, travel-related, trip-related, and
vehicle-related component, is accounted for in a single emission factor, which
is applied uniformly over the entire link. The overall concept is identical
to that for Methods 1 and 2.
First, an activity factor is derived describing both the quantity of
vehicular travel in terms of VMT, and the relevant operating conditions, such
as travel speed, vehicle type mix, and hot and cold start percentages. Based
on the operating characteristics, an emission factor is derived using the
MOBILE2 emission model and applied to the travel quantity to yield total
emissions. The primary difference between Method 3 and Methods 1 and 2 is
that Method 3 permits the assessment of emissions at a much finer level.
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Whereas Methods 1 and 2 develop emission estimates based on total network VMT
or major system (expressways, arterials, minor arterials, etc.) VMT, and a
single emission factor for the network or major system, Method 3 derives
emission estimates based on specific VMT and emission factors for each of the
hundreds of individual links that comprise the highway network. The advantage
of Method 3 is that it has the capability of providing a more highly detailed
assessment of emissions because of the much greater resolution of actual
operating conditions throughout the entire highway network. This ability
enables Method 3 to be used in air quality modeling and control strategy
assessment as well as for basic inventory development. The disadvantage is
that the entire process is more complicated than either Methods 1 or 2 and,
therefore, requires a higher level of expertise.
4.6.2 OVERVIEW OF THE TRANSPORTATION PLANNING PROCESS
Since the transportation planning process plays a key role in this
method, it is useful to discuss some of the fundamental concepts associated
with that process. A basic requirement in the process of analyzing regional
transportation characteristics is to develop an understanding of travel in
terms of where travel activity occurs, what factors stimulate travel, and how
the basic demand is satisfied.
The general methods and many of the models used by transportation
planners are standard ones developed by the FHWA and the Urban Mass Transit
Administration (UMTA) and included, respectively, in the PLANPAC/BACKPAC and
UTPS computer program batteries. However, one who is not routinely involved
with transportation planning and analysis is not likely to be required to
directly utilize the models and data output therefrom without the assistance
of a competent transportation planner. The intent here is to present the most
basic concepts of transportation planning so that the air quality analyst who
has no familiarity at all with the processes involved can begin to understand
the relationships that exist between transportation and air quality planning
activities. This will provide a starting point for the air quality analyst in
terms of identifying procedures that can be applied in the development of a
detailed emission inventory. It will not supplant the requirement for
extensive involvement by transportation planning staff during the conduct of
the inventory. The procedures and activities described in this overview are
carried out by transportation planners and not by air quality personnel.
In studying travel, the region is divided into numerous areas called
analysis zones. These analysis zones range in size from one block La the
central business district (CBD) to several square miles in the less densely
developed fringe areas. Zones are typically irregularly shaped, the
boundaries often being streets, river banks, political or census boundaries,
etc., but the intent is that each zone represent some more or less homogeneous
land use pattern. The number of zones designated depends on the size and
complexity of the planning region and may range from around 100 for smaller
urban areas to several hundred for large urban areas. Several zones may be
combined for different types of analyses to form analysis districts.
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Once the analysis zones and districts are delineated, the highway network
that will be used throughout the planning process is designated. This
planning network consists primarily of the principal roadways in the region,
usually limited to expressways, major and minor arterials, some
collector-distributor streets, and a few local streets. The network is then
divided into links by designating node points at intersections, analysis zone
boundaries, political boundaries, river Crossings, etc. Again, the number of
individual links that result is a function of the size and complexity of the
regional highway system. Some larger systems may contain over 1,000 links.
The centroid of activity for each analysis zone is identified and is connected
to the highway network by one or more pseudo-highway links called centroid
connectors. The entire network is then analyzed to determine various
characteristics of each link, such as current traffic volume carried (average
daily traffic, or ADT), typical operating speed, capacity, number of lanes,
lane width, whether curb parking is permitted, condition of the road surface,
and others. These data, along with the node designations, link length, and
various other information, are then used to form a record of each link. In
the computer systems typically used, this file is called the Historical
Record. A typical format for each link record is shown in Figure 4-2.
Detailed population, land use, and economic data are gathered for each
analysis zone, and interviews may be conducted to determine the typical travel
patterns of residents in each zone. The interviews attempt to tabulate, for
each person residing at a particular location, the origin and destination of
each trip; the time, purpose, and frequency of each trip; the travel mode
used; and other similar data. Similar interviews are conducted of motorists
entering the study area, although these focus primarily on identifying the
origin, destination, and purpose of the particular trip being made when the
interview is conducted. This entire data set is then analyzed to determine
(1) the total number of trips produced in each analysis zone, by trip purpose;
(2) the distribution of trips produced in each analysis zone to all other
analysis zones (trip interchanges); (3) the distribution of trips by mode and
purpose; and (4) the causal aspects of tripmaking. These analyses provide the
basis for forecasting travel demand ior future year development scenarios.*
The zone-to-zone travel demand, or trip distribution, is then input with
the historical record to a traffic assignment model that distributes the auto
trips over the highway network based on parameters such as travel speed, total
*Many urban areas are now using disaggregate techniques to estimate travel
demand. These techniques do not require the use of a zone system, but base
travel demand on the household. Disaggregate techniques are more data-
efficient than earlier techniques. Several disaggregate models are available
in the UTPS package of computer programs.
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Columns
Contents
1
2-6
7
8-12
13
14-17
18
19-21
22-24
25-28
29-31
32-36
37-38
39
40
41
42-44
45-47
48-51
52-54
55-59
60-61
62
63
64
65
66
67
68
69-70
71-74
75-78
79
80
Unused (perhaps identification)
a-node number
a-node leg number (0-3)
b-node number
b-node leg number (0-3)
Distance (XX.XX)
T or S for time or speed (a-b)
Time or speed (a-b) (X.XX/XX.X)
Turn penalty codes at node b
Hourly capacity (a-b)
Conversion factor (VPH/ADT)
Directional count (a-b)
Street width (a-b)
Parking (a~b)
Unused (a-b)
T or S for time or speed (b-a)
Time or speed (b-a) (X.XX/XX.X)
Turn penalty codes at node a
Hourly capacity (b-a)
Conversion factor (VPH/ADT)
Directional count (b-a)
Street width (b-a)
Parking (b-a)
Unused (b-a)
Administrative classification
Functional classification
Type facility
Surface type
Type area
Predominant land use
Link location
Route number
Condition
Unused
Source: Reference 12.
Figure 4-2. Link data contained in a Typical Historical Record File,
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trip time, volume to capacity, etc. The traffic assignment model is typically
run several times before a satisfactory distribution results. Each time it is
run, comparisons are made between the total assigned volumes and actual
measured volumes crossing a screenline, which usually cuts through several
primary travel corridors. Satisfactory results are indicated when the total
assigned and measured volumes are within approximately 10 percent of one
another and the volumes assigned to individual links appear reasonable given
the function that the link fulfills. The process is repeated with a new net
of trip distribution parameters that reflect future year land use, population,
and socioeconomic conditions. Also, new highway facilities may be added to
the highway network. The result is an estimate of the base year and future
travel demand on the regional highway system.
4.6.3 INVENTORY DEVELOPMENT
The basis for deriving activity factors for the regional highway network
is data output from the transportation planning program. The first step in
the entire highway vehicle inventory process is to determine exactly what data
are available from the planning agency. Of concern at the early stages of
inventory development is the calendar year or years represented in the
existing planning data base. Typically, detailed highway systems analyses are
performed for a base year and at least one horizon year, neither of which may
match the desired inventory years. Base years currently tend to reflect 1977
through 1979, while horizon years of 1990, 1995, and 2000 are commonly used.
A decision must be made regarding the methods to be used to develop data
reflecting the desired inventory base year if it is different from the
transportation planning base or horizon year. The decision may be to simply
adjust the transportation planning data to suit the inventory requirements by
interpolation, or to regenerate the highway network data from new trip
generation, distribution, and traffic assignment modeling runs. If the
inventory results are to be used to perform detailed air quality modeling and
to assess the impacts of mobile source emission control measures,
consideration should be given to regenerating the required data in its
entirety. On the other hand, if the inventory is not to be used for these
purposes, it is more practical to interpolate between the base year and the
horizon year to obtain data for the desired inventory base year.
The next requirement is to determine how the transportation planning data
are to be translated to emission estimates. Since the historical record
essentially provides the necessary travel data, it could be used to manually
tabulate the travel characteristics of each link. Many urban areas have
developed their own emission calculation computer programs based on MOBILE1 or
MOBILE2, and have interfaced the programs with their transportation planning
models. There are several computer models available that are designed to
directly interface with the PLANPAC/BACKPAC and UTPS models to produce
emission estimates or to produce aggregations of individual highway link data,
which are then used as input to an appropriate emission model; four of these
are described below.
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4.6.3.1 HWYEMIS1
The first of these models is called HWYEMIS1, which was developed by and
is available from the FHWA.^3 Input required consists of:
Historical record containing
Network description
Link speed
Average daily traffic (ADT) volume on each link
Area type
Predominant land use
Functional classification
Time interval of the analysis
Percentage of ADT occuring during each time interval
Other input required by the emission model
Vehicle age distribution
Vehicle type distribution
Percentage of cold and hot starts
Ambient temperature
Others as discussed previously (Section 4.4.3)
HWYEMIS1 uses the historical record and other input to derive an emission
factor for each link, and applies this factor to the product of the link
length and the ADT for each time interval to yield link emissions. The model
varies cold and hot start percentages as a function of both time of day and
location (i.e., CBD, residential area, commercial location). If various data
elements such as vehicle age distribution or vehicle type distribution are not
directly input, default values are assigned by the emission model. HWYEMISl
produces a link-by-link file of emissions for each time interval. An
additional computer routine from the PLANPAC/BACKPAC battery called SAPLSM can
be linked to the HWYEMISl program to produce tabulations of emissions within
grid cells. This type of output is necessary for most air quality modeling
efforts.
Nonnetwork VMT are not included in the historical record. Therefore, a
method must be developed for accounting for this additional travel.
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Nonnetwork VMT reflects intrazonal trips. The VMT associated with these trips
is estimated as the product of the number of intrazonal trips occurring in the
analysis zone, and one-half the radius of the analysis zone as measured along
major travel routes (alternatively, the length of the centroid connector may
be used). If gridded emission output is required, the nonnetwork VMT should
be assigned to specific links.
The MOBILEl emission model is currently included in the HWYEMIS1
program. MOBILEl has been superceded by MOBILE2, therefore, the HWYEMIS1
program should be modified by substituting emission models before applying it
to the emission inventory effort. Since MOBILEl and MOBILE2 are compatible
the substitution is not difficult.
4.6.3.2 APRAC-2
The second computer model that can be used to calculate emissions is
APRAC-2,^ which is available through the U.S. Environmental Protection
Agency. Input required by APRAC-2 is similar to that for HWYEMIS1. APRAC-2
can, however, compute link speeds based on volume-to-capacity ratios (V/C),
when capacity is input, or the speed parameter specified in the historical
record can be used. APRAC-2 accounts for non-network VMT either as a constant
percentage of network VMT, or as a variable percentage based on the general
locale. If traffic volumes contained in the historical record represent
average annual daily traffic (AADT), a seasonal adjustment factor must be
provided. This model is also capable of responding in detail to variations in
both total link volume and directional volumes as a function of time of day.
This capability requires detailed input concerning the hourly traffic patterns
by general locale.
APRAC-2 has been updated several times since it was originally introduced
in 1977. The more recent editions contain the MOBILEl emission model, whereas
the earlier ones included emission factors from Supplement 5 of AP-42.^ The
emission model should be updated by substituting MOBILE2 before it is used.
4.6.3.3 Other Transportation Models
Two additional computer models are available that can be used in the
development of regional emission inventories. The basic difference between
these and the two models described above, however, is that these models are
not really link-based ones. They do provide the capability of using regional
transportation planning data to generate emission estimates at various subsets
of the region.
