1

MEMORANDUM

TO: Jim Eddinger, U.S. Environmental Protection Agency, OAQPS

FROM: Amanda Singleton and Graham Gibson, ERG

DATE: 23 March 2010

SUBJECT: Development of Baseline Emission Factors for Boilers and Process Heaters at 

Commercial, Industrial, and Institutional Facilities

1.0 INTRODUCTION

This memorandum discusses the processes used to develop baseline emission factors for 

boilers and process heaters based on data reported by industry in the 2008 Questionnaire for 

Boilers, Process Heaters, Incinerators and Other Combustion Units (ICR No. 2286.01, OMB 

Control No. 2060-0616, EPA Form No. 5900-122) and the 2009 Test Plan for Boilers and 

Process Heaters (ICR No. 2286.03, OMB Control No. 2060-0616, EPA Form No. 5900-122). 

ERG developed two databases: 1) a comprehensive survey database containing all data reported 

by industry during the 2008 Combustion Survey (herein referred to as the Survey Database1

) and 

2) a comprehensive emission database containing all the stack test results, continuous emissions 

monitoring (CEMS) data, and fuel analysis data reported in the 2008 Combustion Survey and the 

2009 Phase II Test Plan (herein referred to as the Emission Database2). A data dictionary and 

description of all the fields contained in the Survey Database are summarized in other 

memoranda3. The standardization of reported emission data in both the Survey and Emission 

databases is also described in other memoranda4. 

The development of baseline emission factors followed a four-step process: First, a list 

of unique combustion units reported in the Survey database was compiled. Next, the reported 

fuels combusted and control devices installed were categorized. Third, for all units reporting 

emission data, all available emission data for a unique combustion unit were averaged and 
2

assigned as a unit-specific baseline emission factor. Finally, to fill data gaps at units not 

reporting emission data, the emission data from other units assigned to the same fuel, control 

device, and combustor design categories were averaged in order to develop an average baseline 

emission factor for similar types of units.

Baseline emission factors were developed for 23 specific pollutants based on the fuel and 

control device combinations or fuel and combustor design combinations utilized by the 

combustion devices reported in the questionnaire. These emission factors will be used to 

determine the control devices necessary to meet emission limits and estimate potential emission 

reduction for the National Emission Standards for Hazardous Air Pollutants for boilers and 

process heaters at Industrial, Commercial and Institutional facilities.

This memorandum is divided into the following sections:

1.0 Introduction

2.0 Grouping Data According to Fuel Type, Control Device, and Combustor Design 

3.0 Development of Unit-Specific Emission Factors

4.0 Development of Average Baseline Emission Factors

5.0 Baseline Averages for Area Sources

6.0 References

Appendix A: Glossary

Appendix B: Fuel and Control Device Groupings

Appendix C: Estimated Percent Reductions from Control Device Groupings

Appendix D: Baseline Emission Factors for Boilers and Process Heaters at Major Sources

Appendix E: Baseline Emission Factors for Boilers at Area Sources

NOTE: Technical terms and acronyms used in the text, tables, and appendices of this 

memorandum are described in Appendix A.
3

2.0 GROUPING DATA ACCORDING TO FUEL TYPE, CONTROL DEVICE, AND 

COMBUSTOR DESIGN

The first step of the baseline emission factor process involved targeting select pollutants, 

developing a comprehensive list of all combustion units reported in the questionnaire, and 

categorizing combustion units according to standardized fuel groups, control devices, and 

combustor designs reported the questionnaire. The procedures used to characterize the 

qualitative data from the questionnaire into appropriate groups are discussed in this section.

2.1 Pollutants

Baseline emission factors are specific to a certain type of pollutant. Twenty-three

different pollutants were targeted in this analysis, all of which are listed in Table 1. Although 

data were reported for more than 24 pollutants, baseline emission factors were only developed 

for those listed in Table 1 because these pollutants represent pollutants regulated under Section 

112 of the Clean Air Act (as amended in 1990) (CAA), or represent surrogates for pollutants 

regulated under the CAA, or represent pollutants that EPA uses to quantify the human health 

benefits resulting from a rulemaking. 

Table 1 – Pollutants Assigned Baseline Emission Factors

Pollutant

Antimony (Sb) Arsenic (As)

Beryllium (Be) Cadmium (Cd)

Carbon Monoxide (CO) Chlorine (Cl2)

Chromium (Cr) Cobalt (Co)

Filterable Particulate 

Matter (total) (PM-filter) Formaldehyde

Filterable Particulate 

Matter of less than 2.5 

microns (PM 2.5)

Hydrogen Fluoride (HF)
4

Pollutant

Hydrogen Chloride (HCl) Manganese (Mn)

Lead (Pb) Nickel (Ni)

Mercury (Hg) Selenium (Se)

Oxides of Nitrogen (NOx) Total Hydrocarbons (THC)

Sulfur Dioxide (SO2)

Total Mass Dioxins/Furans 

(PCDD/PCDF)

Volatile Organic Compounds (VOC)

2.2 Developing a Comprehensive List of Combustion Units

Each record in the Data: Unit Design/Operation table of the Survey Database correlates 

to a single combustion unit. The information for this table was derived from section II.B of the 

Questionnaire5. In addition, small, gas-fired boilers or process heaters were reported under 

section II.A of the Questionnaire. The definition of a small, gas-fired combustion unit is any unit 

firing natural gas, propane, liquefied petroleum gas (LPG), or refinery gas with a design capacity 

less than 10 million British thermal units per hour (MMBtu/hr). These groups of small 

combustion units, each treated as a single combustion unit for the purpose of developing baseline 

emission factors, are only present in the Data: GCP and CombustionControls table of the Survey 

Database.

