United States Office of Air Quality EPA-454/R-99-006

Environmental Protection Planning and Standards April 1999

Agency Research Triangle Park, NC 27711

Air

Emissions Inventory Guidance for

Implementation of Ozone and Particulate Matter 

National Ambient Air Quality Standards

(NAAQS) and Regional Haze Regulations
Emissions Inventory Guidance for

Implementation of Ozone and Particulate Matter 

National Ambient Air Quality Standards

(NAAQS) and Regional Haze Regulations

Issued By:

Emission Factor and Inventory Group

Emissions, Monitoring and Analysis Division

Office of Air Quality Planning and Standards

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

April 1999
ii

DISCLAIMER

THIS DOCUMENT HAS BEEN REVIEWED BY THE OFFICE OF AIR QUALITY PLANNING AND

STANDARDS. MENTION OF TRADE NAMES OR COMMERCIAL PRODUCTS DOES NOT

CONSTITUTE ENDORSEMENT OR RECOMMENDATION FOR USE.
MEMORANDUM

SUBJECT: Emission Inventory Implementation Guidance 

FROM: J. David Mobley, Acting Director

 Emissions, Monitoring & Analysis Division (MD-14)

TO: Addressees

We are pleased to provide you with the emission inventory portion of our implementation

guidance for the ozone and particulate matter National Ambient Air Quality Standards (NAAQS)

and regional haze regulations. This guidance has undergone an extensive internal and external

review process including the Regional Offices and the States. We believe that it strikes a good

balance between granting the States flexibility in developing their emission inventories and

specifying the Environmental Protection Agency’s (EPA) emission inventory requirements.

The major topics covered by this guidance are:

• The relationship of this guidance to other emission inventory guidance

• Specification of emission inventory base year

• Inventory approval

• Pollutants to be inventoried

• Sources to be inventoried

• Geographic coverage

• Temporal basis of emissions

• Modeling inventories

• Data reporting requirements

• Quality assurance

• Documentation

In addition to the hard copy, this guidance is also available electronically at

www.epa.gov/ttn/chief/ei_guide.html. Select the document from the Table of Contents.
If you would like more information, please contact me at (919) 541-4676. If you would

prefer, your staff may contact William Kuykendal, of my staff, at (919) 541-5372.

Attachment: Emission Inventory Guidance for Implementation of Ozone and Particulate Matter

National Ambient Air Quality Standards (NAAQS) and Regional Haze Regulations, EPA-454/R99-006, April 1999

Addressees:

Deputy Director, Office of Ecosystem Protection, Region I

Director, Environmental Planning and Protection Division, Region II 

Director, Air Protection Division, Region III

Director, Air, Pesticides, & Toxics Management Division, Region IV

Acting Director, Air and Radiation Division, Region V 

Acting Director, Multimedia Planning & Permitting Division, Region VI 

Director, Air, RCRA, and Toxics Division, Region VII

Director, Air and Radiation Program, Region VIII 

Director, Air Division, Region IX 

Director, Office of Air, Region X 

cc: Ellen Baldridge, EMAD

 Fred Dimmick, EMAD

 Bill Hamilton, AQSSD

 Tom Helms, AQSSD

 William Kuykendal, EFIG

 Phil Lorang, OMS 

 Kevin McLean, OCG

 Ned Meyer, EMAD

 David Misenheimer, EFIG

 Joe Paisie, AQSSD

 John Silvasi, AQSSD

 Joe Somers, OMS

 Chris Stoneman, AQSSD

 Joe Tikvart, EMAD

 Mark Wolcott, OMS

 Regional Office Emission Inventory Contacts

wkuykendal/mac/0875/5/10/99/g:\user\share\emadread\99-5.efi\aprnaaqs.wpd

 
July 2, 1999

MEMORANDUM

SUBJECT: Implications of the Court Decision on Emission Inventory Guidance

FROM: J. David Mobley, Acting Director

Emissions, Monitoring and Analysis Division

TO: Addressees

On May 13, 1999, the Environmental Protection Agency (EPA) issued its final version of

the document titled, “Emission Inventory Guidance for Implementation of Ozone and Particulate

Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze Regulations.” On

May 14, 1999, the U.S. Circuit Court of Appeals for the District of Columbia issued a ruling that

remanded the ozone and particulate matter standard and, also called into question what actions, if

any, may be taken to implement the new standards. The purpose of this memorandum is to

clarify what States should do in the context of applying the emission inventory guidance.

The EPA believes that the majority of this guidance covers activities that are allowable by

the Court’s ruling. The development of Statewide emission inventories, as detailed within this

guidance, is necessary to address regional issues, irrespective of the final determination on the

actual National Ambient Air Quality Standards. However, in light of the Court’s ruling, the

references to scheduling associated with SIP submittals contained in Section 2.3 are no longer

appropriate. The guidance does call for development of emission inventories for ozone and

particulate matter and their precursors. Since these are criteria pollutants and are key

components of regional haze, development of emission inventories is still deemed to be

appropriate including the statewide periodic emission inventories for calendar year 1999. Thus, I

think it is appropriate for the Regions and State/local agencies to: (1) discuss plans for

developing emission inventories for 1999; (2) identify appropriate future actions, programs and

associated milestones regarding emission inventories; and (3) identify specific issues which need

resolution prior to making progress on emission inventories.

As the Agency progresses with its deliberations, we will provide more information on

schedules and requirements. Furthermore, we plan to do this before significant efforts by the

States will be required. Therefore, we recommend that you distribute this guidance to your

States and discuss with them the inventory development actions that are appropriate.

If there are any questions in this regard or if there are issues requiring our involvement,

please contact me or Bill Kuykendal at 919-541-5372.
Addressees:

Deputy Director, Office of Ecosystem Protection, Region I

Director, Division of Environmental Planning and Protection, Region II

Director, Air Protection Division, Region III

Director, Air, Pesticides, and Toxics Management Division, Region IV

Acting Director, Air and Radiation Division, Region V

Acting Director, Multimedia Planning and Permitting Division, Region VI

Director, Air, RCRA, and Toxics Division, Region VII

Director, Air & Radiation Program, Region VIII

Director, Air Division, Region IX

Director, Office of Air, Region X

cc: Regional Emission Inventory Contacts

Jeff Clark, MD-10

Jack Edwardson, MD-13

Bill Hamilton, MD-12

Tom Helms, MD-15

Bill Kuykendal, MD-14

David Misenheimer, MD-10

Richard Ossias, OGC

Joe Paisie, MD-15

John Seitz, MD-10

Henry Thomas, MD-14

Lydia Wegman, MD-10
iii

CONTENTS

Page

DISCLAIMER ...................................................................... ii

LIST OF TABLES ................................................................... v

ACRONYMS AND ABBREVIATIONS .................................................. vi

SECTION 1.0

OVERVIEW .................................................................... 1

1.1 PURPOSE ................................................................. 1

1.2 RELATIONSHIP TO EMISSION INVENTORY IMPROVEMENT PROGRAM (EIIP)

GUIDANCE ................................................................ 1

1.3 RELATIONSHIP TO THE CONSOLIDATED EMISSIONS REPORTING RULE (CERR) . 2

1.4 IMPLEMENTATION ........................................................ 2

1.5 SUMMARY OF DOCUMENT CONTENTS ...................................... 3

SECTION 2.0

REGULATORY REQUIREMENTS, DEFINITIONS, AND SUBMITTAL DATES ........... 5

2.1 STATUTORY AND REGULATORY REQUIREMENTS ........................... 5

2.2 TYPES OF INVENTORIES ................................................... 5

2.3 SPECIFICATION OF BASE YEAR ............................................. 6

2.3.1 Ozone .............................................................. 6

2.3.2 Particulate Matter ..................................................... 7

2.3.3 Regional Haze ....................................................... 7

2.4 INVENTORY PREPARATION PLAN .......................................... 7

2.5 INVENTORY APPROVAL ................................................... 9

SECTION 3.0

EMISSION INVENTORY REQUIREMENTS ........................................ 11

3.1 IDENTIFICATION OF INVENTORY USES ..................................... 11

3.2 COMPONENTS OF THE BASE YEAR AND 3-YEAR CYCLE INVENTORIES ........ 12

3.2.1 Pollutants and Pollutant Precursors to Be Inventoried ........................ 12

3.2.2 Identification of Sources and Source Categories to Be Inventoried ............. 13

3.2.3 Geographic Coverage ................................................. 14

3.2.4 Temporal Basis of Emissions ........................................... 15

3.2.5 Rule Effectiveness and Rule Penetration .................................. 15

3.3 MODELING INVENTORIES ................................................. 16

3.3.1 Temporal Allocation Procedures ........................................ 17

3.3.1.1 Point Sources ............................................... 17

3.3.1.2 Area and Mobile Sources ...................................... 19

3.3.2 Spatial Allocation Procedures .......................................... 22

3.3.2.1 Point Sources ............................................... 22

3.3.2.2 Area and Mobile Sources ...................................... 23

3.3.3 Speciation Procedures ................................................ 27
CONTENTS (continued)

Page

iv

SECTION 4.0

DATA REPORTING REQUIREMENTS ............................................ 31

4.1 POINT SOURCES .......................................................... 31

4.2 AREA SOURCES .......................................................... 31

4.3 NONROAD MOBILE SOURCES ............................................. 32

4.4 ONROAD MOBILE SOURCES ............................................... 32

4.5 BIOGENIC AND GEOGENIC SOURCES ....................................... 32

4.6 DEVELOPMENT OF COMPREHENSIVE EMISSION DATA BASE AT EPA ......... 33

4.7 ELECTRONIC DATA TRANSFER REQUIREMENTS ............................ 33

4.7.1 Overview .......................................................... 33

4.7.2 EPA NET Input Format ............................................... 34

4.7.3 AIRS Format ....................................................... 34

4.7.4 EIIP/EDI Format ..................................................... 35

4.7.5 Direct Source Reporting ............................................... 35

4.8 SUMMARY DATA REPORTING ............................................. 36

SECTION 5.0

EMISSION INVENTORY DEVELOPMENT ........................................ 39

5.1 AVAILABLE GUIDANCE ................................................... 39

5.2 NATIONAL EMISSION TRENDS INVENTORY ................................ 39

5.3 POINT SOURCES .......................................................... 40

5.4 AREA SOURCES .......................................................... 41

5.5 MOBILE SOURCES ........................................................ 46

5.5.1 Onroad Mobile Sources ............................................... 47

5.5.2 Nonroad Mobile Sources .............................................. 51

5.6 BIOGENIC AND GEOGENIC SOURCES ....................................... 54

5.6.1 Biogenic Sources .................................................... 54

5.6.2 Geogenic and Other Natural Sources ..................................... 55

SECTION 6.0

QUALITY ASSURANCE/DOCUMENTATION OF THE INVENTORY .................. 57

6.1 QUALITY ASSURANCE .................................................... 57

6.2 DOCUMENTATION OF THE INVENTORY .................................... 58

SECTION 7.0

REFERENCES ................................................................. 63

APPENDIX A

DRAFT CONSOLIDATED EMISSIONS REPORTING (CER) RULE .................... A-1
v

LIST OF TABLES

Table Page

3.3-1. Default Hourly VMT Fractional Profile ........................................... 22

3.3-2. Stack Parameter Ranges Used in the Initial Screening ................................ 23

3.3-3. Area Source Spatial Surrogates .................................................. 25

3.3-4. Four-digit Area Source Category Codes and the Predominant Area Source Spatial Surrogate . 26

4.8-1. Statewide Ozone Precursor Emissions by Source Sector .............................. 36

4.8-2. Statewide PM2.5 and Precursor Emissions by Source Sector ........................... 37

5.3-1. Point Sources of Emissions ..................................................... 42

5.4-1. Area Sources of Emissions ..................................................... 44

5.4-2. Crustal Sources of Emissions ................................................... 46

5.5-1. Mobile Sources of Emissions ................................................... 47

5.5-2. PART5 Vehicle Classes ....................................................... 51

5.6-1. Natural Source Categories and Pollutants Emitted ................................... 54

6.2-1. Outline for Format/Contents for SIP Emission Inventory Reports ....................... 60
vi

ACRONYMS AND ABBREVIATIONS

AFS AIRS/Facility Subsystem

AIRS Aerometric Information Retrieval System

ALAPCO Association of Local Air Pollution Control Officials

AMS Area and Mobile Subsystem

ANSI American National Standards Institute

BEIS-2 Biogenic Emissions Inventory System-2

BIOME Biogenic Model for Emissions

BSFC brake specific fuel consumption

CAA Clean Air Act

CARB California Air Resources Board

CASAC Clean Air Act Scientific Advisory Committee

CB-IV Carbon Bond IV

CEMS Continuous emission monitoring system

CERR Consolidated Emissions Reporting Rule

CG cloud-to-ground

CHIEF Clearing House for Inventories and Emission Factors

CNG compressed natural gas

CO carbon monoxide

EC elemental carbon

EDI Electronic Data Interchange

EDR electronic data reporting

EFIG Emission Factor and Inventory Group

EIIP Emission Inventory Improvement Program

EKMA Empirical Kinetic Modeling Approach

EMS Emission Modeling System

EPA Environmental Protection Agency

FAA Federal Aviation Administration

FHWA Federal Highway Administration

FTP file transfer protocol

GTM gross ton miles

GCVTC Grand Canyon Visibility Transport Commission

HAP hazardous air pollutant

HCs hydrocarbons

HDDV heavy-duty diesel vehicle

HDGV heavy-duty gasoline vehicle

HONO gaseous nitrous acid

HPMS Highway Performance Monitoring System

IC intra-cloud

I/M inspection and maintenance

IPP Inventory Preparation Plan

LDDT light-duty diesel truck

LDDV light-duty diesel vehicle

LDGT light-duty gasoline truck

LDGV light-duty gasoline vehicle

LPG liquid petroleum gas

LTOs landing and takeoffs
ACRONYMS AND ABBREVIATIONS (continued)

vii

MoVEM Motor Vehicle Emissions Estimates Model

NAAQS national ambient air quality standard

NAICS North American Industry Classification System

NAPAP National Acid Precipitation Assessment Program

NET National Emission Trends

NH3 ammonia

NMHC nonmethane hydrocarbons

NMOG nonmethane organic gases

NO nitric oxide

NO2 nitrogen dioxide

NOx oxides of nitrogen

NTTAA National Technology Transfer and Advancement Act

OAQPS Office of Air Quality Planning and Standards

OC organic carbon

OMB Office of Management and Budget

OMS Office of Mobile Sources

OTAG Ozone Transport Assessment Group

OTC Ozone Transport Commission

PCBEIS-2.2 Personal Computer version of the Biogenic Emission Inventory System-2.2

PCC process category code

PM particulate matter

PM10 particles with an aerodynamic diameter less than or equal to a nominal

10 micrometers

PM2.5 particles with an aerodynamic diameter less than or equal to a nominal

2.5 micrometers

QA quality assurance

QC quality control

RADM Regional Acid Deposition Model

RE rule effectiveness

ROG reactive organic gas

ROM Regional Oxidant Model

RP rule penetration

RVP Reid vapor pressure

SAEWG Standing Air Emissions Work Group

SAPRC California Statewide Air Pollution Research Center

SAQM SARMAP Air Quality Model

SARMAP San Joaquin Valley Air Quality Study/Atmospheric Utilities Signatures, Predictions

and Experiments Regional Modeling Adaption Project

SCC source classification code

SIC Standard Industrial Classification

SIP State Implementation Plan

SO2sulfur dioxide

SO4sulfate

SOx oxides of sulfur
ACRONYMS AND ABBREVIATIONS (continued)

viii

STAPPA State and Territorial Air Pollution Program Administrators

TAFF Temporal Allocation Factor File

TCA 1,1,1-trichloroethane

TDM travel demand model

TEA-21 Transportation Equity Act for the 21st Century

THC total hydrocarbons

TOG total organic gases

TTN Technology Transfer Network

UAM Urban Airshed Model

UMRA Unfunded Mandates Reform Act

U.S. United States

UTM universal transverse mercator

VMT vehicle miles traveled

VOC volatile organic compound(s)
1

SECTION 1.0

OVERVIEW

1.1 PURPOSE

The purpose of this guidance document is to define required elements of emission inventories

necessary to meet State Implementation Plan (SIP) requirements for complying with the 8-hour ozone

national ambient air quality standard (NAAQS), the revised particulate matter NAAQS and the regional

haze regulations. For the particulate matter NAAQS, the emphasis in this guidance is on particulate

matter with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers (PM2.5). However,

the earlier PM10 (particulate matter with an aerodynamic diameter less than or equal to a nominal

10 micrometers) NAAQS is still in effect and, therefore, States should continue to inventory PM10 as

well. The required elements include those for compiling and reporting the emission inventories to the

United States (U.S.) Environmental Protection Agency (EPA).

For the 8-hour ozone NAAQS, this guidance applies to all nonattainment area classifications except

“transitional.” Transitional ozone areas are nonattainment areas that may be able to demonstrate

attainment of the 8-hour NAAQS through actions intended to meet the 1-hour NAAQS. An example

would be areas in the East that can demonstrate attainment of the 8-hour NAAQS as a result of actions

taken in response to the oxides of nitrogen (NOx) SIP call. Emission inventory guidance for these

transitional areas is included in Implementation Guidance for the Revised Ozone and Particulate Matter

(PM) National Ambient Air Quality Standards (NAAQS) and the Regional Haze Program,

1

 Section 3

“SIP Requirements for Transitional Areas,” Subsection b “Emission Inventory, Modeling and Attainment

Demonstration.”

Ozone, regional haze, and a significant portion of PM2.5 are produced in the air by the combination

of pollutants (“precursor pollutants”) from many of the same local emission sources. In addition, studies

have identified the long-range transport of pollutants as contributing to ambient air violations and

visibility impairment. Therefore, this guidance document emphasizes the importance of preparing a

single, statewide inventory for all pollutant emissions that contribute to the formation of ozone, PM2.5,

and regional haze.

1.2 RELATIONSHIP TO EMISSION INVENTORY IMPROVEMENT PROGRAM

(EIIP) GUIDANCE

This document is a guide for State and local agencies for the requirements for submitting their

emission inventories for the 8-hour ozone and PM2.5 NAAQS, and for the regional haze program. It is

not a procedures document covering the methods for compiling and documenting emissions inventories. 

The Emission Inventory Improvement Program (EIIP) has been and will continue to develop the

procedures for compiling and documenting emission inventories for point, area, nonroad mobile, onroad

mobile, biogenic, and geogenic source categories. Thus, the EIIP guidance compliments this

requirements document.
2

The goal of EIIP is to provide cost-effective, reliable inventories by (1) improving the quality of

emissions information; and (2) developing systems for collecting, calculating, and reporting emissions

data. The goal is achieved by developing a set of “preferred and alternative methods” for all inventory

associated tasks. This standardization improves the consistency of collected data and results in increased

usefulness of emissions information. The EIIP will reach its goal through development of:

• Preferred methods for collecting data and calculating emissions;

• Improved reporting systems;

• Procedures for quality control; and 

• More consistent guidance. 

The EIIP is a jointly sponsored effort of the State and Territorial Air Pollution Program

Administrators/Association of Local Air Pollution Control Officials (STAPPA/ALAPCO) and EPA, and

is an outgrowth of the Standing Air Emissions Work Group (SAEWG). Funding is provided by

State/local agencies through the federal 105 grant programs. The EIIP Steering Committee and technical

committees are composed of State, local, industry, and EPA representatives. The EIIP maintains a web

site which provides the documents prepared by EIIP as well as periodic updates on EIIP activities and

products. The web site address is: http://www.epa.gov/oar/oaqps/eiip/. The documents prepared by the

EIIP should, where appropriate, be used instead of existing emission inventory procedures guidance.

1.3 RELATIONSHIP TO THE CONSOLIDATED EMISSIONS REPORTING RULE

(CERR)

The EPA is preparing the Consolidated Emissions Reporting Rule (CERR) to improve and simplify

the reporting of emission inventory information. A draft of the CERR is provided in Appendix A of this

document. The preparation of the CERR will assist State and local agencies to:

• Determine and integrate the various emissions reporting requirements;

• Improve reporting efficiency; and 

• Provide flexibility for data gathering and reporting.

Numerous State and local agencies requested that EPA consolidate its various air emissions

reporting requirements. This should increase the efficiency of the emission inventory program and

provide more consistent and uniform data. Consolidating reporting requirements will enable agencies to

better explain to program managers and the public the necessity for a consistent inventory program. This

action, while including new data collection requirements for PM2.5, its precursors, and hazardous air

pollutants (HAPs), reduces the reporting requirements for other criteria pollutants.

This document incorporates the 8-hour ozone, PM2.5, and regional haze emission inventory

requirements of the draft rule presented in Appendix A. This guidance document and the CERR were

developed in parallel, and this guidance document is being released before the CERR is published in its

final form. While the CERR is undergoing the rulemaking process, EPA believes that there is sufficient

existing statutory authority to implement the provisions contained in this guidance document. If there are

conflicts between this guidance document and the final rule, the final rule will take precedence.

1.4 IMPLEMENTATION

Section 2.3 of this document provides details of SIP inventory implementation schedules. 

Implementation of the 8-hour ozone NAAQS began after it was finalized in July 1997. Similarly,

implementation of the regional haze regulations will begin after they are finalized in the spring of 1999.
3

The implementation of the PM2.5 NAAQS will not occur until after the Clean Air Act Scientific

Advisory Committee (CASAC) completes its review of the standard in 2002. However, because many of

the same sources produce emissions that contribute to ozone and PM2.5 formation and visibility

impairment, EPA encourages States to coordinate emission inventory planning and development efforts

for ozone, regional haze, and PM2.5 as they develop their required inventories for ozone. EPA believes

that the States should take advantage of the opportunity to produce a PM emission inventory while they

are collecting data and preparing their ozone precursor inventory. Coordination of emission inventory

planning and development efforts will help to reduce the burden associated with preparing separate

inventories, improve the accuracy of emission inventories through the application of consistent methods,

improve regional modeling studies, and improve coordination of control strategy development. 

1.5 SUMMARY OF DOCUMENT CONTENTS

Section 2 of this document summarizes the regulatory requirements for emission inventories for the

8-hour ozone and PM2.5 NAAQS, and the regional haze regulations. This section also provides a brief

overview of the types of inventories that States will need to prepare for their SIPs, specifies the year for

which the base year inventories are to be prepared, and provides a time line illustrating the relationship

between the schedules for submittal of emission inventories and other SIP milestones. Section 2.0 also

discusses the emission inventory planning and approval process.

Section 3 identifies and explains the key requirements for ozone, PM, and regional haze SIP

emission inventories. The topics covered include requirements for the inventory base year and periodic

inventories; uses of the inventories; defining the pollutants and pollutant precursors, and sources and

source categories, to be inventoried; geographic coverage of inventories; temporal basis of emissions;

application of rule effectiveness (RE) and rule penetration (RP); and modeling inventories. For modeling

inventories, this section explains the procedures by which emissions in a completed base year or

projection year inventory are temporally allocated, spatially allocated, and speciated for use in a

photochemical grid model. By explaining these procedures, it is anticipated that State and local agencies

will be able to provide more complete and accurate data to increase the accuracy of the procedures.

Section 4 provides brief definitions and data element reporting requirements for stationary point and

area, nonroad mobile, onroad mobile, biogenic, and geogenic emission sources. This section also

specifies data reporting and electronic data transfer requirements, and discusses how the emission

inventories submitted by State and local agencies are compiled into a comprehensive emission data base

at EPA.

Section 5 addresses emission inventory development requirements for the base year and periodic

emission inventories. This section provides an overview of the types of emission sources and pollutants

expected to be considered for inclusion in an inventory, and cross-references existing emission inventory

development procedures by source category and pollutant where available. Section 5 also emphasizes the

importance for State and local agencies to collect the best activity data available for their inventories. 

The EPA recognizes that emission factors are either currently not available or have higher uncertainty for

some pollutants [e.g., PM2.5 and ammonia (NH3)], and is conducting ongoing research to develop new

and improved emission factors. Therefore, because it is difficult to collect high-quality activity data

retrospectively, emphasis should be placed on collecting good activity data for the base year inventory. 

As emission factors are developed or improved, the factors can be applied to the activity data to improve

emission estimates.
4

The final section of this document, Section 6, discusses the importance of including quality

assurance (QA) and quality control (QC) procedures in the inventory planning and development process,

and the importance of preparing sound documentation for the inventories.
5

SECTION 2.0

REGULATORY REQUIREMENTS, DEFINITIONS,

AND SUBMITTAL DATES

This section reviews the Clean Air Act (CAA) provisions and associated regulations that require

States to compile and submit air pollution emission estimates to EPA. It also reviews inventory types,

emission inventory submittal dates, Inventory Preparation Plans (IPPs), and the EPA approval process.

2.1 STATUTORY AND REGULATORY REQUIREMENTS

EPA interprets Section 110(a)(2)(F) of the CAA (codified in 40 CFR 51 Subpart Q) as requiring

SIPs to provide for the reporting of criteria air pollutants for all areas under the general SIP requirements

of section 110. In addition, EPA interprets section 172(c)(3) as providing the Administrator with

discretionary authority to require other emissions data as deemed necessary for SIP development in

nonattainment areas to attain the NAAQS. This statutory authority provides a basis for requiring SIPs to

provide for a periodic inventory of PM10 emissions for PM10 nonattainment areas, PM2.5 emissions and

emissions of the PM2.5 precursors NH3, NOx, and oxides of sulfur (SOx). Section 169(A) provides

authority for emission inventories to be required in SIPs developed to protect visibility in Federal Class I

areas.

2.2 TYPES OF INVENTORIES

For the purpose of developing SIPs to demonstrate compliance with the 8-hour ozone NAAQS,

PM2.5 NAAQS, and regional haze rule, there are three basic kinds of inventories that are necessary. 

These three are the base year, periodic, and modeling inventories. Because of the increasingly regional

nature of air quality analysis and planning, all three types of inventories should be prepared on a

statewide basis. The base year inventory is the primary inventory from which the other two inventories

are derived. Thus, all inventories should be consistent with data provided in the base year inventory. 

The CAA calls for States to ensure that the base year inventory is comprehensive, accurate, and current

for all actual emissions. The inventory should include emissions estimates from stationary point and area

sources (from both anthropogenic and biogenic origin), onroad mobile sources, and nonroad mobile

sources.

Every 3 years after the base year inventory is developed, States are required to develop periodic

inventories (in the future to be called the 3-year cycle inventory) based on actual emissions. This

inventory is used to measure overall emission reduction trends and meet information requests from the

general public. These inventories will be important to future modeling studies and emissions trading

programs.