The first of these models is the Community Aggregate Planning Model,^
or CAPM, which is a sketch planning model contained in the UTPS battery. CAPM
is used to calculate auto and truck travel (VMT) and speeds for an entire
region, for different settings (e.g., CBD, commercial areas, residential
areas, etc.), or for "communities," which are areas that are approximately the
size of analysis districts. Input to CAPM includes trip generation and trip
4-43
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distribution data, and area, predominant land use, and lane-miles of arterial
roadways (including expressways) in each community or locale. The model
generates VMT and speed data for each subarea or roadway system (either
arterials or expressways), by time of day. The output data are then used as
the basic activity factors for each area or highway system, and are input into
the MOBILE2 model along with other requisite data (i.e., cold and hot start
data, ambient temperature, distribution of VMT by vehicle type and vehicle
age, etc.) to derive the emission estimates.
The second model is an outgrowth of the CAPM model and is referred to as
the Regional Highway Emissions Model (RHEM).16 RHEM computes the total
regional VMT, and then distributes this VMT to various functional roadway
categories, by hour of the day, and generates a corresponding estimate of
average travel speed. The input required includes:
Regional auto trips
Regional truck trips
Travel time for work trips
Area of region
Auto trips through the region
Truck trips through the region
Lane miles of freeways
Lane miles of surface arterials
Trip and travel time data are available from trip generation and distribution
analyses, and from the historical record. Other sources, such as street
inventories and area base maps may also be required.
As with the CAPM model, the output from RHEM is used as input to the
MOBILE2 emission model to derive estimates of highway source emissions.
4.7 METHOD 4—'ESTIMATING EMISSIONS USING A HYBRID MODELING APPROACH
This method is a modification of Method 3. Essentially, the concept
involved is that a higher degree of accuracy can be obtained in the
inventorying process if the three vehicular emission components—that is,
vehicle related, travel related, and trip related components—are considered
separately. No formal methods are currently documented for performing this
type of analysis, therefore, the intent here is to present basic concepts
rather than actual methods.
It can be expected that this method will be much more data intensive than
any of the other methods. A logical starting point in determining whether it
4-44
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should be applied in a given area is to assess the quality and quantity of
existing transportation planning data. Specifically, this method requires
that detailed trip data be available so that both the number and types of trip
productions and attractions can be determined. It is expected that this
hybrid approach would require supplementary data collection in some
applications, and additional data analysis in all instances.
4.7.1 OVERVIEW OF METHOD 4
In this method, detailed transportation planning data are used to develop
estimates of highway source emissions by individual emission component. The
results obtained using this hybrid approach will provide a higher degree of
resolution in the overall inventory in terms of both time and space. This
method is most appropriate where it is expected that the results will be used
for detailed air quality modeling and control strategy assessment.
As indicated, this method differs from Method 3 in that each emission
component is considered separately using different analytical techniques.
Travel related emissions are estimated using either HWYEMIS1, APRAC-2, or some
other appropriate technique as described in Method 3. Trip-end emissions
associated with cold and hot starts, and with hot-soak emissions, are assessed
based on the detailed analysis of trip productions and attractions for each
analysis zone. Finally, vehicle related emissions associated with evaporative
losses due to changes in ambient temperature over the course of a day, are
analyzed using essentially the same data as are used in estimating
trip-related emissions.
The basic emission model used is MOBILE2. With this hybrid approach,
there is currently no standard program that allows direct computer processing
of the trip and vehicle related emission components. These must be calculated
manually, or special computer programs prepared for integrating the trip
characterizations with the appropriate MOBILE2 emission factors.
4.7.2 ESTIMATING TRAVEL RELATED EMISSIONS
Since the overall method is intended to provide a high degree of
resolution in the inventory, it can be assumed here that a gridded emission
output is required. The travel component of the inventory can be conveniently
handled using either the HWYEMIS1 or APRAC-2 models described above. The only
difference here is that the input data will indicate that no cold or hot
starts are occurring on any of the links. Also, the ICEVFG parameter in the
MOBILE2 program must be either a 2 or 3, which then requires the user to
specify the number of trips per day and the mileage per trip parameters
normally used to calculate the vehicle and trip related emission components.
The values input for the trips per day and miles per trip parameters will be
0, resulting in MOBILE2 computing an emission factor for each link that
reflects only travel related emissions.
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4.7.3 ESTIMATING TRIP RELATED EMISSIONS
For the analysis of hydrocarbon emissions, two separate components are
associated with trip emissions. The first component includes hot-soak
emissions, which result from evaporation of fuel in the carburetor and intake
system after the engine has been shut off. These losses tend to occur during
the first hour after the engine has been shut off, but it is likely that the
greatest quantity of these emissions are produced during the first several
minutes after shutdown. To derive an estimate of the hot soak emissions
produced in an analysis zone, the number of auto driver trips (both interzonal
and intrazonal) associated with the zone must be determined. The trip tables
generally available will merely indicate the total trip attractions to each
zone on a daily basis, therefore, if an hourly distribution is desired, some
further analysis is required. If the trip record files are available, a
special computer analysis can be made to define the arrival time distribution
of trips by destination. Alternatively, the entire regional trip data set can
be analyzed by purpose and time of occurrence to identify general time
distributions, which can then be applied to each zone. Once an estimate of
the number of trips terminating in each zone during each hour has been
derived, an emission factor, in grams per trip, can be applied to yield total
emissions per hour per zone.
The second component of the trip related emissions applies to
hydrocarbons, as well as carbon monoxide and oxides of nitrogen. This is the
cold- and hot-start emissions increment. This component can be analyzed in
any of several ways. The most straightforward of these methods is to use the
empirical methods developed by Ellis for the FHWA^ that consider cold and
hot starts to be a function of trip purpose and locale. Because of
significant variations in travel among urban areas, local data should be used
when applying this method. The specific methods are described in detail in
Reference 17. A major concern in applying this method is the age of the
travel data. If the data are more than 5 years old, and the area has been
growing, travel patterns may have changed and the cold and hot start
percentages may no longer be valid. Alternatively, hourly trip data can be
assessed on an analysis district basis to identify the number of trips
beginning each hour as a function of the parking duration prior to beginning
the trip. Note that the larger the analysis zone, the less spatial resolution
will be reflected in the emission inventory. The minimum parking duration
that will cause a cold start to occur depends on the model year of the
vehicle—for pre-1975 vehicles, which did not have catalytic converters, the
cold soak time required to produce a cold start is about 4 hours, whereas for
a post-1974 vehicle with a catalytic converter, the minimum soak time is 1
hour. The relative percentages of catalytic and noncatalytic vehicles changes
over time. Therefore, the cold start distribution will also change (cold
start precentages are increasing). Once the cold start percentages for the
analysis district have been identified, they can be applied to the individual
analysis zones contained in the district to determine the number of trips
beginning in the cold mode. To calculate the cold start emissions, an
emission factor and a VMT quantity must be derived. To calculate the emission
factor, a value for travel speed must be designated. This value can be the
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approximate average speed for all travel in the analysis zone. In terms of
VMT per trip, the product of the average trip speed and the travel time in the
cold mode (based on Reference 18, a value of 200 seconds is recommended) will
yield VMT. An assumption that can be made, which simplifies the analysis, is
that the entire cold-start increment occurs in the zone where the trip
originates. This cold-start VMT must be removed from the VMT calculated under
Travel Related Emissions (Section 4.7.2) for each zone to avoid double
counting. If it is desired to assign the cold-start emissions to specific
links, References 17 and 18 should be consulted to determine which types of
links in various locales are most likely to be carrying vehicles operating in
the cold-start mode during different time periods.
4.7.4 ESTIMATING VEHICLE RELATED EMISSIONS
Vehicle related emissions result from the expansion of fuel vapor in the
fuel tank, due to the increase in ambient temperature during the day. The
MOBILE2 evaporative emission factor for hydrocarbons includes these emissions,
but a more detailed inventory may be desired. No formal procedure exists for
preparing such an inventory, but emission estimates are possible. Given the
cause of these emissions, it can be assumed that diurnal emissions are likely
to occur between the hours of 6 a.m. and 6 p.m. A detailed assessment of
these emissions could be made by determining the average number of vehicles in
each analysis zone hourly during this time period. This number will already
have been determined during the estimation of trip related emissions (Section
4.7.3). An appropriate emission factor is then applied to each hourly zonal
total. Reference 10 contains evaporative emission factors for cars and trucks
on a grams per day basis. If these factors are applied on an hourly basis and
under the assumption that the emissions actually occur during only 12 hours of
the day, the hourly rate would be equal to one-twelfth of the daily rate as
specified in Reference 10.
4.7.5 TOTAL EMISSIONS
The total emissions are the sum of the individual components. The travel
related and trip related components can be described in terms of link
emissions, whereas the vehicle related component is considered on an areawide
basis. If a gridded emission format is used, the vehicle related emissions
will have to be assigned to individual grids using a manual method that
considers the area of the analysis zone contained in the grid cell. The
travel and trip related emissions can be handled by the previously mentioned
gridding programs since, again, these are primarily link emissions.
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References for Chapter 4.0
1. Procedures for Emission Inventory Preparation, Volume III: Area Sources,
EPA-450/4-81-026c, U.S. Environmental Protection Agency, Research
Triangle Park, NC, September 1981.
2. User's Guide to MOBILE2 (Mobile Source Emissions Model),
EPA^t60/3-81-006, U.S. Environmental Protection Agency, Office of Mobile
Source Air Pollution Control, Ann Arbor, MI, March 1981.
3. Compilation of Air Pollutant Emissions Factors. Third Edition and
Subsequent Supplements, AP-42. U.S. Environmental Protection Agency,
Research Triangle Park, NC, October 1980.
4. Compilation of Air Pollutant Emission Factors: Highway Mobile Sources,
EPA-460/3-81-005, U.S. Environmental Protection Agency, Office of Mobile
Source Air Pollution Control, Ann Arbor, MI, March 1981.
5. Highway Statistics—(Various Years), U.S. Department of Transportation,
Federal Highway Administration, Highway Statistics Division (HHP-40),
Washington, DC, Annual Report.
6. Motor Fuel Consumption Reports—MF26G, U.S. Department of Transportation,
Federal Highway Administration, Vehicles, Drivers, and Fuels Branch
(HHP-43), Washington, DC, Monthly Reports.
7. 1977 Census of Transportation—Truck Inventory and Use Survey (Individual
States and U.S.). U.S. Department of Commerce, Bureau of the Census,
Social and Economic Statistics Administration, Washington, DC, 1977.
8. Fuel Emission Inventory Requirements for 1982 Ozone State Implementation
Plans, EPA-450/4-80-016, U.S. Environmental Protection Agency, Research
Triangle Park, NC, December 1980.
9. Procedures for Emission Inventory Preparation, Volume I: Emission
Inventory Fundamentals, EPA-450/4-81-026a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, September 1981.
10. How to Perform the Transportation Portion of Your State Air Quality
Implementation Plan, Technical Guidance of the U.S. Department of
Transportation, Federal Highway Administration, and the U.S.
Environmental Protection Agency, DOT/FHWA 6/80, November 1978.
11. National Functional System Mileage and Travel Summary, From the 1976
National Highway Inventory and Performance Study, U.S. Department of
Transportation, Federal Highway Administration, Office of Highway
Planning.
12. Computer Programs for Urban Transportation Planning. PLANPAC/BACKPAC,
General Information Manual, U.S. Department of Transportation, Federal
Highway Administration, Washington, DC, April 1977.
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13. HWYEMIS1 Program Documentation, U.S. Department of Transportation,
Federal Highway Administration, Urban Planning Division, Washington, DC,
February 1979.
14. Users Manual for the APRA-2 Emissions and Diffusion Model, Stanford
Research Institute, Menlo Park, CA, June 1977.
15. CAPM Users Guide and Air Quality Planning with CAPM, U.S. Department of
Transportation, Federal Highway Administration, Washington, DC, 1978.