An inventory of all the combustion units contained in the Data: Unit Design/Operation 

table as well as the small, gas-fired units in the Data: GCP and CombustionControls table. This 

inventory was then filtered down to only combustion units classified as boilers or process heaters

at major sources of hazardous air pollutant (HAP) emissions. This resulted in a total of 13,434

unique boilers and process heaters, with 6,391 of those being small, gas-fired units.

2.3 Fuel Categories

The Questionnaire provided a drop-down list containing 134 different fuels and materials 
5

and it also allowed users to self-report additional types of fuels and materials not included in the 

list. These fuels were categorized into one of the 11 fuel categories listed in Table 2. A list 

mapping each fuel category in Table 2 to specific fuel types reported in the survey can be found 

in Table B.1 of Appendix B. Since many boilers and process heaters fire multiple types of fuels, 

a fuel hierarchy was established to assign each multi-fuel boiler and process heater to a specific 

fuel category.

For units firing multiple fuels, fuel categories were assigned based on the percentage of 

the total heat input contributed by each fuel. A threshold of 25 percent was used in order to 

assign a fuel category based on the hierarchy listed in Table 2. For example, if the total heat 

input at a unit was comprised of 80 percent coal and 20 percent natural gas, it was placed in the

Coal category because the unit was combusting at least 25 percent coal on a heat input basis. In 

order for a combustion unit to be classified as any fuel lower in the hierarchy, each of the fuels 

ranked higher must all contribute less than 25 percent to the unit’s total heat input. For example, 

if a combustion unit’s total heat input was comprised of 20 percent coal and 80 percent natural 

gas, it was placed in the Natural Gas category.

Table 2 – Categorical Fuel/Material Hierarchy

Rank Fuel Category

1 Coal

2 Bagasse

3 Wet Biomass

4 Dry Biomass

5 Heavy Liquids

6 Light Liquids

7 Process Gases

8 Natural Gas
6

Rank Fuel Category

9

Other Non-Process Gases

(including refinery gas, 

LPG, propane, hydrogen)

10 Other Fuels

11 Waste

For baseline purposes, petroleum coke was included in the Coal category. Any 

unspecified type of biomass was assumed to be dry biomass. The liquid fuel categories 

encompass both fossil- and non-fossil-derived fuels in liquid form such as sludges. Emissions 

data from tests conducted while combusting waste were not included in baseline calculations. 

The definition of waste is detailed in another memorandum7.

2.4 Control Device Categories

Control devices reported in the Questionnaire were categorized according to their ability 

to remove certain types of pollutants. Since certain control devices target different types of 

pollutants, the pollutants themselves were first categorized into groups. Table 3 shows the 

groupings created for these pollutants.

Table 3 – Pollutant Groupings

Category Constituent Pollutants

Inorganic HAP and SO2

Hydrogen Chloride (HCl)

Hydrogen Fluoride (HF)

Chlorine (Cl2)

Sulfur Dioxide (SO2)

Mercury (Hg) Mercury (Hg)

Particulate Matter (PM) Filterable Particulate Matter
7

Category Constituent Pollutants

PM2.5

Non-Mercury Metallic HAP

Antimony (Sb)

Arsenic (As)

Beryllium (Be)

Cadmium (Cd)

Chromium (Cr)

Cobalt (Co)

Lead (Pb)

Manganese (Mn)

Nickel (Ni)

Selenium (Se)

Organic HAP and CombustionBased Pollutants

Carbon Monoxide (CO)

Formaldehyde

Oxides of Nitrogen (NOx)

Total Hydrocarbons (THC)

Volatile Organic Compounds 

(VOC)

Total Mass Dioxins/Furans

Total Mass Dioxins/Furans 

(PCDD/PCDF)

Control devices were reported in many separate sections in the Questionnaire. All control 

device data reported with the emission test and CEMS data, as well as the in the Data: Control 

Device table in the Survey Database, were identified for each combustion unit. Each of the 
8

control configurations reported for a boiler or process heater was further categorized to reflect 

only the control device or devices that are effective at removing any of the pollutants in Table 3. 

Control devices that have little or no effect on any of the pollutants listed in Table 3 were 

classified as having no control equipment installed. For example, selective catalytic reduction 

(SCR) is not effective in reducing the concentration of any pollutants listed in Table 3. Thus, 

any combustion unit that employed SCR was classified as having no air pollution control device 

(APCD). Similarly, if a combustion unit reported a control configuration of an electrostatic 

precipitator coupled with SCR, the “total baseline control” was standardized to “Electrostatic 

Precipitator.” Further, if a unit reported more than one control device that was effective at 

removing a particular pollutant, the most efficient control device was included in the “total 

baseline control.” For example, if a unit reported a multiclone and electrostatic precipitator, the 

total baseline control was standardized to “Electrostatic Precipitator”.

These standardized control configurations were classified into groups based on their 

effectiveness in the removal of the pollutants listed in Table 3. Control groups were created for 

Inorganic HAP and SO2, Metallic HAP, Mercury, and Particulate Matter. Since add-on control 

technologies reported in the questionnaire do not achieve reductions in dioxin/furan, organic 

HAP, CO, or THC, no control groups were assigned to the Organic HAP group. For each group 

of pollutants, control devices were ranked according to their effectiveness and assigned to a 

group. The lowest numbered groups represent the best-performing controls for a particular set of 

pollutants. For example, a wet scrubber is recognized to be the most effective control device at 

removing acid gases in the Inorganic HAP and SO2 group. Thus, a wet scrubber would be 

assigned to “Control Group 1” for those pollutants. A wet scrubber is also expected to remove 

modest amounts of particulate matter and metallic HAP, and it was assigned to “Control Group 

3” for the Metallic HAP pollutant group, behind spray dryer/FF and spray dryer/ESP control 

configurations. A list of the standardized “total baseline control” configurations and their 

groupings for the Inorganic HAP and SO2, Mercury, Particulate Matter, and Metallic HAP can 

be found in Tables B.2.A through B.2.D, respectively, of Appendix B.