Modeling inventories are required for developing the attainment demonstration. A modeling

inventory, defined as an inventory that will be processed through an “emissions preprocessor,” is only

prepared for a specific modeling application. The inventory requirements specified in this guidance will

support modeling, but do not require a modeling inventory per se. Modeling inventories are based on

either allowable or actual emissions depending on the purpose of the modeling. For example, modeling
6

inventories are based on the actual emissions for model performance evaluation. For control measure

evaluations and the attainment demonstration, the modeling inventory is based on actual emissions for

the base year and projected allowable emissions for the attainment year.

As an alternative to using allowable emissions for projections for the 8-hour ozone standard, current

EPA policy allows the use of actual emissions in certain circumstances. For sources or source categories

that are currently subject to a regulation, and where the State does not anticipate subjecting the source(s)

to additional regulation, the projected emissions may be based on actual emissions. In addition, for

sources or source categories that are currently unregulated and are not expected to be subject to future

regulations, the projected emissions may be based on actual emissions. For all other sources (i.e.,

sources that are expected to be subject to additional regulation), the projections should be based on the

new allowable emissions (including RE). Where a State chooses to project emissions using a different

approach than described above, the State should get the approval of the appropriate EPA Regional Office

before proceeding. In addition, the State should provide complete documentation of the approach and

documentation and technical justification of any assumptions. For PM10 and PM2.5, current EPA policy

only permits the use of allowable emissions in projections to future years. EPA is reviewing the policy

for all pollutants to determine if more realistic projected emission estimates can be obtained.

Previously, modeling inventories were only specifically required for areas performing

photochemical grid-based modeling to demonstrate attainment of the 1-hour ozone NAAQS; however,

recent events have shown that most States also need access to emissions data outside their borders. 

Regional approaches such as the Ozone Transport Assessment Group (OTAG), the Ozone Transport

Commission’s (OTC) NOx baseline study, and the Grand Canyon Visibility Transport Commission’s

(GCVTC) study have emphasized the need for regional (multi-State) emission inventories. Regional

modeling is expected to become even more prevalent as areas develop attainment plans for the 8-hour

average ozone and the PM2.5 NAAQS, and to develop plans and demonstrate progress toward meeting

regional haze visibility goals. Thus, needs for multi-State inventories to support grid-based modeling are

increasing.

Countywide emission estimates are needed for all counties. Where a State is unable to provide this

information, EPA’s National Emission Trends (NET) inventory can be used for regional analyses. States

that are performing modeling analyses generally have to make emission estimates for more than just a

nonattainment area. In the absence of State-prepared emissions data, the NET inventory may be used. 

Without additional State scrutiny, however, the risk of incorrect air quality estimates is increased.

2.3 SPECIFICATION OF BASE YEAR

This section specifies the base year for the emission inventory that States should use in the

development of their SIPs for ozone, PM, and regional haze. In each case, the base year was determined

by considering when the SIP was due, and the time needed to prepare the SIP, perform the modeling

studies, and prepare the emission inventory. In selection of the base year, consideration was also given to

the 3-year frequency of emission inventory preparation in the CERR, as well as, conserving State

resources by using a single inventory year for multiple applications.

2.3.1 Ozone

States are strongly encouraged to select 1999 as the base year for the emission inventory for the

8-hour ozone NAAQS. That is, EPA suggests that the base year inventory for the ozone NAAQS should

be representative of calendar year 1999. However, this guidance permits a State to select any year from

1996 to 1999 as its base year. If this inventory will be used as a part of a regionwide modeling domain,
7

then all of the States in that domain should agree to use the same base year. The appropriate EPA

Regional Office(s) should be involved in selection of the base year. The State should detail in its IPP

(see section 2.4 for more information on IPPs) the base year selected, or specify the process for selecting

a base year if a regionwide domain is necessary.

2.3.2 Particulate Matter

A base year for the PM2.5 NAAQS inventory and a submittal date for the inventory cannot be

specified until the NAAQS review is complete in 2002. However, it is important that States should begin

in 1999 to identify and characterize their sources of PM and PM precursors. Some of the PM precursors

will already be inventoried as part of the ozone inventory (VOC and NOx) and the acid rain reporting

provisions (SOx). The only additional requirement for the States is that they include PM2.5 and PM10 and

the precursor NH3 as they characterize their sources. To ensure progress toward developing a PM

inventory, States, for example, should estimate the PM2.5 and PM10 emissions from all of their point

sources at the same time they estimate ozone precursor emissions. If the NAAQS review upholds the

current PM2.5 standard, States with monitoring data available for designations in 2002 to 2005 will need

to have a base year of 2002 for their emission inventory.

2.3.3 Regional Haze

The base year for the emission inventory for developing regional haze control strategy SIPs will be

contingent on the final regional haze rule, but is likely to be the same as the base year for developing

nonattainment area SIPs under the PM2.5 NAAQS. Therefore, as with PM2.5, States should begin in 1999

to identify and characterize their sources. Again, to ensure progress toward developing a regional haze

inventory, the States may want to do this as they estimate ozone precursor emissions.

The Transportation Equity Act for the 21st Century (TEA-21), passed in June 1997, includes revised

time lines for regional haze and PM2.5 SIP submittals. PM2.5 nonattainment areas are to be designated in

the 2002 to 2005 time frame, and PM2.5 SIPs would be due 3 years later, in the 2005 to 2008 period. For

these same geographic areas, regional haze SIPs would be due at the same time. The TEA-21 also

requires regional haze SIPs to be submitted within 1 year for the geographic areas designated attainment

or unclassifiable for PM2.5. These regional haze SIPs would be due in the 2003 to 2006 time frame.

EPA is considering the possibility of an optional approach whereby States could commit to

participation in future regional planning efforts and have coordinated deadlines for regional haze control

strategy SIPs covering the geographic areas designated nonattainment, attainment, and unclassifiable for

PM2.5. States committing to regional planning efforts may need to conduct preliminary technical analyses

characterizing interstate pollutant transport. To perform such analyses, which would precede more

detailed analyses for the development of control strategies, the States may need to use the 1999 base year

inventory.

2.4 INVENTORY PREPARATION PLAN

IPPs are used as a planning tool to guide inventory preparation and ensure that emission estimates

are of high quality and are consistent with CAA requirements. IPPs provide States with the opportunity

to tell their EPA Regional Office how they plan to compile their required inventories and allow EPA to

provide feedback to avoid having States use approaches that are inconsistent. Because EPA has

attempted to be as flexible as possible on how it allows States to meet the CAA inventory requirements,

EPA is now requiring States to submit detailed IPPs which describe how the inventory is developed, what

it includes, and what assumptions are being made. States should prepare and submit these IPPs for the
8

8-hour ozone and PM NAAQS and the regional haze program statewide emission inventories. States that

prepared earlier IPPs for the 1-hour ozone or the PM10 NAAQS can use these IPPs as the starting point

for the 8-hour ozone, PM2.5, and regional haze IPPs. IPPs can also serve as standard operating procedures

for the States for future inventory preparation and as documentation of inventory procedures to other

neighboring States in regional planning efforts.

The IPPs should include descriptions of inventory objectives and general procedures. One of the

first steps in developing the IPP is to define the purpose and scope of the inventory. This includes

identifying items such as base year for the inventory, the pollutants to be inventoried, the emissions

sources and source categories, the geographical boundaries of the inventory, the spatial and temporal

scales of the emissions, and the application of controls and regulations, including RE and RP. The IPPs

for inventories that report VOC emissions should include the State’s definition of VOC and what species

are included. The IPPs should also contain a schedule or time line for when the States plan to submit

their inventories or inventory components to EPA. This schedule/time line should also show how the

inventory preparation or review process will mesh with the application of these inventories in

atmospheric modeling. If the State plans to submit an inventory in components (e.g., point sources, area

sources, etc.), the IPP should so indicate, along with their submittal dates by component. Final submittal

dates should be consistent with the ultimate inventory dates required by EPA (see section 2.3).

The IPP should contain the following sections, including separate sections to address the point, area,

nonroad mobile, onroad mobile, and biogenic portions of the inventory:

C Introduction

This section includes items such as: a description of the inventory objectives, including how this

IPP is structured, what it contains, who is responsible for the inventory, and who is compiling it; the

geographic area covered by the inventory; the base year of the inventory (see section 2.3); the

pollutants included in the inventory (see section 3.2.1); and the temporal resolution of the inventory.

C Point Source Inventory

Topics to be discussed in this section include: how sources are identified and located; what data

collection methods are used; the basis for activity data and emissions estimates; how control

efficiencies are identified and applied; whether RE and RP are applied and their values (see section

3.2.5); and how temporally resolved emissions are prepared and supplied (see section 3.2.4).

C Area Source Inventory

This section identifies what source categories are included in the inventory (see section 3.2.2), how

emissions are estimated, how data are identified and collected, whether RE and RP are applied and

their values (see section 3.2.5), how emissions are temporally and spatially resolved and supplied

(see sections 3.2.4 and 3.3), and how double-counting of emissions is avoided.

C Nonroad Mobile Source Inventory

This section includes details on what source categories are included in the inventory (see section

3.2.2), how emissions are estimated, how data are identified and collected, and how emissions are

temporally and spatially resolved and supplied (see sections 3.2.4 and 3.3).
9

C Mobile Source Inventory

This section includes the State’s approach for determining vehicle miles traveled (VMT) (see

section 5.5.1), specification of the mobile source emissions model used, specification of key

assumptions for the model, including parameters such as temperature, speeds, existing inspection

and maintenance (I/M) programs, etc., and how emissions are temporally and spatially resolved (see

sections 3.2.4 and 3.3).

C Biogenic Source Inventory

This section identifies what source categories are included in the inventory (see section 3.2.2), how

emission are estimated, how data are identified and collected, and how emissions are temporally and

spatially resolved and supplied.

C Documentation Approach

This section describes how the inventory and its procedures are documented and how the data are

stored and managed (see section 6.2). In addition, this section includes information on how the data

are transmitted to EPA (see section 4.7).

C Quality Assurance Plan

This section includes a description of the inventory QA program and QA/QC procedures, as well as

specification of the inventory data quality objectives (DQOs) (see section 6.1).

Each State should negotiate its IPP submittal schedules with its EPA Regional Office. The State and

its Regional Office should agree in advance on the time table for submitting the IPP and the approval

process that will be used by the EPA Regional Office. EPA Headquarters and Regional Offices will

work together to promote consistency of IPP review and approval, while allowing maximum flexibility to

the States in their inventory preparation process.

During the preparation of their IPPs, States are referred to Volume I of the EIIP guidance which

discusses emission inventory planning and development.2 Chapter 2 of Volume IV, Quality

Assurance/Quality Control, of the EIIP guidance provides additional information on planning and

documentation of inventory development and QA activities.3

2.5 INVENTORY APPROVAL

States should negotiate the emission inventory approval process with their respective EPA Regional

Office. Of the emission inventories that States submit to EPA, those that are deemed to be of “regulatory

significance” will require EPA approval. In general, this means that the approval process will include the

emission inventory as a component of a SIP submittal, or other significant action by the State, that

requires EPA review and approval. This represents a change from the policy with the 1990 inventories,

which required States and EPA to subject the 1990 inventory to a public hearing and regulatory approval. 

This modification recognizes, and thus eliminates, the additional burden to States to have a separate

inventory approval process. This modification also allows inventory revisions to continue to occur after

initial compilation as application of the inventory in control strategy evaluation and urban or regional

scale modeling reveals where improvements/adjustments are needed.
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SECTION 3.0

EMISSION INVENTORY REQUIREMENTS

The purpose of this section is to identify and explain the key elements to be included in statewide

SIP emission inventories that should be prepared by State and local agencies to comply with the 8-hour

ozone NAAQS, PM2.5 NAAQS, and regional haze rule. If a State or local agency is unclear on how this

guidance applies to its specific situation, it should consult with its EPA Regional Office for clarification. 

This section identifies the uses and required components of the base year and modeling inventories

discussed in this guidance document. This section also discusses the temporal allocation, spatial

allocation, and speciation methodologies used to process the inventories for input to photochemical air

quality models to enable State and local agencies the opportunity for supplying data to improve the

methodologies.

3.1 IDENTIFICATION OF INVENTORY USES

The uses of inventories determine the information that should be included in the inventories. The

emission inventories covered by this guidance document will be used by State and local agencies to

develop their SIPs to demonstrate attainment of the 8-hour ozone NAAQS, PM2.5 NAAQS, and regional

haze rule. As discussed in section 2.2, these inventories include the base year and modeling inventories. 

These inventories will also be used by regional planning bodies and EPA to support regional and national

analyses, which in turn will be given to State and local agencies to support development of their SIPs.

The base year inventory is the starting point from which the other SIP inventories are derived. One

of its key purposes is to support air quality modeling and control measure analyses to determine the types

and amounts of emission reductions needed to demonstrate attainment. Emissions trading programs

could also be based on the inventory if emissions trading programs are adopted as a measure of

implementing controls. The results of these studies are then used by State and local agencies to identify

the emission sources for control, and to develop and adopt the control measures that should be included

in the overall control strategy for a SIP. The draft CERR presented in Appendix A specifies the data

elements that State and local agencies should include in their inventories.

Recent studies have indicated that the long-range transport of precursor emissions contribute to

elevated ozone and PM2.5 levels and visibility impacts in down-wind areas. Thus, EPA will support State

and local agencies in conducting regional scale photochemical modeling for all three of these programs

to provide State and local agencies with a number of critical data bases for use in developing their

attainment demonstration and maintenance SIPs. Since EPA has recently published a regional NOx

control strategy for reducing ozone levels for 22 eastern United States and the District of Columbia, this

support in the near term is expected to focus on PM2.5 and regional haze SIP development. To support

this effort, EPA will compile inventories that will include a blend of inventory data submitted by State

and local agencies with inventory data developed by EPA. EPA developed data will be used to fill gaps

in State data and for certain source types where EPA has developed accurate and comprehensive

emission estimates (e.g., electric utility sources). EPA is developing a Data Incorporation Plan which

will document in detail how EPA plans to use State and EPA developed data. These inventories will be

stored in a central repository termed the NET data base. The EPA will also improve the NET data base

for other regional studies as the needs arise. The NET data base will be updated annually with the
12

emphasis on incorporating State data using the 3-year cycle inventories submitted by State and local

agencies.

3.2 COMPONENTS OF THE BASE YEAR AND 3-YEAR CYCLE INVENTORIES

3.2.1 Pollutants and Pollutant Precursors to Be Inventoried

This section identifies the pollutants that must be included in the base year and a 3-year cycle

inventory for the 8-hour ozone NAAQS, PM2.5 NAAQS, and regional haze rule. Because many sources

emit more than one of the precursor pollutants, and because the precursor pollutants have the potential to

be transported across State boundaries, it is important that State and local agencies develop a single

statewide inventory of pollutants to support integrated, regional scale modeling, and control strategy

development for ozone, PM2.5, and regional haze.

For the 8-hour ozone NAAQS, the pollutants to be inventoried are volatile organic compounds

(VOC), NOx, and carbon monoxide (CO). 

For the PM2.5 NAAQS, the pollutants to be inventoried are primary emissions (including

condensibles) of PM10 and PM2.5, and the precursor emissions SOx, NH3, VOC, and NOx. The EPA is

requiring PM10 emissions to be reported because PM10 is a criteria pollutant and PM10 emissions are

needed as an input to air quality simulation models when modeling PM2.5.

For regional haze, the pollutants to be inventoried include all of the pollutants and precursor

pollutants identified for ozone and PM, except for CO. While elemental carbon (EC) and organic carbon

(OC) will be identified in default speciation profiles, more locally-specific data should be collected

where available as an input to model preprocessing. Where such data are available, they should be

provided to EPA to help in improving EPA’s speciation profiles. State/local agencies can contact EPA’s

Emission Factor and Inventory Group (EFIG) for more information.

EPA’s current regulatory definition of VOC (40 CFR § 51.100) excludes constituents considered to

be negligibly photochemically reactive. These include methane, ethane, methylene chloride, 1,1,1-

trichloroethane (TCA), several Freon compounds, acetone, perchloroethylene, and others. It is

anticipated that additional compounds may be exempted from this VOC definition. The exempt

compounds are considered negligibly reactive, although some can influence the formation of ozone when

present in sufficient amounts. In preparing the base year inventory, States should consider how the VOC

data are to be used in air quality modeling studies and the techniques available to the State in estimating

VOC emissions. Therefore, should a State or local agency encounter a situation where its emission

estimation methodology includes emissions exempted from EPA’s definition of VOC, it should consult

with its modeling staff and EPA Regional Office for guidance and include its plan for addressing the

situation in its IPP. States should specify in their documentation what they are reporting as VOC.

Generally, the emission factors used to estimate organic emissions represent nonmethane

hydrocarbons (NMHCs). Because of this, it is generally assumed that inventories do not have methane,

and part of the modeling procedure “automatically” adds back that missing VOC component. Therefore,

inventory preparers should not have to do anything further specific to methane. State and local agencies

should confirm this with their air quality modeling staff.

 At a minimum, it is of utmost importance to document what the inventory contains (e.g., specify

what VOC species are included and any negligibly reactive VOC that are segregated/excluded). If the
13

State is reporting VOC as defined by EPA (40 CFR § 51.100), the State should simply state this in both

the IPP and the inventory documentation. 

The PM2.5 and PM10 emission values that should be reported in the inventory should be primary PM. 

For the purpose of this guidance document, the following definitions apply:

• PRIMARY PM: Particles that enter the atmosphere as a direct emission from a stack or an

open source. It is comprised of two components: Filterable PM and Condensible PM.

• FILTERABLE PM: Particles that are directly emitted by a source as a solid or liquid at stack

or release conditions and captured on the filter of a stack test train.

• CONDENSIBLE PM: Material that is vapor phase at stack conditions, but which condenses

and/or reacts upon cooling and dilution in the ambient air to form solid or liquid PM

immediately after discharge from the stack.

• SECONDARY PM: Particles that form through chemical reactions in the ambient air well

after dilution and condensation have occurred. Secondary PM is usually formed at some

distance downwind from the source. Secondary PM is NOT reported in the emission

inventory.

In reporting their PM emissions to the EPA, States should report the following:

• Primary PM2.5 (or Filterable PM2.5 and Condensible PM individually. Note that all Condensible

PM is assumed to be in the PM2.5 size fraction)

• Primary PM10 (or Filterable PM10 and Condensible PM individually) 

It is preferred that the States report the two separate components rather than the single combined

Primary PM values, if known. This information is important to assist in the development of new

emission factors for condensible PM. If only the filterable component is known, report it as “filterable.” 

In addition, States may also choose to report the following:

• Total Primary PM Measured (or Filterable Total Primary PM Measured and Condensible PM

individually)

These two PM components are the components measured by a stack sampling train such as EPA

Method 5 and have no upper particle size limit.

States should be careful to identify the PM components that they are reporting using the above

terms. If a State does not identify what PM components are being reported, the EPA will assume that the

emissions represent only the Filterable PM component.

3.2.2 Identification of Sources and Source Categories to Be Inventoried

The base year inventory should include all stationary point and area, nonroad mobile, onroad

mobile, biogenic, and geogenic emission sources present within each county within a State. Even if there

are areas within a State that do not have significant emissions, the State should still prepare a statewide

inventory (the State may, however, elect to use the NET inventory data for those areas). EPA’s EFIG

maintains the Clearing House for Inventories and Emission Factors (CHIEF) web site
14

(http://www.epa.gov/ttn/chief/) to provide access to the latest information and tools for identifying

emission sources and estimating emissions of air pollutants and preparing air emission inventories. The

CHIEF web site provides access to the list of point, area, and mobile source classification codes (SCCs).

Note that EPA plans to revise the current SCC reporting system. The new reporting codes, likely to

be termed process category codes (PCCs), will be accommodated by the NET input format. Once the

new reporting system is established, EPA will accept an emission inventory based on either SCCs or

PCCs (i.e., EPA will not set a deadline by which time States are required to use the new system). EPA

expects to develop a crosswalk for converting codes from the existing reporting system to the new

system. In addition, for point source reporting under the CERR, a State is required to specify the

Standard Industrial Classification (SIC) code. The U.S. Department of Commerce, Bureau of the Census

has developed the North American Industry Classification System (NAICS) to replace the SIC system. 

The NAICS was developed jointly by the United States, Canada, and Mexico to provide new

comparability in statistics about business activity across North America. Correspondence tables to map

NAICS codes to SIC codes (or SIC codes to NAICS codes) have also been developed by the Bureau of

the Census.

Section 5.0 of this document provides tables which list in detail the source categories that EPA

believes are significant sources for the pollutants in the tables. This section also lists the source

categories for which EIIP procedures guidance has been developed. As new EIIP guidance is issued for

source categories discussed in section 5.0, the EIIP guidance should be used in lieu of the section 5.0

information, and can be accessed through the EIIP web site at http://www.epa.gov/oar/oaqps/eiip/. 

3.2.3 Geographic Coverage

The base year inventory must be prepared for all sources for the entire State regardless of the

attainment status of counties within the State. Even if there are areas within a State that do not have

significant emissions, the State must still prepare a statewide inventory. The State may elect to use the

EPA supplied NET inventory for those areas. Emissions for area, nonroad mobile, onroad mobile,

biogenic, and geogenic emissions should be provided at the county level. The geographic location of

emissions for point sources should be defined by their coordinates [i.e., latitude and longitude (decimal

degrees) or universal transverse mercator (UTM)]. 

Because of the regional nature of the pollutants, statewide inventories are necessary to support air

quality modeling to identify the scale of the pollutant problem (i.e., local versus regional), which in turn

will support evaluation and development of cost-effective control strategies. The draft CERR in

Appendix A specifies the criteria for defining point sources in attainment and nonattainment areas and

the frequency for reporting point source data. The draft CERR also specifies the criteria for defining

area, nonroad mobile, onroad mobile, and biogenic sources, and the reporting frequencies for these

sources. The draft CERR includes reporting requirements for all NAAQS criteria pollutants and

precursors, the Section 110 NOx SIP Call, and HAPs. Although this guidance document is only

concerned with the 8-hour ozone and PM2.5 NAAQS, and the regional haze rule, State and local agencies

are encouraged to coordinate their emission inventory development efforts for these other programs to

minimize duplication of effort while compiling their inventories for the 8-hour ozone and PM2.5 NAAQS,

and the regional haze rule.
15

3.2.4 Temporal Basis of Emissions

This section addresses the temporal resolution of the emissions data that should be provided in the

base year and 3-year cycle inventories. Discussion of how emissions are temporally allocated for air

quality modeling purposes is provided in section 3.3.1. Temporal adjustments to annual emissions

included in the inventory are made because of seasonal differences in the rate of emissions or activity, or

to apportion emissions to a particular season or day. State and local agencies should consult EIIP

guidance for temporal adjustment procedures. It is important that State and local agencies develop a

single integrated annual statewide inventory.

For the 8-hour ozone NAAQS emission inventory, VOC, NOx, and CO emissions should be reported

as actual annual and actual summer weekday. Summer weekday emissions are defined as an average

day’s emissions for a typical summer day during the ozone season. These temperature data are provided

to the air quality model by meteorological inputs developed for the specific days which are modeled. 

This information, in turn, is used by emissions models to “adjust” initial information provided by the

State. It is only necessary to choose a summer weekday and make note of the diurnal temperature pattern

used on a selected day. The emissions model will make adjustments for temperatures observed on the

actual days which are modeled. For modeling purposes, EPA also urges providing estimates for a

weekend day, which may reflect different activity levels and patterns. Note that in certain situations,

weekend emissions may dominate some episodes, and, therefore, the inventory will be needed to support

those analyses.

For the PM2.5 NAAQS and regional haze rule emission inventories, direct emissions (including

condensibles) of PM10 and PM2.5, and the precursor emissions VOC, NOx, SOx, and NH3 should be

reported as actual annual. Temporal allocation of the inventories to other time scales (e.g., daily) will be

made during preprocessing of the inventories for modeling, based on temporal allocation profiles. 

Alternatively, the State or local agency may choose to include actual temporally resolved emissions data

in its inventory (see section 3.3).

The State or local agency should discuss in its IPP its approach for preparing and supplying

temporally resolved emissions. 

3.2.5 Rule Effectiveness and Rule Penetration

For ozone inventories, RE is still required as it has been in the past (i.e., each State or local agency

should negotiate the application of RE and RP with its EPA Regional Office and include the decisions in

its IPP). The inventory documentation should note when RE or RP are applied and what the factors are.

RE reflects the ability of a regulatory program to achieve all the emission reductions that could have

been achieved by full compliance with the applicable regulations at all sources at all times. The concept

of applying RE in a SIP emission inventory has evolved from the observation that regulatory programs

may be less than 100 percent effective for some source categories. Should a State include RE, it should

be applied to all sources that are affected by a regulation and for which emissions are determined by

means of emission factors and control efficiency estimates. Thus, the RE factor is only applied to

controlled emission sources (point) or source categories (area). No RE is needed in cases where no

control is applied or there is no applicable regulation. Several factors should be taken into account when

estimating the effectiveness of a regulatory program. These include: (1) the nature of the regulation

(e.g., whether any ambiguities or deficiencies exist, whether test methods and/or recordkeeping

requirements are prescribed); (2) the nature of the compliance procedures (e.g., taking into account the

long-term performance capabilities of the control); (3) the performance of the source in maintaining
16

compliance over time (e.g., training programs, maintenance schedule, recordkeeping practices); and

(4) the performance of the implementing agency in assuring compliance (e.g., training programs,

inspection schedules, follow-up procedures). For further information on RE, the reader is referred to

EPA guidelines for estimating and applying RE for ozone and CO SIP base year inventories.4

Rule penetration is an estimate of the extent to which a regulation covers emissions from an area

source category for a specified control area (e.g., county, group of counties making up a nonattainment

area, or statewide). Thus, RP is applied to the control efficiency for a regulation to account for less than

100 percent coverage of the emissions for an area source category. For example, if a control measure is

applied to an area source fuel combustion category to control emissions from the largest emission sources

within the category, then RP could be applied to the control efficiency for the control measure to account

for the percentage of emissions for the source category that are affected by the control measure. For area

sources, RP and RE should be applied at the SCC level. 

For information on applying RE, State/local agencies can consult the EIIP draft document Emission

Inventories and the Proper Use of Rule Effectiveness, available at the following web site: 

http://www.epa.gov/ttnchie1/eiip/pointsrc.htm.

For PM2.5 and regional haze inventories, large contributions to overall emissions are of an

uncontrolled area source nature, and there is insufficient evidence to draw broad conclusions on the

application of RE/RP. Therefore, RE/RP will not be applied to PM2.5 and regional haze inventories.

EPA is currently reviewing its policy on RE and RP. If changes to the existing policy are made,

EPA will announce these changes through a policy memorandum.

