OFFICE OF INSPECTOR GENERAL 


Catalyst for Improving the Environment 

Evaluation Report 

EPA Can Improve Emissions 

Factors Development and 

Management

 Report No. 2006-P-00017 

 March 22, 2006 
Report Contributors: Patrick Milligan 

 Frank Martinsky 

 Kevin Good 

Bill Nelson 

Abbreviations 

CAFO Concentrated Animal Feeding Operation 

CO Carbon Monoxide 

EFPAG Emissions Factors and Policy Applications Group (within EPA) 

EPA Environmental Protection Agency 

FIRE Factor Information Retrieval 

FMFIA Federal Managers’ Financial Integrity Act 

GAO Government Accountability Office 

kg kilograms 

MACT Maximum Achievable Control Technology 

NEI National Emissions Inventory 

PEI Probabilistic Emissions Inventory 

NOX Nitrogen Oxides 

OAQPS Office of Air Quality Planning and Standards 

OIG Office of Inspector General 

PM2.5 Fine Particulate Matter 

VOC Volatile Organic Compound 
U.S. Environmental Protection Agency 2006-P-00017 


Office of Inspector General March 22, 2006


At a Glance


Catalyst for Improving the Environment 

Why We Did This Review 

We sought to determine 

whether the air emissions 

factors used by the 

Environmental Protection 

Agency (EPA) are of 

acceptable quality for making 

key environmental decisions, 

and whether EPA’s process 

for developing, improving, 

and rating emissions factors 

is sufficient to meet users’ 

needs. 

Background 

Emissions factors are broad 

estimates of the emissions 

generated from a source, such 

as a factory. Nationally, 

emissions factors are used for 

about 80 percent of emissions 

reporting. An emissions 

factor is a representative 

value that attempts to relate 

the quantity of a pollutant 

released with an activity rate 

associated with the release. 

Emissions factors underlie 

many environmental 

decisions. Recently, States 

and industry have been 

developing emissions factors 

and submitting them to EPA. 

For further information, 

contact our Office of 

Congressional and Public 

Liaison at (202) 566-2391. 

To view the full report, 

click on the following link: 

www.epa.gov/oig/reports/2006 

/20060322-2006-P-00017.pdf 

EPA Can Improve Emissions Factors 

Development and Management

 What We Found 

EPA has made progress in emissions factors development since our review of the 

program in 1996, but a large number of factors continue to be rated low. The 

number of EPA-rated factors increased by nearly 94 percent, from 8,838 in 1996 to 

17,110 in 2004. However, the percentage of emissions factors rated below average 

or poor increased from 56 percent in 1996 to 62 percent in 2004. 

Emissions factors, intended for use in developing emissions inventories, have been 

inappropriately used for key environmental decisions beyond their intended use. 

For example, emissions factors have been used for non-inventory purposes, such as 

setting permit limits and reporting the level of air pollution control at specific 

facilities. For three industry sectors EPA examined, inappropriate use of emissions 

factors contributed to more than one million tons of pollutants not being controlled. 

Demand for emissions factors is increasing, and will continue for a broad array of 

environmental decisions, including measuring and reporting environmental 

progress. This pertains not only to existing factors but to those that still need to be 

developed, especially emissions factors for sources of fine particulate matter. If 

EPA can improve the quality of its factors, this should improve environmental 

decision-making for reducing air pollution. Improving the quality of emissions 

factors is an extremely challenging task that may take EPA years to address. 

The quality of many emissions factors remains low in part because EPA did not 

have a sufficient process for developing, improving, and rating emissions factors, 

nor did EPA have a comprehensive strategic plan. We found inconsistent 

emissions factors guidance, continuing reliance on a qualitative rating system when 

a quantitative range of uncertainty is needed, and insufficient program funding 

when needs are increasing. 

What We Recommend 

We are making a number of recommendations to EPA to, among other things, 

develop emissions factors guidance that addresses the development and appropriate 

use of emissions factors for non-inventory purposes; establish a rating system that 

provides the quantitative range of uncertainty for emissions factors for both 

inventory and non-inventory purposes; work with industry, State and local agencies, 

and others to leverage available resources for meeting increasing demands for new 

factors; and establish a workgroup to develop a comprehensive strategic plan for the 

Emissions Factors Program, and ensure that requested resources are used to achieve 

program goals. In response to the draft report, the Agency stated that our 

recommendations generally align with its current improvement efforts. 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF 

INSPECTOR GENERAL 

March 22, 2006 

MEMORANDUM 

SUBJECT: 	 EPA Can Improve Emissions Factors Development and Management 

 Report No. 2006-P-00017 

FROM: 	 J. Rick Beusse /s/ 

Director for Program Evaluation, Air Issues 

TO: 	 William L. Wehrum 

Acting Assistant Administrator for Air and Radiation 

This memorandum transmits the results of an Office of Inspector General (OIG) evaluation of 

emissions factors development and management. This report contains findings that describe how 

the U.S. Environmental Protection Agency (EPA) can improve emissions factors development 

and management, as well as corrective actions the OIG recommends. This report represents the 

opinion of the OIG and the findings contained in this report do not necessarily represent the final 

EPA position. Final determinations on matters in the report will be made by EPA managers in 

accordance with established procedures. 

Action Required 

In accordance with EPA Manual 2750, as the action official, you are required to provide a 

written response within 90 days of the final report date. The response should address all 

recommendations. For the corrective actions planned but not completed by the response date, 

please describe the actions that are ongoing and provide a timetable for completion. Where you 

disagree with a recommendation, please provide alternative actions for addressing the findings 

reported. 

We appreciate the efforts of EPA officials and staff in working with us to develop this report. If 

you or your staff have any questions regarding this report, please contact me at 919-541-5747 

or Pat Milligan at 215-814-2326. 
Table of Contents 


At a Glance 

Chapters 

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


Purpose .......................................................................................................... 1

Background .................................................................................................... 1

Scope and Methodology................................................................................. 6 


2 	 Use of Unreliable Emissions Factors Adversely Impacts


 Key Environmental Decisions ............................................................................. 8 


EPA Rated More Factors But Quality of Many Factors Remains Low ........... 8 


Misuse of Emissions Factors Resulted in Significant Unidentified and 


 Uncontrolled Emissions........................................................................ 10 


Increasing Demand for New Emissions Factors Illustrates Continued 


 Importance of Emissions Factors Program .......................................... 13 


Conclusion...................................................................................................... 14

3 	 EPA’s Management of Emissions Factors Program Needs Improvement ...... 15

Conflicting Guidance Issued for Emissions Factors ....................................... 15 


Rating System Does Not Define Appropriate Uses........................................ 17 


Inadequate Funding Provided and Used........................................................ 19 


Recent EPA Efforts Made to Revamp Emissions Factors Program............... 21 


Comprehensive Plan Needed to Improve Data Collection and 


Set Priorities ......................................................................................... 22 


Conclusions.................................................................................................... 24

 Recommendations ......................................................................................... 25

Agency Comments and OIG Evaluation......................................................... 26 


Appendices 

A Details on Scope and Methodology..................................................................... 28 


B Details on Concentrated Animal Feeding Operations Air Emissions .............. 31 


C Agency Response to Draft Report....................................................................... 32 


D OIG Evaluation of Agency Response.................................................................. 35 


E Distribution ........................................................................................................... 37

Chapter 1 

Introduction 

Purpose 

Quantifying air emissions is a vital aspect of air pollution programs. 

Regulatory authorities and others use emissions values in: (1) developing 

emissions inventories, (2) identifying and evaluating control strategies, 

(3) determining applicability of permit and regulatory requirements, and 

(4) assessing risks. Emissions factors are broad estimates of the emissions 

generated from a source, such as a factory. These factors are the most 

commonly used estimate for establishing emission values, and are used 

nationally for about 80 percent of emissions reporting. 

The Environmental Protection Agency (EPA) has long recognized the 

importance of emissions factors, particularly for developing emissions 

inventories. Over the last 10 years, permitting authorities, source owners 

and operators, and a few Agency programs have begun using emissions 

factors for purposes other than generating a national emissions inventory. 

For example, emissions factors have been used to develop emissions 

control strategies, determine applicability of permitting and regulatory 

requirements, establish permit limits, ascertain the effects of sources, and 

develop emissions reduction strategies. Therefore, the impact of the 

quality of the factors is far greater than it would be if they were used only 

for the inventory. Because emissions factors underlie so many 

environmental decisions, the objectives of our evaluation were to 

determine whether: 

x	 Emissions factors are of an acceptable quality for use in key 

environmental decisions made by EPA and State and local 

agencies; and 

x	 The Agency’s process for developing, improving, and rating 

emissions factors is sufficient to meet key users’ needs. 

Background 

In the 1960’s and early 1970’s, emissions estimation methods came about 

due to the need to estimate air pollution emissions. EPA first developed 

emissions factors from source test data used to develop new emissions 

standards in the 1970’s. At that time, factors were mostly used to develop 

emissions inventories. In the 1980’s and 1990’s, EPA expenditures on 

source testing declined, yet during the same time period the demand for 

emissions data expanded as emissions factors were increasingly used for 

1

non-inventory decisions. As noted in our prior report, EPA’s emissions 

factor program resources were surpassed by the need for more and 

improved emissions data.1 Recently, EPA reorganized the Agency’s 

emissions factors program in an effort to address this challenge. 

What Are the Ways of Obtaining Air Emissions Information? 

