Emissions Inventory Guidance for Ozone [& PM] NAAQS Implementation and Regional Haze Regulations

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* NOTE: Ozone NAAQS implementation requirements are currently being assessed as part of the Implementation 

of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements; Proposed 

Rule (78 FR 34178, June 6, 2013) (Hereinafter, “Proposed Ozone Implementation Rule”). Accordingly, the guidance 

provided in this document addresses the options that were addressed in the Proposed Ozone Implementation 

Rule, which may or may not be adopted in the final rule. The guidance provided in this draft document is not final, 

and to the extent that the Final Ozone Implementation Rule takes a different approach than contained in this 

guidance, the Final Rule will dictate what is required for the necessary emissions inventories. Once the Final 

Ozone Implementation Rule is published, EPA will revise this guidance to reflect the regulations and requirements 

adopted in the final rule.

In addition, PM NAAQS implementation requirements are currently undergoing review as part of the planned 

proposed PM2.5 Implementation Rule, so those requirements are not summarized in this draft guidance. Instead, 

this draft includes the use of “[PM Implementation Placeholder]” text where necessary. Once that rule is finalized, 

this guidance will be updated and the [PM Implementation Placeholder] text will be replaced with the PM-specific 

guidance associated with that rule.

DRAFT

Emissions Inventory Guidance for 

Implementation of Ozone [and Particulate 

Matter]

* National Ambient Air Quality 

Standards (NAAQS) and Regional Haze 

Regulations
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Table of Contents

List of Tables ................................................................................................................................................. v

Acronyms and Abbreviations Used in this Guidance................................................................................... vi

1 Introduction ..........................................................................................................................................1

1.1 Purpose .........................................................................................................................................1

1.2 Other Inventory Guidance and Resources....................................................................................2

1.3 Summary of Relevant Statutory Provisions ..................................................................................4

1.4 Summary of Guidance Contents...................................................................................................7

2 SIP Inventory Overview.........................................................................................................................8

2.1 Recommended Steps for Building the Inventory Parts of a SIP....................................................8

2.2 Discuss the Inventory Approval Process with EPA......................................................................10

2.3 Planning and Modeling Inventory Components.........................................................................11

2.3.1 Ozone SIP Inventory Components......................................................................................11

2.3.2 Annual and 24-Hour PM2.5 SIP Inventory Components ......................................................12

2.3.3 Regional Haze SIP Inventory Components..........................................................................12

2.4 Other Relevant Federal Emissions Reporting Requirements......................................................13

2.5 Emissions Inventory Definitions..................................................................................................14

2.5.1 Source Category/Data Category .........................................................................................15

2.5.2 Types of Emissions: Annual, Seasonal, Actual, Potential, and Allowable ...........................15

2.5.3 Duration and Timing of Emissions ......................................................................................17

2.5.4 Data Elements.....................................................................................................................17

2.5.5 Throughput and Activity .....................................................................................................17

2.5.6 Emission Factors..................................................................................................................18

2.5.7 Emissions Reporting Data Elements ...................................................................................18

2.5.8 Point Sources ......................................................................................................................20

2.5.9 Nonpoint Sources................................................................................................................21

2.5.10 On-road Mobile Sources.....................................................................................................21

2.5.11 Nonroad Mobile Sources ....................................................................................................22

2.5.12 Events..................................................................................................................................22

2.5.13 Biogenic Sources.................................................................................................................22

2.5.14 Inventory Codes..................................................................................................................23
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2.5.15 Point source Facility Details................................................................................................24

2.5.16 Alternative IDs.....................................................................................................................26

2.5.17 Location Definitions............................................................................................................27

2.5.18 Control Data Elements........................................................................................................27

2.5.19 EIS Sectors, Tiers, and Facility Type ....................................................................................28

2.5.20 Other Terms........................................................................................................................29

3 SIP Inventory Requirements and Recommendations.........................................................................30

3.1 Inventory Component Timing .....................................................................................................30

3.2 Inventory Preparation Plan.........................................................................................................31

3.3 Base Year Inventory ....................................................................................................................33

3.4 Rate of Progress and Reasonable Further Progress Baseline NAA Inventory.............................34

3.4.1 ROP/RFP Requirements and Timing....................................................................................34

3.4.2 ROP/RFP Inventory Guidance .............................................................................................35

3.5 Periodic Inventory.......................................................................................................................36

3.5.1 Ozone Periodic Inventory....................................................................................................36

3.5.2 Regional Haze Current Year Inventory................................................................................38

3.6 Emissions Statement Requirement for SIPs................................................................................39

3.7 Maintenance Inventories............................................................................................................39

3.8 Projected Inventories..................................................................................................................40

3.8.1 Attainment Year Projected Inventories..............................................................................40

3.8.2 Rate of Progress and Reasonable Further Progress Emissions Reductions........................41

3.9 Public Hearings............................................................................................................................42

3.10 Submit Inventory Parts of SIP to the EPA ...................................................................................43

4 Developing Current Emissions inventories.........................................................................................47

4.1 Inventory Years...........................................................................................................................47

4.2 Pollutants and Pollutant Precursors to Include in Inventories...................................................49

4.2.1 Condensable PM emissions ................................................................................................49

4.2.2 Regulatory Definition of VOC..............................................................................................49

4.2.3 Treatment of Methane .......................................................................................................50

4.3 Identification of Priority Sources................................................................................................51

4.4 Spatial Extent ..............................................................................................................................53

4.4.1 Nonattainment Areas with Partial Counties.......................................................................53
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4.4.2 Point Source Locations Needed for Modeling of Traditional Nonpoint Sources................55

4.4.3 Shapefile-based Inventories................................................................................................55

4.4.4 Link-based On-road Mobile Emissions and Travel Demand Models ..................................56

4.5 Temporal Basis............................................................................................................................56

4.6 Emission Factors for SIP Emissions Inventories..........................................................................57

4.7 Inventory Data Codes..................................................................................................................59

4.7.1 Codes to Use for Nonattainment Area Inventories............................................................59

4.7.2 How to Request New Codes or Code Retirements.............................................................59

4.8 Estimation of Base Year Emissions..............................................................................................60

4.8.1 Stationary Point ..................................................................................................................60

4.8.2 Stationary Nonpoint............................................................................................................64

4.8.3 On-road Mobile...................................................................................................................68

4.8.4 Nonroad Mobile Equipment ...............................................................................................69

4.8.5 Other Nonroad Mobile........................................................................................................70

4.8.6 Biogenic and Geogenic Sources..........................................................................................78

4.8.7 Wildland Fires .....................................................................................................................81

4.9 Quality Assurance .......................................................................................................................82

4.9.1 QA Reference Materials and Planning ................................................................................83

4.9.2 Types of Problems in Emissions Inventories.......................................................................83

4.9.3 Checks Available Through the EPA’s Emissions Inventory System .....................................84

4.9.4 Inventory Comparisons.......................................................................................................85

4.9.5 Checking Data Codes...........................................................................................................86

4.9.6 Point Versus Nonpoint and Reconciliation .........................................................................86

4.9.7 Ranking Techniques............................................................................................................87

4.9.8 Outlier Analyses..................................................................................................................88

4.9.9 Using Maps to QA Nonpoint Emissions ..............................................................................89

4.9.10 Expected Pollutants ............................................................................................................89

4.9.11 Facility and Release Point Locations...................................................................................90

4.9.12 Release Point Parameters...................................................................................................91

4.9.13 Biogenic QA/QC...................................................................................................................92

4.9.14 Timing of QA and Follow-up ...............................................................................................92

5 Developing Projected Emissions Inventories......................................................................................94
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5.1 Projected Emissions Overview....................................................................................................94

5.2 Identify and Prioritize Key Sectors and Regions for Projections.................................................95

5.3 Collect Available Data and Models for Each Sector Needing Projections ..................................96

5.3.1 Stationary Sources ..............................................................................................................96

5.3.2 On-Road Mobile Sources ....................................................................................................99

5.3.3 Nonroad Mobile Equipment ...............................................................................................99

5.3.4 Other Nonroad Mobile Sources........................................................................................100

5.3.5 Other Projection Resources..............................................................................................101

5.4 Evaluate and Refine Data for Projections in Inventory Region.................................................104

5.5 QA for Projected Inventories....................................................................................................104

6 References ........................................................................................................................................106
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List of Tables

Table 1: List of estimation resources for emissions inventories...................................................................2

Table 2: Steps for building the inventory parts of a SIP................................................................................9

Table 3: Tangible products for possible inclusion in inventory efforts.......................................................10

Table 4: Ozone SIP emissions inventory components................................................................................11

Table 5: PM2.5 SIP emissions inventory components..................................................................................12

Table 6: Regional Haze SIP emissions inventory components....................................................................13

Table 7: Point source reporting thresholds (potential to emit) for criteria pollutants in the Air Emissions 

Reporting Rule..............................................................................................................................21

Table 8: Timing of emissions inventory components.................................................................................30

Table 9: Checklist of elements to consider for including in Inventory Preparation Plans..........................32

Table 10: Conditions for AERR submittal to meet ozone periodic inventory requirement........................37

Table 11: Conditions for AERR submittal to meet regional haze periodic inventory requirement............38

Table 12: Suggested Elements of an Emissions inventory SIP ....................................................................43

Table 13: Summaries to include in the background ...................................................................................45

Table 14: Summaries to include in the point sources section....................................................................46

Table 15: Summaries to include in the nonpoint and mobile sources sections.........................................46

Table 16: Source types expected to include condensable PM+..................................................................49

Table 17: Hierarchy of emission factors for use in point source emissions inventories ............................58

Table 18: List of nonpoint categories, pollutants, and available approaches and tools.............................65

Table 19: Aircraft SCCs and Data Categories in EPA Estimates...................................................................71

Table 20: Commercial marine SCCs and emission types in EPA emissions.................................................74

Table 21: Commercial marine vessel recent regulations and impacted pollutants ...................................74

Table 22: : Current EPA methods for commercial marine vessel emissions...............................................75

Table 23: Locomotive SCCs.........................................................................................................................77
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Acronyms and Abbreviations Used in this Guidance

AEO Annual Energy Outlook

AERR Air Emissions Reporting Rule

APU Auxiliary power unit

BEIS Biogenic Emissions Inventory System

BELD3 Biogenic Emissions Land Use Database, version 3

AT Air Taxis

C1 Category 1 (marine vessel)

C2 Category 2 (marine vessel)

C3 Category 3 (marine vessel)

CAA Clean Air Act

CAMD Clean Air Markets Division

CAP Criteria air pollutant

CAS Chemical Abstracts Service

CEMS Continuous Emissions Monitoring System(s)

CMV Commercial marine vessel

CNG Compressed natural gas

CO Carbon monoxide

CO2 Carbon dioxide

DARS Data Attribute Rating System

DOE Department of Energy

ECA-IMO Emissions Control Area-International Maritime Organization

EDMS Emissions and Dispersion Modeling System

EGU Electric Generating Unit

EIA Energy Information Administration

EIIP Emissions inventory Improvement Program

EIS Emissions Inventory System

EMCH Emissions Modeling Clearinghouse

EPA Environmental Projection Agency

EPMM Electric Power Market Model

ERTAC Eastern Regional Technical Advisory Committee

FAA Federal Aviation Administration

FHWA Federal Highway Administration

FIPS Federal Information Processing Standards

FRS Federal Registry Service

GA General aviation

GHG Greenhouse gas

GIS Geographic Information Systems

GloBEIS Global Biosphere Emissions and Interactions System

GSE Ground support equipment

HAP Hazardous air pollutant
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Hg Mercury

HCl Hydrochloric acid

IPM Integrated Planning Model

IPP Inventory Preparation Plan

LPG Liquified petroleum gas

LTO Landing and takeoff

MARKAL Market Allocation (model)

MEGAN Model of Emissions of Gases and Aerosols from Nature

MIMS Multimedia Integrated Modeling System

MOVES Motor Vehicle Emissions System

NAAQS National Ambient Air Quality Standards

NAA Nonattainment area

NAICS North American Industry Classification System

NATA National Air Toxics Assessment

NEEDS National Electric Energy Data

NEI National Emissions Inventory

NEMS National Energy Modeling System

NESHAP National Emission Standard for Hazardous Air Pollutants

NH3 Ammonia

NLDN National Lightning Detection Network

NMIM National Mobile Inventory Model

NONROAD Nonroad emissions model

NMHC Non-methane hydrocarbon

NOX Nitrogen Oxides

O3 Ozone

OAP Office of Atmospheric Programs

OAQPS Office of Air Quality Planning and Standards

OAR Office of Air and Radiation

OECA Office of Enforcement and Compliance Assurance

ORIS Office of Regulatory Information Systems

OTAQ Office of Transportation Air Quality

PM Particulate matter

PM2.5 Particulate matter with diameter 2.5 microns and less

PM10 Particulate matter with diameter 10 microns and less

QAPP Quality Assurance Project Plan

RICE Reciprocating Internal Combustion Engines

RFP Reasonable Further Progress

ROP Rate of Progress

SCC Source classification code

SIP State implementation plan

SMOKE Sparse Matrix Operator Kernel Emissions

SO2 Sulfur Dioxide
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SSM Startup, Shutdown, and Malfunction

STEEM Ship Traffic, Energy and Environmental Model

TAF Terminal Area Forecast

TCA 1,1,1-trichloroethane

TDM Travel demand model

TIP Tribal Implementation Plan

TOG Total organic gases

TRI Toxics Release Inventory

U.S. United States

USDA U.S. Department of Agriculture

VMT Vehicle miles traveled

WFU Wildland fire use

WLF Wildland fire

WRF Weather Research and Forecasting

VOC Volatile organic compounds
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1 Introduction

1.1 Purpose

This document provides guidance on how to develop emissions inventories to meet state 

implementation plan (SIP) requirements for complying with the 8-hour ozone national ambient air 

quality standard (NAAQS)1, [the daily and annual fine particulate matter (PM2.5) NAAQS]

2

, and the 

regional haze regulations. It is intended for use by the United States (U.S.) Environmental Protection 

Agency (EPA) regional offices; state, local and tribal air quality management authorities; and the general 

public. This guidance is designed to implement national policy on these emissions inventories as 

embodied in the Clean Air Act (CAA), the Proposed Ozone SIP Requirements Rule (also called the 

Proposed Ozone Implementation Rule)3, the PM2.5

4

Implementation Rule5, and the Regional Haze Rule.

This document does not substitute for provisions or regulations of the CAA enumerated above, nor is it a 

regulation itself. As the term “guidance” suggests, it provides recommendations on how to implement 

the inventory requirements. Thus, it does not impose binding, enforceable requirements on any party, 

nor does it assure that the EPA will approve all instances of its application, as the guidance may not 

apply to a particular situation based upon the circumstances. 

The EPA and state, local, and tribal decision makers retain the discretion to adopt approaches on a caseby-case basis that differ from this guidance where appropriate. Final decisions by the EPA regarding a 

particular SIP demonstration will only be made based on the statute and regulations, and will only be 

made following a final submission and after notice and opportunity for public review and comment. 

Interested parties are free to raise questions and objections about the appropriateness of the 

application of this guidance to a particular situation; the EPA will, and state, local, and tribal air agencies

should, consider whether or not the recommendations in this guidance are appropriate in that situation.

 

1

As noted on the title page, Ozone NAAQS implementation requirements are currently being assessed as part of the 

Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements; 

Proposed Rule (78 FR 34178, June 6, 2013) (Hereinafter, “Proposed Ozone Implementation Rule”). Accordingly, the guidance 

provided in this document addresses the options that were addressed in the Proposed Ozone Implementation Rule, which 

may or may not be adopted in the final rule. The guidance provided in this draft document is not final, and to the extent that 

the Final Ozone Implementation Rule takes a different approach than contained in this guidance, the Final Rule will dictate 

what is required for the necessary emissions inventories. Once the Final Ozone Implementation Rule is published, EPA will 

revise this guidance to reflect the regulations and requirements adopted in the final rule.

2

As noted on the title page, PM NAAQS implementation requirements are currently undergoing review as part of the

planned proposed PM2.5 Implementation Rule, so those requirements are not summarized in this draft guidance. Instead, this 

draft includes the use of “[PM Implementation Placeholder]” text where necessary. Once that rule is finalized, this guidance 

will be updated and the [PM Implementation Placeholder] text will be replaced with the PM-specific guidance associated with 

that rule.

3

Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan 

Requirements; Proposed Rule (78 FR 34178, June 6, 2013)

4

PM2.5 is particulate matter with diameter 2.5 microns and less

5

Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements, 

proposed rule anticipated in mid 2014.
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Through the provisions of the Tribal Authority Rule, tribes are not required to develop emissions 

inventories. If tribes choose to develop an emissions inventory that may become part of a SIP or Tribal 

Implementation Plan (TIP) inventory covered by this guidance, the tribes are encouraged to follow the 

provisions of this guidance. Notwithstanding the possible development by local and tribal air agencies, 

inventories prepared for NAAQS implementation will be called SIPs in the remainder of this document.

1.2 Other Inventory Guidance and Resources

This document is a guide for state, local, and tribal air agencies (called “air agencies” in this guidance) 

for preparing and submitting their emissions inventories for the 8-hour ozone NAAQS and [PM 

Implementation Placeholder], and for the regional haze program. It is not a procedures document that 

comprehensively covers the methods for compiling and documenting emissions inventories. 

Furthermore, the predecessors to this guidance have historically relied on separate guidance documents 

to add information for various specific purposes. In Section 2.3, we list the various inventory 

components needed for 8-hour ozone, PM2.5, and regional haze implementation and identify the 

associated sections of this guidance and other relevant guidance materials.

In addition to this guidance, the “Guidance on the Use of Models and Other Analyses for Demonstrating 

Attainment for Air Quality Goals for Ozone, PM2.5, and Regional Haze” (http://www.epa.gov/ttn/

scram/guidance_sip.htm), or “Modeling Guidance”, covers the creation of emissions inventories for use 

in air quality modeling. These modeling inventories differ from the inventories covered in this 

document in that they usually have a larger spatial extent (i.e., a multi-state area as opposed to just the 

nonattainment area) and require extra processing steps to obtain the spatial and temporal resolution of 

the air quality model input species. To the extent the Modeling Guidance covers future-year emissions, 

efforts have been made to harmonize the future-year guidance in that Guidance with the information 

included in Section 5 of this document.

A number of inventory development resources are available for use by air agencies for estimating base 

year emissions inventories. Table 1 provides these references and a brief description of how they can be 

used. More information on how these resources can be applied is provided in Sections 4 and 5.

Table 1: List of estimation resources for emissions inventories

Resource and website Description 

National Emissions Inventory (NEI)

(www.epa.gov/ttn/chief/

eiinformation.html)

Summaries of the latest NEI data and documentation are 

available from links provided at this website. More detailed 

data are available to air agencies from the Emissions

Inventory System (EIS).

Emission Factors used for the National 

Emissions Inventory (NEI)λ

(www.epa.gov/ttn/chief/

eiinformation.html)

The National Emissions Inventory (NEI) program provides 

emissions estimation tools (that include emission factors) 

and point-source emission factors based on EPA rule 

development efforts. In many cases, these factors are more 

recent than those in WebFire and AP-42, and agencies are 

encouraged to rely on these where available. 

Emissions Inventory System The EIS allows for summaries and extraction of detailed data 
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Resource and website Description 

(www.epa.gov/ttn/chief/eis/) for use by air agencies. The EIS allows both state-submitted 

as well as the composite EPA-state data used for the NEI to 

be queried and downloaded. Training on reports is also 

available, and Appendix A provides an EIS quick reference for 

county and facility reports.

Local-scale emissions inventory

development

(www.epa.gov/ttn/chief/

local_scale/)

In 2010, the EPA completed a project to assess the building 

of multi-pollutant inventories at the scale of nonattainment 

areas. A project description and the final report are 

available; the latter documents the recommended actions 

for state and local agencies that want to develop local-scale 

emissions inventories, including SIP planning inventories.

Electric Generating Unit emissions data 

from Continuous Emissions 

Monitoring Systems (CEMS)

∆

(ampd.epa.gov/ampd)

Carbon dioxide (CO2), nitrogen oxides (NOX), sulfur dioxide 

(SO2), and heat input data from Electric Generating Units 

(EGUs) collected by the EPA. Heat input data can be used to 

estimate hourly emissions of other pollutants using emission 

factors.

Emissions Inventory Improvement 

Program (EIIP) Documentation, 

Volumes 1-9. (www.epa.gov/ttn/

chief/eiip/techreport/)

Emissions estimation procedures for point, area (nonpoint) 

and mobile sources. While much of the information included 

in these reports is still relevant, the EIIP documentation for 

point and nonpoint sources has some outdated parts, and 

the sections below indicate some of those limitations and 

alternative resources. The EIIP documentation for mobile 

sources (volume 4) is out of date because it refers to 

previous versions of EPA emissions models. Use more 

current resources, listed below for mobile sources and fires. 

While EIIP is also out of date for biogenic sources, these 

sources are relevant only for modeling inventories and not 

for the inventories covered by this guidance.

Emission Factors – WebFire and 

AP-42 (www.epa.gov/ttn/chief/

efpac/index.html)

Emission factors are used to estimate emissions, generally by 

multiplying by some activity value for that emissions activity, 

where no better method of emissions quantification or 

estimation is available. AP-42 is not an appropriate source 

of emission factors for mobile sources other than road dust.

General Principles for the 5-Year 

Regional Haze Progress Reports for 

the Initial Regional Haze State 

Implementation Plans 

(www.4cleanair.org/Documents/

haze_5year_4-10-13.pdf) 

This document has been developed by the EPA for the EPA 

regional offices and states in preparing and reviewing the 

5-year progress reports for the initial regional haze SIPs. This 

document summarizes and clarifies the requirements for the 

first 5-year reports, including emissions inventory aspects.
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Resource and website Description 

Motor Vehicle Emissions System 

(MOVES) (www.epa.gov/otaq/

models/moves/)

The model, technical documentation, and guidance on the 

use and application of the MOVES model for on-road mobile 

sources.

Nonroad Emissions model (NONROAD) ‡

(www.epa.gov/otaq/nonrdmdl.htm)

The model and technical documentation on the use of the 

NONROAD model for nonroad equipment. 

National Mobile Inventory Model 

(NMIM) (www.epa.gov/otaq/

nmim.htm)

NMIM is also used in conjunction with NONROAD. It runs 

NONROAD but includes some additional features, such as 

the computation of ammonia (NH3) emissions.

Mobile sources Policy and Guidance

(www.epa.gov/otaq/

stateresources/policy/)

Webpage that provides state and local agencies with 

direction on how to implement strategies for controlling 

emissions from mobile sources. Includes links to guidance 

documents that describe process for securing SIP air quality 

credits for voluntary and innovative emission reduction 

programs.

Transportation Conformity

(www.epa.gov/otaq/

stateresources/transconf/)

General information, policy and technical guidance about 

transportation conformity.

λ From this main web page, obtain factors using the link to the latest available NEI or NEI Plan.

∆ Select “Data Sets and Published Reports”.

‡ The NONROAD model is expected to be superseded by the MOVES model once nonroad sources are included in MOVES.

In addition to base year emissions, emissions projections are needed for a variety of reasons, including 

redesignation maintenance plans, the attainment projected inventory for a nonattainment area (NAA), 

and air quality modeling for attainment plans. In Section 5, this guidance provides information on 

methods for emissions projections. The EPA provides emissions projections data and documentation as 

part of its modeling platforms, which are available at the Emissions Modeling Clearinghouse

(http://www.epa.gov/ttn/chief/emch/index.html). On-road mobile source projections are covered in the 

on-road mobile regulatory documentation associated with MOVES. Nonroad mobile projections are 

included as part of the NMIM and the NONROAD model documentation for nonroad equipment and as 

part of this documentation in the nonroad mobile sources part of Section 5.

1.3 Summary of Relevant Statutory Provisions

Numerous sections of the CAA apply to the implementation of emissions inventory requirements. This 

section provides a brief synopsis of some of those sections that may be relevant for reference in later 

sections of this guidance. All of the sections below are a part of CAA Title I – Programs and Activities.

 Section 110(a) describes the basic requirements for SIPs, which provide for 

implementation, maintenance, and enforcement of the NAAQS. 

o Section 110(a)(1) specifies parameters for infrastructure SIPs

o Section 110(a)(2) specifies a “notice and public hearing” process is needed

o Section 110(a)(2)(F) specifies that infrastructure SIPs shall require, as may 

be prescribed by the EPA Administrator, “periodic reports on the nature and 

General
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amounts of emissions and emissions-related data” from stationary sources.

o Section 110(a)(2)(K) requires infrastructure SIPs to include air quality 

modeling as determined necessary by the Administrator and allows the EPA

to require the submission upon request of data related to that air quality 

modeling.

o Section 110(a)(2)(J) addresses requirements related to Part C of the CAA, 

related to prevention of significant deterioration and visibility protection.

 Section 110(p) requires states to submit “reports” according to the Administrator’s 

schedule, “relating to emissions reductions, vehicle miles traveled, congestion 

levels, or any other information the Administrator may deem necessary to assess 

the development effectiveness, need for revision, or implementation of any plan or 

plan revision” for a SIP. Also known as “infrastructure SIP” requirements, readers 

should refer to the “Guidance on Infrastructure State Implementation Plan (SIP) 

Elements under Clean Air Act Sections 110(a)(1) and 110(a)(2); September 2013; 

http://www.epa.gov/oar/urbanair/sipstatus/infrastructure.html.

General

 Sections 169A and 169B focus on visibility protection for Federal class I areas and 

require the EPA to promulgate regulations establishing requirements for 

implementation plans to assure reasonable progress towards improving visibility. To 

do this, the EPA has codified the regional haze program requirements in 40 CFR

51.308 and 51.309.

Regional 

Haze

 Section 172(c)(3) is a part of Part D, Subpart 1, which describes NAA SIP 

requirements for all criteria air pollutants (CAPs) – carbon monoxide, lead, nitrogen 

dioxide, ozone, particulate matter, and sulfur dioxide – that, unless superseded by 

subsequent NAAQS-specific subparts, apply to SIPs for NAAs submitted to the EPA. 

This section includes a requirement that such SIPs include a current inventory of 

actual emissions in a NAA. It allows the EPA Administrator to require periodic 

updates needed to determine if the general requirements of nonattainment SIPs

(i.e., Subpart 1) are met.

General

 Section 175A describes maintenance plans, which are SIP revisions that provide for 

the maintenance for 10 years of any primary NAAQS for which an area has been 

redesignated to attainment and may include additional control measures necessary 

to ensure this maintenance. Updated emissions inventories are to be included in a 

maintenance plan.

General
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 Section 182(a)-(f) provide SIP requirements for areas designated as nonattainment 

for the ozone NAAQS and classified as Marginal and above.

o Section 182(a)(1) requires a current and comprehensive inventory of actual 

emissions of all sources of ozone precursors to be included in a SIP.

o Section 182(a)(3)(A) requires periodic inventories to be provided until an 

area is redesignated to attainment no later than the end of each 3-year 

period after the submission of the inventory for 182(a)(1).

o Section 182(a)(3)(B) requires areas classified as Marginal and above to 

include in their SIP a requirement for stationary sources of NOX and volatile 

organic compounds (VOC) to provide the state with a statement showing 

actual emissions of NOX and VOC. 

o Section 182(c) defines major sources for areas classified as Serious as 

sources that emit or have the potential to emit at least 50 tons of VOC per 

year.

o Section 182(d) defines major sources for areas classified as Severe as 

sources that emit or have the potential to emit at least 25 tons of VOC per 

year.

o Section 182(e) defines major sources for areas classified as Extreme as 

sources that emit or have the potential to emit at least 10 tons of VOC per 

year.

o Section 182(f) requires that all major source requirements for VOC also 

apply for NOX unless a waiver is received.

Ozone

 Section 182(b)(1) includes SIP requirements for ozone NAAs classified as Moderate 

and above. 

o Section 182(b)(1)(A) requires a rate of progress (ROP) demonstration, and 

describes requirements for annual reductions in VOC and NOX emissions as 

necessary to attain the ozone NAAQS. 

o Section 182(b)(1)(B) requires a baseline emissions inventory for NOX and 

VOC from all anthropogenic sources in the NAA to be included in ozone SIPs 

for purposes of ROP/RFP. 

Ozone

 Section 182(c)(2) provides a SIP requirement for ozone NAAs classified as Serious 

and above. 

o Section 182(c)(2)(A) requires an attainment demonstration based on 

photochemical modeling. A modeling inventory is needed for the 

attainment demonstration analysis.

o Section 182(c)(2)(B) requires a RFP demonstration, and describes 

requirements for a timeline of VOC emissions reductions. RFP 

demonstrations must include baseline emissions for comparison against the 

emissions reductions.

Ozone
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 Section 182(j)(1) requires states in a multi-state ozone NAA to take all reasonable 

steps to coordinate, substantively and procedurally, the revisions and 

implementation of SIPs for a multi-state ozone NAA. Ozone

 Section 189(a)(2) in Part D, Subpart 4 provides a different and earlier schedule (18 

months rather than 3 years) for PM SIPs than does the general provision in Part D, 

Subpart 1. PM2.5

 Section 189(b)(3) (also Part D, Subpart 4) defines major sources in Serious PM NAAs 

as sources that emit 70 tons per year of PM10. Inventories for PM SIPs for Serious 

NAAs should include these smaller point sources using the lower threshold. The 

appropriate threshold for PM2.5 areas needs to be defined by an EPA rule.

PM2.5

1.4 Summary of Guidance Contents

This guidance document will define parts of and considerations for emissions inventories to meet SIP 

requirements for complying with the 8-hour ozone NAAQS, [the PM NAAQS (24-hour and annual)], and 

the regional haze regulations. Section 2 provides an overview of the creation, documentation, and 

submission of the planning inventories. Section 3 has subsections for each of the separate inventory 

requirements or recommendations, with details provided for all requirements except the base year and 

projected emissions inventories. Sections 4 and 5 provide the detailed guidance on developing base year 

emissions inventories and projected emissions inventories, respectively.
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2 SIP Inventory Overview

There are two categories of emissions inventories associated with SIP development: planning

inventories and modeling inventories. Modeling inventories are used for modeled attainment 

demonstrations. Planning inventories are any other inventories associated with SIPs. The primary focus 

of this guidance is the planning inventories, whereas the emissions modeling guidance guidance is 

provided separately in the Modeling Guidance document (see Section 1.2).

Generally, the EPA recommends that the planning inventories and modeling inventories be consistent, 

though there are exceptions. The exceptions are noted where they arise throughout this guidance and 

the Modeling Guidance; however, the EPA encourages air agencies to minimize inconsistencies. 

The many aspects of planning inventories are covered more thoroughly in Section 3. These aspects 

include the timing for submitting the various inventory components, the inventory preparation plan

(IPP), the base year NAA inventory, the RFP baseline inventory, the ozone periodic inventory, the ozone 

emissions statement requirement for SIPs, the maintenance inventory, the attainment projected 

inventory for the NAA, public hearings, and inventory approval by the EPA.

In this section, we provide an overview of the creation, documentation, and submission of the planning 

inventories. Section 2.1 lists the various steps associated with building the planning inventory parts of a 

SIP and identifies the relevant sections of this document that address those steps. The discussions 

between air agencies and the EPA regarding the inventory approval process is described in Section 2.2. 

In Section 2.3, we list all of the required inventory components, including modeling inventories that are 

needed for ozone, PM2.5, or regional haze, but otherwise defer to the Modeling Guidance for the factors 

for air agencies to consider in building those inventories. In Sections 2.4, and 2.5, we describe other 

federal emissions reporting requirements that are relevant to NAAQS implementation and provide 

definitions of key terms needed to understand, develop, and submit emissions inventories for SIPs. 

2.1 Recommended Steps for Building the Inventory Parts of a SIP

Throughout this document, we describe many technical components that could be included in

inventories in a SIP for ozone, PM2.5, or regional haze implementation. Before air agencies start to create 

those components, it is important to recognize that there is a process associated with building them. 

This section describes the process agencies should undertake for a successful inventory development 

and submittal effort. 

The inventory development process involves both required and optional steps. Some optional steps may 

be taken by the air agency if it believes it is in its best interest to do so, and optional steps can also 

become critical to a particular SIP development process and identified as such by an EPA regional office. 

Thus, a fundamental part of the process is establishing and maintaining open lines of communication 

between the air agency and the respective regional office. The regional office should be viewed by the 

air agency as the typical starting point for questions related to planning and modeling inventory 

development, and the regional office staff will direct questions needing EPA headquarters input as they 

arise.
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A key aspect of this guidance is identifying opportunities for states to leverage existing work to help 

them meet the implementation requirements. This starts in Section 2.4 with a description of how work 

done in support of the National Emissions Inventory can be helpful for the SIP inventory work. 

Table 2 provides a list of steps for completing the planning inventory and related parts of a SIP. The list is 

provided in groups of steps that occur in phases presented roughly in chronological order. The second 

column of the table indicates the section(s) of this document the give more information on the 

particular step.

Table 2: Steps for building the inventory parts of a SIP

Inventory-related SIP development step Document 

section

Planning

 Review this guidance. All

 Become familiar with inventory development resources.

1.1

1.2

 During development of the Inventory Preparation Plan, clarify and discuss the

inventory approval process that your regional office will use, including all 

requirements, reporting formats and elements to be included, timing, and 

technical documentation contents.

2.2

(general)

3.1 (timing)

 Understand required and potentially required inventory components for the SIP. 

Determine which inventories must be created for your SIP. 2.3

 Understand inventory definitions and data requirements. 2.5

 Understand timing requirements of submitted components. 3.1

 Prepare and finalize the Inventory Preparation Plan. 3.2

 Understand requirements and choose key inventory features, including inventory 

year(s), the pollutants and precursors to be included, and priority emissions 

sources.

4

Creating Inventories

 Assess what inventories already exist that can be used as a starting point.

2.4

3.3

 Create base-year planning inventories. 4

 Quality assure and refine base year inventory data in accordance with the IPP 

and/or Quality Assurance Project Plan (QAPP).

4.9

 Create projected planning emission inventories. 5

 Quality assure and refine projected planning emission inventories in accordance 

with the IPP and/or QAPP.

Preparing Documentation

 Review requirements with respective regional office in light of the particular 

challenges associated with a given SIP development process, such a first 

nonattainment SIP development for a state, area, or air agency staff.

2.2

 Prepare documentation. 3.10

Public Hearings 3.9

Submit to the EPA for Approval 3.10
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2.2 Discuss the Inventory Approval Process with EPA

Early in the SIP planning process, air agencies should discuss the emissions inventory approval process 

for that specific SIP with their respective EPA regional office. These discussions should address the

tangible items (e.g., reports, data files, summary spreadsheets) that will be delivered to the EPA as

necessary to support EPA’s review and approval. Of the emissions inventories that air agencies submit to 

the 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 emissions inventory as a component of a SIP 

submittal that requires EPA review and approval.

As new issues arise during the SIP development process, air agencies or the EPA regional offices may 

need to reassess the previously discussed inventory approval process. Both agencies should be aware of 

possible changes that are needed as the inventory development process occurs, and either party should 

raise concerns about the need for discussion and possible revision of the process. Details of the process 

and documentation can be modified through additional discussions as the need arises. As the inventory 

development process works far better when lines of communication remain open, the EPA encourages 

periodic coordination meetings or check-ins during the inventory development periods.

Table 3 provides a list of tangible reports, summaries, and data files that could be included as part of the 

inventory efforts for SIPs. While many of these items are needed to meet statutory and/or regulatory 

requirements, the form of reports, summaries, and data files to be included need to be clarified by the 

regional office at the start of the inventory development process for SIPs. States should discuss and 

confirm with the EPA regional office the items to be included in the SIP to avoid inadvertent omission of 

items required for approval of the inventory parts of the SIP.

Table 3: Tangible products for possible inclusion in inventory efforts

Inventory Item for SIPs Ozone [PM2.5

+

]

Regional 

Haze

Planning Inventories

Inventory Preparation Plan X X

Emissions Inventory Report, with explanations of methods, 

quality assurance and emissions summaries. All inventories 

can be included in such a report, including base year and

projected inventories. The inventories to be included 

depend on the NAAQS, the nonattainment classification, 

and the stage of implementation (initial SIP, redesignation, 

etc.).