3.3 MODELING INVENTORIES

This section explains the procedures by which emissions in a completed base year or projection year

inventory are temporally allocated, spatially allocated, and speciated for use in a photochemical grid

model. By explaining these procedures, it is anticipated that State and local agencies will be able to

provide more complete and accurate data to increase the accuracy of the procedures. Note, however, that

the information on preparing gridded inventories is presented for informational purposes and is not

required for States. The procedures discussed are those applied in the emission inventory preprocessor

currently being used by EPA, which, for this purpose, is based on the Emissions Modeling System,

version 1995 (EMS-95). The procedures more than likely will be revised to incorporate improvements to

the emission inventory/modeling interface, therefore, State and local agencies should consult with their

modeling staff and EPA Regional Office to verify the procedures that will be used to process their

inventory data for modeling, and make adjustments as needed. Once these decisions have been made,

State and local agencies should document their approach in the IPP. As such, the following discussion of

EMS-95 is presented as an example of a method to process data for photochemical grid modeling, and

States are not required to use EMS-95.

It is possible that States will need to develop microscale, day-specific inventories to support air

quality modeling efforts. These detailed emission inventories may be developed for any number of

state-specific purposes, including model performance evaluation. However, if States develop a more

detailed modeling inventory, the emissions do not need to be reported to EPA.
17

3.3.1 Temporal Allocation Procedures

Because of the different data elements reported for point, area, and mobile sources, the preprocessor

contains separate procedures for temporally allocating their emissions. The following sections describe

the procedures used for point, area and mobile sources, respectively. 

3.3.1.1 Point Sources

EMS-95 temporally allocates emissions estimates based on source-specific operating schedule data

that are input to the preprocessor. EMS-95 recognizes the following forms of operating schedule data:

C monthly throughput fractions (January through December)

C seasonal throughput fractions (where winter = December, January, and February;

spring = March, April, and May; summer = June, July, and August; and fall = September,

October, and November)

C hours per year in operation

C days per year in operation

C weeks per year in operation

C days per week in operation

C hours per day in operation

Any, none, or all of the operating schedule data can be supplied. If no operating schedule data are

supplied, EMS-95 uses a default operating schedule based on SCC-specific profiles for point sources. 

However, custom profiles were not available and were not incorporated into EMS-95 for all SCCs. 

Therefore, in many cases the SCC-specific profiles simply reflect 24 hours per day, 7 days per week, and

12 months per year of operation.

If some or all of the operating data are provided, EMS-95 uses a hierarchy of the operating schedule

data to determine how to compute the temporal factors. In this hierarchy, the monthly temporal factor is

computed first, followed by the weekly temporal factor, then the daily temporal factor, and finally, the

24 hourly temporal factors.

To determine the monthly temporal factor, EMS-95 employs the following steps:

C Step 1. If valid monthly throughput values are available, the monthly temporal factor is set to

the monthly throughput value of the month being modeled.

C Step 2. If a value is not obtained in Step 1 and valid seasonal throughput values are available,

the monthly temporal factor is set to one-third of the seasonal throughput value of the season

being modeled.

C Step 3. If monthly and seasonal throughput values are not available, the monthly temporal

factor is set to 0.083 or 1/12 for equal monthly throughput values.

To determine the weekly temporal factor, EMS-95 determines the number of days in the month

being modeled and divides that value by 7 days per week.

To determine the daily temporal factor, EMS-95 examines the values for days per week in operation. 

If it is a valid value (i.e., from 0 to 7), no additional action is needed to determine days per week for that

source. If it does not have a valid value, EMS-95 assigns a value by examining the hours per year in
18

operation, days per year in operation, and weeks per year in operation fields, and using the following

assumptions:

C hours per year in operation (houryear)

– if 0 < houryear #850, then days per week = 2

– if 850 < houryear #1250, then days per week = 3

– if 1250 < houryear #1670, then days per week = 4

– if 1670 < houryear # 2100, then days per week = 5

– if 2100 < houryear # 2500, then days per week = 6

– if 2500 < houryear, then days per week = 7

C days per year in operation (dayyear)

– if 0 < dayyear #110, then days per week = 2

– if 110 < dayyear #160, then days per week = 3

– if 160 < dayyear #210, then days per week = 4

– if 210 < dayyear # 260, then days per week = 5

– if 260 < dayyear # 315, then days per week = 6

– if 315 < dayyear, then days per week = 7

C weeks per year in operation (weeks)

– if 0 < weeks #7, then days per week = 1

– if 7 < weeks # 13, then days per week = 2

– if 13 < weeks #19, then days per week = 3

– if 19 < weeks #26, then days per week = 4

– if 26 < weeks # 33, then days per week = 5

– if 33 < weeks # 39, then days per week = 6

– if 39 < weeks, then days per week = 7

To determine the hourly temporal factor, EMS-95 checks the hours per day in operation field for the

source, and if there is a valid value, EMS-95 takes no other actions to determine the hours per day in

operation value for the sources. If there is not a valid value, EMS-95 assigns a value by examining the

hours per year in operation, days per year in operation, and weeks per year in operation fields. If any of

these fields have a valid value, hours per day in operation is assumed to be 8. If hours per day in

operation or days per week in operation cannot be assigned through the methods described here, hours

are assumed to be 24 and days are assumed to be 7.

EMS-95 uses the temporal factors to allocate emissions to hourly values. The temporal factors are

applied based on how the emissions estimates were reported to the preprocessor (as annual average, dayspecific, or average day emissions).

C If the emissions data are annual average emissions, reported emissions are multiplied by

(1) the product of monthly temporal factor divided by the weekly temporal factor, then by

(2) the day of week temporal factor, and then by (3) the hourly temporal factor, to get the

hourly emissions estimate.

C If the emissions data are average day emissions and the monthly factor, weekly factor, or day

of week factor is zero, then emissions are assumed to be zero for each hour.
19

C If the emissions data are average day emissions and none of the factors (the monthly temporal

factor, weekly temporal factor, or day of week factor) is zero, then emissions are multiplied by

the hourly factor.

C If the emissions data are reported as day-specific emissions, then the emissions are multiplied

by day-specific hourly temporal factors.

The States are encouraged to provide the modelers with as much operating data as possible for each

point source. Use of actual data results in more accurate temporal allocation, and less data manipulation

and fewer assumptions from the preprocessor.

3.3.1.2 Area and Mobile Sources

EMS-95 uses the Temporal Allocation Factor File (TAFF) developed for the 1985 National Acid

Precipitation Assessment Program (NAPAP) to temporally allocate area source emissions. The temporal

allocation factors take the form of three sets of fractional multipliers, as follows:

(1) Four seasonal factors divide the annual total into four subtotals representing emissions for each

season.

(2) Three daily factors per season divide each seasonal total into three subtotals representing

emissions for a typical weekday, Saturday, and Sunday in each season.

(3) Twenty-four hourly factors per day divide each daily total into 24 subtotals representing

emissions for each hour of the day.

The seasonal multipliers for each record sum to one, as do the hourly multipliers for each season/day

combination. Since daily emissions totals represent emissions for one typical weekday, Saturday, or

Sunday in each season, the overall equation for daily allocation factors is:

(65 x weekday factor) + (13 x Saturday factor) + (13 x Sunday factor) = 1

where a season is defined as 91 days (13 weeks).

Temporal allocation factors were developed for the area source categories in the 1985 NAPAP area

source file. Depending on the magnitude of emissions within the category and the availability of data,

some factors were resolved to the regional, State, or county level (i.e., different sets of factors for each

region, State, and county for a given source category). Table 2-1 of The 1985 NAPAP Emissions

Inventory: Development of Temporal Allocation Factors5 (herein referred to as the TAF document) lists

the NAPAP area source categories, including the level of resolution for each temporal pattern. 

Appendix D of the TAF document contains the listing of all 212 unique temporal profiles used to allocate

area source emissions, including a key to the temporal profile usage. Section 2 of the TAF document

describes how the temporal allocation factors were developed for each area source category.
20

The following example profile listing was excerpted from Appendix D of the TAF document.

PROFILE

DAY

NBR SEA DAY

HR

01

HR

02

HR

03

HR

04

HR

05

HR

06

HR

07

HR

08

HR

09

HR

10

HR

11

HR

12

HR

13

HR

14

HR

15

HR

16

HR

17

HR

18

HR

19

HR

20

HR

21

HR

22

HR

23

HR

24

A001 1 621 0110 051 051 051 057 057 057 048 048 048 047 047 047 028 028 028 016 017 016 038 037 038 047 048 047

2 621 0110 051 051 051 057 057 057 048 048 048 047 047 047 028 028 028 016 017 016 038 037 038 047 048 047

3 621 0110 051 051 051 057 057 057 048 048 048 047 047 047 028 028 028 016 017 016 038 037 038 047 048 047

4 201 0110 083 083 083 110 110 110 127 127 127 013 013 013 000 000 000 000 000 000 000 000 000 000 000 000

5 201 0110 083 083 083 110 110 110 127 127 127 013 013 013 000 000 000 000 000 000 000 000 000 000 000 000

6 201 0110 083 083 083 110 110 110 127 127 127 013 013 013 000 000 000 000 000 000 000 000 000 000 000 000

7 000 0000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

8 000 0000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

9 000 0000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

10 178 0110 067 067 067 106 106 106 120 120 120 000 000 000 000 000 000 000 000 000 000 000 000 040 040 040

11 178 0110 067 067 067 106 106 106 120 120 120 000 000 000 000 000 000 000 000 000 000 000 000 040 040 040

12 178 0110 067 067 067 106 106 106 120 120 120 000 000 000 000 000 000 000 000 000 000 000 000 040 040 040

Using the key in Appendix D, profile A001 corresponds to NAPAP area source categories 001 through

006 (residential fuel - anthracite coal, bituminous coal, distillate oil, residual oil, natural gas, and wood,

respectively) for the State of Alabama. Under the DAY NBR column:

1 = winter weekday

2 = winter Saturday

3 = winter Sunday

4 = spring weekday

5 = spring Saturday

6 = spring Sunday

7 = summer weekday

8 = summer Saturday

9 = summer Sunday

10 = fall weekday

11 = fall Saturday

12 = fall Sunday

The numbers in the SEA column represent the seasonal factors used to divide the annual emissions into

seasonal totals. For profile A001, the winter seasonal factor is 621, which means that 62.1 percent of the

total annual activity occurs in the winter.

The numbers in the DAY column represent the daily factors used to divide the seasonal emissions

into typical weekday, Saturday, and Sunday emissions. For profile A001, the winter weekday factor is

0110, which means that 1.10 percent of the seasonal activity occurs during each weekday.

The numbers in each HR column represent the hourly factors. For profile A001 on a winter

weekday, the fraction for HR 1 is 051, which means that 5.1 percent of the total daily activity for this

source category occurs during hour 1 of the day.

States and local agencies can review the area source temporal allocation factors used by EMS-95,

and, if they feel that the these factors are not representative of actual activity for a specific area source

category in their area, they may submit alternative profiles to be used with their area source emissions

inventory. If an agency elects to submit alternative temporal allocation factors, it should clearly indicate

which categories the alternative factors should be applied to, as required in the CERR.

The Motor Vehicle Emissions Estimates Model (MoVEM) is used to compute emissions estimates

from onroad mobile sources in EMS-95. MoVEM is a true model because it computes gridded, hourly
21

emissions estimates from fundamental traffic and emissions data (e.g., VMT, vehicle mix, emission

factors). VMT estimates are temporally allocated by MoVEM in the following manner. Prior to

computing the motor vehicle emissions estimates, MoVEM adds gridded, hourly temperatures and

adjusts the VMT to the specific modeling day. The temperature data are used to obtain the correct

emissions factor from the MOBILE emissions factors lookup tables. Through the application of the

following equations, MoVEM computes the day-specific, diurnal and nondiurnal, hourly VMT.

dvmti,j,l,h,m,n = ddayvmti,j,l,m,n ( adjday ( adjmonth ( dvmt_profi,j,l,h

ovmti,j,l,h,m,n = odayvmti,j,l,m,n ( adjday ( adjmonth ( ovmt_profi,j,l,h

dvmti,j,a,f,m,n = ddayvmti,j,a,f,n ( adjday ( adjmonth ( dvmt_profi,j,a,f,h

ovmti,j,a,f,m,n = odayvmti,j,a,f,n ( adjday ( adjmonth ( ovmt_profi,j,a,f,h

where: dvmt is the diurnal VMT;

ddayvmt is the total day diurnal VMT;

adjday is the day-specific VMT adjustment factor supplied through the ASCII input file

adjstvmt.mv;

adjmonth is the month-specific VMT adjustment factor supplied through the ASCII input file

adjstvmt.mv;

dvmt_prof is the hour-specific, diurnal VMT fractional profile factor;

ovmt is the nondiurnal VMT;

odayvmt is the total day nondiurnal VMT;

ovmt_prof is the hour-specific, nondiurnal VMT fractional profile factor;

i is the State index;

j is the county index;

h is the hour index;

l is the link identifier index;

a is the area type index;

f is the facility type index;

m is the east-west grid cell index; and

n is the north-south grid cell index.

If the user supplies limited data to MoVEM, MoVEM can apply a variety of default values to

compute motor vehicle emissions estimates. For temporally allocating VMT, MoVEM applies the

following default fractional profile for estimating hourly VMT from day-specific and month-specific

VMT supplied by the user (Table 3.3-1). 
22

Table 3.3-1. Default Hourly VMT Fractional Profile

Emission

Hour

1 2 3 4 5 6 7 8 9 10 11 12

Diurnal 0.000 0.000 0.000 0.000 0.000 0.129 0.021 0.100 0.095 0.095 0.166 0.199

Other 0.016 0.010 0.003 0.006 0.010 0.026 0.053 0.064 0.055 0.048 0.050 0.052

13 14 15 16 17 18 19 20 21 22 23 24

Diurnal 0.079 0.116 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Other 0.054 0.055 0.059 0.070 0.074 0.070 0.058 0.046 0.037 0.033 0.028 0.022

3.3.2 Spatial Allocation Procedures

To prepare emissions for photochemical modeling, these emissions should be spatially allocated

both horizontally and vertically. Horizontal spatial allocation refers to placing the emissions in the

proper grid cell on the emissions modeling grid to be used in the modeling exercise. Vertical spatial

allocation refers to placing the emissions in the proper layer, that is, distance into the atmosphere, in

which emissions are deposited. Spatial allocation procedures used for point sources are different than

those used for area and mobile sources. Procedures used for spatial allocation of point source and

area/mobile source emissions are described below.

3.3.2.1 Point Sources

Horizontal Spatial Allocation

Point sources are spatially allocated to an emissions modeling grid by the UTM coordinates of a

stack or by the UTM coordinates of the facility. These geographic coordinates should be supplied as part

of the point source inventory. If they are supplied as latitude/longitude coordinates rather than UTM

coordinates, they must be converted to UTM prior to input to EMS-95.

The EMS-95 Point Source Location Processor prepares an ASCII file of point source identifiers and

point source UTM locations. The Point Source Grid Processing Module reads the ASCII file that was

generated by the Point Source Location Processor, generates the appropriate ARC/INFO® coverages, and

prepares two ASCII files:

• a file which contains point source identifiers and grid cell location

• a file which contains point source identifiers and latitude/longitude coordinates

Point sources that have neither stack coordinates nor facility coordinates are placed in the center of the

county, and EMS-95 reports on the point sources so placed. The process of assigning grid coordinates to

point sources is an ARC/INFO® function; therefore, the technical formulation is embedded within the

ARC/INFO® software. Please refer to the ARC/INFO® documentation for a discussion on coverage

manipulation.6
23

Vertical Spatial Allocation

The vertical layer that point source emissions are deposited in is based on the plume rise of the

emissions. The plume rise of emissions is calculated based on the stack parameters supplied in the point

source inventory. Therefore, it is important that State/local agencies provide accurate stack parameters

(height, diameter, gas exit temperature, velocity, and flow rate) as part of their point source inventory

submissions.

An important feature of the EMS-95 Point Source module is its ability to provide an initial screening

of the stack parameters (i.e., height, diameter, flow rate, gas exit temperature) for validity. Table 3.3-2

identifies the range of each stack parameter that is used in the initial screening. Stack parameters that fall

outside of this range are flagged by EMS-95 as suspect parameters.

Table 3.3-2. Stack Parameter Ranges Used in the Initial Screening

Range Height

(feet)

Diameter

(feet)

Flowrate

(cubic feet/minute)

Velocity

(feet/second)

Temperature

( F)

minimum 0.01 0.01 0.01 0.01 0.01

maximum 1,500.00 100.00 100,000.00 98.40 2,000.00

Since the stack parameters are used to compute plume rise, that is, the distance into the atmosphere

that the stack emissions rise, they are critical in the air quality modeling process. Based on the OTAG

experience and previous modeling experience, approximately 20 to 30 percent of the stacks will have one

or more incorrect stack parameters. In some cases, the incorrect stack parameters will result in emissions

that are released above the top of the modeling domain; hence, the impact on air quality from elevated

point source emissions will be underestimated. In many past efforts, the errant parameters have gone

uncorrected; hence, the resulting air quality modeling results may be suspect.

3.3.2.2 Area and Mobile Sources

Horizontal Spatial Allocation

Most area and mobile source inventories contain countywide emissions. Emissions modeling grids

are not based on political boundaries and in almost all cases they represent smaller areas than counties. 

Therefore, countywide area and mobile source emissions must be allocated to grid cells prior to

photochemical modeling.

One of the most important functions of the EMS-95 Area Source Model is the allocation of

countywide area source emissions estimates to individual grid cells. In general, spatial surrogates

approximate the location and magnitude of the emissions for the area source. For example, residential

natural gas combustion is well approximated by single family housing, and population can be used to

estimate the number of gasoline service stations. The user is required to define the spatial surrogates

(e.g., population, housing, urban area, etc.). For each spatial surrogate, the user must define what data

(categories of land use/land cover, population counts, housing counts, etc.) contribute to the surrogate. 

The user also assigns each area source category (e.g., residential natural gas combustion, dry-cleaning

operations) to a unique spatial surrogate (e.g., housing, population). 
24

srgk

c,i,j'

jx,c,i,j

val x

c,i,j

jx,c

val x

c

aceea

i,j'acee a(srg k,ai,j

After the user has populated the appropriate files, EMS-95 grids the necessary data sets per the

requirements of the user-defined spatial surrogates. Spatial surrogates, and their data source, that have

been used in prior modeling exercises are shown in Table 3.3-3.7 In some cases a surrogate (e.g.,

agriculture) will not exist in a county though an emissions estimates for an area source category

(e.g., farm harvesting equipment) may be assigned to the surrogate. In such a case, the area source

category is assigned a secondary surrogate (e.g., rural). If the secondary surrogate also does not exist in

the county, the population surrogate acts as the default since population covers the entire domain. Note

that it is possible to recombine the data in Table 3.3-3 to develop other area source spatial surrogates, if

so desired. EPA encourages the use of the best available, most representative, data for use as the spatial

surrogates.

The surrogate is computed as the sum of the values that comprise the surrogate in a grid cell divided

by the sum of the values that comprise the surrogate in a county, as shown in the following equation:

where: srg is the spatial surrogate value (0 < srg < 1)

k is the surrogate index (e.g., index to urban, population)

i, j is the grid cell identifier

val is value of the component that comprises the spatial surrogate (length, area, count)

x is the spatial surrogate component index (e.g., index to dryland, cropland)

c is the county identifier (e.g., 17,031 Cook County, Illinois)

Spatial allocation of the area source emissions estimates is accomplished using the following equation:

where: acee is the county-specific area source emissions estimate

a is the county-specific area source category index

i, j is the grid cell identifier

srg is the spatial surrogate value (0 < srg < 1)

k is the surrogate index assigned to area source category a

Because there are over 340,000 State/county/area source category combinations, it is not possible to

list all spatial surrogate assignments here. However, Table 3.3-4 identifies the 4-digit area source

category code (note that area source category codes are ten digits long), a brief description of the area

source category, and the predominant area source spatial surrogate to which the area source category has

been assigned.

For mobile sources, VMT is spatially allocated to grids, prior to calculation of emissions by

EMS-95. The Motor Vehicle Emissions Estimates Model (MoVEM) is used to compute emissions

estimates from onroad mobile sources in EMS-95. After VMT input data (i.e., monthly and daily VMT

adjustments; speed adjustments; vehicle mix profiles; countywide VMT; and network speeds) files have

been read and checked, MoVEM prepares the necessary network coverages. The off-network system is

derived from the U.S. Department of Transportation Federal Highway Administration (FHWA) version

2.1 nationwide planning network.8 The off-network coverage is gridded by overlaying the emissions
25

Table 3.3-3. Area Source Spatial Surrogates7

Surrogate Description

Agriculture Derived from the LCC25 data base.9 Comprised of the categories: dryland,

cropland, and pasture; irrigated cropland and pasture; mixed dryland/irrigated

cropland and pasture; grassland/cropland mosaic; and woodland/cropland

mosaic. Resolution of data is 1.1 kilometers. Surrogate exists for both U.S. and

Canada.

Airports Derived from the post-1990 TIGER/Line data base.10 Comprised of major

national and international commercial airports and large private airstrips. Point

value; no resolution. Surrogate exists only for U.S.

Area Derived from grid coverage developed by EMS-95 Grid Definition Model. 

Resolution of data is 1,000 meters. Surrogate exists for both U.S. and Canada.

Housing Derived from the post-1990 census data base.11 Comprised of all single and

multiple family housing units. Resolution of data is census tract (about 2,000

meters). Surrogate exists only for U.S.

Inverse housing Derived from the post-1990 census data base.11 Resolution of data is census

tract (about 2,000 meters). Surrogate exists only for U.S.

Inverse

population

U.S. data derived from the post-1990 census data base.11 Resolution of data is

census tract (about 2000 meters). Canadian data are derived from gridded world

population data12 with resolution of about 5'. Surrogate exists for both U.S. and

Canada.

Major highways Derived from the Federal Highway Authority v.2.0 national planning network.8

Resolution of data is 3000 meters. Surrogate exists only for U.S.

Population Derived from the post-1990 census data base.12 Resolution of data is census

tract (about 200 meters). Canadian data are derived from gridded world

population data12 with resolution of about 5'. Surrogate exists for both U.S. and

Canada. 

Ports Derived from the post-1990 TIGER/Line data base.10 Comprised of major

national and international commercial shipping ports. Point value; no resolution. 

Surrogate exists only for U.S.

Railroads Derived from the National Railway Network.13 Resolution of data is 3,000 meters. 

Surrogate exists only for U.S.

Water Derived from LCC25 data base9 and post-1990 census data base.11 Comprised

of the water category plus ocean. Resolution of LCC25 data base is 1.1 kilometer

and resolution of census data base is census tract (about 2,000 meters). 

Surrogate exists for both U.S. and Canada.

Rural All areas not Urban. Resolution of data is census tract (about 2,000 meters). 

Surrogate exists for both U.S. and Canada.

Urban Derived from the post-1990 census data base.11 Determined to be all areas with

populations of 25,000 or more. Resolution of data is census tract (about 2,000

meters). Canadian data are derived from the LCC25 Canada data base.9

Surrogate exists for both U.S. and Canada.
26

Table 3.3-4. Four-digit Area Source Category Codes and the Predominant

Area Source Spatial Surrogate

4-digit

Area

Source

Category

Major Category Description

(2-digit Area Source Category)

Minor Category Description

(4-digit Area Source Category)

Predominant

Area Source

Spatial

Surrogate

2101 Stationary Source Fuel Combustion Electric Utility Population

2102 Stationary Source Fuel Combustion Industrial Population

2103 Stationary Source Fuel Combustion Commercial/Institutional Population

2104 Stationary Source Fuel Combustion Residential Housing

2199 Stationary Source Fuel Combustion Total Area Source Fuel Combustion Population

2260 Mobile Sources Off-highway Vehicle Gasoline 2-Stroke Population

2265 Mobile Sources Off-highway Vehicle Gasoline 4-Stroke Population

2270 Mobile Sources Off-highway Vehicle Diesel Population

2275 Mobile Sources Aircraft Airports

2280 Mobile Sources Marine Vessels Commercial Ports

2282 Mobile Sources Marine Vessels Recreational Water

2283 Mobile Sources Military Population

2285 Mobile Sources Railroads Railroads

2294 Mobile Sources Paved Roads Population

2296 Mobile Sources Unpaved Roads Population

2301 Industrial Processes Chemical Manufacturing: SIC 28 Population

2302 Industrial Processes Food and Kindred Products: SIC 20 Population

2303 Industrial Processes Primary Metal Production: SIC 33 Population

2304 Industrial Processes Secondary Metal Production: SIC 33 Population

2305 Industrial Processes Mineral Processes: SIC 32 Population

2306 Industrial Processes Petroleum Refining: SIC 29 Population

2307 Industrial Processes Wood Products: SIC 24 Population

2308 Industrial Processes Rubber/Plastics: SIC 30 Population

2309 Industrial Processes Fabricated Metals: SIC 34 Population

2310 Industrial Processes Oil and Gas Production: SIC 13 Inverse population

2311 Industrial Processes Construction: SIC 15 - 17 Population

2312 Industrial Processes Machinery: SIC 35 Population

2325 Industrial Processes Mining and Quarrying: SIC 14 Population

2390 Industrial Processes In-process Fuel Use Population

2399 Industrial Processes Industrial Processes: NEC Population

2401 Solvent Utilization Surface Coating Population

2415 Solvent Utilization Degreasing Population

2420 Solvent Utilization Dry Cleaning Population

2425 Solvent Utilization Graphic Arts Population

2430 Solvent Utilization Rubber/Plastics Population

2440 Solvent Utilization Miscellaneous Industrial Population

2460 Solvent Utilization Miscellaneous Nonindustrial: All Classes Population

2461 Solvent Utilization Miscellaneous Nonindustrial: Commercial Population

2465 Solvent Utilization Miscellaneous Nonindustrial: Consumer Population

2500 Storage and Transport ***UNKNOWN*** Inverse housing

2501 Storage and Transport Petroleum and Petroleum Product Storage Inverse housing

2505 Storage and Transport Petroleum and Petroleum Product Transport Population

2510 Storage and Transport Organic Chemical Storage Inverse housing

2601 Waste Disposal, Treatment, and Recovery On-site Incineration Inverse housing

2610 Waste Disposal, Treatment, and Recovery Open Burning Inverse housing

2620 Waste Disposal, Treatment, and Recovery Landfills Inverse housing

2630 Waste Disposal, Treatment, and Recovery Wastewater Treatment Population

2640 Waste Disposal, Treatment, and Recovery TSDFs Population

2660 Waste Disposal, Treatment, and Recovery Leaking Underground Storage Tanks Population

2801 Miscellaneous Area Sources Agriculture Production - Crops Agriculture

2805 Miscellaneous Area Sources Agriculture Production - Livestock Agriculture

2810 Miscellaneous Area Sources Other Combustion Inverse population

2830 Miscellaneous Area Sources Catastrophic/Accidental Releases Inverse population

2850 Miscellaneous Area Sources Health Services Population
27

modeling grid over the off-network coverage, and in the same manner that the area source spatial

surrogates are computed, an off-network VMT surrogate is computed for each area type/facility type

combination. That is, each area type/facility type segment is apportioned to a grid cell in the emissions

modeling domain. Once the networks have been gridded, the corresponding countywide VMT, which is

identified by area type and facility type, is gridded. Though it is extensive, consisting of over 400,000

miles of roadways, the FHWA network does not adequately define all area type/facility type

combinations for which countywide VMT are defined. In such cases, the VMT is apportioned via the

area source population surrogate.