2.5 Combustor Designs

Since formation of organic HAP is influenced by the design of a combustion chamber, 
9

boilers and process heaters firing solid fuels were classified according to combustor design. 

Combustor design categories depended on the fuel category the unit was assigned to. Table 4

lists the combustor design subcategories within each fuel category.

Table 4 – Combustor Designs

Fuel Category Combustor Designs

Coal

Fluidized Bed

Pulverized Coal

Stoker/Sloped Grate/Other

Bagasse, Wet Biomass, and 

Dry Biomass

Dutch Oven/Suspension Burner

Fluidized Bed

Fuel Cell

Gasifier

Stoker/Sloped Grate/Other

Residual/Heavy Liquids N/A

Distillate/Light Liquids N/A

Process Gases N/A

Natural Gas N/A

Other Non-Process Gases N/A

Other Fuels N/A

Stoker boiler designs include spreader stokers, overfeed stokers and mass feed stokers.

These boilers feed fuel to a grate and forced air and combustion controls coordinate the air and 

fuel supply to the boiler. Pulverized coal boilers pulverize the coal down to a powder and then 

inject the powdered fuel and air into the combustion chamber where the fuel combusts in 
10

suspension. Both dutch ovens and suspension burners are often designed to handle fuels with 

higher moisture contents (e.g., logging and timber residue, bagasse). In dutch ovens, the fuel is 

distributed onto grates and air flows up through the grates provides oxygen for combustion, cools 

the grates, and dries the fuel. Underfire air partially burns the fuel and then combustion of the 

volatile gases is completed in a secondary chamber. For suspension burners, fuel particles are 

combusted after being pneumatically suspended in an airstream. 

Combustion units were assigned to a combustor design based on the information reported 

in the Data: Unit Design/Operation table of the Survey Database. If a unit did not enter 

combustor design information, or if the combustor design reported was reported as a type other 

than those listed above it was placed in the Stoker/Sloped Grate/Other category since stoker 

designs represent the majority of boilers and process heaters designed to burn biomass or coal.

Some emissions data represents more than one combustion unit. In these cases, the 

combustor design for each individual combustion unit was reviewed. If all of the units shared 

the same combustor design, that common combustor design was used to characterize the data. If 

the multiple combustion units represented multiple combustor designs, the data was not used for 

baseline calculations because it did not belong to any combustor design subcategory. Instead, its 

combustor design category was labeled as “Multiple Combustor Designs”.

Sometimes a combustion unit reported more than one type of combustor design, in the 

Survey Database and a hierarchy was used to classify that unit to one of the combustor design 

categories. For coal units, the hierarchy was pulverized coal units, followed by fluidized beds 

and then stokers. Other designs not classified as pulverized coal, stoker, or fluidized bed were 

included in the stoker design category. For biomass units, the hierarchy was fluidized bed,

followed by stokers (including sloped grate), dutch ovens and suspension burners, fuel cells, and 

then gasifiers. Other designs not classified as, stoker, fluidized bed, fuel cell, dutch oven, or 

gasifiers were included in the stoker category.

3.0 DEVELOPMENT OF UNIT-SPECIFIC EMISSION FACTORS

Before an average baseline emission factor could be developed for a certain pollutant, 

each combustion unit was first assigned its own unit-specific emission factor where data were 

available. The process of assigning unit-specific emission factors is discussed in this section.
11

3.1 Selecting the Data Source for Unit-Specific Data Averages

Emission was reported in several sections of the 2008 Combustion Survey and some 

sources reported additional emission data under the 2009 Phase II ICR testing. Only emission 

data that could be standardized to common units of measured were used to determine unitspecific emission factors. The procedures used to standardize emission data are discussed in 

another memorandum.2 Standardized emission test, CEMS monitoring data, and fuel analysis 

data were averaged for each boiler reporting these data. For units reporting multiple types of 

emission data, Table 5 shows the hierarchy for determining which data source was used as the 

basis for the baseline emissions at the boiler or process heater.

Table 5 – Hierarchy for Determining Unit-Specific Baseline Emission Factors

Rank Condition

1

If a unit had emission test averages and CEMS data averages and the values were 

within the same order of magnitude, CEMS and emission test averages were 

averaged together.

2 If a unit had emission test and CEMS data averages and the values were not 

within the same order of magnitude, only the emission test average was used.

3 If a unit had only an emission test average, that value was used.

4 If a unit had only CEMS data, the average of the reported CEMS data was used.

5

If an uncontrolled unit designed to burn liquid fuels had no emission test or 

emission monitoring data but reported fuel analysis data for metallic HAP, 

mercury, or chlorine (standardized to hydrogen chloride), the average of all the 

standardized fuel analysis data in the unit’s fuel category (light or heavy liquid)

was assigned as the unit’s baseline emission factor. 

6

Boilers or process heaters with no emission test or CEMS data, as well as liquidfired units with no fuel analysis data were not assigned a unit-specific emission 

factor and were assigned to an average baseline emission factor as discussed in 

Section 4. 

3.2 Assigning Appropriate Fuels and Control Devices

Similar to how unit-specific emission factor values came from different data sections of 
12

the survey, fuel and control device data were often reported in multiple sections of the survey. 

Tables 6-7 show the hierarchies used to determine the fuel and control device, respectively, for 

each unit-specific emission factor.

Table 6 – Hierarchy for Determining Fuels for Unit-Specific Emission Factors

Rank Source

1

If emission test or CEMS data were available, the fuels reported during these 

tests or monitoring periods were used. Tests on multiple fuels or control 

configurations were assigned separate record identifiers as discussed in Section 

3.1.1

2 Small, gas-fired units (as defined in Section 2.2 above) located at refineries 

(NAICS code 324) were assumed to be combusting refinery gas.

3 The remaining small, gas-fired units (as defined in Section 2.2 above) were 

assumed to be combusting natural gas.

4 A combination of all fuels listed as being routinely combusted for that specific 

combustion unit as listed in the Data: Materials Combusted table of the Survey 

Database.

5 The fuel associated with the design capacity of the combustion unit as listed in 

the Data: Unit Design/Operation table of the Survey Database.

6

A combination of all fuels listed as being combusted for that specific facility as 

listed in the Data: FuelAnalysis Background Information table of the Survey 

Database.

Table 7 – Hierarchy for Determining Control Devices for Unit-Specific Emission Factors

Rank Source

1

If emission test or CEMS data were available, the control devices reported to be 

installed during these tests or monitoring periods were used. Tests on multiple 

fuels or control configurations were assigned separate record identifiers as 

discussed in Section 3.1.1.

2

A combination of all current control devices reported to be installed on the 

combustion unit as listed in the Data: Control Device table of the Survey 

Database.

3 If no control device information was reported for a combustion unit, it was 

assumed to have no add-on control devices.
13

Rank Source

4

Since cyclones are often considered integral equipment to a boiler and not an 

add-on control device, units combusting coal and/or biomass who did not report 

having any controls installed were assumed to have a cyclone installed for 

Metallic HAP and Particulate Matter control. The ‘total baseline control’ 

category for these units remained classified as having no HAP control, but solid 

fuel boilers without reported controls and with cyclone/multiclone reported 

control assigned to the same control group for Metallic HAP and Particulate 

Matter. .

After the preferred data source for fuels combusted and control devices installed were 

determined, the reported fuels were assigned to fuel categories described in Section 2.3 and the 

reported control devices were assigned to control groups, as described in Section 2.4. These 

categories allowed baseline emission factors to be developed for each combination of fuel and 

control device.

Several times, combustion units reported different fuel and control configurations

associated with emissions data than the controls and fuels reported with monitoring data. In 

these cases, the fuel and control device data from both sources were reviewed, and the data 

deemed most representative of current operations were assigned to the unit. Routinely 

combusted fuels were reported in the Data: Materials Combusted table of the Survey Database. 

Current control device data were reported in the Data: Control Device table of the Survey 

Database. The fuel and control information reported with the testing and monitoring data were 

compared to these tables in order to determine the most representative fuel and control

configuration. Emission and monitoring data for alternate fuel or control configurations at the 

unit were not considered when calculating a unit-specific baseline emission factor, but they were 

included when calculating average baseline emission factors for units with similar fuel and 

control device configurations. 

3.3 Emission Test and CEMS Data Averages

Emission data averages were created using the standardized data in the Data: 

EmissionsTest and Data: CEMS tables of the Emission Database. If a unit reported the results of 

an stack test to be non-detect, the detection limit was used as the basis for the average. Emission 

test data were available for all pollutants listed in Table 3 of this memorandum. Monitoring data 
14

was reporting in the Survey Database on a daily average basis for CO, SO2, NOx, and Filterable 

PM. Facilities were unable to report emission monitoring data as non-detect in the Survey 

Database since the template to enter CEMS data required a numerical value. 

Many combustion units reported emission test information for multiple fuel and control 

configurations. For example, some units reported control configurations that represent current 

control configurations presently installed on the unit as well as control device configurations that 

were installed prior to complying with the 2004 vacated NESHAP for Industrial, Commercial, 

and Institutional Boilers and Process Heaters. Other units that tend to operate on multiple fuel 

types may have reported multiple stack tests, for example one unit may have reported a test

based on firing natural gas and another test while firing fuel oil. In order to appropriately group 

emission test and monitoring data, a record identifier was created to distinguish between 

different combinations of fuel and control device configurations. 

Next, the average (mean) of all the emission test runs with the same record identifier was 

calculated. For a combustion unit with only one fuel and control device combination, the record 

number was assigned as “1.” For combustion units with multiple combinations of fuel and 

control device configurations, additional record numbers were assigned. For example, if a 

combustion unit with a wet scrubber reported two emission tests, one burning coal and the other 

burning oil, two record identifiers numbers were given. The coal/wet scrubber combination was

assigned a record number of “1” whereas the oil/wet scrubber combination was assigned “2.” 

The maximum number of record identifiers assigned to a combustion unit was four, representing 

four unique combinations of fuel type and control device configurations.

An average (mean) of all the monitoring data with the same record identifier was also 

calculated. For most sources, this was a 30 day average, but some sources reported multiple 30-

day periods in the Survey Database. For combustion units that reported both emission test and 

monitoring data with similar fuel and control configurations, the same record identifier was used 

for both sets of data in order to allow the two datasets to be averaged, when deemed appropriate. 

The calculated means for the emission test and monitoring data were compared, and if the mean 

of each dataset was on the same order of magnitude, the emission test and emission monitoring 

data were averaged together and assigned to the unit-specific baseline emission factor. If the 

emission test and emission monitoring data were not of the same order of magnitude, only the 

average emission test data was used to establish baseline emission for the unit. An order of 
15

magnitude was defined to be within a factor of 10. 

3.4 Fuel Analysis Data Averages

The process of standardizing mercury and chlorine fuel analysis concentrations into 

standardized emission factors is discussed in other memoranda2. Fuel analysis data from 

uncontrolled liquid fuels were standardized for chlorine (converted to HCl), Hg, and other metals 

(Sb, As, Be, Cd, Cr, Co, Pb, Mn, Ni, Se). Since these HAP are fuel-based contaminants, and not 

a product of combustion, the constituents within the fuel are expected to be emitted in the 

exhaust gas.

Since the liquid fuels are often delivered to a facility and used in multiple combustion 

units at the facility, fuel analysis data were reported in Survey Database and Emission Database 

at the facility level. As a result, unit-specific emission averages could not be generated. Instead, a 

list of uncontrolled combustion units designed to burn liquid fuels and reported combusting 

liquid fuels as per Section 2.3 above was developed from the Survey Database. Next, all of the 

fuel analysis data for liquid fuels at facilities with an uncontrolled liquid unit were identified and 

classified as either heavy or light liquids according to Appendix B1 of this memorandum. 

Because purchased liquid fuels such as fuel oils 1-6 are subject to ASTM specifications and are 

expected to be relatively homogenous from delivery to delivery, fuel analysis averages were not 

calculated for a specific facility or unit. Instead, each uncontrolled liquid unit was assigned to an

average baseline emission factor that was calculated by taking the mean of the all standardized 

fuel analysis data for bio liquids, diesel fuel, jet fuel, kerosene, and #2 and #4 oil for units in the 

light liquid fuel category and the mean of all standardized fuel analysis data for black liquor, #5 

and #6 oil, rectified methanol, red oil, and on-spec used oil for units in the heavy liquid category. 

For example, facilities A and B each have an uncontrolled unit combusting distillate liquid fuel

and reported fuel analysis data for chlorine. Both combustion units would have each been 

assigned the same HCl fuel analysis average generated for light liquids.

Some fuel analysis data was reported as a mixture of fuels. If a liquid fuel was reported 

as a mixture, the corresponding data was not used to generate an average. Fuel analysis data for 

any type of sludge was not used to calculate fuel analysis averages. 

4.0 DEVELOPMENT OF AVERAGE BASELINE EMISSION FACTORS
16

For units that did not report emission test, CEMS or fuel analysis data for one of the 

pollutants in Table 1, average baseline emission factors were developed using data from other 

boilers and process heaters with similar controls, fuels, and combustor designs. In several cases 

it is possible for certain pollutants to be based on unit-specific data, where data was reported, and 

the data gaps not reported were filled with average baseline emission factors. The process of 

identifying data suitable for use in an average baseline emission factor and calculating the 

average baseline emission factors is discussed in this section.

4.1 Baseline Criteria

Baseline averages were developed to represent emissions from units firing similar fuel 

types that have similar control devices. Any emission test or emission monitoring data reported

in the Survey Database when combusting any amount of waste material was not included in 

baseline average calculations. Fuel analysis data for liquid wastes, or fuel analysis data that was 

reported for a combination of liquid fuels and waste was not used in baseline average 

calculations. The definition of waste is detailed in another memorandum7

. While baseline 

averages were calculated for the Other fuel category, they were not used since all of the units in 

the boiler and process heater inventory were assigned to one of the other nine fuel categories in 

Table 3. 

4.2 Development of Averages

To calculate an average baseline emission factor for each pollutant, all unit-specific 

emission factors assigned in section 3.0 were averaged for similar groups of controls, fuel types 

and combustor designs. Since inorganic HAP and SO2, metallic HAP, Hg, and PM, are fuelbased HAP that can be controlled with add-on pollution control devices, the unit-specific 

emission factors were averaged across all units with a common fuel category and control group. 

Formaldehyde, NOx, and CO, are combustion-based pollutants and their emissions are

influenced by the design of combustion chamber. Further, emissions of NOx and carbon 

monoxide can be affected by NOx controls such as low NOx burners, overfire-air, or flue gas 
17

recirculation. As a result, the unit-specific emission factors were averaged across all units with a 

common fuel category, combustor design, and NOx control configuration. Baseline averages for 

THC and PCDD/PCDF are also driven primarily by the design of the combustion chamber, and 

the unit-specific emission factors were averages across all units with a common fuel and 

combustor design category. Based on the data reported under Phase II, emissions of THC and 

PCDD/PCDF at units firing natural gas and refinery gas differed significantly depending on 

whether the unit was equipped with NOx controls, and so baseline emission factors for THC and 

PCDD/PCDF at these gas-fired units were established by averaging data from other gas fired 

units with similar NOx control configurations.

4.3 Filling Data Gaps

After calculating averages emission factors for each of the pollutants in Table 1 for the 

unique combinations of fuels, control devices, and combustor designs there were some pollutants 

that did not have any emission data available to calculate an average baseline emission factor. 

For inorganic HAP and SO2, metallic HAP, Hg, and PM, control efficiencies were assigned to 

the control groups based on literature available on pollutant removal efficiencies of various 

control devices. A list of the pollutant-specific percent reductions can be found in Appendix C. 

The percents listed in Appendix C are the expected reductions a given control device could 

achieve compared with pollutant emissions without control devices installed. 

There were no data gaps for the organic HAP pollutants for gaseous and liquid fuels. The 

average baseline formaldehyde emissions from coal-fired fluidized bed boilers were 

approximated using the average emission from coal-fired stoker/sloped grate/other boilers. For 

THC, formaldehyde and NOx emissions from dutch oven/suspension burners firing wet biomass, 

the baseline emissions were approximated using the emissions from dutch oven/suspension 

burners firing dry biomass. For the one unit that was classified as a gasifier burning dry 

biomass, its emissions assigned to the emissions from the dry biomass Stoker/Sloped 

Grate/Other category since gasifier is an “other” type of unit. Data gaps in the Bagasse fuel 

category were filled using the Wet Biomass averages from the same subcategory since Bagasse 

is considered to be a very wet type of biomass.
18

4.4 Review of Outlier Data

After baseline emission factors were developed for each possible subcategory, the 

average values were reviewed to look for uncharacteristically high or low values. Unexpectedly 

high or low values were flagged and the individual data points that comprised the average were 

investigated. An example of flagged values for a given pollutant would be if the uncontrolled 

baseline emission factor was lower than that of any other control group for that same pollutant

and the same fuel category.