X X

Spreadsheets of emissions summaries included in the inventory 

report

X X

Detailed emissions inventory files, databases, or spreadsheets X X

Modelin

g 

Inventori

es

Modeling Demonstration Report – The emissions information can 

be a section in a larger report or could have its own report. 

The content should include methods, quality assurance, and 

emissions summaries for the modeling inventories, 

X X
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including projected inventories. A statewide emissions 

summary is needed, and this can be included in the 

planning inventory SIP for convenience.

Spreadsheet summaries of emissions inventory used for modeling X X

Detailed emissions inventory files, databases, or spreadsheets X X

Detailed data about emissions controls used to model attainment X X

Other

Emission Statement SIP showing the state’s program to require 

sources to submit emissions statements annually X

+

PM2.5 Implementation Placeholder

2.3 Planning and Modeling Inventory Components

The ozone, PM2.5, or regional haze implementation rules have specific inventory requirements for SIPs to 

support attainment, maintenance, and/or reasonable progress. Additionally, there are possible 

inventory details that could be required or advisable for various reasons. One distinction between the

inventory requirements of the Ozone and PM2.5 Rules versus the Regional Haze Rule is that the former

requires inventories for NAAs, while the latter requires statewide inventories. This section provides a list

for each of the three rules for the required and possible inventory components of SIPs, with additional 

details for the types of planning inventories. 

2.3.1 Ozone SIP Inventory Components

The Proposed Ozone Implementation Rule (40 CFR Part 51, Subpart AA), when finalized, will provide the 

regulatory requirements for inventories of actual emissions that support ozone NAAQS implementation 

by air agencies. In Table 4 below, we list the inventory components that could be part of an ozone SIP 

and identify the governing portion of the CAA and the applicable guidance in which they are addressed.

For state or other air agencies that perform modeled attainment demonstrations, please also refer to 

the Modeling Guidance (http://www.epa.gov/ttn/scram/guidance_sip.htm), which includes a section on 

emissions inventories for modeling. As part of that guidance, summaries are described for statewide 

inventories. For convenience, these summaries of modeling inventories can be submitted with the 

emissions inventory SIP even though they are not essential for meeting the planning inventory 

requirements. In areas where modeled attainment demonstrations are not a required part of a SIP, the 

state or other air agency would not need to provide the statewide inventories for ozone.

Table 4: Ozone SIP emissions inventory components

Inventory Component Required by CAA? 

(CAA Section)

Guidance Sections and/or 

Document(s)

Inventory Preparation Plan This document, Section 3.2

Base year NAA inventory Yes

182(a)(1)

This document, Section 3.3 and 

Section 4

ROP/RFP baseline NAA inventory (part of 

the ROP/RFP plan(s); for Moderate 

and above areas)

Moderate & above:

182(b)(1)(B)

Serious & above: 

182(c)(2)(B)

This document, Section 3.4 and 

Section 4
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Inventory Component Required by CAA? 

(CAA Section)

Guidance Sections and/or 

Document(s)

Periodic NAA inventory Yes

182(a)(3)

This document, Section 3.5 and 

Section 4

Maintenance NAA inventory

Yes+

175A(a)

This document, Section 3.7 and 

Section 4

Attainment projected inventory for the 

NAA‡

This document, Section 3.8 and 

Section 5

Source Emission Statements 

requirement for SIPs

Yes

182(a)(3)(B) This document, Section 3.6

Inventories for modeled attainment 

demonstrations (base and projected 

attainment year)

Yes∆

182(c)(2)(A)

Modeling Guidance. Summaries of 

statewide inventories (base and 

projected attainment year) are 

needed for review by the EPA.

Public hearing requirement for SIP 

inventories

Yes

110(a)(2)

This document, Section 3.9

Planning inventory documentation This document, Section 3.10

+ Maintenance NAA inventories are only associated with maintenance SIPs rather than attainment demonstration SIPs.

‡ If this inventory is the mechanism by which the ROP/RFP plan requirements will show the emissions reductions required for 

ROP/RFP, then this inventory or its summary would necessarily become part of the ROP/RFP plan(s). Motor vehicle emissions 

budgets for purposes of transportation conformity are the on-road portion of the projected emissions associated with the 

ROP/RFP plan.

∆ While modeling inventories are not an explicit requirement of the CAA, it is presumed here that states would not be able to 

perform credible modeled attainment demonstrations without modeling inventories.

2.3.2 Annual and 24-Hour PM2.5 SIP Inventory Components

[PM Implementation Placeholder]

Table 5: PM2.5 SIP emissions inventory components

Inventory Component Required by CAA? 

(CAA Section)

Guidance Sections and/or 

Document(s)

2.3.3 Regional Haze SIP Inventory Components

The Regional Haze Rule (40 CFR Part 51, Subpart P) provides the regulatory requirements for inventories 

of actual emissions supporting regional haze implementation by state or other air agencies. In Table 6

below, we list the inventory components that could be part of a Regional Haze SIP and identify the 

applicable guidance.

States are also required to periodically report on emissions progress at 5-year intervals to ensure that 

they are on track to meet the established visibility goals. To make this comparison, states have to 
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compare the inventories from two distinct time periods. These reports are due in the form of a SIP 

revision every five years. Additional information is available on how to select inventories for comparison 

in “General Principles for the 5-Year Regional Haze Progress Reports for the Initial Regional Haze State 

Implementation Plans” (http://www.4cleanair.org/Documents/haze_5year_4-10-13.pdf).

Unlike the requirements for the ozone and PM2.5 NAAQS, the Regional Haze Rule requires statewide 

planning inventories rather than inventories for only a smaller NAA. The Regional Haze Rule in 40 CFR

51.308(d)(4)(v) also requires the statewide inventory of emissions to include emissions for a “baseline” 

year and for the most recent year in which data are available (“current year”). In practice, the “baseline” 

inventory has needed to reflect a year from the 2000-2004 baseline period. A separate “current year” 

inventory requirement exists, and for the initial Regional Haze SIPs, the baseline year and current year 

inventories are fulfilled with the same inventory. For the subsequent 5-year progress report and 10-year 

SIP revisions, the current year inventory will reflect an updated inventory from that initial baseline using 

a more current year.

Table 6: Regional Haze SIP emissions inventory components

Inventory Component Required?

(CAA Section)

Guidance Sections and/or 

Document(s)

Inventory Preparation Plan This document, Section 3.2

Baseline statewide inventory Yes

169A(b)+

This document, Section 3.3 and 

Section 4

Current year statewide inventory Yes

169A(b)+

This document, Section 3.5 and 

Section 4

Progress Report, including an updated 

current year statewide inventory and 

other emissions summaries and analyses

Yes

169A(b)+

This document, Section 3.5 and 

Section 4

Projected statewide inventory 

Yes

169A(b)+

This document, Section 3.8 and 

Section 5

Inventories for modeled reasonable progress 

(baseline and projected) Yes‡ Modeling Guidance

Public hearing requirement for SIP 

inventories

Yes

110(a)(2) This document, Section 3.9

Planning inventory documentation This document, Section 3.10

+ CAA 169A(b) provides the authority to provide guidelines to the states on appropriate techniques and methods to implement 

the visibility protection goals in the CAA. This has been done through regulations as codified in 40 CFR 51.308 and 51.309.

‡ While modeling inventories are not an explicit requirement of the CAA, it is presumed here that states would not be able to 

perform the required modeling credibly without modeling inventories.

2.4 Other Relevant Federal Emissions Reporting Requirements

The Air Emissions Reporting Rule (AERR), 40 CFR Part 51, Subpart A, requires states to provide to the 

EPA annual statewide emissions inventory data, regardless of whether that state has nonattainment 

areas. This regulation requires reporting of actual emissions of carbon monoxide (CO), NOX, VOC, SO2, 

PM2.5, particulate matter with diameter ten microns and less (PM10), and NH3. For PM2.5, the AERR 

requires states to report primary (i.e., “direct”) PM2.5, which is defined as the sum of filterable PM2.5 and 
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condensable PM. The agencies are required to report the filterable PM2.5 and condensable PM 

separately where they are present from the source. States may delegate the reporting requirements to 

local air agencies. Tribes can also submit these data to the NEI, but are not required to do so. These data 

are used by the EPA’s Office of Air and Radiation’s (OAR) Office of Air Quality Planning and Standards 

(OAQPS) to build the NEI, and a complete version that includes all sources of emissions (with minor 

exceptions) is released every three years.

The AERR includes both triennial and annual statewide reporting requirements, with more extensive 

reporting requirements for triennial inventory years. For the interim annual inventories, reporting is 

limited to emissions data from only the larger point sources (Type “A” sources), as defined by Appendix 

A of 40 CFR Part 51, Subpart A. For the triennial inventories, lower point source thresholds are given in 

Appendix A, consistent with the definition of major sources in 40 CFR Part 70. All other sources of 

emissions must be reported as nonpoint or mobile sources on a county basis in the triennial 

submissions. Additionally, lower point source thresholds may apply to ozone, PM10

6

, and CO NAAs, 

depending on the area’s nonattainment classification.

The AERR requirements are relevant for SIP planning inventory purposes in several ways. First, the AERR 

and its associated EIS (data system) provide the appropriate format for inventories for electronic 

transfer to the EPA. Second, AERR-based inventories are often used as a starting point for SIP 

inventories. Third, in some cases, AERR submissions can meet some of the inventory requirements 

described in this document. Finally, the resources provided by the EPA for states to meet their AERR 

reporting obligations, such as emissions inventory tools and models, associated documentation, 

emission factors, new emissions methods, and quality assurance approaches, can assist inventory 

developers when making inventories for SIP planning and modeling purposes.

As a point of clarification, air agencies must meet all relevant planning inventory SIP requirements 

regardless of the availability or use of the EPA data associated with the AERR/NEI process. While the EPA

resources can be helpful to states in meeting those requirements, the SIP requirements and the 

associated public review and regional office approval process are independent requirements that must 

be met. It would not be sufficient to merely point to the EPA’s publication of the NEI as having met the 

SIP emissions inventory requirements. However, it may be sufficient for a state to submit as a SIP 

revision an inventory that contains some or all of the same data as in the NEI, with sufficient justification 

and public comment process.

2.5 Emissions Inventory Definitions

Emissions inventory work requires knowledge of many terms and codes. In this section, we define the 

terms relevant to inventories that are used throughout this document. This section also references 

external materials needed for obtaining definitions of all valid fields that can be used for building 

inventories, which are based on the tables used to submit data to the EPA for the AERR. Many 

definitions relevant for emissions inventories are defined in the CAA or codified in the AERR and the 

implementation rules. These are included here for convenient reference in this document to have in a 

 

6

At this time, there is no separate lower reporting threshold for PM2.5.
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single location and because these terms are used throughout this document. Without these definitions, 

the meaning of the subsequent sections would be less clear. The sample below is not intended to 

represent a comprehensive list of inventory related definitions.

2.5.1 Source Category/Data Category

Traditionally, the term “source category” has been used to identify the major types of emissions 

inventory groupings: stationary point sources, stationary area (or nonpoint) sources7, on-road mobile 

sources, nonroad mobile sources. In addition, fires and biogenic sources are sometimes included as 

additional source categories.

In practice, some inventories have started including large moveable facilities, such as asphalt plants, in 

the point sources inventory without associating them with a specific county. Additionally, some mobile 

sources such as locomotives and commercial marine vessels (CMVs) are treated as nonpoint data (i.e., 

the formatting of it) for the purpose of reporting these data to the EPA (see also Section 4.8.5 as well as 

the EIS information referenced in Table 1). Similarly, rail yards are treated as point data.

With the advent of the EIS at the EPA, the preferred term for indicating subsets of inventory data has 

become “data category” rather than “source category”, because the groupings have much more to do 

with how the data are created and the data structure than the features of the actual emissions sources 

included in the category. For example, locomotives and commercial marine vessels are included in the 

nonpoint data category for inventories in the EIS, but in fact are nonroad mobile sources. Additionally, 

the EIS ushered in a new data category called “events,” which are typically wildfires or prescribed fires

(agricultural fires are part of the nonpoint data category), but in principle could include other significant, 

short-duration, emissions events8.

2.5.2 Types of Emissions: Annual, Seasonal, Actual, Potential, and Allowable

Various terms are used in this and other documents to reference various types of emissions. Here, we 

provide a brief list of definitions associated with various emissions types.

Annual emissions are defined in the AERR (40 CFR 51.50) as actual emissions for a plant, point, or 

process that are measured or calculated to represent a calendar year. This means that annual emissions 

should include all emissions of the relevant sources at a facility or from a nonpoint or mobile process 

occurring during a calendar year. In general, unless otherwise specified, annual emissions means actual 

emissions, as defined below.

Summer day emissions means an average day’s emissions for a typical summer work weekday. The state 

will select the particular month(s) in summer and the day(s) in the work week to be represented. The 

 

7

Over time, stationary area sources have been renamed “nonpoint” sources to avoid confusion with the air toxics 

regulatory term “area sources”, which in fact are often sources that meet the criteria pollutant definition of point 

sources. Likewise, the term “stationary” is often ignored in common use for both the point source and nonpoint 

labels.

8 While the EIS is not currently configured to accept event data other than for fires, this means that the idea of an 

“event” could be expanded to other types of events that are not currently inventoried because of the difficult 

nature and non-routine nature of these types of emissions.
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selection of conditions should be coordinated with the conditions assumed in the development of 

ROP/RFP plans and/or emissions budgets for transportation conformity to allow comparability of daily 

emissions estimates. The EPA advises states to make these decisions in consultation with their regional 

office. 

[PM2.5 Implementation Placeholder]

Actual emissions means the emissions of a pollutant from an affected source determined by taking into 

account actual emission rates associated with normal source operation and actual or representative 

production rates (i.e., capacity utilization and hours of operation) (40 CFR 51.491). This is in contrast 

with potential emissions or allowable emissions. See Section 4.1 for a description of selecting a year for 

creating actual emissions estimates.

Startup, Shutdown, and Malfunction (SSM) emissions are emissions that occur during startup, 

shutdown, or malfunctions at industrial facilities. The emissions rate during these periods can be much 

larger than the routine emissions rate9. More about the startup and shutdown emissions in the SIP 

inventory context are described in Sections 4.3 and 4.8.1.

Potential to emit means the maximum capacity of a stationary source to emit a pollutant under its 

physical and operational design (40 CFR 51.301). Also called “potential emissions,” 40 CFR 51.301 also 

defines this term to specific that any physical or operational limitation on the capacity of the source to 

emit a pollutant including air pollution control equipment and restrictions on hours of operation or on 

the type or amount of material combusted, stored, or processed, shall be treated as part of its design if 

the limitation or the effect it would have on emissions is federally enforceable. Secondary emissions do 

not count in determining the potential to emit of a stationary source.Ä

As described in “Potential to Emit: A Guide for Small Businesses” (EPA-456/B-98-003), potential to emit 

considers the design of your equipment and can also consider certain controls and limitations on the 

operation of the equipment. Potential emissions can be expressed as potential controlled emissions,

which are the pollutant emissions while a source is operating at the maximum design capacity, a 

schedule of 8760 hours per year, and considering the efficiency of the control equipment. In contrast, 

potential uncontrolled emissions are simply the pollutant emissions while the source is operating at the 

maximum design capacity and a schedule of 8760 hours per year without factoring in controls.

Allowable emissions means the emissions of a pollutant from an affected source determined by taking 

into account the most stringent of all applicable SIP emissions limits and the level of emissions 

consistent with source compliance with all federal requirements related to attainment and maintenance 

of the NAAQS and the production rate associated with the maximum rated capacity and hours of 

operation (unless the source is subject to federally enforceable limits which restrict the operating rate, 

or hours of operation, or both) (40 CFR 51.491).

 

9

On February 12, 2013, the EPA proposed SIP calls for 36 states whose SIPs include exemptions for excess 

emissions during SSM periods or other provisions with respect to excess emissions during SSM events that 

appear to be inconsistent with Clean Air Act requirements. See 

http://www.epa.gov/airquality/urbanair/sipstatus/emissions.html for more information.
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2.5.3 Duration and Timing of Emissions

Inventory start date means the first day of the inventory period. This can be used for compiling and 

reporting monthly or other shorter period emissions, including events.

Inventory end date means the last day of the inventory period. This can be used for compiling and 

reporting monthly or other shorter period emissions, including events.

Inventory year or Emissions year means the year for which emissions estimates are reported (40 CFR 

51.50).

See also “Emission Type” in codes Section 2.5.14.

2.5.4 Data Elements

The term data elements means parts of a data file that contain individual items of data. These are also 

called fields or variables. Examples of key data elements associated with emissions inventories include 

emissions; activity; emission factors; state/county identifiers; facility, unit, and process identifiers; plant 

names; control measure codes; and process codes. This list is just a sample and is not intended to 

represent a comprehensive list of required codes (see also Section 2.5.7).

Note that emissions data categories (Section 2.5.1) are not a data element per se, but rather emissions 

inventory submissions usually are broken out into separate datasets for each data category.

2.5.5 Throughput and Activity

Throughput means a measurable factor or parameter that relates directly or indirectly to the emissions 

of an air pollution source during the period for which emissions are reported (40 CFR 51.50). Throughput 

is also called activity. Depending on the 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, miles travelled, or number of existing units. Activity 

throughput is typically the value that is multiplied against an emission factor to generate an emissions 

estimate. Consequently, it is important to coordinate activity used for a given emissions source with the 

available emission factors for that source10.

There are some special types of activities always used for certain categories. Examples for mobile 

sources include:

Vehicle Miles Traveled (VMT): The number of miles travelled within a year or as an average daily value 

for all vehicles within a group (e.g., vehicle type, fuel type, and county). See also MOVES Technical 

Guidance (http://www.epa.gov/otaq/models/moves/index.htm#sip).

Vehicle population: The number of vehicles of a certain type and fuel usage within a group (such as a 

county).

 

10 Some air agencies have raised the concern that throughput at industrial facilities is considered confidential 

business information, however, this field is required by the AERR. Since this field is “emission data” required by 

the AERR, it cannot be protected as CBI under CAA § 114(c).
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Equipment population: The number of nonroad equipment units of a certain type and fuel usage within 

a group (such as a county).

2.5.6 Emission Factors

An emissions factor is a representative value that attempts to relate the quantity of a pollutant released 

to the atmosphere with an activity associated with the release of that pollutant. These factors are 

usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of 

the activity emitting the pollutant (e.g., kilograms of particulate emitted per megagram of coal burned). 

Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these 

factors are simply averages of all available data of acceptable quality, and are generally assumed to be 

representative of long-term averages for all facilities in the source category (i.e., a population average). 

Emission factors have long been the fundamental key to developing emissions inventories for air quality 

NAAQS implementation. More information on emission factors is available from the Emission Factors 

and Policy Applications Center (http://www.epa.gov/ttn/chief/efpac/index.html) on the EPA website.

The general equation for emissions estimation is:

 

where:

E = emissions,

A = activity total,

EF = emission factor, and

ER = overall emission reduction efficiency percent.

The ER term is the combination of the relevant percents related to emissions controls and rules that 

reduce emissions, as listed in Section 2.5.18.

Emission factors are not limited to factors that are only represent broad national industry averages 

published by the EPA. Emission factors can also be stack-, process-, unit-, or facility-specific, depending 

on the basis of the source test information. Whether for a single facility or a group of facilities of the 

same type, it is still considered an emission factor for the purposes of this guidance.

2.5.7 Emissions Reporting Data Elements

The Proposed Ozone Implementation Rule and [PM2.5 Implementation Placeholder] refers to the AERR 

and this guidance for information on reporting data elements. Since the AERR is focused on emissions 

submitted for the annual NEI inventory, it only includes definitions for those data and fields that are 

required by the NEI program. Notably, for ozone SIP inventories, summer day emissions are required, 

but have been proposed in an AERR revision to be optional for NEI submittal purposes. Thus, the 

proposed AERR revision no longer defines summer day emissions. Thus, the summer day emissions are

defined in the sections above.

[PM2.5 Implementation Placeholder]
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The many required and optional data elements for emissions inventories are described in Excel files 

called Staging Requirements. These files are comprehensive for all of the required and optional fields 

that can be submitted to the EPA for SIP inventories, not only the submissions for the NEI. The shared 

field list for NEI and SIP inventories helps air agencies by promoting clarity and familiarity through 

common data element definitions across multiple inventory requirements. The descriptions provided in 

those Excel files are very limited, so this document provides additional information for the most 

important of these fields. These spreadsheets are available at the EIS Training website at 

http://www.epa.gov/ttn/chief/eidocs/training.html#eis using the links for “Staging Table 

Requirements.”

Although many fields in the Staging Requirements are optional for official reporting purposes, some of 

these fields can be critical for inventory development for SIPs and even the NEI. By optional, we mean 

those fields that are either not explicitly required by the AERR or that are not enforced as needing to be 

provided to successfully submit the data to the EPA. The list below identifies fields that are “optional”

but that are strongly recommended to be included in all emissions inventories, documentation, and 

reporting as applicable for the sources in the state or NAA. For example, control parameters are optional 

only because emissions controls do not exist on every unit and process in an inventory, thus the EPA

cannot enforce this as a required field. However, the control information is required by the AERR when 

it exists as part of the source.

Unit Description: This field describes the unit in words. It can be invaluable in determining incorrect 

source classification codes (SCCs).

Unit design capacity: Unit design capacity means a measure of the size of a point source, based on the 

reported maximum continuous throughput or output capacity of the unit (40 CFR 51.50). Useful for 

boilers, this field is needed when trying to understand the cost per ton of pollutant emissions reduced 

associated with controls on boilers. The cost per ton is generally higher for smaller boilers. The design 

capacity can be critical in SIP planning for insuring that good decisions are made about controls on 

stationary boilers and other units. While required by the AERR, the EIS does not enforce this field as 

many states do not have this information available. By including these data in SIP inventory 

development, states can help to further improve the data available to them for decision making as well 

as for consideration by the EPA.

Control measure: This field is a unique code for the type of control device or operational measure (e.g., 

wet scrubber, flaring, process change, ban) used to reduce emissions (see 40 CFR 51.50). When 

assessing whether an emissions source can be further controlled to contribute emissions reductions 

needed for attainment, it is imperative to know whether there is a control measure included on a unit or 

process. The type of measure is also needed to understand whether other controls can be added. The 

associated data elements such as control efficiency, capture efficiency, rule effectiveness, and rule 

penetration are all useful as well for the same reasons. These latter control parameters are also needed 

when calculating potential controlled emissions.
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Alternative facility names or identifiers: This field can be very useful in matching the facility with other 

databases, such as the Toxics Release Inventory, the Federal Registry System, or the National Electric 

Energy Data System (NEEDS) database. If air agencies change their agency IDs (facility, unit, process, and 

release point) from one year to the next, this table can help prevent creating duplicates in the EIS and 

other databases.

EIS IDs: While the EIS Facility ID, Unit ID, Process ID, and Release Point ID (see Section 2.5.15) are not 

required by the AERR or for SIP inventories, it is the standard by which the EPA compiles and reports all 

point source inventories. The EPA reports and modeling all use these EIS IDs, and so to the extent air 

agency databases can use these IDs in their data systems, it helps facilitate matching across the many 

purposes for inventories.

Release Point Geographic Coordinates: As described in Section 2.5.17, the EIS and inventories generally 

can have location coordinates (i.e., latitude/longitude) for a facility or at individual release point 

locations. 

2.5.8 Point Sources

As defined by the AERR in 40 CFR 51.50, point sources are large, stationary (non mobile), identifiable 

sources of emissions that release pollutants into the atmosphere. A point source is a facility that is a 

major source under 40 CFR part 70 for one or more of the pollutants for which reporting is required by 

40 CFR 51.15 (a)(1). This does not include the emissions of hazardous air pollutants, which are not 

considered in determining whether a source is a point source for ozone, PM2.5, and regional haze 

emissions inventory development and reporting. These point sources can be associated with a single 

point or group of points in space. Examples of important point source emissions categories include 

power plants, industrial boilers, petroleum refineries, cement plants, and other industrial plants.

According to the ozone and PM2.5 implementation rules, the AERR governs the size above which sources 

are inventoried as point sources. While the AERR also requires data from state agencies for use in the 

NEI, the AERR emissions point source thresholds apply to all inventories provided to the EPA, including 

SIP inventories. The AERR bases the criteria on a potential to emit emissions size threshold. Table 7

provides the potential to emit reporting thresholds included in the AERR. “Type B” is the terminology in 

the rule that represents the lower emissions thresholds required for point sources in the triennial NEI 

years. For evaluating this criterion, it is appropriate to use potential controlled emissions for controlled 

sources. As shown in the table, special requirements apply to NAA sources, where even lower thresholds 

may apply depending upon the severity of the NAA classification.

Air agencies may include point sources at even lower levels in their NEI or SIP-related inventories. The 

AERR potential to emit thresholds simply provide a minimum requirement. Depending on the nature of 

the nonattainment problem and the need to characterize smaller sources as point sources, the EPA

regional offices may require or encourage lower thresholds so air agencies can produce effective SIPs.

Type A source means a large point source with potential annual emissions of any CAP or CAP precursor 

greater than or equal to the corresponding emission threshold listed in the AERR and in this section.
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Type B source means a point source smaller than a Type A source with potential annual emissions of 

any CAP or CAP precursor greater than or equal to the relevant Type B emission threshold listed in the 

AERR and in this section. Type B point sources are required by the AERR to be included in a state or local 

inventory submission for point sources in the triennial years and are applicable to SIP planning and 

modeling inventories as well.

Table 7: Point source reporting thresholds (potential to emit) for criteria 

pollutants in the Air Emissions Reporting Rule11

Pollutant

Triennial NEI thresholds: potential to emit (tons/yr)

Everywhere

(Type B sources) NAA sources*

1 SO2................. ≥ 100 ≥ 100

2 VOC or NOx.... ≥ 100 O3 (Moderate) ≥ 100

3 VOC or NOx.... ................................. O3 (Serious) ≥ 50

4 VOC or NOx.... ................................. O3 (Severe) ≥ 25

5 VOC or NOx.... ................................. O3 (Extreme) ≥ 10

6 CO .................. ≥ 1000 O3 (all areas) ≥ 100

7 CO .................. ................................. CO (all areas) ≥ 100

8 Pb................... ≥ 5

12 ≥ 5

9 PM10 ............... ≥ 100 PM10 (Moderate) ≥ 100

10 PM10 ............... ................................. PM10 (Serious) ≥ 70

11 PM2.5 .............. ≥ 100 ≥ 100

12 NH3................. ≥ 100 ≥ 100

* Special point source reporting thresholds apply for certain pollutants by type of NAA. 

The Clean Air Act specifies specific pollutants for separate NAAQS as follows: 

Ozone: VOC, NOX, CO; CO: CO; PM10: PM10.

2.5.9 Nonpoint Sources

Nonpoint sources are also called “area sources”. These sources collectively represent individual sources 

of emissions that have not been inventoried as specific point or mobile sources. These individual sources 

treated collectively as nonpoint sources are typically too small, numerous, or difficult to inventory using 

the methods for the other classes of sources. Examples of key nonpoint sources include residential 

combustion, institutional and commercial boilers, agricultural burning, industrial and non-industrial 

solvents and graphic arts, degreasing, most agricultural sources, and sources of dust including roads and 

construction.

2.5.10 On-road Mobile Sources

On-road mobile sources are also called “highway mobile sources.” These sources are the motor vehicles 

(e.g., automobiles, buses, trucks) traveling on local and highway roads. A motor vehicle is any selfpropelled vehicle used to carry people or property on a street or highway (40 CFR 51.50). On-road 

mobile sources should be estimated by the latest recommended on-road mobile source models. 

 

11 On June 6, 2013, the EPA proposed to lower the reporting threshold for lead to 0.5 tons/yr. The lead threshold, 

however, is not relevant for this guidance because it does not cover lead NAAQS implementation.

12 The 5 ton threshold for lead is proposed to be reduced to 0.5 ton as of March, 2014.
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Currently, that means the MOVES model (http://www.epa.gov/otaq/models/moves/) for all states but 

California, and the EMFAC13 model (http://www.arb.ca.gov/msei/modeling.htm) for California.

2.5.11 Nonroad Mobile Sources

Nonroad mobile sources are also called “off-highway” mobile sources. These are defined as a nonroad 

engine or nonroad vehicle. As per 40 CFR 51.50, a nonroad engine is an internal combustion engine 

(including the fuel system) that is not used in a [on-road] motor vehicle or a vehicle used solely for 

competition, or that is not affected by sections 111 or 202 of the CAA. Also as per 40 CFR 51.50, a

nonroad vehicle is a vehicle that is run by a nonroad engine and that is not a [on-road] motor vehicle or 

a vehicle used solely for competition. Examples of nonroad mobile sources include aircraft, airport 

ground support equipment, locomotives, CMVs, construction equipment powered by an internal 

combustion engine, agricultural equipment powered by an internal combustion engine, and lawn and 

garden engines and equipment. 

There are a variety of tools for estimating emissions from nonroad mobile sources. The EPA develops 

and maintains approaches for aircraft, locomotives, and CMVs, which are documented as part of the NEI 

program (for the latest approaches, refer to the latest NEI documentation available at 

http://www.epa.gov/ttn/chief/eiinformation.html). The EPA also has developed and maintains the 

NONROAD model (http://www.epa.gov/otaq/nonrdmdl.htm), which can also be run using NMIM

(www.epa.gov/otaq/nmim.htm)

14

. Air agencies may update and customize the model inputs to give 

better emissions estimates for their state. California has developed and used a state-specific approach 

for estimating its nonroad source emissions, called OFFROAD2007 

(http://www.arb.ca.gov/msei/offroad/downloads/models/offroad2007_1215_exe.zip), which has now 

been replaced by category-specific methods for many categories (see 

http://www.arb.ca.gov/msei/categories.htm#offroad_motor_vehicles). As described by the website, the 

OFFROAD2007 model is still the default approach for categories not listed with newer methods on the 

website.

2.5.12 Events

The EIS (starting with the 2008 NEI) introduced a new data category called events, which are discrete 

and large emissions sources that individually occur over a short period of time, but which can 

collectively result in a significant amount of emissions. Example events captured by this data category 

include naturally occurring wildfire and a managed prescribed burns. In EIS, these data are stored as 

day-specific events that can span many days for a given fire/event. More information on events data 

and its unique nature is available in Section 4.8.7.

2.5.13 Biogenic Sources

For the purposes of creating emissions inventories, biogenic emissions come from natural sources. They 

need to be accounted for in photochemical grid models, as many types of biogenic emissions are 

 

13 The EMFAC model name is not an acronym. The documentation and website for EMFAC do not include a further 

explanation of the name.

14 EPA is working to replace NMIM with the MOVES model. The latest recommended approaches will be included 

on the EPA’s Office of Transportation and Air Quality Websites.
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widespread and ubiquitous contributors to atmospheric chemistry leading to ozone and PM formation. 

In the NEI, only the emissions from vegetation and soils are included, but other relevant sources include 

volcanic emissions, lightning, and sea salt spray.

Biogenic emissions from vegetation and soils are computed using models which utilize spatial 

information on vegetation and land use and environmental conditions of temperature and solar 

radiation to apply emission factors. The model inputs are typically horizontally allocated (gridded), and 

the outputs are gridded biogenic emissions which can then be summed for use in planning inventories 

and speciated and utilized as input to photochemical grid models. As described in Section 4.8.6, a variety 

of models are available to estimate the emissions from vegetation and soils.

2.5.14 Inventory Codes

The list provided below is a sample of the codes that can be used in building inventories; it is not a 

comprehensive list of codes that should be used in building inventories. The EIS is the repository for the 

most updated valid codes used for building inventories. Dozens of tables of codes are available to EIS 

users from the “Reporting Code Tables” link on the EIS Gateway. For others who do not have access to 

the EIS (e.g., contractors not working for a state, international users, and the general public), the EPA

periodically posts Microsoft ® Access ® compilations of these codes at the main NEI website under the 

“EIS Code tables (including SCCs)” link.

Source classification codes: An SCC means a process-level code that describes the equipment and/or 

operation [or practice] that is emitting pollutants (40 CFR 51.50)

15

. These codes are 8 digits for point 

sources and 10 digits for nonpoint and mobile sources. The codes have multi-level descriptions, which 

are included in the EIS codes table. These codes are also used in the emission factors online database 

WebFire (www.epa.gov/ttn/chief/efpac/index.html).

North American Industry Classification System (NAICS) codes: The NAICS codes are U.S. Department of 

Commerce's codes for businesses by products or services and have replaced Standard Industrial 

Classification codes. They are assigned to facilities in inventories to identify the primary industrial 

activity of the facility.

Federal Information Processing Standards (FIPS) state and county codes: Federal Information Processing

Standards (FIPS) codes means the system of unique identifiers maintained by the National Institute of 

Standards and Technology, which are used to identify counties and county equivalents (e.g., parishes, 

boroughs) of the U.S. and its territories (e.g., American Samoa, Guam, Northern Mariana Islands, Puerto 

Rico, and US Virgin Islands). In the EIS Codes Tables, additional codes have been added to support 

offshore regions and sources, such as asphalt plants, that do not remain in a single county during the 

entire year.

 

15 Several air agencies have raised the concern that SCC at industrial facilities is considered confidential 

business information. However, this field is “emission data” required by the AERR and thus cannot be 

provided as CBI under CAA § 114(c).
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Tribal codes: A three-digit code that represents the American Indian Tribe or Alaskan Native entity. The 

EIS Table also identifies which EPA region is associated with the tribe. These codes are used instead of 

FIPS state and county codes when reporting emissions from tribal areas.

Pollutant codes: Pollutant code means a unique code for each reported pollutant assigned by the 

reporting format specified by the EPA for each inventory year (40 CFR 51.50). All of the criteria 

pollutants except for Lead have codes that describe them: CO, NOX, VOC, SO2, NH3, PM10-PRI, PM10-

FIL, PM25-PRI, PM25-FIL, and PM-CON. Lead and the hazardous air pollutants (HAPs) use numerical 

codes16 to represent them, for example elemental lead is 7439921 and elemental mercury is 7439976.

Control measure codes: Control measure means the name of the type of control device (e.g., wet 

scrubber, flare, baghouse) or practice (e.g., product substitution). The EIS Code Tables use a three-digit

numeric control measure code to represent each of the different types of controls, and identifies each 

as a device or a practice. The control device type codes were updated with additional codes in 2013. 

These codes are required when control devices are present because they are critical to understanding 

the nature of the emissions source and the possibility of additional emissions reductions to achieve 

attainment.

Emission calculation method: This field is the code describing how the emissions for a pollutant were 

calculated, e.g., by stack test, continuous emissions monitor, EPA emission factor, etc. (40 CFR 51.50). 

This is a required field for inventories because it allows the EPA to get some sense of the quality of the 

emissions estimate. Comment fields can also be used to further explain the origin of the emissions 

estimate.

Reporting period type: This field is the code describing the time period covered by the emissions 

reported, i.e., annual, 5-month ozone season, summer day, or winter (40 CFR 51.50). This field is also 

called the emission type code in some references.

2.5.15 Point source Facility Details

See also Section 2.5.7, which points to the spreadsheets available that list all required and optional 

emissions inventory data elements.

Facility Inventory means the data tables of all facility information included in the EIS, but could also be 

used to refer to similar data tables for any inventory storage system. The facility inventory is the 

complete list of facilities, units, processes, and stacks associated with all point sources. It is designed to 

be the latest repository of facility information and needs updating only when changes occur to facilities. 

The facility inventory concept was intended to allow facility data to be constant except where real 

changes occur, allowing easier building and submitting of inventories and encouraging the use of 

consistent facility IDs, unit ID, process ID, and stack IDs from one inventory year to the next.