States may use an emissions preprocessor that spatially allocates mobile source emission estimates

instead of VMT, as is done for MoVEM. In these cases, the following horizontal spatial allocation

surrogates are provided as suggestions for spatially allocating non-exhaust emissions from

non-commercial vehicles: for diurnal and evening hot soak emissions, single family housing locations

may be an appropriate surrogate; employment data may be a suitable surrogate for allocating morning hot

soak evaporative emissions.

Vertical Spatial Allocation

Both area and mobile source emissions are assumed to be ground-level sources, that is, deposited

into the surface layer. Therefore, no vertical spatial allocation is needed for these sources.

3.3.3 Speciation Procedures

Prior to describing the methods employed by EMS-95 to speciate emissions supplied by the

emissions submodels, it is necessary to describe the difference between discrete and lumped-model

speciation:14

• discrete speciation - refers to splitting emissions for a pollutant into individual chemical

compounds. For example, total organic gases (TOG) emissions from automobile exhaust may

consist of 50 or more identified organic compounds (e.g., benzene, hexane, formaldehyde,

etc.). Discrete speciation is performed using speciation profiles containing weight fractions for

each chemical compound (e.g., profiles found in EPA’s SPECIATE data base);

• lumped-model speciation - refers to splitting emissions for a pollutant into groups of

components that represent numerous discrete compounds. The groups of components are

referred to as lumped-model species. The lumped-model species for TOG are developed using

split factors that are specific to the type of chemical mechanism employed by the

photochemical model to be used.

For example, the UAM model uses the Carbon Bond IV (CB-IV) mechanism, therefore

discrete compounds are lumped together based on the compounds’ carbon bond structure. The

single carbon-carbon bond hydrocarbon compounds, for instance, are lumped into the paraffin

(PAR) lumped-model species. For the California Statewide Air Pollution Research Center

(SAPRC) mechanism employed by the Regional Acid Deposition Model (RADM) and the San

Joaquin Valley Air Quality Study/Atmospheric Utilities Signatures, Predictions and

Experiments Regional Modeling Adaption Project (SARMAP) Air Quality Model (SAQM),

discrete compounds are lumped together based on their relative reactivity with the hydroxyl

radical.
28

sfi,j'

i j

xmfi,k

mwk

C xnumj,k

The EMS-95 Speciation Model performs lumped-model speciation of TOG emissions. For NOx

emissions, these are discretely speciated into nitric oxide (NO) and nitrogen dioxide (NO2) (and

sometimes HONO). SOx is discretely speciated into SO2 and SO4. The chemical mechanisms supported

by EMS-95 for lumped-model speciation of TOG are the CB-IV and SAPRC mechanisms. However,

EMS-95 does have a module that allows for the use of any other chemical mechanism for developing

split factors (referred to as the External CB-IV Split Factors Module).

The following equation is used to compute CB-IV split factors for TOG emissions:

where: sf = CB-IV split factor (moles of lumped-model species/gram TOG

i = the TOG species profile index

j = the CB-IV lumped-model species index

k = the index for the discrete TOG species in the emissions stream

xmf = mass fraction of discrete TOG species in the emissions stream (grams discrete

TOG species/gram TOG)

mw = molecular weight of the discrete TOG species in the emissions stream (grams

of discrete TOG species/mole of discrete TOG species)

xnum = assignment of lumped-model species to discrete TOG species (moles of

lumped-model species/mole of discrete TOG species)

For the most recent version of EMS-95 (e.g., the version used during the OTAG modeling), the

lumped-model split factors were derived from discrete speciation profiles from EPA’s SPECIATE data

base. For other versions of EMS-95, other sources of speciation data may have been used to derive split

factors. Therefore, users should check with their source of the EMS-95 software to determine the origin

of speciation data. As mentioned above, revised split factors can be derived using the External CB-IV

Split Factors Module, if better discrete speciation profiles or lumped-model species assignments (i.e.,

xnum in the equation above) exist. For SIP modeling efforts, any such revisions should be coordinated

with the EPA Regional Office.

The EMS-95 Speciation Model also performs a reactive organic gas (ROG) to TOG adjustment to

account for some emissions measurement techniques that do not capture all of the discrete hydrocarbon

compounds in the emissions stream. This adjustment must be performed since the speciation profiles are

based on TOG, not ROG.

The NO and NO2 split factors for NOx are based on an assumed composition of 90 percent by mass

NO as NO2 and 10 percent NO2. However, the NO mass can vary between 89 and 95 percent by

weight.12 For a small number of cases, HONO mass is also included in the speciation (less than 2 percent

of NOx mass).

In summary, EMS-95 speciates the gridded, hourly emission estimates with the use of the following

equation:12

chemest = ee x rogtotog x (sf/divisor)
29

where: chemest = gridded, hourly lumped-model species emissions estimate (moles/hour)

ee = gridded, hourly emissions estimate (grams/hour)

rogtotog = ROG-to-TOG conversion factor (unitless)

sf = lumped-model species split factor (unitless)

divisor = a conversion factor for lumped-model species other than the TOG species

described above

The development of split factors, sf, for TOG species other than biogenic species are described

above. For biogenic species, the split factors are as follows:

C 1.0 for biogenic isoprene (ISOP)

C 0.5 for olefins from biogenic terpenes [OLETERP (e.g., one-half mole of olefins from each mole

of biogenic terpenes)]

C 6.0 for paraffins from biogenic terpenes (PARTERP)

C 1.5 for higher molecular weight aldehydes from biogenic terpenes (ALD2TERP)

C 0.5 for olefins from other biogenic VOC (OLEOVOC)

C 8.5 for paraffins from other biogenic VOC (PAROVOC)

C 0.5 for nonreactive organic compounds from other biogenic VOC (NROVOC)

C 0.97 for SO2 (97 percent of SOx is SO2; the remaining 3 percent SO4 is dropped)

C 1.0 for aerosols (AERO)

C 1.0 for CO

C 0.9 for NO (as NO2) and 0.1 for NO2, as described above for NOx

The divisor in the above equation is used to convert emissions from a mass to a molar basis. For

biogenic emissions, the divisor consists of a conversion from micrograms to kilograms and the assumed

molecular weight of the biogenic species: 68.12 for ISOP; 136.23 for TERP; and 86.00 for OVOC. The

divisors used in the equation are obtained from Reference 11 and are given below:

C 1.0 for non-biogenic TOG species

C 8.812 x 1010 for biogenic ISOP

C 1.3623 x 1011 for biogenic OLETERP, PARTERP, and ALD2TERP

C 8.6 x 1010 for biogenic OLEOVOV, PAROVOC, and NROVOC

C 30.0 for NO

C 46.0 for NO2

C 64.0 for SO2

C 1.0 for AERO

C 28.0 for CO
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31

SECTION 4.0

DATA REPORTING REQUIREMENTS

The draft CERR requires specific data elements to be reported by States to EPA for point, area,

nonroad mobile, onroad mobile, and biogenic source categories. The following sections summarize the

reporting requirements for each of these four major source sectors, as well as biogenic and geogenic

emission source categories. Electronic data transfer options are also discussed. The draft CERR,

including the preamble, is included as Appendix A to this report, and is referenced where appropriate.

Required data elements for States subject to the Section 110 NOx SIP call budgets are listed in the

draft CERR to demonstrate how Section 110 reporting can be coordinated with reporting for other

emissions inventory requirements. The NOx SIP call data reporting requirements support a rulemaking

that establishes NOx emissions budgets for 23 eastern States to decrease the transport of ozone across

State boundaries. States should be aware that this guidance document only addresses the 8-hour ozone,

PM2.5, and regional haze emission inventory requirements of the draft CERR.

4.1 POINT SOURCES

Point sources are large, stationary, identifiable emissions sources that release pollutants into the

atmosphere. Sources are generally defined by State or local agencies as point sources if they annually

exceed a specified pollutant emissions threshold. These thresholds may vary by State, but EPA has

established certain minimum point source thresholds for both pollutant nonattainment areas and

attainment areas.

According to the draft CERR, States should report data for point sources on both an annual and

triennial basis, starting with the 1999 inventory. Point sources are divided into two categories for

reporting purposes: Type A and Type B. Type A sources represent larger point sources and emissions

for these sources are required to be reported every year. Type B sources include those point sources not

reporting under the Type A source requirement. The reporting frequency for Type B sources has been

established as once every 3 years.

The pollutant emission thresholds that define Type A and Type B sources, as well as the data items

required, are listed in Appendix A, Table 2a. The emissions thresholds also vary depending on whether a

point source is located in a pollutant nonattainment area or attainment area (but the data items are the

same regardless of attainment status). It should also be noted that additional stack data elements, while

not required for annual point source reporting, should be reported every 3 years.

4.2 AREA SOURCES

Area sources are smaller sources that do not qualify as point sources under the relevant emissions

cutoffs. Area sources encompass more widespread sources that may be abundant, but that, individually,

release small amounts of a given pollutant. Examples of area sources include dry cleaners, residential

wood heating, autobody painting, and consumer solvent use.
32

Every 3 years, beginning with the 1999 inventory, States should submit to EPA area source

emissions data representing all relevant area source categories for the entire State. The data items

required for area source reporting are listed in Table 2b of Appendix A.

4.3 NONROAD MOBILE SOURCES

Nonroad mobile sources can be defined as mobile and portable internal combustion powered

equipment not generally licensed or certified for highway use. Nonroad engines can be classified

according to distinct nonroad equipment categories, ranging from small lawn and garden equipment to

heavy-duty construction equipment, large aircraft, and diesel locomotives. These general categories

comprise specific types of applications (e.g., chainsaws, front mowers, and leaf blowers/vacuums are

examples of lawn and garden applications).

Every 3 years, States should submit to EPA a statewide nonroad mobile source emissions inventory,

starting with the 1999 inventory. Table 2c of Appendix A presents the data items required to be reported

for mobile sources (both nonroad and onroad). For nonroad sources, the activity is typically expressed in

terms of horsepower-hours, the amount of fuel consumed, or hours of use (not VMT as listed in Table 2c,

which applies to onroad mobile sources). If States make changes to the default NONROAD model

inputs, discussed in more detail in Section 5.5.3, these input files should be submitted to EPA along with

the nonroad data elements.

4.4 ONROAD MOBILE SOURCES

 Onroad mobile sources are defined as those vehicles registered for use on public roadways, and

include automobiles, light-duty and heavy-duty trucks, buses and motorcycles. Onroad emissions are

comprised of both exhaust (i.e., tailpipe) and non-exhaust (e.g., refueling, tire and brake wear)

components.

States are required to submit a statewide onroad mobile source emissions inventory on a 3-year

basis, starting with the year 1999. Table 2c of Appendix A presents the data items required to be

reported by States for onroad mobile sources. The MOBILE model input files should also accompany

the onroad mobile source data, so that these inputs are available for national and regional air quality

modeling studies.

4.5 BIOGENIC AND GEOGENIC SOURCES

Biogenic and geogenic sources are natural (i.e., nonanthropogenic) emissions sources. Biogenic

sources are biological sources of ozone precursor emissions such as trees, agricultural crops, or microbial

activity in soils or water. VOC and NOx emissions can also result from geological activity, most notably

from seeps of oil or natural gas, volcanoes, and fumaroles (i.e., vapor or gas vents in a volcanic region). 

Soil wind erosion is a geogenic source of PM10 and PM2.5 emissions (although in the past this process has

also been considered to be an anthropogenic fugitive dust component of PM emissions inventories). In

addition, lightning may also be a significant contributor to natural NOx emissions in an inventory area. 

Table 2d of the draft CERR specifies the data elements for biogenic and geogenic source reporting.

According to the draft CERR, a baseline biogenic emissions inventory is required to be established

for each State. Triennial updates to this baseline inventory are only required if land use characteristics

used in determining biogenic emissions have changed, or if a new method is used to determine emissions. 

To the extent that the EPA develops a biogenic baseline for the specified base year inventory [e.g., using

Biogenic Emissions Inventory System-2 (BEIS-2)], it would be acceptable and practical for a State to use
33

these EPA-generated emission estimates as the basis for their SIP planning and modeling inventories. 

However, States may use non-BEIS-2 estimates if they believe they have more representative data for

estimating biogenic emissions, and can demonstrate better quality emissions data.

The EPA also encourages States to prepare an inventory of all significant geogenic sources in the

inventory area. EPA-generated PM emissions for wind erosion are expected to be available for use by

States in their SIP base year and 3-year cycle inventories, but if other geogenic sources are contributing

to either PM, regional haze, or ozone precursor emissions, these should be inventoried as well.

4.6 DEVELOPMENT OF COMPREHENSIVE EMISSION DATA BASE AT EPA

The EPA is establishing the NET ORACLE data base to store and distribute the EPA’s NET

inventory. The NET data base will serve as a central repository for EPA, State/local agencies, and the

general public to access the national inventory to use in air quality modeling, tracking progress in

meeting CAA requirements, setting policy and answering questions from the public. The NET data base

is being redesigned in ORACLE using the data elements and data relationships defined by the EIIP Data

Model, discussed in section 4.7. The NET ORACLE data base is expected to be completed in 1999 and

the NET Input Format is available now.

The EPA has announced that it will be closing out the emissions component of the Aerometric

Information Retrieval System (AIRS)/Facility Subsystem (AFS) effective September 30, 2000. States

should anticipate this and are encouraged to develop plans for using the NET data base with their

emission inventory data.

4.7 ELECTRONIC DATA TRANSFER REQUIREMENTS

4.7.1 Overview

To facilitate the transfer of the State-generated inventory data, the EPA has supported the

development of standard data transfer through the EIIP. Electronic reporting of inventory data is an issue

that is dynamic and changing. States should use resources such as EPA’s Data Submission section at

http://www.epa.gov/ttn/chief/ei for tracking the latest developments related to emissions reporting.

According to the draft CERR, four basic options for electronic data reporting exist:

C EPA NET data base format

C AFS format (for prior source data only)

C EIIP/Electronic Data Interchange (EDI) format

C Direct source reporting for Title IV sources and sources participating in regional NOx trading

programs (e.g., 40 CFR Part 96).

All of these electronic formats will accommodate the data transfer of annual and average summer day

emissions. Note that any State that submits complete data in these formats has met EPA emission

reporting requirements.

These reporting options are discussed in more detail in the sections that follow. If an agency

submits their data in another electronic format (i.e., aside from one of the acceptable formats), EPA may
34

not be able to enter their data into the EPA system (because of limited resources). In these cases, EPAgenerated default data may be used to represent emissions for the area. In addition, although not listed as

an option in the CERR, the EPA has acknowledged that some State or local agencies may choose to

update the NET data by overwriting the NET distribution file. However, the potential for transcription

errors is high, and, if significant revisions are necessary to improve the EPA NET data, this option is not

recommended.

Note that prior to using the EIIP/EDI data transfer procedure, States should contact EFIG to

determine the status and operating procedure for supporting this option.

4.7.2 EPA NET Input Format

The NET Input Format creates relational, normalized data sets which conform to the relational

standards and structure of the NET ORACLE data base. The relational nature of the format design

enables it to be mapped to a wide variety of data base structures.

The basic steps for data transfer using the EPA NET data base format include:

(1) Map State inventory data to the EPA NET data base format.

(2) Program a conversion utility to translate data in the State’s data base to EPA NET data base

input format files, using the mapping scheme developed in Step 1. (Software needed for the

translation could be any data base or spreadsheet program or other data handling system

capable of generating files compatible with the NET file structure. Some States’ data storage

systems may be able to be programmed to output stored data in the correct format.)

(3) Use the software developed in Step 2 to translate State’s data into EPA NET data base files.

(4) Transfer the EPA NET data base files to EPA/EFIG.

Detailed user documentation for the NET Input Format is available on EPA’s Internet web site at

http://www.epa.gov/ttn/chief/ei under “Data Submission.” The documentation includes important user

conventions and code tables, as well as format specifications and data submission procedures.

4.7.3 AIRS Format

The AIRS format has been used for electronic reporting for previous inventories and is still the

primary inventory data storage vehicle for several States. Using the AIRS format is a valid method to

make an electronic inventory submittal, but States should be aware that this method of reporting is

limited to point source information. For States that choose to submit point source data via AIRS/AFS, it

will be necessary to use one of the other data transfer options to submit area, mobile, and biogenics data.

To accommodate point source data submittals in the AIRS/AFS format, a utility will be available in

AFS, and used by EPA to translate AFS-formatted data into a NET-compatible format. This will allow

EPA to move point source data from AFS into the NET data base to complete the national emission

inventory for point, area, mobile, and biogenic sources. Further information about how to use AIRS/AFS

can be found on the Office of Air Quality Planning and Standards (OAQPS) Technology Transfer

Network (TTN) web page at the following address: http://www.epa.gov/ttn/airs/.
35

4.7.4 EIIP/EDI Format

The EIIP has developed a data transfer format using existing EDI standards. Electronic Data

Interchange is a nonproprietary data exchange technique created and maintained by the American

National Standards Institute (ANSI). The EIIP/EDI format can provide a common data exchange format

for federal, State and local government agencies, and eventually for industry, to exchange emissions

inventory information electronically using a single data transfer format.

The EIIP/EDI format was developed and tested as a prototype data transfer demonstration with two

pilot States and EPA. The technical documentation necessary for the EDI data transfer prototype

demonstration may be found on the EIIP web page, under Data Management Committee Procedures

Documents. Also included is the document Results of the EIIP EDI Prototype Data Transfer

Demonstration, which best describes how the EIIP EDI data transfer is accomplished and the purpose of

the different technical documents.

The EDI data transfer procedure may be available to State/local agencies through EPA assistance. 

While the EIIP successfully tested the use of EDI through its prototype demonstration, the EPA is

determining how to best establish and support EDI data transfer procedures across the Agency.

The general steps involved in the EIIP/EDI data transfer process are: 

(1) Identify a commercially available EDI translator that is compatible with the data application

and local computing system environment. (The initial participants are using the same EDI

translator, provided as part of the EIIP prototype system.)

(2) Program the translator using the EIIP/EDI technical documents. (The programming of the

shared EDI translator is provided as part of the EIIP prototype system.)

(3) Define the loader file format for the translator. (The loader file format for the shared translator

is provided as part of the EIIP prototype system.)

(4) Program a conversion utility to extract and map the State data into the appropriate fields of the

loader file format.

(5) Convert the extract file of State data to an EDI formatted file, using the EDI translator. 

(6) Transfer the EIIP/EDI standard format file to EPA. 

Inventory data that have been converted to the EIIP/EDI standard format can be made available to

the EPA or any other requestor by sending it on a floppy disk, electronically through Internet E-mail, or

by providing a downloadable file on an Internet file transfer protocol (FTP) site. Prior to using the

EIIP/EDI data transfer procedure, States should contact EFIG to determine the status and operating

procedure for supporting this option. 

4.7.5 Direct Source Reporting

Certain point sources may already be reporting electronic emissions data directly to EPA. For

example, electricity-generating units subject to Title IV Acid Rain monitoring and reporting provisions

must report continuous emission monitoring system (CEMS) data in a specified electronic data reporting

(EDR) format to EPA. In addition, large industrial combustion sources participating in regional NOx
36

mass emissions trading programs (e.g., under 40 CFR Part 96) are allowed to submit data using this

method. This CEMS data may not directly fulfill reporting requirements for all pollutants that would

constitute a State’s ozone, PM, or regional haze SIP submittal. However, EPA acknowledges this to be a

viable data option where reporting requirements overlap, and would like to encourage and facilitate the

use of continuous emission monitoring data by States and EPA. One possible option may involve the

calculation of emissions for pollutants not reported under Part 75 or Part 96 (e.g., PM10, PM2.5) by

applying emission factor ratios to the highly temporally-allocated emission estimates available for other

pollutants such as NOx and SO2.

To avoid duplication of effort, the EPA envisions that these emissions data will either be: 

(1) transferred into EPA’s central emissions data base after submittal by the source; or (2) if a State

prefers, the data can be made available to States for incorporation into their emissions inventory, which

ultimately will be entered into EPA’s NET data base.

4.8 SUMMARY DATA REPORTING

In addition to the detailed emissions data submitted in electronic form, the EPA recommends that

general summaries of the emissions inventory data be compiled and submitted by States. EPA

Headquarters and EPA Regional Offices will use these summaries for easy and efficient comparison with

other States’ inventories, and as a check for approximate and valid ranges of emissions. Examples of

statewide emissions summaries are presented in Tables 4.8-1 and 4.8-2. States may also want to consider

summarizing pollutant emissions by county.

Table 4.8-1. Statewide Ozone Precursor Emissions by Source Sector

Source Type

VOC Emissions CO Emissions NOx Emissions

tons/yr lbs/day tons/yr lbs/day tons/yr lbs/day

Point Sources

Area Sources

Onroad Mobile Sources

Nonroad Mobile Sources

Biogenic Sources

TOTAL EMISSIONS
37

Table 4.8-2. Statewide PM2.5 and Precursor Emissions by Source Sector

Source Type

PM2.5

Emissions

VOC

Emissions

NOx

Emissions

SO2

Emissions

NH3

Emissions

tons/yr tons/yr tons/yr tons/yr tons/yr

Point Sources

Area Sources

Onroad Mobile Sources

Nonroad Mobile Sources

Biogenic Sources

TOTAL EMISSIONS
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39

SECTION 5.0

EMISSION INVENTORY DEVELOPMENT

5.1 AVAILABLE GUIDANCE

EPA has developed numerous guidance documents to assist State/local agencies in developing

emissions inventories for various pollutants. These include the EIIP guidance documents, AP-42,15 and

older documents such as Procedures for the Preparation of Emission Inventories for Carbon Monoxide

and Precursors of Ozone, Volume I.

16 These documents can be accessed using EPA’s CHIEF web site at

http://www.epa.gov/ttn/chief/. The EIIP guidance documents are EPA’s most recent emission inventory

development guidance and should be the primary source of guidance for State/local agencies. In

addition, emission inventory software is available through EPA’s State Emissions Inventory Software

Clearinghouse found at the following address: http//www.epa.gov/ttn/airs/afs/reeng/clearhse.html.

For PM, EFIG will be developing a “getting started” web page in 1999. This web page, titled

“PM2.5 Emission Inventory Resource Center,” will be active by summer 1999 and will be available at 

http://www.epa.gov/ttn/chief/eiip/pm2.5inventory/. While EIIP is currently developing relevant guidance

material, the “getting started” web site will be prepared and available before these additional materials.

EPA is also evaluating its current projections guidance, Procedures for Preparing Emissions

Projections,

17 to determine how it should be updated/revised to reflect the requirements of the new

NAAQS, regional haze, and other programs. State/local agencies should refer to the existing projections

guidance, until new guidance is issued by EPA.

5.2 NATIONAL EMISSION TRENDS INVENTORY

EPA develops the NET inventory every year and will provide it to the States. The NET contains

statewide emission estimates for all of the pollutants and pollutant precursors required by this guidance. 

The NET is comprehensive and includes emission estimates for point sources, area sources, mobile

sources, and biogenic sources. EPA believes that some State and local agencies will find the NET to be a

useful tool in preparing their emission inventories required by this guidance. If States choose to use the

NET in their inventory preparation, EPA would suggest the following as a means of prioritizing their

inventory efforts and resources:

• Point Sources - this should be the States’ main point of emphasis. The NET point source data

are best for utility emissions since a national data base is available from the Department of

Energy.

• Area Sources - States should review their area source emission estimates in the NET. The

State may want to concentrate their efforts on the large area source categories. In general, the

greatest opportunity for improving the NET area source estimates is for the State or local

agency to develop locally specific activity data.

• Mobile Sources - if State or local agencies choose to use the NET onroad emission estimates as

a starting point, improvements in the estimates can be made by providing locally specific
40

inputs to the MOBILE model and more precise estimates of VMT. Improvements to the

nonroad estimates can best be made by using the EPA NONROAD model when it becomes

available.

• Biogenic Sources - The NET biogenic estimates are believed to be reliable. However, if State

or local agencies want to improve these estimates, locally specific land use/land cover data can

be obtained.

5.3 POINT SOURCES

Volume II of the EIIP guidance documents includes major chapters that address various combustion,

manufacturing, and production activities that are point sources.18 Information in these chapters should be

used to estimate ozone and PM2.5 precursor emissions where they address the source categories of

interest. The EIIP point source chapters within Volume II at various States of production are as follows:

C Chapter 2: Preferred and Alternative Methods for Estimating Air Emissions from Boilers

C Chapter 3: Preferred and Alternative Methods for Estimating Air Emissions from Hot-Mix

Asphalt Plants

C Chapter 4: Preferred and Alternative Methods for Estimating Fugitive Air Emissions from

Equipment Leaks

C Chapter 5: Preferred and Alternative Methods for Estimating Air Emissions from

Wastewater Collection and Treatment

C Chapter 6: Preferred and Alternative Methods for Estimating Air Emissions from

Semiconductor Manufacturing Facilities

C Chapter 7: Preferred and Alternative Methods for Estimating Air Emissions from Surface

Coating Operations

C Chapter 8: Preferred and Alternative Methods for Estimating Air Emissions from Paint and

Ink Manufacturing Facilities

C Chapter 9: Preferred and Alternative Methods for Estimating Air Emissions from Metal

Production Facilities

C Chapter 10: Preferred and Alternative Methods for Estimating Air Emissions from Oil and

Gas Field Production and Processes

C Chapter 11: Preferred and Alternative Methods for Estimating Air Emissions from Plastic

Products Manufacturing

Each industry- or source-specific document contains a brief description; identification of emission points;

an overview of methods available for estimating emissions; example calculations for each technique

presented; a brief discussion on quality assurance and quality control; and the SCCs needed for entry of

the data into a data base management system. The SCCs included in each volume apply to the process

emission points, in-process fuel use, storage tank emissions, fugitive emissions, and control device fuel
41

(if applicable). More details on PM emission inventories will be available in a “getting started” web site

on PM, available in the summer of 1999.

Table 5.3-1 lists potential point source categories. This table is presented as a guide to aid

State/local agencies in focusing their point source emission inventory efforts, and is based on an analysis

of EPA’s NET data base. The table shows where in EPA’s data base significant point source emissions

occur. The H (high), M (medium), and L (low) designations indicate the level of significance of a source

category’s emissions to the overall emissions of that pollutant. A T indicates that emissions of the

pollutant may occur from that category but are not considered significant. A blank cell indicates that no

emissions of the pollutant were recorded in EPA’s NET data base for that source category. Note that

local priorities for inventory development may vary depending on the nature of sources in the area. 