16. Regional Highway Emissions Model (RHEM), U.S. Department of
Transportation, Federal Highway Administration, Urban Planning Division
(HHP-22), Washington, DC.
17. Determination of Vehicular Cold and Hot Operating Fractions for
Estimating Highway Emissions, U.S. Department of Transportation, Federal
Highway Administration, Washington, DC, September 1978.
18. Determination of Percentages of Vehicles Operating in the Cold-Start
Mode, EPA-450/3-77-028, U.S. Environmental Protection Agency, Research
Triangle Park, NC, August 1978.
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5.0 EMISSIONS FROM AIRCRAFT
Pollutants are emitted from aircraft whenever the engines are operating.
In the context of emission inventory development, however, the concern is
limited to those portions of the flight that occur between ground level and an
altitude defined as the above ground level inversion height. Within this
layer, the air is fairly stable and aerosol emissions tend to diffuse rather
than be transported away. As a result, emissions occurring below the ground
level inversion height have an affect on air quality at ground level, owing to
the mixing that occurs within the air cell.
Emission characteristics vary as a function of both the type of aircraft
and the operating mode. Aircraft can be categorized broadly as either civil
or military. Civil aircraft include all categories of fixed and rotary wing
craft from the smallest single engine, privately owned and operated, to the
largest commercial aircraft. Within the civil category, two subcategories are
often discussed—commercial, and general. Commercial aircraft are used in
regularly scheduled flights, while general aviation includes all nonmilitary
aircraft not used in scheduled service. In the development of emission
inventories, it is necessary to account for specific types of aircraft using
each airfield.
Aircraft emissions are affected by the throttle power setting—that is,
the percentage of maximum power that the engines are producing at a given
time. However, the power setting is fairly predictable based on the specific
operating mode in which the aircraft is operating. For purposes of the
inventory development, five operating modes are of interest:
Approach,
Taxi/idle in,
Taxi/idle out,
Takeoff, and
Climb out.
Collectively, these five modes form the Landing-Takeoff (LTO) cycle, which
provides a basis for allocating aircraft emissions to a specific region.
The development of a complete emission inventory for a region requires
that an accounting be. made of all emission sources, including aircraft. The
objective of this section is to delineate methods that can be used to prepare
and maintain an inventory of emissions from aircraft, as part of a
comprehensive inventorying program.
5-1
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5.1 OVERVIEW OF INVENTORY METHODS
Emissions from aircraft are estimated using a set of activity factors,
that reflect the specific type of aircraft and their operating
characteristics, and emission factors, developed by the U.S. Environmental
Protection Agency (EPA) which are reported in Compilation of Air Pollutant
Emission Factors,^ hereafter referred to as AP-42. The activity factors are
developed for individual types of aircraft owing to the wide variation in
emission characteristics associated with each type. A listing of the specific
types of aircraft, currently in service, in each category is shown in Tables
5-1 and 5-2.
Activity factors describe the time spent in each of the five operating
modes (i.e., approach, taxi/idle in, taxi/idle out, takeoff, and climb out) as
the aircraft completes a Landing-Takeoff (LTO) cycle. Emission factors for
each type of aircraft have been developed in terms of emissions produced per
hour of operation in each of the five operating modes. Therefore, the product
of the activity factor and the emission factor is the quantity of emissions
produced.
In terms of developing estimates of emissions from aircraft, the largest
effort is in the derivation of the activity factors. The principal airports
handling commercial and general aircraft are required by the Federal Aviation
Administration to maintain detailed records of both the number and types of
aircraft using the facility. Therefore, a data base can be established
without much difficulty. It is more difficult to obtain similar information
for military airfields since the data may have some security classification
that would prohibit its release. However, military facilities are required to
report emissions to the regional EPA office in whose jurisdiction they are
located.
Two methods can be applied to derive emission estimates. The first
involves the application of emission rates that reflect a generalized
Time-In-Mode (TIM) scenario for each LTO cycle, for each type of aircraft.
The required activity factor for this method is simply the number of LTO
cycles for each type of aircraft. A more detailed analysis that considers
more specifically the actual TIM for each airport facility can be
performed. For this more detailed method, the activity factor is the actual
TIM for each of the five modes that comprise the LTO cycle, for each type of
aircraft. Both methods are described in detail in the following sections.
5.2 METHOD 1—USE OF A GENERALIZED TIME-IN-MODE SCENARIO TO ESTIMATE EMISSIONS
This method provides a relatively quick indication of the emissions
produced by aircraft operations in an area. It is, however, based largely on
a set of simplifying assumptions that limit the accuracy.
The method involves derivation of a set of activity factors, which define
the number of each type of aircraft using each airport facility. Once the
activity factors have been defined, an emission factor for the type of
5-2
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TABLE 5-1. CIVIL AIRCRAFT CATEGORIES USED IN
EMISSION INVENTORY DEVELOPMENT
Aircraft
_JNy_'_ Mfg. Type Model/Series
Supersonic transport
BAC/Aerospatiale Concorde
Short, medium, long range
and jumbo jets
BAG 111-400
Boeing 707-J20B
Boeing 727-200
Boeing 737-200
Boeing 747-200B
Boeing 747-200B
Boeing 747-200B
Lockheed L1011-200
Lockheed L1011-100
McDonnell-Douglas DC8-63
McDonnell-Douglas OC9-50
McDonnell-Douglas DC10-30
Air carrier turboprops -
commuter, feeder line and
freighters
Beech 99
GD/Convair 580
DeHavilland Twin Otter
Fairchild F27 and FH227
Grumman Goose
Lockheed LI 88 Electra
Lockhead L!00 Hercules
Swearingen Metro-2
Business jets
Cessna Citation
Dassault Falcon 20
Gates Learjet 24D
Gates Learjet 35, 36
Rockwell International
Shoreliner 75A
Business turboprops
(EPA Class P2)
Beech B99 Airliner
DeHavilland Twin Otter
Shorts Skyvan-3
Swearingen Merlin IITA
General aviation piston
(EPA Class PI)
Cessna 150
Piper Warrior
Cessna Pressurized
Skymaster
Piper Navajo Chieftain
Source: Reference 1, p. 3.2.1-3.
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aircraft is applied, which yields an estimate of the quantity of emissions
produced. The two steps—derivation of the activity factor, and calculation
of emissions—are discussed in the following sub-sections.
5.2.1 DERIVATION OF AN ACTIVITY FACTOR
The primary requirements in order to derive the activity factor are a
listing of the number of LTO cycles occurring at each airport facility, by
type of aircraft. The first step in this process is to identify all airports,
including privately owned, publicly owned, and military. Private air strips
typically do not warrant consideration owing to the relatively low level of
activity associated with their operation. The source of this information is
likely to be the analyst's familiarity with the area being inventoried;
although other sources such as maps and directories can also be used.
References 2 and 3 provide a list of airports with Federal Aviation
Administration (FAA) control towers, which are the most active civil airports,
for each state.
After identifying airports, the next step is to determine the number of
LTO cycles that occurred during the inventory year, by aircraft type. For
commercial aircraft, this information can be obtained directly from Table 7 of
Reference 3, which lists total departures by aircraft type for each airport in
the U.S. where scheduled service is available. This Reference is published
annually and provides total annual statistics; it is usually published during
the fall of the year subsequent to the reporting year. An excerpt from Table
7 of Reference 3 is presented here in Figure 5-1, to indicate the type and
format of data contained therein. For general aviation activity, Reference 2
should be consulted. Table 4 of Reference 2 (an excerpt from which is shown
here in Figure 5-2, for illustrative purposes) shows itinerant, local, and
total operations* by air carrier, air taxi, general aviation, and military
aircraft, for each airport in the U.S. that has an FAA-operated control
tower. Each operation accounted for in the table represents one landing or_
one takeoff, therefore the total operations divided by 2 equals the number of
LTO cycles. For this method, further disaggregation of general aviation
aircraft is not warranted. If the desired inventory year is different (more
recent) from the year represented by the most current editions of References 2
and 3, adjustments can be made by obtaining as much data for the desired year
as is available, and using it to provide a basis for estimating the relative
level of activity between the two years. This requires direct interviews with
airport officials to obtain the necessary data. The adjustment factor is:
f = E 0 / £ 0.R (5-1)
= J =
*Itinerant operations refer to flights that leave from or originate away from
the general area of the airport (beyond 20 miles radius), while local flights
occur entirely within a 20-mile radius of the airport, although the origin or
destination may not be at the airport. It should be noted that military
airfields are not included in this table.
5-5
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TAbLt "> HiCAL YhAfr \ 979
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where f = adjustment factor to be applied to adjust year k data to
reflect inventory year j;
0£ i = total operations for n months of inventory year j, based on
data obtained from the airport facility; and
Oik = total operations for n months of year k, based on data obtained
from the airport facility.
The adjusted data for the inventory year is:
0 = f x (5-2)
where 0-i = total adjusted number of aircraft operations for inventory
year j,
0^ = total aircraft operations reported in References 2 and 3 for
year k, and
f = adjustment factor derived in Equation (5-1).
Separate adjustment factors can be derived from commercial and general
aviation activity.
The number of operations occuring at military airfields may be more
difficult to obtain. The Air Force releases a summary of the number of
opertions occurring at its facilities under the title of Air Traffic Control
Operations ,^ but specific data regarding the types of aircraft involved are
not routinely available. In specific instances, the operations officer at the
installation should be contacted to determine what data can be made
available. As a minimum, the total number of military aircraft operations for
a particular year should be determinr.ble. In addition, military installations
are required to report air pollution data to the U.S. Environmental Protection
Agency. State and local agencies should contact their regional EPA office for
these data.
5.2.2 CALCULATION OF EMISSIONS
The basis for calculating emissions from the aircraft operations
determined in the previous step is a set of emission factors provided for
civil and military aircraft, respectively, in Tables 3.2.1-9 and 3.2.1-10 of
AP-42.1 These emission factors are presented in terms of total quantity of
pollutant produced during each LTO cycle, by type of aircraft. For commercial
aircraft, the activity data derived from Reference 3 are in terms of aircraft
departures, the number of which is equal to the number of LTO cycles. On the
other hand, the aircraft activity data contained in Reference 2, for general
5-8
-------
other hand, the aircraft activity data contained in Reference 2, for general
aviation (as well as for the other categories), is for specified aircraft
operations, which are either a landing or a takeoff; therefore, the total
operations must be divided by 2 to obtain the number of LTD cycles. Emissions
are calculated by:
E.. = (LTO). x (ELTO).. (5-3)
where Ej4 = total emissions of pollutant i, in pounds or kilograms,
produced by aircraft type j;
(LTO)j = number of LTO cycles by aircraft type j; and
(ELTO)ij = emission rate, in pounds or kilograms of pollutant i per
LTO cycle, for aircraft type j.
The emission factor for each type of commercial aircraft is obtained from
Table 3.2.1-9 in AP-42.1 It may not be possible to identify specific types
of aircraft in either the general aviation category or the military category.
Where this occurs, a general emission factor, in grams of pollutant produced
during each LTO cycle can be applied; these general factors were developed by
the EPA and are presented here in Table 5-3.
5.3 METHOD 2—ANALYSIS OF TIME-IN-MODE TO ESTIMATE EMISSIONS
This method is used where more detailed air quality modeling is
contemplated, therefore justifying a more comprehensive analysis of emissions
produced by aircraft activity. The focus of this method is the actual time
spent in each of the five modes (i.e., approach, taxi/idle in, taxi/idle out,
takeoff, and climbout) by each type of aircraft. Whereas Method 1 utilizes a
generalized set of assumptions regarding the time spent in each mode during
TABLE 5-3. COMPOSITE LTO CYCLE EMISSION FACTORS FOR THREE GENERAL
AIRCRAFT CATEGORIES
Emission factor (Ibs per LTO cycle)
Category Particulates SOX NOX HC CO
Commercial
General avaiation
Military
1.18
0.02
15.23
2.84
0.01
1.43
26.93
0.028
9.16
30.66
0.41
27.1
67.46
18.8
48.8
Source: Charles 0. Mann. U.S. Environmental Protection Agency, Office of Air
Quality Planning and Standards. Telephone conversation on 10 March
1981.