 

16 These numerical codes are the unique numerical identifiers assigned and maintained by the Chemical Abstracts 

Service (CAS) and are often referred to as CAS numbers or CAS registry numbers. The CAS numbers often appear 

with dashes embedded in the string of numbers, but these are dropped for most inventory reporting purposes.
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Physical address means the location address (street address or other physical location description), 

locality name, state, and a postal zip code of the facility. This is the physical location where the 

emissions occur; not the corporate headquarters or a mailing address (40 CFR 51.50).

Site name (also called Facility Site Name) means the name of the facility emitting emissions that are 

included in the inventory (40 CFR 51.50). 

EIS ID means any facility, unit, process, or release point (stack) ID generated by the EIS and intended to 

remain constant for the life of that facility, unit, process, or stack across inventory years. The proper 

names of the EIS IDs in the EIS system are EIS Facility Site Identifier, EIS Emission Unit Identifier, EIS 

Emission Process Identifier, and EIS Release Point Identifier.

Agency ID means any facility, unit, process, or release point (stack) ID generated by an agency reporting 

emissions to the EPA. These IDs are used in the air agency data systems and may not match the EIS IDs 

described above. The EPA tracks both the EIS IDs and Agency IDs within the EIS. Using consistent agency 

IDs from year to year is highly encouraged, as it allows the EPA to more readily see which facilities are 

being reported for the AERR requirements. Using inconsistent Agency IDs can result in duplicative 

facilities, units, processes, and release points within the EPA data systems.

Facility ID code (also called “Facility site identifier)” means the unique codes for a plant or facility 

treated as a point source, containing one or more pollutant-emitting units (40 CFR 51.50). The EPA's 

reporting format for a given inventory year may require several facility ID codes to ensure proper 

matching between databases, e.g., the state's own current and most recent facility ID codes, the EPAassigned facility ID codes, and the ORIS (Department of Energy) ID code if applicable.

Unit ID code means a unique code for the unit that generates emissions, typically a physical piece of 

equipment or a closely related set of such equipment (40 CFR 51.50). An example of a closely related set 

of equipment is a boiler and its control equipment. The EPA's reporting format for a given inventory year 

may require multiple unit ID codes to ensure proper matching between databases, e.g., the state's own 

current and most recent unit ID codes, the EPA-assigned unit ID codes if any, and the ORIS (Department 

of Energy) ID code if applicable.

Process ID code is also called the “emission process identifier” and it means a unique code for the 

process generating the emissions, typically a description of a process (40 CFR 51.50).

Release Point ID code means a unique code for the point where emissions from one or more processes 

release into the atmosphere (40 CFR 51.50). Traditionally called a Stack ID, but this was changed with EIS 

to acknowledge that many emissions releases do not come from stacks, such as fugitive emissions.

Release point type code means the code for physical configuration of the release point (40 CFR 51.50). 

The physical configurations include fugitive, vertical, horizontal, goose neck, vertical with rain cap, and 

downward-facing vent. The first two types are by far the most common. The release point type is 

particularly important for dispersion modeling needed for permitting, risk modeling, and other 

purposes.
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Release Point Diameter Measure (or Stack diameter) means the inner physical diameter of a stack (40 

CFR 51.50). This should be measured at the exit release point of the emissions, and the expected 

reported units are feet.

Release Point Height Measure (or Stack height) means physical height of a stack above the surrounding 

terrain (40 CFR 51.50). Expected reported units are feet.

Release Point Exit Gas Flow Rate Measure (or Exit gas flow rate) means the numeric value of the flow 

rate of a stack gas (40 CFR 51.50). Various units are permitted by the EIS.

Release Point Exit Gas Temperature Measure (or Exit gas temperature) means the numeric value of the 

temperature of an exit gas stream in degrees Fahrenheit (40 CFR 51.50). 

Release Point Exit Gas Velocity Measure (or Exit gas velocity) means the numeric value of the velocity of 

an exit gas stream (40 CFR 51.50). Various units are permitted by the EIS.

2.5.16 Alternative IDs

In addition to the primary facility, unit, process, and release point IDs, alternative IDs can be very useful 

for matching information in a given inventory to other databases. In the case of the EIS, it stores not 

only the EIS unique IDs, but also the air agency IDs. Other IDs are stored as well, including the following:

EIA Plant Code (a.k.a ORIS Plant Code). This plant ID is defined by the U.S. Department of Energy (DOE) 

Energy Information Administration (EIA) and used in its EIA-767 form. It has previously been defined as 

the Office of Regulatory Information System (ORIS) code, though that term is no long used by DOE. The 

EPA’s Office of Atmospheric Programs’ (OAP) Clean Air Markets Division (CAMD) uses whatever code 

was originally assigned to the facility as the tracking code for compiling data for its emissions markets in 

support of the acid rain program and NOX trading, in particular the CEMS data. 

CAMD Unit ID. In addition to the EIA facility IDs, CAMD uses unit IDs for storing the emissions markets 

data as well. The EIS stores the unit codes used by CAMD as an alternative ID called “EPACAMD,” and 

the values are usually based on the CAMD hourly CEMS data reports. These have historically also been 

referred to as ORIS Boiler or ORIS Unit IDs, though that reference is no longer valid.

IPM/NEEDS ID. The EPA Integrated Planning Model (IPM) is used to forecast future-year electricity 

demand and emissions. Underlying this model is the National Electric Energy Data System (NEEDS)

database that contains the generation unit records used to construct the “model” plants that represent 

existing and planned/committed units in EPA modeling applications of IPM. This database mostly uses 

IDs that are often the same as the EIA Plant Codes and the CAMD Unit IDs, but this database has more 

units than are included in the hourly CEMS data. In the EIS, the EPA stores these alternative IDs as 

“EPAIPM” IDs.

Toxics Release Inventory (TRI) ID is used by the EPA’s Office of Environmental Information to build the 

Toxics Release Inventory from facility-submitted facility-total emissions to air, water, and land. This 

database includes NH3, which is why it can be relevant to the NAAQS for PM2.5 implementation. In the 

EIS, the EPA stores these alternative IDs as “EPATRI” IDs.
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Federal Registry Service (FRS) ID is used by the EPA’s Office of Environmental Information to link many 

EPA databases with facility information (see http://www.epa.gov/enviro/html/fii/index.html). 

2.5.17 Location Definitions

Geographic locations are critical in point source inventories for identifying the location of the emissions. 

In the EIS, locations can be provided for both the facility center and for individual release points. Fugitive 

release points have additional parameters that can be specified such as the orientation of the release, 

and these parameters are listed in the spreadsheets available that list all required and optional 

emissions inventory data elements, referenced in Section 2.5.7.

Latitude Measure (or just latitude) is the measure of the angular distance on a meridian north or south 

of the equator. Reported as decimal degrees.

Longitude Measure (or just longitude) is the measure of the angular distance on a meridian east or west 

of the prime meridian. Reported as decimal degrees.

Horizontal Accuracy Measure is the measure of accuracy (in meters) of the latitude/longitude 

coordinates. 

In addition, refer to http://www.epa.gov/oei/ for more information on the proper usage of the following 

code set.

Horizontal Collection Method Code is the method used to determine the latitude/longitude coordinates 

for a point on the earth. For example, 001 is address matching-house number, and 004 is address

matching nearest intersection.

Horizontal Reference Datum Code represents the reference datum used to determine the 

latitude/longitude coordinates. Options are: 001 (North American Datum of 1927), 002 (North American 

Datum of 1983) and 003 (World Geodetic System of 1984).

Geographic Reference Point Code represents the place for which geographic coordinates were 

established. Code value should be 106 (e.g., point where substance is released). 

2.5.18 Control Data Elements

Control efficiency means the efficiency by which a control device or measure reduces emissions for a 

particular pollutant. For emissions reporting in accordance with the AERR, this data element applies for 

both point and nonpoint sources and is called the “Percent Control Measures Reduction Efficiency.” For 

point sources, the data element is included in the “Control Pollutant Table” of the facility staging tables.

For nonpoint sources, the data element is included in the “Control Pollutant Table” of the nonpoint 

staging tables. In the EIS, it is a percent and should be reported as a value greater than or equal to 0.1 

and less than or equal to 99.9 (the EIS allows for one decimal place only).

Capture efficiency means the percentage of an exhaust gas stream actually collected for routing to a set 

of control devices (40 CFR 51.50). It is sometimes combined within the value for the control efficiency, 

but unlike control efficiency it is not pollutant-specific. For emissions reporting in accordance with the 
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AERR, this data element is for point sources only, and it is called “Percent Control Capture Efficiency” and 

is included in the “Control Approach Table” of the facility staging tables. It is a percent and should be 

reported as a value greater than or equal to 0.1 and less than or equal to 99.9 (the EIS allows for one 

decimal place only).

Control Effectiveness means the percentage of time or activity throughput that a control approach is 

operating as designed, including the capture and reduction devices. This percentage accounts for the 

fact that controls typically are not 100 percent effective because of equipment downtime, upsets and 

decreases in control efficiencies (40 CFR 51.50). 

Control effectiveness is an estimate of the portion of the reporting period's activity for which the overall 

control system or measure (including both capture and control measures) were operating as designed 

(regardless of whether the control measure is due to rule or voluntary). It applies to both point and 

nonpoint sources and is not pollutant-specific. For point source emissions reporting in accordance with 

the AERR, this data element is called “Percent Control Approach Effectiveness” and is included in the 

“Control Approach Table” of the facility staging tables. For nonpoint source emissions reporting in 

accordance with the AERR, this data element is also called “Percent Control Approach Effectiveness” and 

is included in the “Control Approach Table” of the nonpoint staging tables. In the EIS, it is a percent and 

should be reported as a value greater than or equal to 0.1 and less than or equal to 99.9 (the EIS allows 

for one decimal place only). For nonpoint, see also “rule effectiveness,” below.

Rule penetration means the percentage of a nonpoint source category activity that is covered by the 

reported control measures (40 CFR 51.50). For emissions reporting in accordance with the AERR, this 

data element is called “Percent Control Approach Penetration” and is included in the “Control Approach 

Table” of the nonpoint staging tables. In the EIS, it is a percent and should be reported as a value greater 

than or equal to 0.1 and less than or equal to 99.9 (the EIS allows for one decimal place only).

Rule effectiveness means a rating of how well a regulatory program achieves all possible emissions 

reductions. It is analogous to the “control effectiveness” above and in fact for emissions reporting in 

accordance with the AERR, this information is reported using the EIS Control Effectiveness field for 

nonpoint (see above).Rule effectiveness has traditionally been associated with nonpoint controls rather 

than point source controls. Like control effectiveness, it should reflects the assumption that controls 

typically are not 100 percent effective because of equipment downtime, upsets, decreases in control 

efficiencies, noncompliance, and other deficiencies in emission control. Rule effectiveness adjusts the 

control efficiency from what could be realized under ideal conditions to what is actually emitted in 

practice due to less than ideal conditions. The definition above is from the current version of the AERR 

(40 CFR 51.50) that is proposed to be replaced in 2014.

2.5.19 EIS Sectors, Tiers, and Facility Type

Because emissions inventories are large and detailed, most reports about emissions inventories include 

summaries of the contents of those emissions. Some summaries use the data categories described 

above (point, nonpoint, on-road, nonroad, events, and biogenic). For other summaries, that level of 
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detail is not enough. The EIS SCC tables provide three other mechanisms for summaries, all of which 

depend on SCC.

First, the SCCs have a four-part description, and the first three levels of this description could be used as 

a summary category. Second, the SCCs are assigned to “Tiers” using the fields “Tier 1 Description,” “Tier 

2 Description,” and “Tier 3 Description.” These Tiers have been used traditionally as part of many EPA 

reports and trends for criteria emissions. While wildfires are included in the “Miscellaneous” Tier 1, 

wildfires are sometimes separately broken out from Miscellaneous because of their natural origin and 

because they can be a large contributor for some pollutants. Finally, the EIS Sectors can be used to 

summarize emissions (this is the field “Sector” in the EIS SCC code table). The EIS Sector was added with 

the creation of the EIS and allocates emissions to about 60 categories with multi-pollutant inventories in 

mind. Whereas the Tiers are more useful for criteria pollutants, the EIS Sectors work better for the 

combination of HAPs and CAPs. The EIS Sectors can also be further aggregated to provide custom 

summaries; one example of this is presented in the report “2008 National Emissions Inventory: Review, 

Analysis and Highlights” (EPA-454/R-13-005, May 2013).

2.5.20 Other Terms

High electricity demand day (HEDD) means a summer day when demand for electricity is high. A study of

the Northeast Corridor17 air quality has indicated that NOX emissions from EGUs during HEDD periods 

may be significantly greater than emissions that occur on an average summer day.

Distributed generation means the use of small power generators sited at or near the point of energy 

consumption. This usually occurs during periods of peak energy demand or emergency loss of the 

normal EGU generating capacity. Distributed generation sources of electricity can include rooftop solar 

or wind sources, biomass combustion, as well as backup fossil fueled generators or other engines. The 

combustion sources of distributed generation can cause emissions that could be of interest for SIP 

planning purposes.

 

17 “High Electric Demand Day and Air Quality in the Northeast.” White Paper Prepared by the Northeast States for 

Coordinated Air Use Management. June 5, 2006. Available at: http://www.nescaum.org/documents/highelectric-demand-day-and-air-quality-in-the-northeast/final-white-paper-hi-electric-demand-day-06052006.pdf.
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3 SIP Inventory Requirements and Recommendations

As described in Section 2, there are many required and potentially required inventory efforts needed as 

part of a SIP development effort. This section covers the fundamental attributes of planning inventories 

and their preparation. The topics covered include the timing of the various inventory components

(Section 3.1), the inventory preparation plan (Section 3.2), the base year inventories (Section 3.3), the 

ROP/RFP baseline NAA inventory (Section 3.4), the ozone periodic inventory (Section 3.5), the ozone 

emissions statement requirement for SIPs (Section 3.6), maintenance inventories (Section 3.7), the 

projected inventories (Section 3.8), public hearings (Section 3.9), and submitting the inventory to the 

EPA for approval (Section 3.10). The details of inventory preparation for base year inventories and 

projected inventories are left for Sections 4 and 5, respectively.

3.1 Inventory Component Timing

Table 8 provides the timing requirements and recommendations (for optional items) for the inventory 

components of SIPs. Where this table is inconsistent with the ozone, PM2.5, or regional haze regulatory 

text that is applicable at the time a SIP is prepared and reviewed, the regulations have precedence over 

the information provided here.

Table 8: Timing of emissions inventory components

Inventory Component Required+: Timing

Inventory Preparation Plan Prior to preparation of emissions inventories covered by 

the SIP.

Base year NAA inventory Ozone Within 2 years of the effective date of designations

ROP/RFP baseline NAA 

inventory Ozone

Moderate & above: Within 3 years of the effective date 

of designations.

Serious & above: Additional plan within 4 years.

Periodic NAA inventory Ozone The end of each 3-year period after SIP submittal until 

the NAA is redesignated to attainment.

Source Emission Statements 

requirement for SIPs Ozone Within 2 years of the effective date of designations.

Base case statewide inventory Ozone‡ With modeled attainment demonstration (for 

convenience, can be included with the inventory SIP).

Attainment projected 

inventory for the NAA

With SIP and/or ROP/RFP plan. On-road portion can 

become the motor vehicle emissions budget.

Baseline statewide inventory∆ Haze With Regional Haze SIP (by December 17, 2007) and 

every 10 years beginning on July 31, 2018.

Projected statewide inventory

Ozone‡

Haze

With modeled attainment demonstration (for 

convenience, can be included with the inventory SIP)

With Regional Haze SIP (by December 17, 2007) and 

every 10 years beginning on July 31, 2018.

Progress Report, including 

periodic statewide inventory Haze Every 5 years from submittal of initial Regional Haze SIP.

Public hearing All Prior to submittal of inventory for approval by the EPA.
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Inventory Component Required+: Timing

Inventory documentation All With associated inventory.

Maintenance NAA inventory Ozone After attainment, with a redesignation SIP.

+ PM2.5 requirements undergoing review and updating pending the proposed PM2.5 Implementation Rule.

‡ Only required in association with modeled attainment demonstration.

∆ The baseline inventory and current inventory are treated here as they are in practice: as a single inventory.

3.2 Inventory Preparation Plan

Air agencies can use IPPs as a planning tool to guide inventory preparation and to help ensure that 

emission estimates are of a high quality and consistent with CAA requirements. In some cases, the EPA

regional offices will have a preset list of expectations for air agencies to include in their SIP and will 

provide this information to the agency at the start of the SIP planning process. In these cases, an IPP 

may not be needed, especially for air agencies with prior SIP development experience for a particular 

NAAQS.

The IPPs are an opportunity for state and local agencies to tell their EPA regional office how they plan to 

compile their emissions inventories and allow the EPA to provide feedback prior to the agency spending 

resources in preparing their inventory. They can also allow the EPA regional offices to coordinate to 

maintain consistency across attainment plans where that is advisable. The IPPs can be especially 

valuable for agencies with new nonattainment problems, less experienced inventory staff or for 

agencies otherwise needing additional feedback on inventory development.

If used, IPPs precede the development of inventories; therefore, the timing of IPPs is early in the SIP 

planning process. The EPA recommends that air planning agencies coordinate with their regional office

on the need for a plan, the timing of delivery of the plan, the response time back from the EPA on the 

plan, and any other IPP approval process details. Agencies should recognize that time may also be 

needed in their planning schedule to address the EPA comments on the plan, while the EPA regional 

offices will attempt to provide as timely feedback as possible. 

A high quality IPP could be a strong foundation for the emissions inventories used in planning and/or 

attainment modeling, which are themselves critical pieces of SIP development; therefore, the IPP should 

include enough details for the EPA to properly assess what the agency plans to do. The content can 

include a number of key elements, a checklist for which is provided in Table 9. The actual elements to 

include in a specific IPP can depend on a number of factors, depending on the needs of the state or local 

agency as well as the EPA for understanding the inventory plans.
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Table 9: Checklist of elements to consider for including in Inventory Preparation Plans

IPP Element

Essential for a 

High Quality 

IPP?

Inventory objectives – the purpose and scope of the inventory Y

The inventory year(s) and rationale for selecting them Y

The pollutants to be included, including the expected definition of VOC (for inventories 

needing VOC) Y

A list of inventories to be included with the SIP, including the forms (i.e., files, 

summaries) that the agency intends to include in their SIP Y

Plans for (or results of) identifying the most important source sectors to the 

nonattainment problem Y

The source categories to be included, the emissions level(s) for defining point sources, 

and if available, the expected priority for these Y

The plans for compiling the inventory, including any other known inventories and how 

the agency plans to assess and improve upon what is already available

A summary of expected approach differences among different inventories that could 

be the same (e.g., between a base year NAA inventory and a base year modeling 

inventory)

For projected inventories:

The drivers for future-year emissions growth and reductions Y

+

The source categories to be forecast Y

+

The expected approaches for forecasting each source category Y

+

A plan for public review

Important sources of emissions or other inventory uncertainties

Quality assurance steps to be taken Y

A schedule for inventory preparation, review, and submission to the EPA, including any 

plans to submit pieces of the inventory separately and in accordance with 

regulatory timeline requirements

Y

+

If a projected inventory is required.

In addition to Table 9, other inventory planning resources may be of use for agency planning purposes. 

During the preparation of their IPPs, state and local agencies are referred to Volume I of the EIIP 

guidance available at http://www.epa.gov/ttn/chief/eiip/techreport/volume01, which discusses 

emissions inventory planning and development. While somewhat out of date, the EIIP volumes still can 

help guide new inventory developers. Users of that document should defer to this guidance where 

newer information is provided, such as updated versions of mobile models. For stationary point sources, 

a good resource is EIIP Volume II, Chapter 1, Section 3. For nonpoint sources, EIIP Volume III, Chapter 1, 

Section 2 gives nonpoint-specific planning information. The mobile source volumes for EIIP are more out 

of date and the Office of Transportation and Air Quality (OTAQ) mobile source guidance is preferable.

A quality assurance plan should always be a part of the IPP. In cases where a more formal QAPP is 

developed, the QAPP will satisfy the need for an IPP quality assurance plan. In some cases, the EPA 

regional offices will include a QAPP or other QA requirement as part of their CAA Section 105 grant to a 

state that typically includes funding for emissions inventory development.
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For quality assurance planning, Chapter 2 of Volume VI, “Quality Assurance Procedures and DARS 

software” (www.epa.gov/ttn/chief/eiip/techreport/volume06) provides some general guidance for 

quality assurance and some specific approaches to uncertainty evaluation. Other quality assurance 

resources include Section 4.9 of this guidance, and quality assurance steps described in the latest NEI 

Technical Support Documentation available at the latest NEI documentation page link on the main NEI 

web page (http://www.epa.gov/ttn/chief/eiinformation.html). Where air agencies are relying on their 

NEI submission as a starting point for meeting any SIP inventory requirements, a QAPP developed for 

that air agency’s NEI submission may offer a starting point for the SIP inventory QAPP.

3.3 Base Year Inventory

The purpose of the base year inventory is to provide a current and comprehensive data source for 

emissions contributing to the air quality problem addressed by the SIP. In the case of ozone and PM2.5, 

the inventory requirement is for the NAA, whereas for regional haze, the inventory requirement is for a 

statewide inventory. As listed in Table 4 and Table 5, the ozone [PM2.5 Implementation Placeholder]

requirements can also include statewide inventories as part of the modeled attainment demonstration, 

and these can be included as separate inventory submissions included with the NAA inventory.

The general SIP provisions in CAA section 172(c)(3) explains that base year inventories should include a 

“comprehensive, accurate, current inventory of actual emissions from all sources” in the applicable area. 

Details associated with preparing a base year inventory are provided in Section 4, including selection of 

year(s), temporal extent, spatial extent, pollutants to include, approaches for developing emissions, data 

codes, and quality assurance. Additionally, CAA section 182(a)(1) provides a specific base year inventory 

requirement for ozone SIPs.

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

While inventories used for the ROP/RFP baseline, modeling, emissions projections, and other 

inventories will not necessarily be identical to the base year inventory, these inventories should relate to 

the base year inventory with regard to the emissions sources included, pollutants, temporal aspect, and 

other key aspects that allow the SIP to be a coherent and connected plan across the various inventories. 

For planning purposes, the base year inventory provides a way for decision makers to consider the 

sources of emissions that contribute relevant pollutants and consider emissions reductions strategies 

needed for the SIP.

Section 4.1 covers the choice of inventory years for the base year inventory. The choice of the inventory 

year for the planning is a critical one that significantly impacts the workload of inventory staff and 

greatly depends on availability of data and timing of other inventory efforts required by the EPA.

Section 4.2 covers the pollutants to be included in the base year inventory. These pollutants differ 

depending on the nature of the air quality problem for a given SIP. Where feasible, the EPA encourages 

planning agencies to include precursors for all ongoing nonattainment problems in a state, to promote 

efficiency in preparing multiple base year inventories, and to allow for the consideration of emissions 

reduction strategies that improve air quality across multiple air quality concerns and nonattainment 
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issues. In addition, states may wish to include emissions of HAPs, which can have co-benefit reductions 

associated with strategies aimed at reducing ozone, PM2.5, and/or regional haze.

The spatial and temporal extent of the base year inventories are also an important inventory 

characteristic. These topics are covered fully in Sections 4.4 and 4.5. Each of the implementation rules 

for ozone, PM2.5, or regional haze has different considerations and requirements associated with the 

planning inventories. For example, ozone NAA inventories must include both annual and seasonal (i.e., 

summer day) emissions, whereas the regional haze inventories are only annual.

For ozone [and PM2.5], the implementation rule[s] requires inventories for the NAA. These inventories 

are called the base year inventory for the NAA. For regional haze, the inventory is commonly called the 

baseline inventory. For clarity here, we also call the regional haze inventory the baseline statewide

inventory to distinguish it from a NAA inventory. These inventories may need to be updated through 

multiple iterations of a SIP, when they are used a baseline inventories for assessing progress for 

ROP/RFP or regional haze. More on this issue is provided in Section 3.4.2 on RFP/ROP for ozone and 

Section 3.5.2 on current year inventories for regional haze.

3.4 Rate of Progress and Reasonable Further Progress Baseline NAA 

Inventory

The ROP/RFP baseline NAA inventory is necessary for ozone NAAs designated as Moderate and above. 

This baseline inventory is part of a plan or plans that meet the RFP requirements as described by the 

CAA and the Proposed Ozone Implementation Rule, and summarized here.

3.4.1 ROP/RFP Requirements and Timing

CAA section 182(b)(1)(A) requires Moderate and above NAAs to submit a plan to ensure a 15 percent

VOC reduction (accounting for growth) by 6 years after the NAA designation, which is the Moderate area 

maximum attainment date. The 15 percent reduction requirement is commonly called “rate of progress”

or ROP. According to the Proposed Ozone Implementation Rule, air agencies must submit this plan 

within 3 years after the area’s nonattainment designation. This timing aligns with the Moderate NAA 

deadline for submitting attainment demonstration SIPs.

In addition, CAA section 182(c)(2)(B) requires each Serious and above ozone NAA to submit a plan to 

achieve at least a further annual 3 percent VOC reduction. Additionally, CAA Section 182(c)(2)(C) allows 

for substitution of NOX for VOC emissions reductions in the plan under certain conditions. This 

requirement is also called “annual RFP.” As described by the Proposed Ozone Implementation Rule, the 

annual RFP requirement applies for any remaining 3-year periods out to the attainment date beyond the 

first 6 years. According to the Proposed Ozone Implementation Rule, air agencies with Serious and 

above NAAs must submit this plan within 4 years after the area’s nonattainment designation. This timing 

aligns with the Serious and above NAA deadline for submitting attainment demonstration SIPs; 

however, these NAAs still must submit the plan for ROP within 3 years.

States maintain the flexibility to submit plans early to provide more time for implementation of their SIP 

control measures. The EPA recommends that states complete their ROP/RFP plans as expeditiously as 
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practicable after designation to provide as much time as possible for sources to implement the emission 

reductions.

The associated terminology for the various plans and inventories can be confusing, and so the 

terminology used in this guidance is described here. In this guidance, we use “ROP/RFP plan” to refer

generally to all plans – i.e., those addressing just the 15 percent ROP requirement for Moderate areas as 

well as plans additionally addressing the annual RFP requirement. For Serious and above areas, since the 

timing allows that two separate plans for ROP and annual RFP could be submitted (i.e., at 3 years and 4

years after designations, respectively), it may also be necessary to refer to such plans separately. 

Consequently, this guidance uses “ROP/RFP plan(s)” to allow for the idea that multiple plans could be 

submitted. Lastly, in the case where the individual plans must be referenced, they will be called “ROP 

plan” and “RFP plan.”

3.4.2 ROP/RFP Inventory Guidance

The same ROP/RFP baseline NAA inventory is used for all ROP/RFP plan(s), regardless of whether they 

address the ROP requirement (for Moderate areas) or both ROP and annual RFP (for Serious and above). 

As implied by the name, these inventories include emissions data just for the NAA region and not other 

areas in a state. The purpose of the ROP/RFP baseline NAA inventory is to provide a reference point for 

determine the emissions reductions that must be achieved for the 15 percent VOC (or NOX) reduction 

and the subsequent 3 percent reductions for Serious areas and above out to the attainment date.

For ozone, VOC and NOX should be included in the ROP/RFP baseline NAA inventory. Further, the EPA 

expects that the year of the ROP/RFP baseline NAA inventory will be the same year used for the base 

year inventory for the NAA.

[PM2.5 Implementation Placeholder]

For Ozone, the ROP/RFP baseline NAA inventory emissions should be provided using the same base year 

as is used for base year inventory for the nonattainment area. In most cases, the ROP/RFP baseline 

inventory should also have the same emissions values as are in the base year inventory for the NAA. One 

key exception is that biogenic emissions should not be included in the ROP/RFP baseline. 

In some limited situations, the EPA has proposed that states have the option of selecting an appropriate 

and justifiable alternative year for the ROP/RFP baseline NAA inventory, given that they follow certain 

requirements (see 78 FR 34190-34191). If this proposal is finalized and a state chooses to use an 

alternative ROP/RFP baseline year, this also changes the year to use for the base year inventory for the 

NAA so that the baselines are using the same year. The EPA also expects that the spatial extent of the 

ROP/RFP baseline NAA inventory will also match the base year NAA inventory so that they are both 

either “whole county” inventories or both consistently “partial county” inventories. Section 4.4.1

provides more information on partial county inventories.

In the event that updated ROP/RFP plan(s) are needed after initial submittal to meet the requirements 

of the Proposed Ozone Implementation Rule, the ROP/RFP baseline NAA inventory may also need to be 

updated. This can occur with significant methods changes, such as updated mobile models. For example, 
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after an initial ROP/RFP plan has been submitted as part of a SIP, a new mobile model may become 

available that alters the emissions estimates. It would be inconsistent to compare estimates from a new 

mobile model at the end of a 6-year period to estimates using an old model at the beginning of that 6-

year period, and so the EPA could be unable to determine whether a 15 percent reduction (or 

subsequent 3 percent reductions) can be (or has been) achieved by an ROP/RFP plan. Thus, an updated 

ROP/RFP baseline NAA inventory may need to be created using the updated mobile model to 

appropriately meet the requirements of the Proposed Ozone Implementation Rule.

Additional ROP/RFP emissions reductions guidance is provided in Section 3.8.2.

[PM2.5 Implementation Placeholder]

3.5 Periodic Inventory

The Ozone Implementation Rules requires a periodic inventory for the NAA, and the Regional Haze Rule 

requires a “current year” statewide inventory. These inventories should be consistent with the base year 

(“baseline” for regional haze) inventory in the temporal extent (seasonal, annual, or both), spatial extent 

(statewide, NAA counties, partial counties), and sources inventoried. In some cases, it may also be 

advisable to have the emissions inventory methods of the periodic inventory consistent with the base 

year inventory, but this decision should be made in consultation with the relevant EPA regional office.

Regional offices may consider additional relaxation of the consistency recommendation above in specific 

instances.

3.5.1 Ozone Periodic Inventory

For ozone, the requirement in 182(a)(3)(A) is that the periodic inventory be submitted no later than

each 3-year period after the submission of the base year NAA inventory. This language provides the 

flexibility to air agencies to submit sooner than 3 years, but not later than 3 years. If any other current 

NAA inventory is being submitted to the EPA for any reason, including ROP/RFP plans, then states 

should consider also using that data to meet the periodic inventory requirement. Also, if the air agency 

comes into attainment and receives a Clean Data Determination prior to the 3-year period, or if a 

maintenance plan (with a maintenance inventory) is being submitted prior to or in sync with this 3-year 

timetable, then the these actions are very likely to make it unnecessary for the air agency to submit a 

separate ozone periodic inventory.

Since the periodic inventory requirement in the CAA does not specify the degree of detail required for 

the periodic inventory, the EPA has defined the necessary components through the AERR. Thus, whether 

the inventory is submitted as a separate submission or through the AERR, it would need to be consistent 

with requirements of the AERR in order to meet the statutory periodic inventory requirements.

The periodic inventory does not have regulatory significance, unless it is relied on for purposes of a 

planning requirement such as an attainment demonstration or ROP/RFP plan. Rather, it is a check-in 

with the air agency on how the emissions are trending. All inventories for the ozone NAAQS (other than 

the periodic inventory) have some regulatory significance because they are associated with required 

submissions such as maintenance plans, ROP/RFP plans, and modeled attainment demonstrations. 

These inventories all have public hearing requirements as described in Section 3.9. As such, if a periodic 
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inventory is not serving another purpose that has regulatory significance, the EPA has established a 

policy for deferring the public hearing on the periodic emission inventories and the approval of these 

inventories (see “Public Hearing Requirements for 1990 Base-Year Emission Inventories for Ozone and 

Carbon Monoxide Nonattainment Areas”, September 29, 1992; 

http://www.epa.gov/ttn/chief/old/memos/ei/phr_sep1992.pdf). This policy defers the public hearing 

requirements until the time an area takes a regulatorily significant action that relies on the inventory, 

such as adopting and submitting their attainment demonstration and/or ROP/RFP plans. However, in 

deciding whether to rely on that guidance, it is important to note that the EPA cannot act on the 

inventory submission until the public hearing requirement has been completed, and until that time, the 

EPA may face litigation alleging that it has failed to act on the inventory as required by the CAA. 

To meet the periodic inventory requirement for ozone, the periodic inventories must include both 

annual and summer day emissions values. Since these emissions fields are both allowed to be submitted 

to the EPA through EIS for the AERR, it is possible that the submission could meet the periodic inventory 

requirement if the conditions listed in Table 10 apply. As with all SIP requirements, air agencies should 

coordinate with the regional office regarding what is appropriate for a particular NAA.

Table 10: Conditions for AERR submittal to meet ozone periodic inventory requirement

Condition Comment

Public hearing requirement

To the extent it is not practical to coordinate public hearing 

requirements with an NEI submission and the periodic inventory is 

not being used for a SIP action with regulatory significance, it may be 

possible to rely on the EPA’s guidance to defer the public hearing 

(“Public Hearing Requirements for 1990 Base-Year Emission 

Inventories for Ozone and Carbon Monoxide Nonattainment Areas”, 

September 29, 1992).

Annual and summer day 

emissions must both be 

submitted for the NAA 

counties

If summer day emissions cannot be extracted from the EIS (as is the 

case in 2014), using an AERR submission to meet the periodic 

inventory requirement is only acceptable if approved by the regional 

office.

Emissions are submitted for 

mobile sources.

Ongoing review of the AERR may result in requiring mobile model 

inputs and making emissions data optional. If this occurs, the SIP 

periodic inventory must still include emissions. Thus, emissions 

would need to be submitted for the NAA counties regardless of any 

AERR requirements to be able to meet the periodic ozone inventory 

requirement.

Complete – all sectors

Using the AERR to meet the periodic inventory requirement is only 

possible during triennial years because the EIS only accepts nonpoint 

and mobile data during these years, and these data categories must 

be included to be complete.

Submitted within 3 years 

since the base year 

inventory.

It is acceptable to be less than 3 years, after which time the triennial 

submissions would be every three years.

Partial county approach 

approved by regional office

The EIS does not support partial counties. In some cases, it may be 

acceptable to use the entire county emissions for the periodic 
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Condition Comment

submission.

Notification If the AERR approach is approved, the regional office should be 

notified in writing when the submission has been completed. 

Documentation Must be created. Submission is at the request of the EPA regional 

office.

3.5.2 Regional Haze Current Year Inventory

For the Regional Haze Rule, an updated current year inventory is required with each 5-year progress 

report or 10-year SIP revision. This is a complete statewide annual inventory that follows the 

requirements of the initial baseline inventory (included in the original Regional Haze SIP). States can 

choose to use the most recent NEI year or another year that can be justified. Since the Regional Haze 

requirement is an annual period and statewide requirement, it better matches the AERR reporting 

requirements, and so the AERR inventories can more readily meet the requirement for the current year

inventory requirement. 

While the triennial AERR years and reporting requirements will match the needs for reporting current 

year inventories for regional haze, the SIP inventory public hearing requirement will make it extremely 

challenging for an actual AERR submission (primarily for NEI purposes) to meet the current year 

inventory requirement of regional haze SIPs. Notwithstanding this challenge, the conditions listed in 

Table 11 provide guidance to state agencies for using the AERR submittal to meet their current year 

obligation.

Table 11: Conditions for AERR submittal to meet regional haze periodic inventory requirement

Condition Comment

Public hearing requirement

The regional haze current year inventory requires a public hearing, 

and this requirement must be met even when attempting to use the 

AERR submission to meet this requirement. The EPA expects that it 

will be very difficult to complete the public hearing requirement in 

time for the AERR submission.

Complete – all sectors

Submitting all sectors is only allowed by the EIS in triennial years, 

and so the year used for a current year inventory would need to be 

a triennial NEI year. For the submitted data to be used, the AERR 

requirements must be met for point, nonpoint, on-road mobile, 

nonroad mobile, and fires. In addition, emissions must be submitted 

for all sectors even when the AERR allows inputs to be submitted 

instead of emissions.

Notification If the AERR approach is approved, the regional office should be 

notified in writing when the submission has been completed. 

Documentation Must be created. Submission is at the request of the EPA regional 

office.

Regarding the choice of a year, the most recent NEI year will always be sufficient for EPA. However, the 

year of the inventories for the 5-year periodic inventories (and 10-year SIP revisions) are not required to 
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be the same as an NEI year. Using a non-NEI year will usually occur in cases where another year has 

been chosen for other reasons, such as a SIP developed for a different NAAQS. In this case, air agencies

should note that it will be easier to justify a newer year than the most recent NEI year as opposed to 

trying to justify an older year. This is because the purpose of the current year inventory is to provide a 

current estimate of emissions. It is presumed that because of ongoing control programs for mobile and 

stationary sources, which get additional reductions each year, more current year inventories will reflect 

more progress towards the goals of emissions reductions in support of the regional haze standards.

3.6 Emissions Statement Requirement for SIPs

For ozone NAAs, states should develop emission reporting programs for VOC and NOX sources in 

accordance with CAA section 182(a)(3)(B). The required state program and associated regulation defines

how states obtain emissions data directly from facilities and report it to the EPA as part of SIP 

inventories and for the AERR. This is called an Emission Statement regulation, and it outlines how 

facilities must report emissions and facility activity data to an air agency. Once the air agency develops 

the Emission Statement regulation, the regulation should be sent to the EPA as a SIP for approval. As an 

element of a SIP, the public hearing requirements apply to the Emission Statement SIP.

To properly implement the emissions reporting requirements, Emission Statement regulations should be 

coordinated carefully with the AERR and any associated guidance and specifications, the Modeling 

Guidance, and this guidance. The required and optional data elements needed for inventories 

(described in Section 2.5.7) should be included as fields for reporting to the EPA. Where the AERR/EIS 

has required fields, those fields should be required by the Emission Statement regulations.

Additional details on developing emission statement regulations can be found in a dated, but still 

relevant guidance document entitled “Guidance on the Implementation of an Emission Statement 

Program (DRAFT),” available at http://www.epa.gov/ttn/chief/eidocs/draft-implement_jul1992.pdf. 

Where data elements to be collected are mentioned, users of that guidance should defer to the 

paragraph above, explaining that data elements should be coordinated with AERR/EIS requirements and 

the recommendations in this guidance for optional fields.

3.7 Maintenance Inventories

Maintenance inventories reflect the emissions conditions associated with a NAAQS redesignation to

attainment following an initial area designation of nonattainment. Thus, the base year for the 

maintenance inventory should reflect emissions during the time period when attainment was measured. 

Otherwise, all attributes of the base year inventory apply. A maintenance inventory is a component of a 

maintenance plan and is therefore submitted to the EPA as a SIP revision. Thus all guidance for 

completeness, temporal extent, spatial extent, public hearings, documentation, and summaries applies

to these inventories.

The on-road portion of the inventory for the relevant pollutants and precursors for the last year of the 

maintenance plan would be the motor vehicle emissions budget(s) that are required for maintenance 

areas by 40 CFR 93.118(b). States may elect to also establish motor vehicle emissions budgets for the 

interim year or years for which they have submitted inventories or for the base year of the maintenance 
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plan. Those decision should be made through the interagency consultation process that is required by 

CAA section 176(c)(4)(D) and 40 CFR 93.105.

Specific additional guidance for maintenance plan SIPs is also available in the memorandum entitled 

“Maintenance Guidance Document for Certain 8-hour Ozone Areas Under Section 110(a)(1) of Clean Air 

Act” (available at http://www.epa.gov/ttn/caaa/t1pgm.html).

3.8 Projected Inventories

The purpose of the projected inventories is to provide an emissions estimate for a year beyond the base 

year. These inventories are also called future-year inventories. The projected inventories are used for 

modeled attainment demonstrations and ROP/RFP plans. For the modeled attainment demonstration, 

the projected inventory represents the emissions needed to attain a NAAQS (according to the modeling) 

in a future year. For the ozone ROP/RFP plan(s), expected percent reductions of pollutants on specific 

timetables need to be shown. Calculating expected reductions involves estimation of emissions 

reductions, which can result in a projected inventory that shows the remaining emissions after those 

reductions have occurred.

3.8.1 Attainment Year Projected Inventories

As listed in Table 4, there are two possible attainment year projection inventories. The first is the 

attainment projected inventory for the NAA. The second is the projected inventory for the modeled 

attainment demonstration, and it is presumed that the requirement for the modeled attainment 

demonstration also requires this inventory.

As described in Section 3.8.2, one possible use of the attainment projected inventory for the NAA is for 

showing emissions reductions associated with an ROP/RFP plan for ozone. While it is conceivably 

possible to estimate the emissions reductions (rather than future year emissions inventories) required 

by the ROP/RFP plan, the most common way to estimate the reductions is by creating future-year 

inventories and then calculating the difference between the ROP/RFP baseline and the attainment 

projected inventories for the NAA.

In addition, the on-road mobile portion of the attainment projected inventory for the NAA can serve as

the motor vehicle emissions budgets for VOC and NOX. Since these budgets are required for 

transportation conformity purposes by 40 CFR 93.118(b), such inventories provide a convenient and 

consistent way to meet that requirement. In this case, the on-road inventory should be created in 

accordance with transportation conformity guidance

(http:/www.epa.gov/otaq/stateresources/transconf/).

Creating projected inventories includes a large number of data sources and requires estimates for 

stationary point, nonpoint, on-road mobile, and nonroad mobile sources. In addition, some areas may 

choose to use average fires to represent these highly variable (from year to year) and large contributors 

to emissions. Biogenic sources are not generally forecast into the future because they are so dependent 

on meteorology. Section 5 covers the details on projected inventories.

[PM2.5 Implementation Placeholder]
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3.8.2 Rate of Progress and Reasonable Further Progress Emissions Reductions

As described in Section 3.4 and the Proposed Ozone Implementation Rule, Moderate and above NAAs 

must have a plan for meeting a 15 percent VOC emissions reduction (ROP plan) within 6 years after the 

NAA designation. Serious and above NAAs must also have a plan (RFP plan) to meet a requirement for 

an additional 3 percent per year VOC reduction (annual RFP) for each 3-year period after the initial

6 years (after the NAA designation) until the attainment date. In both cases, the VOC reductions can be 

substituted with NOX reductions when specific conditions apply. Serious and above areas may submit 

two separate plans since the annual RFP plan is due one year later. Collectively, this guidance calls these 

plans the ROP/RFP plan(s).

In particular for the ROP requirement, an attainment year projected inventory for the NAA can also 

meet the ROP requirement by providing a projected inventory that shows the 15 percent VOC (or NOX, 

as applicable) reductions when compared to the ROP/RFP baseline NAA inventory. For Serious and 

above areas, an additional projected inventory may be needed to meet the ROP requirement. This is 

because the ROP requirement at 6 years can be earlier than the expected attainment date. In the case 

for Serious and above areas, ROP plans cannot use the projected attainment inventory for the NAA, but 

rather should use an inventory projected at the 6-year interval.

To estimate the emissions reductions associated with ROP/RFP plans, air agencies should rely on the 

same techniques as for other projection purposes, which are described in Section 5. When these 

reductions are calculated by creating projected inventories, the on-road portion of the inventories may 

also need to follow transportation conformity guidance

(http:/www.epa.gov/otaq/stateresources/transconf/) so that it can be used to set the motor vehicle 

emissions budgets.

The emissions projections should include emissions growth where it occurs, emissions reductions 

intentionally included to meet the reductions needed for ROP/RFP, as well as emissions reductions 

occurring for other reasons (e.g., as co-benefits from implementation of other NAAQS and from national 

mobile source or stationary source rules). These emissions projections will result not only in estimated 

reductions (which are required to be included in the ROP/RFP plans), but also in projected emissions 

inventories. Thus, the EPA recommends that summaries of these inventories are included in the 

ROP/RFP plan(s) to communicate the emissions reductions by comparing against the ROP/RFP baseline 

NAA inventory. 
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3.9 Public Hearings

Emissions inventories are considered a part of the SIP under the CAA (see Sections 172(c)(3) and 

182(a)(1)(A)); therefore, emissions inventories are required to be included in the public participation 

associated with SIPs as specified in CAA 110(a)(2). Traditionally, states have submitted their emissions 

inventories along with other elements of the SIP, and emissions inventories must be approved or 

disapproved by the EPA under Section 110(k), including assessing the requirement that it was subject to 

a public hearing at the state level.

18

Additionally, there are policy reasons that support the need for emissions inventories to be approved 

with the SIP. Some emissions inventories must be used as a basis for ozone RFP plans for areas classified 

as Moderate or above. Additionally, all NAAs seeking redesignation to attainment will rely on an 

emissions inventory for purposes of submitting a maintenance plan under Section 175(A). Because the 

emissions inventories and projections play such a fundamental role in determining the reductions 

necessary to attain and maintain the standard, they need to receive full public scrutiny and be formally 

incorporated into the SIP.

However, because the regulatory consequences of the inventories are delayed, the EPA believes that it 

is appropriate to provide a “de minimus” deferral of the state public hearing requirement up to such 

time as a public hearing is held on the regulatory provisions. Thus, the EPA recommends that the 

hearing on the base year NAA inventory be held in conjunction with the hearing on the associated 

regulatory plan. For areas classified as Moderate or above, the state would need to provide the EPA with 

verification that a public hearing was held for the emissions inventory no later than the time the state

submits an ROP plan, which is due first. For Marginal ozone NAA, such verification would be due when 

and if the state submits a maintenance plan for redesignation. However, to the extent a Marginal area is 

“bumped-up” and, therefore, is required to submit a RFP plan, the verification would be due as for 

Moderate and above areas.

Under this approach, where emissions inventories are used in the development of an ROP/RFP plan or 

attainment demonstration, states can defer the public hearing on these inventories until the time the 

areas adopt and submit their RFP plans and/or attainment demonstrations that rely on such inventories. 

The EPA would not take action to approve or disapprove such inventories until the state completes the 

state public participation process. If a state opts to submit a consolidated SIP submittal, this should not 

be an issue. This approach is consistent with the historical approach taken since 1992, available in 

“Public Hearing Requirements for 1990 Base-Year Emissions Inventories for Ozone and Carbon 

Monoxide Nonattainment Areas” (see http://www.epa.gov/ttn/oarpg/t1/memoranda/o_ei1992.pdf).

 

18 A public hearing must be offered for every SIP submittal but a hearing does not need to actually occur if no one requests a 

hearing. The detailed requirements for public notice and hearings are given in 40 CFR 51.102. See also Attachment B of 

“Regional Consistency for the Administrative Requirements of State Implementation Plan Submittals and the Use of Letter 

Notices,” EPA memorandum dated April 6, 2011, from Janet McCabe, Deputy Assistant Administrator for the Office of Air & 

Radiation to the Regional Administrators, www.epa.gov/airquality/urbanair/sipstatus/docs/FINALSIPGuidelinesSubLtrsPN.pdf.
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3.10 Submit Inventory Parts of SIP to the EPA

The structure of what the air agency will provide is integral to the emissions inventory SIP submittal 

process, since the list of tangible data items and documentation forms the basis of what the EPA will 

review and ultimately approve for a SIP. A Microsoft® Word ® format template for air agencies to use for 

organizing the inventory portion of their SIPs is under development19. Table 12 provides the suggested 

inventory elements of an Emissions inventory SIP that corresponds to the template and indicates 

whether they are relevant for ozone, [PM2.5 Implementation Placeholder], and/or regional haze SIPs. 

Refer to the tables in Section 2.3 for more information on which are required and which are optional. 

This section (and Table 12) does not include RFP inventories since those are submitted with a separate 

ROP/RFP plan. Similarly, it does not include information needed for a modeling attainment 

demonstration submittal to the EPA, with the exception of the inclusion of statewide inventory 

summaries for ozone and PM2.5 SIPs for areas that have modeled attainment demonstrations as part of 

their SIP requirements.

Table 12: Suggested Elements of an Emissions inventory SIP

SIP Planning Inventory Documentation Element Ozone PM2.5

+ Haze 

Background: Includes key elements explained in this guidance, such as the 

nature of the air quality problem (or arrival at attainment status for 

maintenance SIPs), priority source categories and point sources, 

pollutants covered, spatial extent, and other key inventory aspects.

Y Y

 Overall Base Year Emissions Summaries: All emissions are for 

relevant pollutants only. Data categories would minimally be point, 

nonpoint, nonroad mobile, and on-road mobile, though more 

detailed categories are acceptable. Biogenic sources and other 

sources can optionally be included as well, and may be required by 

regional offices for areas doing modeled attainment demonstrations.

See 

Table 

13

See 

Table 

13

 Overall Projected Attainment Year Emissions Summaries: The same 

as the base year summaries except using the attainment projected 

inventory for the NAA. These summaries are optional for the ozone 

Emissions inventory SIP. For ozone and when developed in accordance 

with transportation conformity guidance, the on-road portion also 

can set the motor vehicle emission budgets for VOC and NOX. If not 

provided in the Emission Inventory SIP, the summaries would be 

needed in the Modeled Attainment Demonstration.

See 

Table 

13

Stationary Point Sources:

 Introduction with more detailed documentation of the emissions 

from stationary point sources, including the point source emissions 

threshold, how the point sources were identified, how emission 

estimates were made including emission factors, activity data, and 

control assumptions.

Y Y

 

19 At the time of this draft, the template is not yet available. It will be a replacement for the “Example 

Documentation Report for 1990 Base Year Ozone and Carbon Monoxide State Implementation Plan Emissions 

inventories, March 1992”, located at http://www.epa.gov/ttn/chief/publications.html#general. 
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SIP Planning Inventory Documentation Element Ozone PM2.5

+ Haze 

 This section includes additional point source emissions summaries. 

These summaries should include at a minimum: the county, Agency 

Facility ID, plant name, physical address, total control efficiency, key 

control devices, NAICS code, and emissions with and without rule 

effectiveness applied. The Agency Facility ID or some other ID should 

be included that can easily map to the EPA facility records in EIS. This 

can be more difficult when air agencies change their Agency Facility 

IDs.

See 

Table 

14

See 

Table 

14

Stationary Area (Nonpoint) Sources: 

 Introduction with more detailed documentation of the emissions 

from stationary nonpoint sources, including how the nonpoint 

sources were identified, the model version used, which sources were 

not addressed and why, how partial county emissions were 

estimated, and how emission estimates were made including models 

or tools, emission factors, activity data, and control assumptions.

Y Y

 This section includes additional nonpoint source emissions 

summaries. For county and emissions processes reported that have 

reductions associated with rules, these summaries should include any 

control efficiencies or rule effectiveness assumed and emissions with 

and without rule effectiveness applied. Projected attainment year 

emissions summaries may also be required for areas performing 

modeled attainment demonstrations.

See 

Table 

15

See 

Table 

15

Nonroad Mobile Sources

 Introduction with more detailed documentation of the emissions 

from nonroad mobile sources, including now the nonroad mobile 

sources were identified, which sources were not addressed and why, 

how partial county emissions were estimated, and how emissions 

estimates were made including model version, source of input data, 

input and output data files, and any post-processing methods used to 

develop the inventory.

Y Y

 This section includes additional nonroad source emissions 

summaries. Projected attainment year emissions summaries may also 

be required for areas performing modeled attainment 

demonstrations.

See 

Table 

15

See 

Table 

15

On-road Mobile Sources

 Introduction with more detailed documentation of the emissions 

from on-road mobile sources, the model and version used, how 

partial county emissions were estimated, and how emissions 

estimates were made including sources of input data, input and 

output data files, and any post-processing methods used to develop 

the inventory.

Y Y

 This section includes additional on-road source emissions summaries. 

Projected attainment year emissions summaries may also be required 

for areas performing modeled attainment demonstrations.

See 

Table 

15

See 

Table 

15
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SIP Planning Inventory Documentation Element Ozone PM2.5

+ Haze 

Other Sources

 A description of other sources in the emissions inventory not 

included in the planning inventories and reasons why they are not 

included.

Y Y

 This section includes summaries, if available, of other sources of 

emissions. Projected attainment year emissions summaries may also 

be required for areas performing modeled attainment 

demonstrations.

See 

Table 

15

See 

Table 

15

Demonstration of Public Hearing: A brief description of the public hearing 

process, a summary of the results, and any other relevant materials. The 

purpose of this section is to provide evidence for the public hearing and what 

the air agency learned through the process.

+

PM2.5 is included here only as a placeholder for subsequent versions of this guidance.

Table 13 provides the summaries to include in the background section. In the table, “data category” is 

consistent with the definition provided in Table 12 and Section 2.5.1. If both the base year inventory and 

the attainment projected inventory are included in the background, then the same summaries should 

generally be provided for both.

Table 13: Summaries to include in the background 

Emissions Summaries Ozone PM2.5

+ Haze

Emissions for the state by data category Y

‡

Y

Annual base year emissions for the state by county and data category Y

‡

Y

Annual base year emissions for the NAA by data category Y

Annual base year emissions for the NAA by data category and county (or 

partial county)∆

Y

Summer day base year emissions for the NAA by data category Y

Summer day base year emissions for the NAA by data category and county (or 

partial county)λ

Y

+ PM2.5 is included here only as a placeholder for subsequent versions of this guidance.

‡ For SIPs that include air quality modeling, this section can include both summaries of the planning and the modeling 

inventories. Since modeling domains are usually much larger, multi-state areas, the resolution of the modeling inventory 

summaries depends on the modeling guidance and the preferences of the regional office. One option is to include countylevel detail for the state(s) included in the NAA, but state-level detail for surrounding states.

∆ Providing both the county and partial county could provide more flexibility for states when submitting periodic inventories.

λ Partial county emissions can be included rather than, or in addition to, full county, where applicable.

Table 14 provides the minimal requirements for summaries to include in the point sources section. If 

both the base year inventory and attainment projected inventory are included in the background, then 

the same summaries should generally be provided for both.
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Table 14: Summaries to include in the point sources section

Emissions Summaries Ozone PM2.5

+ Haze

Annual base year emissions for each point source as a facility total, within the 

state.

Y

Annual base year emissions for each point source as a facility total, within the 

NAA. 

Y

Summer day base year emissions for each point source as a facility total, 

within the NAA.

Y

+ PM2.5 is included here only as a placeholder for subsequent versions of this guidance.

Table 15 provides the minimal requirements for summaries to include in the nonpoint and mobile 

sources sections. If both the base year inventory and the attainment projected inventory are included in 

the background, then the same summaries should generally be provided for both. 

Table 15: Summaries to include in the nonpoint and mobile sources sections

Emissions Summaries Ozone PM2.5

+ Haze

Annual base year emissions by county and SCC (or SCC group‡), within the 

state.

Y

Annual base year emissions by county and SCC (or SCC group), within the 

NAA.

Y

Summer day base year emissions by county and SCC (or SCC group), within 

the NAA.

Y

+ PM2.5 is included here only as a placeholder for subsequent versions of this guidance.

‡ See additional information below on SCC groups.

SCC groups for on-road and nonroad mobile sources can be useful in limiting size of summaries without 

much loss of information. For example, SCC groups can be formed for grouping by vehicle type and fuel, 

dropping the road classifications. Vehicle types can be further grouped into light duty and heavy duty. 

The amount of grouping appropriate depends on what a particular summary and SIP are trying to 

communicate. SCC groups can be suggested as appropriate by regional offices or air agencies as part of 

the consultation for what will be included in the emissions inventory SIP.
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4 Developing Current Emissions inventories

This section covers the decisions that states will need to make regarding any “current” emissions 

inventory, including a base year NAA or state inventory, RFP baseline inventory, periodic inventory (for 

ozone or regional haze), or maintenance inventory. As a reminder, all inventories described in this 

section are inventories of actual emissions; these inventories do not contain emissions based on 

potential to emit nor allowable emissions.

4.1 Inventory Years

A fundamental step in creating a base year inventory is the choice of inventory year. The Ozone, PM2.5

and Regional Haze Implementation Rules include specific language regarding the choice of inventory 

years, and those regulatory requirements supersede any guidance provided in this section. Since the 

purpose of the base year inventory is to represent relatively current emissions conditions, there is a 

general preference for using as recent a year as practical. This means that the year of emissions 

estimates is usually several years earlier than the year in which the inventory work is done, given the 

time that it takes to compile an emissions inventory (for example, an inventory with 2014 emissions may 

not be compiled until 2016).

Ozone

The primary considerations in choosing a baseline inventory year as covered in this guidance are (1) the 

implementation rule requirements, (2) the appropriateness for use as an ROP/RFP baseline year, and 

(3) the availability of data. This is in contrast to inventories used for air quality modeling, for which 

meteorology, and availability of ambient data are the primary considerations, with inventory availability 

secondary. This is because the meteorological conditions selected should be associated with ozone 

formation that is representative of either the ambient data relied upon for designation to 

nonattainment or recent ambient data, as appropriate. Choosing a year based solely on inventory 

availability could result in choosing an inappropriate year (considering ambient measurements and the 

meteorology that led to those measured concentrations). As a result, the base year(s) used in the 

planning inventories can be different than the modeling base year and associated modeling inventory.

The consideration of the implementation rule requirements means that the inventory base year should 

be one of the three years of ambient data used for designation of the NAA or another applicable year as 

described in the implementation rules and here. The idea behind this connection is that the inventory 

should represent the emissions conditions in the local area associated with the nonattainment problem. 

Given this purpose, situations may arise where the most applicable available inventory is not one of 

these three ambient-data years. 

Two examples of such situations are offered here. In the first case, a newer inventory may be advisable. 

Because of time that it takes for designations to occur and the period allowed for SIP submittal, a 

significant increase in emissions could occur between the designation period and the time SIPs are 

submitted. This has occurred in some areas due to oil and gas development, for example. In these cases, 

it may be more appropriate to use an inventory year that is newer than one of the three years of data 
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used for designations, to represent the higher emissions or different source mix associated with a more 

current year. Another example is that in an area where mobile sources are a small part of the emissions 

inventory, emissions may not have changed much from a year prior to the three-year period of ambient 

data. In this case, an available inventory prior to one of the three years may sufficiently represent the 

inventory. In both cases, the air agency preparing the SIP should explain these issues as part of its 

justification for not using one of the three years.

The consideration of the appropriateness for the ROP/RFP baseline year means that states should 

consider that that base year will be the same for the ROP/RFP baseline. In general, states will select a 

year within the three year period associated with the ambient data used to make the nonattainment 

designation. Within this time period, a large source of emissions may be reduced. If a state chooses a 

year after those reductions have occurred, then the state would not get the benefit of those reductions 

in meeting their ROP/RFP requirements. In addition if those emissions were a key part of the 

nonattainment problem, then the choice of the later year would not follow the guidance that the year 

selected be representative of the conditions leading to nonattainment.

Lastly, the consideration of “availability” is simply what data are (or will be) available to the air agency 

during the time alloted for SIP preparation. Often, the triennial NEI year inventories (as described above) 

are useful starting points for meeting the various “current” inventory requirements associated with SIPs. 

For these triennial NEI years, states are already required to have prepared and provided to the EPA

complete inventories of criteria pollutants and precursors important for ozone, PM2.5, and regional haze 

SIPs. Other inventories may also be available, for example, one that was developed to meet planning 

requirements for one NAAQS may be a useful starting point for the inventory for a planning requirement

for a different NAAQS. A secondary benefit of using an NEI year is that NEI data are available for all 

states, and information from more than one state may be needed for attainment demonstration 

modeling purposes. Additionally, other data needed for modeling (e.g., meteorology and SMOKE inputs) 

are more likely to be available from the for the triennial NEI years.

Regional Haze

The Regional Haze Rule includes both a baseline inventory requirement and a current year inventory 

requirement. Under 40 CFR 51.308(d)(3)(iii), the rule states that “The baseline emissions inventory year 

is presumed to be the most recent year of the consolidate [sic] periodic emissions inventory.” For the 

initial regional haze SIPs, the year used should have fallen between and inclusive of the 2000 to 2004 

baseline period. Most areas used 2002 as their baseline inventory year in their initial SIPs based on an 

OAQPS memo about this issue (see http://www.epa.gov/ttn/naaqs/aqmguide/collection/cp2/

20021118_wegman_2002_base_year_emission_sip_planning.pdf).

Also for regional haze, an updated current year inventory is required with each 5-year progress report or 

10-year SIP revision. In both cases, states can choose to use the most recent NEI year (the 

“presumption” of the rule) or another year that can be justified. In general, it will be easier to justify a 

newer year than the most recent NEI year than an older year, since the purpose of the updated current 

year inventory is to provide an estimate of emissions for the most recent year possible. It is presumed 

that because of ongoing control programs for mobile and stationary sources, which get additional 
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reductions each year, more recent year inventories will reflect more progress towards the goals of 

emissions reductions in support of the regional haze goals.

4.2 Pollutants and Pollutant Precursors to Include in Inventories

This section describes the pollutants and precursors that should be included in the planning inventories

for the ozone, PM2.5, and regional haze rules. Pollutants for ROP/RFP inventories are also described in 

Section 3.4.2. 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, EPA encourages air

agencies to develop inventories for all pollutants where possible to support integrated, regional-scale 

modeling, and control strategy development for ozone, PM2.5, and regional haze.

The CAA 172(c)(3) requires “the relevant pollutant or pollutants” to be included in inventories for SIPs. 

The ozone, PM2.5 and regional haze implementation rules include specific language regarding the 

pollutants and precursors to be included, and those regulatory requirements supersede any guidance 

provided in this section.

For the 8-hour ozone NAAQS, the pollutants to be inventoried are VOC, NOX, and CO. For ROP/RFP 

baseline NAA inventory for ozone, only VOC and NOX should be included (though CO could also be 

included in the same inventory if it also serves as the attainment projected inventory for the NAA).For 

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

identified for ozone and PM2.5, except for CO.

[PM2.5 Implementation Placeholder]

4.2.1 Condensable PM emissions

[PM2.5 Implementation Placeholder]

Table 16: Source types expected to include condensable PM+

EIS Sectors (and subsectors)

Subsectors and 

Degree of 

Condensable

Data 

Categories

+

This table is included as a placeholder pending the addition of PM2.5 to this draft guidance.

4.2.2 Regulatory Definition of VOC

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

negligibly reactive in atmospheric photochemistry. These include methane, ethane, methylene chloride, 

1,1,1-trichloroethane (TCA), several Freon compounds, acetone, perchloroethylene, and others. States 

should use the CFR reference above to find the complete list. Over time, 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; for example, methane

impacts on ozone have been observed in areas of high methane emissions associated with oil and gas 

development. The emission factors used to estimate organic emissions generally account for

nonmethane hydrocarbons (NMHCs). 
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For SIP purposes, state, local and tribal agencies should report VOC as defined by the EPA (40 CFR

51.100(s)). This is the case regardless of the treatment of methane for modeling inventories, which is 

addressed in more detail in the next subsection.

4.2.3 Treatment of Methane

The treatment of methane in emissions inventories may be relevant for emissions used in modeled 

attainment demonstrations. Methane is not expected in other planning inventories associated with SIPs. 

This section is included in this guidance, however, to explain the context for which methane emissions 

can be important and to specifically note its possible relationship to the VOC emissions that are 

associated with SIP planning inventories. In some cases, air agencies interested in considering non-VOCbased estimates of methane in their modeling inventories may optionally choose to consider methane 

as part of non-modeling inventories as well.

The air quality models used for modeled attainment demonstrations use methane as one of the 

modeled pollutants. However, these models have typically used a fixed concentration of methane that 

does not change. Thus, typical applications have not used methane emissions from emissions 

inventories.

Unlike the air quality models, the emissions processing steps to prepare emissions inventories for use in 

air quality models do compute methane emissions. Methane has traditionally been calculated by 

applying a factor to the VOC emissions to calculate total organic gases (TOG). These TOG emissions are 

then split during emissions processing into “model species,” which include methane. With the low 

reactivity of methane and the absence of its use in air quality modeling for ozone, the VOC-to-TOG 

factors and the methane part of the speciation factors were not given much scrutiny. Previous versions 

of this guidance encouraged inventory developers to simply use the default VOC-to-TOG factors that 

were associated with the speciation profiles without further analysis, since the methane emissions were 

not used. This approach may still be appropriate for most or all NAAs for their modeled attainment 

demonstration.

In limited situations, air agencies may want to investigate the extent that methane emissions play a role 

in ozone episodes. Hence, additional efforts going beyond the use of the default VOC-to-TOG profiles 

and default methane fractions from the speciation profiles may develop over time. In this case, it may 

be of interest to include methane emissions inputs to air quality models to achieve sufficient model 

performance for a modeled attainment demonstration. Approaches can include incorporating methane 

emissions from other sources into emissions inventories used for modeled air quality. For example, the 

MOVES model estimates methane emissions directly, so there would be no need to use VOC speciation 

to estimate those emissions. Air agencies considering methane as a contributing factor should consult 

with their EPA regional office to discuss the best sources for such data as this inventory development 

area is undergoing many changes at this time. Furthermore, more specific VOC-to-TOG factors and 

speciation profiles may be useful, particularly for analysis related to areas of very high methane 

emissions. These issues are all associated with modeled attainment demonstrations, and do not affect 

the VOC emissions reported as part of the emissions inventory SIP.
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4.3 Identification of Priority Sources

The Proposed Ozone Implementation Rule and previous PM2.5 Implementation Rule refer to the AERR 

requirements for creating the inventories used for SIPs. This includes the AERR requirement that 

inventories must include all sources of emissions. Thus, inventories used for SIPs are expected to be 

complete, with emissions from all sources (other than de minimus sources) characterized in some way.

In addition to better understood and routine emissions sources, emissions from known or quantifiable 

fugitive sources such as leaking tanks or valves should be included in inventories when these emissions 

can be quantified in both the base and future years and because their reductions could help in achieving 

attainment. These emissions should not be excluded based on an invalid assumption that they are 

“malfunctions”. In addition, startup/shutdown emissions should be included in inventories (see Section 

4.8.1).

While completeness is required, there is no requirement that all parts of an emissions inventory be 

completed with the same degree of rigor. Because emissions inventory development is time consuming 

and expensive, it is wise for inventory developers to focus their resources on the sources of emissions 

making up the bulk of the pollutants relevant for the NAAQS in question. To the extent that an inventory 

is to be used for multiple NAAQS or for multi-pollutant analysis, then the larger sources important for all 

relevant pollutants should be characterized with as much technical rigor as is feasible.

Fortunately, existing inventories can help states guide their initial understanding of the sources of 

pollutants in a particular area. Air agencies can rely on the latest NEI or previously compiled SIP 

inventories to guide further development. The NEI is commonly used as a starting point for state and 

regional planning purposes for NAAQS implementation and regional haze planning. The EIS can help by 

providing emissions summaries for counties or groups of counties and for emissions sectors or SCCs.

For additional information, the Particulate Emissions volume of the EIIP technical report (see 

http://www.epa.gov/ttn/chief/eiip/techreport/) provides thorough recommendations for identifying 

sources of PM emissions. These recommendations can be useful for other pollutants as well.

Starting with an existing inventory poses some risks and challenges. Here we try to address the most 

common issues associated with SIP inventories when starting with existing inventories:

1. How do I know which sources in an existing inventory should get further review?

The EPA suggests the following considerations in deciding which sources to be reviewed:

a. The largest contributors to the pollutants of interest (i.e., the pollutants contributing to 

ozone and/or PM2.5 formation) using some coarse groupings, such as the EIS Sectors, 

Tier 2, or Tier 3 groups. 

b. Sources within the NAA (or contributing to it in the case of modeling attainment 

demonstration inventories). Special considerations to sources closest to and upwind of 

violating monitors may deserve special attention.

c. Knowledge about the growth or retraction of a particular sector of the economy. Oil and 

gas production is a recent example of a quickly growing industrial source of emissions.
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d. Considering whether the proportion of emissions associated with a particular source is 

likely to have an impact on the outcome of decisions. Emissions methods/changes for 

sectors that are likely to have a large impact on the planning process should get higher 

priority.

e. Assessing whether the approaches used in the preparation of SIP emissions are updated 

with current approaches, including appropriate emission factors. This is particularly 

important for source categories for which there is large uncertainty and those with 

ongoing research.

2. What if the original inventory does not use good approaches?

The EPA recommends starting with inventories that have available and clear documentation. If 

an inventory developer cannot figure out how the emissions were estimated, then it will be 

difficult to build upon those results.

With documentation, inventory developers should be able to evaluate the quality of approaches 

used. As part of the NEI program, the EPA publishes updated methods for many nonpoint 

emissions categories. The highest quality point source emissions estimates are based on facilityspecific testing, and where not available, current emission factors. Mobile emissions should be 

based on the latest mobile models, using as many location-specific inputs as possible.

If it is determined that a starting inventory does not use the latest methods, it is advisable to 

reassess those emissions with newer methods (or other available inventories) prior to deciding if 

that category requires even further work.

3. If I need to make updates, where are the latest approaches available?

The EPA’s NEI program is a good source of the latest approaches and approaches in 

development. In many cases, multi-jurisdictional organizations also have updated approaches 

for various emissions sectors. The Emissions Inventory Improvement Program volumes still have 

a lot of valuable information on emissions, though some sections are outdated (see 

http://www.epa.gov/ttn/chief/eiip/techreport/). Approaches have historically included AP-42 

and WebFire emission factors, though these resources are outdated for some sectors. For more 

information on updated emission factors, see Section 4.6.

4. What do I do if the NEI approach has added PM or other emissions that I did not report, and I 

think that they are invalid?

The EPA commonly augments PM emissions provided by states in the NEI because many states 

do not report total PM2.5 and neglect the condensable portion of PM emissions (see also Section 

4.2.1). Consistent with the requirements for complete SIP inventories, the EPA works to create a 

complete and accurate NEI. If emissions have been added erroneously, states should make 

those improvements, but should also let the NEI program staff know that there may be a flaw in 

their methods and provide a better source of information. Just because a source has not 

reported condensable emissions does not mean that they do not exist or should not have been 
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characterized. In some cases, states may need to go back to sources to clarify that condensable 

PM emissions must be provided to the state agencies.

Another source for added EPA criteria pollutant and precursor emissions is NH3 for point sources 

from the TRI. Since these are emissions that the facility submits to the EPA through the TRI 

program, they should potentially be included in SIP inventories for PM2.5 SIPs and ideally 

included in inventories provided to the EPA (as a point or nonpoint source). If a state air agency 

believes that these emissions are erroneous or unimportant, some discussion of these sources 

should be included in their SIP as to why the TRI emissions are not being used. For incorrect 

emissions, states should consider coordinating with the facility to improve the emission 

estimates.

4.4 Spatial Extent

The spatial extent of an inventory refers to counties, states, or other geographic regions covered by the 

emissions data. As described in previous sections, inventories needing to be included in SIPs are either 

for the NAA area only (for ozone and PM2.5) or are for the entire state (for regional haze and ozone or 

PM2.5 when modeled attainment demonstrations are needed). Modeled attainment demonstrations use 

emissions from a regional multi-state area. While It is not a SIP requirement to submit an inventory for 

other states, the emissions are needed to do the modeling.

A number of complicating issues related to spatial extent arise with inventories. Below, more 

information is provided on partial counties, when point-source locations are needed for emissions that 

have traditionally been nonpoint sources, shapefile-based inventories, and link-based mobile emissions.

4.4.1 Nonattainment Areas with Partial Counties

In some cases, NAAs do not follow county boundaries. Since most inventories and many underlying 

datasets are available at the county level, this poses a challenge for emissions calculations, in particular 

for nonroad and mobile sources.

Air agencies may wish to use full-county emissions in meeting some SIP requirements, despite the 

designation of partial-county NAAs. The EPA has considered the advisability of using whole-county 

emissions to represent partial county emissions and has determined that this is not possible. In 

particular, using whole-county emissions would pose a challenge for using these inventories for 

ROP/RFP analyses, which can only include reductions within the NAA. Thus, areas designated as partial 

counties should estimate those partial county emissions using one of the approaches described here.

For point sources, Geographic Information System (GIS) technology enables straightforward selection of 

point sources into a partial-county NAA by intersecting a dataset of point source latitude/longitude 

coordinates with a shapefile of the NAA boundaries.

For nonpoint and mobile sources, available inventories and methods are often designed to create 

county totals, making partial counties much more difficult. A variety of acceptable approaches exist for 
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calculating partial county emissions, though the particular approaches chosen should be agreed to as 

part of developing the plan for the SIP planning inventory as described in Section 2.2.

1. Custom calculations: Air agencies could develop a custom approach to estimate emissions using 

activity data estimated for the partial county area. Since many source categories need to be 

estimated, this could be a very labor intensive approach, or could be used for just key categories 

where other approaches are insufficient.

2. Shapefile-based inventories: See Section 4.4.3.

3. Use of spatial allocation surrogates: Some sources of data exist at sub-county resolution, 

including road networks, travel demand model results (see also Section 4.4.4), and census data 

that are available at census tracts or blocks. When the emissions activity can be reasonably

assumed to follow an allocation method based on one such surrogate dataset, GIS techniques 

can be followed to apportion a county emissions estimate to a partial county NAA based on the 

patterns of these sub-county data.

4. Use of gridded modeling data: Modeled attainment demonstrations rely on air quality modeling 

that uses gridded emissions data, which could be resolved at a sub-county resolution. Gridding 

resolutions of 12-km, 4-km, or even 1-km have been used. Similar to what was described above 

in the previous approach, emissions processing relies on spatial surrogates to apportion countylevel data to grid cells needed for modeling. Rather than take a custom spatial surrogate 

approach, these gridded data may be sufficient to apportion county-level data to a partialcounty NAA using GIS overlay techniques. Such an approach would sum the parts of the gridded 

data intersecting the partial county area to provide the partial county area inventory. The 

primary difference in this approach compared to the previous approach is the intermediate step 

of using the gridded data. This could be appealing since those gridded data may already be 

available from modeling done for attainment demonstrations.

5. Expert judgment: When there is no appropriate sub-county data surrogate available, when air 

quality modeling is not part of the SIP process, or when a category is relatively unimportant to 

the SIP planning process, other methods may be advisable. In this case, an air agency should 

explain their rational to the respective EPA regional office and come to agreement on a 

technically reasonable approach. Such approaches could include using the entire county 

estimated emissions, assuming some fraction based on understanding of county activities, or 

taking a area-proportional (uniform distribution) approach. In this latter approach, the partial 

county emissions are assumed to be the total county emissions times the area of the partial 

county divided by the area of the total county.

Since these partial county emissions calculations could need to be done for a variety of inventories and 

for SIP revisions, considerations should be made for the repeatability of the approach so that it does not 

become overwhelming to the analysis. In collaboration with the EPA regional office, a balance needs to 

be found among level of effort, technical credibility, and repeatability.
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The latest EPA spatial allocation data are available on the Emissions Modeling Clearinghouse (EMCH) 

Spatial Allocation website. The latest spatial approaches and data are also available with the latest 

emissions modeling platform data on the EMCH main page. The EIIP Volume III, Chapter 1, Section 4.3

provides some additional information on spatial allocation; however, the examples used for spatial 

allocation approaches are much too old for most applications, and more sophisticated spatial surrogate 

approaches are available than those given as examples. In particular, except in rare circumstances, the 

use of population data as an allocation method is outdated and not recommended. 

4.4.2 Point Source Locations Needed for Modeling of Traditional Nonpoint Sources

In some cases, the details needed in a modeled attainment demonstration push inventory developers to 

use point-source locations for source categories that have traditionally been nonpoint sources. Some 

examples include sources of agricultural ammonia, dry cleaners, and gas stations. Rather than creating a 

much larger point source inventory, one approach is to keep a source as nonpoint, but use an emissions 

processing technique for modeling known as area-to-point allocation.

While this topic is primarily one for consideration in modeling inventories, it is included here because 

the planning inventory often provides a starting point for the modeling inventory (for the NAA counties). 

To the extent that modeling needs can drive additional detail in the planning inventories, this area-topoint feature can allow small sources to be included as nonpoint sources in a planning inventory but still 

allow point source locations to be used for modeling.

In area-to-point allocation, the emissions processor for modeling starts with county-wide estimates and 

a user-provided dataset that allocates county wide emissions to discrete latitude/longitude points 

(within the county). The inventory developer still must obtain the point source locations and proportion 

of countywide emissions, but the point source inventory remains more focused on the largest sources. 

Using an area-to-point allocation approach also avoids having to define stack parameters for inclusion of 

small sources in the point source inventory, which is useful because the stack parameters are not 

necessarily relevant to or available for these source categories.

4.4.3 Shapefile-based Inventories

The EPA collects inventories for the NEI for commercial marine and locomotives using GIS shapefilebased inventories. Rather than including emissions as a county total, the emissions are allocated to 

individual sub-county areas or lines, each with its own GIS polygon shape. This approach was developed 

primarily to support fine scale and risk modeling that are done at a scale finer than most modeled 

attainment demonstrations.

These inventories can be useful for computing partial county emissions for those categories using this 

approach. Otherwise, it may not be necessary to start with the shapefile-based inventories for SIP 

planning, except in circumstances where the CMV and locomotive emissions spatial distribution is 

critical to the modeled attainment demonstration in some way. This may be important in NAAs that 

contain large ports and/or are near major coastal or inland waterways.
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4.4.4 Link-based On-road Mobile Emissions and Travel Demand Models

SIP inventories often put great focus on mobile sources through the use of detailed emissions by 

roadway segments (or links) and the use of travel demand models (TDMs). This possibility is simply 

mentioned here for completeness and is not necessarily recommended, since these efforts are often 

substantial. The approach can also help with partial county emissions estimates. 

4.5 Temporal Basis

Various temporal bases may be needed for meeting different inventory requirements for SIPs. These can 

be different for ozone, PM2.5, and regional haze.

For ozone SIPs, summer day emissions (as defined in Section 2.5.2) are used for the base year inventory 

for the NAA. Additionally, for areas including modeled attainment demonstrations in their SIP, statewide 

ozone summer day emissions and statewide annual emissions may also be important for regional office 

evaluation and approval of the SIP.

Summer day emissions are as defined in Section 2.5.2 and in the AERR20. These emissions should be 

representative of the conditions leading to nonattainment, as recommended by the air agency and

approved by the EPA prior to computing emissions. In instances where ozone values are elevated above 

the level of the NAAQS only in non-summer months or on weekend days, including when winter 

emissions or weekend emissions dominate the episode, the goal of representativeness and the purpose 

behind the definition may support using those emissions instead of limiting the data to “summer” or 

“weekday” emissions.

To calculate summer day emissions, reporting agencies should estimate emissions for a specific period 

(month, week, selected days, or a day) where emissions (and other factors) resulted in ozone values 

above the level of the NAAQS leading to nonattainment. The preference should be given for weekdays 

as previously described, unless there is a reason to use other days. A summer day emissions value 

should be calculated by summing the emissions on those days and dividing by the number of days 

included in the sum. Mobile source emissions models can produce output for an average summer 

weekday or weekend day. Consult the EPA’s MOVES Technical Guidance for details 

(http://www.epa.gov/otaq/models/moves/index.htm#sip).

As noted in the preamble for the Proposed Ozone Implementation Rule, HEDD periods could have 

higher emissions than during other periods that could contribute to ozone formation in a particular 

nonattainment area. Additional contributing factors to HEDD-period impacts include location and timing 

of the HEDD-related emissions, emissions amounts from other sources during the HEDD period, and 

meteorology. If an air agency determines that emissions increases (within a NAA) associated with HEDD 

periods significantly contribute to ozone nonattainment, then the air agency should include those higher 

emissions in the planning inventories: the base year inventory for the NAA (which also serves as the 

 

20 The EPA notes that this definition has been proposed to be removed from the AERR along with the removal of 

the requirement to report summer day emissions to EIS. The EPA recognizes the continued need to include the 

requirement to submit such emissions for the purposes of ozone implementation as well as the need to provide a 

regulatory definition in other portions of the CFR.
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ROP/RFP baseline) and the attainment projected inventory for the NAA. As described above, in 

consultation with the EPA regional office, air agencies select periods to use for defining the appropriate 

days to include in the calculation of summer day emissions that are representative of the conditions 

leading to nonattainment. Thus, air agencies that have determined HEDD periods are important should 

select such periods as part of their summer day emissions estimation approach. As a result, air agencies 

could estimate HEDD emissions in a way that represents an appropriate portion of their NAA emissions 

inventories. More information on how to estimate HEDD-related emissions is provided in Section 4.8.1.

[PM2.5 Implementation Placeholder]

The temporal basis for emissions in regional haze SIPs is always annual actual emissions.

4.6 Emission Factors for SIP Emissions Inventories

Emission factors for SIP development should come from credible sources. The possible sources 

necessarily differ for stationary, on-road mobile, and nonroad sources. The mobile sources with EPA

models are the most straightforward. For all states but California, on-road mobile emissions should be 

estimated with the latest EPA on-road model, MOVES. For California, the most recent EPA-approved 

version of EMFAC should be used. For stationary sources and remaining nonroad mobile categories, 

there are several approaches that can be acceptable, with the guiding principle of using credible sources 

of data. Where emissions inventory SIPs are to be approved by the EPA, inventory developers should 

work with the appropriate EPA regional office to make sure the emission factors are acceptable. 

Air agencies should pay close attention to the methods that they are using to calculate emissions to 

ensure updated approaches are used. It would be difficult for an EPA regional office to approve an 

inventory that used an outdated method for an important part of the inventory if an updated method 

was available at the start of the SIP planning inventory development effort. Since the EPA could have 

multiple approaches posted for the same sector and some of those approaches could be outdated, air 

agencies should not assume that all EPA-posted methods are equivalent and acceptable. For example, 

some emission factors from AP-42 for nonpoint sources are outdated when compared to nonpoint 

methods and factors used for the NEI. The EPA recommends that air agencies refer to the latest NEI 

development web pages and contact regional offices to confirm that their planned approaches are up to 

date. The IPP process described above can be helpful in this process.

For most stationary point sources, air agencies have rules in place that require the submission of point 

source data to the state for air planning purposes. Much of these data are then submitted to the EPA as 

part of the NEI and used as the basis for point source inventories in SIPs. These state rules may have 

their own requirements about emission factors and source tests to be used; where possible, these rules 

should follow this guidance.

The EPA recommends selecting emission factors based on the hierarchy of emission factor sources 

shown in Table 17. The higher up on this hierarchy the emission factor chosen, the better the quality of 

the emissions estimate. Based on the emission factor approach used, the states should also set the 

required “emission calculation method code” (see Section 2.5.14) for inclusion in their inventory data. 
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Other approaches that do not require emissions factors (e.g., CEMS, materials balance, engineering 

judgement).

Table 17: Hierarchy of emission factors for use in point source emissions inventories

Rank Emission Factor Approach

Emission factor 

method code to use

1 Continuous emissions monitoring system 1

2

Facility/process-specific emission factor. Average of representative 

stack tests (on one stack) downstream of controls (or if no controls) 4

3

Single representative facility/process-specific stack test

downstream of controls (or if no controls) 4

4

Facility/process-specific uncontrolled emission factor, plus control 

efficiency. Average of representative stack tests (on one stack) 

upstream of controls, adjusted based on expected control 

efficiency.

24

5

Single representative facility/process-specific stack test upstream of 

controls, adjusted based on expected control efficiency 24

6

Site-specific emission factor. Average of representative stack tests 

across multiple stacks or processes, downstream of controls (or if 

no controls)

10

7

Site-specific uncontrolled emission factor, plus control efficiency. 

Average of representative stack tests across multiple stacks or 

processes, upstream of controls, adjusted based on expected 

control efficiency. Only makes sense when all processes measured 

are fed to the same type/combination of control devices.

30

8 Material balance 3

9 Manufacturer specification 7

10

Best available other emission factor for uncontrolled or including 

controls, which is one of:

EPA emission factor 8

S/L/T emission factor 9

Vendor emission factor 11

Trade group emission factor 12

Other emission factor 13

11

Best available pre-control emission factor, plus control efficiency , 

which is one of:

EPA emission factor, plus control efficiency 28

S/L/T emission factor, plus control efficiency 29

Vendor emission factor, plus control efficiency 31

Trade group emission factor, plus control efficiency 32

Other emission factor, plus control efficiency 33

12 Engineering judgement 2

13

Emission factor with best available speciation profile, one of:

EPA speciation profile 5

S/L/T speciation profile – e.g., to calculate metals emissions 

from filterable PM2.5 or volatile HAP from VOC. 6
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4.7 Inventory Data Codes

Building inventories includes the use of various codes, such as SCCs, state/county FIPS, tribal, control 

measure, NAICS, pollutant and emission method codes. A full accounting of all possible codes is 

available as part of the EIS “Reporting Code Tables,” which are available to EIS users using the 

“Reporting Code Tables” link at the left hand side and are available to non-EIS users (on a somewhat 

more delayed timetable) at http://www.epa.gov/ttn/chief/

eiinformation.html under “EIS Code Tables.” There are more than 60 separate lists of codes that define 

all of the required and optional coded data elements based on the AERR. As we have noted above, the 

AERR is relevant as the rule that codifies the correct development of all inventories submitted to the 

EPA.

4.7.1 Codes to Use for Nonattainment Area Inventories

Air agencies developing inventories for SIP planning should use valid EIS codes in all of their inventories. 

Since codes change over time, the EPA has adopted the approach in the EIS to “retire” codes when no 

longer needed and to add codes when needed. Codes are generally retired in coordination with NEI 

development cycles, ideally retiring codes only when plenty of notice has been provided to states in 

advance of an NEI inventory submission period. As such, codes that are retired may have already been 

used as part of a SIP development process, and that is okay. This is the advantage to retiring codes 

rather than removing them. Conversely, the EPA may not be able to retire a code until an appropriate 

point in the triennial NEI cycle. If an air agency wishes to submit a SIP-related inventory to the EIS for the 

NEI or another purpose, it will need to use valid (and not retired) codes for the year being submitted.

4.7.2 How to Request New Codes or Code Retirements

In general, if a new code is needed for compiling an inventory, then an air agency staff member should 

contact the EPA to request a new code. The recommended contact method is to use the call or email 

using the contact information listed for “Facility Inventory and Point Emissions” on the EIS contacts page 

at http://www.epa.gov/ttn/chief/eis/index. Requests for codes should include which code table(s) are 

affected, why existing codes are not sufficient, and a recommendation for a code and its definition and 

purpose. While the EPA anticipates that code retirement requests will usually come from the EPA rather 

than from external groups, a code retirement request should be made using the same mechanisms.

The EPA most often gets requests for new SCC codes since new emissions processes arise in industries, 

or processes are newly identified as having emissions associated with them. If an air agency inventory 

developer cannot find an appropriate SCC code for an inventory process, a choice needs to be made to 

either use a generic (“miscellaneous”) SCC or to request a new SCC. For cases in which the contribution 

of the emissions process to any one precursor pollutant is minimal, inventory developers may choose to 

report using one of the miscellaneous SCCs. If the process is a significant source of one or more 

pollutants or that process might be a part of a control program, then an SCC request is probably 

warranted. The EPA staff will evaluate the SCC request to make sure that a similar code does not already 
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exist, consider codes that have been created but not yet activated for use in submitted inventories21, 

assess the need for the SCC, and either indicate an existing appropriate SCC to use or assign a new

appropriate code.

4.8 Estimation of Base Year Emissions

This section describes the estimation of base year emissions for use in planning inventories for ozone, 

PM2.5 and regional haze implementation. Subsections cover point, nonpoint, on-road mobile, nonroad 

mobile, biogenic sources, and fires, respectively.

4.8.1 Stationary Point 

Stationary point sources can be estimated through continuous measurements and through more 

traditional methods. EIIP Volume II, Chapter 1, Sections 1 through 7 provide still-relevant information on 

compilation and calculation of point source inventories. Readers developing point source inventories 

should also use that report as a resource.

Sources estimated with CEMS

The best estimate of stationary point source emissions is obtained through the use of CEMS. Several 

pollutants, including NOX, SO2, CO2, and mercury (Hg) can be measured with CEMS. Fuel heat input on an 

hourly basis is usually also be collected as part of the EPA’s CEMS programs, and heat content can be 

used to estimate emissions for other pollutants using emission factors (with specific test-based factors 

preferred). More information and guidance on CEMS can be found at 

http://www.epa.gov/ttnemc01/cem.html and http://www.epa.gov/airmarkets/emissions/

continuous-factsheet.html. 

The vast majority of CEMS-equipped sources use these measurements as part of reporting programs to 

the EPA. In particular, the Acid Rain Program and NOX SIP call and other trading programs collect data as 

part of the EPA’s Clean Air Markets. Through that program, CEMS-based emissions are available through 

the “Data and Maps” resource, including emissions summaries and files ready to be used in the Sparse 

Matrix Operator Kernel Emissions (SMOKE) system used for emissions modeling.

For a few sources, emissions must be reported only for part of the year. In these cases, users of the data 

should be careful not to override the annual emissions estimates for such units with the partial-year 

data included in the CEMS databases. This can be a particular challenge for modeling inventories, where 

the more temporal resolution is useful for the time periods covered, but the other time periods must 

use a different approach to apportion the remaining emissions to the rest of the year.

Other (non-CEMS) sources

EIIP Volume II, Chapter 1, Section 4 provides general emission estimation procedure information. It 

provides a table similar to Table 17, but also focuses on the cost associated with the different 

 

21 Some SCCs are set up for use in collecting source test data and developing emission factors. Sometime after that, 

the SCCs can be used for creating and submitting inventories, depending on the availability of emission factors 

and/or the interest for using those SCCs by industry and air agencies.
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approaches. It acknowledges that the cost incurred with collecting the more specific source test data 

should be commensurate with the need for a higher data quality. Like the EIIP figure, Table 17 also lists 

the more costly (and better) approaches higher on the list. The EIIP volume provides guidance on each 

of the various methods of computing emissions.

The remainder of EIIP Volume II includes chapters that address various combustion, manufacturing, and 

production activities that are point sources. Information in these chapters can be used to estimate 

ozone, PM2.5, and regional haze precursor emissions where they address the source categories of 

interest. In some cases, the EIIP chapters are somewhat dated and so may not cover newer emissions 

processes. In these cases, inventory developers should adapt the techniques or develop new techniques 

to ensure there estimates are relevant to the sources. The EIIP point source chapters within Volume II 

cover topics as follows (numbers correspond to chapter numbers):

2. Boilers

3. Hot mix asphalt plants

4. Fugitive emissions from equipment leaks

5. Wastewater collection and treatment

6. Semiconductor manufacturing

7. Surface coating operations

8. Paint and ink manufacturing

9. Secondary metal production

10. Oil and gas production

11. Plastic products manufacturing

12. Effects of control device efficiencies and malfunctions

13. Stone mining and quarrying

14. Uncontrolled emission factors for criteria pollutants

15. Packaging and graphic arts

16. Chemical 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 (QA) and quality control (QC); and the SCCs 

needed for entry of the data into a database 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 (if applicable).

For NH3 sources, a report is also available in the “nonpoint” section of EIIP entitled “Estimating 

Ammonia Emissions From Anthropogenic Nonagricultural Sources - Draft Final Report” (April 2004) and 

covers many point source processes as well as nonpoint ones. Although a lot of research has been done 

on possible new approaches to agricultural NH3, these have not been completed yet. At this time, the 

EPA augments agricultural NH3 sources only as nonpoint sources, rather than as point sources.
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A final resource is to use the facility-total NH3 from the TRI. For SIP planning inventory purposes, these 

emissions should be apportioned to individual processes, but at least can be a starting point in the 

absence of other information.

Startup/shutdown emissions

Since startup/shutdown emissions are planned and predictable, they should be included in SIP planning 

inventories. In instances when startup/shutdown emissions can be quantified in both the base and 

future years, air agencies should include them in planning inventories because their reduction could 

help in achieving attainment. Since malfunctions are by nature unavoidable and unpredictable and given 

the myriad different types of malfunctions that can occur, malfunction emissions would be difficult to 

estimate and future-year malfunction events cannot be readily predicted. Thus, states are not obligated 

to include malfunction emissions in the base inventory for the NAA, ROP/RFP plans, or attainment 

projected inventory for the NAA.

Startup/shutdown emissions can be quantified by assessing the emissions during startup or shutdown 

periods using traditional emissions estimation approaches of throughput and emission factors. However, 

the throughput and emission factors must be customized for the activity during these periods. 

Generally, emissions rates during these periods are higher and less well characterized than a typical 

operating emissions rate, and so some degree of expert judgement may be needed in assessing these 

emissions.

In addition to estimating the actual emissions during startup/shutdown periods, another approach to 

estimate startup/shutdown emissions is to adjust control parameters via the emissions calculation 

parameters of rule effectiveness or primary capture efficiency. Using these parameters for 

startup/shutdown adjustments is not their original purpose, but can be a simple way to increase the 

emissions and still have a record of the routine versus startup/shutdown portions of the emissions. For 

example, a lower capture efficiency or rule effectiveness can adjust actual emissions to be higher, 

accounting for extra emissions from startup/shutdown activities. In the absence of measurements of 

throughput and/or emissions rates during startup/shutdown periods, expert judgment may need to be 

used to define the adjustment factors to use. This approach, however, can complicate the use of the 

control parameters during development and documentation of control strategies since the control 

parameters reflect things other than controls – thus, care should be taken when using this approach.

Emissions associated with HEDD periods

As described in Section 4.5, when air agencies have determined that emissions associated with HEDD 

periods are important for addressing their nonattainment problem, those air agencies should include 

HEDD-related emissions in their planning inventories. This subsection first describes what information is 

available to help assess when HEDD periods occur and to help provide activity data that could be used as 

part of estimating the associated emissions. Second, this subsection describes how to consider HEDDrelated emissions in planning inventories (e.g., the base year inventory for the NAA) as compared to 

those in modeling inventories.
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Emissions from HEDD periods can include additional emissions from more typical EGU boilers, turbines, 

and other units (collectively called peaking units) and also from combustion-based sources of distributed 

generation such as large back-up generators and other engines. A key challenge in developing emissions 

estimates for HEDD-periods is determining when the peaking units and distributed generation units 

were operating and consequently produced emissions. In the case of peaking units, many of these 

sources have CEMS that record activity and emissions levels, and these data are reported to EPA. In the 

case of distributed generation units, little or no information may be readily available in part because the 

energy produced by the backup generators and other engines is not measured by the independent 

system operators (ISOs), but rather may be experienced by the ISOs as an unmeasured demand 

reduction.

During HEDD periods, energy customers may use backup generators to participate in demand response 

programs. Though some useful information may be available from the ISOs running those programs,

that is not always the case. The specific rules, reporting, and frequency of use will vary by the utility or 

ISO that is offering the demand response program. Demand response program requirements vary and 

can include (a) completely excluding the use of backup generators, (b) allowing the use of backup 

generators and requiring some reporting, and (c) not requiring customers to report anything about

actions taken to provide the demand response. The lack of data on demand response backup activity 

has been noted by others based on past analyses22,23. Where emissions from demand response 

programs may be important, air agencies should first collaborate with their state energy and public 

utility commission counterparts, who may have established mechanisms for information collection and 

sharing. Air agencies may also need to asses the demand response programs in their area by working 

directly with ISOs.

Starting in 2015, the National Emission Standard for Hazardous Air Pollutants (NESHAP) and New Source 

Performance Standards for Reciprocating Internal Combustion Engines (RICE) (40 CFR Part 60, Subparts 

IIII and JJJJ and 40 CFR Part 63, Subpart ZZZZ), also called the RICE rules, will require owners/operators of 

emergency engines participating in emergency demand response programs to report the dates and 

times that the engines operate for emergency demand response as well as engine information such as 

horsepower and model year. While the RICE rules do not require the reporting of NOX emissions or 

information about non-emergency programs, they will start to help provide information useful for 

understanding the activity of these back-up generators and engines, which may also be helpful for ozone 

planning purposes.

While it may continue to be difficult to find data needed for assessing HEDD-related emissions, air 

agencies may still include these emissions in both their modeling inventories and planning inventories. 

The HEDD-related emissions included by air agencies in planning inventories should have some logical 

relationship with the emissions in modeling inventories. The planning inventories will of course be 

limited spatially to the NAA, while the modeling inventories will cover a larger area. Air agencies should 

 

22 White paper: “Air Quality, Electricity, and Back-up Stationary Diesel Engines in the Northeast,” Northeast States 

for Coordinated Air Use Management (NESCAUM), August 1, 2012.

23 See also the Mid-Atlantic Distributed Resources Initiative (MADRI) working group meeting information available 

at http://sites.energetics.com/madri/meetings_2012.html.
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extract the appropriate NAAs to include in the planning inventories. Temporally, the modeling 

inventories will include day- and hour-specific emissions for seasonal or episodic periods, which can 

include HEDD periods, while the planning inventories will be a summer day emissions value. As 

explained in Section 4.5, the days used to calculate the summer day emissions are chosen for the 

particular SIP in consultation with the regional office. Some examples of possible relationships between 

the modeling inventories (episode-specific) and the planning inventories (summer day) are as follows:

 Summer day emissions could be an average across all days of the episode-specific 

emissions used in the modeled attainment demonstration.

 Summer day emissions could be an average of a longer episode or series of episodes that 

overlap with the episodic period used for the modeled attainment demonstration.

 Summer day emissions could be a representative selection of the episodic-specific 

emissions, such as a median emissions value or using a single day emissions value that 

somehow is representative of other days.

These are not the only possible examples. Any approach chosen to determine appropriate HEDD-related 

summer day emissions should be developed in consultation with the regional office and should seek to 

meet the overall goal for the base year inventory. Namely, the NAA inventory should be representative 

of the emissions conditions within the NAA that typically lead to nonattainment problems.

4.8.2 Stationary Nonpoint 

Nonpoint sources collectively represent individual sources that have not been inventoried as specific 

point or mobile sources. These individual sources treated collectively as nonpoint sources are typically 

too small, numerous, or difficult to inventory using the methods for the other classes of sources. 

Stationary nonpoint sources can be estimated through numerous different approaches. Though some 

approaches are outdated, the EIIP Volume III, Chapter 1, Sections 1 through 6 provide relevant 

information on compilation and calculation of nonpoint source inventories. Also, the Volume III 

webpage contain are numerous supplemental reports for specific source categories. 

For many categories, more updated approaches are included in the EPA tools developed for use by air 

agencies in developing inventories. The latest tools are provided as part of the materials for the latest 

NEI – either as developmental materials for an ongoing NEI effort, or as supporting materials to 

document a completed NEI effort.

Table 18 provides a list of emissions categories, pollutants, and available approaches documentation 

and/or tools.
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Table 18: List of nonpoint categories, pollutants, and available approaches and tools

EPA-estimated 

emissions source 

description

Possible 

Overlap 

with 

Point

Available Nonpoint Resources (Posted year)

Agricultural Fertilizer 

Application ag_fertilizer_application_2011.zip (2013)

Agricultural Fires 2011 NEI Technical Support Document, Section 5.2

Agricultural Tilling agricultural_tilling_2801000003_2011.zip (2012)

Animal Husbandry animal_livestock_emissions_2011.zip (2009)

Architectural Coatings surface_coatings_arch_coatings_whaps_2011.zip (2012)

EIIP, Volume III, Chapter 3 (1995)

Asphalt Paving 

asphalt_paving_cutback_2011.zip (2009)

asphalt_paving_emulsified_2011.zip (2009)

EIIP, Volume III, Chapter 17 (2001)

Asphalt Roofing Kettles Y See abstract available with the EIIP Volume III website (2000)

Autobody Refinishing Y surface_coating_automobile_refinishing_2011whaps.zip (2012)

Aviation Gasoline av_gasoline_distribution_stage1.zip (2009)

av_gasoline_distribution_stage2.zip (2009)

Commercial Cooking commercial_cooking_2302002nnn_2011.zip

Consumer & Commercial 

– All personal care 

products

cons_comm_personal_care_products_whaps_2011.zip

EIIP Volume III, Chapter 5 (1996)

Consumer & Commercial 

– All household products

cons_comm_misc_products_whaps_2011.zip

cons_comm_cleaning_products_whaps_2011.zip

cons_comm_auto_aftermarket_whaps_2011.zip

EIIP Volume III, Chapter 5 (1996)

Consumer & Commercial 

– All coatings and 

related products

cons_comm_coatings_and_related_products_whaps_2011.zip

Consumer & Commercial 

– All adhesives and 

sealants

cons_comm_adhesives_sealants_whaps_2011.zip

EIIP Volume III, Chapter 5 (1996)

Consumer & Commercial 

– All FIFRA related 

products

cons_comm_fifra_whaps_2011.zip

Degreasing Y degreasing_whaps_2011_eisformat.zip

Dental Preparation and 

Use 

Documentation for the 1999 Base Year Nonpoint area source National 

Emissions inventory for HAPs, page A-30 (2000)

Dry Cleaning Y

dry_cleaning_emissions_2011_rev.zip

EIIP, Volume III, Chapter 4 (1996)

Dust – Paved Roads roads_paved_2011.zip

Dust – Unpaved Roads roads_unpaved_2011.zip

Dust – Construction

construction_residential_2011.zip

construction_nonresidential_2011.zip

construction_road_2011.zip

Gasoline 

Distribution/Marketing Y

gasoline_distribution_stage_1_bulk_plants_2011.zip (2009)

gasoline_distribution_stage%201%20bulk_terminals_2011.zip (2009)

gasoline_distribution_stage_1_pipelines_2011.zip (2012)

gas_distribution_service_station_unloading_eis_format.zip (2012)
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EPA-estimated 

emissions source 

description

Possible 

Overlap 

with 

Point

Available Nonpoint Resources (Posted year)

gasoline_distribution_stage1_ust_2011.zip (2012)

gasoline_distribution_stage_1_tank_trucks_2011.zip (2012)

gasoline_distribution_stage_2.zip (2012)

EIIP, Volume III, Chapter 11 (2001)

General Laboratory 

Activities

Documentation for the Final 2002 Nonpoint Sector (Feb 2006 version) National 

Emissions inventory for Criteria and HAPs, page A-106 (2006)

Graphic Arts Y

graphic_arts_w_haps_2011.zip (2013)

EIIP Volume III, Chapter 7 (1996)

Human Cremation Y cremation_2011.zip (2000)

Industrial, 

Commercial/Institutional Fuel CombustionY

ici_fuel_combustion_by_state/ (2013)

Estimating Ammonia Emissions From Anthropogenic Nonagricultural Sources -

Draft Final Report (April 2004)

Industrial Surface 

Coating Y

surface_coating_factory_finished_wood_2011whaps.zip (2012)

surface_coating_wood_furniture_2011whaps_rev_4.zip (2012)

surface_coating_metal_furn_2011whaps.zip (2012)

surface_coating_paper_film_foil_2011_whaps.zip (2012

surface_coatings_metal_can_whaps_2011.zip (2012)

surface_coating_machinery_and_equip_whaps2011.zip (2012)

surface_coating_appliances_2011whaps.zip (2012)

surface_coating_electronic_and_other_electical_coatings_whaps_2011.zip

(2012)

surface_coating_motor%20vehicles_whaps_2011.zip (2012)

surface_coating_aircraft_mfg__2011whaps.zip (2012)

surface_coating_marine_mfgwhaps2011.zip (2012)

surface_coating_railroad_whaps_2011.zip (2012)

surface_coating_misc_mfg_2011whaps.zip (2012)

surface_coating_ind_maint_coating_2011whaps.zip (2012)

EIIP, Volume III, Chapter 8 (1997) 

Lamp Breakage (Landfill 

emissions)

Documentation for the Final 2002 Nonpoint Sector (Feb 2006 version) National 

Emissions inventory for Criteria and HAPs, page A-109 (2006)

Lamp (Fluorescent) 

Recycling

Documentation for the Final 2002 Nonpoint Sector (Feb 2006 version) National 

Emissions inventory for Criteria and HAPs, page A-107 (2006)

Landfills Y EIIP, Volume III, Chapter 15 (2001)

Mining and Quarrying mining_and_quarrying.zip (2012)

Oil and Gas Production Y

EPA_Oil_and_Gas_Production_Emission_Estimation_Tool_2011_NEI_V1_4_

20130919.zip (2013)

Open Burning (Leaves, 

Brush, Residential 

Household Waste, Land 

Clearing)

open_burning_yard_waste_2011.zip (2011)

open_burning_yard_waste_2011.zip (2011)

open_burning_msw_2011.zip (2011)

open_burning_land_clearing_debris_2011.zip (2011)

Other Special Purpose 

Coatings Y surface_coating_other_special_purpose_whaps_2011.zip

Pesticide Application

cons_comm_fifra_whaps_2011.zip (2009)

agricultural_pesticides_2011_eis_format.zip (2009)

EIIP Volume III, Chapter 9 (2001)

Portable Gas Cans 

(Residential and portable_fuel_containers_2011.zip (2012)
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EPA-estimated 

emissions source 

description

Possible 

Overlap 

with 

Point

Available Nonpoint Resources (Posted year)

Commercial)

Publicly Owned 

Treatment Works Y potw_2011_rev.zip (2009)

Residential Heating -

Fossil Fuels

residential_consumption_coal.zip (2012) 

residential_consumption_oil_revised_06272012.zip (2012)

residential_consumption_kerosene.zip (2012)

residential_consumption_ng_revised_06222012.zip (2012)

residential_consumption_lpg.zip (2012)

Estimating Ammonia Emissions From Anthropogenic Nonagricultural Sources -

Draft Final Report (April 2004)

See also abstracts available for coal, fuel oil & kerosene, gas & liquified 

petroleum gas (LPG) available with the EIIP Volume III website (1999).

Residential Heating –

Wood

rwc_estimation_tool_2011v1_120612.zip (2012)

EIIP, Volume III, Chapter 2 (2001)

Structure Fires EIIP, Volume III, Chapter 18 (2001)

Traffic Markings traffic_markings_whaps_2011.zip (2012)

EIIP, Volume III, Chapter 14 (1997)

Vehicle Fires See abstract available with the EIIP Volume III website (2000)

Waste Disposal 

(Incineration)

Estimating Ammonia Emissions From Anthropogenic Nonagricultural Sources -

Draft Final Report (April 2004)

As indicated in Table 18 by the column “Possible Overlap with Point,” some source types can have 

emissions in both the point source data category and the nonpoint one. Some categories in the table 

that may have both types of sources are denoted, and this list is based on what has been seen in the 

NEI. The list of categories in this situation depend on an individual state’s policies, such as what the 

emissions size threshold is for a point source and whether any categories are treated as point sources 

despite having low individual emissions.

To prevent overestimation of nonpoint emissions for sectors that also have point sources, it is important 

to perform point/nonpoint reconciliation. This reconciliation starts by subtracting the activity associated 

with the point sources from the total activity data (prior to computing the nonpoint emissions). Since 

point sources often have emissions controls, it is usually not sufficient to just subtract point source 

emissions from total activity-based emissions to prevent double counting. Subtracting controlled point 

source emissions from uncontrolled total activity-based emissions would result in too much nonpoint 

emissions. Rather, the point source activity must be determined and subtracted from total activity to get 

the nonpoint activity estimate. Alternatively, uncontrolled point source emissions can be calculated and 

subtracted from the total activity-based emissions estimates to derive a nonpoint emissions estimate.

Part of developing refined nonpoint emissions estimates for a SIP could involve the use of surveys to 

collect data. Inventory preparers often use survey questionnaires to gather point source emissions 

inventory data. The EIIP Volume III, Chapter 24, written in 2000, provides guidance on developing and 

conducting surveys for area source inventories. Since this document predates some of the newer online 

survey techniques, the sections describing the use of the internet are outdated. As part of the 
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documentation for inventories, survey design and results should be kept and included in any 

documentation reports or appendices.

4.8.3 On-road Mobile 

Emissions from on-road vehicles are the result of several emission processes, including the combustion 

of fuel while vehicles are starting, idling, and moving, evaporation of fuel from the fuel system and 

during refueling, and from brake wear and tire wear.

For all states but California, on-road mobile emissions should be estimated with the latest EPA on-road 

mobile model, MOVES24, following the latest guidance available at 

http://www.epa.gov/otaq/models/moves/index.htm#sip. For California, the most recent EPA-approved 

version of EMFAC should be used.

The available guidance covers using MOVES for inventory development in SIPs in states other than 

California. The guidance focuses on determining what the appropriate inputs are and how MOVES 

should be run to develop emissions estimates for on-road vehicles. It describes when default MOVES

inputs are appropriate for SIPs and regional conformity analysis and what factors to consider for 

providing locality-specific MOVES inputs.

MOVES estimates emissions for mulitple source use types (the terminology that MOVES uses to describe 

vehicle type) and fuel types. MOVES also estimates emissions for different road types that represent 

rural and urban unrestricted and restricted (accessed only by an on or off ramp) access roads, as well as 

off-network emissions such as vehicle starts, evaporative emissions while parked, and hoteling 

emissions when long-haul combination trucks are parked for long periods with the engine running under 

load.

One of the key elements for use of MOVES is creating a Run Specification (RunSpec) file, which defines 

the place and time period of the analysis as well as the vehicle types, road types, fuel types, and the 

emission-producing processes and pollutants that will be included in the MOVES run. The MOVES 

Technical Guidance describes using the MOVES graphical user interface GUI to set up a MOVES run for a 

particular scale (e.g., county), time period, set of pollutants, and the vehicle types, road types, and fuel 

types applicable to a particular area and time.

Another key element for use of MOVES is entering local meteorology, fleet, activity, fuel, and control 

measure information using the County Data Manager. The MOVES Technical Guidance discusses when 

local data should be used in place of model default data, as well as potential sources of local data. 

For some input parameters, there is overlap with the inputs needed for other models, such as the 

nonroad mobile models, for example, meteorology and fuels. Efforts should be made to use the same 

source of data across multiple categories when the inputs are shared. Not doing so calls into question 

 

24 The EPA expects that MOVES 2014 will be released after this draft guidance is released and before this guidance 

is finalized. EPA intends to modify this section as relevant for use of MOVES 2014, including expected changes to 

SCCs. EPA will also modify the MOVES guidance accordingly.
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the validity of one or both approaches. Air agencies should explain the use of shared inputs, or reasons 

for not using them, as part of the documentation provided with their inventories.

4.8.4 Nonroad Mobile Equipment

Nonroad mobile equipment emissions result from the use of fuel in a diverse collection of vehicles and 

equipment, including:

 recreational vehicles, such as all-terrain vehicles and off-road motorcycles;

 logging equipment, such as chain saws;

 agricultural equipment, such as tractors;

 construction equipment, such as graders and back hoes;

 industrial equipment, such as forklifts and sweepers;

 residential and commercial lawn and garden equipment, such as leaf and snow blowers;

 recreational marine vessels, such as power boats.

The EPA’s NONROAD emissions model predicts emissions for all of these nonroad equipment categories. 

Emissions from CMVs, locomotives, and aircraft are estimated in other ways and described in Section 

4.8.5. The NONROAD model includes more than 80 basic and 260 specific types of nonroad equipment 

and further stratifies equipment types by horsepower rating. Fuel types include gasoline, diesel, 

compressed natural gas (CNG), and Liquified Petroleum Gas (LPG).

The NONROAD model estimates emissions for all criteria pollutant and precursors from both exhaust 

and non-exhaust processes (diurnal, refueling spillage, vapor displacement, hot soak, running loss, take 

permeation, hose permeation, and crankcase emissions). NONROAD supports many SIP-related 

inventory development needs, including support for partial counties and seasonal emissions. The EPA 

provides the latest version of the NONROAD model and all information related to its use for inventories 

at http://www.epa.gov/otaq/nonrdmdl.htm. Air agencies should use NONROAD as a resource for 

estimating nonroad mobile emissions and refer to the documentation on the NONROAD website for 

more information. The EPA is currently in the process of incorporating NONROAD model capabilities into 

MOVES. When this update is available, guidance on the transition to using MOVES for estimating 

nonroad emissions will be included on the EPA’s MOVES and NONROAD web pages.

The NONROAD model can be run by itself or using the NMIM interface

(http://www.epa.gov/otaq/nmim.htm). NMIM adds several features to enhance nonroad emissions 

modeling, including:

 The inclusion of all the required county data for the nation in a single database

 A graphical user interface

 Shortcuts for generating national (or multi-region) inventories

 Estimation of 33 HAPs, and 17 dioxin/furan congeners by ratio to various NONROAD output 

parameters

 Distributed processing capability to enhance model performance
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NMIM also includes the now no longer used MOBILE6.2 model for on-road emissions. MOVES has 

replaced NMIM for on-road emissions estimation and, as a result, the use of on-road emissions 

estimates from NMIM is not currently acceptable for any regulatory purpose. 

Based on a user-provided run specification (RunSpec) file and information in the NMIM county 

database, NMIM creates input files for NONROAD for every county and month selected. NMIM then 

runs NONROAD, reads its output files, performs additional processing if necessary, and puts the 

resulting inventory into an output database. Additional processing includes creating HAP emission 

estimates from the CAP estimates. NMIM has post-processing capability that can be applied after the 

inventory is generated. This includes aggregation over months and equipment types. Output can go into 

a database table or into a tab-delimited text file. The format can be normalized (a pollutant on each line) 

or wide (a pollutant in each column).

Air agencies have the option of replacing default model inputs with more representative data. Common 

input adjustments include equipment population, geographic allocations, and local growth rates. If 

agencies make changes to default model values, the agency should submit the input files to the EPA as 

well as a description of why the defaults were changed. Additional guidance on improving nonroad 

estimates for lawn and garden equipment can be found in EIIP, Volume IV, Chapter 3.

For some input parameters, there is overlap with the inputs needed for other models, such as the onroad mobile models, for example, meteorology and fuels. Efforts should be made to use the same 

source of data across multiple categories when the inputs are shared. Not doing so calls into question 

the validity of one or both approaches. Air agencies should explain the use of shared inputs, or reasons 

for not using them, as part of the documentation provided with their inventories.

4.8.5 Other Nonroad Mobile 

The NONROAD model does not provide air agencies with a tool for estimating emissions for CMVs, 

aircraft, and locomotives. Thus, separate methods are used for each of these emissions sectors.

For purposes of reporting data to the EPA, the aircraft emissions are often reported as point sources, 

with this being a requirement for reporting data to the EIS for use in the NEI. Likewise, the CMV and 

locomotive data are included in the nonpoint data category in the EIS. While these sources are still 

mobile sources from the traditional standpoint of common-sense categories, for data formatting and 

reporting purposes in the EIS, they are treated along with these non-mobile data categories.

4.8.5.1 Aircraft

The aircraft sector includes all aircraft types used for public, private, and military purposes. This includes 

four types of aircraft: (1) Commercial, (2) Air Taxis (AT), (3) General Aviation (GA), and (4) Military. A 

critical detail about the aircraft is whether each aircraft is turbine- or piston-driven, which allows the 

emissions estimation model to assign the fuel used, jet fuel or aviation gas, respectively. The fraction of 

turbine- and piston-driven aircraft is either collected or assumed for all aircraft types. NEI data are 

available for this sector for use as a starting point in SIPs, though the NEI includes military aircraft only 

where state or local air agencies have submitted military aircraft emissions data.
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Commercial aircraft include those used for transporting passengers, freight, or both. Commercial aircraft 

tend to be larger aircraft powered with jet engines. ATs carry passengers, freight, or both, but usually 

are smaller aircraft and operate on a more limited basis than the commercial aircraft. GA includes most 

other aircraft used for recreational flying and personal transportation. Finally, military aircraft are 

associated with military purposes, and they sometimes have activity at non-military airports.

The national AT and GA fleet includes both jet- and piston-powered aircraft. Most of the AT and GA fleet 

are made up of larger piston-powered aircraft, though smaller business jets can also be found in these 

categories. Military aircraft cover a wide range of aircraft types such as training aircraft, fighter jets, 

helicopters, and jet-powered and piston-powered planes of varying sizes.

Emissions at airports also include other sources that are a part of the nonroad equipment emissions 

described in Section 4.8.4. These emissions come from aircraft auxiliary power units (APUs) and aircraft 

ground support equipment (GSE) typically found at airports, such as aircraft refueling vehicles, baggage 

handling vehicles, and equipment, aircraft towing vehicles, and passenger buses. In the NEI point source 

inventory, these APUs and GSE are located at the airport facilities as point sources along with the 

aircraft exhaust emissions (though not as part of the aircraft sector). Emissions from APUs and from GSE 

are calculated using the EPA’s NONROAD model.

The EPA collaborates with the Federal Aviation Administration (FAA) to develop and maintain methods 

for estimating aircraft emissions using the Emissions and Dispersion Modeling System (EDMS), which 

estimates emissions from aircraft. The EPA-developed emissions are associated with aircrafts’ landing 

and takeoff (LTO) cycle. The EPA encourages state and local air agencies to collect aircraft activity data 

that can be used in improving estimates using the EPA EDMS-based methods. More details on the EPA 

methods are available in the latest NEI documentation found at 

http://www.epa.gov/ttn/chief/eiinformation.html. 

The aircraft sector includes numerous SCCs as shown in Table 19, and all but two of these are associated 

with the NEI point source inventory. Historically, airport emissions have been calculated as a nonpoint 

source, but with the latest approaches having all airport locations readily available, such a simplification 

is no longer needed. The result of this change from nonpoint to point sources is that most of the SCCs 

are shown as 10-digit SCCs (usually used just for nonpoint sources) but are now used as point SCCs. 

Table 19: Aircraft SCCs and Data Categories in EPA Estimates

SCC Data Category SCC Description EPA estimates

2275001000 Point Mobile Sources; Aircraft; Military Aircraft; Total X

2275020000 Point Mobile Sources; Aircraft; Commercial Aircraft; 

Total: All Types X

2275050011 Point Mobile Sources; Aircraft; General Aviation; Piston X

2275050012 Point Mobile Sources; Aircraft; General Aviation; Turbine X

2275060011 Point Mobile Sources; Aircraft; Air Taxi; Piston X

2275060012 Point Mobile Sources; Aircraft; Air Taxi; Turbine X

2260008005 Point Mobile Sources; Off-highway Vehicle Gasoline 2-

Stroke; Aircraft Ground Support Equipment X
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SCC Data Category SCC Description EPA estimates

2265008005 Point Mobile Sources; Off-highway Vehicle Gasoline 4-

Stroke; Aircraft Ground Support Equipment X

2267008005 Point Mobile Sources; LPG; Aircraft Ground Support 

Equipment X

2268008005 Point Mobile Sources; CNG; Aircraft Ground Support 

Equipment X

2270008005 Point Mobile Sources; Off-highway Vehicle Diesel; 

Aircraft Ground Support Equipment X

2275070000 Point Mobile Sources; Aircraft; Aircraft Auxiliary Power 

Total X

2275085000 Nonpoint Mobile Sources; Aircraft; Unpaved Airstrips; Total

2275087000 Nonpoint Mobile Sources; Aircraft; In-flight (non-LandingTakeoff cycle) X

In June 2012, the EPA published standards for NOX emissions from commercial aircraft engines. 

Information about this rule including fact sheets, test procedures, and emissions documentation is 

available on the EPA website for this purpose (http://www.epa.gov/otaq/aviation.htm). In this rule, the 

EPA adopted Tier 6 and Tier 8 standards for NOX on new aircraft engines, with compliance dates in 2013 

and 2014. Prior rules published in 2005 and 1997 also reduce aircraft NOX emissions with engine 

standards; these rules are also documented on the same website. When estimating emissions from 

aircraft, it is best practice to consider the impacts of these rules for improving the accuracy of emissions 

inventories. This is why the EPA recommends using the EPA EDMS-based approach with locality-specific

data.

State or local air agencies may determine that the EPA default method is not appropriate for SIP 

purposes, though the EPA recommends considering the approach but using more locality-specific

activity information. For areas that have provided the EPA locality-specific airport activity data, the NEI 

estimates may very well provide emissions needed to meet SIP requirements. The EPA method is more 

robust than older methods and includes national control programs as noted below. As shown in the 

table above, the EPA’s methods do not estimate emissions from unpaved airstrips (SCC 2275085000). 

Furthermore, the “in-flight” SCC (2275087000) is covered by the EPA’s method for only lead (Pb) 

emissions and is related to general aviation aircraft that still use leaded fuel. Air agencies may want to 

consider unpaved airstrips and/or in-flight emissions for other pollutants as part of their inventories for 

improved model performance or other reasons, though doing so may not be necessary depending on 

the significance of those emissions in a particular area. Any locality-specific data or custom emissions 

associated with aircraft sources are expected to be included with supporting documentation for the 

emissions inventory used for a SIP.

4.8.5.2 Commercial Marine

The CMV emissions category includes boats and ships used either directly or indirectly in the conduct of 

commerce or military activity. The majority of vessels in this category are powered by diesel engines 

that are either fueled with distillate or residual fuel oil blends. For the purpose of this inventory, we

assume that Category 3 (C3) vessels primarily use residual blends while Category 1 and 2 (C1 and C2) 
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vessels typically use distillate fuels. Another consideration for emissions estimation of CMV sources is 

auxiliary engines. All three types of vessels may have auxiliary engines that are used for onboard power 

generation or other needs.

The C3 inventory includes vessels which use C3 engines for propulsion. C3 engines are defined as having 

displacement above 30 liters per cylinder. C3 inventories typically include emissions from both 

propulsion and auxiliary engines used on these vessels, as well as those on gas and steam turbine 

vessels. Geographically, the inventories include port and interport emissions that occur within the area 

that extends 200 nautical miles from the official U.S. shoreline, which is roughly equivalent to the border 

of the U.S. Exclusive Economic Zone. For national inventories created by the EPA, only some of these 

emissions are allocated to states based on official state boundaries that typically extend 3 nautical miles 

offshore. The EPA recommends that state water boundaries also be used when determining which 

emissions should be included with a particular state or county.

The C1 and C2 vessels tend to be smaller ships that operate closer to shore, and along inland and 

intercoastal waterways, with engines greater than or equal to 37kW. Naval vessels are not included in 

C1 and C2 vessel inventories, though Coast Guard vessels are included. While these C1/C2 vessels are 

most often associated with near-land applications and thus included as within state waters, sometimes 

these vessels are used outside of state waters, particularly in the Gulf of Mexico. In these cases, as with 

C3 vessels the EPA recommends that state water boundaries be used when calculating emissions 

associated with a particular state or county.

The CMV source category does not include recreational marine vessels, which are generally less than 

100 feet in length, most being less than 30 feet and powered by either inboard or outboard engines. The

calculation of these emissions is included in the NONROAD model, and these emissions are therefore 

considered “nonroad equipment”.

The EPA develops and maintains methods for estimating CMVs, and these methods are used as 

“fallback” methods for use in the NEI. They are also available as a fallback for states without other data 

for this sector. At this time, the EPA’s methods are top-down national methods, which apportion 

nationally estimated emissions values to the states and counties. In the latest such approaches (used for 

the 2008 and 2011 NEI), this apportionment includes allocation to GIS shapefiles for ports and underway 

emissions. These shapefiles are available with the latest NEI documentation and include separate files 

for ports and underway. Key differences associated with various EPA methods from the 2002 NEI 

through the 2011 NEI have focused on allocation of emissions to the shapefiles, which has been done in 

collaboration with state and local air agencies.

The current EPA methods also use emissions types. Each of the CMV SCCs requires an appropriate 

emissions type (M=maneuvering, H=hotelling, C=cruise, Z=reduced speed zone), because emission 

factors vary by emission type. For the NEI, each SCC and emissions type combination was allocated to a 

shapefile identifier in the nonpoint inventory. The allowed combinations of SCCs and emission types are 

shown in Table 20. The default values are those assumed when the actual emission type may be 
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unknown; for example, emissions that occur in shipping lanes are assumed to be ‘cruising’ and cannot 

be ‘hotelling,’ which only occurs at ports.

Table 20: Commercial marine SCCs and emission types in EPA emissions

SCC SCC Description Allowed Default

2280002100 Marine Vessels, Commercial Diesel Port M M

2280002200 Marine Vessels, Commercial Diesel Underway C C

2280003100 Marine Vessels, Commercial Residual Port H H

2280003100 Marine Vessels, Commercial Residual Port M H

2280003200 Marine Vessels, Commercial Residual Underway C C

2280003200 Marine Vessels, Commercial Residual Underway Z C

State or local agencies may determine that the EPA default method is not appropriate for SIP purposes 

or may need further refinement by air agencies in developing SIPs. For example, the general calculation 

method may be a reasonable approach, but the activity and spatial allocation achieved from a top-down 

approach could be improved by using the same methods with locally resolved input data to calculate 

emissions for specific areas.

When estimating CMV emissions, reporting agencies should consider national regulations that decrease 

emissions from this sector, such as increasingly stringent emissions requirements for new marine diesel 

engines and sulfur requirements for marine diesel fuel and adjust their estimates accordingly. Emissions 

reductions resulting from requirements for new marine engines are generally not immediately reflected 

in inventories as newer engines are gradually incorporated into the vessel fleet and as older 

engines/vessels are retired. Emissions reductions resulting from the use of lower sulfur fuels are 

generally seen more quickly, though estimating impacts can be complicated by vessels coming from 

other parts of the world with different fuel standards. Table 21 provides a list of more recent relevant 

regulations and associated references for the CMV category. Older Tier 1 and 2 regulations on marine 

diesel engines, dating back to 1999, are also listed on the websites shown in the table.

Table 21: Commercial marine vessel recent regulations and impacted pollutants

Regulation Pollutants impacted Reference

Great Lakes Steamship Repower Incentive Program 

(January, 2012) SO2, PM2.5

www.epa.gov/otaq/

oceanvessels.htm Tier 2 and Tier 3 Emissions Standards for Category 3 

Marine Diesel (April, 2010). Includes both engine 

standards and fuel sulfur limits.

SO2, NOX, PM2.5

Tier 3 and Tier 4 Emission Standards for Category 1 and 2 

Marine Diesel Engines (June, 2008).

PM2.5, NOX

www.epa.gov/otaq/

marine.htm#regs Nonroad Diesel Tier 4 Rule (May 2004). Decreased 

allowable levels of sulfur in marine diesel fuel by 99%, 

taking affect in 2007.

SO2

For states needing to refine their emissions estimates beyond the values produced by the EPA’s default 

methods, Table 22 provides a list of the latest resources for states in better understanding how to 
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calculate emissions for the CMV sources. The newer references are included higher in the table. The

EPA’s recent method updates have occurred in conjunction with rule development efforts, and so some 

of these documents are associated with inventories developed for the rules listed above. Even newer 

methods may become available over time and can be considered for use in SIP planning inventory 

development. Much of this information is also available on the EPA nonroad mobile website under 

“other references”, available at http://www.epa.gov/otaq/nonrdmdl.htm#otherref. Any locality-specific

data or custom emissions associated with CMV emissions are expected to be included with supporting 

documentation for the emissions inventory used for a SIP.

Table 22: : Current EPA methods for commercial marine vessel emissions.

Inventory approach resource CMV Approaches For... Reference

Current Methodologies in 

Preparing Mobile Source 

Port-Related Emissions 

inventories (April, 2009)

Ocean going (generally C3) 

vessels, harbor craft, cargo 

handling,

http://www.epa.gov/sectors/

sectorinfo/sectorprofiles/ports/

ports-emission-inv-april09.pdf

Draft Regulatory Impact 

Analysis: Control of 

Emissions of Air Pollution 

from Category 3 Marine 

Diesel Engines (June, 2009)

Bottom-up port C3 emissions for 

89 deep water and 28 Great Lake 

ports in the U.S. and interport 

emissions from the Waterway 

Network Ship Traffic, Energy and 

Environmental Model (STEEM).

http://www.epa.gov/otaq/regs/

nonroad/marine/ci/420d09002.pdf. 

See Chapter 3.

Final Regulatory Impact 

Analysis: Control of 

Emissions of Air Pollution 

from Locomotive Engines 

and Marine Compression 

Ignition Engines Less than 30 

Liters per Cylinder (May 

2008)

C1 and C2 propulsion, C1 marine 

auxiliary, <37kW commercial 

propulsion, and <37kW marine 

auxiliary.

http://nepis.epa.gov/Exe/ZyPURL.cgi

?Dockey=P10024CN.txt. Chapter 1 

provides more in-depth description 

of engine types, while Chapter 3 

provides emissions calculation 

approach.

Emissions inventory

improvement program

Evaporative VOC emissions from 

marine transport of petroleum 

liquids, including the loading and 

unloading of the petroleum 

liquids.

‡

EIIP, Volume III, Chapter 12 “Marine 

Vessel Loading, Ballasting, and 

Transit”.

‡ These emissions are often included in as part of the nonpoint inventory rather than associated with the CMV 

sector.

Older approaches are also available. In 1999, the EPA sponsored two studies entitled “Commercial 

Marine Activity for Great Lake and Inland River Ports in the United States” and “Commercial Marine 

Activity for Deep Sea Ports in the United States.” Both of these reports are available at 

http://www.epa.gov/otaq/nonrdmdl.htm#otherref. These studies provided activity profiles for 

approximately 150 ocean, lake, and river ports, and present a method for an inventory preparer to 

allocate time-in-mode activity data from one of four typical ports to another port that has similar 

characteristics. Activity profiles for a typical port include: 1) number of vessels in each category; 2) 

vessel characterization, including propulsion size (horsepower), capacity tonnage, and engine age; 3) 
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number of hours at each time-in-mode associated with cruising, reduced speed, maneuvering, and 

hotelling. These methods provide alternative approaches for state and local air agencies in preparing SIP 

inventories, but care should be taken to incorporate the impact of national rules incorporated into the 

newer approaches as documented in Table 22. 

4.8.5.3 Locomotives

The locomotive emissions category includes diesel-electric engines, which use 2-stroke or 4-stroke diesel 

engines and an alternator or a generator to produce the electricity required to power its traction 

motors. The EPA default approach does not include locomotives powered by electricity or steam. It is 

believed that the number of wood or coal driven steam locomotives in the U.S. is currently very small; 

therefore, these types of locomotives are not generally included. In specific instances, if such sources 

are relevant to a NAA, then they may need to be included. The locomotive sources are further divided 

into categories: Class I line haul, Class II/III line haul, Passenger, Commuter, and Yard.

Several definitions come into play in determining the locomotive category, which impacts the SCC that 

should be used.

 Class I railroads are those that operate in many different states over thousands of miles of track. 

They are defined by the U.S. Surface Transportation Board as having annual carrier operating 

revenues of $250 million or more. As of 2014, there were 8 such railroads in the U.S.: Amtrak 

and seven freight railroads, which were designated Class I based on 2011 measurements 

released in 2013 ("Class I Railroad Statistics". Association of American Railroads. April 17, 2013.)

 Class II/III railroads are also known as short line and regional railroads, and they range in size 

from very small (a few carloads of freight per month) to multi-state railroads just under Class I 

size. Class II railroads are defined as having revenues greater than $20.5 million but less than 

$277.7 million for a least three consecutive years. Switching and terminal railroads are excluded 

from Class II status. A Class III railroad is defined as a rail company with annual operating 

revenue of less than $20 million.

 Line haul refers to higher power usage of locomotive engines during extended mileage. It is also 

associated with a test cycle used for estimating emission factors intended to represent 

emissions during line-haul activity.

The EPA develops and maintains methods for estimating locomotive emissions, and these methods are 

used in the NEI in the absence of more updated data from air agencies. They are also available as a 

fallback for states without other data for this sector. The EPA’s 2011 national rail estimates were 

developed by applying growth factors to the 2008 NEI values based on railroad freight traffic data from 

the 2008 and 2011 “R-1” reports submitted by all Class I rail lines to the Surface Transportation Board 

and employment statistics from the American Short Lines and Regional Railroad Association for Class II 

and III. In the latest such approaches (used for the 2008 and 2011 NEI), this apportionment includes 

allocation to GIS shapefiles for line-haul and rail yard emissions. The EPA project report Development of 

2011 Railroad Component for National Emissions Inventory (September 2012) provides the EPA’s latest 

estimation approach and references the 2008 approach as well. The report for the 2008 NEI was another 
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project report, called Documentation for Locomotive Component of the National Emissions Inventory 

methodology (May 2011).

The EPA default method was developed with a consortium of the EPA, state, and industry, led by the 

Eastern Regional Technical Advisory Committee (ERTAC). The ERTAC group provided data and reviewed 

methods as is described in the 2008 NEI Technical Support Document and associated documentation. 

Table 23 lists the locomotive SCCs used in the EPA default methodology. Other SCCs exist as valid SCCs, 

but are not used in the EPA method, so states should consider this when comparing the EPA estimates 

to locality-specific estimates and when merging emissions inventories that include both state/local 

components and the EPA estimates. 

Table 23: Locomotive SCCs

SCC Description EPA Estimated?

Data 

Category

2285002006 Mobile Sources Railroad Equipment Diesel Line Haul 

Locomotives: Class I Operations

Yes – in shape 

files Nonpoint

2285002007 Mobile Sources Railroad Equipment Diesel Line Haul 

Locomotives: Class II / III Operations

Yes-in shape 

files Nonpoint

2285002008 Mobile Sources Railroad Equipment Diesel Line Haul 

Locomotives: Passenger Trains (Amtrak) no Nonpoint

2285002009 Mobile Sources Railroad Equipment Diesel Line Haul 

Locomotives: Commuter Lines no Nonpoint

2285002010 Railroad Equipment Diesel Yard Locomotives no Nonpoint

28500201 Internal Combustion Engines Railroad Equipment 

Diesel Yard

Yes – as point 

sources

Point

State or local agencies may determine that the EPA default method is not appropriate for SIP purposes 

or may need further refinement by air agencies in developing SIPs. A number of ways to improve the 

EPA estimates were noted in the original 2011 report (see 

ftp://ftp.epa.gov/EmisInventory/2011/doc/2008nei_locomotive_report.pdf) that documented the 

approach used for the 2008 NEI. For the Class I line-haul emissions, the report identifies the most 

important considerations such as the rail link-level freight tonnage. Other variables were not addressed 

in the methodology, including track grade and track speed. While the method calculated railroadspecific fleet- averaged emission factors from industry fleet data, it is noted that emissions from 

individual engines are highly variable even for the regulated engine categories depending on variables 

such as the specific locomotive model, operation cycle, and conditions of operation. Furthermore, the 

EPA approach does not address the seasonality of the emissions, while activity levels of different 

engines do vary seasonally and could impact emissions for seasonal inventories. Any locality-specific

data or custom emissions associated with locomotive sources are expected to be included with 

supporting documentation for the emissions inventory used for a SIP.

For the rail yard emissions, the same 2011 report notes additional considerations for improvements. It 

notes that the use of tonnage hauled as an indicator of the amount of switching activity is an 

assumption that could reduce uncertainty. The variability associated with actual switching duty-cycles 
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and in the number of switchers operating at some rail yards seasonally was not considered in the 

method.

Locomotive idling emissions is another issue that is not clearly considered in the default EPA 

methodology and could have an impact on emissions estimates. During normal operations, locomotives 

have numerous reasons why they may remain idling including the switching operations noted above. 

The EPA has included regulations on idle emissions to help address this source. More details on idling 

emissions from locomotives is available in “Control of Emissions from Idling Locomotives” (EPA, March 

2008).

The EPA website on locomotive regulations and locomotive emissions 

(http://www.epa.gov/otaq/locomotives.htm) provides a resource for understanding the regulations that 

apply to locomotives and how those may impact emissions. Only one recent regulation impacts 

emissions from locomotives, while several older regulations also apply. In June 2008, the EPA published 

the Control of Emissions of Air Pollution for Locomotive Engines and Marine Compression Ignition 

Engines Less than 30 Liters Per Cylinder. This rule includes standards for existing and remanufactured 

locomotives, Tier 3 and Tier 4 standards for newly built locomotives, and idle reduction requirements for 

new and remanufactured locomotives. The rule reduces emissions of PM2.5 and NOX. The emissions 

estimation approach used for this rule is available in Chapter 3 of the Regulatory Impact Assessment for 

the rule, and this approach differs from the EPA method used for the NEI. Associated with the rule, the 

EPA developed a fact sheet on locomotive emission factors (April, 2009) that can be used in estimating 

emissions from locomotives.

4.8.6 Biogenic and Geogenic 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 and CO emissions. 

The EPA makes available biogenic emissions estimates as part of the NEI. Starting in 2008 NEI, the 

biogenic vegetation and soil emissions have been included in the official NEI releases. In some cases, 

these EPA-generated emissions may be sufficient for use in SIP inventories other than modeling 

inventories.

Biogenic emissions from vegetation and soils are computed using a model which utilizes spatial

information on vegetation and land use and environmental conditions of temperature and solar 

radiation25. The model inputs are typically horizontally allocated (gridded) data, and the outputs are 

gridded biogenic emissions which can then be speciated and utilized as input to photochemical grid 

models. Several models exist, as described in the following subsections.

 

25 In most cases, ozone, PM, and regional haze modeling includes the emissions from vegetation and soils, but not other

relevant sources such as volcanic emissions, lightning, and sea salt.
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Modeled biogenic vegetation emissions are significant for understanding ozone formation, particularly 

in the Eastern U.S., and the dependence on meteorology makes using case-specific meteorology very 

important. In addition, the impact and model characterization of biogenic terpene and sequiterpene on 

secondary aerosol formation for PM modeling is thought to be important. Emissions data developers

should consider the latest available information on this issue where biogenic sources are key sources in 

their modeling region.

Biogenic Emissions Inventory System (BEIS)

The EPA has developed the Biogenic Emissions Inventory System, version 3.14 (BEIS3.14) for use in 

estimating biogenic emissions. This model runs as a module of the SMOKE system, with the latest 

documentation available at http://cmascenter.org/smoke/. 

The key inputs to BEIS include: 

 Temperature data at 2 meters, which can be obtained from modeled meteorological data, such 

as data from the Weather Research and Forecasting (WRF) Model. Such data are also needed for 

input to air quality models used for modeled attainment demonstrations sometimes needed as 

part of SIPs. The BEIS3.14 documentation has more information on the meteorological inputs.

 Land-use data from the Biogenic Emissions Land Use Database, version 3 (BELD3). BELD3 data 

provides data on the 230 vegetation classes at 1-km resolution over most of North America. 

These data are available at http://www.epa.gov/ttnchie1/emch/biogenic/. These land use data 

can be created with the Multimedia Integrated Modeling System (MIMS) Spatial Allocator 

(http://www.ie.unc.edu/cempd/projects/mims/spatial/). Air agencies can alternatively rely on 

the EPA’s 12-km gridded data for modeling domains that overlap with the EPA national domain, 

provided with the EPA’s latest modeling platform on the Emissions Modeling Clearinghouse.

Other Biogenic Models

Other biogenic models such as Model of Emissions of Gases and Aerosols from Nature (MEGAN)

(http://acd.ucar.edu/~guenther/MEGAN/MEGAN.htm) are acceptable as well, provided that the users 

have demonstrated their suitability for the modeling application (see Modeling Guidance for more 

information). A version of MEGAN has also been incorporated into an air quality model called the WRF 

model coupled with Chemistry (WRF-CHEM) (http://www.acd.ucar.edu/wrf-chem/). California has 

developed a GIS-based biogenic model called BEIGIS (http://www.arb.ca.gov/ei/biogenicei.htm). 

Another model is available called the Global Biosphere Emissions and Interactions System (GloBEIS) 

(http://www.globeis.com/). The EPA previously made a comparison between BEIS and MEGAN

(available at http://www.cmascenter.org/conference/2008/slides/pouliot_tale_two_cmas08.ppt).

BEIS, MEGAN, and other models continue to evolve and so agencies using these models should 

evaluable the suitability of one model over the other as part of a modeled attainment demonstration. 

Once a choice has been made for modeling purposes, emissions should also be summed across the NAA

for inclusion in the base year inventory for the NAA and/or the attainment projected inventory for the 

NAA.
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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 usually less significant than biogenic

sources. However, geogenic wind erosion may contribute substantially to PM emissions in an area. In 

2012, the EPA released CMAQ v5.0 that includes a module that dynamically estimates hourly natural 

emissions of fine and coarse dust particles due to wind action over arid and agricultural land. This allows 

the contribution of this source to be included in a modeled attainment demonstration without the need 

to prepare an emissions inventory first. The windblown dust approach is based on the work of Tong et 

al. (2011) (see also the CMAQ wiki at http://www.airqualitymodeling.org/cmaqwiki/

index.php?title=CMAQv5.0_Windblown_Dust). For the emissions inventory SIP, air agencies using this 

feature should evaluate the results of the CMAQ-based approach to determine if it provides a 

reasonable representation of dust emissions in their modeling domain. Often times, CMAQ 

overestimates ambient crustal matter concentrations without the addition of windblown dust and so 

adding emissions may not be advisable. 

If windblown dust emissions are included in SIP planning, such emissions should be included in the base 

year and attainment projected inventories to meet the requirements for a complete emissions 

inventory. In the case of using CMAQ, this would require that the CMAQ-based emissions be summed 

for the NAA. Since CMAQ produces gridded emissions estimates, air agencies would need to sum 

emissions from the relevant grid cells or portions of cells associated with the NAA and/or other 

geopolitical regions as appropriate. One relevant detail about the AERR regarding windblown dust is that 

they are specifically exempted from the reporting requirements in 40 CFR 51.20(d)

State, local and tribal agencies 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 available at http://www.epa.gov/ttn/chief/eiip/techreport/volume05/index.html. 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.

Lightning produces NO, which is oxidized to NO2 in the presence of ozone or in a photochemically 

reactive atmosphere. This NOX is formed in the mid-upper troposphere and can impact the distribution 

of reactive nitrogen as well as ozone. NO emissions from lightning can be estimated by collecting activity 

data on the cloud-to-ground lightning flashes, assuming a frequency of intra-cloud flashes based on the 

value for cloud-to-ground lightning flashes, and applying appropriate emission factors (in molecules NO 

per flash) to these activity levels. 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 planning inventory 
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purposes. Given the altitude of these emissions, it is not usually important to include these emissions in 

the base year inventory for the NAA or in the attainment projected inventory for the NAA. 

CMAQ v5.0 includes a parameterized approach to estimate NOX emissions and its vertical distribution 

that is generated from lightning. Over the Continental U.S., the approach can use lightning flash totals 

from the National Lightning Detection Network (NLDN). For cases where such data are not available, an 

alternate algorithm can be used that estimates the number of lightning flashes based on the modeled 

convective precipitation. The peer reviewed literature contains both a description of the approach (Allen 

et al., 2011) and a model evaluation (Appel et al., 2010). More information is available from the CMAQ 

v5.0 wiki (see http://www.airqualitymodeling.org/cmaqwiki/

index.php?title=CMAQv5.0_Lightning_NO). 

4.8.7 Wildland Fires 

Because the CAA specifies that planning inventories (e.g., the base year inventory for the NAA) must 

include all sources of emissions, the inventories therefore should include fires. Thus, wildfires and 

prescribed fires, including wildland fire use, should be included in the NAA inventories when they 

overlap with NAA boundaries. Generally, areas will find that the estimates available in the NEI will 

suffice for providing a reasonable estimate of these emissions, with the purpose of providing a general 

idea of the level of contribution to the overall emissions within the NAA.

Wildland fires (WLFs) are generally defined as any non-structure fire that occurs in the wild land (an area 

in which development is essentially non-existent, except for roads, railroads, power lines, and similar 

transportation facilities). The National Wildfire Coordinating Group26 has identified the following two

types of WLFs27:

 Prescribed fire: Any fire ignited by management actions to meet specific objectives (generally 

related to the reduction of the biomass potentially available for wildfires). A written, approved 

prescribed fire plan must exist, and National Environmental Policy Act requirements must be 

met (where applicable) prior to ignition.

 Wildfire: An unplanned, unwanted WLF including unauthorized human-caused fires, escaped 

WLF use events, escaped prescribed fire projects, and all other WLFs where the objective is to 

put the fire out.