State/local agencies should also be aware that some of these source categories may have both point and

area source components, and that they should be careful to avoid double-counting of emissions.

5.4 AREA SOURCES

Area sources are generally described as those sources that are too small, numerous, or difficult to be

inventoried individually. Potential area sources of emissions are given in Table 5.4-1 and potential

crustal (dust) sources of emissions are given in Table 5.4-2. These tables are presented as guides to assist

State/local agencies in focusing their area source emission inventory efforts. The tables are based on an

analysis of EPA’s NET data base and show where in the data base significant area source emissions

occur. As with Table 5.3-1, the H (high), M (medium), and L (low) designations indicate the level of

significance of a source category’s emissions to the overall emissions of that pollutant. A T indicates

that emissions of the pollutant may occur from that category but are not considered significant. A blank

cell indicates that no emissions of the pollutant were recorded in EPA’s NET data base for that source

category. Note that local priorities for inventory development may vary depending on the nature of

sources in the area. State/local agencies should also be aware that some of these source categories may

have both point and area source components, and that they should be careful to avoid double-counting of

emissions.

The EIIP Area Source Committee has issued preferred and alternate emission estimation methods

documents under EIIP Volume III for the following categories:19

C Chapter 2: Residential Wood Combustion

C Chapter 3 Architectural Surface Coating

C Chapter 4: Dry Cleaning

C Chapter 5: Consumer and Commercial Solvent Use

C Chapter 6: Solvent Cleaning

C Chapter 7: Graphic Arts

C Chapter 8: Industrial Surface Coating

C Chapter 9: Pesticides - Agricultural and Nonagricultural
42

Table 5.3-1. Point Sources of Emissions

CATEGORY SO2 PM NH3* VOC NOx CO

Fuel Combustion - Electric Utility

Coal H H T L H L

Gas L T L L M L

Internal Combustion L M T L M L

Oil M L L L L L

Other T T T T T

Fuel Combustion - Industrial

Coal H M T L M L

Gas H M L M M L

Internal Combustion L M T M H L

Oil M M L L M L

Other L H T L L L

Fuel Combustion - Other

Commercial/Institutional Coal M L T T L L

Commercial/Institutional Gas L L L L L

Commercial/Institutional Oil L L L L L

Residential Wood T T T T T

Residential Other T T T T T

Miscellaneous Fuel Combustion except Residential L L L L L

Chemical and Allied Products Manufacturing

Agricultural Chemicals L L M L L L

Inorganic Chemicals M L L L L

Organic Chemicals L M M L L

Paints, Varnishes, Lacquers, Enamels T T L T T

Pharmaceuticals T T L T T

Polymers and Resins T L M L L

Other Chemicals L M M L M

Metals Processing

Ferrous Metals M H L L L M

Nonferrous Metals M M T L L L

Metals Processing NEC L M T L L L

Petroleum and Related Industries

Asphalt Manufacturing L L L L L

Oil and Gas Production L T T M L L

Petroleum Refineries and Related Industries M M L M L L

Other Industrial Processes

Agriculture, Food, and Kindred Products L M L M L L

Construction T

Electronic Equipment T T L T L

Machinery Products T L L L T

Mineral Products M H T L M L

Rubber and Miscellaneous Plastic Products T L M T T
Table 5.3-1 (continued)

CATEGORY SO2 PM NH3* VOC NOx CO

43

Other Industrial Processes (continued)

Textiles, Leather, and Apparel Products

T T L T T

Transportation Equipment T T L T T

Wood, Pulp and Paper, and Publishing Products M H M L L

Miscellaneous Industrial Processes L T L L L

Solvent Utilization

Degreasing T T L T T

Dry Cleaning T T L T T

Graphic Arts T T M T T

Other Industrial L L

Surface Coating L H L

Storage and Transport

Bulk Materials Storage T M T T L

Bulk Materials Transport T

Storage and Transport (continued)

Bulk Terminals and Plants T T M T L

Inorganic Chemical Storage T T T T T

Inorganic Chemical Transport T T T

Organic Chemical Storage T T L L L

Organic Chemical Transport T T L T T

Petroleum and Petroleum Product Storage T T M T L

Petroleum and Petroleum Product Transport T T M T T

Service Stations: Stage I L

Service Stations: Stage II T T L T T

Waste Disposal and Recycling

Incineration L M L L L

Industrial Waste Water T T L T T

Landfills T T L T L

POTWs T T L T T

TSDFs T L T T

Other T T L T T

Miscellaneous

Cooling Towers L L T T

Health Services T

* The emissions from all NH3 source categories need to be better characterized because of their role in the formation

of secondary particles.

Note: The H (high), M (medium), and L (low) designations indicate the level of significance of a source category’s

emissions to the overall emissions of that pollutant.

A T indicates that emissions of that pollutant may occur from that source category, but they are not

considered significant.

A blank cell indicates that no emissions of that pollutant are emitted from that source category based on the

data in EPA’s NET inventory.
44

Table 5.4-1. Area Sources of Emissions

CATEGORY SO2 PM NH3* VOC NOx CO

Fuel Combustion - Electric Utility

Internal Combustion T L L

Fuel Combustion - Industrial

Coal H L L L L

Gas L L L L M L

Internal Combustion T T L L L

Oil H L L L L L

Other L L L L L

Fuel Combustion - Other

Commercial/Institutional Coal L L T L L

Commercial/Institutional Gas L L L L M L

Commercial/Institutional Oil M L L L L L

Residential Wood L H H L M

Residential Other M M L L H L

Miscellaneous Fuel Combustion except Residential L H L L L

Chemical and Allied Product Manufacturing

Inorganic Chemicals T

Organic Chemicals L T

Pharmaceuticals L

Polymers and Resins M

Metals Processing

Ferrous Metals T T

Nonferrous Metals T T

Metals Processing NEC T T T T

Petroleum and Related Industries

Asphalt Manufacturing T T T

Oil and Gas Production L L M L L

Petroleum Refineries and Related Industries M

Other Industrial Processes

Agriculture, Food, and Kindred Products L M T T

Machinery Products T T

Mineral Products T T T L T

Rubber and Miscellaneous Plastic Products T L

Wood, Pulp and Paper, and Publishing Products L T T T

Miscellaneous Industrial Processes L M L L L T

Solvent Utilization

Degreasing H

Dry Cleaning M

Graphic Arts M

Nonindustrial H T T

Other Industrial L
Table 5.4-1 (continued)

CATEGORY SO2 PM NH3* VOC NOx CO

45

Solvent Utilization (continued)

Surface Coating H T T

Solvent Utilization NEC

Storage and Transport

Bulk Materials Storage T

Bulk Terminals and Plants M

Organic Chemical Storage L

Petroleum and Petroleum Product Storage L T

Petroleum and Petroleum Product Transport L

Service Stations: Breathing and Emptying L

Service Stations: Stage I H

Service Stations: Stage II H

Waste Disposal and Recycling

Incineration L M L L L

Industrial Waste Water L

Landfills L T T

Open Burning L H M L L

POTWs M L

TSDFs L T T

Other L

Miscellaneous

Agriculture and Forestry L H M

Catastrophic/Accidental Releases L

Health Services T

Other Combustion (Structure Fires, Forest Fires, Slash

Burning, Prescribed Burning, Managed Burning)

L H H M H

* The emissions from all NH3 source categories need to be better characterized because of their role in the formation

of secondary particles.

Note: The H (high), M (medium), and L (low) designations indicate the level of significance of a source category’s

emissions to the overall emissions of that pollutant.

A T indicates that emission of that pollutant may occur from that source category, but they are not

considered significant.

A blank cell indicates that no emissions of that pollutant are emitted from that source category based on the

data in EPA’s NET inventory.
46

Table 5.4-2. Crustal Sources of Emissions

CATEGORY VOC NOx SO2 CO PM NH3

Natural Sources

Geogenic, Wind Erosion M

Miscellaneous

Agricultural Crops (Tillage) M

Construction M

Paved Roads M

Unpaved Roads H

Other Fugitive Dust (e.g., Mining and Quarrying) M

Note: The impact of crustal sources on PM2.5 ambient concentrations is much lower than would be suggested by

their estimated emissions (relative to other directly emitted PM2.5).

The H (high) and M (medium) designations indicate the level of significance of a source category’s

emissions to the overall emissions of that pollutant.

C Chapter 11: Gasoline Marketing

C Chapter 12: Marine Vessel Loading, Ballasting, and Transfer

C Chapter 13: Autobody Refinishing (currently available as a draft; to be revised in 1999)

C Chapter 14: Traffic Paints

C Chapter 15: Municipal Landfills

C Chapter 16: Open Burning (available as a draft)

C Chapter 17: Asphalt Paving

The EIIP Volume III, Chapter 1 document lists potential activity data sources by category. 

Procedures for the Preparation of Emission Inventories for Carbon Monoxide and Precursors of Ozone,

Volume I (Reference 16) also gives detailed guidance for estimating ozone precursor emissions from area

sources. Agencies should review the EIIP documents carefully for information on the types and sources

of data needed to develop emissions estimates for each source category. Table 5.4-1 lists the area source

categories that EPA believes are significant sources for the pollutants in the table.

5.5 MOBILE SOURCES

Mobile sources consist of both highway vehicles (cars and trucks) and nonroad mobile sources (e.g.,

airplanes, motorboats, farm equipment, etc.). Table 5.5-1 lists mobile source categories that EPA

believes are significant sources of emissions. This table can be used as a guide to assist State/local

agencies in focusing their mobile source emission inventory efforts, and is based on an analysis of EPA’s
47

NET data base. The H (high), M (medium), and L (low) designations indicate the level of significance of

a source category’s emissions to the overall emissions of that pollutant. A T indicates that emissions of

the pollutant may occur from that category but are not considered significant. A blank cell indicates that

no emissions of the pollutant were recorded in EPA’s NET data base for that source category. Note that

local priorities for inventory development may vary depending on the nature of sources in the area.

Table 5.5-1. Mobile Sources of Emissions

CATEGORY SO2 PM NH3* VOC NOx CO

Highway Vehicles

Light-Duty Gas Vehicles and Motorcycles M M M H H H

Light-Duty Gas Trucks M M M H H H

Heavy-Duty Gas Vehicles L L L H M M

Diesels M H L H H M

Off-Highway

Nonroad Gasoline L M ** H M H

Nonroad Diesel M H ** H H M

Aircraft L M ** M M M

Marine Vessels M M L L M L

Railroads M M L L H L

* The emissions from all NH3 source categories need to be better characterized because of their role in the formation

of secondary particles.

** While NH3 emissions may occur from these source categories, at this time EPA does not have the capability to

make an estimate of these emissions.

Note: The H (high), M (medium), and L (low) designations indicate the level of significance of a source category’s

emissions to the overall emissions of that pollutant. 

The following sections discuss the models and data sources for onroad mobile sources and nonroad

mobile sources, respectively.

5.5.1 Onroad Mobile Sources

Onroad mobile source populations are typically characterized according to the following vehicle

categories:

• Light-duty gasoline vehicles (LDGV);

• Light-duty gasoline trucks I (LDGT1);

• Light-duty gasoline trucks II (LDGT2);

• Heavy-duty gasoline vehicles (HDGV);

• Light-duty diesel vehicles (LDDV);

• Light-duty diesel trucks (LDDT);

• Heavy-duty diesel vehicles (HDDV); and

• Motorcycles.
48

Ozone precursor emissions for onroad sources are estimated using the MOBILE emission factor

model developed by EPA’s Office of Mobile Sources (OMS). In general this model generates emission

factors to apply to VMT estimates for each of the above vehicle categories. PART5 is an emission factor

model developed by OMS to estimate onroad emissions for PM10, PM2.5, and SO2. The use of VMT

activity data and both of these onroad mobile emission factor models are discussed further below.

VMT Activity Data

Each State’s highway or transportation agency provides annual data to the FHWA’s Highway

Performance Monitoring System (HPMS). The FHWA uses the data provided by the States to report the

condition of the nations’ highways to Congress. The HPMS compiles VMT at the State level for rural,

small urban, and individual urbanized areas by 12 different road types, and six distinct vehicle types. 

Updated guidance for converting HPMS VMT data to the vehicle classes contained within MOBILE5a is

provided by the EIIP in section 2.0 of the report, Use of Locality Specific Transportation Data for the

Development of Mobile Source Emission Inventories.

20 This report also contains sections addressing

improvements to travel demand model outputs. In 1993, FHWA issued a letter indicating that all urban

areas greater than 50,000 population should have individual HPMS sample panels representative of travel

within those areas.

EPA guidance, Procedures for Emission Inventory Preparation - Volume IV: Mobile Sources,

21

provides a very detailed discussion of HPMS and travel demand models (TDM). Pages 62 to 94 of this

document discuss how to use HPMS data and the more limited cases when TDMs may be used. In

general, HPMS is the preferred method for estimating historical VMT and TDMs are the preferred

method for allocating VMT to the county level and road classes and for calculating growth factors for

future years. The guiding principal of this policy is that the State should provide the same estimate of

travel to the EPA as it uses internally and provides to the FHWA. 

In the unusual circumstance that the State believes that an alternative to HPMS provides a better

estimate of historical VMT, the State should write a letter for inclusion in the SIP to that effect to both

EPA and the FHWA signed by the appropriate authorities, normally the State Department of

Transportation, local metropolitan planning organizations, and the State environmental agency

responsible for submitting the SIP. The letter should document why the State believes its proposed

alternative is superior to HPMS for purposes of estimating historical VMT. The letter should also

address the following three issues:

C How the State proposes to create a historical record, at least back to 1990, so that the SIP

planning elements are internally consistent, in the event that the State proposes to substitute its

alternative approach when satisfying the requirements associated with the 1-hour standard;

C How the State plans to assure that the statistical design and funding level of the alternative

program are stable for an extended period of time to assure that the proposed methodology will

continue to be available for conformity and other analyses; and

C The frequency at which the State plans to update its historical VMT estimates to accommodate

the reporting requirements of the various SIP elements and transportation planning processes.

The approval of the use of any alternative to HPMS will be made by the EPA Regional Office. 

States are encouraged to identify in their IPP their proposed method for determining historical VMT, for

allocating VMT to the county level and road classes, and for calculating growth factors for future years.
49

MOBILE5 Model

Onroad mobile source VOC, NOx, and CO emission factors are calculated using the MOBILE5a

model. MOBILE5a generates exhaust and evaporative emission factors in grams per mile. These factors

are then applied to the VMT activity estimates, discussed above.

Although MOBILE5b was released as an interim update to the MOBILE5a model during August

1997, States are not required to use MOBILE5b. States can continue to use either MOBILE5a or

MOBILE5b until the time that MOBILE6 becomes available. This applies to SIP inventories and

modeling, conformity determinations, and the quantification of emission reductions for open market

trading purposes. The MOBILE5a and MOBILE5b models, user’s guides, and associated documentation

are all available at EPA’s OMS web page at http://www.epa.gov/oms/m5.htm. Guidance concerning the

use of MOBILE6 versus MOBILE5 for preparing the 1999 and projected emission inventories for ozone

and PM SIPs will be issued by OMS after it is determined how all final updates to MOBILE6 emission

factors will affect pollutant emissions inventories. States also have the option of using their own mobile

source emission factor model if they have coordinated its use with OMS.

Although the MOBILE6 model is not yet available, many of the optional local MOBILE5 inputs are

also expected to be used in MOBILE6. To this end, States should plan for compiling a 1999 onroad

inventory using MOBILE6 by developing the best possible set of local inputs for variables such as

registration distribution, I/M program inputs, defining the geographic and temporal applicability of other

control programs (e.g., in which counties and what months is oxygenated fuel used), mileage

accumulation rates, and determining what temperature data will be used for each of the different types of

inventories. It is also recommended that States have methods in place for 1999 for determining fuel

characteristics throughout the State and according to season, including fuel Reid vapor pressure (RVP),

sulfur level, oxygen content, and the makeup of reformulated gasoline. For all types of onroad vehicle

emission modeling (e.g., ozone modeling, 3-year cycle inventories, transportation conformity), having an

accurate, local registration distribution is important to determining accurate emission inventories. 

Because wide differences between actual model year fleet distributions and default distributions in the

MOBILE model have been observed, States are encouraged to use county-specific motor vehicle model

year distributions obtained from their State motor vehicles office. For the 3-year cycle and modeling

inventories, having accurate representations of control programs in place during the modeled time

periods is crucial, particularly for I/M program modeling. For example, if a set of phase-in cutpoints are

being used in an I/M program in 1999, it is important to model that set of cutpoints rather than the final

set of emission cutpoints. On the other hand, for attainment demonstration or projection inventories,

where allowable emissions are calculated, the final planned I/M program may be modeled. Modeling

accurate speeds by roadway type, while important for all inventory types, is particularly important in

transportation conformity modeling. In this case, it is necessary to capture the changes in average speeds

by roadway type or roadway link due to the presence or absence of particular transportation-related

programs. 

Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources (Reference 21)

provides recommendations for determining appropriate values for MOBILE model inputs such as

ambient temperature and speed. EPA encourages the use of non-default inputs by users of the MOBILE

model, but requests that States discuss the selection of any non-default values in documentation

submitted with the onroad mobile source emission inventory.

Several months before the final release of MOBILE6, OMS will make available a working beta

version of MOBILE6 to obtain user feedback on program operation. To allow stakeholder and peer

review of proposed model changes, OMS has posted background reports to describe the various inputs
50

and assumptions used within MOBILE6, available at the following address:

http://www.epa.gov/oms/m6.htm. Examples of changes that are likely to be implemented for the final

MOBILE6 model include:

• incorporate effects of non-FTP, or “off-cycle,” driving patterns on emissions;

• update heavy-duty engine emission conversion factors, including brake specific fuel

consumption (BSFC), fuel economy, non-engine fuel economy improvements, and fuel

densities;

• expand emission factor calculations for four distinct subcategories of HDDVs similar to

PART5 model;

• update evaporative emissions to incorporate real-time diurnal emissions estimates, as well as

improving hot soak, resting loss, and running loss emissions; 

• evaluate effects of fuel characteristics on emissions, including in-use sulfur content and

oxygenates; and

• update default fleet characterization data (registration distributions and average annual mileage

accumulation rates by vehicle type.).

The MOBILE6 web page also lists public workshops being held on MOBILE6.

PART5 Model

PART5 is a model that estimates in-use particulate air pollutant emissions (i.e., PM10, PM2.5, and

SO2) for gasoline and diesel-fueled vehicles and gives emission factors in grams per mile. The model

contains emission factors corresponding to exhaust particulate emissions, exhaust particulate

components, brake wear, tire wear, and reentrained road dust. PART5 contains default values for the

majority of the emission factor calculations, but also allows for user-supplied data for certain inputs. For

the vehicle registration distribution, PART5 uses the same vehicle classifications as the MOBILE model,

except that the MOBILE HDDV class is divided into five subclasses in PART5 (see Table 5.5-2). One

potential method for developing the vehicle distribution for PART5 may be to use the MOBILE model

vehicle class distribution, and apportion the value for MOBILE HDDV among the five PART5 HDDV

subclasses using HDDV sales data, survival rates, and diesel market shares. As indicated in section

5.5.2, MOBILE6 and PART5 vehicle classes may be identical in the future.

Details concerning the inputs to be supplied to the PART5 program are included in the PART5

user’s guide. States can download electronic copies of the user’s guide, as well as the most recent

version of the PART5 model from the OMS web page at the following address: 

http://www.epa.gov/oms/part5.htm. OMS plans to update PART5 by issuing a PART6 model after

MOBILE6 is released. When updated, the PART6 vehicle classes are likely to be identical to vehicle

classes in MOBILE6. In addition, PART6 will reflect any available updated emission factor data

developed by OAQPS. For example, the AP-42 emission factor section for unpaved roads has been

revised, and this latest information will be incorporated into PART6.
51

Table 5.5-2. PART5 Vehicle Classes

Vehicle Class

FHWA

Class

Gross Vehicle

Weight (lbs)

LDGV light-duty gasoline vehicles

LDGT1 light-duty gasoline trucks, I 1 <6,000

LDGT2 light-duty gasoline trucks, II 2A 6,001-8,500

HDGV heavy-duty gasoline trucks 2B - 8B >8,500

MC motorcycles

LDDV light-duty diesel vehicles 1 <6,000

LDDT light-duty diesel trucks 2A 6,001-8,500

2BHDDV class 2B heavy-duty diesel vehicles 2B 8,501-10,000

LHDDV light heavy-duty diesel vehicles 3,4,5 10,001-19,500

MHDDV medium heavy-duty diesel vehicles 6,7,8A 19,501-33,000

HHDDV heavy heavy-duty diesel vehicles 8B 33,000+

BUSES buses

5.5.2 Nonroad Mobile Sources

The EPA’s OMS is developing a computer model, NONROAD, to directly estimate pollutant

emissions in tons for the following nonroad equipment categories: 

• Lawn and Garden

– residential

– commercial

• Construction and Mining

• Agricultural

• Industrial

• Airport Service

• Recreational Vehicles

• Logging

• Recreational Marine

• Light Commercial

• Railway Maintenance

Within these general categories are more specific types of equipment (e.g., 2-wheel tractors, balers,

and combines are examples of 10-digit SCCs within the broader 7-digit SCC defining agricultural

equipment). Because of the variations in hours of use, horsepower, and load factors corresponding to

engines in various applications, these distinctions are necessary. These applications can be further

classified according to fuel and engine type [diesel, gasoline 2-stroke, gasoline 4-stroke, compressed

natural gas (CNG), and liquid petroleum gas (LPG)].

The NONROAD model estimates emissions for six exhaust pollutants: hydrocarbons (HCs), NOx,

CO, PM, SO2, and CO2. Hydrocarbons can be reported as total hydrocarbons (THC), TOG, nonmethane

organic gases (NMOG), NMHC, or VOC. Particulate matter can be reported as total PM, PM10 (which is

equivalent to total PM), or PM2.5. The model also estimates non-exhaust HC emissions, including

crankcase, diurnal, and refueling emissions. The model allows the user to report total HC emissions,
52

which account for both exhaust and relevant non-exhaust components (depending on the engine type and

pollutant). At the present time, reliable nonroad NH3 emission factors are not available, and the

NONROAD model does not generate nonroad NH3 emissions. The EPA anticipates that NH3 emission

factors for nonroad may be available by 2002.

NONROAD allows the calculation of pollutant emissions at the national, State, and county level. 

The model can also estimate sub-county (i.e., nonattainment area) emissions if the necessary inputs to

perform this calculation are supplied by the user. By using estimates of annual activity for each

equipment type, annual emissions inventories can be calculated. Additional inventories can be calculated

on a seasonal (i.e., summer, fall, winter, spring), monthly, or daily (i.e., week or weekend day) basis by

allocating annual activity to these smaller time periods. Past year, present year, and future year

inventories (up to the year 2050) can be generated with this model.

The NONROAD model estimates emissions for each specific type of nonroad equipment by

multiplying the following input variables:

• Equipment population for a specified year, distributed by age, horsepower, fuel type, and

application;

• Average load factor expressed as average fraction of available power; 

• Activity in hours of use per year; and

• Emission factor, accounting for engine deterioration and any applicable new standards.

The emissions are then temporally and geographically distributed using appropriate allocation

factors.

States have the option of replacing default model values with more representative data if available. 

If a State makes changes to default model values such as local equipment populations, geographic

allocations, and local growth rates, States should submit the input files to EPA, as well as a description

and justification of why the defaults were changes. However, EPA does not recommend that

NONROAD users change values for certain model variables, including useful life and scrappage, activity

data (i.e., load factors and hours of use), and emission deterioration factors. This is largely because all of

these variables are related to and affect the overall engine scrappage function. If one of these variables

changes, other variables should be adjusted accordingly. The EIIP has published a report entitled,

Guidance for Estimating Lawn and Garden Activity Levels22 that discusses methods for improving

estimates of local lawn and garden equipment populations according to commercial and residential use.

The OMS has posted technical reports on their web site that describe the various default input

variables. Copies of these reports, as well as the most recent version of the NONROAD model

(including user’s guide) can be downloaded from the web site: http://www.epa.gov/oms/

nonrdmdl.htm#model. In addition, a CD-ROM copy of the model can be obtained from OMS by request.

Commercial Marine Vessels, Aircraft, and Locomotives

The first final version of the NONROAD model will not provide States with a tool for estimating

emissions for commercial marine, aircraft, and locomotives. For further guidance on developing

emission estimates for these nonroad categories, States are referred to EPA guidance, Procedures for

Emission Inventory Preparation, Volume IV: Mobile Sources. Emission factors will ultimately be
53

available in a revised version of Section II of the 5th edition of AP-42, Volume II. The completion date

for this new AP-42 section is uncertain, but when complete, the emission factors will be posted at the

following web site address: http://www.epa.gov/oms/ap42.htm. In the interim, those seeking updated

nonroad mobile source emission factor information should direct inquiries to Mr. Greg Janssen of EPA’s

OMS, at (734) 214-4285; e-mail: janssen.greg@epa.gov. Following is a discussion on the status of

preparing updated guidance for commercial marine, aircraft, and locomotive categories.

The OMS originally intended to incorporate a commercial marine module into the first version of

the NONROAD model. However, due to unexpected complications in developing input data and the

requisite computer code, OMS will discontinue work on the electronic commercial marine module for the

NONROAD model, and concentrate instead on written guidance. This guidance may provide “best

estimate” default emissions inventories for approximately 150 ocean, lake, and river ports, but may allow

for the use of more accurate, locally-specific emissions data if available to the user. The electronic

commercial marine module will be reconsidered for a subsequent update of the NONROAD model.

For aircraft, activity data in the form of landing and take-offs (LTO’s) can be obtained from the

Federal Aviation Administration (FAA). The Federal Aircraft Engine Emission Data Base (FAEED),

developed by the FAA and EPA, is a tool for calculating aircraft emissions. This data base is a

stand-alone application that allows a user to compute pollutant emissions produced by a specified fleet. 

However, users should be aware that emission factor data for newer engine models are not available in

this version of the FAEED. EPA’s OMS will continue to work with the FAA to potentially develop an

updated emissions estimation data base that reflects emissions data for all engine types, and may also

provide the necessary activity data. The FAEED is available at EPA’s OMS web site.

For locomotives (especially Class II and Class III line haul and yard operations), the majority of the

activity data are obtained by directly contacting individual railroads in the inventory area. Written

guidance for estimating locomotive emissions will be prepared by OMS after further investigating input

data availability.
54

5.6 BIOGENIC AND GEOGENIC SOURCES

Biogenic and geogenic sources contribute to pollutant emissions as indicated in Table 5.6-1.