Generally, air emissions information can be obtained through direct 

measures of emissions or by estimating emissions. Under ideal 

circumstances, all emissions data users would derive values from ongoing 

emissions testing, continuous emissions monitoring, or frequent 

calculation using well-accepted engineering principles. However, these 

methods are time and resource intensive. Continuous Emissions 

Monitoring and Source Testing represent ways to directly measure 

emissions, while the others involve estimating. The five basic means of 

obtaining emissions information are discussed below. 

x Continuous Emissions Monitoring: This involves continuously 

measuring pollutants emitted into the atmosphere from a single 

source, such as a smokestack, by placing a monitor at the source. 

This is one of the most reliable methods for measuring emissions, 

but has annual costs ranging from about $10,000 to $50,000 and is 

only required at the largest sources of air pollution. 

x Source Testing: Like Continuous Emissions Monitoring, source 

testing data are generated by placing a monitor at a source, but in 

this case only measures for a limited number of hours. The facility 

uses the monitoring data to calculate an annual emissions total. 

This is also generally more reliable than emissions factors but has 

annual costs of $20,000 for conducting a test every 5 years. While 

some facilities are required to periodically conduct source tests, 

many are not. 

x Material Balance: For some sources with Volatile Organic 

Compound (VOC) emissions, material balance (also known as 

mass balance) assumes that a percentage of the materials used in a 

process will evaporate to become air emissions. Therefore, the 

amount of emissions resulting from evaporation is based on the 

amount of evaporative material used. Recordkeeping to calculate 

material balance costs about $2,000 to $10,000 per year, per 

process. 

x Emissions Calculating Tools: These estimating methods 

represent a more advanced and complicated use of emissions 

 Emission Factor Development, EPA Office of Inspector General (OIG) Report No. 6100306, September 

30, 1996. 

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1
factors and other data, and include models, databases, and other 

pollutant estimating software. 

x Emissions Factors: An emissions factor relates the emissions 

amount of a pollutant with an activity rate associated with its 

release. Emissions factors are essentially averages of available 

data from various sources, such as source tests. The cost for using 

an emissions factor depends on the time to locate the appropriate 

factor. The ability to rapidly locate emissions factors makes this 

one of the least expensive methods for estimating emissions. The 

general equation for emissions estimates is: 

Activity Rate x Emissions Factor = Emissions 

The following example illustrates one way that an emissions factor 

is used. Burning distillate oil in industrial boilers produces carbon 

monoxide (CO) and other emissions. The CO emissions factor for 

this process is 0.6 kilograms (kg) of CO emitted per 1,000 liters of 

oil burned. Assuming the boiler burns 90,000 liters of oil per day, 

the following calculation shows the estimated amount of CO 

emitted per day: 

90,000 liters per day x 0.6 kg CO/1,000 liters = 54 kg of CO/day 

In the absence of direct measures, emissions factors are frequently 

used as a quick, low cost way to estimate emissions. 

How Are Emissions Factors Developed? 

EPA’s Emissions Factors and Policy Applications Group (EFPAG) 

oversees the Emissions Factors Program. EFPAG is part of the Office of 

Air Quality Planning and Standards (OAQPS) within EPA’s Office of Air 

and Radiation. EPA issues the guidance for developing the factors, and 

initially was responsible for developing many of the factors. However, 

industry and States increasingly have been developing emissions factors 

and submitting them to EPA for inclusion in AP-42.2 

EPA guidance states that the following five steps are to be carried out to 

develop emissions factors: 

1.	 Data Collection - For a particular industry sector, EPA collects 

information related to facility process descriptions and source 

emissions test data, if known to exist and available. Sources of 

this information include existing data in EPA databases and 

The Compilation of Air Pollutant Emission Factors, commonly referred to as the “AP-42 series” of 

emissions factors, is the primary guidance and source of rated emissions factors used by EPA. 

3


2
external requests to Federal, State, and local agencies and industry 

trade organizations. 

2.	 Data Evaluation - The data are evaluated to determine which data 

should be used to develop the emissions factor. The data selected 

are known as “test data” and are given test quality ratings. 

3.	 Data Classification - The data are then grouped into clusters of 

similar processes, which will eventually be averaged into an 

emissions factor. 

4.	 Data Calculation - EPA averages the groups and develops a 

numerical emissions factor. The factor is given an overall 

qualitative rating of “A” (excellent) through “E” (poor) based on 

the ratings assigned to the test data and production quality. 

5.	 Published Emissions Factor - The group of processes represented 

by the emissions factor is assigned an existing or new source 

classification code, and the emissions factor is published in 

AP-42. 

How Are Emissions Factors Used? 

Emissions factors are used to develop the emissions data that are the 

cornerstone of a host of important environmental decisions made by EPA; 

State, local, and Tribal agencies; industries; environmental groups; and 

others. These decisions include facility permitting, development of 

control strategies, and compliance and enforcement decisions. According 

to a 2001 Government Accountability Office (GAO) report,3 EPA’s data 

show that, nationally, emissions factors are used for about 80 percent of 

emissions determinations. Emissions factors data are also used to measure 

environmental progress and demonstrate program results under the 

Government Performance and Results Act of 1993.4 Table 1.1 provides 

some of the key uses of emissions factors. 

3 April 2001 GAO Report, EPA Should Improve Oversight of Emissions Reporting by Large Facilities 

(GAO-01-46) 4

 The Government Performance and Results Act holds Federal agencies accountable for measuring program 

outcomes and reporting results annually to Congress and the public. 

4

Table 1.1: Key Uses of Emissions Factors 

Emissions Factors 

Uses Description 

Determining Source 

Classification 

EPA classifies a facility to be a minor or major source by 

determining the facility’s potential to emit; this impacts the level 

of air pollution control equipment needed. 

Establishing and 

Enforcing Permit Limits 

Based on emissions measures or estimates, EPA and States set 

emissions limits via operating permits. 

Permit Fees Using the emissions estimates, States calculate annual fees a 

facility must pay for the emissions released. 

Issuing Maximum 

Achievable Control 

Technology Standards 

EPA writes standards requiring major sources of hazardous air 

pollutants to install the best control technology available for an 

industry sector. 

Plant-wide Applicability 

Limit and Emissions 

Trading 

Both of these regulatory approaches measure emissions from a 

more holistic viewpoint. For plant-wide applicability limits, some 

point sources that increase in emissions are offset by 

corresponding decreases from other point sources at the same 

facility. This same type of offsetting method is used when 

facilities trade emissions credits to other facilities emitting over 

the limit. 

Measuring 

Environmental 

Progress 

The amount of emissions reduced remains a key measure of 

environmental progress. One of the most important databases 

for tracking the amount or emissions reduced is EPA’s National 

Emissions Inventory (NEI). 

Emissions factors play a pivotal role in many decisions, especially in 

measuring environmental progress. For example, every 3 years, EPA 

prepares a national database of air emissions information – the NEI – 

based on emissions factors and other input from States, industry, and other 

stakeholders. This inventory depends heavily on emissions factors for 

stationary sources (such as factories) and mobile sources (such as trucks 

and automobiles). The NEI database contains information on sources that 

emit criteria air pollutants (six common air pollutants that harm human 

health and the environment for which specific standards are set), as well as 

hazardous air pollutants, also known as air toxics. Key uses of the 

inventory include: 

x Conducting air dispersion modeling and analysis; 

x Developing control strategies to reduce pollution levels; 

x Issuing air regulations; 

x Performing risk assessments; 

x Screening sources for compliance investigations; 

x Tracking short- and long-term trends in emissions; and 

x Measuring program results in EPA’s annual performance plan. 

When an area of the country does not meet the National Ambient Air 

Quality Standards, EPA and the States gather information about the 

5

emissions rates of various sources in that area (often derived from 

emissions factors) to target important sources for control. Through its 

annual Trends Report, EPA uses the emissions inventory data to gauge 

progress in meeting its goals of reducing air pollution. Emissions factors 

play a key role in assessing such annual progress. 

How Are Emissions Factors Maintained and Accessed? 

In the AP-42 series of emissions factors, EPA assigns a qualitative rating 

to the emissions factor based on the quantity and quality of the data used 

to develop the factor. The AP-42 series is EPA’s recommended source of 

air pollutant emissions factors for both criteria and hazardous air pollutant 

emissions, and contains over 17,000 rated emissions factors for more than 

200 air pollution source categories. 

The Factor Information Retrieval (FIRE) Data System is a database 

containing both rated and unrated emissions factors. FIRE contains all 

AP-42-rated factors, as well as approximately 4,400 unrated emissions 

factors that EPA recommends for use. FIRE also contains a list of source 

classification codes, and information about industries’ operating systems, 

processes, and chemicals emitted. FIRE incorporates new or revised 

emissions factors from AP-42. 

The Clearinghouse for Inventories and Emissions Factors is EPA’s 

electronic repository of the most up-to-date information on inventories and 

emissions factors, including AP-42 and FIRE. The clearinghouse 

facilitates the exchange of emissions factors and information on emissions 

inventories between Federal, State, and local agencies; industry; private 

citizens; universities; contractors; and foreign governments. The 

clearinghouse also provides historical inventory information and 

emissions estimation guidance. 

Scope and Methodology 

To assess the adequacy of EPA’s Emissions Factors Program, we 

reviewed documentation related to AP-42 emissions factors, including: 

the development and prioritization of emissions factors, the process used 

for rating emissions factors, key uses of emissions factors, and policies 

and procedures for implementing the Emissions Factors Program. We 

also conducted interviews with officials from EPA at both the 

Headquarters and regional levels; officials from several States and an air 

pollution association, and emissions factors experts. We conducted our 

field work from March 2005 to October 2005, in accordance with 

Government Auditing Standards, issued by the Comptroller General of the 

United States. 

6

As part of our evaluation, we considered the results of a prior EPA OIG 

report, Emission Factor Development (Report No. 6100306), dated 

September 30, 1996. 

Additional details on our scope and methodology are in Appendix A. 