Wildland fires are a unique source of emissions with respect to NAAQS attainment planning. For ozone, 

PM2.5, and regional haze planning purposes, these fires are major sources of primary PM2.5 and VOC and 

a moderate source of NOX. They can consequently impact the ambient PM2.5 and ozone; however, they 

have a number of unique properties:

 

26 The National Wildfire Coordinating Group was formed under a cooperative agreement between the 

Departments of Agriculture and the Interior and consists of representatives from each of the Federal land 

management agencies and the National Association of State Foresters.

27 Definitions are derived from the Glossary of Wildland Fire Terminology, National Wildfire Coordinating Group, 

PMS 205, July 2012. Available at http://www.nwcg.gov/pms/pubs/glossary/p.htm.
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 Depending on the fuel source and acreage burned, both prescribed and wildfires can emit 

significant emissions, but emissions from prescribed fires are generally lower due to the burning 

characteristics and the relative amounts of flaming and smoldering emissions. In addition, 

prescribed fires can be used to prevent future wildfires, which are generally larger, hotter, more 

dangerous, and more polluting.

 Wildfires are naturally occurring events for which the emissions are generally not reasonable to 

prevent or control. As such, air agencies may request that the EPA exclude from regulatory 

determinations ambient data influenced by the wildfire if the request meets the criteria, 

schedule, and procedural requirements for an exceptional event set forth in 40 CFR 50.14.28

 Fire emissions can rise very high in the atmosphere on plumes, and the pollutants can be 

transported beyond state boundaries. Fires occurring outside NAAs can have impacts within 

NAAs on days that may not be determined to be exceptional events.

 Since wildfires and prescribed fires generally occur in forests and rangelands, they are less likely 

to be within the boundaries of NAAs, which are usually urbanized areas.

 Fires can also reduce ozone formation because their smoke can block sunlight that otherwise 

would result in more ozone.

4.9 Quality Assurance

As part of the 8-hour ozone NAAQS, PM2.5 NAAQS, and regional haze rules, state, local and tribal

agencies are strongly encouraged to perform QA checks and procedures on their inventories. State, local 

and tribal agencies 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 emissions 

inventory. A well-developed and well-implemented QA program fosters confidence in the inventory and 

in any resulting regulatory and/or control program.

When air agencies are using data from the NEI, additional QA is warranted considering the purpose for 

SIPs is not the purpose for which the NEI was developed. Since a great deal of QA is done on the data 

used for the NEI, must of the QA work has been done and so starting with the NEI can often save time. 

The overall QA program 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 

assurance 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.

 

28 “Treatment of Data Influenced by Exceptional Events; Final Rule” (72 FR 13560, March 22, 2007).
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4.9.1 QA Reference Materials and Planning

The EPA has developed several guidance documents designed to assist state, local and tribal agencies in 

designing and implementing their QA programs. The EIIP Volume VI, available at 

http://www.epa.gov/ttn/chief/eiip/techreport/volume06/index.html, addresses QA issues, including the 

following:

 Chapter 1: Introduction - The Value of QA/QC

 Chapter 2: Planning and Documentation

 Chapter 3: General QA/QC Methods

 Chapter 4: Evaluating the Uncertainty of Emission Estimates

 Chapter 5: Model QA Plan

 Appendix A: Example Audit Report

 Appendix B: Technical Systems Audit Checklist Example

 Appendix C: Example 1 of Data Quality Audit Checklist

 Appendix D: Example 2 of Data Quality Audit Checklist

 Appendix E: Performance Evaluation Checklist Example

 Appendix F: EIIP Recommended Approach to Using the Data Attribute Rating System (DARS)

On October 21 2008, the EPA issued the latest version of the EPA Quality Program Policy (CIO 2106.0). 

This policy supersedes the previous CIO 2105.0 (formerly EPA Order 5360.1 A2). This policy established 

among other things, the requirement for QAPPs for all EPA-supported programs that generate 

environmental data. As described by the EPA Guidance “EPA Requirements for QA Project Plans”:

The purpose of a QA Project Plan is to document planning results for environment data operations and to 

provide a project-specific blueprint for obtaining the type and quality of environmental data needed for a 

specific decision or use.

The orders describing the QA requirements are available at the EPA’s website for Agency-wide Quality 

System Documents (http://www.epa.gov/quality/qa_docs.html). That website also includes 

specifications for non-EPA organizations: “EPA Requirements for Quality Management Plans” 

(EPA/240/B-01/001; March 2001) and “EPA Requirements for QA Project Plans” (EPA/240/B-01/003; 

March 2001). Additional documentation is also available on the same website under the subheading of 

“General Guidance” that air agencies may find helpful in developing their own quality assurance plans 

for their inventory development efforts.

States should also consult with their specific regional office to determine how to meet the quality 

assurance planning requirements for the SIP planning inventory development. 

4.9.2 Types of Problems in Emissions Inventories

Emissions inventories are compiled from a large number of disparate data sources, which can lead to 

many types of data problems. These problems can be divided into value errors and structure errors. 

Value errors are errors in the values of emissions inventory data fields, such as the emissions amounts, 

incorrect codes, missing values that are required, or incorrect data such as facility names, stack heights, 

or latitude/longitude locations. Correct quality assurance can identify these errors and allow data 

developers to correct them before the data are used for their intended purpose.
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Structure errors refers to those data problems that cause databases to not work, such as missing records 

in relational database tables (e.g., “widows” and “orphans”), duplicate records (i.e., multiple records 

that represent the same emissions, causing double counting), or incorrect formats (e.g., the wrong 

number of fields, missing fields that are required, mismatched data types, such as integer versus text). 

Data with no structure errors are described as having good “data integrity.” Generally, these types of 

problems should be automatically prevented by using robust data systems to manage the data in ways 

that match the expected downstream data use, but this is not always the case. For example, data 

systems managing emissions inventory data should be developed with the AERR requirements in mind, 

since these are the governing requirements for SIP-related inventories.

4.9.3 Checks Available Through the EPA’s Emissions Inventory System

While many inventories used for SIPs are not also submitted to the EPA through its EIS (the system the 

EPA uses to build the NEI), the EIS does have a large number of documented QA checks that the system 

performs as it is loading data submitted by air agencies. This automated QA provides a large number of 

data integrity checks that air agencies can consider including in their own data systems or checking as 

part of their inventory QA. To access a list of these checks, EIS users must use the EIS Gateway and use 

the “QA Checks” link under the “Reference Data” heading on the left of the Gateway interface. The 

checks are not otherwise published on the EPA’s website and can be requested by non-EIS users by 

submitting a request to the EIS Gateway access contact listed at the EIS contacts website 

(http://www.epa.gov/ttn/chief/eis/index.html). The list has more than 600 data checks that are 

performed automatically by the EIS. While many of these checks are only relevant for getting data into 

the EIS, they promote standardization of inventories and proper formatting in accordance with the 

AERR, which (as noted previously) provides the EPA’s standards for inventory preparation including for 

SIP inventories.

Since the timing of development of SIP inventories is rarely, if ever, coincident with the timing required 

for submitting emissions for the NEI, it is generally not feasible for air agencies to submit SIP inventories 

to EIS. However, the same types of checks can and should be done on SIP inventories to insure 

appropriate inventory quality.

The EIS checks include both critical errors and warnings. Critical errors prevent data getting into the EPA 

data system until they are corrected, whereas warnings allow the data to go through, but may need to 

be resolved to ensure the data transmitted to the EPA are correct. Examples of critical errors include:

 Checks that data codes for required fields use valid values (for the given inventory year; see also 

Section 4.7)

 Fields required by the AERR and for data integrity are present

 Certain fields are within a critical range check (e.g., a year is between 1900 and 2050, stack 

height is between 1 and 1300 meters)

 Certain fields have appropriate lengths (e.g., ZIP codes are between 5 and 10 characters)

 Percentages are provided as percentages (1 to 100) and not as a fraction

 Data element types (e.g., integer, text, numerical) of required data fields are provided 

consistent with their required type.
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 MOVES county database submission contains the correct files

 NMIM county database submission contains the correct files

 Conflict with pollutants reported for grouped pollutants versus individual members of the 

group.

 If stack diameter information is reported, the release point exit gas flow rate or velocity should 

be reported. Both may also be reported.

Examples of warnings include:

 Checks that data codes for optional fields use valid values (for the given inventory year)

 Data value is longer than the allowable width (some text fields will be truncated if longer than 

what the EIS allows).

 Emissions value is outside of a presumed valid range

 Exit Gas Stack temperature is outside an appropriate range

 When submitting monthly data, all months are not submitted together

 File names of mobile data files use incorrect file extensions

 Data element types (e.g., integer, text, numerical) of optional data fields are inconsistent with 

their required type.

4.9.4 Inventory Comparisons

Inventory comparisons can be used in multiple ways to effectively identify problems in new inventories. 

This is most useful when a high-quality prior inventory is already available. In states with a long history 

of developing SIPs, past inventories will be readily available for such comparisons. In states with new or 

emerging attainment problems, the EPA suggests comparing SIP inventories to the NEI. Even when the 

comparisons reveal problems not with the new inventory but with the one being compared, this can 

increase confidence in the inventory of interest.

Emissions are one of the obvious things to compare, and these comparisons are usually done on a 

pollutant-by-pollutant basis for pollutants important to a given analysis. As noted in the section on 

ranking techniques (Section 4.9.7), ranked emissions (e.g., facility, unit, county, SCC group) can be 

compared to the same ranked emissions from other inventories. Such comparisons will often identify 

differences worth further exploration when one large source appears on one list and not the other. 

In addition to ranking, all records across an inventory (or inventory summary) can be compared and 

percent differences can be computed. This is usually done by computing “new emissions – old 

emissions” divided by “old emissions”. Large or unexpected percent differences can be investigated 

further to make sure that the differences have some reasonable explanation, such as newer emissions 

being controlled, a downturn in activity for one inventory, process changes, fuel changes, or a partial or 

complete facility closure. In some cases, methods changes may be the reason for such differences, 

including updated emission factors or test data.

For nonpoint emissions, graphical inventory comparisons can be useful. This can be done not only using 

calculated percent differences or ranking, but also using GIS techniques to map county level emissions 
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and their differences. It can be very useful to map the old emissions, new emissions, and the computed 

difference or percent difference side-by-side. This can reveal areas of large emissions that have 

significantly changed from one inventory to the next, raising questions for further exploration. When 

comparing to an EPA inventory that used EPA methods for a particular sector, this could reveal that the 

SIP planning inventory is a better inventory with updated methods, or it could reveal that outdated 

methods are being used. In any case, having made the comparison will help inventory developers 

understand the potential improvements that could be made or that have been made, which will help in 

understanding reviewers’ expected reactions to the data.

For multi-state inventories needed for SIP development, state-to-state comparisons may be useful in 

addition to county maps. This is especially true if emissions for one state were developed differently 

from emissions for another state. The EPA encourages states to work together to promote consistent 

approaches across a multi-state NAA, but a final QA check of the consistency can be done using the 

comparison techniques described here. 

4.9.5 Checking Data Codes

As described in Section 4.7, air agencies should check the inventory data codes they are using against 

valid codes. Valid codes are defined by the EPA within the EIS. Air agencies that start with the NEI may 

significantly minimize the burden of this recommendation.

4.9.6 Point Versus Nonpoint and Reconciliation

Several quality assurance issues arise related to point versus nonpoint sources and inventories: 

(1) correct identification of point sources, (2) prevention of double counting across point and nonpoint, 

and (3) prevention of missing nonpoint emissions.

Minimum thresholds are specified in the AERR for which sources with facility total potential to emit

emissions above those thresholds must be treated as a point source in SIP planning inventories. This is 

more fully explained in Section 2.5.7, with lower thresholds relevant for ozone and PM NAAs. Air

agencies should implement a QA check (or otherwise have a data collection process) that ensures all 

facilities with potential-to-emit emissions (potential controlled emissions, if applicable) that are greater 

than these thresholds are included in their inventory as point sources. See also Section 2.5.2 for more 

information on calculating potential emissions.

When a particular type of source includes contributions from both point and nonpoint sources, double 

counting can occur. QA steps should be taken to ensure that double counted emissions have been 

prevented. A good example of this is smaller boilers. Both point source facilities (based on the potential 

to emit thresholds) and smaller facilities are likely to have emissions from non-industrial boilers. For 

instance, some large institutional facilities such as hospitals may be included as a point source with their 

associated boiler emissions, whereas smaller institutional facilities are not included as point sources and 

would thus be included as a nonpoint source under an “institutional/commercial” boiler SCC. 

The EPA provides calculation approaches for many nonpoint emissions that allow for subtracting out the 

activity of the point source parts prior to estimating nonpoint emissions, including that for the 

institutional/commercial boiler example. This is called “point/nonpoint reconciliation”. Whether 
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nonpoint emissions are estimated by the EPA or by air agencies, an assessment of quality should be 

done to ensure that sectors associated with both point and nonpoint sources do not double count 

emissions. See also Section 4.8.2 for additional information on preventing double counting. A list of 

source sectors with potential point/nonpoint overlap is provided in Table 18 above and in the latest NEI 

Technical Support Document, available at http://www.epa.gov/ttn/chief/eiinformation.html.

A third type of QA should be done for categories that have both point and nonpoint contributions. It 

involves an assessment of potentially missing nonpoint emissions. Since the requirement for SIP 

inventories is to include emissions from all sources, it is not sufficient to exclude nonpoint emissions 

when part of a sector is covered by point sources, unless it can be shown that the nonpoint portion is 

negligible. At a minimum, air agencies should consider the tools available from the EPA to estimate 

nonpoint sectors (see Section 4.8.2) and evaluate whether or not their point source inventory covers all 

of the activity associated with the nonpoint categories. For inventory years not covered by EPA tools, 

agencies should compare point total activity as collected from point sources versus the same type of 

activity data used in the EPA tools. For example, US DOE fuel consumption data can be used for 

industrial, commercial, and institutional boilers. The source of the activity data used for the latest EPA 

nonpoint methods is included in the descriptions of those methods in the nonpoint tools described in 

Section 4.8.2 and with the latest NEI documentation.

4.9.7 Ranking Techniques

Ranking emissions records can be a very useful tool to identifying value errors in emissions values or 

other numeric inventory data fields, or at least in finding records that need further investigation. 

Ranking involves first defining a set of sources and a level of aggregation of emissions and then ordering 

those emissions values from highest to lowest or lowest to highest. This analysis must be done one 

pollutant at a time. An analyst then considers whether those sources at the top of the list make sense.

Point sources, facility level emissions ranking

For point sources, ranking can be done at the facility total, unit total, or process level (i.e., at the SCC 

level), and each level has its place for reviewing inventories. A facility level ranking can often be followed 

by subsequent investigation to understand the reasons (at the unit and/or process level) for very high or 

very low values. An analyst using a ranking procedure would assess the facilities with the largest 

emissions and seek to understand whether they make sense. For example, for combustion products 

such as NOX or SO2, one would expect to see large EGUs and other industrial sources. Ranking of 

emissions values is usually done for one pollutant at a time, reviewing most carefully those pollutants 

that are most critical to the particular purpose of the inventory. For example, an inventory supporting 

ozone analysis would want to review NOX and VOC most carefully.

It can be useful to compare the list of top facilities for a given pollutant from one inventory to a previous 

or alternative inventory for a given state or NAA. This can raise questions regarding large changes from 

one inventory to another, which could be explained (e.g., a decrease due to controls) or could identify a 

problem (e.g., a missing value or data entry problem). In addition, facility-level ranking can use 
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additional grouping such as by industry code (i.e., NAICS), to identify unexpectedly high or low emissions 

for facilities within a particular industry.

Point sources, sub-facility emissions ranking

Unit- and process-level summaries can additionally be ranked for more specific analyses. For example, 

all boilers could be ranked and particularly high or low emissions values investigated. Similarly, all 

natural gas processes at particular unit types (e.g., boilers) or by industry (NAICS) could be ranked. These 

rankings can show real variations, but they can also find incorrect values that stand out when ordered 

and reviewed in this way. There are many variations that could produce useful results, and which ones 

are useful for a particular inventory depends on many factors and the purpose of the inventory.

Nonpoint and mobile source ranking

Nonpoint and mobile emissions can also be ranked as technique to help with QA. Since these inventories 

are primarily compiled at the county/SCC resolution, the ranking can be done only at combinations of 

county, SCC, and for specific pollutants. Total county nonpoint emissions could be ranked to look for 

overly high or low values, but the same effect can be accomplished in a visual way with mapping 

approaches (see Section 4.9.9). Specific SCCs can also be selected and the emissions by county ranked, 

or individual counties selected and SCCs ranked and compared to other counties.

Since nonpoint emissions are based on various types of activity data that also has a county or other 

spatial resolution (such as census tract), these activity data can be used to “normalize” the nonpoint 

emissions prior to ranking. For example, emissions coming from households (e.g., residential heating, 

residential wood combustion, consumer solvents) can be divided by population or housing data and 

ranked for identify possibly strange results. Since some of the activity data used for these categories 

starts with state or regional resolution and is subdivided to apportion to the county resolution, such 

comparisons can reveal illogical outcomes of such approaches. For example, while it makes sense that 

residential wood combustion occurs more per household in rural areas, it wouldn’t make sense for a 

very low population county to have a disproportionate amount of emissions and urban areas have none.

4.9.8 Outlier Analyses

One result of the ranking approaches described above will be to identify outliers. However, such ranking 

is a relatively unsophisticated way of identifying such outliers. A more robust approach can be used for 

point sources where states have the underlying activity data reported by facilities on a per-process 

basis. Dividing emissions by activity values would produce a set of implied emission factors, or rates. The 

rates for a similar set of processes (based on SCC) and control devices in use might be expected to be 

within an order of magnitude of each other. Emission rate values that are too far outside the expected 

relationship could be further investigated to better understand the source of any unexpected values, 

which might include an error in the units of measure or the presence of controls or an incorrect SCC, as 

well as data entry errors for emission values or other related fields.
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4.9.9 Using Maps to QA Nonpoint Emissions

Nonpoint and mobile source emissions data are associated with states and counties and therefore are 

ideal candidates for mapping with GIS software. By mapping emissions values for individual SCCs or 

groups of SCCs, data analysts can identify unexpected patterns in the data that could signal an error in 

creating the data. Though it is technically more challenging to use GIS software, this approach can often 

be more valuable than ranking in identifying data problems.

Like the ranking techniques, GIS maps can also use emissions data normalized by some other underlying 

or related spatial data, such as population, land use, urban/rural designations, or housing. This type of 

information is increasingly available online from the U.S. Census Bureau and other sources. Data 

analysts can use the other data to identify unexpected relationships that possibly indicate bad 

assumptions made in the underlying methods.

4.9.10 Expected Pollutants

Air agencies can use their expertise with emissions sources to identify which pollutants are expected 

from particular processes. For example, NOX is always expected as a by-product of combustion 

processes. Conversely, analysts can identify pollutants that are not expected from a particular process, 

such as SO2 from an evaporative process. Once identified, such lists can be used to cross-check 

inventories to identify either problems with reported emissions, pollutant codes used, or process codes 

used. For example, if a combustion process doesn’t have NOX emissions, it could be that the wrong 

pollutant code was used in reporting the NOX and it’s showing up as something else. Or, the process 

itself may be incorrectly using a combustion process code.

Expected pollutants can also help with making sure the correct PM components are provided for PM 

inventories, in particular that condensable PM emissions are included in the total PM emissions and that 

both filterable and condensable PM emissions are reported. This issue was described in Section 4.2.1

along with a list of the types of sources expected to have such emissions.

Some emissions data analysts may not be familiar with various sources enough to know which pollutants 

should be expected. For point sources, agency staff can rely on the sum total of all reported data across 

multiple sources for a particular process to get a good idea of what should be expected. For example, if 

all but one industrial boiler burning natural gas reported VOC, then it would be worth further 

investigation as to why VOC was not reported for that one. Since the AERR specifies that all criteria 

pollutants must be reported if any one pollutant exceeds the potential to emit threshold, one should 

expect that similar processes from multiple facilities would have many, if not all, the same pollutants.

There are other ways to identify expected pollutants. These include looking at past inventories created 

by the same air agency or looking at the NEI. Another way is to see what emission factors are available 

for the process in Webfire. While these are not foolproof ways of finding expected pollutants, they can 

be very helpful. Comparing a draft inventory with such a list can also identify unexpected pollutants to 

consider. Used with ranking techniques, knowing what pollutants are expected can also help when you 

find zero or null values for a facility, unit, or process.
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4.9.11 Facility and Release Point Locations

Facility and release point (e.g., stack) locations are key elements of inventories that are used primarily in 

preparation of inventories for air quality modeling and also in permit modeling. Facility locations are 

also used in mapping point sources for various public communications purposes and to help understand 

the nature of air quality problems influenced by local sources. While facility resolution is acceptable for 

many modeling applications, including 12-km gridded modeling, the need for release point locations 

increases for finer resolution modeling. Thus, for 4-km or 1-km modeling, release point location 

information should be considered.

With regard to the more detailed release point coordinates, the EPA recognizes the need for air agencies 

to leverage SIP inventory development efforts for possible use for other inventory needs. Thus, air 

agencies should be particularly attuned to release point geographic coordinates for sources that could 

be involved in permitting or risk analysis. For regulatory dispersion modeling, release point location is 

critical (rather than only facility location).

The EPA’s EIS and other inventory data systems support two types of locations: facility and release 

point. There are four key errors that can occur, and each can be identified with their own type of check, 

as listed below.

 Facility is not consistent with the state/county FIPS code

This error can be found using GIS, SAS®or other calculations to compare the latitude/longitude 

location with the county boundaries using some tolerance. Because county boundaries have 

varying degrees of accuracy, a tolerance should be used that allows for locations near, but not 

always 100% within, county boundaries.

 Facility location is not consistent with the physical location of the facility

Since some facilities can be on very large tracts of land, facility locations developed using 

geocoded addresses or facility entrances are often not accurate with regard to the actual 

location of the facility. For emissions inventory purposes, the EPA encourages that facility 

locations be positioned on top of a part of the facility that emits one or more pollutants, and the 

facility centroid is often sufficient for doing so. Using freely available mapping software such as 

Google Maps, latitude/longitude locations can be plotted on satellite images to ensure that 

values are on top of an emitting source and not on the road, at the corporate headquarters, or 

in some other invalid location.

 Release point location is not consistent with facility location

This check is only useful once the facility location is accurate. Such an error can be found using

GIS, SAS® or other calculations to determine the distance between the facility location and the 

release point locations. Alternatively, a subtraction of the absolute values of the latitudes and 

longitudes can be used to determine the difference in degrees. If that linear distance or the 

distance in degrees is greater than some preset criteria, then the locations can be investigated 

further. For some types of facilities such as refineries or major chemical complexes, the facilities 

may be very spread out and therefore may have legitimately large distances between release 

points.
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 Release point location is not consistent with the physical location of the release points

For many applications, even including some SIP modeling applications, all release points using 

the same (usually facility) latitude/longitude is sufficient. However, with the availability of 

inexpensive GPS technology, it is more realistic for facilities to collect and submit individual 

release point location information. Furthermore, for some types of analysis, particular fine scale 

modeling for permitting and risk analysis, correct release point locations can make the 

difference between a good analysis and a useless one. It is very difficult to check the accuracy of 

release point locations, but using mapping software overlaid on satellite images can provide 

some sense of whether the release points are meaningful or not. Coordinates reported to oneten-thousandth of a degree (four digits after the decimal point) give a precision of 

approximately 30 feet. Thus, a simple check to see if such values are useful is to examine the 

number of decimal places included in a given database.

Since a facility’s location is not likely to change, the EPA has implemented a procedure in the EIS that 

allows latitude/longitudes to be locked, meaning that they cannot be changed accidently during a data 

exchange with a state. We encourage air agencies to implement a similar approach in their data systems 

so that the efforts of QA done on one inventory can be inherited by other inventories created by that 

agency. Locking mechanisms prevent the data from being changed inadvertently through a new data 

collection that relies on data from an unverified data source. Thus, a comparison of the locations used in 

the SIP inventory to any locked and verified site coordinates in EIS would also highlight potential errors 

for resolution.

4.9.12 Release Point Parameters

Like release point locations, release point parameters (also called stack parameters) are key elements of 

inventories that are used primarily in preparation of inventories for air quality modeling. The release 

point parameters impact the modeling of emissions from facilities because they specify details of the 

way the emissions are released; for example, they specify how high off the ground the pollutants are 

emitted and the exit velocity and temperature of those emissions. One basic and important distinction 

for release points is whether the release point is a stack or a fugitive emissions, and different types of 

parameters are specified for stacks than for fugitive emissions sources.

Correct release point parameters for stacks are important for modeling done for Ozone and PM2.5

modeled attainment demonstrations as well as modeling done for Regional Haze SIPs, whereas fugitive 

release parameters are not as critical for that purpose. This is because stack emissions parameters 

impact the modeling of plume rise and therefore determine how high the emissions rise in the modeled 

layers of the air quality model. Fugitive emissions are emitted in the modeled surface layer with no 

additional characterization. This is in contrast to more detailed plant-level modeling (i.e., done for 

permit modeling or risk modeling purposes), where both stack and fugitive parameters are critical. 

Because the focus of this document is on SIP purposes, we focus on stack parameters here.

Stack parameters included in the EIS and historically are stack height, stack diameter (at the exit point of 

the emissions), exit gas velocity, exit gas flow rate, and exit gas temperature. Additionally, a release 

point type is available in the EIS to specify a code for whether the “stack” has a particular orientation of 
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vertical, horizontal, goose neck, vertical with rain cap, or a downward facing vent. Valid release point 

codes are available in the EIS reporting code tables in the EIS Gateway.

QA for stack parameters can be done using several of the QA methods already described. Range checks 

can be applied; these can be the default EIS range checks (see Section 4.9.3) or range checks developed 

by an air agency. A more robust range check could be developed for specific types of processes 

associated with a release point or for specific NAICS codes. For example, one would expect higher stacks 

for EGUs than for lumber mills. Additionally, ranking techniques can be applied to stack parameters (see 

Section 4.9.7), including options for grouping ranked stack parameters by facility, unit, process and/or

specific types of facilities, units, or processes. This is somewhat complicated by the fact that multiple 

units or processes can feed a given release point, and when this happens, the predominant unit or 

process could be used for grouping purposes. Finally, more sophisticated outlier analysis could 

additionally be used, by finding correlations between stack parameters such as height and diameter and 

investigating those combinations that statistically fall outside an expected relationship or ratio.

4.9.13 Biogenic QA/QC

Biogenic emissions are somewhat more challenging to QA than emissions for other source categories 

because they may be generated differently (i.e., as part of a gridded, hourly modeling exercise rather 

than more basic inventory development techniques). The following list provides some basic checks that 

can be done as part of the generation of biogenic emissions:

1. Check the biogenic emissions tool logs for warnings/errors.

2. Check the logs to confirm that the expected inputs were used.

3. Compare state or county total emissions to another year or case’s biogenic emission totals.

4. Ensure that summer emissions are greater than winter emissions. This can be done by summing 

the emissions across the modeled summer days (e.g., May-October) and for the other models 

and then comparing the totals on a state and/or county basis. As a quick (but less rigorous) 

check, example summer hourly or daily emissions can be visually compared to example winter 

hourly or daily emissions using software that displays the gridded emissions.

5. Visually inspect sample days of the gridded, hourly emissions using software that displays the 

gridded emissions. The VOC emissions should generally be higher in southern latitudes because 

of warmer temperatures. This difference should be more pronounced in winter in cases where 

the southern areas have more actively growing vegetation. The NO emission should generally be 

higher in agricultural areas with significant fertilizer application.

4.9.14 Timing of QA and Follow-up

As air agencies, as well as the EPA regional offices, work quickly to meet relevant inventory and SIP 

deadlines, data problems are exacerbated when they are discovered too late in the process. A key part 

of making sure that a QA plan is effective is deciding (as part of the planning) when a given QA check is 

to be done and ensuring (as part of implementing that plan) that it is actually done. To do this 
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effectively, QA steps should be timed in a QA plan at the earliest possible time that the step can be 

performed so that errors are caught as early in the process as possible. Furthermore, assurances must 

be put in place that someone is confirming that the checks have been done along the way, so that errors 

get caught. At the end of the data development process, some accounting for the history of the QA 

should be available along with the data, so that others can confirm that the checks have been done and 

can be reassured. Where possible, evidence of completion of each QA step should be referenced, such 

as a comparison report.
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5 Developing Projected Emissions Inventories

5.1 Projected Emissions Overview

Emissions estimates for future years29 are called “emissions projections” or “projected emissions.” These 

projections include emissions growth (due to increased or decreased activities) and emissions controls 

due to regulations, settlement agreements (or consent decrees), fuel-switches, or other programs that 

reduce emissions in specific ways in the future. For point sources, emissions projections can also include 

facility and/or unit-level shutdowns due to settlement agreements (or consent decrees) and/or 

ownership decisions. 

The primary goal in making projections is to obtain a reasonable and technically credible estimate of 

future-year emissions that accounts for key variables. The EPA encourages the air agencies to 

incorporate in their analyses the variables that have historically been shown to drive their economy and 

emissions, as well as the changes in growth patterns and regulations that are expected to take place 

between the time of their base year and projected attainment year. For details on which future year(s) 

should be modeled for attainment demonstrations, readers should refer to the Modeling Guidance 

(http://www.epa.gov/ttn/scram/

guidance_sip.htm).

The EPA’s latest projection approaches and data are available as a part of the EPA’s “emissions modeling 

platform” development. These platforms are released and updated periodically in accordance with the 

EPA regulatory and analysis activity on the Emissions Modeling Clearinghouse at 

http://www.epa.gov/ttn/chief/emch. While each platform comes with a single or limited set of future 

years included, the data and thoroughly documented approaches can help air agencies to develop and 

improve their own emissions projections.

While dated, the 1999 EIIP report entitled “Procedures For Preparing Emissions Projections” 

(http://www.epa.gov/ttn/chief/eiip/techreport/volume10/x01.pdf) introduces the basic concepts 

behind emissions projections issues and approaches. The concepts of control efficiency, capture 

efficiency, rule effectiveness, and rule penetration were introduced in Section 2.5.18. The EIIP document 

provides information on how to use these factors to estimate projected emissions. However, some key 

features of this document need to be updated, including the reference to the Economic Growth and 

Analysis System, which is no longer supported by the EPA. Other outdated concepts include the 

assumption that economic growth can be a good indicator of emissions growth. While some correlation 

can exist, it cannot be assumed but rather must be demonstrated for a particular industry or facility. The 

correlation has not been well observed historically in the NEI data because of various issues including 

technology improvements and fuel-switching that often reduce emissions without regulation.

 

29 Technically, projected emissions could be made from a base year to a year that has already occurred when data 

are not yet available for a very recent year. However, for the purposes of the remainder of this guidance, we will 

assume projected emissions refers to future year projected emissions.
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In this section, we will address an overall approach for tackling emissions projection issues that 

incorporates use of this document and points out where other approaches or new data are available to 

amend the information included in that report.

The EPA recommends that developers of projected emissions take the steps in the bulleted list below. 

Each of these steps corresponds to a subsequent subsection.

 Identify sectors of the inventory that require projections and sectors for which projections are 

not advisable, and prioritize these sectors based on their expected impact on the modeling 

region (Section 5.2).

 Collect the available data and models that can be used to project emissions for each of the 

sectors (Section 5.3).

 For key sectors, determine what information will impact the projection results the most, and 

ensure that the data values reflect conditions or expectations of the inventory region (Section 

5.4.

 Quality assurance (Section 5.5)

5.2 Identify and Prioritize Key Sectors and Regions for Projections

Emissions data developers should evaluate their inventories for those sectors and regions that are most 

critical to their modeling results. The purpose of identifying these key sectors is to direct more resources 

and efforts to estimating future-year emissions for these sectors in the subsequent steps.

Sectors can be subsets of the larger groups of stationary area, on-road mobile, nonroad mobile, and 

point sources. For ozone modeling, it will be most important to ensure correct projections for sectors 

with higher NOX emissions. In larger urban areas that contain VOC-limited regions, sectors with higher 

VOC emissions will also be important. Mobile sources are typically large contributors to both VOC and 

NOX; therefore, they are usually a priority in estimation of future-year emissions, particularly for urban 

areas. For PM and regional haze modeling, the relative importance of primary PM2.5 emissions and its 

precursors will depend on the area of the country. Primary PM2.5 emissions may be important in urban 

areas or areas heavily influenced by local sources such as residential wood combustion or industrial 

facilities. In the East, SO2 emissions may be of primary importance. For PM2.5 planning, NOX, VOC, and 

NH3 will vary in importance depending on the particular situation, which needs to be assessed as part of 

the SIP planning process.

Emissions data developers should consider the proximity of the emissions and the expectation of longrange transport when reviewing projection assumptions. Those emissions that have an impact on the 

nonattainment status (whether transported from outside areas or locally generated) should be given 

highest priority in evaluating the projection assumptions. For example, less priority can be given to 

emissions from distant states and/or for pollutants that do not transport from those states to the NAA.

In some cases, there are sectors that are very difficult or highly uncertain to project into the future. 

Wildfire emissions is a common example of such a sector, since models are not readily available that 

estimate the magnitude and location of future-year emissions. In these cases, it is reasonable to create 
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an “average year” inventory and temporal distribution of the emissions. Other approaches to futureyear fire emissions include holding the emissions constant at the same levels as included in the base 

year.

5.3 Collect Available Data and Models for Each Sector Needing Projections

For each sector needing projections (and in particular for the priority sectors), air agency staff should 

collect and review growth and control information. The sources of such information depend upon the 

sector of interest. Some data resources and approaches are available and provided here, and new data 

and approaches will become available subsequent to the publication of this document. The information 

provided here is a snapshot of information that will grow and adapt over time, and emissions modelers 

should seek out such new information as part of this step.

Emissions modelers can rely on available default data for sectors and regions with lower priority for 

consideration (as described in the previous section). For sectors and regions that are important to 

modeling the NAA, emissions modelers should spend additional effort obtaining improved information 

from other modeling applications (such as modeling done by RPOs or other states) or developing the 

improved information themselves.

As mentioned previously, the EPA provides control assumptions with its modeling data used for 

promulgating air quality rules and impact assessments. The EPA approaches typically include the 

impacts of federal rules that have been finalized. Impacts of proposed rules are rarely included, as the 

changes in emissions impacts can be very large between the proposed and final rules. These data are 

posted at the Emissions Modeling Clearinghouse at http://www.epa.gov/ttn/chief/emch . Sometimes, 

more current information is available than is available from the EPA, for example, when reconsideration 

amendments are developed and finalized after the EPA has publicly released its projected inventories. In 

the subsequent subsections, we focus on sources of growth information.

5.3.1 Stationary Sources

Section 2 of the EIIP projections document gives details about projection of point-source emissions, 

though a great deal has changed since 1999. One thing that has stayed the same is that there are two 

major subsets of point sources: EGUs and non-EGUs. 

The EPA uses the IPM to model future electricity demand and emissions trading programs that now 

dominate the prediction of future-year emissions from EGUs. According to the IPM users document:

“IPM is a multi-regional, dynamic, deterministic linear programming model of the U.S. 

electric power sector. It provides forecasts of least cost capacity expansion, electricity 

dispatch, and emission control strategies while meeting energy demand and environmental, 

transmission, dispatch, and reliability constraints. IPM can be used to evaluate the cost and 

emissions impacts of proposed policies to limit emissions of SO2, NOX, carbon dioxide (CO2), 

mercury (Hg), and HCl from the electric power sector.”
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More information on IPM is available at (http://www.epa.gov/airmarkt/progsregs/epa-ipm/index.html). 

Additionally, IPM-based emissions are posted by CAMD on the EPA’s website 

(http://ampd.epa.gov/ampd/). 

Other EGU projection models exist and could be used for estimation of future-year emissions. A recently 

developed approach by the ERTAC benefits from an in-depth collaboration among a large multi-state 

region. Other examples include the National Energy Modeling System (NEMS), the Electric Power 

Market Model (EPMM) and the Market Allocation (MARKAL) model. There is also a Northeast-specific 

version of MARKAL called NE-MARKAL.