The unit-specific averages were inspected for these problematic values in order to 

determine if there was a problem with any of the reported data used in the average. Several 

factors led some data to be disregarded, such as emissions monitoring data from periods of 

startup or malfunction, errors with the reported units of measure, misclassification of units, fuels 

burned, or control devices installed. Where possible, changes were made to the reported data in 

the Emission Database and the updated values were used to recalculate baseline emission factors. 

If reported data was identified as an outlier, it was not used in the average baseline emission 

calculations, but was used for a unit’s site-specific baseline emission factor. 

In addition to reviewing the average baseline values for outliers, the full range of unitspecific emission data was also reviewed to identify any uncharacteristically high or low values 

that could over or underestimate the expected emission reduction estimates resulting from the 

proposed rule. 

4.5 Establishing Baseline Emissions for PM2.5 and VOC

Baseline emission factors for particulate matter less than 2.5 microns (PM2.5) were 

estimated as a percentage of filterable PM baselines. PM2.5 is a select portion of total filterable 

PM based on particle size, so it is correct to assume that a portion of total filterable PM will 

always be PM2.5. The ratios of PM2.5 to total filterable PM were based on reported emission 

test data for both pollutants, and were specific to fuel types and control devices. The fractions of 

PM2.5 ranged from 0.07 to 1. Details on the fractions for each fuel and control device group are 

presented in Appendix D-3. Using the fuel category and control device configuration assigned 
19

to each unit, a baseline emission factor for PM2.5 was estimated by multiplying the appropriate 

PM2.5 fraction by the filterable PM baseline emission factor assigned to the unit. 

Similar to the method used to generate PM2.5 baseline emission factors, VOC emission 

factors were generated as a portion of THC baseline emissions. Monitoring data reported from 

the 2009 Test Plan was used to calculate an average (mean) VOC-to-THC ratio that could be 

applied to all THC baseline emission factors. Only data from the 2009 Test Plan was used 

because it was the only source of data that correlated THC and VOC data points over a multi-day 

period. VOC ratios were not calculated for each subcategory because there was only data 

available for six total boilers and process heaters. A VOC-to-THC ratio was generated for each 

monitoring data point that was not noted to be during a period of start-up, shutdown, or 

malfunction. A statistical quartile analysis was performed on the set of ratios in order to remove 

any outliers. The remaining ratios were then averaged in order to get a total VOC-to-THC ratio, 

which was applied to each THC baseline emission factor subcategory. It was assumed that this 

ratio would not fluctuate between different fuel categories or control devices. Based on 

monitoring data available from these six sources, THC emissions are composed of 57% VOC. 

The data used to calculate this percentage is presented in Appendix D-4.

4.6 Establishing Baseline Emissions for Total Mass Dioxins/Furans

Baseline emission averages for total mass dioxins/furans were calculated differently than 

the rest of the pollutants due to the way dioxin/furan data was reported in the Emission Database. 

Facilities were able to report a total mass emission value, or total mass values for 17 individual 

dioxin/furan congeners and a group of “other congeners”. Table 8 lists the dioxin/furan 

congeners used to calculate total dioxin/furan emissions.

Table 8 – Dioxin/Furan Congeners

Total Mass Dioxin/Furan Congeners

1,2,3,4,6,5,7,8 OCDD 1,2,3,7,8 PeCDD

1,2,3,4,6,5,7,8 OCDF 1,2,3,7,8 PeCDF

1,2,3,4,6,7,8 HpCDD 1,2,3,7,8,9 HxCDD
20

1,2,3,4,6,7,8 HpCDF 1,2,3,7,8,9 HxCDF

1,2,3,4,7,8 HxCDD 2,3,4,6,7,8 HxCDF

1,2,3,4,7,8 HxCDF 2,3,4,7,8 PeCDF

1,2,3,4,7,8,9 HpCDF 2,3,7,8-TCDD

1,2,3,6,7,8 HxCDD 2,3,7,8-TCDF

1,2,3,6,7,8 HxCDF Other Congeners

Only Phase II data was used to generate dioxin/furan averages because Phase I data was 

not received for individual congeners and data reported in Phase I were not reported on a total 

mass basis. For each emission test, a total mass dioxin/furan value was generated for each run. 

If the facility reported a total dioxin/furan value or detection limit, it was used. If no numerical 

value or detection limit was provided, the sum of the values of the congeners listed in Table 8 

was used to calculate a total mass of dioxin/furan emissions. The total dioxin/furan value for 

each run was averaged to get a test average specific to a combustion unit. These averages were 

used as unit-specific emission factors for their respective combustion units. 

To calculate average baseline emission factors, these test averages were averaged across 

units in the same fuel and combustor design. Baseline emission factors were not generated for 

TEQ dioxins/furans. Baseline emission factors for total mass dioxins/furans for major and area 

sources are presented in Appendices D-1 and E, respectively.

5.0 BASELINE AVERAGES FOR AREA SOURCES

Although a small number of area source facilities with boilers and process heaters 

reported emission data in the Survey Database, there was not sufficient data available to create a 

separate set of baseline emission averages for area source boilers. Instead, the average baseline 

emission factors calculated for major source boilers and process heaters were used to establish 

the baseline emissions from area source model units used to estimate the impacts of the proposed 

rulemaking.

Based on data available in the Survey Database, Title V permits for area source boilers, 
21

and data from the National Forest Service Fuels for Schools program, most boilers at area 

sources are uncontrolled1,8. Further, the distribution of control devices on solid fuel area source 

boilers units in Pennsylvania and Wisconsin indicate that 8 percent of wood/biomass boilers

greater than 10 MMBtu/hr in these two states do not have any listed control, and the other 92 

percent have an mechanical collector (e.g., multiclone, cyclone) control device installed. Further, 

53 percent of coal boilers in Pennsylvania do not have any listed control. The remaining boilers 

firing solid fuels at area sources have an mechanical collector control device. Using this 

information on control devices, we assigned average baseline emission factors for the area source 

model units according to Table 9 below. 