7

Chapter 2 

Use of Unreliable Emissions Factors 

Adversely Impacts Key Environmental Decisions 

EPA has made progress in emissions factors development since our 1996 

review, primarily in the increased number of factors receiving ratings on 

quality. However, the large percentage of low quality factors has not 

diminished. EPA officials have identified the inappropriate use of 

emissions factors for key environmental decisions, such as permit limits 

and the level of air pollution control equipment installed at specific 

facilities, resulting in the release of significant amounts of unidentified 

and uncontrolled emissions. For example, according to EPA enforcement 

records, three industries – petroleum refineries, wood products, and 

ethanol production – operated with insufficient control equipment 

primarily because emissions limits were significantly underestimated due 

to the emissions factors used. EPA, through separate enforcement actions, 

required companies in these industries to install additional emissions 

controls, resulting in the combined reduction of over one million tons of 

pollutants. 

Absent EPA intervention through enforcement actions or stringent 

guidance, industries will have little incentive to ensure that the emissions 

factors used are of known and acceptable quality. This pertains not only 

to existing factors but to ones that still need to be developed, especially 

quality factors for sources of fine Particulate Matter. For example, factors 

will be used by EPA and States to develop fine Particulate Matter control 

strategies. As EPA continues to measure and report progress in reducing 

harmful air pollutants, it needs to improve the quality of emissions factors 

estimates. This will improve environmental decision-making related to air 

pollution and human health. 

EPA Rated More Factors But Quality of Many Factors 

Remains Low 

In our September 1996 OIG report, we noted that emissions factors were 

unavailable for many sources of air pollution and, when available, many 

were unreliable. This was attributed to significant funding cuts that 

materially affected EPA’s ability to meet an increased demand for quality 

emissions factors. Table 2.1 shows that, as of March 1996, EPA rated 

56 percent of the emissions factors as either below average or poor 

(24 percent plus 32 percent, respectively). As of September 2004, that 

number had increased to 62 percent (28 percent plus 34 percent, 

respectively). EPA based its ratings on test methods, quantity of data, and 

8

whether the facilities tested represented a sufficient random sample of the 

industry.

 Table 2.1: Comparison of Emissions Factors Ratings (March 1996 and September 2004) 

Factor 

Rating 

Qualitative 

Description 

As of March 1996 As of September 2004 

Number of 

Factors 

Percent 

of Total 

Number of 

Factors 

Percent 

of Total 

A Excellent 1,270 14% 2,135 12% 

B Above Average 1,190 13% 1,829 11% 

C Average 1,513 17% 2,619 15% 

D Below Average 2,077 24% 4,740 28% 

E Poor 2,788 32% 5,787 34% 

Total 8,838 17,110 

Our 1996 OIG report emphasized the need for EPA to invest more 

resources in the emissions factors program and to develop alternative 

approaches to factor development by increasing industry and State 

involvement. The Agency did increase its emissions factors efforts, as 

evidenced by the increased number of factors it had rated since the 1996 

OIG review. Since March 1996, EPA nearly doubled the number of rated 

emissions factors, from 8,838 to 17,110. As of September 2004, 4,409 

emissions factors, or about 20 percent of the total of 21,519, were still 

listed as unrated. Overall, the number of rated emissions factors has 

increased, which reflects some improvement in the quality of emissions 

factors. For example, emissions factors that previously had a lower rating 

received a higher rating, and some factors previously not rated have been 

rated. 

Additionally, since our 1996 report the Agency has taken the following 

steps to improve the Emissions Factors Program: 

x Surveyed emissions factor users, including States and industries, 

on their emissions factors needs. 

x Initiated the development of an automated database to store test 

data results for future emissions factors development. 

x Worked with an industrial association to develop new emissions 

factors. 

x Began a pilot project to adjust emissions factors for non-inventory 

use. 

An EFPAG pilot project is assessing two industry sectors – hot mix 

asphalt plants, and pulp and paper plants. The goal of the pilot is to 

evaluate the impact of adjusting excellent- and above average-rated 

emissions factors for uncertainty. Emissions factors are used widely for 

hot mix asphalt plants by source owners and regulatory authorities, 

9

particularly in calculating production limits below thresholds that would 

trigger aspects of the air operating permits program. Pulp and paper plants 

generally rely on emissions factors to calculate fugitive hazardous air 

pollutants and VOCs from these plants. In some instances, these 

emissions can account for 60 to 80 percent of a site’s emissions. 

EFPAG’s study found that if emissions factors were adjusted to better 

account for uncertainty, almost all of the 3,600 hot mix asphalt plants in 

the United States likely would have to recalculate production limits. As a 

result, some plants would be unable to retain their synthetic minor source 

status, thus making them subject to the Title V air operating permits 

program and, as a result, potentially subject to stricter regulations and 

State or local air toxics rules. EFPAG also found the use of adjusted 

emissions factors may cause some revisions to State Implementation Plan 

model projections, causing some plants to reduce emissions below current 

levels. 

Misuse of Emissions Factors Resulted in Significant 

Unidentified and Uncontrolled Emissions 

To date, EFPAG’s pilot study has identified the potential emissions impact 

and possible regulatory consequences of using emissions factors to 

estimate emissions. There are several instances where the actual 

emissions impact from misuse of emissions factors has been identified, 

and this impact has been substantial. For example, we examined three 

industries where EPA officials indicated emissions factors were not 

acceptable for the decisions being made – petroleum refineries, wood 

products, and ethanol production. For these three large industries, EPA 

had indicated emissions were significantly underestimated due to the 

emissions factors used. As a result of pollutants not being previously 

identified or controlled, EPA, through separate enforcement actions, had 

required companies to install additional emissions controls, resulting in the 

reduction of over one million tons of pollutants for the three industries 

combined. 

According to EPA enforcement records, for years the three industries 

operated with insufficient control equipment because the emissions limits 

in permits and the annual emissions reported by the individual industry 

facilities significantly understated the actual amount of emissions released 

into the atmosphere. EPA decided to examine the reliability of the 

emissions factors measures for each industry sector and, using new, more 

accurate measures, found actual emissions to be much higher. Table 2.2 

illustrates emissions reductions, civil penalties, and control investments by 

each industry. 

10

Table 2.2: Summary of Air Violations for Three Industries Related to 

Emissions Factors Use 

Industry Companies Sites 

Civil 

Penalties 

(millions) 

Control 

Investment 

(millions) 

Pollutants 

Removed 

(tons) 

Petroleum Refineries 57 57 $45.0 $2,600.0 765,000 

Wood Products 5 * 21 $289.0 * $175.0 177,000 

Ethanol Production 14 91 $6.6 $240.5 116,750 

Total ** 76 169 $340.6 $3,015.5 1,058,750 

* This information available for only three wood products companies. 

 ** These companies represent a portion of the industry, not the entire industry. 

Through consent agreements reached with facilities in these sectors, EPA 

and the States required more stringent permits and installation of 

additional pollution controls to lower emissions. EPA staff indicated the 

problems noted for these three industries regarding poor quality emissions 

factors are occurring in many other industries. For the three industries, 

emissions estimating techniques were improved as a result of EPA 

enforcement actions. However, correcting such problems through 

enforcement actions is both costly and time-consuming. Increased 

scrutiny of the use of emissions factors is needed if expected 

environmental benefits are to be realized. Details on each of the three 

industries follow. 

Petroleum Refineries 

Air quality problems in the Houston-Galveston area demonstrate the 

serious consequences in terms of cost and effectiveness of air pollution 

control strategies related to the petroleum industry. Because EPA 

declared the Houston-Galveston area in severe noncompliance with 

Federal air quality standards for ozone,

5

 the metropolitan area was 

required to develop a control strategy to reduce Nitrogen Oxides (NOX) 

and VOC emissions. Based on modeled ozone predictions using 

emissions inventory data, Texas devised a strategy to reduce ozone 

precursor emissions that called for the reduction of NOX emissions by 

90 percent. 

In August 2000, Texas conducted a comprehensive research project 

assessing source contributions to the State’s air quality problems. Based 

on the comparison of ambient measurements of VOC concentrations to the 

reported emissions inventory estimates, the Texas 2000 Air Quality Study 

found that VOC emissions from petroleum refineries were significantly 

under reported in the emissions inventory. This primarily involved under 

 Ground-level ozone is not emitted directly into the air, but is created by chemical reactions between NOX 

and VOC in the presence of heat and sunlight. 

11


5
reporting of emissions from flares,6

 process vents, and cooling towers, as 

well as from fugitive emissions (leaks). The under-reporting was caused 

largely due to the use of poor quality emissions factors. The quality of 

one emissions factor was so poor that for short durations, actual emissions 

from the flaring process could be as much as 50 times higher than 

emissions calculated using the emissions factor. This was because the 

factor did not account for variables such as the composition of the fuel 

being burned and the efficiency of the flaring equipment. This emissions 

factor was developed in the early 1980’s and had not been updated at the 

time of the 2000 Texas review. 

Texas revised its emissions estimates based on its 2000 review, using 

improved emissions estimating techniques and new modeling. The 

revised estimates showed that additional VOC reductions would be needed 

to meet national air quality standards, while required NOX reductions 

under the State Implementation Plan could be eased from 90 to 80 percent. 

As a result of what happened in Houston-Galveston, the regional planning 

authority in the Philadelphia area decided to more closely study refinery 

VOC emissions. The study disclosed many of the same problems noted 

for the Houston-Galveston area, and recommended that Texas’ guidelines 

be used when estimating emissions. The California Bay Area Air Quality 

Management District also closely examined emissions estimates, found 

similar results, and issued a new rule to obtain more accurate emissions 

estimates to ultimately reduce emissions. 