Table 5.6-1. Natural Source Categories and Pollutants Emitted

Source

Pollutant

VOC NOx PM10 PM2.5

Biogenic

– Vegetation T

– Soil Microbial Activity T

Geogenic

– Oil and Gas Seeps T

– Wind Erosion T T

Other Natural

– Lightning T

– Stratospheric Injection* T

– Oceans* T

* NOx emissions from each of these sources contribute 2 percent or less of the total global NOx

budget, and will not be discussed further.

5.6.1 Biogenic Sources

Biogenic sources are a subset of natural emissions sources that may contribute significantly to an

emissions inventory. Vegetation (i.e., forests and agriculture) is the predominant biogenic source of

VOC and is typically the only source that is included in a biogenic VOC emissions inventory. Microbial

activity in the soil contributes to natural biogenic NOx emissions.

States are referred to the EIIP document, Volume V, Biogenic Sources Preferred Methods,

23 for a

detailed description of some of the biogenic source emissions that should be considered when preparing

an emissions inventory. One of the major constituents of biogenic emissions, isoprene, is highly

photoreactive. Because of this characteristic, inclusion of biogenic emissions is deemed essential for

photochemical air quality modeling for ozone. In addition, some biogenic VOC may ultimately

contribute to secondary particle formation, and would therefore be important with respect to a PM or

regional haze inventory. Computer models available for States to estimate speciated biogenic emissions

include the following:

• BEIS-2;

• The Personal Computer version of the BEIS-2.2 (PCBEIS-2.2); and

• Biogenic Model for Emissions (BIOME).

The BEIS-2 model and PCBEIS-2.2 can be used to estimate speciated VOC emissions from

vegetation, as well as NOx emissions from soils. BIOME can be used to estimate speciated VOC

emissions from vegetation. 
55

The BEIS-2 is a stand-alone processor that produces biogenic estimates for use with several existing

air quality models, including the Urban Airshed Model (UAM), Regional Oxidant Model (ROM) and

RADM. As such, the model is the preferred method for generating biogenic estimates required for air

quality modeling. The BEIS-2 model also estimates biogenic emissions from soil, which may be a

significant source of NOx emissions in rural areas. PCBEIS-2.2 output is typically used only for

inventory reporting purposes [and in some cases for Empirical Kinetic Modeling Approach (EKMA)

runs]. Other alternative (but less preferable) methods for estimating biogenic emissions are also

discussed in Volume V of the EIIP document.

Although States are encouraged to develop their own independent biogenic emission estimates, the

EPA will allow States to use EPA-generated BEIS-2 emission estimates as the basis for their SIP

planning and modeling inventories. States should note that biogenic emissions are required in a

projected year inventory. However, unless there are anticipated changes in land use or vegetation

patterns for the modeling area, it is appropriate to assume that biogenic emissions will remain the same

between the base year and projected year. It is expected that the output from BEIS-2, as well as any

updates to this emissions model, will be compatible as input to the planned regional air quality model,

MODELS3.

EPA is updating the BEIS-2 model and plans to release BEIS-3 in late 1999. BEIS-3 will be based

in part on data collected for the Ozark Isoprene Experiment, and is expected to generate lower emission

estimates than BEIS-2 for some areas due to adjustments in estimates of ground cover vegetation. In

addition, EPA recently updated PCBEIS-2.2 with the release BEIS-2.3. Further details on the status of

biogenic emissions modeling are available at EPA’s web page at

http://www.wpa.gov/asmdnerl/biogen.html.

5.6.2 Geogenic and Other Natural Sources

Geogenic emissions are primarily the result of oil or natural gas seeps and soil wind erosion. In

addition, lightning may also be a significant contributor to natural NOx emissions in an inventory area. 

Volcanoes and fumaroles (i.e., vapor or gas vents in a volcanic region) can be additional sources of

geogenic emissions.

As a source of ozone precursor emissions, geogenic sources are less significant than biogenic

sources. However, geogenic wind erosion can contribute substantially to PM emissions in an area. As

indicated in Section 4.5, EPA typically generates PM10 and PM2.5 emissions for wind erosion, and these

estimates are expected to be available for use by States in their SIP base year and 3-year cycle

inventories. At this time, the emission estimation methodology for wind erosion is being refined by EPA

to produce more representative PM estimates for this category.

States should also prepare an inventory of all other significant geogenic sources in the inventory

area. Methods for estimating VOC emissions from oil and gas seeps, as well as NOx emissions from

lightning, are described in the EIIP document, Volume V, Biogenic Sources Preferred Methods. For oil

and gas seeps, the preferred method is to develop a local emission factor based on the study of oil or gas

seeps in the inventory area. The document also describes an alternative method developed by the

California Air Resources Board (CARB)24 that includes simplifying assumptions for oil or gas seeps

whose specific flow rates and volatile fractions have not been studied and are not known. 

Lightning produces NO, which is oxidized to NO2 in the presence of ozone or in a photochemically

reactive atmosphere. Because lightning is not a direct source of NO2, accounting for this source category

is more important for air quality modeling purposes than for SIP inventory purposes. NO emissions from
56

lightning can be estimated by collecting activity data on the cloud-to-ground (CG) lightning flashes,

assuming a frequency of intra-cloud (IC) flashes based on the value for CG lightning flashes, and

applying appropriate emission factors (in molecules NO per flash) to these activity levels.
57

SECTION 6.0

QUALITY ASSURANCE/

DOCUMENTATION OF THE INVENTORY

6.1 QUALITY ASSURANCE

As part of the 8-hour ozone NAAQS, PM2.5 NAAQS, and regional haze rule, States will be required

to perform QA checks and procedures on their inventories. States can develop and select the QA

procedures they will perform, and should include the details of their QA program (including specific

procedures) in their IPPs.

The purpose of QA is to ensure the development of a complete, accurate, and consistent emission

inventory. A well-developed and well-implemented QA program fosters confidence in the inventory and

in any resulting regulatory and/or control program.

The overall QA program consists of two components: QC and external QA activities. Quality

control is a system of routine technical activities designed to measure and control the quality of the

inventory as it is being developed. The QC system provides routine and consistent checks and

documentation points in the inventory development process to verify data integrity, correctness, and

completeness; identifies and reduces errors and omissions; maximizes consistency within the inventory

preparation and documentation process; and facilitates internal and external inventory review processes. 

Quality control activities include technical reviews, accuracy checks, and the use of approved,

standardized procedures for emission calculations, and should be included in inventory development

planning, data collection and analysis, emission calculations, and reporting.

External QA activities include a planned system of review and audit procedures conducted by

personnel not actively involved in the inventory development process. The key concept in the QA

activities is an independent, objective review by a third party to assess the effectiveness of the internal

QC program and the quality of the inventory, and to reduce or eliminate any inherent bias in the

inventory process.

An effective QA program includes planning, numerous QC checks during the inventory development

process, and QA audits at strategic points in the process. EPA has developed several guidance

documents designed to assist State/local agencies in designing and implementing their QA programs. 

The EIIP Volume VI address QA issues, including the following:3

C Chapter 1: Introduction - The Value of QA/QC

C Chapter 2: Planning and Documentation

C Chapter 3: General QA/QC Methods

C Chapter 4: Evaluating the Uncertainty of Emission Estimates

C Chapter 5: Model QA Plan
58

These documents can be downloaded from EIIP’s web site at http://www.epa.gov/oar/oaqps/eiip/. 

Additional EPA QA guidance is found in the following documents:

C Guidance for the Preparation of Quality Assurance Plans for O3/CO SIP Emission

Inventories25

C Quality Assurance Program for Post-1987 Ozone and Carbon Monoxide State Implementation

Plan Emission Inventories26

C Quality Review Guidelines for 1990 Base Year Emission Inventories27

Section 4.0 of this document provides State and local agencies with information on how to submit

their data to EPA. Once EPA receives these data, the data will undergo an interim processing step as

EPA performs automated QA checks on the submitted data. The data that pass these checks will be

entered into the NET. EPA will inform a State or local agency when data it has submitted have not

passed the automated checks. State and local agencies will be given the opportunity to correct and

resubmit these data to EPA.

To assist State and local agencies in the QA process, EPA will make available to these agencies the 

QA checks that EPA will run on their submitted data. States may decide to pre-screen their data using

these QA checks prior to submitting their data to EPA. 

6.2 DOCUMENTATION OF THE INVENTORY

The written presentation to support an emissions inventory submittal for the ozone and PM2.5

NAAQS, as well as the regional haze rule, should contain documentation that is sufficiently detailed for

EPA to evaluate how the emission inventory was prepared. The EPA requires that States prepare

adequate documentation; the level of detail required in the documentation should be agreed upon with the

Regional Office and specified in a State’s Inventory Preparation Plan. This section refers to prior

guidance issued by EPA to assist in developing appropriate documentation for emission inventories.

Written documentation of calculation, assumptions, and all other activities associated with

developing the emission estimates is a key element of the QA program. Documentation of the work that

is actually performed during inventory development includes documentation of calculations (hand

calculations, spreadsheets, and data bases), documentation of the QA program implementation, and

documentation of the results (the inventory report). Examples of topics requiring good documentation in

the inventory development process include:

C point/area source cutoffs to demonstrate that double-counting of emissions does not occur

C point source information on survey mailout procedures, tracking and logging of returned

surveys, and verification procedures for source test data

C adjustments made to source test data to represent longer periods of time, seasonal influences,

etc.

C data obtained from permit and compliance files

C adjustments made for applicable rules, including control efficiency, RP, and RE
59

C information obtained on emission factors and activity data (primarily for area sources)

C data references

C adjustments made for local conditions and assumptions made to adjust for scaling up emissions

to account for nonreported sources

C VMT, traffic speeds, miles of roadway for each roadway class, hot- and cold-start percentages,

vehicle age distribution, etc., for the mobile source documentation

Chapter 2 of the EIIP’s Volume VI, titled Planning and Documentation provides valuable, detailed

guidance on documenting inventory components.

For a complete example of how an inventory should be compiled and documented, States are

referred to the document, Example Documentation Report for 1990 Base Year Ozone and Carbon

Monoxide State Implementation Plan Emission Inventories.

28 This document provides States with a list

of elements deemed to be essential for documenting an emissions inventory in written form. An outline

for the organization and content of a State’s inventory report is presented in Table 6.2-1. This table

references another document entitled Example Emissions Inventory Documentation for Post-1987 Ozone

State Implementation Plans.

29 This document also addresses inventory documentation requirements, but

was not explicitly designed to address 1990 inventories. However, much of the guidance provided for

post-1987 inventories would still be applicable for inventories developed for the new ozone and PM2.5

NAAQS, and regional haze rule. In addition, although these documents focus on ozone precursor and

CO emission inventories, the principles defined in these reports would also apply to PM and regional

haze inventories.

Another guidance document, Quality Review Guidelines for 1990 Base Year Emission Inventories

presents review guidelines for State and local agencies to use as a self-check prior to submitting the

inventories they prepare to EPA. This document presents checklists for States to use to verify that

effective QC and QA practices are applied to an inventory during the process of developing and

documenting an emissions inventory. EPA does not intend to use this document to determine whether or

not to approve a State’s inventory submittal. As stated in Section 2.5, Inventory Approval, the inventory

approval process will be negotiated between the EPA Regional Office and the State. Rather, EPA

believes that the checklists represent sound practice and will be a useful tool in the development of a

State’s inventory.
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Table 6.2-1. Outline for Format/Contents for SIP Emission Inventory Reports

I. Cover and Title Page

A. Title (geographic area, type of inventories, pollutants, base year)

B. Responsible agency

C. Report date (date completed/distributed)

D. Preparer (if different from responsible agency - e.g., contractor)

II. Table of Contents

A. Contents

B. Tables

C. Figures

III. Introduction

A. Reason for report being prepared, purpose

B. Geographic area covered, base year, type of inventory (ozone SIP, PM SIP, Regional

Haze), pollutants included (VOC, NOx, CO, SO2, PM10, PM2.5, NH3)

C. Brief discussion of contents of report

D. Discussion of automated data systems used

E. Major problems, deficiencies, portions of inventory not included

F. List of primary guidance documents and references used (EPA guidance documents,

EIIP documents, AP-42, etc.)

G. List of contacts for each distinct portion of the inventory

IV. Summary

A. Emissions (annual and seasonal) of each pollutant by major category

B. See example tables and graphics given in Example Emissions Inventory

Documentation for Post-1987 Ozone State Implementation Plans (EPA-450/4-89-

018)

V. Documentation of Emissions Methods/Data Estimates

A. Stationary Point Source Emissions

1. discussions of procedures and methodologies

2. example surveys/questionnaires

3. list of plants by primary product and total emissions

4. point source emissions summary
Table 6.2-1 (continued)

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B. Stationary Area Source Emissions

1. discussion of procedures and methodologies

2. list of source categories and emissions

3. calculations and discussion for each source category

4. area source emissions summary

C. Mobile Source Emissions

1. Nonroad Mobile Sources

a. same information as for stationary area sources

2. Onroad Vehicles

a. mobile model inputs and outputs

b. VMT estimates

c. documentation (can put all or part in Appendices)

d. mobile source emissions summary

e. discussion of procedures and methodologies

VI. Quality Assurance/Quality Control (QA/QC)

A. QA/QC plan - discussion of QA/QC methodologies used

B. Results

C. QA procedures can also be discussed in individual source category sections
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63

SECTION 7.0

REFERENCES

1. Implementation Guidance for the Revised Ozone and Particulate Matter (PM) National Ambient Air

Quality Standards (NAAQS) and the Regional Haze Program, U.S. Environmental Protection

Agency, Research Triangle Park, NC, 1998.

2. Introduction to the Emission Inventory Improvement Program, Volume I, U.S. Environmental

Protection Agency, Research Triangle Park, NC, July 1997.

3. Quality Assurance/Quality Control, Volume VI, EIIP, U.S. Environmental Protection Agency,

Research Triangle Park, NC, 1997.

4. Guidelines for Estimating and Applying Rule Effectiveness for Ozone/CO State Implementation Plan

Base Year Inventories, EPA-452/R-92-010, U.S. Environmental Protection Agency, Research

Triangle Park, NC, November 1992.

5. The 1985 NAPAP Emissions Inventory: Development of Temporal Allocation Factors, EPA-600/7-

89-010d, U.S. Environmental Protection Agency, Research Triangle Park, NC, April 1990.

6. ARC/INFO User’s Guide: Map Projections and Coordinate Management, Concepts and

Procedures, and ARC/INFO, Command References: ARCTM Command References, Commands J-Z

(PROJECT).

7. Russell, A.G., R. McNider, J. Moody, and J.G. Wilkerson. Emissions Modeling Protocol: 

Meteorological, Emissions and Air Quality Modeling for an Integrated Assessment Framework in

Support of the Southern Appalachian Mountains Initiative, prepared for the Southern Appalachian

Mountains Initiative (SAMI), Asheville, NC, June 1998.

8. Federal Highway Planning Network version 2.1, U.S. Department of Transportation, Bureau of

Transportation Statistics, Federal Highway Administration, Washington, DC, 1998. (Web site

address: http://www.bts.gov/gis/ntatlas/networks.html)

9. Kinnee, E., C. D. Geron, T. Pierce, and T. Birth, Creation of a land use inventory for estimating

biogenic ozone precursor emission in the United States, submitted for publication in Ecological

Applications, 1995.

10. TIGER, U.S. Department of Commerce, Bureau of the Census, Washington, DC, 1998. (Web site

address: http://www.census.gov/geo/www/tiger/)

11. MABLE/Geocorr V2.5: The Geographic Correspondence Engine, U.S. Department of Commerce,

Bureau of the Census, Washington, DC, 1988. (Web site address: http://www.census.gov/plue/)

12. Gridded Population Data of the World, Consortium for International Earth Sciences Network, 1998. 

(Web site address: http://www.ciesin.org/datasets/gpw/globaldem.doc.html)
64

13. National Railway Network 1:100,000, U.S. Department of Transportation, Bureau of Transportation

Statistics, Federal Highway Administration, Washington, DC, 1998. (Web site address: 

http://www.bts.gov/gis/ntatlas/networks.html)

14. Wilkinson, J. G., C. F. Loomis, D. E. McNally, R. A. Emigh, T. W. Tesche. Technical Formulation

Document: SARMAP/LMOS Emissions Modeling System (EMS-95), AG-90/TS26 and AG-90/TS27,

prepared for the Lake Michigan Air Directors Consortium, Des Plaines, IL and The Valley Air

Pollution Study Agency, Technical Support Division, Sacramento, CA, prepared by Alpine

Geophysics, Pittsburgh, PA, 1994.

15. Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition and Supplements, U.S.

Environmental Protection Agency, Research Triangle Park, NC, 1997.

16. Procedures for the Preparation of Emission Inventories for Carbon Monoxide and Precursors of

Ozone, Volume I, EPA-450/4-91-016, U.S. Environmental Protection Agency, Research Triangle

Park, NC, May 1991.

17. Procedures for Preparing Emissions Projections, EPA-450/4-91-019, U.S. Environmental

Protection Agency, Research Triangle Park, NC, July 1991.

18. Preferred and Alternative Methods for Estimating Air Emissions, Volume II, Point Sources

Preferred Methods, EIIP, U.S. Environmental Protection Agency, Research Triangle Park, NC.

19. Preferred and Alternative Methods for Estimating Air Emissions, Volume III, Area Sources

Preferred Methods, EIIP, U.S. Environmental Protection Agency, Research Triangle Park, NC.

20. Preferred and Alternative Method for Estimating Air Emissions, Volume IV, Mobile Sources,

Chapter 2, Use of Locality Specific Transportation Data for the Development of Mobile Source

Emission Inventories, EIIP, U.S. Environmental Protection Agency, Research Triangle Park, NC,

September 1996.

21. Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources, EPA-450/4-81-016d

(Revised), U.S. Environmental Protection Agency, Research Triangle Park, NC, September 1992.

22. Preferred and Alternative Method for Estimating Air Emissions, Volume IV, Mobile Sources,

Chapter 3, Guidance for Estimating Lawn and Garden Activity Levels, EIIP, U.S. Environmental

Protection Agency, Research Triangle Park, NC, September 1997.

23. Preferred and Alternative Methods for Estimating Air Emissions, Volume V, Biogenic Sources

Preferred Methods, EIIP, U.S. Environmental Protection Agency, Research Triangle Park, NC,

May 1996.

24. Emission Methodology for Oil and Gas Seeps, California Air Resources Board, Sacramento, CA,

1993.

25. Guidance for the Preparation of Quality Assurance Plans for O3 /CO SIP Emission Inventories,

EPA-450/4-88-023, U.S. Environmental Protection Agency, Research Triangle Park, NC,

December 1988.
65

26. Quality Assurance Program for Post-1987 Ozone and Carbon Monoxide State Implementation Plan

Inventories, EPA-450/4-89-004, U.S. Environmental Protection Agency, Research Triangle Park,

NC, March 1989.

27. Quality Review Guidelines for 1990 Base Year Inventories, EPA-450/4-91-022, U.S. Environmental

Protection Agency, Research Triangle Park, NC, September 1991.

28. Example Documentation Report for 1990 Base Year Ozone and Carbon Monoxide State

Implementation Plan Emission Inventories, EPA-450/4-92-007, U.S. Environmental Protection

Agency, Research Triangle Park, NC, March 1992.

29. Example Emissions Inventory Documentation for Post-1987 Ozone State Implementation Plans,

EPA-450/4-89-018, U.S. Environmental Protection Agency, Research Triangle Park, NC,

October 1989.
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APPENDIX A

DRAFT CONSOLIDATED EMISSIONS

REPORTING (CER) RULE

NOTE: THE ATTACHED DRAFT CER RULE IS BEING REVIEWED WITHIN EPA AND

MAY CHANGE. IT IS INCLUDED AS A DRAFT TO SHOW STATE AND LOCAL AGENCIES

WHAT EPA’S CURRENT INTENTIONS ARE. WHEN THE CER RULE BECOMES FINAL, IT

WILL TAKE PRECEDENCE OVER ALL APPLICABLE PORTIONS OF THIS GUIDANCE.
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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[AD-FRL- ]

RIN

Consolidated Emissions Reporting

AGENCY: Environmental Protection Agency (EPA)

ACTION: Proposed rule

SUMMARY: EPA is proposing this rule to improve and simplify emissions

reporting. Many state and local agencies asked EPA to take this action to: 

determine reporting requirements; improve reporting efficiency; provide

flexibility for data gathering and reporting; better explain to program

managers and the public the need for a consistent inventory program. 

Consolidated reporting should increase the efficiency of the emission

inventory program and provide more consistent and uniform data. Although EPA

is proposing the submission of more data for PM2.5, its precursors, and HAPs,

it is proposing to reduce the reporting requirements for other criteria

pollutants.

DATES: Submit comments on or before [insert date 45 days after date of

publication in the Federal Register].

ADDRESSES: Send comments (in duplicate, if possible) to: Air and Radiation

Docket (6102), US Environmental Protection agency, Attn: Docket No. A9840, 401

M Street, SW, Washington, DC 20460.

FOR FURTHER INFORMATION CONTACT: Steven Bromberg, Emissions, Monitoring, and

Analysis Division (MD-14), Office of Air Quality Planning and Standards, U.S.

Environmental Protection Agency, Research Triangle Park, North Carolina,

27711, Telephone: (919) 541-1000, email:bromberg.steve@epamail.epa.gov.

SUPPLEMENTARY INFORMATION: 

I. AUTHORITY

 Sections 110(a)(2)(F), 110(a)(2)(K), 110(a)(2)(J),112, 182(a)(3)(B),

172(c)(3), 182(a)(3)(A), 187(a)(5), 301(a)
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II. BACKGROUND

Emission inventories are critical for the efforts of state, local, and

federal agencies to attain and maintain the National Ambient Air Quality

Standards (NAAQS) that EPA has established for criteria pollutants such as

ozone, particulate matter, and carbon monoxide. Pursuant to its authority

under section 110 of Title I of the Clean Air Act, EPA has long required State

Implementation Plans (SIPs) to provide for the submission by States to EPA of

emission inventories containing information regarding the emissions of

criteria pollutants and their precursors (e.g., volatile organic compounds

(VOCs)). EPA codified these requirements in 40 CFR part 51, subpart Q in 1979

and amended them in 1987.

The 1990 Amendments to the Clean Air Act (Act) revised many of the

provisions of the Clean Air Act related to the attainment of the NAAQS and the

protection of visibility in mandatory class I Federal areas (certain national

parks and wilderness areas). These revisions establish new periodic inventory

requirements applicable to certain areas that were designated nonattainment

for certain pollutants. For example, section 182(a)(3)(A) required States to

submit an inventory every 3 years (3-Year cycle) for ozone nonattainment areas

beginning in 1993. Emissions reported must include VOC, NOx, and CO for

point, area, mobile (onroad and nonroad), and biogenic sources. Similarly,

section 187(a)(5) requires States to submit an inventory every 3 years for CO

nonattainment areas for the same source classes, except biogenic sources. 

EPA, however, did not codify these statutory requirements in the CFR, but

simply relied on the statutory language to implement them.

EPA recently revised both the ozone and particulate matter NAAQS. EPA

established an 8-hour ozone standard that replaces the 1-hour ozone standard

applicable at the time of the 1990 Clean Air Act Amendments. EPA also revised

the PM10 standards and established new standards for PM2.5 and regional haze.

EPA also recently promulgated the NOx SIP Call (§51.122) which calls on 22

States and the District of Columbia to submit SIP revisions providing for NOx

reductions in order to reduce the amount of ozone and ozone precursors
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transported between states. As part of that rule, EPA established reporting

requirements to be included in the SIP revisions to be submitted by States in

accordance with that action.

This proposal consolidates the various reporting requirements that already

exist in one place in the CFR and establishes new ones for the PM2.5 NAAQS and

regional haze. 

In this action, we refer to these types of inventories as the following:

C Point source inventories 

C 3-Year cycle inventories 

C NOx SIP call inventories 

The Rule also takes advantage of data from Emission Statements available to

states but not reported to EPA. As appropriate, states may use this data to

meet their reporting requirements for point source data. Combining data from

these activities gets the most information from sources with the least burden

on the industry and less effort by state and local government agencies. By

treating this information as a comprehensive emission inventory, states and

local agencies may do the following:

C measure their progress in reducing emissions.

C have a tool they can use to support future trading programs.

C set a baseline from which to do future planning. 

We intend these inventories to help nonattainment areas develop and meet

SIP requirements to reach the NAAQS. Inventories represent a typical work

week’s daily emissions for peak nonattainment seasons, such as summer for O3

and winter for CO. 

States use data obtained through current annual reporting requirements (in

the future to be called Point Source inventory) to record emissions from large

sources and to track progress in reducing emissions from them. States get 3-

Year cycle data from stationary sources with lower yearly emission levels and

use them with the point source inventories to update their emission inventory

every 3 years. States use this updated data to do the following:
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C measure trends in emission reductions 

C demonstrate emission changes from previous years 

C answer the public’s request for information

As noted above, this proposal would require the submission of emissions

inventories to support the implementation of the new PM2.5 standards and

regional haze. States will need to inventory direct emissions of PM2.5 and its

precursors beginning in 2003 for the inventory year 2002. States will also

have to estimate direct emissions of soil dust and PM2.5 precursor emissions of

condensible organics and ammonia. These PM2.5 related data elements are needed

as input to emission models. The Administrator has determined that States

should submit statewide point and 3-Year cycle inventories for PM10, PM2.5, and

regional haze, consistent with the data requirements for 3-Year cycle

inventories for O3 and CO. Sections 110(a)(2)(F) and 172(c) provide ample

statutory for this proposal as it relates to criteria pollutants. Section

110(a)(2)(F) provides that SIPs are to require “as may be prescribed by the

Administrator...(ii)periodic reports on the nature and amounts of emissions

and emissions-related data from such sources.” Section 172(c)(2)(3) provides

that SIPs for nonattainment areas are to “include a comprehensive, accurate,

current inventory of actual emissions from all sources of the relevant

pollutant or pollutants in such area, including such periodic revisions as the

Administrator may determine necessary to assure that the requirements of this

part are met.” Additional statutory authority for emissions inventories from

1-hour ozone nonattainment areas is provided by section 182(a)(3)(A) and for

emissions inventories from CO nonattainment areas is provided by section

187(a)(5). Section 301(a) provides authority for EPA to promulgate

regulations embodying these provisions.

In addition to the emission inventory provisions related to NAAQS

pollutants, EPA is also proposing emission inventory provisions regarding

hazardous air pollutants (HAPs). EPA is proposing these provisions under

authority of section 301(a) which authorizes the Administrator to prescribe

such regulations as are necessary to carry out her functions under the Act. 
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Title V of the Act requires the Administrator to perform an oversight role

with respect to State issued permits, including permits issued to major

sources of HAP emissions. In order to determine whether that program is being

appropriately and lawfully administrated by the States with respect to major

HAP sources, a HAP emission inventory is necessary. These regulations

requiring States to submit such an inventory to EPA are authorized by section

301(a). 