5-9
-------
the LTO cycle, this method allows the analyst to specify the duration of each
mode to reflect actual conditions prevailing at the airport and to calculate
emissions accordingly. In an overall sense, the two methods are similar in
that the basis for estimating emissions is the time-in-mode associated with
the LTO cycle,
5.3.1 DERIVATION OF AN ACTIVITY FACTOR
In this method emphasis is placed on deriving an activity factor that is
sensitive to local conditions affecting emissions attributable to aircraft
operations. Certain meteorological conditions affect the amount of pollution
contributed by aircraft operations, since only a portion of the total
emissions produced by these sources has an effect on ground level
concentrations. Specifically, only emissions produced while the aircraft is
operated within the limits of the above ground inversion are of interest. The
layer between the ground and the top of the inversion is referred to as the
mixing layer and is described in terms of its depth or height. Mixing height
varies, for example, as a function of geographical location, topography, wind
conditions, cloud cover, season of the year, and time of day. Variations in
mixing height are illustrated in Figures 5-3, 5-4, and 5-5, which,
respectively show mean summer morning, mean summer afternoon, and mean winter
afternoon mixing heights. The variations in this parameter as a function of
both time of day and season are readily apparent. The implication is that the
portion of emissions produced while the aircraft is aloft that should be
ascribed to the area being inventoried is also a function of diurnal and
temporal variations in the local mixing height. For emission inventorying
purposes, the specific modes during the LTO cycle that are affected by
variations in the mixing height are the approach mode and the climbout modes.
Implicit in the Method 1 technique is the assumption that the mixing depth is
3000 feet (914 meters).1
Specific time-in-mode (TIM) for all modes in the LTO cycle are implicitly
assumed in Method 1. The TIM for approach and climbout are based on the
performance characteristics of each type of aircraft and the 3000 foot mixing
height. Taxi/idle in and taxi/idle out TIMs are based on empirical data from
a large metropolitan airport during the busiest period of the day.'*'-' The
resulting TIMs for these two modes used in Method 1 tend to be longer than
those likely to occur during most periods of the day at any airport. The TIM
for the takeoff mode is a function of the performance characteristics of the
aircraft, and therefore is not likely to be affected by local conditions.
Specific TIMs assumed in Method 1 are presented here in Table 5-4.
The first step in deriving activity factors for Method 2 is to identify
alL airports and determine the number of types of aircraft using each airport
during the period to be represented by the inventory. The same basic data
sources are used for both Methods 1 and 2. However, it is more desirable to
identify the specific types of all aircraft, including general aviation and
military aircraft, for Method 2. If specific data concerning general aviation
aircraft operations cannot be obtained from the airport operations officials,
then census data developed by the Federal Aviation Administration (FAA) and
5-10
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5-13
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TABLE 5-4. TIME-IN-MODE DATA USED TO DEVELOP GENERALIZED EMISSION
FACTORS FOR LTO CYCLES
Time-in-mode (minutes)
Aircraft
category
Commercial
carrier3
General
aviation3
Military15
Taxi/
Aircraft type idle out
Jumbo, long
and medium
range jet
Turboprop
Transport —
piston
Business jet
Turboprop
Piston
Helicopter
Combat
USAF
USN
Trainer —
Turbine
USAF T-38
USAF general
USN
Transport —
Turbine
USAF general
USN
USAF B-52
and KC-135
Military —
Piston
Military —
Helicopter
19.0
19.0
6.5
6.5
19.0
12.0
3.5
18.5
6.5
12.8
6.8
6.5
9.2
19.0
32.8
6.5
8.0
Takeoff
0.7
0.5
0.6
0.4
0.5
0.3
-
0.4
0.4
0.4
0.5
0.4
0.4
0.5
0.7
0.6
-
Climbout
2.2
2.5
5.0
0.5
2.5
5.0
6.5
0.8
0.5
0.9
1.4
0.5
1.2
2.5
1.6
5.0
6.8
Taxi/
Approach idle in
4.0
4.5
4.6
1.6
4.5
6.0
6.5
3.5
1.6
3.8
4.0
1.6
5.1
4.5
5.2
4.6
6.8
7.0
7.0
6.5
6.5
7.0
4.0
3.5
11.3
6.5
6.4
4.4
6.5
6.7
7.0
14.9
6.5
7.0
Total
32.9
33.5
23.2
15.5
33.5
27.3
20.0
34.5
15.5
24.3
17.1
15.5
22.6
33.5
55.2
23.2
28.6
-t-j •— f-mr —
Source: Reference 1, Tables 3.2.1-3 and 3.2.1-4.
aReference 4.
bReference 5. 5-14
-------
reported in Census of U.S. Civil Aircraft^ can be used to identify the types
of aircraft registered with FAA in the county or counties being inventoried.
Appendix B of Reference 6 lists the number of general aviation aircraft
registered in each county in the U.S. by engine type (i.e., piston, turboprop,
and turbojet), number of engines, and seating capacity for both fixed wing and
rotory wing aircraft. The data regarding the type distribution of aircraft
registered in the county is used as the basis for a type distribution for all
general aviation aircraft using the airports in the inventory area.
As part of the data collection effort regarding the types of aircraft
using the region's airports, information must be obtained on certain
characteristics of each type of aircraft. Specifically, the number and type
of engine used (i.e., piston, turboprop, or turbojet), its manufacturer, and
the model designation must be identified. This information is required since
the aircraft emission factors that will be applied are specified by engine
type, model, and manufacturer, and are presented in terms of emissions per
hour of operation in each mode, per engine. This information can be obtained
from Tables 3.2.1-1 and 3.2.1-2 of Reference 1 (see Tables 5-1 and 5-2, here)
and from References 3 and 6.
The next step is to derive specific TIM data for each type of aircraft.
This is done separately for the approach and climbout modes, the taxi/idle out
and taxi/idle in modes, and the takeorf mode. The TIMs for the approach and
climbout modes can be estimated for each aircraft type using local
meteorological data representing the inventory period. Specifically, mixing
height data is usually maintained on an ongoing basis by the weather station
at each airport. The inversion height is measured and recorded several times
each day; therefore mixing height data for several periods during any
particular day should be available. The mixing height used should reflect a
weighted average for a day during the season for which emissions are being
inventoried. The weighted height is:
(5-4)
where H = weighted average mixing height, in feet or meters, during the
day of interest;
N£ = number of LTO cycles occurring period i on the day of interest;
and
H£ = mixing height, in feet/meters, during period i on the day of
interest.
5-15
-------
To calculate H, data must be available concerning the diurnal
distribution of LTO cycles. This information can be obtained from the airport
operations office. Mixing height data are obtained from the airport weather
station.
To calculate TIMs for the approach and climbout modes for each type of
aircraft, data contained in Table 5-4 (from Reference 1, Tables 3.2.1-3 and
3.2.1-4) are adjusted as a function of the relative difference between the
local weighted average mixing height, and the assumed mixing height on which
the TIMs in Table 5-4 were based. Specifically, TIMs are calculated as:
TIM1 = (H / H ) x TIM (5-5)
app as app
TIM1 , = [(H-500) / (H -500)] x TIM , (5-6)
elm as elm
where TIM'app = adjusted approach time-in-mode, in minutes, reflecting
local mixing height;
H = weighted average mixing height, in feet or meters, for the
local area during the day of interest;
Has = assumed mixing height, in feet or meters, from which TIMs
were computed in Reference 1, which has a value of 3000
feet;
= time-in-mode, in minutes, for the approach mode from Table
5-4;
= adjusted climbout time-in-mode, in minutes, reflecting
local mixing height; and
= time-in-mode, in minutes, for the climbout mode from Table
5-4.
In Equation (5-6) the H and Has values are both decreased by 500 feet to
account for the fact that the climbout mode begins after the aircraft is
actually airborne and the throttle power setting is cut back from 100 percent
to 75 percent. This point where the power setting is cut back, ends the
takeoff mode and initiates the climbout mode. It is assumed here that a
representative altitude where this change of mode occurs is 500 feet.
The next step is to define the TIMs associated with taxi/idle in and
taxi/idle out modes. The only method that can be used to derive local values
for these TIMs is to observe actual aircraft operations at the facility being
considered. If field studies cannot be made, then the alternative is to use
5-16
-------
the values shown in Table 5-4. It is not likely that in the context of
emission inventory development, significant improvements could be made in the
accuracy of the TIM data for the taxi/ idle mode presented in Table 5-4. These
values should be used unless some readily available data indicate otherwise.
In most instances, data concerning the specific types of military
aircraft operating at military bases will not be available. A general
indication of the distribution of aircraft by category (i.e., jet transports,
piston engine transports, trainers, high performance aircraft, etc.) may be
determinable. These general categories should be used where more specific
data cannot be provided. The source for military data is the airfield
operations officer and the regional U.S. Environmental Protection Agency
office.
5.3.2 CALCULATION OF EMISSIONS
The emissions produced by each type of aircraft during each mode of the
LTO cycle are calculated as a function of the TIM, the number of engines used
by the particular type of aircraft, and the mode-specific emission factor for
each type of aircraft (actually, for each type of aircraft engine). The
following equation illustrates the calculation:
5
E. = £ (TIM../60) x (EF. ) x (NE ) (5-7)
XJ ^=1 -" J J
where E^j = total emissions, in pounds, of pollutant i produced by
aircraft type j;
TIMjk = time-in-mode, in minutes, for mode k for aircraft type j;
= emission factor, in pounds of pollutant i per hour of
operations in mode k, for each engine used on type j
aircraft; and
NEj = number of engines used on type j aircraft.
Total emissions produced by the entire source category is:
ETi ' Eij (5"
J=l
where E^i = total emissions, in pounds, of pollutant i produced by types j
through n aircraft operating in the inventory area; and
Ei = defined in Equation (5-7).
5-17
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5.4 INVENTORY MAINTENANCE
Two factors are of concern in terms of inventory maintenance. First,
changes in the level of activity at a particular facility will result in an
increase or reduction of emissions. General trends in airport activity can be
monitored using the data provided in References 2 and 3, which are annual
publications. The second factor concerns changes in the types of aircraft
using the facility. The current trend in the airlines industry (in fact, in
all segments of the transportation industry) is to replace older equipment
with modern, fuel efficient types. This turnover in the types of aircraft
being used, will also be reflected in the emissions produced. Periodic
reviews must be made of the literature to remain current in terms of the types
of changes occurring in the types of aircraft being used, and also in terms of
the relative differences in the emission characteristics of the older and
newer aircraft. The intent should be to remain cognizant of revisions in
either recommended emission inventorying techniques, or in basic emission
factors for each emission source.
Every airport will have non-aircraft originated emissions as a result of
operation (off-highway fuel use, plane and vehicle fueling, fuel storage,
fugitive dust). It is imperative that these emissions be accounted for in the
emission inventory. Procedures for estimating these emissions are presented
in Volumes II and III of this series.®>9
5-18
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References for Chapter 5.0
1. Compilation of Air Pollutant Emission Factors, Third Edition and
Supplements, AP-42, U.S. Environmental Protection Agency, Research
Triangle Park, NC, October 1980.
2. FAA Air Traffic Activity, U.S. Department of Transportation, Federal
Aviation Administration, Office of Management Systems, Washington, DC,
Published annually.
3. Airport Activity Statistics of Certified Route Air Carriers, U.S.
Department of Transportation, Federal Aviation Administration, Office of
Management Systems, Washington, DC, Published annually.
4. Control of Air Pollution for Aircraft and Aircraft Engines, 38 FR 19088,
July 17, 1973.
5 . Air Pollution Emission Factors for Military and Civil Aircraft,
EPA-450/3-78-117, U.S. Environmental Protection Agency, Research Triangle
Park, NC, October 1978.
6. Census of U.S. Civil Aircraft, U.S. Department of Transportation, Federal
Aviation Administration, Office of Management Systems, Washington, DC,
Published annually.
7. Mixing Heights, Wind Speeds, and Potential for Urban Air Pollution
Throughout the Contiguous United States, U.S. Environmental Protection
Agency, Research Triangle Park, NC, January 1972.
8. Procedures for Emission Inventory Preparation—Volume II: Point Sources,
EPA-450/4-81-026b, U.S. Environmental Protection Agency, Research
Triangle Park, NC, September 1981.
9. Procedures for jmission Inventory Preparation—Volume III: Area Sources,
EPA-450/4-81-026c, U.S. Environmental Protection Agency, Research
Triangle Park, NC, September 1981.
5-19
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6.0 EMISSIONS FROM RAILROADS
The primary interest when inventorying railroads is emissions from
locomotives. Railroad locomotives used in the U.S. are primarily of two
types—electric and diesel-electric. Electric locomotives are powered by
electricity generated at stationary power plants and distributed by either a
third rail or overhead catenary system. Emissions are produced only at the
electrical generation plant, which is considered a point source and therefore
not of interest here. A diesel-electric locomotive, on the other hand, uses a
diesel engine and generator to produce the electricity required to power its
electric traction motors. Emissions produced by large diesel engines are of
interest in emission inventory development. Methods are presented here for
inventorying emissions from diesel-electric locomotives.
Other locomotives may be in use, including steam locomotives,
diesel-hydraulic, and gas-turbine locomotives. Their numbers and emissions
are insignificant compared to diesel-electric locomotives. Steam locomotives
are used in very localized operations, primarily as tourist attractions.
These locomotives are insignificant in terms of the quantity of emissions that
they produce. Diesel-hydraulic locomotives are generally high-horsepower
units used in areas where trains must be hauled over steep grades. Given the
similarity between these locomotives and diesel-electric locomotives, emission
estimates can be developed using the same methods. Gas turbine locomotives
have been used to some extent since the early 1950 "s for various line-haul
operations. Their numbers are insignificant relative to diesel-electric and
electric locomotives.
6.1 OVERVIEW OF INVENTORY METHODS
Presented here are two basic methods for inventorying emissions from
diesel-electric locomotives. Both methods require the derivation of an
activity factor, and an appropriate emission factor defined as a function of
the activity factor. The first approach uses the quantity of fuel consumed
for railroad operations, which represents the activity factor, and an emission
factor from AP-42 defined in terms of emissions produced per gallon of fuel
burned. The second approach is somewhat more detailed, involving the
derivation of work output estimates for locomotives and the application of an
emission factor from AP-42. Each method is presented separately in following
sections.
6.2 METHOD 1—EMISSION ESTIMATES BASED ON FUEL USE
This approach to inventorying emissions from railroad locomotives
involves the derivation of an activity factor based on the quantity of fuel
used by locomotives. The estimated fuel use is then used with an emission
factor, defined in terms of quantity of pollutant produced per gallon of fuel
burned, to derive the emission estimates.
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6.2.1 DERIVATION OF THE ACTIVITY FACTOR
The activity factor for locomotives operating in the study area can be
derived using any of several methods. All are based on allocating a share of
the total fuel used state-wide by locomotives to smaller areas of the state.
Annual fuel use by railroad locomotives is reported for each state in a
U.S. Department of Energy publication entitled Energy Data Reports.-^ This
report is published during the last quarter of the year subsequent to the
reporting year (i.e., data for 1978 were published in November 1979).
The allocation of state-wide fuel use to a study area is based on
identifying an appropriate surrogate parameter whose relative distribution
(study area to state-wide) can be assumed to approximate the relative level of
railroad activity. Surrogates are railroad track mileage, freight density,
and population. The use of each of these to apportion state-wide fuel use
data is discussed separately.
6.2.1.1 Apportioning State Fuel Use Data Based on Track Mileage
This method of apportioning state fuel use to a particular region assumes
that usage is directly proportional to miles of track.* Study area fuel use
by locomotives is estimated as:
Qi = QT x (Mi/MT) (6-1)
where Qi = the estimated quantity of fuel consumed in study area i, in
gallons/year;
0/£ = the quantity of fuel used in the state by railroads, obtained
from Reference 2, in gallons/year;
M£ = the miles of active railroad track located in study area i;
and
M-j = total miles of active railroad track located in the state.
Total and study area track mileage can be obtained by state from several
sources. The first source to consider is the State Transportation agency.
Since the mid 1970"s, states have been required to develop and maintain a
comprehensive rail transportation plan in order to be eligible for funding
under the Federal Railroad Administration's Federal Rail Service Assistance
Program.^ These plans contain data concerning rail service within the state
and also define various characteristics of the rail network, including
mileage. The rail plan document and the state agency responsible for its
publication are, therefore, valuable sources of data.
*Excluding track used exclusively by electric locomotives,
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Another source of information for state track mileage is a document
published periodically by the Association of American Railroads, entitled
Railroad Mileage by States.^ This document tabulates, for each state the
number of miles of right-of-way operated by each railroad company, and the
track-miles operated by terminal and switching companies. The most current
edition was published in December 1978 reflecting mileage as of December 1977.*
There is no single data source that can be specified here for obtaining
track-miles for sub-areas of states (i.e., emission inventory study areas).
Tabulations of track-mile data may be available for counties, SMSAs, or urban
areas from some state transportation agencies, or from the county or
metropolitan planning organization within whose jurisdiction the study area is
located. Alternatively, track-miles can be obtained by direct measurement
from an appropriate map, such as the County Series maps (obtained from the
state transportation agency), U.S. Geologic Survey maps, U.S. Transportation
Zone Maps, or locally prepared maps. If direct measurements are used, the
mileage parameter should be the same as that reflected by the state-level
data; that is, if the state-level data are in terms of total right-of-way
miles, the measured parameter for the study area should also be right-of-way
miles.**
In urban areas, measuring railroad (track or right-of-way) mileage can
become somewhat confusing, particularly around switch yard and terminal
areas. It is desirable to account for the higher level of activity in
terminal areas and switchyards, yet measuring the actual track mileage in
these areas may be very difficult and the use of the total track miles in
these areas may overstate their significance. Instead, it is recommended
that, in areas with railroad terminals, siding tracks be ignored. A siding
track is a dead end track that has no further branches along its length.
These are apparent when examining a map.
For switchyards, an expedient method is used which accounts for
switchyard activity as a function of urban area population, rather than track
mileage. The distance through the switchyard is measured and multiplied by a
factor that varies according to the population of the area where the
switchyard is located. These factors are shown in Table 6-1.
*At the time of publication of this document, the 1978 edition of Railroad
Mileage by States was the most recent edition.
**It is noted that in the literature, mileage statistics are often specified
in terms of route-miles, which is synonymous to right-of-way miles.
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TABLE 6-1. SWITCHYARD MILEAGE FACTORS (f)
Urban area population Switchyard factor
Less than 50,000 5
50,000-100,000 10
100,000-250,000 15
Over 250,000 20
In Equation (6-1), the value of M^, track-mileage within study area i, is
determined from:
Mi - MMLi + MSi + (fi X MSYi} (6"
where M-[ = track mileage within study area i;
^MLi = miles of mainline and branch line track (or right-of-way) in
area i;
Msi = miles of spur track in area i;
MSYi = total distance, in miles, through all switchyards located
in area i; and
f-L = the switchyard mileage factor from Table 6-1.
6.2.1.2 Apportioning State Fuel Use Data Based on Freight Density
An alternative method for apportioning statewide fuel consumption
involves the use of freight density statistics for the primary rail line
branches in the state. Freight density is the gross ton-miles carried per
track mile. In this statistic, gross ton-miles accounts for the total weight
of both freight and railroad cars moved over the track. Freight density
statistics are obtained from several sources, including State Rail Plans,
state agencies responsible for rail planning or regulation, and direct
interviews with railroad officials.
An equivalent density factor must be derived for intercity and commuter
rail activity. This factor is developed for passenger train traffic for each
line as a function of frequency of service (trains per year), the typical
makeup of the train (that is, the number of cars), and the route mileage of
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the line. This information can be obtained from direct interviews with
railroad officials. The density is:
D.. = W x N .. x N . x 10 (6-3)
ji cji TJi
where Dif = the annual passenger train density in million gross ton-miles
per track mile on line j, in area i;
W = average gross weight of a passenger car, in tons (in the
absence of specific data, a value of 60 tons can be used);
= typical number of cars in trains using line j, in area i; and
= frequency of service on line j, in area i; in trains per year.
Passenger line mileage and density must be calculated for the entire
state by substituting values reflecting state-wide values for Nc and NX
into Equation (6-3).
The estimated fuel use in the inventory area is derived by:
m m
£ (LiDJi + >- /L-D- 1-
T \ *J "J /
-i • w * j.;"; j.;'.-
s (vj,* s (LA
where Q^ and Qj are as defined in Equation (6-1),
m
^J(L.D-). = the summation of the product of individual rail line length
j L (in miles) and density D (in millions of gross ton-miles
per mile), for freight lines j through m within study area i;
n
2J(L.D.) = the summation of the product of individual rail line length
j L (in miles), and density D (in millions of gross ton-miles
per mile), for freight lines j through n within state s;
™ i i
2J(L.D.). = the summation of the product of individual rail line length
j L (in miles) and density D (in millions of gross ton-miles
per mile), for passenger lines j through m within study
area i; and
V> ' '
2^, (L.D.) = the summation of the product of individual rail line length
j L (in miles) and density D (in millions of gross ton-miles
per mile), for passenger lines j through n within state s.
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6.2.1.3 Apportioning State Fuel Use Data Based on Population
This is the easiest method to apply since it relies on population data,
which are usually available. The study area fuel use is estimated from:
Q£ = QT x (Pi/PT) (6-5)
where Qi and Q^ are as defined in Equation (6-1),
P£ = area i population, and
P-J = total statewide population.
6.2.2 DERIVATION OF EMISSION ESTIMATES
To derive an estimate of the emissions produced in the study area as a
result of railroad activity, an emission factor is applied to the fuel use
estimated, Q£. The emission factors used are obtained from AP-42, Table
3.2.2-1.1
The estimated annual emissions of each pollutant is:
E . =0. x EF (6-6)
pi xi p
where Epi = mass of emissions (in tons or kg per year) of pollutant p,
produced by railroad locomotives in area i;
Q.[ = annual quantity of fuel used by locomotives in study area i;
and
EFp = emission factor for pollutant p, from Table 3.2.2-1 in
Reference 1.
6.3 METHOD 2—EMISSION ESTIMATES BASED ON WORK OUTPUT
A more accurate estimation of emissions produced by railroad locomotives,
than Method 1 provides, can be effected through a more detailed examination of
the usage of rail lines. The intent is to derive an activity factor based on
the estimated total annual or daily horsepower-hours (work output) expended by
different types of locomotives. The activity factor is then used with an
emission factor to develop the emission estimate.
6.3.1 DERIVATION OF THE ACTIVITY FACTOR
Activity factors in terms of horsepower-hours per day or year by
locomotive type are derived for each rail line, as well as for all switchyards
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and terminals. The data required to develop the activity factors must be
obtained by direct interviews with railroad officals involved in operations.
Interviews (as opposed to sending questionnaires) are required if this method
is to yield more precise results than those of Method 1.
6.3.1.1 Data Requirements and Collection
Rail operations can be categorized as line-haul, transfer, or switch
activity. Line-haul operations concern the movement of trains between urban
areas, with only limited switching activity to add or delete cars from the
train. Transfer activity is the movement of trains among yards generally
within the same urban area. Here, both line-haul and switching operations
occur but the size of the trains is much smaller than for the line-haul
category, and the switching activity occurs primarily in terminal areas. The
last category, switching, refers to the movement of train cars within rail
classification yards and to terminals located in or near these switchyards.
Owing to the significant differences in both the types of locomotive used and
the conditions under which they are operated (hence, in emission
characteristics), it is necessary to develop separate activity factors for
each type of operation.
The first step in the derivation of activity factors is to obtain maps of
the study area that depict the rail lines and indicate the operator of each.
County Series maps, U.S. Geologic Survey maps, U.S. Department of
Transportation Zone Maps, or locally prepared maps can be used.
The next step is to contact each railroad to arrange an interview with an
appropriate official—usually one involved with operations. The purpose of
the interview is to obtain data for each rail line concerning:
the number of trains per day (per week or per year) using each line;
the estimated average number of locomotive units per train for each line;
the average operating speed over the line; and
the length of the line.
This information must be defined separately for line-haul and transfer
operations. For switching operations, an estimate of the daily, weekly, or
annual locomotive-hours of operation is required.
Also during the interview, information should be obtained concerning the
type of locomotives routinely used on each line for each type of operation.
The specific locomotive categories that are of interest are defined in terms
of engine type and horsepower class. The requirement is to determine the
distribution of each locomotive type, for each type of operation, on each rail
line. Specific locomotive categories include:
2-cycle supercharged, by horsepower rating;
2-cycle turbocharged, by horsepower rating; and
4-cycle, by horsepower rating.
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Horsepower rating can be aggregated by range, using:
600-899 horsepower (hp),
900-1199 hp,
1200-1599 hp,
1600-1999 hp,
2000-2399 hp,
2400-2999 hp,
3000-3599 hp,
3600-4199 hp, and
4200 hp and over.
For each rail line, as well as for each switchyard and terminal, a data file
should be developed similar to that shown in Figure 6-1.
The data should represent each rail line, or various segments of each
rail line if operations are different on each segment. Also, information
concerning temporal and diurnal rail traffic patterns and other points that
could have a bearing on emissions in the future (e.g., expansion or
contraction of service, new service, new equipment, etc.) should be identified.
6.3.1.2 Calculation of the Activity Factor
The two sets of data (rail line specific and locomotive specific)
obtained for each line are analyzed to derive an estimate of the daily or
annual locomotive-hours or use, by each type of locomotive (engine type and
horsepower class), for each type of operation (line-haul, and transfer)*,
using:
*Locomotive-hours for switching operations should be obtained directly from
the interviews.
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Interview By: Date:
Person Interviewed: Title:
Affiliation: Phone No.
Address:
Rail Line:
General Location: From: To:
Line or segment length: miles.
Calendar Year Represented:
Line-Haul Operations:
Number of trains per day, week, or hear (state which)
Average number of locomotives per train:
Average train speed: mph
Percentage of locomotives by type:
Record percentage of all line-haul locomotives using the line by
locomotive type:
Percentage of Locomotives by Type
Maximum Horsepower Rating
600- 900- 1200- 1600- 2000- 2400- 3000- 3600- Other
Engine Type 900 1200 1600 2000 2400 3000 3600 4200 (specify)
2-Cycle,
Supercharged
2-Cycle,
Turbocharged ^
4-Cycle
Figure 6-1. Interview record/data file for railroads.
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Transfer Operations:
(Record same data as for line-haul)
Switching Operations:
Record the average daily, weekly, or annual (specify which) locomotive-
hours expended in switching operations for each locomotive type:
-Hours of Operation by Locomotive Type
Engine Type
Maximum Horsepower Rating
600- 900- 1200- 1600- 2000- 2400- 3000-
900 1200 1600 2000 2400 3000 3600
3600- Other
4200 (specify)
2-Cycle,
Supercharged
2-Cycle,
Turbocharged
4-Cycle
Remarks: Indicate seasonal usage patterns, projected levels of service, etc.,
that might have an impact on emissions.
Figure 6-1 (continued).
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h. = (L/S) x (P ) x (N) (6-6)
K iC
where h^ = daily or annual hours of operation of locomotive type k, within
the study area;
L = length, in miles (kilometers), of the line being analyzed within
the study area;
S = average train speed in miles (kilometers) per hour, over the line;
I?k = percent of total equipment-hours for the line represented by
locomotive type k; and
N = number of trains per day (or year) times the number of type k
locomotives per train.
The next step is to calculate the work output in horsepower-hours for each
type of locomotive for each of the three types of operation. This is done
using:
w, = 1 x P, x h, (6-7)
k k k
where w^ = work output for locomotive type k, in horsepower-hours;
1 = load factor, which accounts for variations in output during the
operation of a locomotive;
P^ = available horsepower, taken as the average for the horsepower
range class (see Figure 6-1) for locomotive type k; and
h^ = daily hours of operation per day (or year) by locomotive type k,
from Equation (6-6).
The load factor, 1, in Equation (6-7) has a value of 0.4 for line-haul, 0.2
for transfer, and 0.06 for switching-operations. The result will be a work
output estimate for each type of locomotive used in each of three types of
operation, for each rail line or segment thereof.
6.3.2 CALCULATION OF EMISSIONS
Emissions are computed for each rail line based on the estimated work
output by each locomotive category, from Equation (6-7), and an emission
factor defined in terms of grams of pollutant per horsepower-hour for each
type of locomotive. The emission factors are found in Tabla 3.2.2-2 of
AP-42.1 Table 3.2.2-2 in AP-42 contains emission factors for the following
locomotive categories:
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2-cycle, .supercharged switch engines;
2-cycle, supercharged road engines;
2-cycle, turbocharged road engines;
4-cycle, switch engines; and
4-cycle, road engines.
To use these emission factors, assume that the breakpoint between road
engines and switch engines in Table 3.2.2-2 of AP-42 is 1800 horsepower;
therefore the emission factors for switch engines will be used for calculating
emissions for locomotives less than 1800 horsepower, while the road engine
emission factors would be used for locomotives rated at 1800 horsepower or
more.
6.4 TEMPORAL DISTRIBUTION
Seasonal variations in railroad activity occur. Temporal variations in
activity are determined through direct interviews with officials associated
with the railroads operating within the study area.
It is also necessary, in some applications, to develop an estimate of
daily emissions during a specific season (e.g., during the summer if the
inventory is to support ozone modeling efforts). Where seasonal variations
are judged insignificant, daily emissions can be estimated by dividing the
total annual emissions produced by 300 days per year. Similarly, if a
particulate month reflects exceptionally high activity, the daily emissions
can be estimated by dividing the total estimated emissions for that month by
24 days per month.
Although most railroads operate 24 hours a day all year, the day—per-year
and day-per-month figures suggested here are intended to weight emissions
toward a weekday when most activity, and hence emissions, occur. If more
precise data are available from local sources, they should be used.
6.5 EMISSION FORECASTS
The railroad industry is experiencing both growth and contraction,
depending largely on the geographic location considered. The most reliable
indications regarding future levels of activity are obtained by direct
interviews with officials representing the railroads in the study area.
Alternatively, a general scenario for future railroad activity has been
proposed by the Association of American Railroads,9 which provides a basis
for projecting future emissions for inventorying purposes.
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References for Chapter 6.0
1. Compilation of Air Pollution Emission Factors, Third Edition and
Supplements, AP-42, U.S. Environmental Protection Agency, Research
Triangle Park, NC, October 1980.
2. Energy Data Reports, Sales of Fuel Oil and Kerosene, Department of
Energy, Washington, DC, DOE/EIS-0113/77, Published annually.
3. Part 266, 49 CFR, U.S. Department of Transportation.
4. Railroad Mileage by States, Association of American Railroads,
December 31, 1977.
5. Exhaust Emissions from Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines. Part 1. Locomotive Diesel Engines and
Marine Counterparts, APTD-1490, U.S. Environmental Protection Agency,
Research Triangle Park, NC, October 1972.
6. Young, T. C., Unpublished Data from the Engine Manufacturers Association,
Chicago, IL, May 1970.
7. Hanley, G. P., Exhaust Emission Information on Electro-Motive Railroad
Locomotives and Diesel Engines, General Motors Corp., Warren, MI, October
1971.
8. Wiltsee, Kenneth W., Jr., A Methodology and Inventory for Fuel Use and
Emissions from Railroads in the St. Louis Air Quality Control Region for
the Regional Air Pollution Study, Walden Division of Abcor, Inc., April
1977.
9. Yearbook of Railroad Facts, Association of American Railroads,
Washington, DC, Published annually.
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7.0 EMISSIONS FROM VESSELS
In some areas a significant amount of recreational and commercial marine
activity occurs, which contributes to the region's total emission output. In
spite of the relatively small emission contribution generally attributed to
marine activity, an accounting must be made of these sources if the overall
emission inventory is to be considered complete. The purpose of this chapter
is to define methods used to inventory and estimate emissions produced by
marine activity.
For purposes of developing emission inventories, marine activity can be
classified as either recreational or commercial (including military). These
two categories reflect differences in both vessel size and usage
characteristics, and reflect basic differences in the methods applied to
estimate emissions. Recreational boating includes vessels generally less than
100 feet in length, most being less than 30 feet. These vessels are powered
either by outboard or inboard engines. Outboard engines range in size from
1 horsepower to over 200 horsepower, are gasoline powered (Otto cycle), and
are usually designed to operate on a 2-stroke cycle. Inboard engines range in
size upwards from less than 10 horsepower for auxiliary engines or from
approximately 60 horsepower for main engines, and may be either gasoline or
diesel. Most of these engines tend to resemble automobile engines in terms of
basic design, size, and performance. A third category—inboard/outboard—
utilize an inboard engine with an outboard drive assembly. These can be
considered with the inboard category for purposes of emission inventory
development.
There tends to be very little control or regulation regarding the use of
recreational vessels. States usually require that boats be registered and
some regulation exists on safety, but there usually are no agencies at any
level of government that maintain data regarding the actual usage—location
and hours of operation—of recreational vessels.
Commercial vessels include all boats and ships used either directly or
indirectly in the conduct of commerce or military activity. These include
vessels ranging in size from 20-foot charter boats to the largest tankers and
military vessels, which can exceed 1000 feet in length. In spite of the large
range of vessels represented by this category, several points of commonality
exist that are particularly relevant in terms of emission production. First,
the majority of vessels in this category are powered either by diesel engines
or steam turbines. Diesel engines are used throughout the range of vessels in
this category, are the engine most often used in large foreign vessels, and
are becoming more popular in the U.S. as well.1
Advances in the design of very large, low-speed, 2-cycle diesel engines
have resulted in the production and use of engines ranging up to 36,000
shaft-horsepower (SHP). Although heavier and requiring more maintenance than
steam turbine propulsion systems, the low speed diesel engine is capable of
significantly more efficient fuel use. Current large diesels may have a
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specific fuel consumption rate as low as 0.35 Ib per SHP-hour, compared with a
typical rate of 0.56 Ib per SHP-hour for steam boiler/turbine systems using
essentially the same type fuel. In addition to steam turbine and diesel
propulsion, gas turbine powered vessels may be found. These are used
primarily on certain military vessels designed for high speed operation, or on
high performance civilian vessels such as hydrofoils or surface-effect
vehicles. On larger military vessels, these systems are often used only when
the vessel is out to sea, while during maneuvering operations in port areas
auxiliary diesel engines are used. The gas turbine engines used on high
performance vessels are very similar to aircraft engines. Most commercial and
larger military ships produce their own power while at dockside for operating
winches, pumps, ventilation fans, refrigeration, lights and electrical
equipment, etc. Older steam turbine vessels may operate one main boiler at
reduced draft to power an auxiliary turbine-generator. More commonly, an
auxiliary diesel engine-generator set is used. The exact dockside power
requirements vary greatly depending on the type and size of the ship and the
type of cargo handling equipment on board.
The second common element among vessels in this category is the type of
fuel used. The predominant fuel is oil, both distillate and residual grades,
which is used in all motorships and most steamships. The trend today is for
the use of heavy oil, typically Number 6 or Bunker C, in both large diesel
engines and steam generators. Moderate speed diesel engines usually require a
blend of distillate and residual oil for satisfactory operation. Smaller
diesels, and many medium and low speed diesels operating at part throttle
while maneuvering in port, require distillate oil, although a fraction of it
may be residual. Other fuels are used but only to a limited extent. Wood,
coal, and bagasse may be used in some very limited applications, although
there appears to be some movement towards coal.* Also, nuclear powered ships
are in use, although when dockside or maneuvering in port, an auxiliary power
system is typically used. The number of nuclear powered vessels is small
enough that no special consideration need be given them in developing the
emission inventory.
The methods described below for estimating emissions do not require a
significant amount of highly detailed information on the region's marine
activity. The general nature of the inventorying methods presented reflects
both the impracticality of developing a highly detailed accounting of vessel
characteristics and activity for a particular area, and the lack of a detailed
compilation of emission factors for the range of vessel types that are
currently used. Further, the relative contribution by vessels to the areawide
*At least one very large coal-fired ship is being constructed by General
Dynamics in Quincy, Massachusetts. This ship will use a fluidized-bed
combustion system rather than the stoker used on earlier ships. When
completed, this ship will be used to supply coal to electric power plants at
coastal locations along the Atlantic Coast.
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emission burden is small. As a practical matter, there is little value in
expending a disproportionate share of the total inventory resources on this
particular source category.
7.1 OVERVIEW OF METHODS
Estimates of emissions produced by marine vessels are developed using an
activity factor and an emission factor. The activity factor is the estimated
quantity of fuel used by vessels operating in an area. It is emphasized that
the method is limited to emissions produced by fuel burned in a vessel's
boilers or engines, either to move the vessel or provide power for onboard
utilities (heat, lights, refrigeration, ventilation, etc.). Evaporative
emissions produced during tanker loading and unloading operations, or
refueling a vessel are calculated by the methods presented in Volumes II and
III of this series^s^ and are not calculated by this method.
The emission factors used are found in AP-42. These factors are
presented in terms of mass of pollutant produced per gallon of fuel burned by
outboard and inboard motors used for recreational boating, by several types of
motorships and steamships, and by auxiliary power systems operating dockside.
The methods presented here will provide a reasonable estimate of the
emissions produced by marine activity in a county or urbanized area where it
can be expected that this source is relatively minor (contributing less than
5 percent of the area's total for any pollutant). If a more detailed estimate
of emissions from this source is required, the general procedure used is the
same as described here, except that the activity factors would be derived in
much greater detail. The degree that the emission estimates can be improved,
however, is constrained by the general nature of the emission factors
currently available.
7.2 ESTIMATING EMISSIONS FROM RECREATIONAL BOATING ACTIVITY
The approach to estimating emissions from recreational boating activity
involves the application of a fuel use estimate and an emission factor. The
fuel use estimate represents the total quantity of gasoline and diesel fuel
consumed annually by pleasure boats. The estimates are developed separately
for inboard and outboard craft.
An estimate of the quantity of fuel used by pleasure craft operating in
the study area is derived indirectly by using boat registration data, a usage
factor, and an activity distribution factor. This indirect approach is
necessary because direct fuel sales data are not available from any government
or private agency.
The first step in the process is to obtain boat registration data for the
state. These data should specify the number of inboard and outboard boats
and, if possible, the number of inboard boats using diesel engines and the
number using gasoline engines. This information can be obtained from the
agency responsible for maintaining the boat registration activity for the
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state, or, alternatively, estimates of the population of pleasure boats by
state can be obtained from private associations, such as the National
Association of Engine and Boat Manufacturers.5 if the distribution of
inboard boats by engine type is not available, a default distribution of
70 percent gasoline and 30 percent diesel can be assumed.1^
The next step is to develop an estimate of the number of boats that are
actually used in each part of the state. This is accomplished by applying the
assumption that boat use is directly proportional to the surface area of water
bodies available for use. The general equation for estimating the number of
pleasure boats that operate in the study area is:
N. = (N ) x (A-/A) (7-1)
1 o IS
where N£ = the estimated number of recreational boats that are used
in area i;
Ns = the total number of recreational boats registered in the state;
A£ = the surface area of lakes, ponds, rivers, and coastal waters
used for boating in area i; and
As = the surface area of lakes, ponds, rivers, and coastal waters
used for boating in the state.
Separate values of N£ should be derived for outboard and inboard
craft. Further, if a boat size (length) distribution can be determined for
inboard craft, it may be useful to differentiate between water bodies where
any size craft is likely to be used and those where only smaller (less than
20 feet in length) craft are used, and to allocate usage separately for these
two size categories of inboard craft.
The total surface area of water bodies within the state, As, and within
the study area, A£, can be derived by direct measurement from a suitably
scaled map, or can be obtained from a publication entitled Area Measurement
Reports—Areas of (Specified State),6 published by the Bureau of the
Census,* which reports surface area measurements of land, water, and total
area for each county or other civil division, whether Bureau of the Census
data or measured data are used, coastal waters must be included. The area of
coastal water is derived by measurement, and applying the assumption that the
area's outer limit extends 1 mile out from and parallel to the shore line.
There is no formal method for differentiating between water facilities limited
to boats smaller than 20 feet and areas available to all pleasure craft. This
differentiation must be accomplished subjectively, although general
assumptions used should be based on some knowledge of the water facilities.
*Although these documents are currently out of print and therefore not
available from the Bureau, copies can be found in libraries.
7-4
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It is reasonable to assume that the use of larger inboard craft will be
limited to major rivers, large lakes, and coastal waters, whereas the smaller
inboard craft and all outboard boats will be used on any water body were power
boating is permitted. The result is an estimate of the number of boats in
each of two or three categories (outboard and inboard, or with inboards
further categorized by two size classes) that operate within each study area.
The next step is to derive an estimate of the quantity of fuel used by
each category of boat. The equation for the quantity of fuel used annually by
motor boats of any type is:
= N.
x f .
J
x C
(7-2)
where
Qij =
Nij
the annual quantity of fuel, in gallons, used by boat
category j in area i;
the number of category j boats used in area i, from
Equation (7-1);
f4 = a fuel consumption factor, in gallons per hour, for category j
boats; and
C = a usage factor describing the expected annual hours of operation
of recreational boats.
The fuel consumption factor used is either 1.5 gallons per hour for outboard
engines or 3.0 gallons per hour for all inboard engines.?»°»' The usage
factor, C, is dependent on the geographic location of the area and is found by:
where 10
M
C = 10 x M (7-3)
the assumed number of hours per month of recreational boat
operation; and
the number of months per year during which the monthly mean
temperature exceeds 45°F for areas north of 43° latitude, 48°F for
areas between 37°
37° latitude.
and 43° latitude, and 55°F for areas south of
The value of M for a particular area is obtained from climatological data
published by the U.S. Department of Commerce.^0
The quantity of fuel for inboard boats, computed from Equation (7-2),
will reflect the total combined gasoline and diesel usage. At this point,
estimates of the quantity of each type of fuel must be made. This is
accomplished by using either data obtained from boat registration statistics
7-5
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or default values. If registration data are available indicating the
distribution of gasoline and diesel craft by size, the estimated quantities of
gasoline and diesel fuel used in the area should be based directly on this
distribution—that is, if P percent of inboard craft under 20 feet in length
are diesel powered, then P percent of the total quantity of fuel used by
inboard boats less than 20 feet in length is assumed to be diesel, while
(100-P) percent is gasoline. If the registration data only indicate the
percent of total craft that are diesel, then it should be assumed that all
craft under 20 feet are gasoline powered; therefore, only fuel used by the
larger inboard craft will be separated into diesel and gasoline components
(using the same method described previously). If no registration data are
available regarding the percentage of diesel- and gasoline-powered boats, and
separate estimates were developed for fuel used by large and small inboard
boats, assume that all of the smaller inboards are gasoline powered, and that
30 percent of the large inboards are diesel while the remaining 70 percent are
gasoline powered. If no data on the distribution of engine types are
available and no distinction was made between large and small inboard craft,
assume that 15 percent of the total fuel used by inboards is diesel and
85 percent is gasoline. In any event, assume that all fuel used by outboard
craft is gasoline. Depending on the level of detail applied, one of the
following sets of fuel use data will be developed:
Set 1: Gasoline used by outboards,
Gasoline used by small inboards,
Gasoline used by large inboards,
Diesel used by small inboards, and
Diesel used by large inboards.
Set 2: Gasoline used by outboards,
Gasoline used by small inboards,
Gasoline used by large inboards, and
Diesel used by large inboards.
Set 3: Gasoline used by outboards,
Gasoline used by inboards, and
Diesel used by inboards.
The final step is to compute emission estimates. This requires the
application of an emission factor for each pollutant to the quantity of fuel
consumed, or:
E.. = Q.. x EF. (7-4)
iJP iJ JP
where Ejjp = the quantity of emissions of pollutant p, produced annually in
area i, by category j boats;
Qij = the quantity of fuel used in area i by category j boats; and
EFjp = the emission factor for pollutant p for category j boats.
7-6
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The emission factors, EFp, for each type of boat are included in Table 7-1.
TABLE 7-1. AVERAGE EMISSION FACTORS FOR RECREATIONAL BOATS
Pollutant3
Gasoline-powered
outboard motors
(lb/103 gal)
Gasoline-powered
inboard motors
(lb/103 gal)
Diesel-powered
inboard motors
(lb/103 gal)
so2
CO
HC
N02
6.4
3300
1100
6.6
6.4
1240
86
131
27
140
180
340
aParticulate emissions are considered negligible.
Source: Reference 4, AP-42, Tables 3.2.3-5 and 3.2.4-1.
The total emissions produced by pleasure craft is the aggregate of
emissions produced by each of the individual categories.
7.2.1 TEMPORAL DISTRIBUTION OF EMISSIONS
Recreational boating activity is highly seasonal with the most activity
occurring during the summer. Monthly variations in boating activity can be
estimated based on inquiries made to marinas or boating clubs, or it can be
assumed that 75 percent of the activity occurs during the months of June,
July, and August. Further, it can be assumed, in the absence of actual data,
that the average daily activity during the peak week of the summer is equal to
1.5 percent of the total annual activity, as measured by fuel use.
7.3 EMISSIONS FROM COMMERCIAL VESSELS
Two methods are available for estimating emissions from commercial and
military vessels. The first method is based on the quantity of fuel sold for
marine use, from which emissions are estimated using a standard set of
assumptions regarding the percentage of fuel sold that is actually used within
the port area, and the emission rate associated with the use of the fuel. The
second method attempts to provide a more accurate estimate based on ship
movement data. Both methods are described here.
7.3.1 FUEL SALES METHOD
Sales data for residual and distillate fuel oil used for marine purposes
are compiled by the U.S. Department of Energy and published annually as state
summaries.^ To apportion state fuel sales to a particular harbor or port,
7-7
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the relative level of activity within the harbor must be established. To do
this, an inventory of vessel activity must be obtained for both the harbor and
statewide. Such an inventory is published by the Corps of Engineers in
Waterborne Commerce of the United States.^2 in part 2 of that document, a
table is provided for each port within a state, indicating the number of
commercial vessels, by size (draft), that enter and leave.
In apportioning total statewide marine fuel sales, distillate fuel and
residual fuel are considered separately. To apportion residual fuel, the
assumption is made that only vessels with a draft of 18 feet or more use
residual oil. The apportioning factor for residual oil sold in port i is:
fri = 18)/(IW (7-5)
where Fr£ = the apportioning factor for residual fuel used in port i,
= the number of vessels using port i with a draft of 18 feet
or greater, and
= the total number of vessels using all ports within the state
with a draft of 18 feet or more.
The estimated quantity of residual oil sold in port i is computed as the
product of the statewide marine fuel sales, in gallons or barrels, and the
apportioning factor, fr£.
The quantity of distillate oil sold in port i is estimated in a similar
fashion. The Waterborne Commerce of the United States-^ document is used to
determine the total number of vessels with drafts of 18 feet or more and those
with drafts of less than 18 feet, using port i, and the total number of ports
within the state. The apportioning factor for distillate fuel in port i is:
fdi - [(Ni<18) + 2(Ni>18)1/[(Ns<18) + 2(Ns>lB>] (7'6)
where fi8 = the number of vessels with 18 feet or more of draft using
~ port i,
Ns
-------
In Equation (7-6), larger vessels (i.e., those drawing 18 feet or more)
are weighted by a factor of 2, which accounts for both the greater quantity of
fuel used by these vessels while moving, and the use of auxiliary power
generation systems by these larger vessels while at dockside. The estimated
quantity of distillate fuel sold in port i is the product of the total
distillate fuel sold in the state for marine use and the apportioning factor,
fdi-
All of the fuel sold in port i is not used there. An assumption can be
made, however, that 25 percent of the residual oil and 75 percent of the
distillate oil sold in port i is used there. This is based on methods
developed by the U.S. Environmental Protection Agency.' The total estimated
quantities of residual and distillate oil used in port i are:
0 . = 0.25 x f . x 0 for residual, and (7-7a)
ri ri xrs
Q, . = 0.75 x f , . x Q , for distillate (7-7b)
xdi di xds
where Qr£ and Q^i = the quantities of residual and distillate oil,
respectively, used in port i;
fri and f
-------
TABLE 7-2. AVERAGE EMISSION FACTORS FOR COMMERCIAL MOTORSHIPS
BY WATERWAY CLASSIFICATION
Pollutant
Sulfur oxides
kg/103 liter
lb/103 gal
Carbon monoxide
kg/103 liter
lb/103 gal
Hydrocarbons
kg/103 liter
lb/103 gal
Nitrogen oxides
kg/103 liter
lb/103 gal
River
3.2
27
12
100
6.0
50
33
280
Emission factors
Great Lakes
3.2
27
13
110
7.0
59
31
260
Coastal
3.2
27
13
110
6.0
50
32
270
Source: Reference 4—Emission factors in AP-42 are subject to
revision; the above factors should be checked before
use to ensure that they are current.
TABLE 7-3. AVERAGE EMISSION FACTORS FOR COMMERCIAL STEAMSHIPS
Pollutant
Emission factors3 (lb/103 gal)
Particulates
Sulfur oxides
Carbon monoxide
Hydrocarbons
Nitrogen oxides
10.0
159 x (fuel sulfur content, in percent)
Negligible
3.2
36.4
aFor commercial steamship hoteling.
Source: Reference 4—Emission factors in AP-42 are subject to
revision; the above factors should be checked before
use to ensure that they are current.
7-10
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7.3.2.1 Underway Emissions
Underway emissions occur while the vessel is entering, leaving, or
maneuvering in port. Estimates of the quantity of emissions produced by
underway vessels can be developed by estimating the average travel time by
vessels entering, maneuvering, and leaving the port, applying a fuel
consumption factor, and applying an emission rate based on the quantity of
fuel used.
Vessels with a draft of less than 18 feet are assumed to be powered by
diesel engines and use only distillate oil, while those vessels with a draft
of 18 feet or more are assumed to be either diesel or steam powered. Although
large diesel-powered vessels are capable of burning residual oil, it is
assumed that distillate is used while underway or maneuvering in port.
Further, it is assumed that all steamships use residual oil at all times.
To estimate average travel time, the distance between the outer limits of
the study area and a theoretical centroid of activity within the port is
determined. This distance is increased by 120 percent to account for
maneuvering and leaving port, and divided by an assumed average speed in port
of 8 miles per hour to yield the estimated average underway travel time of
each vessel using the port. This is:
t = (2.2d)/8 = 0.275d (7-8)
where t = average travel time for vessels using the port, and
d = the distance in statute miles between the outer limit of the
study area and the assumed centroid of port activity.
Fuel consumption rates for vessels operating in port are provided in
Table 7-4. Different rates are given for motorships and steamships. The
method used to derive the distribution of motor vessels and steamships
involves determining the relative number of American and foreign registered
vessels, since essentially all large American vessels are steam powered while
most foreign vessels are powered by diesel engines. This information can be
obtained from the port authority or Coast Guard station having jurisdiction.
Once fuel use associated with underway operations has been computed,
emissions can be calculated by applying emission factors from Table 7-5.
Emissions are calculated from:
7-11
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TABLE 7-4. FUEL CONSUMPTION RATES IN GALLONS PER HOUR
FOR VESSELS OPERATING IN PORT AREAS
Vessel size
(draft in feet)
Fuel consumption rate (gal/hr)
Motor vessels Steamships
5
10
44
128
160
Source: Reference 13.
TABLE 7-5. EMISSION FACTORS FOR VARIOUS GENERAL CATEGORIES OF VESSELS
OPERATING IN PORT AREAS
Emission factors (Ib/lCH gal) b
Motor vessels
Pollutant <6a ^6 <12b >12 <18C
Carbon monoxide 47.3 99.7 62.2
Hydrocarbons 51.1 44.5 16.8
Nitrogen oxides 389.3 338.6 167.2
Sulfur oxides 27. Od 27. Od 27. Od
Particulates -
y vessel size (draft in feet)
Steamships
>18d >18e
110.0 3.5
50.0 0.7
270.0 55.8
27.0 159 x (fuel sulfur
content, in percent)
20.0
300-hp engine, cruise mode.
500-hp engine, cruise mode.
C900-hp engine, 2/3 mode.
Coastal vessels.
Q
Residual oil, cruise mode.
Source: Reference 4.
7-12
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E.. = 0. . x EF. (7-9)
iJP iJ JP
where Eijp = the quantity of emissions of pollutant p produced annually by
category j vessels operating within area i waters;
Q£4 = the quantity of fuel, in gallons, consumed by vessel type j;
and
EFip = the emission factor for pollutant p and vessel type j, from
Table 7-5.
7.3.2.2 Dockside Emissions
Large vessels (i.e., those with a draft of 18 feet or more) produce
emissions while dockside since either auxiliary diesel generator systems or
the main boilers are operated to supply power for the vessels' utilities.
Further, the boilers on most steamships in port for less than 2 days are
rarely shut down because of the relatively long time required to restart and
prepare them for operation. To estimate the quantity of emissions produced by
these vessels, an estimate of the average number of days in port must be
developed and a fuel consumption rate determined. After the total quantity of
fuel consumed in port is estimated, an emission factor is applied to derive
the actual emission estimate.
The average duration of stay for large commercial vessels is between
1 and 3 days. An estimate for a particular port can be derived by inquiring
to the port authority, Coast Guard, or shipping company, or a default value of
3 days can be used.
The fuel consumption rates for steamships and motor vessels are assumed
to be 1900 gallons per day of residual oil and 660 gallons per day of
distillate oil, respectively.^-* Again, the assumption is that all American
vessels are steamships while foreign vessals are motorships. Fuel used by
each type of vessel while in port is calculated from:
Qijk - Nij x Dij x fj <7
where Qijk = total annual fuel consumption of fuel type k (either residual
or distillate oil), in area i, by type j vessels;
N£J = total number of type j vessels (either steamships or
motorships)using the port;
Dij = average duration of stay for vessel type j in area i; and
fj = fuel consumption rate for vessel type j (assumed to be
1900 gallons per day of residual oil for steamships and
660 gallons per day of distillate oil for motor vessels).
7-13
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Emissions produced by the ships while at dockside are:
E' . . = Q'. . x EF' . (7-11)
iJP iJ JP
where E'j4p = the quantity of emissions of pollutant p produced annually
by category j vessels while at dockside in area i waters;
Q'ii = t-ne quantity of fuel, in gallons, consumed at dockside by
vessel type j; and
EF'jp = the emission factor for pollutant p and vessel type j,
from Table 7-6.
TABLE 7-6. EMISSION FACTORS FOR VESSELS AT DOCKSIDE
Pollutant
Particulates
Sulfur oxides
Carbon monoxide
Hydrocarbons
Nitrogen oxides
Emission
Motorships
Negligible
27
44b
59b
364b
factors (lb/103 gal)
Steamships3
10.0
159 x (fuel sulfur content,
in percent)
Negligible
3.2
36.4
aResidual oil used for hoteling mode.
b500-KW generator operated at 75 percent rated output.
Source: Reference 4.
7.3.3 TEMPORAL DISTRIBUTION OF EMISSIONS
To identify seasonal variations in emissions, monthly tabulations of
vessel activity can be obtained from the local port authority.
7-14
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References for Chapter 7.0
1. Personal communication with Mr. George Dooley, Bethlehem Ship Building
Co., Sparrows Point, MD, March 1981.
2. Procedures for Emission Inventory Preparation—Volume II: Point Sources,
EPA-450/4-81-026b, U.S. Environmental Protection Agency, Research
Triangle Park, NC, September 1981.
3. Procedures for Emission Inventory Preparation—Volume III; Area Sources,
EPA-450/4-81-026c, U.S. Environmental Protection Agency, Research
Triangle Park, NC, September 1981.
4. Compilation of Air Pollutant Emission Factors, Third Edition and
Supplements, AP-42, U.S. Environmental Protection Agency, Research
Triangle Park, NC, October 1980.
5. Boating: A Statistical Report on America's Top Family Sport, National
Association of Engine and Boat Manufacturers, New York, NY, Annual
publication.
6. Area Measurement Report—Areas of (Specified State), GE-20 Series, U.S.
Department of Commerce, Bureau of the Census, Washington, DC, Issued
1964-1970.
7. Procedures for the Preparation of Emission Inventories for Volatile
Organic Compounds—Volume I (Second Edition), EPA-450/2-77-028, U.S.
Environmental Protection Agency, Research Triangle Park, NC, September
1980.
8. Exhaust Emissions From Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines—Part 2, Outboard Motors, APTD-1491, U.S.
Environmental Protection Agency, Research Triangle Park, NC, January 1973.
9. Exhaust Emissions From Uncontrolled Vehicles and Related Equipment Using
Internal Combustion Engines—Part 1, Locomotive Diesel Engines and Marine
Counterparts, APTD-1490, U.S. Environmental Protection Agency, Research
Triangle Park, NC, October 1972.
10. Local Climatological Data: Annual Summary with Comparative Data, U.S.
Department of Commerce, Washington, DC, Published annually.
11. Energy Data Reports. Sales of Fuel and Kerosene, U.S. Department of
Energy, Washington, DC, Published annually.
12. Waterborne Commerce of the United States, U.S. Army, Corps of Engineers,
Ft. Belvoir, VA, Published annually.
13. Pearson, J. R., "Ships as Sources of Emissions," Presented at the Annual
Meeting of the Pacific Northwest International Section of the Air
Pollution Control Association, Portland, OR, 1969.
7-15
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-450/4-81-026d J
4. TITLE AND SUBTITLE
Procedures for Emission Inventory Preparation
Volume IV: Mobile Sources
3. RECIPIENT'S ACCESSION NO.
6. PERFORMING ORGANIZATION CODE
5. REPORT DATE
September 1981
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Monitoring and Data Analysis Division
Office of Air Quality Planning and Standards
9 PERFORMING ORGANIZATION NAME AND ADDRESS
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
EPA Project Officer: A. A. MacQueen
16. ABSTRACT
Procedures are described for compiling the complete comprehensive emission
inventory of the criteria pollutants and pollutant sources. These procedures
described are for use in the air quality management programs of state and local
air pollution control agencies.
Basic emission inventory elements—planning, data collection, emission esti-
mates, inventory file formatting, reporting and maintenance—are described.
Prescribed methods are presented; optional methods are provided. The procedures
are presented in five (5) volumes:
Volume I, Emission Inventory Fundamentals
Volume II, Point Sources
Volume III, Area Sources
Volume IV, Mobile Sources
Volume V, Bibliography
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boufevard, 12th Ftonr
Chicago, IL 60604-3590
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Emission Inventory Mobile Sources
Inventory
Source Inventory
Emissions Source
Emissions Files Formatting
Questionnaire
Air Quality Management
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
18. DISTRIBUTION STATEMENT
19 SECURITY CLASS I'l'lm Report)
21. NO. OF PAGES
133
20 SECURITY CLASS (This, page}
22. PRICE
EPA Form 2220—1 (Rev. 4—77) PREVIOUS EDITION is OBSOLETE
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