Wood Products7 

In 1988, EPA began investigating a suspected nationwide pattern of Clean 

Air Act violations by a prominent wood products company. EPA found 

that the company had failed to obtain required permits for new 

construction and other modifications at some of its facilities. The 

company had used a poor quality emissions factor for estimating VOC 

emissions and, as a result, claimed it was not subject to the permitting 

requirements. This emissions factor underestimated VOC emissions 

because it was derived from a test method that substantially understated 

VOC emissions containing oxygen. The industry subsequently developed 

a new emissions factor that adequately accounted for VOC emissions 

containing oxygen. 

6

 Flaring is an engineering practice that provides for process equipment to immediately release gases to a 

device (a flare) where they can be quickly and safely incinerated. The proper use of flaring is a good 

engineering practice because flares can prevent damages, fires, explosions, and injuries to employees. 7

 The wood products industry sector includes manufacturers of plywood, panelboard, medium density 

fiberboard, and oriented strand board. The drying and pressing processes involved in this sector are a large 

source of emissions. 

12

EPA used this information as the basis for successfully negotiating the 

largest Clean Air Act civil penalty ever collected by EPA (up to that time), 

and the second largest under any environmental statute. Under the terms 

of a consent decree, the company was required to pay $11.1 million in 

civil penalties and install state-of-the-art pollution control equipment 

valued at $70 million. In the 1990’s, EPA reached consent agreements 

with three other wood product companies after identifying similar 

violations. In addition to civil penalties, the consent agreements instructed 

the companies to install the Best Available Control Technology to reduce 

VOC emissions, conduct compliance audits, and obtain appropriate 

permits. 

 Ethanol Production 

In 2002, based on recent success in the wood products industry, EPA 

began investigating Clean Air Act violations by ethanol production 

companies. These companies use corn to manufacture ethanol for 

blending with automobile fuel, and during processing burn off gases that 

emit VOCs into the atmosphere. The ethanol emissions factor was 

developed using the same test method as wood products and again 

underestimated the amount of VOCs being emitted into the atmosphere. 

EPA alleged that these companies knowingly used a faulty emissions 

factor for permitting. 

In October 2002, EPA announced consent agreements with 12 ethanol 

plants to install air pollution control equipment. EPA estimated that VOC 

emissions will be reduced by 2,400 to 4,000 tons per year and CO by 

2,000 tons per year. The settlement also will result in estimated annual 

reductions of NOX by 180 tons, Particulate Matter by 450 tons, and 

hazardous air pollutants by 250 tons. 

Increasing Demand for New Emissions Factors Illustrates 

Continued Importance of Emissions Factors Program 

As EPA and the States move forward with efforts to identify and regulate 

sources emitting excess levels of air pollution, there will be increased 

demand for new emissions factors, especially for sources of fine 

Particulate Matter (PM2.5). 

By April 2008, EPA and States will need to identify sources of PM2.5, 

determine the amount of emissions from these sources, and ensure that 

sufficient emissions control equipment is installed at sources located in 

non-attainment areas. In 1997, EPA established the PM2.5 standard and in 

December 2004 designated areas as being in nonattainment with the 

standard. In April 2005, these designations became effective for 208 U.S. 

counties impacting a total population of 88 million people. By April 2008, 

13

States are required to submit a plan that identifies the sources of PM2.5, 

how much PM2.5 each source emits, and the actions planned for adequately 

regulating these sources. The quality of emissions factors will directly 

impact the effectiveness of the plans. An implementation plan must show 

how an area in nonattainment will reduce emissions to meet the standards 

as soon as possible, but no later than 2015, and include supporting 

technical analyses based on emissions factor-developed emissions 

estimates. 

The Concentrated Animal Feeding Operations industry provides another 

example of an area that currently does not have factors but needs them. 

Appendix B provides details on EPA’s efforts to address emissions factors 

in this area. 

Conclusion 

Although EPA has made progress in emissions factors development since 

our 1996 review, the need for better quality emissions factors has outpaced 

the Agency’s efforts to improve existing factors and develop new ones. 

EPA’s use of poor quality emissions factors information has hampered 

environmental decisions, resulting in more than one million tons of 

uncontrolled emissions spanning years, and an increased risk of adverse 

health effects. This also places a disproportionate emissions reduction 

burden on those facilities that use good quality emissions factors. 

Although our evaluation did not address the cost impacts of rectifying the 

inappropriate use of emissions factors, we believe these costs are 

substantial to both EPA and the States. For each of the three industries we 

reviewed (petroleum refineries, wood products, and ethanol production), 

there are, at a minimum, the following costs for addressing each industry: 

rewriting permits and determining the proper emissions limits, issuing 

regulations to require increased air pollution controls, and the legal actions 

(settlement or litigation) necessary to ensure industry complies with the 

new regulations. 

The three industries represent a very small portion of the universe of 

emissions estimates derived through the use of emissions factors. More 

effort in examining other key emissions factors may identify significant 

amounts of additional unregulated pollutants. Incomplete or unreliable 

emissions information can have serious consequences in terms of the 

effectiveness and cost of air pollution control strategies. The public will 

have little confidence in either the success or equity of EPA’s decisions if 

those decisions are based on questionable emissions data. 

14

Chapter 3 

EPA’s Management of Emissions Factors 

Program Needs Improvement 

EPA did not have a sufficient process for developing, improving, and 

rating emissions factors. While the Agency has taken various steps to 

improve the Emissions Factors Program, we noted deficiencies in four key 

areas that resulted in the use of poor and low quality emissions factors: 

x Lack of consistent emissions factors guidance. 

x Continued use of a rating system that only provides subjective 

information. 

x Insufficient funding for the program. 

x Not having a clear strategic plan. 

Given the vast number of emissions sources using factors and the differing 

uses of emissions factors for making significant environmental decisions, 

addressing these deficiencies will require a long-term, multi-year, 

coordinated effort among EPA, State and local agencies, industry, and 

others. EPA will need to assert its leadership to ensure that, in the future, 

emissions factors are only allowed to be used in accordance with yet to be 

issued EPA guidance on their proper use. In fiscal year 2003, OAQPS 

began a reevaluation of the Emissions Factors Program to standardize and 

streamline the emissions data collection and reporting process, establish 

procedures for defining data uncertainty and using emissions factors in 

non-inventory applications, and establish an outreach program to 

communicate changes to emissions factors stakeholders. However, to 

make the needed improvements to the Emissions Factors Program, EPA 

will need increased focus and direction, including fully developed goals 

and objectives. 

Conflicting Guidance Issued for Emissions Factors 

While introductory text to AP-42 states that emissions factors may be 

appropriate for situations such as making source-specific emissions 

estimates for area-wide emissions inventories, the text does not 

recommend emissions factor use except for inventory purposes. However, 

the text acknowledges that emissions factors may be used for site-specific 

purposes as a last resort (emphasis added) provided appropriate caveats 

concerning their limitations are in place. We noted three occasions where 

EPA has issued guidance on the use of emissions factors for sourcespecific purposes that conflicted with the intent of AP-42 emissions 

15

x

guidance – that is, that emissions factors not be used at individual sources. 

Caveats on emissions factors use in these programs varied and may have 

resulted in data being used for purposes outside EPA’s intended use of 

emissions factors. For example: 

Even though AP-42 specifically states that the use of emissions factors 

for site-specific permit limits is not recommended, EPA issued air 

permit guidance documents approving the use of emissions factors to 

set permit limits at individual facilities. In response to concerns that 

Title V operating permits were too costly and burdensome to 

implement, in July 1995, EPA issued guidance, White Paper for 

Streamlined Development of Part 70 Permit Applications, stating that 

facilities could use emissions factors estimates to determine emissions 

limits in the permit applications. Similarly, in August 2000, EPA 

issued draft guidance that provided flexibility and allowed State and 

local permitting agencies to use site-specific emissions factors as well 

as other relevant emissions factors. EPA eventually rescinded the 

2000 guidance but plans to re-introduce parts of it. 

x EPA’s New Source Review Program applies to sources undertaking 

major plant modifications, and involves determining the source’s 

potential to emit. The New Source Review Workshop allows the use 

of AP-42 emissions factors in estimating emissions to determine a 

facility’s potential to emit. EPA’s flexible permitting approach for 

New Source Review, known as the Plant-wide Applicability 

Limitation, provides greater flexibility by allowing some emissions 

points within a facility to increase emissions provided the overall 

emissions remain below the plant-wide limit. Current rules for permit 

limitations provide wide latitude in allowing the use of emissions 

factors. 

x EPA allowed the use of emissions factors in a recent reconsideration 

of a Maximum Achievable Control Technology (MACT) standard,8 

even though AP-42 specifies that emissions factors should not be used 

for such source-specific purposes. MACT standards specify the 

emissions control standards that must be achieved by an affected 

industry. However, if the emissions factor understates actual 

emissions, the facility may be required to install controls that do not 

effectively reduce emissions to an acceptable level; conversely, an 

overstatement may cause the industry to unnecessarily and unfairly be 

required to install more costly controls. In a July 2005 reconsideration 

of a rule, EPA made monitoring requirements less stringent by 

allowing the use of emissions factors. However, almost all of the 

July 30, 2004 Environmental Protection Agency, 40 CFR Part 63: [OAR-2003-0048; FRL-XXXXX][RIN 2060-AM78] National Emission Standards for Hazardous Air Pollutants: Plywood and Composite 

Wood Products; Reconsideration of original rule dated July 29, 2005. 

16


8 
66 emissions factors EPA allowed for this MACT rulemaking were 

either unrated or received a rating of poor or below average. 

EFPAG officials said that the currently planned guidance for noninventory uses of emissions factors should address the more appropriate 

applications of emissions factors in these programs. 