The NEMS model (available at: http://www.eia.gov/oiaf/aeo/overview/) was developed by EIA and uses 

Annual Energy Outlook (AEO) projections of energy supply, demand and prices, and it couples with 

regulatory/SIP and trading assumptions and known future control installations to create future year 

NOX, SO2 and heat input estimates. The EPMM is a private sector EGU model, but some discussion can 

be found in these reports: http://www.ladco.org/reports/rpo/emissions/

eug_growth_methodologies_methods_final_report_pechan.pdf and 

http://www.publicpower.org/files/PDFs/EPRItoEPA.pdf. The MARKAL model is a data-driven energy 

system optimization model geared more towards basic, preliminary analyses of energy policies at EGUs 

but does not provide plant-specific detail like IPM. MARKAL is relevant for other sectors and more 

information is included in Section 5.3.5.

To prevent double-counting of emissions sources, emissions developers should be careful to match the 

sources of emissions from external models such as IPM with the base year emissions sources. This helps 

to ensure that the EGU part of the point source inventory is separated from the non-EGU part based on 

the facilities included in the future-year EGU model. In the case of IPM, the facilities are defined using 

NEEDS. The NEEDS records should be compared to the base year point inventory using the ORIS Plant ID 

field from both. In some cases (e.g., co-generation facilities), only some of the units at the facilities are 

included in NEEDS; therefore, the separation of EGUs from non-EGUs should be done at the unit level, 

not by facility. One resource for this information is also in the NEI, which contains a field that indicates 

whether the units are NEEDS units or not.

Additional considerations for projecting point source EGU emissions without the IPM model are also 

provided in the EIIP projection document. However, several of the references in that document are now 

out of date, as follows.

 The latest SCC codes are available as described in Section 2.5.14.

 The AP-42 emission factor website is now http://www.epa.gov/ttn/chief/ap42/index.html.

 The website with further information about point source inventories is 

http://www.epa.gov/ttn/chief/eiip/techreport/. This guidance includes more updated 

information than the EIIP report.

 The reference in the Table 2.1-1 web link is no longer applicable. Instead, the following 

information can be used to help provide similar information:

o Energy consumption by industry report, 2002:

http://www.eia.doe.gov/oiaf/analysispaper/industry/consumption.html
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o Annual Energy outlook report, early release 2014: 

http://www.eia.gov/forecasts/aeo/er/index.cfm

The references in Table 2.1-2 are also out of date and should be updated as follows:

 U.S. EPA Emissions trends reports. These reports can be used to provide the historical trends of 

emissions sectors based on the NEI: http://www.epa.gov/air/airtrends/

 Integrated Planning Model: http://www.epa.gov/airmarkt/progsregs/epa-ipm/index.html

 Multiple Projections System - is no longer in use

 California Emission Forecasting System: http://www.arb.ca.gov/ei/drei/maintain/database.htm

For nonpoint sources, Section 3 of the EIIP projections document provides additional details about 

projecting nonpoint-source. However, several of the references or statements in that document are now 

out of date, as follows.

 The web sites for SCCs, AP-42 emission factors, and more information about area-source 

inventories are out of date. These should be updated to the same sites as were listed in the 

point sources section above. Furthermore, this guidance includes more updated information 

than the EIIP report referenced.

 The ASEM model mentioned in Section 3.2 of the EIIP projection document was not completed 

and is not available.

 The references in Table 3.1-2 are out of date and should be updated as follows:

o U.S. EPA Emissions trends reports. These reports can be used to provide the historical 

trends of emissions sectors based on the National Emissions inventory: 

http://www.epa.gov/air/airtrends/

o Multiple Projections System is no longer in use

o California Emission Forecasting System: 

http://www.arb.ca.gov/ei/drei/maintain/database.htm

Since 2006 (EPA, 2006a), the EPA has been assuming that emissions growth does not track with 

economic growth for many stationary sources (both point and nonpoint). This “no-growth” assumption 

is based on an examination of historical emissions and economic data. Emissions (as of 2005) had 

declined for several years and those reductions could not be directly attributed to specific control

programs despite increasing economic-based growth factors for many metrics over the same time 

period. While the EPA continues to work toward improving the projection approach in its own work, we 

are still using this no-growth assumption for many emissions sectors. Of course, where air agencies have 

better data about the expected growth in emissions or the possibility of sources reaching their permit 

limits, that information should be included in developing more refined emissions projections.

The EPA creates and uses data that quantify assumed base year growth (projections), controls, 

settlement agreements (or consent decrees), and other unit and facility-specific information on nonEGU point and stationary area sources. These are included in the most recent emissions platform 

Technical Support Document (TSD) available at the Emissions Modeling Clearinghouse. The TSDs include

the methodologies and background information for projecting sources such as Portland Cement, oil and 
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gas, industrial/commercial/institutional boilers, residential wood combustion, agricultural sources, fuel 

sulfur rules, corn and cellulosic ethanol and biodiesel plants, and several other categories. 

In addition, the EPA encourages air agencies to consider the latest settlement agreements and consent 

decrees that are updated periodically by the EPA’s Office of Enforcement and Compliance Assurance 

(OECA) at: http://www.epa.gov/enforcement/.

The tools and data sources described in Section 5.3.5 below should also be considered for use for 

projection of point and nonpoint stationary source emissions.

5.3.2 On-Road Mobile Sources

As described in Section 4.8.3, for all states but California, on-road mobile emissions should be estimated 

with the latest EPA on-road mobile model, MOVES, following the EPA’s latest guidance available at 

http://www.epa.gov/otaq/models/moves/index.htm#sip. For California, the latest EPA-approved 

version of EMFAC should be used.

Emissions preparation with MOVES for projected emissions is much like preparation for a base year. 

MOVES includes assumptions about emissions reductions associated with national emissions programs 

including the effects of national vehicle and fuel standards. Some MOVES inputs, such as meteorology, 

should be the same as for the base year inventory. Others, such as VMT and vehicle population should 

be grown/reduced to reflect expected changes in population and activity. MOVES default estimates for 

future VMT and vehicle population are based on national growth rates and should not be used for SIP 

inventory purposes because growth rates vary substantially from county to county.

Because of the change to the using the MOVES model and the newer guidance provided on the OTAQ 

websites, the EIIP projections document is no longer relevant for on-road mobile sources.

5.3.3 Nonroad Mobile Equipment

Section 5 of the EIIP projections document provides details about projecting nonroad mobile sources. 

While some information is still valid, several of the references or statements in that document are now 

out of date, as follows.

 The name “Office of Mobile Sources” has changed to “OTAQ” and it’s primary website is

http://www.epa.gov/otaq/index.htm.

 The EPA’s NONROAD model has been completed and has been used in a variety of ways by the 

EPA, states, and local agencies. The website for the NONROAD model is 

http://www.epa.gov/otaq/nonrdmdl.htm.

 NMIM, a free, desktop application has been developed by the EPA to help configure inputs and 

develop emissions inventories for the nonroad mobile sector. NMIM is available at: 

http://www.epa.gov/otaq/nmim.htm.

 According to a California Air Resources Board website, category-specific inventory models and 

methods have replaced most uses of California’s OFFROAD model. The information on 

California’s nonroad emissions is available at 

http://www.arb.ca.gov/msei/categories.htm#offroad_motor_vehicles. 
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Emissions preparation with NONROAD or NMIM for projected emissions is much like preparation for a 

base year. NONROAD includes assumptions about emissions reductions associated with national 

emissions programs. NONROAD also includes assumptions about national growth in nonroad activity 

and equipment population. Local estimates of future activity and equipment populations should be 

substituted for the national estimates when possible.

5.3.4 Other Nonroad Mobile Sources

Aircraft, locomotives, and CMV sources of emissions do not have a specific model designed for 

projections, and so additional effort is needed for these three inventory components.

For aircraft emissions, FAA data can be used to estimate growth for aircraft emissions. The FAA provides 

summary historical and forecast statistics on passenger demand and aviation activity at U.S. airports. 

The summary level forecasts are based on individual airport projections. The Terminal Area Forecast 

(TAF) includes forecasts for active airports in the National Plan of Integrated Airport Systems (NPIAS). 

The TAF system can be accessed at https://aspm.faa.gov/main/taf.asp. The TAF system allows users to 

create their own forecast scenarios. The TAF database, which contains a query data application, allows 

the public to access and print historical and forecast (up to 2040) aviation activity data by individual 

airport, state or FAA region. Air agencies can use this information to adjust their base year emissions 

based on projected airport activity.

For locomotives and marine vessel emissions, the best source of data on the impact of national rules 

from OTAQ is the websites provided for each of the rules and their associated Federal Register notices. 

As described for the base year emissions in Section 4.8.5, the locomotive marine rule information is 

included at the website http://www.epa.gov/otaq/nonrdmdl.htm#otherref. For CMV sources, Table 21

(from the base year emissions section) provides a good list of individual rules and references. Since each 

rule is different, there is no single guidance that can be made about how these should be incorporated. 

However, the EPA incorporates these data into their modeling platforms, and the most recent projection 

methodologies are documented in the TSDs included with the modeling platforms on the Emissions 

Modeling Clearinghouse at http://www.epa.gov/ttn/chief/emch.

Additionally for C3 vessels, emissions data are available from an Emissions Control Area-International 

Maritime Organization (ECA-IMO) project. These emissions are available at a fine-grid resolution and are 

subject to various engine and fuel standards in the future. Like base year emissions, air agencies should 

consider the state versus federal waters when deciding what parts of the ECA-IMO data to use (see 

Section 4.8.5.2). Growth/control factors have been developed for this C3 CMV inventory, and the EPA is 

using them for future year C3 CMV inventory development. The ECA-IMO rule for C3 CMV can be found 

at http://www.epa.gov/otaq/oceanvessels.htm. New approaches are likely to develop over time, and so 

air agency staff should consult the web pages listed here for the latest available information. The latest 

EPA modeling platform projection methodology for C3 marine emissions is also available in the latest 

emissions modeling platform TSD at the Emissions Modeling Clearinghouse mentioned previously.
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5.3.5 Other Projection Resources

In addition to sector-specific resources, there are other sources of information that projection 

developers can use for more than a single sector as information to help determine the most applicable 

growth rates for the modeling region. These include the Bureau of Labor Statistics “Employment 

Outlook”, Census Bureau data, Trade Organizations and individual facilities, and the Chemical Economics 

Handbook. The following paragraphs provide a brief description and additional references for each of 

the sources of data just listed. 

Sources for EPA nonpoint methods

As described in Section 4.8.2, the EPA develops methods for numerous nonpoint methods. Each of these 

methods depends on some surrogate activity. Many of these activity sources come from U.S. 

Department of Agriculture (USDA), DOE, and Department of Labor databases available online. Appendix 

B provides a list of nonpoint sectors and associated activity reports and websites. These data do not 

include future-year projections, but may include newer information than were used for estimating the 

base year information. As such, these data can help with understanding the possible changes in activity 

(and perhaps emissions) from the date of the underlying base year activity data to the present day. It 

should be noted that emissions for one year (e.g., 2011) may be estimated using activity data from a 

prior year (e.g., 2009) because of timing needed for preparing the data does not match with the timing 

of the release of the underlying data. When emissions are estimated using data earlier than the 

emissions base year, it further strengthens the benefit of newer activity data. Furthermore, these 

datasets often include historical trends, which could be of use in understanding what may happen in the 

future.

REMI

The Regional Economics Model, Inc. (REMI) model provides a private-sector resource to forecast 

industry changes into the future. It includes aspects of four major economic modeling approaches: 

input-output, general equilibrium, econometric, and economic geography. The REMI integrated 

modeling approach builds on the strengths of each of these approaches. It attempts to reflect the idea 

that changes that affect industry sectors that are highly interconnected to the rest of the economy will 

often have a greater economic impact than other industries. Free online webinars are available that 

provide an overview of REMI’s economic impact models including a live demonstration and 

question/answer period. More information is available on the REMI website at 

http://www.remi.com/the-remi-model. 

EMPAX-CGE

Another private-sector tool, the Economic Model for Environmental Policy Analysis- Computable 

General Equilibrium (EMPAX-CGE) is a regional economic model designed to estimate regional 

macroeconomic impacts of environmental regulations on the U.S. economy. EMPAX-CGE is useful for 

evaluating the linkages between various sectors of the economy (i.e., industries, household, trade) that 

result from environmental regulations and their associated compliance costs. More information on the 

EMPAX-CGE economic model is available at: http://www.epa.gov/ttnecas1/EMPAXCGE.htm.
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MARKAL

The MARKAL model is a public sector, data-driven, energy-system optimization model. A user inputs the 

structure of the energy system to be modeled and data to characterize each of the technologies and 

resources included in the model run. MARKAL calculates the least cost set of technologies over time to 

satisfy specific demands, using linear and mixed-integer linear programming techniques. Outputs of the 

model include the technological mix at intervals in the future, energy demand, and estimates of criteria 

and GHG emissions, among others. The U.S. DOE uses MARKAL for its System for the Analysis of Global 

Energy Markets (SAGE) model. SAGE is used to produce EIA’s annual International Energy Outlook.

The EPA has applied MARKAL for technology and emissions evaluations, which required the 

development of the U.S. EPA MARKAL technology database (EPANMD). This technology-rich database 

represents the major sectors in the U.S. energy system, including the commercial, industrial, residential, 

transportation, and electricity generation sectors. The U.S. DOE’s AEO and the NEMS were used to 

construct the energy supply, demand, and technology characterizations. Data for technologies not 

represented in the AEO and NEMS were derived from other widely recognized authoritative sources 

(e.g. Electric Power Research Institute’s Technical Assessment Guide and DOE’s Office of Transportation 

Technology’s Quality Metrics report). More information on the EPA’s use of MARKAL and the EPANMD

can be found at http://www.epa.gov/nrmrl/appcd/climate_change/markal.htm and EPA report number 

NRMRL-RTP-375 (EPA, 2006b).

Control Strategy Tool (CoST)

The purpose of CoST is to estimate the emission reductions and engineering costs associated with 

control strategies applied to point, nonpoint, and mobile sources of air pollutant emissions to support 

the analyses of air pollution policies and regulations. Control strategy results can be exported to CSV 

files or viewed in a graphical table that supports sorting, filtering, and plotting. The results can also be 

merged with the original inventory to create controlled emissions inventories that can be exported to 

files that can be input to the emissions model SMOKE. CoST allows for user-supplied control measures 

data, provides tracking of analyses and outputs, and supports built-in quality assurance. 

The Control Measure dataset focuses on criteria pollutants and their precursors, and it includes primary 

control efficiencies, co-pollutant control efficiencies, and control costs. The data also includes an 

extensive set of mobile source control measures. More information on the Control Measure dataset and 

CoST is available at http://www.epa.gov/ttn/ecas/cost.htm. 

Annual Energy Outlook

The EIA’s AEO forecast data was a primary input for the final version of EGAS. However, with EGAS no 

longer being supported by the EPA, the latest versions of the AEO are the best available source of 

socioeconomic forecast data for many industrial sectors. The latest AEO data are available at: 

http://www.eia.gov/forecasts/aeo/er/index.cfm.
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Census Bureau

The U.S. Census Bureau provides data on total employees, total payroll, number of establishments, and 

value of shipments by NAICS code (2 digit - 6 digit) for specific years. This database is ideal for examining 

changes in the number of establishments between the two latest available years and also for historical 

changes. However, it does not provide data beyond the current year (and sometimes not even that 

recent) so its trend information is limited to these three “snapshots.” Therefore, these data are useful 

primarily to evaluate emissions changes from the base year to the present (or most recently available 

year) and comparing to the data included in the AEO. The census data are available at 

http://www.census.gov/2010census/data/.

Trade Organizations and individual facilities

Trade organizations can also be a helpful resource because they often have projections for future-year 

growth of their industry and may be aware of pending facility closures or new facility construction. This 

resource is most relevant for large industrial sources that usually are included in point source 

inventories. In addition, emissions modelers should consider contacting large sources of emissions in 

their modeling region for their expectations of emissions growth or reduction. In many cases, large 

industries may be willing to provide such information when presented with what will be used if no 

additional information can be provided. Additional information may be found in permit applications for 

future development or controls at individual facilities. Except in the case of permit applications, 

emissions projections developers should be aware of possible conflicts of interest for this source of 

information. For example, industry groups or facilities may have an incentive to under-represent futureyear emissions in hopes of avoiding additional requirements for reducing emissions. However, many 

industrial representations have been valuable stakeholders who are interested in providing accurate 

information.

Chemical Economics Handbook

The Chemical Economics Handbook, produced by SRI Consulting (a part of IHS, Inc.

30), is a series of 

reports on prices, production and consumption of hundreds of chemical industry products and 

commodities. Past and current information on chemical products and commodities is available, and 

projections of future prices, production and consumption are often available. Reports on specific 

industries are also available. Reports at an industry level can often be used to verify the efficacy of 

future industry modeling results. Each report is updated every 3 years. Projections, some up to 5 years 

from the current day, are often prepared using proprietary methods. Reports are available by 

subscription, and can be obtained as hard copy, CD, or at 

http://www.sriconsulting.com/CEH/Public/index.html.

 

30 A number of other industry reports appears to be available from the IHS home page from the “Industries” tab. 

Some of these websites appear to have databases available for a fee, but they have yet not been assessed by EPA 

for applicability to emissions projections.
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5.4 Evaluate and Refine Data for Projections in Inventory Region

For key sectors, emissions projections developers should determine what information will impact the 

projection results the most, and ensure that the data values reflect conditions or expectations of the 

modeling region. The key information is identified based on a combination of base-year emissions data 

and growth and control rates. An iterative process is helpful to complete this step, as follows:

1. Estimate future-year emissions by combining the base-year emissions with the projection 

information (as described in the EIIP document referenced in Section 5.1).

2. Review future-year emissions data to identify large sectors of key pollutants (e.g. NOX, SO2, 

PM2.5, NH3 and VOC). Emissions summaries by state/SCC or state/NAICS for point sources can be 

helpful for this step to consolidate the data to review.

3. For the largest future-year emissions sectors, review the growth and control assumptions, 

compare among all available data sources, and/or collect additional information to refine the 

assumptions. A representative growth rate should be identified from the available data sources 

and all information known about the sources and sectors. Stakeholder review of the data can be 

helpful during this step; for example, an industrial facility with large projected emissions may be 

able to review the data and provide additional information (e.g., expected capacities, fuels or 

controls) for a more informed future-year emissions estimate.

4. Additionally, data developers should also compare the future-year emissions to base-year 

emissions, and if economic-based growth is used, to identify overall growth rates for industrial 

sectors and scrutinize excessively high growth rates, especially when associated with significant 

emissions.

5. Using the new information, repeat step 1 and continue these steps until a satisfactory futureyear projection across the entire inventory has been completed.

Emissions models (e.g., CoST, SMOKE, MOVES, NONROAD/NMIM, etc.) provide the capability to create 

future-year inventories using base year inventories and projection information. Emissions modelers will 

need to convert the projected emissions data into specific formats for input to these models. Prior to 

starting this step, data developers should determine which emissions model will be used to perform the 

calculations and make sure that the type of information needed by the model is being collected.

5.5 QA for Projected Inventories

As mentioned in the previous subsection, final review of the inventories is an iterative process. During 

each iteration, adaptations of the methods described in Section 4.9 can be used for QA of projected 

emissions inventories. The following list gives examples of some of the ways of the methods for base 

year inventories can be adapted for projected emissions inventories.

 The same checks used for finding structure errors for base year emissions should be used for 

ensuring the projected inventories use the correct structures. The EIS checks are less relevant 

since projected emissions are more likely to be in a modeling format (since they are used for 

modeling) than are base year inventories. Even so, data developers should make sure that data 
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structure or formatting problems do not lead to incorrect emissions data being used in planning 

inventories or modeling.

 Like base year inventories, data codes should be compared to lists of valid codes. It is just as 

important to have future-year SCCs be valid as it is for base year SCCs.

 Ranking techniques can be used to identify facilities, units, and processes that have been grown 

to unrealistic values. Ranking sources by emissions values can identify any that rise to the top of 

the list of largest sources without a good reason why. Ranking techniques can also be used for 

projected nonpoint emissions data.

 Inventory comparisons can be made between projected and base year inventories to help make 

sure:

o Location information is consistent between base and future year (needed for modeling 

only).

o Release point parameters are consistent between base and future year. Where controls 

have been added, one may expect that the release point parameters could change, for 

example, with higher stacks or lower exit gas temperatures. (needed primarily for 

modeling).

o Emissions increases and decreases at the facility, unit, and process level are consistent 

with what is expected.

o Emissions increases and decreases at the county and county/SCC levels are consistent 

with what is expected. If certain sectors are being held constant (i.e., no better 

data/approaches are available), then data developers can confirm that these sectors did 

not change emissions.
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6 References

Allen, D. J., Pickering, K. E., Pinder, R. W., Henderson, B. H., Appel, K. W., and Prados, A.: Impact of 

lightning-NO on Eastern United States photochemistry during the summer of 2006 as 

determined using the CMAQ model, Atmos. Chem. Phys. Discuss., 11, 17699-17757, 

doi:10.5194/acpd-11-17699-2011, 2011.

Appel, K. W., Foley, K. M., Bash, J. O., Pinder, R. W., Dennis, R. L., Allen, D. J., and Pickering, K.: A multiresolution assessment of the Community Multiscale Air Quality (CMAQ) Model v4.7 wet 

deposition estimates for 2002–2006, Geosci. Model Dev. Discuss., 3, 2315-2360, 

doi:10.5194/gmdd-3-2315-2010, 2010.

EPA, 2006a. Regulatory Impact Analyses, 2006 National Ambient Air Quality Standards for Particle 

Pollution. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, 

October, 2006. Docket # EPA-HQ-OAR-2001-0017, # EPAHQ-OAR-2006-0834. Appendix D: 

http://www.epa.gov/ttn/ecas/regdata/RIAs/Appendix%20D--Inventory.pdf.

EPA, 2006b. Shay, C. L., S. Yeh, J. Decarolis, D. H. Loughlin, C. L. Gage, And E. Wright. EPA U.S. National 

MARKAL Database: Database Documentation. U.S. Environmental Protection Agency, 

Washington, DC, EPA/600/R-06/057, 2006.

Daniel Q. Tong, George E. Bowker, Shan He, Daewon W. Byun, Rohit Mathur, Dale A. Gillette, 

"Development of a Windblown Dust Module within the Community Multi-scale Air Quality 

(CMAQ) Model: Description and Preliminary Applications in the Continental United States," 

submitted to the Journal of Geophysical Research, June, 2011 
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Appendix A

Emissions Inventory System - Quick Reference

How to Create County and Facility NOx and VOC Summaries for Select Counties

Create a summary of NOX and VOC emissions BY SECTOR and COUNTY for a group of counties

1. Select "Request Reports" from the left hand sidebar on the EIS Gateway.

2. Under the Emissions Summaries heading, select “By Geography.”

3. Select Report Type "County by Sector."

4. Click the Data Set or Selection bar. This brings you to a “filter” that allows you to select an 

inventory on which to run a report. 

To find the 2008 National Emissions Inventory (NEI), type in “gpr” in the search box under the 

Data Set or Selection. Then select (click on it with the mouse) the version of the NEI you want –

for example"2008 V2_0 GPR" is version 2.0 of the 2008 NEI (alternatively, select your agencies’ 

submitted inventory or that for another state). To find the 2011 NEI, type in “2011 NEI” and 

select the “2011 NEI v1 with biogenics” (for example). Other versions and inventories will be 

published over time, so contact the EPA at info.chief@epa.gov to ask for the name of the latest 

inventory released in EIS.

5. Click on the Pollutants bar to access the pollutant filter. Use the search box provided and type in 

“VOC” and select that resulting row for VOC (click on it with the mouse). Repeat this for NOX. 

Typing both filters at the same time will not work.

6. Because we are looking at counties, go directly to the County filter. DO NOT SELECT A STATE 

FIRST from the State filter (this will select all counties in selected states, even if you then select 

specific counties in the county filter). Use the search box in the County filter to find the counties 

of interest either by name or State/County FIPS code. Select the counties of interest by clicking 

on those rows. If no counties are selected, all counties will be returned.

7. Lastly, select your Sectors using the Sectors search box. If no sectors are selected, the report will 

be created with all sectors. The EIS Sectors are explained in more detail in Section of the 2011

NEI Technical Support Document.

8. Click the "Request Download" button at the bottom of the screen. These reports are run by EIS

every 15 minutes and are available under the Report Download section on the left hand sidebar 

of the Gateway. 

Note: Using the “Run Report” button will give you a faster response and display the summary on 

the screen, but may not include all records for your report. A warning is given at the top of the 

screen if the “Run Report” result is incomplete.

Create a summary of NOX and VOC emissions BY FACILITY for a group of counties 

For access to the Emissions Inventory System (EIS), refer to https://eis.epa.gov/eis-system-web.

See also Online EIS training “Reports – May 2012” at http://www.epa.gov/ttn/chief/eidocs/training.html
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1. Select "Request Reports" from the left hand sidebar on the EIS Gateway.

2. Under the Emissions Summaries heading, select “By Facility.”

3. Select Report Type “Facility”. For more detailed (sub-facility) data, you may select “Emissions 

Unit” or “Emissions Process.”

4. Follow Step 4 in the list above.

5. Follow Step 5 in the list above.

6. Follow Step 6 in the list above.

7. Lastly, you may refine your search even more using the optional filters of Facility Types, NAICS,

or Source Classifications. If you do not use these filters, all facilities for the selected counties 

that include NOX and VOC emissions will be returned in the report.

8. Follow Step 8 in the list above.
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Appendix B

EPA Nonpoint Methods and Associated Activity Data and 

Websites
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Category Data Type

Last 

Release 

Date

Data Lag 

(years) Report Source Link

Agriculture Production - Livestock Livestock 

Population Feb 2009 2 Census of Agriculture USDA http://www.agcensus.usda.gov/

Agriculture Production - Livestock Livestock 

Population

Continuous 

Updates USDA NASS Quick Stats USDA http://www.nass.usda.gov/Data_and_Statistics/Quick_Stats/

Asphalt Paving - Cutback Cutback 

Asphalt Use

2008 Asphalt Usage Survey for the 

United States and Canada Asphalt Institute http://www.asphaltinstitute.org/

Asphalt Paving - Cutback VMT 2011 2 Highway Statistics 2009 FHWA http://www.fhwa.dot.gov/policyinformation/statistics/2009/

Asphalt Paving - Emulsified Emulsified 

Asphalt Use

2008 Asphalt Usage Survey for the 

United States and Canada Asphalt Institute http://www.asphaltinstitute.org/

Asphalt Paving - Emulsified VMT 2011 2 Highway Statistics 2009 FHWA http://www.fhwa.dot.gov/policyinformation/statistics/2009/

Aviation Gasoline Distribution -

Stage 1

AvGas 

Consumption July 2010 1.5 Petroleum Supply Annual EIA http://www.eia.gov/oil_gas/petroleum/data_publications/petroleum_supply_annual/psa_volume1/psa_volume1.html

Aviation Gasoline Distribution -

Stage 2

AvGas 

Consumption July 2010 1.5 Petroleum Supply Annual EIA http://www.eia.gov/oil_gas/petroleum/data_publications/petroleum_supply_annual/psa_volume1/psa_volume1.html

Commercial Cooking Population March 2011 1.5 Population Estimates Program 

GCT-T1: Population Estimates

U.S. Census 

Bureau http://www.census.gov/popest/eval-estimates/eval-est2010.html

Construction Dust -

NonResidential Construction

Value of 

Construction 2011 1

Annual Value of Construction Put in 

Place

U.S. Census 

Bureau http://www.census.gov/construction/c30/c30index.html

Construction Dust -

NonResidential Construction

Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Construction Dust -

NonResidential Construction

Construction 

Costs Producer Price Index U.S. Dept. of Labor http://www.bls.gov/ppi/#tables

Construction Dust - Residential 

Construction Housing Units May 2011 1.5 Annual Housing Units Authorized by Building Permits CO2010A

U.S. Census 

Bureau http://www.census.gov/const/www/permitsindex.html

Construction Dust - Residential 

Construction Housing Starts June 2011 New Privately Owned Housing Units Started for 2011

U.S. Census 

Bureau http://www.census.gov/const/startsua.pdf

Construction Dust - Residential 

Construction

Ratio for 5 or 

more units

Table 2au. New Privately Owned 

Housing Units Authorized 

Unadjusted Units for Regions, 

Divisions, and States 2009

U.S. Census 

Bureau http://www.census.gov/const/C40/Table2/tb2u2009.txt

Construction Dust - Residential 

Construction

Types of 

Foundation 2011 1

Type of Foundation in New OneFamily Houses CompletedU.S. Census 

Bureau http://www.census.gov/const/C25Ann/sftotalfoundation.pdf

Construction Dust - Road 

Construction VMT 2011 2 Highway Statistics 2009 FHWA http://www.fhwa.dot.gov/policyinformation/statistics/2011/
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Category Data Type

Last 

Release 

Date

Data Lag 

(years) Report Source Link

Construction Dust - Road 

Construction Housing Starts June 2011 New Privately Owned Housing Units Started for 2011

U.S. Census 

Bureau http://www.census.gov/const/startsua.pdf

Fertilizer Application Commercial 

Fertilizer Usage Commercial Fertilizers

Association of 

American Plant 

Food Control 

Officials

http://www.aapfco.org/aapfcopubs.html

Fuel Combustion - Commercial Fuel Sales 2011 2 Fuel Oil and Kerosene Sales EIA http://www.eia.gov/dnav/pet/pet_cons_821use_dcu_nus_a.htm

Fuel Combustion - Commercial Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Fuel Combustion - Commercial Gov't Payrolls Census of Governments U.S. Census 

Bureau http://www.census.gov/govs/

Fuel Combustion - Commercial Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Fuel Combustion - Industrial Fuel Sales 2011 2 Fuel Oil and Kerosene Sales EIA http://www.eia.gov/dnav/pet/pet_cons_821use_dcu_nus_a.htm

Fuel Combustion - Industrial Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Fuel Combustion - Industrial Energy 

Consumption June 2009 3.5 2006 Manufacturing Energy Consumption Survey EIA http://www.eia.gov/emeu/mecs/mecs2006/2006tables.html

Fuel Combustion - Industrial Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Gasoline Distribution - PFCs

Gasoline Distribution - Stage 1 Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Gasoline Distribution - Stage 1

Fuel 

Consumption July 2010 1.5 Petroleum Supply Annual EIA http://www.eia.gov/oil_gas/petroleum/data_publications/petroleum_supply_annual/psa_volume1/psa_volume1.html

Gasoline Distribution - Stage 2

Industrial Fuel Combustion Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Industrial Fuel Combustion Fuel Sales 2011 2 Fuel Oil and Kerosene Sales EIA http://www.eia.gov/dnav/pet/pet_cons_821use_dcu_nus_a.htm

Industrial Fuel Combustion Energy 

Consumption June 2009 3.5 2006 Manufacturing Energy Consumption Survey EIA http://www.eia.gov/emeu/mecs/mecs2006/2006tables.html

Industrial Fuel Combustion Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Open Burning - Household Waste Solid Waste 

Generation 2011 2

Municipal Solid Waste in the United 

States: 2009 Facts and Figures EPA http://www.epa.gov/epawaste/nonhaz/municipal/msw99.htm
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Category Data Type

Last 

Release 

Date

Data Lag 

(years) Report Source Link

Open Burning - Household Waste Population March 2011 1.5 Population Estimates Program 

GCT-T1: Population Estimates

U.S. Census 

Bureau http://www.census.gov/popest/eval-estimates/eval-est2010.html

Open Burning - Land Clearing Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Open Burning - Land Clearing Housing Units May 2011 1.5 Annual Housing Units Authorized by 

Building Permits CO2010A

U.S. Census 

Bureau http://www.census.gov/const/www/permitsindex.html

Open Burning - Land Clearing Value of 

Construction 2011 0

Annual Value of Construction Put in 

Place

U.S. Census 

Bureau http://www.census.gov/const/www/totpage.html

Open Burning - Land Clearing Housing Starts June 2011 0

New Privately Owned Housing Units 

Started for 2011

U.S. Census 

Bureau http://www.census.gov/const/startsua.pdf

Open Burning - Land Clearing Ratio for 5 or 

more units

Table 2au. New Privately Owned 

Housing Units Authorized 

Unadjusted Units for Regions, 

Divisions, and States 2009

U.S. Census 

Bureau http://www.census.gov/const/C40/Table2/tb2u2009.txt

Open Burning - Leaves and Brush Solid Waste 

Generation 2011 2

Municipal Solid Waste in the United 

States: 2009 Facts and Figures EPA http://www.epa.gov/epawaste/nonhaz/municipal/msw99.htm

Open Burning - Leaves and Brush Population March 2011 1.5 Population Estimates Program 

GCT-T1: Population Estimates

U.S. Census 

Bureau http://www.census.gov/popest/data/index.html

Paved Road Dust VMT 2011 2 Highway Statistics 2009 FHWA http://www.fhwa.dot.gov/policyinformation/statistics/2009/

Publicly Owned Treatment Works Wastewater 

Flow Sept 1999

Wastewater Flow Projections for 

POTWs and Privately and Federally 

Owned Treatment Works in 2000, 

2005, and 2010

EPA http://yosemite.epa.gov/ee/epa/ria.nsf/vwAN/S99-21.pdf/$file/S99-

21.pdf

Publicly Owned Treatment Works Wastewater 

Flow Ask WATERS Database EPA http://iaspub.epa.gov/waters10/query_tool.criteria?srept_no=165&branding=15

Residential Coal Coal 

Distribution Feb 2011 3 Annual Coal Distribution EIA http://www.eia.gov/cneaf/coal/page/coaldistrib/a_distributions.html

Residential Coal Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Residential Coal House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,

Residential Distillate Fuel Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Residential Distillate Fuel House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,
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Category Data Type

Last 

Release 

Date

Data Lag 

(years) Report Source Link

Residential Kerosene Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Residential Kerosene House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,

Residential LPG Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Residential LPG House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,

Residential Natural Gas Fuel 

Consumption 2011 2 State Energy Data System (SEDS) EIA http://www.eia.doe.gov/emeu/states/_seds.html

Residential Natural Gas House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,

Residential Wood Timber Output 2011 2 Timber Products Output Survey USDA http://srsfia2.fs.fed.us/php/tpo_2009/tpo_rpa_int1.php

Residential Wood House Heating 

Fuel Type Data Set - SF 3 - Table H40 U.S. Census Bureau

http://factfinder.census.gov/servlet/DatasetMainPageServlet?_prog

ram=DEC&_submenuId=&_lang=en&_ts=,

Residential Wood Equipment 

Type

American Housing Survey for the 

United States: 2009, Table 2-4: 

Selected Equipment and Plumbing

U.S. Census 

Bureau http://www.census.gov/hhes/www/housing/ahs/ahs09/ahs09.html

Residential Wood Metropolitan 

Characteristics 2011 2

American Housing Survey 

Metropolitan Data

U.S. Census 

Bureau

http://www.census.gov/hhes/www/housing/ahs/metropolitandata.ht

ml

Solvent Usage - Other Population March 2011 1.5 Population Estimates Program 

GCT-T1: Population Estimates

U.S. Census 

Bureau http://www.census.gov/popest/eval-estimates/eval-est2010.html

Solvent Usage - Other Business 

Patterns 2011 2 County Business Patterns U.S. CensusBureau http://www.census.gov/econ/cbp/index.html

Solvent Usage - Surface Coatings Population March 2011 1.5 Population Estimates Program 

GCT-T1: Population Estimates

U.S. Census 

Bureau http://www.census.gov/popest/eval-estimates/eval-est2010.html

Solvent Usage - Surface Coatings Business 

Patterns 2011 2 County Business Patterns U.S. Census Bureau http://www.census.gov/econ/cbp/index.html

Unpaved Road Dust VMT 2011 2 Highway Statistics 2009 FHWA http://www.fhwa.dot.gov/policyinformation/statistics/2009/
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