Table 9 – Baseline Emission Factor Assignments to Area Source Boilers

Area 

Source 

Model 

Unit

Pollutant Type Corresponding Major Source Baseline 

Emission Factor Category

Biomass

Fuel-based pollutants Average of wet and dry biomass for 

uncontrolled/cyclone controlled

Combustion-based pollutants Average of wet and dry biomass stokers with 

NOx control

Coal

Fuel-based pollutants Uncontrolled/cyclone controlled coal

Combustion-based pollutants Coal stokers with NOx control

Residual 

Liquid

Fuel-and-combustion-based 

pollutants Uncontrolled heavy liquid

Distillate 

Liquid

Fuel-and-combustion-based 

pollutants Uncontrolled light liquid

Fuel-based pollutants include: PM, Hg, metallic HAP, inorganic HAP, and SO2

Combustion-based pollutants include: THC, CO, PCDD/PCDF, and formaldehyde

6.0 REFERENCES

[UNDER DEVELOPMENT]

1. Survey Database version X. Date. 

2. Emission Database Version X. Date.

3. Memorandum from Susan McClutchey and Amanda Singleton, ERG, to Jim Eddinger, 
22

EPA, Data Dictionary for Major Source Boiler and Process Heater Database. April, 

2010.

4. Memorandum from Graham Gibson and Amanda Singleton, ERG, to Jim Eddinger, EPA, 

Standardization of Reported Data from the Questionnaire for Boilers, Process Heaters, 

Incinerators and Other Combustion Units. April XX, 2010.

5. Answer Key

6. Survey Overview Document

7. Waste definition memo??

8. Memorandum from Jim Eddinger to Docket MACT Floor Analysis for the Industrial, 

Commercial, and Institutional Area Source Boilers Area Source MACT Floor Database. 

April 2010.
23

APPENDIX A

GLOSSARY
24

Table A.1: Glossary

Term Description

APCD Air pollution control device. An add-on exhaust stack technology 

that reduces the concentrations of HAP in exhaust gas.

Btu British thermal unit. A unit of measurement for energy.

CO Carbon monoxide. A common pollutant produced due to the 

incomplete combustion of fuel.

HAP Hazardous air pollutant. See Table 1 for a list of all HAP associated 

with this rulemaking effort.

Hg Mercury. This abbreviation is used to refer to both the mercury 

pollutant itself as well as the pollutant group created for it.

Inorganic A pollutant category that is comprised of the pollutants hydrogen 

chloride (HCl), hydrogen fluoride (HF), and chlorine (Cl2).

LPG Liquefied petroleum gas. A hydrocarbon fuel derived from 

petroleum, stored under pressure in the liquid phase.

Metallic HAP A pollutant category that is comprised of the pollutants antimony 

(Sb), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr),

cobalt (Co), lead (Pb), manganese (Mn), nickel (Ni), and selenium 

(Se).

MMBtu/hr One million British thermal units per hour. A unit of measurement 

for thermal energy.

NOx Nitrogen oxides. A grouping of binary compounds composed of the 

elements nitrogen and oxygen, including nitric oxide (NO), nitrogen 

dioxide (NO2), nitrous oxide (N2O), dinitrogen trioxide (N2O3), 

dinitrogen tetroxide (N2O4), and dinitrogen pentoxide (N2O5).

Organic An organic compound is characterized as any compound containing 

carbon, not including carbonates, carbon oxides, cyanides, and 

allotropes of carbon. For this analysis, organic refers to a pollutant 

category that is comprised of the pollutants formaldehyde, volatile 

organic compounds, and total hydrocarbons (THC).

PCDD/PCDF The total mass of polychlorinated dibenzodioxins/polychlorinated 

dibenzofurans. The sum of reported masses for 18 congeners 

including: 1,2,3,4,6,5,7,8 OCDD; 1,2,3,4,6,5,7,8 OCDF; 1,2,3,4,6,7,8 

HpCDD; 1,2,3,4,6,7,8 HpCDF; 1,2,3,4,6,7,8,9 OCDD; 1,2,3,4,7,8 

HxCDD; 1,2,3,4,7,8 HxCDF; 1,2,3,4,7,8,9 HpCDF; 1,2,3,6,7,8 

HxCDD; 1,2,3,6,7,8 HxCDF; 1,2,3,7,8 PeCDD; 1,2,3,7,8 PeCDF; 

1,2,3,7,8,9 HxCDD; 1,2,3,7,8,9 HxCDF; 2,3,4,6,7,8 HxCDF; 

2,3,4,7,8 PeCDF; 2,3,7,8-TCDD; and 2,3,7,8-TCDF. 

PM Filterable particulate matter (all sizes). 

PM2.5 A portion of total filterable particulate matter consisting of particles 

less than or equal to 2.5 μm in diameter.
25

Term Description

SO2 Sulfur dioxide. A common pollutant produced from the combustion 

of fuels with high sulfur content.

TEQ An alternative method for quantifying the toxicity of dioxin/furan 

congeners relative to the congener 2,3,7,8-TCDD. TEQ values used 

in this analysis are based on the 2005 World Health Organization 

toxic equivalency factors.

THC Total hydrocarbons. Refers to the total sum of hydrocarbon

compounds emitted during an emission test, standardized using

propane as the reference compound.

VOC Volatile organic compound. Any compound of carbon, excluding 

carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or 

carbonates, and ammonium carbonate, which participates in 

atmospheric photochemical reactions.
26

APPENDIX B

Fuel and Control Device Groupings
27

Table B.1: Fuel Category Constituents

Rank Fuel Category Inclusive Fuels

1 Coal

Anthracite Coal 

Bituminous Coal

Petroleum Coke

Sub-bituminous Coal

2 Bagasse Bagasse

3 Wet Biomass Wood: Bark

Wood: Unadulterated Timber

4 Dry Biomass

Hog Fuel

Plant-based Agricultural Residue

Sanderdust

Unspecified Biomass1

Wood: Lumber

5 Residual/Heavy 

Liquids

Alcohol: Ethanol

Alternative Liquid Fuel

Black Liquor

Deinking Residuals

Hexane

Industrial Sludge

Mixed liquid residues

No. 5 Fuel oil

No. 6 Residual oil

Other Petroleum-based Oils

Process coproduct liquid

Rectified methanol

Red oil (steam stripper steam condensate, incl terpenes, 

terpenoids, methanol, TRS)

Tall oil, tall oil derivatives

Turpentine

Used Petroleum-based Oils (unknown spec)

Used Petroleum-based Oils (on-spec)

6 Distillate/Light 

Liquids

Animal Fat/Oils/Tallow

Bio liquids

Diesel fuel

Jet Fuel

JP-8 Aviation Fuel

Kerosene

No. 2 Distillate

No. 4 Fuel oil

Vegetable Oil

yellow grease (used cooking oil)
28

Rank Fuel Category Inclusive Fuels

7 Process Gases

Acid Gas

Biogas

Blast Furnace Gas

CO gas

Coke Oven Gas

Ethane

Isobutane

Landfill Gas

Methane

Noncondensable Gas (includes stripper offgas)

Petrochemical process gas

Process coproduct gas

Process Gas

Pulp mill gas

8 Natural Gas Natural Gas

9 Other Non-Process 

Gases

Hydrogen

LPG

Pilot Gas

Propane

Refinery gas

10 Other Fuels

Knots and Knotter Rejects

Nitrile pitch residue

Paper and Paper Residues

Paper Pellets

Process coproduct solid

Reinjection char

Stripper condensate

Tire Derived Fuel (TDF) with metals removed

Wax
29

Rank Fuel Category Inclusive Fuels

11 Waste

1,4-butanediol

Boiler Cleaning agents

Cardboard

Cellulose fuel (balcones cubes)

Coal Refuse

Construction/Demolition Derived Material

Contraband

Envirofuel pellets/cubes

Filters

Fuel cubes (paper diaper clippings/refuse)

Municipal Sludge

Oily Paper Residues

Oily Rags

Paint Rags/Residues

Plastics

Refuse

Refuse Derived Fuel (RDF)

Resin Solid Residues

Screen Rejects

Spent Alcohol

Tar

Tire Derived Fuel (TDF) without metals removed

Tires (whole)

Toluene

Used Petroleum-based Oils (off-spec)

Used Solvents

Waste Derived Liquid Fuel

Wood: Treated

1 Unspecified biomass was reported in the questionnaire as “Biomass” and was assumed to be dry.
30

Table B.2.A: Inorganic and SO2 Control Groupings

Control Group Control Device

1

Spray Dryer

Wet Scrubber

Wet Scrubber

2

Dry Scrubber

Dry Scrubber (Lime Injection)

Scrubber (unknown)

3

Dry Sorbent Injection

Duct Sorbent Injection

Furnace Sorbent Injection

Wet Lime Injection

Wet Sorbent Injection

4 Venturi Scrubber

5

Activated Carbon Adsorption or Injection

Cyclone or Multiclone

Dry Electrostatic Granular Filter

Electrified Filter Bed (EFB)

Electrostatic Precipitator

Fabric Filter

Mist Eliminator

No HAP APCD Control
31

Table B.2.B: Mercury (Hg) Control Groupings

Control Group Control Device

1 Activated Carbon Adsorption or Injection

2

Fabric Filter/Dry Srubber (Lime Injection)/SNCR

Fabric Filter/Wet Lime Injection

Fabric Filter/Dry Scrubber

Fabric Filter/Dry Sorbent Injection

Fabric Filter/Duct Sorbent Injection

Fabric Filter/Furnace Sorbent Injection

Fabric Filter/Spray Dryer

Fabric Filter/Wet Scrubber

3 Fabric Filter

4 Wet Scrubber

5 Venturi Scrubber

6

Cyclone or Multiclone

Dry Electrostatic Granular Filter

Dry Scrubber

Dry Sorbent Injection

Duct Sorbent Injection

Electrified Filter Bed (EFB)

Electrostatic Precipitator

Mist Eliminator

No HAP APCD Control

Scrubber (unknown)

Spray Dryer
32

Table B.2.C: Particulate Matter (PM) Control Groupings

Control Group Control Device

1 Fabric Filter

2 Electrified Filter Bed (EFB)

Electrostatic Precipitator

3 Venturi Scrubber

4 Wet Scrubber

5 Cyclone or Multiclone

Dry Electrostatic Granular Filter

6

Activated Carbon Adsorption or Injection

Dry Scrubber

Dry Sorbent Injection

Duct Sorbent Injection

Mist Eliminator

No HAP APCD Control

Scrubber (unknown)

Spray Dryer
33

Table B.2.D: Metallic HAP Control Groupings

Control Group Control Device

1 Fabric Filter

2 Electrified Filter Bed (EFB)

Electrostatic Precipitator

3 Venturi Scrubber

4 Wet Scrubber

5 Cyclone or Multiclone

Dry Electrostatic Granular Filter

6

Activated Carbon Adsorption or Injection

Dry Scrubber

Dry Sorbent Injection

Duct Sorbent Injection

Mist Eliminator

No HAP APCD Control

Scrubber (unknown)

Spray Dryer
34

APPENDIX C

PERCENT REDUCTIONS

(See Excel spreadsheets)
35

APPENDIX D

MAJOR SOURCE BASELINE EMISSION FACTORS

(See Excel spreadsheet)
36

APPENDIX E

AREA SOURCE BASELINE EMISSION FACTORS

(See Excel spreadsheet)