States are developing programs to regulate Hazardous Air Pollutants (HAPs)

that are listed in section 112(b)(l) and their Title V programs must include

permits for all HAP sources emitting major quantities of HAPs (10 tons of one

HAP or 25 tons of multiple HAPs per year). Thus, the Administrator believes

including HAPs in the point source inventory is appropriate and necessary. 

This information will help us support the HAP programs (MACT determinations,

support to residual risk, Urban Area source program, and the Great Waters

program). 

What is the purpose of the Consolidated Emissions Reporting Rule (CERR)?

The purpose of this rule is threefold:

C simplify emissions reporting,

C offer options for data exchange, and

C unify reporting dates for various categories of inventories. 

Previous requirements may have, at times, led to inefficient

reporting. This rule provides options for reporting that

allow States to match normal activities with federal

requirements. 

This action consolidates the requirements of emission inventory programs

for point sources, 3-Year cycles, and NOx SIP Calls.

How are the CERR’s requirements different from existing requirements?

(a) additional pollutants

Your State’s inventory will add PM2.5, PM2.5 precursors, and HAPs to the

criteria pollutants.
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(b) geographic coverage of inventory

Your State now reports point source emissions statewide and emissions from

area and mobile sources by nonattainment area. Your State’s new inventory

will be statewide by county for all source types, regardless of the attainment

status.

(c) frequency of reporting

Your State will continue to report emissions from very large point sources

(See Table 1) annually. Your State has a choice to report smaller point

sources every 3 years or one-third of the sources each year. Your State will

continue to report emissions from nonattainment areas for area and mobile

sources every 3 years. Attainment areas will be required, for the first time,

to report area and mobile source emissions.

How will EPA use the data collected under this reporting requirement?

EPA uses emission inventories to form realistic public policy by the

following:

C modeling analyses, 

C projecting future control strategies, 

C tracking progress to meet requirements of the Clean Air Act, 

C calculating risk, and 

C responding to public inquiries. 

Why does EPA want my State’s data?

Most of the information EPA needs are readily available from States

because of the State’s efforts to follow the Clean Air Act and its amendments. 

Using data States have already estimated or collected is a cheaper, more

efficient way for us to get information to analyze. EPA can pull your data

into a central repository of emissions data and extract what we need to

fulfill our mandates.

How will others use my data collected under this requirement?

 Recent events have shown that some states need emissions data for areas

outside their borders. Programs such as the Ozone Transport Assessment Group,

the Ozone Transport Commission NOx Baseline study, and the Grand Canyon
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Visibility Transport Commission demonstrated this need. As we recognize

pollution as a regional problem, agencies will need multistate inventories

more often to do such things as regional modeling. 

We can meet our common needs by creating a central repository of data from

state and local agencies, or a group of regional emissions data bases. Such

repositories offer the advantage of ready access and availability, common

procedures for ensuring the quality of data, and an ability to meet the

general needs of many potential users.

What happens if EPA doesn’t get my agency’s emissions data?

If we don’t receive your emissions information at the time this rule

specifies, we’ll use whatever we have to produce emissions data for your

agency. Congress often mandates our analyses, so we depend on you to complete

them. If we don’t get your data, we must find other ways to compile similar

information.

We can estimate your agency’s inventory by an of the following:

C national allocation (top down) methods,

C projecting from previous data, or

C using our best judgment. 

For area and mobile sources, our methods usually represent your emissions

reasonably well. For point sources, our estimates are less accurate. We have

to estimate activity and plant parameters based on general knowledge rather

than using your specific information.

The Act provides for other actions against a State if we do not receive

your data. For example, if a State does not provide emissions data for NAAQS

pollutants, EPA may take actions such as making findings of failure to

implement, that are authorized in instances where a State fails to fulfill SIP

obligations. As the HAP emissions data would be required by this regulation,

States could face consequences under section 113 for failure to comply with a

regulation.
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III. ADMINISTRATIVE REQUIREMENTS

A. Executive Order 12866

Under Executive Order 12866 (58 FR 51735, October 4, 1993), we must

determine whether the regulatory action is “significant” and therefore subject

to review by the Office of Management and Budget (OMB) and to the Executive

Order’s requirements. We’ve determined this action is “significant” and

therefore does require OMB review, based on the Order’s definition of a

“significant” regulatory action as one that is likely to result in a rule that

may do any of the following:

1. Have an annual effect on the economy of $100 million or more or

materially harm the economy, a sector of the economy, productivity,

competition, jobs, the environment, public health or safety, or State and

local governments or communities. The ICR (EPA ICR No. 0916.09) analysis

shows that the costs to implement the Rule are less than $100 million.

2. Create a serious inconsistency or otherwise interfere with an action

taken or planned by another Agency. The rule will increase data consistency,

thus assisting other Agencies.

3. Materially alter the budgetary effect of entitlements, grants, user

fees, or loan programs or the rights and obligations of those who receive

them. Grant funds are being increased to State agencies.

4. Raise novel legal or policy issues arising out of legal mandates, the

President’s priorities, or the principles in the Executive Order.

B. Paperwork Reduction Act 

Today’s action does require new information for newly regulated pollutants

but reduces reporting for previously regulated pollutants. It revises part 51

to consolidate old reporting requirements and recognizes new reporting needs

for PM2.5 and HAPs. The Office of Management and Budget has approved the

current information collection requirements in part 51 under the Paperwork

Reduction Act, 44 U.S.C. 3501 et seq. and has assigned OMB control number

2060-0088 (EPA ICR No. 916.07). A new information request (EPA ICR No.
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0916.09) that covers the new reporting requirements is being submitted to OMB

(OMB control number 2060-0088) for approval.

C. Impact on Small Entities

Under the Regulatory Flexibility Act we don’t need to analyze this

proposed regulation’s flexibility because it doesn’t affect small entities

whose jurisdictions cover fewer than 50,000 people. Under 5 USC 605(b), I

certify that this action won’t significantly affect the economic well-being of

a substantial number of small entities. Also, because this modification is

minor, it requires no additional review.

D. E.O. 13045: Children’s Health Protection

Executive Order 13045: “Protection of Children from Environmental health Risks

and Safety Risks” (62FR19885, April 23, 1997) applies to any rule that: (1) is

determined to be “economically significant” as defined under E.O. 12866, and

(2) concerns an environmental health or safety risk that EPA has reason to

believe may have a disproportionate effect on children. If the regulatory

action meets both criteria, the Agency must evaluate the environmental health

or safety effects of the planned rule on children, and explain why the planned

regulation is preferable to other potentially effective and reasonably

feasible alternatives considered by the Agency.

EPA interprets E.O. 13045 as applying only to those regulatory actions

that are based on health or safety risks, such that the analysis required

under section 5-501 of the Order has the potential to influence the

regulation. This rule is not subject to E.O. 13045 because it is based on

technology performance and not on health or safety risks.

E. The National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of

1995 (NTTAA), Pub L. No. 104-113, § 12(d) (15 U.S.C. 272 note) directs EPA to

use voluntary consensus standards in its regulatory activities unless to do so

would be inconsistent with applicable law or otherwise impractical. Voluntary

consensus standards are technical standards (e.g., materials specifications,

test methods, sampling procedures, and business practices) that are developed
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or adopted by voluntary consensus standards bodies. The NTTAA directs EPA to

provide Congress, through OMB, explanations when the Agency decides not to use

available and applicable voluntary consensus standards.

This proposed rule making does not involve technical standards. Therefore,

EPA is not considering the use of any voluntary consensus standards.

F. Unfunded Mandates Reform Act

 Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), P.L. 104-4,

establishes requirements for Federal agencies to assess the effects of their

regulatory actions on State, local, and tribal governments and the private

sector. Under section 202 of the UMRA, EPA generally must prepare a written

statement, including a cost-benefit analysis, for proposed and final rules

with “Federal mandates” that may result in expenditures to State, local, and

tribal governments, in the aggregate, or to the private sector, of $100

million or more in any one year. Before promulgating an EPA rule for which a

written statement is needed, section 205 of the UMRA generally requires EPA to

identify and consider a reasonable number of regulatory alternatives and adopt

the least costly, most cost-effective or least burdensome alternative that

achieves the objectives of the rule. The provisions of section 205 do not

apply when they are inconsistent with applicable law. Moreover, section 205

allows EPA to adopt an alternative other than the least costly, most costeffective or least burdensome alternative if the Administrator publishes with

the final rule an explanation why that alternative was not adopted. Before

EPA establishes any regulatory requirements that may significantly or uniquely

affect small governments, including tribal governments, it must have developed

under section 203 of the UMRA a small government agency plan. The plan must

provide for notifying potentially affected small governments, enabling

officials of affected small governments to have meaningful and timely input in

the development of EPA regulatory proposals with significant Federal

intergovernmental mandates, and informing, educating, and advising small

governments on compliance with the regulatory requirements.
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EPA has determined that this rule does not contain a Federal mandate that

may result in expenditures of $100 million or more for State, local, and

tribal governments, in the aggregate, or the private sector in any one year. 

The additional work required by this rule takes advantage of information

already in the possession of reporting groups. Using existing data leverages

past work and reduces the burden of this rule. This conclusion is supported by

the analysis done in support of EPA ICR No. 0916.09, OMB control number 2060-

0088. Thus, today’s rule is not subject to the requirements of sections 202

and 205 of the UMRA.

G. Executive Order 12875: Enhancing the Intergovernmental Partnership

Under Executive Order 12875, EPA may not issue a regulation that is not

required by statute and that creates a mandate upon a State, local or tribal

government, unless the Federal government provides the funds necessary to pay

the direct compliance costs incurred by those governments, or EPA consults

with those governments. If EPA complies by consulting, Executive Order 12875

requires EPA to provide to the Office of Management and Budget a description

of the extent of EPA’s prior consultation with representatives of affected

State, local and tribal governments, the nature of their concerns, copies of

any written communications from the governments, and a statement supporting

the need to issue the regulation. In addition, Executive Order 12875 requires

EPA to develop an effective process permitting elected officials and other

representatives of State, local and tribal governments to provide meaningful

and timely input in the development of regulatory proposals containing

significant unfunded mandates.

Today’s rule does not create a mandate on State, local, or tribal

governments. As explained in the discussion on UMRA (Section III.D), this

rule does not impose an enforceable duty on these entities. Accordingly, the

requirements of section 1(a) of Executive Order 12875 do not apply to this

rule.
A-14

H. Executive Order 13084: Consultation and Coordination with Indian Tribal

Governments

Under Executive Order 13084, EPA may not issue a regulation that is not

required by statute, that significantly or uniquely affects the communities of

Indian tribal governments, and that imposes substantial direct compliance

costs on those communities, unless the Federal government provides the funds

necessary to pay the direct compliance costs incurred by the tribal

governments, or EPA consults with those governments. If EPA complies by

consulting, Executive Order 13084 requires EPA to provide to the Office of

Management and Budget, in a separately identified section of the preamble to

the rule, a description of the extent of EPA’s prior consultation with

representatives of affected tribal governments, a summary of the nature of

their concerns, and a statement supporting the need to issue the regulation. 

In addition, Executive Order 13084 requires EPA to develop an effective

process permitting elected officials and other representatives of Indian

tribal governments to provide meaningful and timely input in the development

of regulatory policies on matters that significantly or uniquely affect their

communities.

Today’s rule does not significantly or uniquely affect the communities

of Indian tribal governments. Accordingly, the requirements of section 3(b)

of Executive Order 13084 do not apply to this rule.

CONSOLIDATED EMISSIONS REPORTING, PAGE 13 OF 38 

List of Subjects in 40 CFR Part 51

Environmental protection, Administrative practice and procedure, Air pollution

control, Intergovernmental relations, Reporting and record keeping

requirements.

 

Dated: Carol M. Browner,

Administrator.
A-15

For the reasons stated in the preamble, title 40, chapter I, of the Code

of Federal Regulations is proposed to be amended as follows:

PART 51 -- [AMENDED]

1. The authority citation for part 51 continues to read as follows:

Authority: 42 U.S.C. 7401-7671q.

2. Part 51 is amended by adding subpart A to read as follows:

Subpart A - Emission Inventory Reporting Requirements

Sec.

51.001 For what sources must States do emissions reporting?

GENERAL INFORMATION FOR INVENTORY PREPARERS

51.005 Who is responsible for actions described in this rule?

51.010 What tools are available to help prepare and report

emissions data?

51.015 How does my State reduce the effort for reporting?

SPECIFIC REPORTING REQUIREMENTS

51.020 What data does my State need to report to EPA?

51.025 What are the emission thresholds that separate point and area 

sources?

51.030 What geographic area must my State’s inventory cover?

51.035 When does my State report the data to EPA?

51.040 In what form should my State report the data to EPA?

51.045 Where should my State report the data?

Appendix A to Subpart A of Part 51 - Tables and Glossary

§51.001 For what sources must States do emissions reporting?

(a) Point sources for which States must report emissions annually under

§51.321 are defined as follows:

(1) For PM10, PM2.5, ammonia, sulfur oxides, VOC, and nitrogen

oxides, any plant that actually emits at least 90.7 metric tons (100 tons) per

year of any pollutant.
A-16

(2) For carbon monoxide, any plant that actually emits at least

907 metric tons (1000 tons) per year.

(3) For lead and lead compounds measured as elemental lead, any

plant that actually emits at least 4.5 metric tons (5 tons) per year.

(4) For HAPs, any plant that actually emits at least 10 tons per

year of any HAP or at least 25 tons per year of two or more HAPs combined.

(b) Annual reporting applies only to an emission point within the

plant that emits:

(1) For PM10, PM2.5, ammonia, sulfur oxides, VOC and nitrogen

oxides, at least 22.7 metric tons (25 tons) per year.

(2) For carbon monoxide, at least 227 metric tons (250 tons) per

year.

(3) For lead or lead compounds measured as elemental lead, at

least 4.5 metric tons (5 tons) per year.

(4) For HAPs, at least 10 tons per year of one HAP or 25 tons per

year of two or more HAPs.

GENERAL INFORMATION FOR INVENTORY PREPARERS

§51.005 Who is responsible for actions described in this rule?

State and local agencies whose geographic coverage include any point,

area, mobile, or biogenic sources must inventory these sources and report this

information to EPA.

§51.010 What tools are available to help prepare and report emissions data?

(a) We urge your State to use estimation procedures described in

documents from the Emission Inventory Improvement Program (EIIP). Their

procedures are standardized and ranked according to relative uncertainty for

each emission estimating technique. Using this guidance will enable others to

use your State’s data and be able to evaluate its quality and consistency with

other data. If your State chooses not to use the EIIP estimating methods,

your State should follow the procedures EIIP recommends for assigning

appropriate uncertainty scores to your emission estimates.
A-17

(b) Your State should use traditional estimating procedures for HAPs

(emission factor x activity level) as the EIIP documents describe. However,

if your State has developed a speciation profile unique to a local source, you

may use it instead of the traditional approach to estimate emissions.

§51.015 How does my State reduce the effort for reporting?

(a) Compiling smaller point source (Type B) and 3-Year cycle inventories

means much more effort every 3 years, but your state may ease this workload

spike by reporting one-third of your Type B point and 3-Year cycle sources

each year. For these sources, your State will therefore have data from 3

successive years at any given time, rather than from the single year in which

it is compiled. If your State needs to inventory the entire category of Type

B point and 3-Year cycle sources in a single year, your State should report

this data instead of a third of the estimates each year. If your State is a

NOx SIP Call state as defined in §51.122, your State can’t use these optional

reporting frequencies for NOx. 

(b) If your State needs a base year emission inventory for a selected

pollutant, your State must compile an inventory of all affected source

categories for the specified year.

(c) If your State choose the method of reporting one-third of your Type

B sources and 3-Year cycle sources each year, your State must compile each

year of the 3 year period identically. For example, if a process hasn’t

changed for a source category or individual plant, your State must use the

same emission factors to calculate emissions for each year of the 3 year

period. If your State has revised emission factors during the 3 years for a

process that hasn’t changed, resubmit previous year’s data using the revised

factor. If your State uses models to estimate emissions during any year of

the 3 year period, make them identical for all 3 years.
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SPECIFIC REPORTING REQUIREMENTS

§51.020 What data does my State need to report to EPA?

(a) Pollutants. (1) Report emissions of the following:

(I) Sulfur oxides.

(ii) VOC. 

(iii) Nitrogen oxides.

(iv) Carbon monoxide.

(v) Lead and lead compounds.

(vi) Particulate matter.

(vii) PM10.

(viii) PM2.5.

(ix) PM2.5 precursors.

(x) HAPs.

(2) See Table 3 of appendix A to this subpart for the HAPs covered under

this rule. Table 4 of appendix A to this subpart contains the priority list

of HAPs to be inventoried. If your State has inventory data for any of the

remaining HAPs listed in Table 3 of appendix A to this subpart, we encourage

you to submit this information along with the data on Table 4 of appendix A to

this subpart HAPs. If your State can show that a HAP has a residual risk of

less that one in a million, it does not have to report that pollutant.

(b) Supporting information. Report the data elements in Table 2a through

2d of appendix A to this subpart. Depending on the format you choose to

report your State data, additional information not listed in Tables 2a through

2d will be required. Specific instructions for your State system format

should be consulted. Any you don’t report we’ll have to generate with our own

techniques. We may ask you for other data to meet special requirements.

(c) Confidential data. We don’t consider the data in Tables 2a through

2d of appendix A to this subpart confidential, but some states limit release

of this type of data. If Federal and State requirements are inconsistent,

consult your EPA Regional Office for a final reconciliation.
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§51.025 What are the emission thresholds that separate point and area

sources?

(a)(1) Use the following actual emissions thresholds in attainment areas

for point source reporting: 

(I) At least 100 tpy for SOx, VOC, NOx, PM10, PM2.5.

(ii) At least 1000 tpy for CO.

(iii) At least 5 tpy for Pb.

(iv) At least 10 tpy for HAPs.

(2) See Table 1 of appendix A to this subpart for reporting thresholds

on point sources in nonattainment areas. 

(b) Your State has the option to inventory and report any stationary

sources below these thresholds as point or area sources. If you have lower

emission thresholds for point sources in your state, you should use them. See

Table 1 of appendix A to this subpart for thresholds to report 3-Year cycle

data and Tables 2a through 2d of appendix A to this subpart for data elements

to report.

(c) In moderate PM10 nonattainment areas your State should inventory

sources emitting at least 100 tpy (actual) as point sources. In serious PM10

nonattainment areas, this requirement applies to sources emitting at least 70

tpy (actual). Inventory PM2.5 sources emitting at least 100 tpy (actual) as

point sources. Inventory ammonia (a precursor to PM2.5) as a point or area

source. We recognize that some HAPs in Table 3 of appendix A of this subpart

may be precursors to PM2.5, so, your State may inventory them as point or area

sources, as appropriate.

(d) A HAP point source is any stationary facility emitting at least 10

tpy (actual) of any individual HAP, or at least 25 tpy for any combination of

HAPs. Your State has the option to inventory and report facilities emitting

less than these thresholds as point or area sources. If your State has lower

emission thresholds for point sources, you should use them. 
A-20

 (e) Reexamine the list of HAP facilities each year of the cycle. Work

with your EPA Regional Office periodically to examine the HAP sources being

inventoried and insure they’re relevant.

§51.030 What geographic area must my State’s inventory cover?

Because of the regional nature of these pollutants, your State’s

inventory must be statewide, regardless of an area’s attainment status. 

§51.035 When does my State report the data to EPA?

Your State must report data for all inventory types 12 months (by

December 31) after the end of the calendar year. 

(a) Point source.(1) As seen in Table 1 of appendix A to this subpart,

your State should divide your point source inventory into two subsets - Type A

source inventory and Type B source inventory - with different reporting

frequencies. Report actual annual emissions from Type A point sources each

calendar year. Review stack data (height, diameter, flow rate, temperature,

velocity, and stack number) every 3 years and send in changes shown in Table

2a of appendix A to this subpart.

(2) For point sources within your state that your State is controlling

to meet the NOx reductions in § 51.121, submit estimates of NOx annually for

the ozone season.

(b) 3-Year cycle. (1) Your State should send EPA its annual and daily

estimates of actual emissions every 3 years for Type B point sources and area

and mobile sources. For Type B point source inventories, include facilities

not reported under the Type A source requirement. Area data includes sources

below the thresholds for Type B point sources. Report HAPs on the same

frequency as the Type B inventories. Your State may report emissions from

one-third of your State’s Type B, area, and mobile sources each year or from

all sources every 3 years. 

(2) Your State and your EPA Regional Office may tailor the reporting by

selecting sources that most affect your agency. 

(3) We encourage your State to integrate your State’s own reporting

requirements with EPA’s. If your State legislature requires HAP data
A-21

reporting, contact your EPA Regional Office to reconcile your state and

federal reporting requirements.

(4) If sources within your state are controlled to meet NOx reductions

in §51.121, your State must report all their NOx area and mobile source data

every year.

(c) Other. Your State must establish an initial baseline for biogenic

emissions. Your State need not submit more biogenic data unless land use

characteristics or the methods for estimating emissions change. If either of

these variables change, your State must report new biogenic emissions during

the reporting period in the following year as shown in Table 2d of appendix A

of this subpart.

§51.040 In what form should my State report the data to EPA?

(a) For better access by everyone, report emissions in your State in an

electronic format using one of the following options: 

(1) Submit your State’s data in the EIIP/NET Input format.

(2) Submit your State’s data in the AIRS-AFS format.

(3) Submit your State’s data in the EIIP/EDI format.

(b) Some meta data describing your submission are not listed in Tables

2a through 2d of appendix A of this subpart are also required. Because

electronic reporting technology continually changes, contact your EPA Regional

Office for acceptable formats. You should consult specific instructions for

your State system format to determine additional requirements not listed in

Tables 2a through 2d. You can find specific instructions for each optional

format at the following Internet addresses:

(1) EIIP/NET Input format - 

www.epa.gov/ttn/chief/index.html#Data

(2) AIRS-AFS format - www.epa.gov/ttnairs1/afs/

(3) EIIP/EDI format - 

www.epa.gov/ttn/chief/eiip/techrep.htm#dmproc
A-22

§51.045 Where should my State report the data?

(a) Your State may continue entering your data to the EPA AIRS system

using the AFS format for point sources.

(b) If your State uses either the EIIP/NET Input format the EIIP/EDI

format, you State submits or reports data by either providing it to another

party directly or notifying the other party that it is available in the

specified format and at a specific electronic location (FTP site). For an

individual plant your State may continue to report data directly to us under

40 CFR part 96 or Subpart H of 40 CFR Part 75.

(c) For the latest information on data reporting procedures, call our

Info Chief help desk at (919)541-1000 or email to info.chief@epamail.epa.gov.

Appendix A to Subpart A of Part 51 - Tables and Glossary
A-23

Table 1. Summary of Requirements For Reporting Emission Inventories

Provision Point Source Inventory NOx SIP Call

Inventory

3-Year Inventory

Type A

Sources1

Type B

Sources1

CAA

citation

§ 110(a)(2)(F) §110(a)(2)(F),

§ 112

§110(a)(2) § 172(c)(3),

§ 182(a)(3)(A),and

§ 187(a)(5), § 112

Frequency

of

reporting

Annual Every 3 years Annual Every 3 years

Estimating

period

Annual Annual and

Daily4

Five month

season

Annual and Daily4

Areas to

which

provision

applies

Entire U.S.

(Statewide)

Entire U.S.

(Statewide)

NOx SIP Call

areas

(Statewide)

Entire U.S.

(Statewide)

Pollutants

and source

size

thresholds

Pollutant 

 tpy2

SOx 2,500

NOx 2,500

VOC 250 

PM10 250

PM2.5 250

CO 2,500

Pollutant 

 tpy

SOx 100

NOx 100

VOC 100

PM10 100

PM2.5 100

CO 1,000

Pb 5

3HAPs 10

Pollutant

tpy

NOx 100

Lesser

thresholds

to be

defined by

state. 

All sources

not

inventoried

as point

sources

shall be

inventoried

as area or

mobile

sources and

reported

only if

they are to

be

controlled

to meet

emission

budget.

Pollutant

Ozone NA areas5: 

 tpy

VOC 10

NOx 100

CO 100

CO NA areas5:

CO 100

PM-10 NA areas5:

PM10 70 (serious)

PM10 100 (moderate)

PM2.5 NA areas5:

PM2.5 100

Ammonia may be

inventoried as a

point or area source

Inventory includes:

! Point sources 

specified tpy.

! Area sources <

specified tpy.

! Onroad mobile

sources.

! Nonroad mobile

sources.

! Biogenic sources.

1 Previously, the Type A sources and the Type B sources together constituted the annual inventory

(40 CFR Part 51.321-323); all such sources were required to report annually.

2 tpy = tons per year.

3 A HAPs point source is defined as a stationary source emitting 10 tpy or more of any individual

HAP, or 25 tpy or more of any combination of HAPs. Facilities emitting less than these threshold

amounts will be inventoried and reported as area sources unless already inventoried as a point

source.

4 Ozone daily emissions = summer work weekday; CO daily emissions = winter work weekday; PM daily

emissions = to be defined in consultation with Regional office.