Rating System Does Not Define Appropriate Uses 

The current rating system for emissions factors does not provide the user 

with a tool to adjust the emissions factor based on use. This system 

provides a subjective A through E rating system that is of minimal value 

to the user because the system does not quantify the level of uncertainty 

used in the ratings. EPA places too much emphasis on the amount of test 

data used to develop the factor, and not on the quality of that data. If there 

is a significant amount of test data, the factor is rated high, even though 

the data may be of poor quality. Further, even if a factor is rated “poor,” it 

will still be used. An emissions factors tool that quantifies uncertainty 

would provide users with valuable information for adjusting the emissions 

factor as appropriate; taking into account the level of uncertainty during 

calculations can give the user a better understanding of the variations 

between actual emissions and emissions factors calculations. 

Quantifying the uncertainty of an emissions factor requires a more 

rigorous analysis of the test data to establish a range of uncertainty for 

emissions estimates. The Agency has been aware of such techniques, and 

over the past 10 years has funded several studies exploring the use of 

analytical techniques for quantifying uncertainty. In addition, the National 

Research Council and the NARSTO9 organization reported that EPA 

should increase the use of quantifying uncertainty in the development of 

emissions data. Also, EPA Order 5360.1 requires EPA to assess the 

quality of its data, and EPA’s current emissions factors rating system is 

not consistent with the Order’s data quality requirements. 

EPA officials told us that the majority of emissions factors are developed 

using 10 points of data or less, which is substantially less than the 30 to 50 

data points recommended for the development of a valid statistical 

analysis. Without incurring the additional cost of obtaining more data, the 

Agency can perform EPA-accepted statistical analysis on existing data to 

provide users with an uncertainty rating. This will allow users to quantify 

the uncertainty of emissions data developed from emissions factors. 

 Formerly an acronym for “North American Research Strategy for Tropospheric Ozone,” NARSTO is a 

public/private partnership, whose membership spans government, utilities, industry, and academia 

throughout Mexico, the United States, and Canada. Its primary mission is to coordinate and enhance 

policy-relevant scientific research. 

17


9
EPA and interested stakeholders agree that the benefits of conducting 

additional analysis outweigh the additional resources needed to quantify 

the uncertainty. A range for the emissions estimate will allow the user to 

understand how much lower or higher actual emissions vary when 

compared to the emissions factor calculated estimate. For example, 

instead of an emissions factor being 30 pounds of emissions per 1,000 

gallons of fuel consumed, the factor would have a quantifiable range – 

between 20 and 40 pounds – depending on the variables and uncertainties. 

An uncertainty expert we contacted quantified the uncertainty of two key 

A-rated emissions factors in EPA’s AP-42 database. Both factors are 

rated “Excellent” – the highest level. Further, the two emissions factors 

represented a significant amount of emissions nationwide – estimated 

emissions from a total of 32,569 coal-fired boilers. The potential 

variances when uncertainty is considered are shown in Table 3.1. 

Table 3.1: Effect of Emissions Factors Uncertainty on Estimates for Coal-fired Boilers* 

Boiler Type 

Emissions 

Estimate 

(NOX 

Emissions) 

Emissions Change Due to 

Factor Uncertainty Estimate of Probable 

Emissions (tons) 

Low High 

Factor 

Uncertainty 

Emissions 

Range (tons) 

Wall-fired 1,336,190 -41.4% to 

+33.2% 996,798 783,007 1,779,805 

Tangential-fired 751,581 -31% to 

+27% 435,917 518,591 954,508

 * Emissions factors ranges: Wall-fired (12.9 – 29.3) lb/ton; Tangential-fired (10.4 – 19.0) lb/ton 

As Table 3.1 illustrates, EPA’s best-rated NOX emissions factor for one 

type of coal-fired boiler (wall-fired) has an uncertainty range of plus 33.2 

to minus 41.4 percent, meaning actual emissions nationwide could range 

from 783,000 tons to 1.8 million tons. Thus, without knowing the 

uncertainty associated with an emissions factor, the approximately 

1.3 million tons reported for wall-fired boilers may be nearly as high as 

1.8 million tons. Quantified uncertainty information provides a tool to the 

user to make more informed decisions for defining the appropriate uses of 

the emissions factor. Depending on the situation, the user can adjust the 

emissions factor based on this uncertainty. The following three uses of 

emissions factors demonstrate how factors can be adjusted: 

x If the factor is being used for a national estimate, the user would 

most likely choose an estimate toward the middle of the range (this 

is because of the law of large numbers and the likelihood that overand under-estimates may tend to cancel each other out). 

18

x If the factor is being used to establish a permit limit at a specific 

facility, the user may need to select an estimate on the lower or 

higher end of the range, depending on variables and uncertainties. 

x If the factor is being used for emissions trading or offsetting, an 

appropriate use may be the low end of the emissions factor range. 

The uncertainty tool could allow the user to select an appropriate 

adjustment based on its use. Improving emissions factors will largely 

depend on the extent to which EPA can minimize the limitations 

associated with uncertainty. Without knowing the possible range of the 

estimate, users are not adequately informed of the risks associated with 

using the emissions factor. 

Inadequate Funding Provided and Used 

Currently, EPA’s emissions factors workload is largely dictated by 

stakeholder needs, and EPA does not have a well-documented plan for 

prioritizing its work. Understandably, EPA officials have had to operate 

in a reactive mode, focusing on State and industry requests involving 

specific emissions factors. However, managing emissions factors 

development in this manner does not allow a systematic approach to 

ensuring the most critical emissions factors are receiving the appropriate 

priority. 

EPA stated in its 1997 Federal Managers’ Financial Integrity Act 

(FMFIA) Assurance letter that it would request a substantial increase in 

funding for the development of emissions factors. As shown in Table 3.2, 

although EPA did request significant amounts of funding for the 

Emissions Factors Program since our 1996 report, it received about 

25 percent or less of the amount requested for 3 of the 7 years (1999, 

2000, and 2002). However, EPA actually spent significantly less on the 

Emissions Factors Program than had been appropriated, because EPA 

officials said emissions factors funds had been reprogrammed to other air 

program activities considered to be higher priority. As shown in 

Table 3.2, over the past 7 years, EPA spent between 29 percent and 

72 percent of the money it received, with about half of the funds received 

being reprogrammed. From 1999 to 2005, the program received 

$10,657,000, and spent a total of $5,301,000. It should be noted that there 

has been renewed emphasis on emissions factors since the program was 

reorganized in 2003 (see next page). For example, the amount of funding 

spent in Fiscal Years 2004 and 2005 increased substantially from the two 

previous years, although 2005 expenditures were still 59 percent lower 

than 2001 expenditures. 

19

Table 3.2: Funding of the Emissions Factors Program – by Fiscal Year 

Budgetary Activities 1999 2000 2001 2002 2003 2004 2005 

Requested Amount $4,100,000 $4,950,000 $5,096,000 $3,075,700 $2,590,400 $1,539,500 $4,652,600 

Amount Received 1,100,000 1,200,000 3,215,600 873,900 1,029,700 1,595,600 1,642,200 

Amount Spent 323,500 490,000 2,326,500 310,000 320,000 573,000 958,000 

Amount Reprogrammed (776,500) (710,000) (889,100) (563,900) (709,700) (1,022,600) (684,200) 

Over the past 5 years, there have also been several changes in the types of 

activities performed by the Emissions Factors Program, as shown in 

Table 3.3. With the exception of 2005, consistent funding has been 

devoted to maintaining the databases. Program improvements were nonexistent in 2002 and 2003; however, they have been a primary emphasis 

during the past 2 years. With the exception of spending $200,000 to help 

develop one emissions factor in 2005, the Emissions Factors Program has 

largely not been involved in developing specific emissions factors since 

2001, when over $1 million was spent. 

Table 3.3: Emissions Factors Program Expenditure Analysis – by Fiscal Year * 

Activities 1999 2000 2001 2002 2003 2004 2005 

Maintenance of Emissions 

Factors Databases 

$180,800 $221,000 $225,000 $245,000 $275,000 $234,500 $75,000 

Development of Specific 

Emissions Factors 

71,600 269,000 1,132,000 65,000 45,000 43,000 260,000 

Emissions Factors 

Program Improvements 

71,100 0 969,500 0 0 295,500 623,000 

Total $323,500 $490,000 $2,326,500 $310,000 $320,000 $573,000 $958,000 

* Does not include Administrative and Training Expenditures 

Given the increasing need for emissions factors and a relatively small 

budget, EPA will need to better leverage industry resources to obtain 

better emissions factors data. Although EPA recognizes the need to 

prioritize emissions factors work and has made efforts to do so, a welldocumented set of short- and long-term priorities does not yet exist. In its 

1997 FMFIA assurance letter, OAQPS stated it would refocus the 

Emissions Factors Program by prioritizing the most critical emissions 

factors, and hired a contractor to publish a document prioritizing 

emissions factors development. In 2002, the contractor published a 

document, Recommended Source Categories for AP-42 Chapter Update 

and Emission Test Program, also called the Scoping Study. One OAQPS 

official said the Scoping Study was intended to be the blueprint for future 

work, resource allocation, and other key program decisions. To date, EPA 

has not used the study to prioritize its emissions factors work. EPA 

officials said that they do not believe they can properly prioritize the 

competing needs of all of the emissions factors stakeholders to arrive at a 

common priority list to improve emissions factors. 

20

We agree that while developing a priority list of emissions factors is a 

challenge, it is critical for effectively managing the program. Emissions 

factors users at both the State and Federal levels said that EPA needs to 

prioritize its emissions factors work and fill the gaps that currently exist. 

Also, the Air Quality Management Work Group to the Clean Air Act 

Advisory Committee recommended that EPA review existing emissions 

factors to identify the most significant needs. 

Recent EPA Efforts Made to Revamp Emissions Factors 

Program 

EPA had recognized it did not have a sufficient process for developing, 

improving, and rating emissions factors. Therefore, in fiscal year 2003, 

OAQPS began a reevaluation of the Emissions Factors Program to: 

x Identify ways to make the program more responsive to the broad 

and diverse range of emissions factors users; 

x Identify methods that would expand the capabilities for improving 

the number and quality of available emissions factors; 

x Identify and implement ways to improve and expedite the 

emissions factors development process; 

x Characterize the deficiencies of using emissions factors by 

quantifying the uncertainties associated with the varied uses; and 

x Provide users with alternative methods of quantifying emissions to 

reduce the levels of uncertainty and to increase the accountability 

of stakeholders. 

Upon conclusion of the re-evaluation, EFPAG decided to revamp the 

Emissions Factors Program with the primary goal of improving emissions 

quantification through the use of better tools and knowledge of 

uncertainty. The revamping plan includes three specific tasks: 

(1) standardizing and streamlining the emissions data collection and 

reporting process, (2) establishing procedures for defining data uncertainty 

and using emissions factors in non-inventory applications, and 

(3) establishing an outreach program to communicate changes to 

emissions factors stakeholders. 

Specifically, EFPAG officials said they developed an electronic reporting 

tool that establishes a standardized emissions test report format with builtin quality assurance checks. They said use of this format will enable State 

and local air pollution control offices to readily assess the quality of 

submitted emissions test reports and to share those report results with 

others. As the tool is used, results from routine emissions tests should be 

easier to gather and those results should already be quality assured. 

21

Consistent use of the tool should increase both the quantity and quality of 

emissions factors. 

For non-inventory programs such as New Source Review and Title V 

permitting, EFPAG conducted case studies identifying the impact of overor under-estimating source emissions through use of emissions factors. 

Acting on the results of those studies, statistical analyses of excellent and 

above average emissions factors were performed to determine the range of 

uncertainty associated with these factors. EFPAG indicated it is preparing 

those analyses for external peer review, and at the same time, is assessing 

the impact of adjusting emissions factors for non-inventory programs. 

Once the analyses are validated, EFPAG plans to develop guidance for 

using emissions factors for non-inventory programs, and where applicable, 

the adjustments needed for emissions factors use for each program. 

EFPAG officials said that this guidance will improve emissions estimates 

and decisions based on those estimates by reducing the uncertainty 

inherent with emissions factors use. 

Finally, EFPAG is upgrading the existing Internet Web site, named 

WebFIRE, from a static to an interactive mode. Future plans for this 

newly-designed Web site include the ability to collect, screen, and adapt 

emissions data from the electronic reporting tool; calculate average 

emissions factors; and provide individual users with site-specific values 

that incorporate associated uncertainties tailored to their specific program 

application in accordance with future guidance. WebFIRE is also to 

provide the means to distribute new emissions factors, guidance, and 

procedures, as well as other means to better provide emissions 

information. 

EPA should be commended for its efforts, but should place greater 

emphasis on improving the quality of these factors. EFPAG agreed that it 

should expand the electronic rating tool to include pollutants other than 

Particulate Matter, ensure the guidance specifies how program specific 

adjustments are to be made, and program the interactive portion of 

WebFIRE to accept new data and to calculate specific adjustments. 

Comprehensive Plan Needed to Improve Data Collection and 

Set Priorities 

The lack of a comprehensive strategic plan hinders EPA’s ability to ensure 

the program is moving in the right direction, meeting its goals and 

objectives, and achieving the desired results. Some key areas the plan 

should include are short- and long-term goals and objectives; steps and 

measures to gauge progress in meeting the goals; timeframes for meeting 

milestones; and a process for reassessing and, when appropriate, revising 

the plan. A coordinated and well-thought-out plan will enable EPA to 

22

identify cost-efficient methods of obtaining more and better data, establish 

a communication strategy, and establish a system for prioritizing 

emissions factors development. EPA has made efforts to address these 

key areas, although it is not clear how these efforts fit into EPA’s broader, 

long-term plans. 

Over the past 30 years, EPA’s Emissions Factors Program has relied 

largely on scavenging for source data to develop emissions factors and 

often uses source data originally gathered for other purposes. For 

example, in the 1970’s, the program benefited from the source testing 

conducted by EPA for the development of new emissions standards. 

Throughout the 1980’s and 1990’s, the amount of EPA-funded source 

testing steadily declined, with a corresponding increase in industry-funded 

source testing. Through its own initiative, industry will sometimes 

conduct source testing to test emissions, but because the industry is not 

required to submit the data, EPA often is not aware of the data. 

EPA needs to develop a system where it can gain access to the millions of 

dollars worth of industry-generated source testing data. Currently, EPA is 

working on an information system that it believes will provide the muchneeded data to the stakeholders who need to develop emissions factors. If 

successful, this will be an important step toward sharing valuable data. 

However, EPA will also need to develop incentives for industry to share 

this information with the Agency. One way would be for EPA to issue 

guidance in accordance with EPA Order 5360.1 requiring and allowing 

only appropriate use of emissions factors for the environmental decisions 

to be made. 

Recognizing that implementation of this criteria may take some years, in 

the interim EPA could allow facilities to use the upper bounds of an 

emissions factor’s uncertainty range. Also, if a facility believes the higher 

emissions rate stipulated by EPA’s new guidance does not reflect its actual 

emissions, the facility could conduct stack or other testing and share this 

information with EPA in an effort to decrease the uncertainty of the 

emissions factor. The facility may be encouraged to do this in an effort to 

lower the upper bounds of the emissions factor uncertainty range and its 

resulting emissions estimate. Over time, as more facilities submit test 

data, EPA may have sufficient information to decrease the uncertainty of 

poor quality emissions factors and thus improve the estimates for an entire 

source category. 

EPA also needs to establish a communications strategy. Emissions 

Factors Program officials said that there are many air quality stakeholders 

with useful information, and accessing this knowledge pool can improve 

the development of emissions factors. EPA has conducted some outreach, 

through workshops and surveys, but the absence of a formalized 

23

communication strategy has resulted in valuable information not being 

identified. A more formal communication strategy will allow greater 

feedback and strengthen information sharing. EPA specifically needs to 

share information with stakeholders from four key areas: 

x Emissions inventories 

x Permitting 

x Industry 

x Enforcement 

In 2004, EPA implemented the Emissions Factors Improvement Project 

survey to solicit stakeholder feedback about the Emissions Factors 

Program and what improvements were needed. Of the 58 respondents, 37, 

or about 64 percent, said they did not submit data to EPA. About onethird of the 37 said they did not provide data to EPA because they did not 

know they should or how they should go about it. In addition, officials we 

interviewed from Regional Planning Organizations, the State and 

Territorial Air Pollution Program Administrators and the Association of 

Local Air Pollution Control Officials, State and Federal emissions 

inventory and permitting officials, and academia stated that they have 

limited or no contact with EPA on emissions factors. Instead of relying on 

stakeholders to contact them, EPA should systematically contact a broad 

range of stakeholders to gain access to information and knowledge that 

could improve the development of emissions factors. 

The information system that EPA is developing should increase 

stakeholders’ ability to provide additional data and access other useful 

emissions factors data. However, the system will not be effectively used 

unless EPA takes steps to ensure that stakeholders are aware of the 

information system and its advantages. Procedures should be included in 

a communications strategy to regularly solicit key information from 

stakeholders. 

Conclusions 

EPA officials describe the emissions inventory as the foundation for the 

air program, upon which everything else is built. Emissions factors 

estimates are used to develop much of this inventory and, as such, are 

critical measures woven into the fabric of many air quality managers’ 

most important decisions. Equally important, the models used to forecast 

changes in air quality under alternative reduction scenarios are also 

heavily reliant on accurate emissions factors and subsequent pollutant 

estimates. One common use of these models provides decision-makers 

with the information needed to develop control strategies to lower air 

emissions. Other types of emissions factors driven models are those used 

to identify the sources of pollution and link those sources to specific 

24

pollutants, selecting sites for increased monitoring, testing emission 

reduction scenarios to predict what impact they would have on pollutants 

of concern, and predicting changes in future concentrations. The results of 

these analyses shape EPA’s air quality planning. Use of inaccurate or 

incomplete data such as emissions factors can lead to costly, unjustified 

controls and/or exposures to pollutants that could negatively affect human 

health and welfare. Further, these analyses help define which industries 

need to be regulated, what level of controls are needed to achieve the 

desired results, which sources should be targeted for enforcement 

initiatives, and which pollutants are of the utmost concern. Emissions data 

also influences EPA’s decisions in studying health effects, performing risk 

and exposure assessments, and identifying safe levels of air pollution. 

The reliability and accuracy of the emissions estimates has far-reaching 

implications for how EPA sets its priorities and allocates the scarce 

resources available to meet the increasingly complex and daunting 

challenges of identifying the most cost-effective approaches to making the 

air cleaner. Emissions factors estimates, for all the uses noted above, are 

at the core of this process. Our findings verified that these factors remain 

significantly uncertain or unknown, despite their critical role. In fact, 

these factors are drawn upon by scientists, industry, States, and others and 

the rating system guiding their use does not meet the requirements of the 

Agency’s data quality order. While more resources have been requested 

to improve these factors, EFPAG has continued to receive significantly 

less money than needed over 6 of the last 7 years. Also, for the money it 

did receive for emissions factors, OAQPS redirected over half of these 

funds to other air program activities for 5 of those 7 years. 

If EPA continues to use insufficient measures, such as poor and unknown 

quality emissions factors, to determine program results, the Agency may 

be overstating its progress to Congress and the public. That is, EPA may 

not be reaching the goals it has claimed to reach and the air may not be as 

clean as the Agency claims. If progress is overstated, it may also result in 

EPA and States making misinformed decisions on selecting the most 

promising future actions for improving the quality of the air. 

Recommendations 

We recommend that the Acting Assistant Administrator for Air and 

Radiation: 

3-1 	 Establish a workgroup with representatives from emissions 

inventory, permitting, industry, and enforcement, to develop an 

emissions factors guidance document that addresses: 

(a) The appropriate and prohibited uses of emissions factors. 

25

(b) The intended use of the emissions factors estimates and how to 

adjust the estimates to more accurately reflect the use. 

(c) 	How to develop localized and site-specific emissions factors. 

(d) How to account for emissions factors uncertainty in newly 

developed factors and key existing factors. 

(e) 	Mechanisms for facilities and industry sectors to follow in 

developing and providing to EPA emissions factors that meet 

EPA Order 5360.1 data requirements. 

3-2 	 Develop and implement a comprehensive strategic plan that 

focuses on addressing future challenges expected in the Emissions 

Factors Program. The plan should address development of: 

(a) 	Criteria for prioritizing emissions factors development, for 

both new factors and selected existing factors that have the 

most environmental impact. 

(b) A communications and partnering strategy that results in 

sustained feedback from key emissions factors users, including 

EPA and State permit and enforcement officials, and industry. 

(c) 	An information system that streamlines the collection of source 

test data for the development of emissions factors. 

(d) Steps to ensure emissions factors uncertainty analysis is 

included in the development, rating, and intended uses of 

emissions factors. 

(e) 	A Quality Management Plan that ensures data used for the 

development of emissions factors meet data quality 

requirements. 

3-3 Once a comprehensive strategic plan is completed, have the 

Director for OAQPS ensure that all funds received for the 

Emissions Factors Program are actually spent on the program and 

not reprogrammed to other air activities. 

Agency Comments and OIG Evaluation 

The Agency concurred with our recommendations and stated that they 

generally align with its current improvement efforts. The Agency agreed 

that developing more emissions factors with less uncertainty is important 

in advancing the air program’s inventory tools, but also noted that there is 

a need for even more accurate and representative emissions data for noninventory uses – data obtained through direct emissions measurements. 

We agree with the need for direct measurements of emissions, and believe 

26

that appropriate guidance from EPA on the proper uses of emissions 

factors would provide substantial incentives for industries and State, local, 

and tribal agencies to work together to obtain such direct measurements. 

However, we also recognize that it may be years before such data are 

obtained and provided to EPA. 

The full Agency response is in Appendix C. A more detailed analysis of 

Agency comments and our evaluation of those comments are in Appendix 

D. The Agency will need to address each recommendation and provide 

details and milestones on its plans to address the OIG recommendations 

within 90 days, including: 

x The status of EPA’s efforts to establish a workgroup to develop 

guidance for recommendation 3-1, which addresses the appropriate 

and prohibited uses of emission factors. EPA should also explain 

the intended use of emissions factors estimates and how to adjust 

the estimates to more accurately reflect the use. 

x Actions taken or planned to develop and implement a 

comprehensive strategic plan, or submit a completed plan that 

includes the five elements listed for recommendation 3-2. 

x Specific steps taken or planned, as per recommendation 3-3, to 

ensure that funds received for the Emissions Factors Program are 

spent on the program and not reprogrammed to other air activities. 

27

Appendix A 

Details on Scope and Methodology 

We conducted interviews with officials from: EPA’s OAQPS and Office Enforcement 

and Compliance Assurance; air permitting officials from EPA Regions 4 and 6; North 

Carolina and Indiana air pollution control agencies; State and Territorial Air Pollution 

Program Administrators and the Association of Local Air Pollution Control Officials 

(STAPPA/ALAPCO); and the Western Regional Air Partnership and Midwest Regional 

planning organizations. We reviewed and discussed with these officials selected reports 

related to emissions factors, including: 

x An April 2005 NARSTO report, Improving Emission Inventories for Effective Air 

Quality Management Across North America: A NARSTO Assessment 

x Two National Academy of Sciences reports: The Scientific Basis for Estimating 

Air Emissions from Animal Feeding Operations: Interim Report (2002); and Air 

Emissions from Animal Feeding Operations: Current Knowledge, Future Needs 

(2003) 

x EPA’s Proposed Amendments to Air Toxics Regulations for the Plywood and 

Composite Wood Products Industry, July 18, 2005 

x EPA’s Compilation of Air Pollutant Emission Factors, Volume 1: Stationary 

Point and Area Sources, AP-42, Fifth Edition, issued January 1995 

x A June 2004 EFPAG survey report, Summary of Emissions Factors Improvement 

Project Fact Finding Survey 

x EPA’s Procedures for Preparing Emission Factor Documents, November 1997 

x Minutes from four Emissions Factors Development Workshops (Florida 

Conference – June 2004; Research Triangle Park (North Carolina) Conference – 

November 2004: and two Washington, DC Conferences – August 2004) 

x WHO’S COUNTING? The Systematic Underreporting of Toxic Air Emissions, 

June 2004, a joint study by the Environmental Integrity Project and the 

Galveston-Houston Association for Smog Prevention 

x Evaluating Petroleum Industry VOC Emissions in Delaware, New Jersey and 

Southeastern Pennsylvania Final Report, October 2003, Mid-Atlantic Regional 

Air Management Association 

To assess management controls, we reviewed the Office of Air and Radiation’s and 

OAQPS’s fiscal year 2004 Integrity Act Annual Assurance Letters. 

To obtain an understanding of the quantification of uncertainty of emissions factors, we 

interviewed an emissions factors uncertainty expert from North Carolina State University 

and reviewed technical papers associated with the subject. 

28

Methodology Used to Calculate Emissions Factors Uncertainty for 

Coal-fired Boilers in Table 3.1 

Emissions estimates were obtained from the draft 2002 EPA National Emissions 

Inventory (NEI). Factor uncertainty ratings were obtained for each source type from an 

emissions factors uncertainty expert. Probable emissions estimates were calculated by 

applying the uncertainty rating to emissions estimates, which results in a probable low 

and high range of emissions. This is known as the probabilistic emissions inventory, or 

PEI. Using the PEI allowed us to illustrate uncertainty in the NEI. PEI is a function of 

the reported emissions and the emissions factor uncertainty (UFEF) and activity data 

uncertainty (UFAF). It is the probable range of emissions values in which the reported 

individual emissions would be found. To calculate the PEI associated with a portion of 

the NEI, we obtained the reported emissions value for two Source Categorization Codes. 

The UFEF for each source category was multiplied by the point estimate of the emissions 

for each category (from 2002 NEI) and summed over the two categories to arrive at a 

PEI: 

PEI = Ȉ [(UFEF) (UFAF) (EI)] 

For this formula, PEI is summed over all source categories that have reported emissions 

(lb/yr). 

We reviewed the following documents related to this analysis: 

x Report 99-267 (1999), North Carolina State University, Raleigh, North Carolina 

x 2002 Emissions (NEI); Air Pollution Control Lecture Notes, North Carolina State 

University 

x Emission Inventory: Planning for the Future, October 28-30, 1997, Research 

Triangle Park, North Carolina 

x Journal of the Air & Waste Management Association, 2003 

x Environmental Science and Technology, 2004 

x Quantitative Analysis of Uncertainty and Variability in Environmental Policy 

Making, 1992 

x Risk Analysis, 2004 

Prior Coverage and Followup 

We followed up on EPA’s actions on previous recommendations from EPA OIG Report 

No. 6100306, Emission Factor Development, September 30, 1996. As part of this 

followup work, we reviewed OAQPS’s fiscal years 1997 and 1998 Integrity Act Annual 

Assurance Letters. We had found that EPA was providing poor and unreliable emissions 

factors to the user community. We recommended that the development of emissions 

factors be included as an Agency material weakness in FMFIA reporting. In its response 

to the draft report, EPA recognized the significant role of emissions factors, and as such, 

indicated it would take the following corrective action: 

29

x Refocus the program to address the most critical factors needed. 

x Request nearly four times the amount of contract resources in the fiscal year 1999 

budget request to the Office of Management and Budget. 

x Request $5 million of additional funding from Congress for Particulate Matter 

research in fiscal year 1998 to be used for developing Particulate Matter 

emissions factors. 

Details on what we found as a result of our followup, as well as recommendations, are in 

Chapters 2 and 3 of this current report. 

We also reviewed two other reports that addressed emissions factors development, 

although we did not do followup. These were a GAO report, EPA Should Improve 

Oversight of Emissions Reporting by Large Facilities (GAO-01-46), April 2001; and an 

EPA OIG report, Substantial Changes Needed in Implementation and Oversight of 

Title V Permits If Program Goals Are To Be Fully Realized (2005-P-00010), March 9, 

2005. 

Limitations 

Our work contained the following limitations: 

x We did not review emissions factors for all pollutants from all sources. 

x We did not review any emissions factors for mobile sources. 

x The quantified uncertainty information in Table 3.1 for two NOX emissions 

factors is unpublished data provided by the North Carolina State University 

emissions factors uncertainty expert, who was contracted by EPA to perform the 

uncertainty analysis. 

30

Appendix B 

Details on Concentrated Animal 


Feeding Operations Air Emissions 


Concentrated Animal Feeding Operations (CAFOs) are agricultural entities that raise 

animals in confined areas and pose a potential environmental risk as a result of the high 

concentrations of animals and their waste. Air emissions from agriculture sources 

generally have characteristics that make them difficult to control through the more 

conventional control technologies used at industrial sources. The difficulty and cost of 

monitoring agricultural pollution sources is a reason that CAFOs are largely unregulated 

regarding air emissions. 

EPA asked the National Academy of Sciences to evaluate the scientific information 

needed to address CAFO air emissions issues.10 The Academy found that the basic data 

needed for effective regulation and management of CAFO emissions do not exist. 

Reasonably accurate estimates of air emissions from CAFOs at the individual farm level 

will require defined relationships between air emissions and various factors. The 

Academy also found that directly measuring emissions from CAFOs is not feasible and 

existing emissions factors are generally inadequate. A major effort will be required to 

develop useful CAFO emissions factors. 

EPA’s need for better data has led to an agreement between EPA and some sectors of the 

animal industry to monitor air quality on farms. This voluntary agreement calls for a 

2-year national air monitoring study on emissions. Data developed from this study will 

be used to develop emissions factors. As part of the agreement, EPA indicated it will 

provide certain legal protections for past and current emissions violations for farms that 

participate. Environmental advocates have criticized EPA for providing this protection, 

and a former EPA staff attorney said EPA should not suspend its enforcement authority 

when the Clean Air Act already requires facilities to provide this data. However, 

according to EPA, this settlement will result in CAFO operators funding scientifically 

credible methodologies for estimating emissions as recommended by the National 

Academy of Sciences in its 2003 report. 

Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs (2003) 

31


10 
Appendix C 

Agency Response to Draft Report 

February 23, 2006 

MEMORANDUM 

SUBJECT: 	 Draft Evaluation Report: EPA Can Improve Emissions Factors 

Development and Management, Assignment No. 2005-00279 

FROM: 	 William L. Wehrum (Elizabeth Craig for) 

Acting Assistant Administrator 

TO: 	 J. Rick Beusse 

Director for Program Evaluation, Air Issues 

Office of Inspector General 

Thank you for the opportunity to comment on the draft evaluation report, “EPA Can 

Improve Emissions Factors Development and Management,” dated December 21, 2005. 

My staff also appreciated the opportunity to work with you to incorporate comments on 

the prior versions of the draft report. 

The emissions factor (EF) concept was developed in 1970 by the Office of Air 

Quality Planning and Standards National Air Data Branch to estimate emissions from the 

millions of emitters in the U.S. for which measurements were either impossible to make 

or had not yet been made. EFs were, and still are, the first step toward quantifying 

emissions in a basic way for estimating annual emissions. EFs represented a significant 

advance over previous estimating techniques or policies and were necessary and adequate 

for their time. 

While we agree that EFs are inherently uncertain and imperfect, See Appendix D 

developing more EFs or more certain EFs is important in advancing the air Note 1 

program’s inventory tools. However, we believe that focusing our efforts 

only on EF development obscures the real need for more accurate and representative 

emissions data for non-inventory uses. We believe the air program needs more direct 

measurements of emissions for our advanced models, strategies, and national programs. 

This need was emphasized strongly by the National Research Council of the National 

Academies in its report, “Air Quality Management in the United States” (National 

Academies Press, 2004). Currently, we are moving toward better emissions monitoring 

requirements for all major polluters that will enhance our response to environmental 

challenges. 

32

The recommendations provided by the Office of the Inspector 

General generally align with our current EF program improvement See Appendix D 

efforts. However, the report could better emphasize that: (1) EFs are Note 2 

just the first step toward quantifying emissions in a basic way; and (2) 

EPA is shifting its efforts toward more direct, continuous monitoring and measurement of 

emissions from all major emissions sources. 

For example, EPA is currently: (1) working on a process to quantify the uncertainties 

associated with the applications of EFs, and (2) establishing procedures to incorporate 

additional data into calculating EFs to reduce the uncertainty associated with the EF. 

Even with the ability to incorporate uncertainty into the application of an EF, EFs remain 

estimates and not direct emissions measurements. More advanced, accurate, continuous, 

and short-term determinations of emissions are needed for major emitters, and these goals 

can only be reached by shifting to direct emissions measurement and monitoring systems. 

Additional editorial comments are provided in the attachment. If you have any 

questions or need clarification, please contact Peter Tsirigotis of my staff at 

(919) 541-9411. 

33

Attachment 

(1) The draft evaluation report makes several references to the misuse or 

inappropriate use of EFs. These references should be linked to the misuse or See Appendix D 

inappropriate use of EFs in non-inventory programs or applications. We note the Note 3 

following places in the draft evaluation report where clarification would be 

appropriate: 

x At a Glance, What We Recommend, 1st paragraph -- We are making a number of 

recommendations to EPA to, among other things, develop emissions factors guidance that 

addresses the development and appropriate use of factors in non-emissions inventory programs; 

x At a Glance, What We Found, 2nd paragraph -- Emissions factors have been inappropriately 

used for key environmental decisions of non-emissions inventory programs, such as setting 

permit limits and reporting the level of air pollution control at specific facilities. 

x Chapter 1, Purpose, 2nd paragraph, 1st bullet -- Emissions factors are of an acceptable 

quality for use in key environmental decisions made by EPA and State and local agencies 

for non-emissions inventory programs; 

(2) In addition, clarification is appropriate in the following sections: 

See Appendix D 

3⁄4 Chapter 1, Background – In the paragraph on Source Testing and Note 4 

Material Balance, the cost figures are stated as absolute, when in reality 

they vary from pollutant to pollutant. The cost information would be more accurately 

expressed in ranges: 

x Source Testing -- $10,000 to $50,000 annual cost; 

x Material Balance -- $2,000 to $10,000 per year per process. 

3⁄4 Chapter 3, Rating System Does Not Define Appropriate Uses and At a 

See Appendix D Glance, What We Found – The information in the bullets below Table 3.1 Note 5 in Chapter 3, Rating System Does Not Define Appropriate Uses more 

correctly characterizes the adjustments to applying EFs based on data 

uncertainty in inventory applications. It would be appropriate to express this smaller 

range of potential errors in the example cited at the bottom of paragraph three in the What 

We Found section. 

3⁄4 Chapter 3, Comprehensive Plan Needed to Improve Data Collection and See Appendix D 

Set Priorities – The second paragraph in this section includes some Note 6 

clarifying historical context. Placing this text in the introduction (Chapter 

1, Purpose section) would provide this historical context at the outset of the report. 

34

Appendix D 

OIG Evaluation of Agency Response 

Note 1 – 	 We agree that emissions factors are the first step in quantifying estimates of 

actual emissions and that direct measures are the preferred emissions measure. 

We also agree with the Agency’s increased efforts to obtain more direct 

emissions measures, such as monitoring data, for non-inventory uses. We 

have revised the report to reflect these points. However, considering the 

extensive use of emissions factors today for both inventory and non-inventory 

uses, we believe that emissions factors may continue to be used extensively 

for the foreseeable future. For example, in responding to a March 2004 EPA 

OIG report,11 EPA informed us that it did not have the statutory authority to 

require the submission of hazardous air pollutant monitoring data from State 

and local agencies. Emissions factor-developed emissions inventory data will 

continue to be used frequently as a cost-effective method of estimating 

emissions, as compared to more expensive emissions measurements such as 

direct emissions monitoring. In the future, increased monitoring data may 

reduce the use of emissions factors for major sources; however, mobile and 

area sources are more likely to rely on emissions factors for a longer period of 

time. Therefore, we continue to believe that emissions factors may continue 

to be an integral part of the Air program for a significant length of time, and 

as such, should receive the resources needed to improve factor quality and the 

reliability using these estimates. 

Note 2 –	 We are encouraged that EPA believes our recommendations generally align 

with EPA’s current Emissions Factors Program improvement efforts, and 

based on our work, we would agree. We do, however, differ somewhat on our 

views of the projected use of emissions factors in the future. Please see 

Note 1 for details. 

Note 3 – We revised the report to reflect the use of emissions factors in “non-inventory 

programs or allocations,” where appropriate. For example, in the At a Glance, 

What We Recommend, first paragraph, we added that we believe guidance is 

needed for the non-inventory uses of emissions factors. However, in 

Chapter 1, Purpose, second paragraph, first bullet, we did not change this 

because our objectives were to address both inventory and non-inventory uses 

of emissions factors. 

Note 4 –	 We agree with this comment and have made these changes to our draft report. 

Note 5 –	 Due to space limitations in the “At a Glance” section of the final report, we 

could not accommodate the Agency’s desire that we more fully characterize 

EPA’s Method for Calculating Air Toxics Emissions for Reporting Results Needs Improvement, Report No. 2004­

P-00012, March 31, 2004 

35


11
an illustration of the impact of emissions factor uncertainty on estimates of 

emissions nationwide; however, we have added such an illustration on 

page 18 below Table 3.1, and removed our discussion of this information in 

the “At a Glance.” 

Note 6 –	 We agree with this comment and added a paragraph to the background section 

in Chapter 1 to provide the requested historical context to the Emissions 

Factors Program. 

36

Appendix E 

Distribution 

EPA Headquarters 

Office of the Administrator 

Acting Assistant Administrator for Air and Radiation 

Assistant Administrator for Research and Development 

Agency Followup Official 

Agency Followup Coordinator 

Audit Followup Coordinator, Office of Air and Radiation 

Audit Followup Coordinator, Office of Research and Development 

General Counsel 

Associate Administrator for Congressional and Intergovernmental Relations 

Associate Administrator for Public Affairs 

Director, Office of Air Quality Planning and Standards 

Deputy Director, Office of Air Quality Planning and Standards 

Director, Emissions Standards Division 

Acting Director, Emissions, Monitoring and Analysis Division 

Director, National Exposure Research Laboratory 

Audit Liaison, Office of Air Quality Planning and Standards 

EPA Regions 

Regional Air Program Directors 

EPA Office of Inspector General 

Acting Inspector General 

37