5 Thresholds apply to nonattainment areas only; remainder of state uses Type B Source thresholds

to distinguish between point and area sources.
A-24

Table 2a. Data Elements that States Must Report for Point Sources

Data Elements Annual Every 3 Years 

Entire

US

NOx SIP

Call

Entire

US

NAA NOx SIP

Call

Emission levels VOC 250

NOx 2500

SOx 2500

PM10 250

PM2.5 250

CO

2500

NOx 100

Lesser

thresholds

to be

defined by

state

VOC 100

NOx 100

SOx 100

PM10 100

PM2.5 100

CO 1000

Pb 5

3HAPS 10

NH3

1VOC 10

1NOx 100

1PM10 70

1CO 100

NOx 100

Inventory year

Inventory start date

Inventory end date

Inventory type

State FIPS code

County FIPS code

Federal ID code

(plant)

Federal ID code

(point)

Federal ID code

(process)

Site name

Physical address

SCC

Heat content

(fuel)(annual)

Ash content

(fuel)(annual)

Sulfur content

(fuel)(annual)

Heat content

(fuel)(seasonal)

Source of fuel heat

content

Pollutant code

Activity/throughput

(annual)

Activity/throughput

(daily)2

Activity/throughput

(NOx ozone season)

Source of

activity/throughput

(NOx ozone season)

Work weekday emissions
Data Elements Annual Every 3 Years 

Entire

US

NOx SIP

Call

Entire

US

NAA NOx SIP

Call

A-25

Annual emissions

NOx Ozone season

emissions

Area classification

Emission factor

Source of emission

factor

Winter throughput(%)

Spring throughput(%)

Summer throughput(%)

Fall throughput(%)

Hr/day in operation

Start time (hour)

Day/wk in operation

Wk/yr in operation

Federal ID code (stack

number)

X stack coordinate

(latitude)

Y stack coordinate

(longitude)

Stack Height

Stack diameter

Exit gas temperature

Exit gas velocity

Exit gas flow rate

SIC/NAICS

Design capacity

Maximum nameplate

capacity

Primary control eff(%)

Secondary ctl eff (%)

Control device type

Rule effectiveness (%)

1 Both daily and annual emission estimates required

2 May be derived from annual or seasonal throughput.

3 Any stationary facility emitting 10 tpy or more of any individual HAP, or 25 tpy or more of any

combination of HAPs.
A-26

Table 2b. Data Elements that States Must Report for Area and 

 Nonroad Sources

 Data Elements Annual Every 3 Years

Entire

US

NOx

SIP

Call

Entire

US

NAA NOx SIP

Call 

Emissions levels 1VOC <10

1NOx <100

1PM10 <100

1PM2.5

<100

1CO <100

HAPS <10

NH3

1NOx <100

Inventory year

Inventory start

date

Inventory end date

Inventory type

State FIPS code

County FIPS code

SCC

Emission factor

Source of emission

factor

Activity/throughput

level (annual)

Activity/throughput

(daily)2

Activity/throughput

(NOx ozone season)

Source of

activity/throughput

(NOx ozone season)

Total

capture/control

efficiency (%)

Rule effectiveness

(%)

Rule penetration

(%)

Pollutant code

Summer/winter work

weekday emissions

Annual emissions

NOx Ozone season

emissions
 Data Elements Annual Every 3 Years

Entire

US

NOx

SIP

Call

Entire

US

NAA NOx SIP

Call 

A-27

Source of emissions

data

Winter throughput

(%)

Spring throughput

(%)

Summer throughput

(%)

Fall throughput (%)

Hr/day in

operations

Day/wk in

operations

Wk/yr in operations

 1 Both daily and annual emission estimates required

 

2 May be derived from annual or seasonal throughput.
A-28

Table 2c. Data Elements that States Must Report for Onroad Mobile Sources

Data Elements Annual Every 3 Years

Entire

US

NOx

SIP

Call

Entire

US

NAA NOx SIP

Call

Inventory year

Inventory start

date

Inventory end date

Inventory type

State FIPS code

County FIPS code

SCC

Emission factor1

Activity (VMT by

Roadway Class)

Source of activity

data

Pollutant code

Summer/winter work

weekday emissions

Annual emissions

NOx ozone season

emissions

Source of emissions

data

 

1 Mobile model input files should be submitted
A-29

Table 2d. Data Elements that States Must Report for Biogenic Sources

Data Elements Annual Every 3 Years

Entire

US

NOx

SIP

Call

Entire

US

NAA NOx SIP

Call

Inventory year

Inventory start

date

Inventory end date

Inventory type

State FIPS code

County FIPS code

SCC

Pollutant code

Summer/winter work

weekday emissions

Annual emissions
A-30

Table 3. Hazardous Air Pollutants (HAPs)

______________________________________________________________________________

 Chemical Abstracts Chemical Abstracts

Service Pollutant Service Pollutant 

 Number Number 

____________________________________

75-07-0 Acetaldehyde

60-35-5 Acetamide

75-05-8 Acetonitrile 

98-86-2 Acetophenone

53-96-3 2-Acetylaminofluorene

107-02-8 Acrolein

79-06-1 Acrylamide 

79-10-7 Acrylic acid

107-13-1 Acrylonitrile

107-05-1 Allyl chloride 

92-67-1 4-Aminobiphenyl

62-53-3 Aniline

90-04-0 o-Anisidine

1332-21-4 Asbestos

71-43-2 Benzene (including

benzene from gasoline)

92-87-5 Benzidine

98-07-7 Benzotrichloride

100-44-7 Benzyl chloride

92-52-4 Biphenyl

117-81-7 Bis(2ethylhexyl)

phthalate (DEHP)

542-88-1 Bis(chloromethyl) ether

75-25-2 Bromoform

106-99-0 1,3-Butadiene

156-62-7 Calcium cyanamide

105-60-2 Caprolactam 

(Removed 6/18/96, 

61FR30816)

133-06-2 Captan

63-25-2 Carbaryl

75-15-0 Carbon disulfide

56-23-5 Carbon tetrachloride

463-58-1 Carbonyl sulfide

120-80-9 Catechol

133-90-4 Chloramben

57-74-9 Chlordane

7782-50-5 Chlorine

79-11-8 Chloroacetic acid

532-27-4 2-Chloroacetophenone

108-90-7 Chlorobenzene

510-15-6 Chlorobenzilate

67-66-3 Chloroform

107-30-2 Chloromethyl methyl

ether

126-99-8 Chloroprene

1319-77-3 Cresol/Cresylic acid

 (mixed isomers) 

95-48-7 o-Cresol

108-39-4 m-Cresol

106-44-5 p-Cresol

98-82-8 Cumene

____________________________________

N/A 2,4-D 

 (2,4-Dichlorophenoxyacetic Acid)

 (including salts and

esters)

72-55-9 DDE (1,1-dichloro-2,2-

bis(p-chlorophenyl)

ethylene)

334-88-3 Diazomethane

132-64-9 Dibenzofuran 

96-12-8 1,2-Dibromo-3-

chloropropane 

84-74-2 Dibutyl phthalate 

106-46-7 1,4-Dichlorobenzene 

91-94-1 3,3'-Dichlorobenzidine 

111-44-4 Dichloroethyl ether

 (Bis[2-

chloroethyl]ether) 

542-75-6 1,3-Dichloropropene 

62-73-7 Dichlorvos 

111-42-2 Diethanolamine 

64-67-5 Diethyl sulfate 

119-90-4 3,3'-Dimethoxybenzidine 

60-11-7 4-Dimethylaminoazo

benzene

121-69-7 N,N-Dimethylaniline

119-93-7 3,3'-Dimethylbenzidine

79-44-7 Dimethylcarbamoyl

chloride 

68-12-2 N,N-Dimethylformamide 

57-14-7 1,1-Dimethylhydrazine

131-11-3 Dimethyl phthalate

77-78-1 Dimethyl sulfate 

N/A 4,6-Dinitro-o-cresol

 (including salts)

51-28-5 2,4-Dinitrophenol

121-14-2 2,4-Dinitrotoluene 

123-91-1 1,4-Dioxane

 (1,4-Diethyleneoxide)

122-66-7 1,2-Diphenylhydrazine

106-89-8 Epichlorohydrin

 (l-Chloro-2,3-

epoxypropane)

106-88-7 1,2-Epoxybutane 

140-88-5 Ethyl acrylate 

100-41-4 Ethylbenzene

51-79-6 Ethyl carbamate

 (Urethane) 

75-00-3 Ethyl chloride

 (Chloroethane) 

106-93-4 Ethylene dibromide

 (Dibromoethane)

107-06-2 Ethylene dichloride

 (1,2-Dichloroethane)

107-21-1 Ethylene glycol 
A-31

151-56-4 Ethyleneimine

 (Aziridine)

75-21-8 Ethylene oxide 

96-45-7 Ethylene thiourea 

75-34-3 Ethylidene dichloride 

 (1,1-Dichloroethane)

50-00-0 Formaldehyde

76-44-8 Heptachlor 

118-74-1 Hexachlorobenzene

87-68-3 Hexachlorobutadiene 

N/A 1,2,3,4,5,6-

Hexachlorocyclyhexane

 (all stereo isomers,

including lindane)

77-47-4 Hexachlorocyclopentadiene

67-72-1 Hexachloroethane 

822-06-0 Hexamethylene

diisocyanate

680-31-9 Hexamethyl-phosphoramide

110-54-3 Hexane

302-01-2 Hydrazine 

7647-01-0 Hydrochloric acid

 (Hydrogen chloride [gas

only])

7664-39-3 Hydrogen fluoride

 (Hydrofluoric acid)

123-31-9 Hydroquinone

78-59-1 Isophorone 

108-31-6 Maleic anhydride

67-56-1 Methanol 

72-43-5 Methoxychlor 

74-83-9 Methyl bromide

 (Bromomethane)

74-87-3 Methyl chloride

 (Chloromethane) 

71-55-6 Methyl chloroform

 (1,1,1-Trichloroe-thane)

78-93-3 Methyl ethyl ketone

 (2-Butanone)

60-34-4 Methylhydrazine

74-88-4 Methyl iodide

 (Iodomethane)

108-10-1 Methyl isobutyl 

 ketone(Hexone)

624-83-9 Methyl isocyanate 

80-62-6 Methyl methacrylate 

1634-04-4 Methyl tert-butyl ether

101-14-4 4,4'-Methylenebis(2-

chloroaniline) 

75-09-2 Methylene chloride

 (Dichloromethane)

101-68-8 4,4'-Methylenedi-phenyl

diisocyanate

 (MDI)

101-77-9 4,4'-Methylene-dianiline 

91-20-3 Naphthalene 

98-95-3 Nitrobenzene

92-93-3 4-Nitrobiphenyl 

100-02-7 4-Nitrophenol 

79-46-9 2-Nitropropane

684-93-5 N-Nitroso-N-methylurea

62-75-9 N-Nitrosodime-thylamine

59-89-2 N-Nitrosomorpholine

56-38-2 Parathion 

82-68-8 Pentachloroni-trobenzene

 (Quintobenzene)

87-86-5 Pentachlorophenol 

108-95-2 Phenol 

106-50-3 p-Phenylenediamine 

75-44-5 Phosgene

7803-51-2 Phosphine 

N/A Phosphorus Compounds 

85-44-9 Phthalic anhydride 

1336-36-3 Polychlorinated

biphenyls

 (Aroclors)

1120-71-4 1,3-Propane sultone 

57-57-8 beta-Propiolactone 

123-38-6 Propionaldehyde 

114-26-1 Propoxur

 (Baygon) 

78-87-5 Propylene dichloride

 (1,2-Dichloropropane)

75-56-9 Propylene oxide

75-55-8 1,2-Propylenimine 

 (2-Methylaziridine)

91-22-5 Quinoline 

106-51-4 Quinone

 (p-Benzoquinone) 

100-42-5 Styrene

96-09-3 Styrene oxide

1746-01-6 2,3,7,8-Tetrachlorodibenzo-p-dioxin

79-34-5 1,1,2,2-Tetrachloroethane 

127-18-4 Tetrachloroethylene

 (Perchloroethylene)

7550-45-0 Titanium tetrachloride

108-88-3 Toluene 

95-80-7 Toluene-2,4-diamine 

584-84-9 2,4-Toluene diisocyanate

95-53-4 o-Toluidine 

8001-35-2 Toxaphene

 (chlorinated camphene)

120-82-1 1,2,4-Trichloro-benzene

79-00-5 1,1,2-Trichloroethane

79-01-6 Trichloroethylene 

95-95-4 2,4,5-Trichlorophenol

88-06-2 2,4,6-Trichlorophenol

121-44-8 Triethylamine 

1582-09-8 Trifluralin 

540-84-1 2,2,4-Trimethyl-pentane

108-05-4 Vinyl acetate 

593-60-2 Vinyl bromide 

75-01-4 Vinyl chloride

75-35-4 Vinylidene chloride

 (1,1-Dichloroethylene)

1330-20-7 Xylenes

 (mixed isomers)

95-47-6 o-Xylene 

108-38-3 m-Xylene 
A-32

106-42-3 p-Xylene 

 Antimony Compounds 

 Arsenic Compounds

 (inorganic including

arsine)

 Beryllium Compounds 

 Cadmium Compounds 

 Chromium Compounds 

 Cobalt Compounds 

 Coke Oven Emissions 

 Cyanide Compounds1

Glycol ethers2 

 Lead Compounds 

 Manganese Compounds 

Mercury Compounds

 Fine mineral fibers3 

Nickel Compounds 

 Polycyclic Organic

Matter4 

 Radionuclides (including

radon)5 

 Selenium Compounds 

 

______________________________________________________________________________

NOTE: Unless otherwise specified, all listings above which contain the word

compounds or glycol ethers include any unique chemical substance that contains

the named chemical (i.e., antimony, arsenic, etc.) as part of that chemical’s

infrastructure. 

1. X’CN where X = H’ or any other group where a formal dissociation may

occur. For example, KCN or Ca(CN)2.

2. (Under review) Glycol Ether draft ptions for defining:

Possible Correction to CAA 112(b)(1) footnote that would be consistent with

OPPTS modified definition.

New OPPTS definition as published is:

R - (OCH2CH2)n - OR’ where:

n = 1,2, or 3

R = alkyl C7 or less

or R = phenyl or alkyl substituted phenyl

R’ = H or alkyl C7 or less

or OR’= carboxylic acid ester, sulfate, phosphate, nitrate or

sulfonate 

CAA’s definition of Glycol ether exactly as in the statute (errors included):

“Includes mono- and di ethers of ethylene glycol, diethylene glycol, and

triethylene glycol 

R - (OCH2CH2)n-OR’ where n = 1,2, or 3

R = alkyl or aryl groups

R’ = R,H or groups which, when removed, yield glycol ethers with

the structure R-(OCH2CH)n-OH. Polymers are excluded from the

glycol category. 

CAA’s definition of Glycol ether with technical correction. (a 2 was left out

of the last formula)
A-33

“Includes mono- and di- ethers of ethylene glycol, diethylene glycol, and

triethylene glycol R-(OCH2CH2)n -OR’ where 

 n = 1, 2, or 3 

R = alkyl or aryl groups 

R’ = R, H, or groups which, when removed, yield glycol ethers with

the structure: R-(OCH2CH2)n-OH. Polymers are excluded from the

glycol category.

3- (Under Review)

4- (Under Review) 

 

5- A type of atom which spontaneously undergoes radioactive decay.

_____________________________________________________

Table 4. Priority Hazardous Air Pollutants (HAPS)

_____________________________________________________

 

 HAP CAS #

Acetaldehyde 75070

Acrolein 107028

Acrylamide 79061

Acrylonitrile 107131

Arsenic & compounds

Benzene 71432

Benzyl chloride 100447

Beryllium & compounds

bis(2-ethylhexyl)phthalate 117817

1,3-Butadiene 106990

Cadmium & compounds

Carbon tetrachloride 56235

Chlorine 7782505

Chloroform 67663

Chromium & compounds

Coke oven emissions

1,2-Dibromoethane

1,2-Dichloroethane 107062

1,4-Dichlorobenzene 106467

1,2-Dichloropropane 78875

1,3-Dichloropropene 542756

1,4-Dioxane

Ethyl acrylate

Ethylene dichloride 107062

Ethylene oxide 75218

Ethylidene dichloride 75343

Formaldehyde 50000

Glycol ethers

Hexachlorobenzene 118741

Hexachlorocyclopentadiene 77474

Hydrazine 302012

Hydrochloric acid 7647010

Lead & compounds

Maleic anhydride 108316

Manganese & compounds

Mercury & compounds

Methyl bromide

Methyl chloride 74873

Methylene chloride 75902

MDI(methylene diphenyl 106688
A-34

diisocyanate) 101688

Nickel & compounds

2-Nitropropane

Phosgene 75445

POM (PAHs)**

Quinoline 91225

2,3,7,8-TCDF/2,3,7,8-TCDD*

Tetrachloroethylene 127184

Trichloroethylene 79016

Toluene 108883

Vinyl chloride 75014

_____________________________________________________

* Inventory as TEQ.

** Inventory as sum of 16 PAH and speciate. 16 PAH compounds include: 

Acenaphthene, Naphthalene, Benzo(b)fluoranthene***, Acenaphthylene,

Phenanthrene, Benzo(k)fluoranthene***, Anthracene, Pyrene, Chrysene***,

Benzo(ghi)perylene, Benz(a)anthracene***, Dibenz(a,h)anthracene***,

Fluoranthene, Benzo(a)pyrene*** Indeno(1,2,3-cd)pyrene***, Fluorene

*** These 7 PAHs are carcinogenic and are usually reported as the sum of

7 PAH.

GLOSSARY

Activity rate/throughput (annual) - A measurable factor or parameter that

relates directly or indirectly to the emissions of an air pollution source. 

Depending on the type of source category, activity information may refer to

the amount of fuel combusted, raw material processed, product manufactured, or

material handled or processed. It may also refer to population, employment,

number of units, or miles traveled. Activity information is typically the

value that is multiplied against an emission factor to generate an emissions

estimate.

Activity rate/throughput (daily) - The beginning and ending dates and times

that define the emissions period used to estimate the daily activity

rate/throughput.

Area classification - The Clean Air Act classification of the nonattainment

area containing the reporting source (transitional, marginal, moderate,

serious, severe, extreme).

Area sources - Area sources collectively represent individual sources that

have not been inventoried as specific point, mobile, or biogenic sources.

These individual sources treated collectively as area sources are typically

too small, numerous, or difficult to inventory using the methods for the other

classes of sources.

Annual emissions - Actual emissions for a plant, point, or process - measured

or calculated that represent a calender year.

Ash content - Inert residual portion of a fuel.

Biogenic sources - Biogenic emissions are all pollutants emitted from

non-anthropogenic sources. Example sources include trees and vegetation, oil

and gas seeps, and microbial activity.

Control device type - The name of the type of control device (e.g., wet

scrubber, flaring, or process change).
A-35

County/parish/reservation (FIPS) - Federal Information Placement System

(FIPS). FIPS is the system of unique numeric codes the government developed

to identify states, counties, towns, and townships for the entire United

States, Puerto Rico, and Guam.

Day/wk in operations - Days per week that the emitting process operates.

Design capacity - A measure of the size of a boiler, based on the reported

maximum continuous steam flow. Capacity is calculated in units of MMBtu/hr.

Emission factor - Ratio relating emissions of a specific pollutant to an

activity or material throughput level. 

Exit gas flow rate - Numeric value of stack gas’s flow rate.

Exit gas temperature - Numeric value of an exit gas stream’s temperature.

Exit gas velocity - Numeric value of an exit gas stream’s velocity.

Fall throughput(%) - Part of the throughput for the three Fall months

(September, October, November). This expresses part of the of annual activity

information based on four seasons - typically spring, summer, fall, and

winter. It can be a percentage of the annual activity (e.g., production in

summer is 40% of the year’s production) or units of the activity (e.g., out of

600 units produced, spring =150 units, summer = 250 units, fall = 150 units,

and winter = 50 units).

Federal ID code (plant) - Unique codes for a plant or facility, containing one

or more pollutant-emitting sources.

Federal ID code (point) - Unique codes for the point of generation of

emissions, typically a physical piece of equipment.

Federal ID code (process) - Unique codes for the process generating the

emissions, typically a description of a process.

Federal ID code (stack number) - Unique codes for the point where emissions

from one or more processes release into the atmosphere.

Heat content - The amount of thermal heat energy in a solid, liquid, or

gaseous fuel. Fuel heat content is typically expressed in units of Btu/lb of

fuel, Btu/gal of fuel, joules/kg of fuel, etc.

Hr/day in operations - Hours per day that the emitting process operates.

Inventory end date - Last day of the inventory period.

Inventory start date - First day of the inventory period.

Inventory type - Type of inventory represented by data (i.e., point, 3-Year

cycle, daily).

Inventory year - The calendar year for which you calculated emissions

estimates.

Maximum design rate - Maximum rate of fuel use based on the equipment’s or

process’ physical size or operational capabilities.
A-36

Maximum nameplate capacity - A measure of a generator’s size that the

manufacturer puts on the unit’s nameplate. The data element is reported in MW

or KW.

Mobile source - A motor vehicle, nonroad engine or nonroad vehicle.

C A “motor vehicle” is any self-propelled vehicle used to

carry people or property on a street or highway.

C A “nonroad engine” is an internal combustion engine

(including fuel system) that is not used in a motor vehicle

or vehicle only used for competition, or that is not

affected by sections 111 or 202 of the CAA.

C A “nonroad vehicle” is a vehicle that is run by a nonroad

engine and that is not a motor vehicle or a vehicle only

used for competition.

NOx ozone season emissions - Actual ozone season emissions for a plant, point,

or process, either measured or calculated. Ozone season emissions for NOx SIP

Call are the emissions between May 1 and September 30. (Note that 40 CFR Part

58 contains a different definition for ozone season monitoring.)

Physical address - Street address of a facility.

Point source - Point sources are large, stationary (non-mobile), identifiable

sources of emissions that release pollutants into the atmosphere. State or

local air regulatory agencies define a plant as a point source whenever it

annually emits more than a specified amount of a given pollutant; these

“cutoff” levels definitions vary among state and local agencies. A stationary

source which emits less than a “cutoff” is an area source.

Pollutant code - A unique code for each reported pollutant assigned in the

EIIP Data Model. The model uses character names for criteria pollutants and

Chemical Abstracts Service (CAS) numbers for all other pollutants. You may be

using SAROAD codes for pollutants, but you should be able to map them to the

pollutant codes in the EIIP Data Model. 

Rule effectiveness (RE) - How well a regulatory program achieves all

possible emission reductions. This rating reflects the assumption that

controls typically aren’t 100 percent effective because of equipment downtime,

upsets, decreases in control efficiencies, and other deficiencies in emission

estimates. RE adjusts the control efficiency.

Rule penetration - The percentage of an area source category covered by an

applicable regulation.

SCC - Source category code. A process-level code that describes the equipment

or operation which is emitting pollutants.

Seasonal activity rate/throughput - A measurable factor or parameter that

relates directly or indirectly to the ozone season emissions of an air

pollution source. Depending on the type of source category, activity

information may refer to the amount of fuel combusted, raw material processed,

product manufactured, or material handled or processed. It may also refer to

population, employment, number of units, or miles traveled. Activity

information is typically the value that is multiplied against an emission

factor to generate an emissions estimate.

Seasonal fuel heat content - The amount of thermal heat energy in a solid,

liquid, or gaseous fuel used during the ozone season. Fuel heat content is

typically expressed in units of Btu/lb of fuel, Btu/gal of fuel, joules/kg of

fuel, etc.
A-37

Secondary control eff (%) - The emission reduction efficiency of a secondary

control device. Control efficiency is usually expressed as a percentage or in

tenths. 

Source of activity rate/throughput data - Source of data from which you got

the activity rate/throughput.

Source of emission factor - Source of data from which you got the emission

factor.

Source of fuel heat content data - Source of data from which you got the fuel

heat content.

SIC/NAICS - Standard Industrial Classification code. NAICS (North American

Industry Classification System) codes will replace SIC codes. U.S. Department

of Commerce’s code for businesses by products or services.

Site name - The name of the facility.

Spring throughput(%) - Part of throughput or activity for the three spring

months (March, April, May). See the definition of Fall Throughput.

Stack diameter - A stack’s inner physical diameter.

Stack height - A stack’s physical height above the surrounding terrain.

Start time (hour) - Start time (if available) that you used to calculate of

emissions estimates. 

State/providence/territory (FIPS) - Federal Information Placement System

(FIPS). FIPS is the system of unique numeric codes the government developed

to identify states, counties, towns, and townships for the entire United

States, Puerto Rico, and Guam.

Sulfur content - Sulfur content of a fuel, usually expressed as a percentage.

Summer throughput(%) - Part of throughput or activity for the three summer

months (June, July, August). See the definition of Fall Throughput.

Summer/winter work weekday emissions - Average day’s emissions for a typical

day. Ozone daily emissions = summer work weekday; CO and PM daily emissions =

winter work weekday.

Total capture/control efficiency - The emission reduction efficiency of a

primary control device, which shows the amount controls or material changes

reduce a particular pollutant from a process’ emissions. Control efficiency

is usually expressed as a percentage or in tenths. 

Type A source - Very large point sources defined by emission thresholds listed

in Table 1.

Type B source - Smaller point sources defined by emission thresholds listed in

Table 1.

VMT by Roadway Class - VMT expresses vehicle activity and is used with

emission factors. The emission factors are usually expressed in terms of

grams per mile of travel. Because VMT doesn’t correlate directly to emissions

that occur while the vehicle isn’t moving, these non-moving emissions are

incorporated into the emission factors in EPA’s Mobile Model.
A-38

Winter throughput (%) - Part of throughput or activity for the three winter

months (December, January, February). See the definition of Fall 

Throughput.

Wk/yr in operation - Weeks per year that the emitting process operates.

Work Weekday - Any day of the week except Saturday or Sunday.

X stack coordinate (latitude) - An object’s east-west geographical coordinate.

Y stack coordinate (longitude) - An object’s north-south geographical

coordinate.
A-39

Subpart Q - [Amended]

 3. Section 51.322 is revised to read as follows:

§51.322 Sources subject to emissions reporting.

The requirements for reporting emissions data under the plan are in

§51.001 of part 51 of this chapter.

4. Section 51.323 is revised to read as follows:

§51.323 Reportable emissions data and information.

The requirements for reportable emissions data and information under the

plan are in subpart A of part 51 of this chapter.
[This page intentionally left blank.]
TECHNICAL REPORT DATA

(Please read Instructions on reverse before completing)

1. REPORT NO.

 EPA-454/R-99-006

2. 3. RECIPIENT'S ACCESSION NO.

4. TITLE AND SUBTITLE

Emission Inventory Guidance for Implementation of Ozone and Particulate

Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze

Regulations

 

5. REPORT DATE

 April 1999

6. PERFORMING ORGANIZATION CODE

7. AUTHOR(S)

Emission Factor and Inventory Group 

 

8. PERFORMING ORGANIZATION REPORT NO.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

 U.S. Environmental Protection Agency

 Office of Air Quality Planning and Standards

 Emissions Monitoring and Analysis Division

 Emission Factor and Inventory Group 

 Research Triangle Park, NC 27711

10. PROGRAM ELEMENT NO.

11. CONTRACT/GRANT NO.

68-D7-0067, Work Assignment 2-07

E. H. Pechan 

12. SPONSORING AGENCY NAME AND ADDRESS

 Director

 Office of Air Quality Planning and Standards

 Office of Air and Radiation

 U.S. Environmental Protection Agency

 Research Triangle Park, NC 27711

13. TYPE OF REPORT AND PERIOD COVERED

Guidance Document

June 1998 - April 1999

14. SPONSORING AGENCY CODE

EPA/200/04

15. SUPPLEMENTARY NOTES

Contact Person: William B. Kuykendal (919) 541-5372

16. ABSTRACT This document provides guidance to State and local agencies for the development of emission inventories. This

guidance is specifically for emission inventories developed for ozone and PM2.5 State Implementation Plans (SIPs). Topics

covered by this guidance include: types of inventories, specification of Base Year, inventory approval, pollutants to be

inventoried, sources to be inventoried, geographic coverage, temporal basis of the inventory, data reporting requirements, and

quality assurance and inventory documentation. 

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS b. IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group

emission inventory, ozone, particulate matter, regional

haze, guidance 

 

18. DISTRIBUTION STATEMENT

 Release Unlimited

19. SECURITY CLASS (Report)

 Unclassified

21. NO. OF PAGES

116

20. SECURITY CLASS (Page)

 Unclassified

22. PRICE

EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE