Date: January 9, 2013

Subject: Kraft Pulping Liquor and Woody Biomass Methane (CH4) and Nitrous Oxide 

(N2O) Emission Factor Literature Review 

EPA Contract No. EP-W-11-054; Task Order No. 04

From: Katie Hanks

Corey Gooden

To: Mike Hannan

U.S. Environmental Protection Agency

Washington, DC 20460 

I. Introduction

On November 16, 2012 the American Forest & Paper Association (AF&PA) and the 

American Wood Council (AWC) petitioned the U.S. Environmental Protection Agency (EPA) to

reconsider and revise the methane (CH4) and nitrous oxide (N2O) emission factors within 40 

CFR Part 98, Subparts AA and C for combustion of spent pulping liquor and wood residuals.

These emission factors are used to calculate and report annual emissions from pulp mill recovery

furnaces and wood-fired stationary combustion units under EPA’s mandatory greenhouse gas 

reporting program (GHGRP). In support of their petition, AF&PA and AWC (the “petitioners”) 

submitted a recent study performed by the National Council for Air and Stream Improvement 

(NCASI), Technical Bulletin 998, which contains new CH4 and N2O emissions test data that 

were not previously available to the GHGRP. Table 1 summarizes the existing GHGRP emission 

factors and the revised emission factors recommended by the petitioners.

Table 1 – Comparison of Existing and Recommended CH4 and N2O Emission Factors

Greenhouse Gas

Existing GHGRP 

Emission Factor

(kg/MMBtu)

Petitioners’

Recommended Emission 

Factor

(kg/MMBtu)

Percent 

Difference 

(%)

Table AA-1 – Spent Pulping Liquor

Methane 0.030 0.0019 94

Nitrous Oxide 0.005 0.00042 92

Table C-2 – Solid Biomass

Methane 0.032 0.0049 85

Nitrous Oxide 0.0042 0.0019 55

The purpose of this memorandum is to review the basis for the current GHGRP spent 

pulping liquor and wood residual combustion emission factors, integrate the new CH4 and N2O 

emissions test data provided in NCASI Technical Bulletin 998 with previously available 
2

emissions test data, and recommend possible regulatory amendments based on this work. Section 

II of this memorandum discusses the recovery furnace (spent pulping liquor) emission factors. 

Section III discusses the wood and wood residuals emission factors.

II. Recovery Furnace CH4 and N2O Emission Factors

A. Recovery Furnace Literature Review 

The CH4 and N2O emission factors for kraft pulping liquor combustion in pulp mill 

recovery furnaces are provided in Table AA-1 of 40 CFR part 98 Subpart AA. Table AA-1 is 

reproduced in Exhibit 1 below. 

The CH4 and N2O emission factors in Table AA-1 were based on the World Resources 

Institute/World Business Council for Sustainable Development (WRI/WBCSD) protocol 

developed by NCASI in 2005.

1 Appendix A1 contains a reproduction of the CH4 and N2O 

emission factor summary table from the WRI/WBCSD protocol and Appendix A2 contains other 

relevant pages from the WRI/WBCSD protocol. As shown in Appendix A1, four international 

references were cited in the WRI/WBCSD protocol.

2,3,4,5 The median of three of the emission 

 1 Calculation Tools for Estimating Greenhouse Gas Emissions from Pulp and Paper

Mills. Version 1.1. July 8, 2005. Prepared by the National Council for Air and Stream

Improvement for The Climate Change Working Group of The International Council of

Forest and Paper Associations (ICFPA). http://www.wbcsd.org/web/projects/forestry/pulp-andpaper-tool-guidance.pdf

2 Japan Paper Association (JPA). 2002. Various personal communications between JPA and Reid 

Miner of NCASI. Tokyo: Japan Paper Association. 

3 Swedish Environmental Protection Agency (Swedish EPA). 2004. Sweden’s national

Exhibit 1

Table AA–1 to Subpart AA of Part 98—Kraft Pulping Liquor Emissions Factors for 

Biomass-Based CO2, CH4, and N2O

Wood furnish

Biomass-based emissions factors

(kg/mmBtu HHV)

CO2 a CH4 N2O

North American Softwood 94.4 0.030 0.005

North American Hardwood 93.7

Bagasse 95.5

Bamboo 93.7

Straw 95.1 a

Includes emissions from both the recovery furnace and pulp mill lime kiln.
3

factors from the references formed the basis for the CH4 emission factors recommended in the 

WRI/WBCSD protocol (0.0025 kg/MMBtu), and the median of two studies was the basis for the 

recommended N2O emission factor (0.002 kg/MMBtu). The second reference (JPA 2002) did not 

have an N2O factor and therefore could not be used in calculating the WRI/WBCSDrecommended median N2O emission factor. The fourth reference (EEA 2004) was mentioned in 

the WRI/WBCSD protocol for comparison, but was not used in calculating the WRI/WBCSDrecommended median CH4 and N2O emission factors.

Given that the WRI/WBCSD CH4 and N2O emission factors were based on only two or 

three references which appeared to be uncertain based on the wide range in emissions from the 

references, the highest of the referenced emission factors was selected for inclusion in the U.S. 

EPA’s GHGRP Table AA-1 as a conservative measure. The highest values chosen from the 

WRI/WBCSD protocol for Table AA-1 were 30 kilograms (kg) of CH4 per terajoule (TJ) which 

converts to 0.030 kg CH4 per million British thermal units [MMBtu] and 5 kg N2O/TJ (0.005 

kg/MMBtu). These emission factors originated from the Swedish EPA report. The 0.030 kg 

CH4/MMBtu and 0.005 kg N2O/MMBtu emission factors were included in the original

greenhouse gas reporting rule (74 FR 16448, April 10 2009).

In their November 2012 petition for rulemaking, the petitioners stated that the current 

Table AA-1 emission factors (0.030 kg CH4/MMBtu and 0.005 kg N2O/MMBtu) are overly 

conservative, especially in light of the new information submitted in NCASI Technical Bulletin 

998. To investigate the petitioners’ concerns, RTI searched for each of the references from the 

WRI/WBCSD protocol to determine whether the references contained actual emissions test data 

that could be compared to the new data in Technical Bulletin 998.

We were unable to locate any formal documentation of the JPA 2002 reference from the 

WRI/WBCSD protocol. We successfully located the remaining references, and found that only 

Fortum 2001 contained actual emissions test data. The Fortum study is discussed further in 

Section II.B of this memorandum.

The Swedish EPA 2004 report documents Sweden’s national GHG inventory but does 

not include actual emissions test data. The N2O emission factor for spent pulping liquor was 

confirmed in the reference documentation, but the CH4 value of 30 kg/TJ was not. It appears that 

the same CH4 emission factor for wood waste was used for spent pulping liquor. Appendix B

provides the emission factor tables from the Swedish EPA report.

 

inventory report 2004 – Submitted under the United National Convention on Climate

Change. Stockholm: Swedish Environmental Protection Agency.

http://www.internat.naturvardsverket.se/documents/pollutants/climate/climate/fcccdata/N

IR.pdf (27 October 2004).

4 Fortum Power and Heat Oy (Fortum). 2001. Methane and nitrous oxide emissions in the 

Finnish energy production. Fortum, Finland: Fortum Power and Heat Oy, Technology.

5 European Environment Agency (EEA). 2004. EMEP/CORINAIR Emission Inventory 

Guidebook - Third edition, September 2004 Update. Copenhagen: European Environment

Agency. http://reports.eea.eu.int/EMEPCORINAIR4/en (27 October 2004).
4

The EEA 2004 reference is an update of the EMAP/CORINAIR Emissions inventory 

guidebook – Third edition. We did not locate the 2004 version of this document, but found that it 

was replaced with a 2006 version (and a 2007 version was available). We were unable to locate 

the 2004 emission factors using the newer document but we note that the EEA 2004 emission 

factor range (as referenced in the WRI/WBCSD protocol) is nearly the same as the range of 

emission factors provided in the 2006 Intergovernmental Panel on Climate Change (IPCC) 

Guidelines (IPCC 2006).

6 The table from IPCC 2006 that contains the spent pulping liquor 

emission factors is reproduced in Appendix C1. The IPCC 2006 emission factors for spent 

pulping liquor are:

• 1 to 18 kg CH4/TJ (0.001 to 0.019 kg CH4/MMBtu) with a recommended default of 3 kg 

CH4/TJ (0.0032 kg CH4/MMBtu), and 

• 1 to 21 kg N2O/TJ (0.001 to 0.022 kg N2O/MMBtu) with a recommended default of 2 kg 

N2O/TJ (0.002 kg N2O/MMBtu)

The IPCC 2006 report refers back to the 1996 IPCC Reference Manual as the source of the 

default emission factors included in IPCC 2006 Table 2.3 for the manufacturing and construction 

industries. However, as shown in Appendix C2, the 1996 Reference Manual does not include 

emission factors for spent puling liquor combustion. We were unable to determine the basis for 

the range of emission factors for spent pulping liquor in either EEA 2004 or IPCC 2006. No 

emissions test data were available in either document. 

B. Recovery Furnace Emissions Test Data

As mentioned previously, the only reference we located with spent pulping liquor CH4

and N2O emissions test data was Fortum 2001. The Fortum report provides emission factors 

derived from Fourier Transform Infrared Spectroscopy (FTIR) and non-dispersive infrared 

(NDIR) testing of two recovery furnaces located at a pulp mill in Finland. One of the furnaces 

was tested twice (once with spent liquor derived from softwood furnish and once with hardwood 

furnish). Appendix D contains the Fortum study. It appears that each test included only one 

measurement (e.g., one test run). The CH4 and N2O emissions averages from all three tests were 

less than or equal to 1 milligram per megajoule (mg/MJ) (0.0011 kg/MMBtu). 

The most commonly referenced compilations of pulp mill emission factors in the U.S. 

include EPA’s AP-42 Section 10.2 on Chemical Wood Pulping (dated September 1990), 7 and

more recent NCASI Technical Bulletins 973 (February 2010) and 884 (August 2004). 8, 9

 6

2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse 

Gas Inventories. Intergovernmental Panel on Climate Change. Accessed at http://www.ipccnggip.iges.or.jp/public/2006gl/index.html

7

AP 42, Fifth Edition, Volume I Chapter 10: Wood Products Industry. Section 10.2 – Chemical 

Wood Pulping. September 1990. Available at 

http://www.epa.gov/ttn/chief/ap42/ch10/final/c10s02.pdf

8 NCASI. Compilation of ‘Air Toxic’ and Total Hydrocarbon Emissions Data for Pulp and Paper 

Mill Sources – A Second Update. Technical Bulletin 973. February 2010. 

9 NCASI. Compilation of Criteria Air Pollutant Emissions Data for Sources at Pulp and Paper 

Mills Including Boilers, Technical Bulletin 884. August 2004.
5

However, no CH4 or N2O emission factors are available in these documents for recovery furnace 

spent pulping liquor combustion.

The recent NCASI Technical Bulletin 998 submitted by petitioners contains FTIR testing 

of eight recovery furnaces using ASTM 6348-03.10 The U.S. EPA reference method for FTIR 

emissions testing is Method 320 (Vapor Phase Organic & Inorganic Emissions by Extractive 

FTIR) in Appendix A to 40 CFR Part 63.11 The ASTM D6348-03 method NCASI used for the 

CH4 and N2O testing is incorporated by reference into 40 CFR 63.14(b) as an approved 

alternative to Method 320 under two national emission standards for hazardous air pollutants 

(NESHAP) affecting the forest products industry.

Technical Bulletin 998 documents emissions testing from three non-direct contact 

evaporator (NDCE) recovery furnaces and five direct contact evaporator (DCE) recovery 

furnaces. All of the recovery furnaces tested processed spent pulping liquor derived from kraft 

pulping of hardwood or softwood feedstock. None of the furnaces processed any spent liquor 

derived from bagasse, bamboo, or straw. The kraft process is the most commonly used pulping 

process in the U.S. No chemical recovery combustion units (CRCU) found at sulfite and 

semichemcial pulp mills were included in Technical Bulletin 998. Under the GHGRP, the Table 

AA-1 CH4 and N2O emissions factors for kraft pulping are used to estimate emissions for spent 

pulping liquor in CRCU because no other information is available. 

Table 2 summarizes the results of the recovery furnace tests from Technical Bulletin 998. 

The number of valid CH4 and N2O test runs ranged from three to 10. Consistent with EPA 

emission factor development procedures, values one half of the method detection limit (MDL)

were used in test averages when some of the test run results were non-detect (ND) but others 

were detected.

Although it might be expected that DCE recovery furnaces could have greater CH4

emissions than NDCE furnaces due to contact of the hot flue gases with incoming pulping liquor 

in the DCE, the ranges of CH4 and N2O emissions reported in Technical Bulletin 998 overlap for 

the NDCE and DCE recovery furnaces. Therefore, it is reasonable for the GHGRP to continue to 

make no distinction between DCE and NDCE recovery furnaces and to consider test data from 

both types of furnaces together in a consolidated emission factor. Similarly, the ranges of the test 

results overlapped for liquor derived from hardwood and softwood feedstocks, and across air 

pollution control device types (wet bottom electrostatic precipitator [WBESP] and dry bottom 

electrostatic precipitator [DBESP]).

 10 ASTM D6348-03, Standard Test Method for Determination of Gaseous Compounds by 

Extractive Direct Interface Fourier Transform Infrared (FTIR) Spectroscopy.

11EPA Method 320. Vapor Phase Organic & Inorganic Emissions by Extractive FTIR. EPA’s 

CFR-promulgated air emissions measurement methods are available at 

http://www.epa.gov/ttn/emc/promgate.html 
Table 2. Summary of Recovery Furnaces Tested in Technical Bulletin 998

CH4, kg/MMBtu N2O, kg/MMBtu

ID

Mill 

type

RF 

type

Spent 

liquor 

feedstock

Other 

fuels Control

No. 

runs

No. 

ND 

runs Min Max Average

No. 

runs

No. 

ND 

runs Min Max Average

BRF5 kraft NDCE softwood DBESP 3 1 0.00039 0.001 0.00093 5 0 0.00062 0.0011 0.00082

DRF1 kraft NDCE softwood DBESP 8 7 0.000034 0.000047 0.000042 7 3 0.00012 0.00018 0.00015

ERF1 kraft NDCE softwood ESP 10 0 0.000065 0.0057 0.0031 10 7 0.000099 0.00065 0.00034

ARF3 kraft DCE softwood

No. 6 

oil DBESP 10 1 0.00008 0.00068 0.0002 9 0 0.00013 0.00043 0.00027

FRF1 kraft DCE unspecified WBESP 6 0 0.002 0.016 0.01 6 0 0.00044 0.00085 0.00065

FRF3 kraft DCE unspecified WBESP 9 0 0.00026 0.0021 0.0011 9 0 0.00034 0.00076 0.00049

GRF1 kraft DCE hardwood DBESP 6 5 0.0001 0.00015 0.00011 6 0 0.00012 0.00031 0.0002

GRF2 kraft DCE hardwood WBESP 5 0 0.0001 0.00016 0.00013 6 0 0.000092 0.00033 0.00019

The average was based on 1/2-MDL values for 

ND runs. Average: 0.00195 0.00039

min 0.000042 0.00015

max 0.01 0.00082

median 0.000565 0.000305
Only one of the eight furnaces tested burned a small amount of fossil fuel during the 

tests. Thus, the emission factors in Technical Bulletin 998 are representative of the biogenic CH4

and N2O emissions from recovery furnaces. Fossil fuel emissions from recovery furnaces are 

estimated separately using equations and emission factors under Subpart C of the GHGRP. 

The petitioners requested that EPA replace the current GHGRP Table AA-1 CH4 and 

N2O emission factors with the average factors from Technical Bulletin 998, specifically 0.0019 

kg CH4/MMBtu and 0.00042 kg N2O/MMBtu. [We note that the petitioners’ recommendation of 

0.00042 kg N2O/MMBtu does not exactly match the average N2O emission factor of 0.00039 kg 

N2O/MMBtu calculated in Table 2, likely due to rounding of the average emission factors from 

each test when they were reported in technical Bulletin 998.] Based upon the literature we 

reviewed, Technical Bulletin 998 appears to be the most recent and comprehensive source of 

U.S. recovery furnace CH4 and N2O emission factors available to date. 

The Fortum 2001 test data (the only other actual emissions data we located) compare 

fairly well with the data in NCASI Technical Bulletin 998. If the Fortum 2001 tests were 

included with the NCASI Technical Bulletin 998 data, the resultant emission factors would be 

0.0018 kg CH4/MMBtu and 0.00052 kg N2O/MMBtu as shown in Appendix E. Inclusion of the 

Fortum 2001 tests would have little effect of the petitioners’ suggested emission factors, but

continued application for the Fortum 2001 data for U.S. pulp mill recovery furnaces is 

questionable in light of more recent test data obtained by NCASI from repeated measurements of 

recovery furnaces at U.S. mills. Table 3 compares the emission factors in the GHGRP to those 

derived considering the Technical Bulletin 998 test data with and without the Fortum 2001 data. 

Table 3. Emission Factors for Spent Liquor Combustion in the GHGRP Table AA-1 

Compared to Emission Factors Derived from Available Emissions Test Data

Reference CH4, kg/MMBtu N2O, kg/MMBtu

GHGRP Table AA-1 0.03 0.005

Revised emission factors 

suggested by petitioners (TB 

998)

0.0019 0.000421

Average of all available data 

(TB 998 and Fortum 2001 as 

shown in Appendix E)

0.0018 0.00052

1. Calculated as 0.00039 in Table 2 of this memorandum, likely due to rounding. 
8

III. Wood and Wood Residuals Combustion CH4 and N2O Emission Factors

A. Wood and Wood Residuals Literature Review

The CH4 and N2O emission factors for combustion of solid biomass are provided in 

GHGRP Table C-2. Table C-2 contains one row for “Biomass Fuels-Solid (All fuel types listed 

in Table C-1).” Table C-1 of the GHGRP provides separate default higher heating values and 

carbon dioxide (CO2) emission factors for each type of solid biomass (wood and wood residuals, 

agricultural byproducts, peat, and solid byproducts). 

The existing Table C-2 emission factors are based on the Tier 1 emission factors for 

wood and wood waste in IPCC 2006. Appendix C1 of this memorandum contains the table from 

IPCC 2006 (Table 2-3) that was the source of the GHGRP Table C-2 solid biomass emission 

factors. The IPCC Tier 1 emission factors ranged from 10 to 100 kg CH4/TJ (0.011 to 0.11 kg 

CH4/MMBtu) and 1.5 to 15 kg N2O/TJ (0.0016 to 0.016 kg N2O/MMBtu). The default emission 

factors recommended by IPCC 2006 were 30 kg CH4/TJ (0.032 kg CH4/MMBtu) and 4 kg 

N2O/TJ (0.0042 kg N2O/MMBtu) on a net caloric value basis.

RTI traced the source of the IPCC 2006 Tier 1 emission factors back to the 1996 

Reference Manual. Relevant excerpts and the reference list from the 1996 Reference Manual are 

provided in Appendix C2 of this memorandum. The 1996 Reference Manual emission factors for 

many different fuels were based on, “the CORINAIR90 database, the CORINAIR 1994 default 

emission factors, the EDGAR Version 2.0 database, National Communications to the FCCC, 

Berdowski, et al. (1993a and 1993b), Radian Corporation (1990) and US EPA (1995).” RTI was 

able to obtain three of these references (National Communications to the FCCC, Radian 

Corporation 1995, and US EPA 1995), but did not find any actual emissions test data in the 

references. RTI was unable to locate the other references from the IPCC Reference Manual. The 

IPCC Reference Manual states that “additional research will need to be undertaken to further 

improve the quality of the emission factors.” The 1996 Reference Manual contained a Tier 2 

emission factor for CH4 of 15 kg CH4 /TJ (0.016 kg CH4/MMBtu) in addition to the Tier 1 

default factors adopted in the GHGRP. The Tier 2 emission factor was based on US EPA 1995.

The 2005 WRI/WBCSD protocol recommended an emission factor of 12 kg CH4/TJ 

(0.012 kg CH4/MMBtu) and 4 kg N2O/TJ (0.0042 kg CH4/MMBtu) based on the median of 

emission factors from various studies, including the IPCC Tier 1 and Tier 2 emission factors. 

Table 4 lists the biomass combustion CH4 and N2O emission factor references from the 

WRI/WBCSD protocol.
9

Table 4. References for the Biomass Emission Factors 

Included in the WRI/WBCSD Protocol

Abbreviated reference 

from WRI/WBCSD

protocol

Full reference

EEA 2004 European Environment Agency (EEA). 2004. EMEP/CORINAIR 

Emission inventory guidebook - Third edition, September 2004 Update. 

Copenhagen: European Environment Agency. 

IPCC 1997 Intergovernmental Panel on Climate Change (IPCC). 1997c. Revised 1996 

IPCC guidelines for national greenhouse gas inventories: Reference manual 

(Vol. 3). IPCC National Greenhouse Gas Inventory Program.

USEPA 2001 United States Environmental Protection Agency (USEPA). 2001. AP-42 

emission factors for wood residue combustion in boilers – Supplement G, July 

2001. Washington, DC: United States Environmental Protection Agency.

Fortum 2001 Fortum Power and Heat Oy (Fortum). 2001. Methane and nitrous oxide 

emissions in the Finnish energy production. Fortum, Finland: Fortum Power 

and Heat Oy, Technology.

NCASI 1980 National Council for Air and Stream Improvement, Inc. (NCASI). 1980. A 

study of wood residue fired power boiler total gaseous non-methane organic 

emissions in the Pacific Northwest. Air Quality Technical Bulletin No.109. 

Research Triangle Park, NC: National Council for Air and Stream 

Improvement, Inc.

NCASI 1985 National Council for Air and Stream Improvement, Inc. (NCASI). 1985. 

Volatile organic carbon emissions from wood residue fired power boilers in 

the Southeast. Technical Bulletin No.455. Research Triangle Park, NC: 

National Council for Air and Stream Improvement, Inc.

JPA 2002 Japan Paper Association (JPA). 2002. Various personal communications 

between JPA and Reid Miner of NCASI. Tokyo: Japan Paper Association.

AEA Tech. 2001 AEA Technology. 2001. UK greenhouse gas inventory 1990-1999: Annual 

report for submission under the Framework Convention on Climate Change. 

Oxfordshire, England: National Environmental Technology Centre.

Swedish EPA 2004 Swedish Environmental Protection Agency (Swedish EPA). 2004. Sweden’s 

national inventory report 2004 – Submitted under the United National 

Convention on Climate Change. Stockholm: Swedish Environmental 

Protection Agency.

The WRI/WCBSD protocol compared the emission factors from the above references to 

the emission factor range presented in EEA 2004. The EEA 2004 reference was not used in 

calculating the WRI/WBCSD-recommended median CH4 and N2O emission factors for woody 

biomass combustion. Appendix A1 contains a reproduction of the CH4 and N2O emission factor 

summary table from the WRI/WBCSD protocol and Appendix A2 contains other relevant pages 

from the WRI/WBCSD protocol.

RTI was unable to locate any formal documentation of the JPA 2002 reference from the 

WRI/WBCSD protocol. We successfully located the remaining references, and concluded that 

only USEPA 2001, Fortum 2001, NCASI 1980, and NCASI 1985 contained actual emissions test 

data. These studies are discussed further in Section III.B of this memorandum.
10

Appendix F presents the table containing emission factors for wood from the AEA 

Technology 2001 report

12 and indicates that the AEA Technology 2001 emission factors were 

based on CORINAIR (1992) and IPCC (1997). Emission factors for “Wood – Other Industry” 

appear to be the source of the emission factors included in the WRI/WBCSD protocol (although

for CH4 our conversions yielded an emission factor an order of magnitude lower than that 

reported in the WRI/WBCSD protocol). Using 20 GJ/t of dry solids, we calculated emission 

factors of 2.4 kg CH4/TJ and 3.5 kg N2O/TJ as opposed to the 24 kg CH4/TJ and 3.4 kg N2O/TJ 

provided in the WRI/WBCSD protocol. Either we were unable to identify the exact emissions 

factors used from the AEA Technology 2001 report, or possibly there was a decimal place typo 

in the WRI/WBCSD CH4 emission factor. The AEA Technology 2001 report did not contain any 

actual emissions test data for woody biomass CH4 and N2O. 

The Swedish EPA 2004 report documents Sweden’s national GHG inventory and did not 

include emissions testing. Appendix B of this memo provides the emission factor tables from the 

Swedish EPA report.

B. Wood and Wood Residuals Emissions Test Data

The only sources of actual emissions test data for CH4 or N2O RTI was able to locate to 

date include EPA’s AP-42 (USEPA 2001), Fortum 2001, NCASI 1980, NCASI 1985 and the 

new test data (new testing and boiler MACT data) used in NCASI Technical Bulletin 998. Tables 

6A and 6B in this section present the test results from each of these references.

The EPA’s AP-42 Chapter 1.6 contains a CH4 emission factor based on four emissions 

tests and an N2O emission factor based on two tests. The 1998 Industrial Combustion 

Coordinated Rulemaking (ICCR) data base was the source of the four CH4 tests. The N2O tests 

were conducted prior to 1993 and referenced from a prior AP-42 report. 

Fortum 2001 is a Finnish study that contains CH4 and N2O emissions testing for six

biomass boilers. Three of the boilers were tested with different fuel mixtures, for a total of nine 

fuel mixture test scenarios. The average of the results for the nine tests was reported in the 

WRI/WBCSD protocol. Review of Fortum 2001 reveals that only five of the tests involved

woody biomass, and three of these tests were for boilers burning 50 percent or more of peat. The 

other four tests were for boilers burning peat or a combination of peat and sludge (which was not 

described as industrial or municipal sludge so we interpreted this sludge to likely differ from 

forest products wastewater treatment residuals). Peat is turf resulting from an accumulation of 

partially decayed vegetation and is arguably different from woody biomass. Table C-1 in the 

GHGRP distinguishes peat from wood and wood residuals. The IPCC 2006 guidelines treat peat 

as fossil carbon due to the long length of time it takes to replace harvested peat.13

 12 http://uk-air.defra.gov.uk/library/reports?report_id=8

13IPCC 2006, p. G.3. http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/0_Overview/V0_2_Glossary.pdf
11

The Fortum 2001 study does not specify the number of measurements (test runs) 

performed during each of the tests, so it is unclear if a three-run test was performed as is 

customary in the U.S. for stack testing. Table 5 below presents the results of the Fortum 2001

testing converted to kg/MMBtu. Poor combustion (e.g., high carbon monoxide emissions) was 

noted for one of the bark boiler tests (BFB2). This test was excluded from the WRI/WBCSD 

protocol. The three tests where at least 50 percent woody biomass was burned are included in the 

summary Tables 6A and 6B later in this section. The BFB2 CH4 test was also included in Table 

6A because the results are the same order of magnitude as two other tests noted in Technical 

Bulletin 998 (also noted for poor combustion). It is reasonable to expect that similar poor 

combustion could occur in some U.S. boilers (as evidenced by the two high CH4 tests in the 

boiler MACT data set documented in Technical Bulletin 998).

Table 5. Fortum 2001 Results from Emission Testing of Biomass Boilers in Finland

Unit Fuel CH4, kg/TJ

CH4, 

kg/MMBtu N2O, kg/TJ

N2O, 

kg/MMBtu

Circulating Fluidised Bed Boilers

CFB1 peat 1 0.0011 < 2 0.0021

CFB1

peat, wood 

(15%) 1 0.0011 4 0.0042

CFB2

peat, wood 

(20%) 1 0.0011 3 0.0032

CFB3 peat < 1 0.0011 26 0.0274

CFB3 bark 1 0.0011 10 0.0105

CFB 

Average 1 0.0011 9.0 0.0095

Bubbling Fluidised Bed Boilers

BFB1 peat 2 0.0021 < 1 0.0011

BFB2 bark * 72 0.0759 < 2 0.0021

BFB3

peat, bark 

(50%) < 1 0.0011 < 2 0.0021

BFB3 peat, sludge 3 0.0032 < 2 0.0021

BFB 

Average 19.5 0.017 3.2 0.0034

Overall 

average 0.0097 0.0061

*Poor combustion conditions.

As mentioned previously, the emission factors reported in the WRI/WBCSD protocol 

from the two NCASI technical bulletins, TB 109 (NCASI 1980) and TB 455 (NCASI 1985) are 

based on actual emissions testing of multiple boilers so the emission factors from the two 

technical bulletins were included in Table 6A. Technical Bulletin 109 contains volatile organic 

carbon (VOC) emissions testing for four boilers, and Technical Bulletin 455 contains VOC 

testing for six boilers. RTI reviewed these technical bulletins and found CH4 concentration data. 

CH4 is usually measured as part of the total organic compounds in a gas, but is not a VOC. CH4
12

is sometimes reported separately if measured in conjunction with VOC. No flow rate data were 

reported with the concentration measurements in the two technical bulletins so we were unable to 

verify the emission factors reported in the WRI/WBCSD protocol or to extract boiler-specific 

CH4 test results from the technical bulletins. The emission factors provided in Table 6A are the 

aggregated emission factors provided in the WRI/WBCSD protocol. 

The 2012 NCASI Technical Bulletin 998 submitted by petitioners contains FTIR testing 

of CH4 and N2O emissions from five pulp mill boilers using ASTM 6348-03. At least 90 percent

of the boiler heat input was from biomass during testing. In addition, NCASI Technical Bulletin 

998 provides results from a review of EPA Method 18 CH4 test data contained in EPA’s boiler 

maximum achievable control technology (MACT) data base for boilers firing more than 80 

percent of heat input as biomass. Predominantly woody biomass boilers of various designs 

(stoker, fluidized bed, fuel cell, dutch oven) firing wood, bark, or wastewater treatment (WWT) 

sludge were studied. 

RTI downloaded the boiler MACT data base referenced by the petitioners14 to determine 

if additional CH4 and N2O tests were available for major or area sources firing predominantly 

woody biomass. Consistent with Technical Bulletin 998, 19 methane tests (using EPA Method 

18) for major source boilers were identified in the data base. The units of measure in the data 

base were parts per million rather than kg/MMBtu. A code-breaker and more information (e.g., 

gas flow rates) would be needed to map the 19 tests in the data base to the 19 tests listed in 

Technical Bulletin 998. We suspect that NCASI used the original boiler MACT test reports to 

assemble the information in Technical Bulletin 998 as opposed to the information directly from 

the data base. No N2O tests were found in the data base (consistent with NCASI Technical 

Bulletin 998 which did not tabulate N2O data from the MACT testing). No additional CH4 or 

N2O tests were identified in the data base for area sources. From this we can infer that all of the 

available biomass CH4 data from the boiler MACT emissions testing data base was used in 

Technical Bulletin 998 (i.e., that tests were not chosen selectively). The control devices used on 

the biomass boilers included particulate matter controls (cyclone or multiclone, electrified filter 

bed [EFB], electrostatic precipitator [ESP], fabric filter) and other controls with unknown (or 

unpredictable) effect on methane (dry sorbent injection followed by an ESP or fabric filter, spray 

dryer and fabric filter, and wet scrubbers).

The new CH4 and N2O emissions test data provided in Technical Bulletin 998 and test 

data from other references are summarized in Tables 6A and 6B. The data shown in these tables 

represent measurements from combustion of various woody biomass fuels in different types of 

boilers. Poor combustion conditions were reported in three of the boilers tested for CH4. 

Combustion conditions can vary from boiler to boiler. For example, it has been documented that 

poor combustion leads to higher CH4 emissions, and fluidized bed combustors may operate 

within a range of combustion temperatures that favors formation of N2O.

15, 16 In addition, other 

 14 May 30, 2012 Boiler MACT Draft Emissions and Survey Results Databases. Available at: 

http://www.epa.gov/ttn/atw/boiler/boilerpg.html

15 Intergovernmental Panel on Climate Change (IPCC). 1997c. Revised 1996 IPCC guidelines for 

national greenhouse gas inventories: Reference manual (Vol. 3). IPCC National Greenhouse Gas 

Inventory Program.
13

wood-fired combustion sources with differing conditions (e.g., direct wood fired dryers) may use 

the GHGRP wood and wood residuals emission factors developed in this memo. Therefore, it 

seems reasonable to retain in Table 6A the tests where poor combustion was suspected as leading 

to higher CH4 emissions in order to account for variability and avoid underestimation of GHG 

emissions from wood-fired combustors. Similarly, given that some of the woody biomass boilers 

that report under the GHGRP are fluidized bed boilers, it seems reasonable to retain the Fortum 

data for fluidized bed boilers in the N2O data set in order to avoid underestimation of N2O 

emissions.

 16 Fortum Power and Heat Oy (Fortum). 2001. Methane and nitrous oxide emissions in the 

Finnish energy production. Fortum, Finland: Fortum Power and Heat Oy, Technology.
14

Table 6A. Methane Emissions Test Data from Technical Bulletin 998 and Other References

Count Data Source Source ID Test Date APCD

CH4, 

kg/MMBtu Min run Max run No. runs note

1

TB 998 -NCASI 

Testing ABB2 7/8/2008 wet scrubber 0.0011 0.00044 0.0016 4 stoker-bark

2 CCB4 12/2/2008 ESP 0.0031 0.0004 0.0077 6 stoker-bark, no. 6 oil

3 DBB1 2/18/2009 ESP 0.00028 0.00017 0.00047 10 stoker-bark

4 FBB1 3/23/2009

2 boilers with 

common wet 

scrubber 0.041 0.017 0.078 10

poor combustion; 2 wood 

stokers

5 GCB3 6/10/2009 Wet scrubber 0.00068 0.00054 0.00099 6 stoker-bark, no. 6 oil

6 TB 998 -MACT HCB1 7/15/2009 Not Reported 0.00012 0.00011 0.00012 3 [all ND] bark, resin wood

7 ICB1 7/14/2009 Not Reported 0.0018 0.0016 0.002 3 hog fuel, MSW, gas

8 JCB2 7/1/2009 Not Reported 0.0076 0.0037 0.01 3 bark, TDF, oil

9 KCB2 8/4/2009 Not Reported 0.00043 0.00029 0.00061 3 bark

10 LCB1 8/13/2009 Not Reported 0.00072 0.00037 0.00092 3 wood/bark

11 MCB3 8/6/2009 Not Reported 0.00032 0.00022 0.00048 3 wood waste

12 NCB1 8/6/2009 Not Reported 0.001 0.0005 0.0014 3 bark

13 OCB4 8/11/2009 Not Reported 0.00023 0.00015 0.00031 2

bark, oil, gas; 1 run omitted 

(0.00371 kg/mmbtu)

14 PCB4 8/5/2009 Not Reported 0.00018 0.00016 0.00021 3 bark, WWT sludge, TDF

15 QCB8 7/29/2009 Not Reported 0.0007 0.00064 0.00076 3 WWT sludge, bark

16 RCB1 9/2/2009 Not Reported 0.0016 0.00046 0.0036 3 bark

17 SCB1 8/14/2009 Not Reported 0.0022 0.00078 0.0047 3

bark, cross ties, gas, WWT 

sludge

18 TCB1 8/11/2009 Not Reported 0.0015 0.00053 0.0024 3 wood

19 UCB2 6/24/2009 Not Reported 0.0027 0.00075 0.005 3

wood/bark, WWT sludge, 

OCC rejects, gas

20 VCB2 8/6/2009 Not Reported 0.0012 0.00055 0.0023 3

bark, WWT sludge, cross 

ties, gas

21 WCB1 7/30/2009 Not Reported 0.0012 0.00093 0.0014 3

bark, OCC rejects, gas, 

WWT sludge

22 XCB1 8/13/2009 Not Reported 0.0052 0.003 0.0056 3 bark

23 YCB1 8/6/2009 Not Reported 0.046 0.032 0.056 3 poor combustion; bark, gas

24 ZCB1 10/8/2009 Not Reported 0.0048 0.0034 0.0046 3 bark

25 AACB1 7/29/2009 Not Reported 0.0048 0.00091 0.011 3 wood/bark

26 ABCB1 7/23/2009 Not Reported 0.0007 0.00063 0.00084 3 bark/wood

27 ACCB1 7/29/2009 Not Reported 0.00051 0.00014 0.00096 3 bark
15

Count Data Source Source ID Test Date APCD

CH4, 

kg/MMBtu Min run Max run No. runs note

28 NCASI 1980 pre-1980 None 0.0086 Avg EF

Pre-1980 stoker ahead of 

control device

29 NCASI 1985 pre-1985 Wet Scrubber 0.0028 Avg EF

Pre-1980 stoker after 

scrubber

30 Fortum 2001 CFB3 pre-2001 None1 0.0011 FB-bark

31 BFB2 pre-2001 None1 0.0759 FB-bark; poor combustion

32 BFB3 pre-2001 None1 0.0011 FB-peat, bark (50%); ND

33 AP-42, Ch 1.6 B109 9/24/1996 Wet Scrubber 0.020 0.037 0.053 3 Bark/Wet Wood

34 B47 6/1/1995 Fabric Filter 0.0030 0.0055 0.0090 3

Wet Wood. B47 & B48 are 

dual stacks on the same 

boiler.

35 B48 6/1/1995 Fabric Filter 0.0052 0.00016 0.025 3

Wet Wood. B47 & B48 are 

dual stacks on the same 

boiler.

36 B49 12/22/1994 ESP 0.0091 0.010 0.032 3 Wet Wood

NCASI Min 0.00012

TB 998 Max 0.046

Average 0.0049

Stdev 0.011

Median 0.0012

All Min 0.00012

Max 0.076

Average 0.0072

Stdev 0.016

Median 0.0016

All but Min 0.00012

Fortum Max 0.046

Average 0.0055

Stdev 0.011

Median 0.0016

Current GHGRP Table C-2 Factor 0.032

1. The report stated that all tests were completed with no limestone feed. 
16

Table 6B. N2O Emissions Test Data from Technical Bulletin 998 and Other References

Count Data Source Source ID Test Date APCD

N2O, 

kg/MMBtu Min run Max run No. runs note

1

TB 998 -NCASI 

Testing ABB2 7/8/2008 wet scrubber 0.0027 0.0014 0.004 5 stoker-bark

2 CCB4 12/2/2008 ESP 0.0015 0.0012 0.0019 6 stoker-bark, no. 6 oil

3 DBB1 2/18/2009 ESP 0.0011 0.00062 0.0013 10 [2 ND] stoker-bark

4 FBB1 3/23/2009

2 boilers with 

common wet 

scrubber 0.00073 0.00028 0.0023 10 [2 ND]

poor combustion; 2 

wood stokers

5 GCB3 6/10/2009 Wet scrubber 0.0034 0.002 0.0048 6 stoker-bark, no. 6 oil

6 Fortum 2001 CFB3 pre-2001 None1 0.0105 FB- bark

7 BFB2 pre-2001 None1 0.0021 FB-bark; ND

8 BFB3 pre-2001 None1 0.0021

FB- peat, bark (50%); 

ND

9 AP-42, Ch 1.6 pre-1993 Not Reported 0.010 FBC-Wet Wood

10 pre-1993 Not Reported 0.0020 Stoker-Wet Wood

NCASI Min 0.00073

TB 998 Max 0.0034

Average 0.0019

Stdev 0.0011

Median 0.0015

All Min 0.00073

Max 0.011

Average 0.0036

Stdev 0.004

Median 0.0021

All but Min 0.00073

Fortum Max 0.010

Average 0.0031

Stdev 0.0032

Median 0.0020

Current GHGRP Table C-2 Factor 0.0042

1. The report stated that all tests were completed with no limestone feed. 
17

Based upon the literature reviewed, Technical Bulletin 998 appears to be the most recent 

and comprehensive source of wood-fired boiler CH4 and N2O emission factors available to date. 

The data presented in Technical Bulletin 998 could be used alone or in conjunction with older 

emissions test data to add a row to the GHGRP Table C-2 with emission factors for wood and 

wood residuals. Table 7 summarizes the current solid biomass emission factors in Table C-2, the 

revised emission factors requested by petitioners based on NCASI TB 998, and other alternatives 

incorporating older emissions test data. The current GHGRP Table C-2 factors are not limited to 

woody biomass and apply for “Biomass Fuels-Solid (All fuel types listed in table C-1).” 

However, the test data presented in Tables 6A and 6B are based primarily on boilers firing wood 

and wood residuals. Therefore, EPA could add a row to Table C-2 for “wood and wood 

residuals” similar to the current Table C-1, and leave the existing Table C-2 biomass factors for 

other forms of solid biomass.

Table 7. Emission factors for Wood and Wood Residuals Derived from the Available Data

Reference CH4, kg/MMBtu N2O, kg/MMBtu

GHGRP (based on IPCC 

2006)

0.032 0.0042

Revised emission factors 

suggested by petitioners (TB 

998)

0.0049 0.0019

Average of all available data 0.0072 0.0036

Average of available data 

without Fortum 2001

0.0055 0.0031

 

IV. Summary and Conclusions

RTI performed a literature review to document the basis for the existing GHGRP CH4

and N2O emission factors in Subpart AA for spent pulping liquor and in Subpart C for solid 

biomass fuels (specifically wood and wood residuals). The purpose of the literature review was 

to locate additional emission testing results that could be compared to new information (NCASI 

Technical Bulletin 998) supplied through a November 2012 petition for rulemaking. RTI found 

that few of the previously referenced sources of CH4 and N2O emission factors were based on 

actual emission test data, and that the few references containing test data were dated and/or based 

on emissions sources outside of the U.S. The information provided in NCASI Technical Bulletin 

998 appears to be the more robust than previous references due to the number and variety of U.S. 

emission sources for which recent test data are provided. The EPA can use the summary 

information presented in this memorandum to consider whether to adopt the emission factors 

suggested by the petitioners based on NCASI Technical Bulletin 998 or to combine the new data 

with previously available emission test data in order to revise the CH4 and N2O emission factors 

in Table AA-1 and C-2. 
Appendix A

Excerpts from the WRI/WBCSD Protocol, Calculation Tools for Estimating Greenhouse 

Gas Emissions from Pulp and Paper Mills, Version 1.1, July 8, 2005

Appendix A1: Biomass Combustion CH4 and N2O Emission Factor Summary Table from the 

WRI/WBCSD Protocol

Appendix A2: Additional Excerpts from the WRI/WBCSD Protocol

Available at: 

http://www.wbcsd.org/web/projects/forestry/pulp-and-paper-tool-guidance.pdf
Appendix B

Emission Factor Tables from Swedish EPA 2004

Available at: 

http://s3.amazonaws.com/zanran_storage/www.lansstyrelsen.se/ContentPages/70817864.pdf
Appendix C

IPCC Emission Factor Documentation

Appendix C1: Portion of 2006 IPCC Guidance Document Table 2.3, Default Emission Factors 

for Stationary Combustion in the Manufacturing Industries and Construction.

Available at: http://www.ipccnggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_2_Ch2_Stationary_Combustion.pdf

Appendix C2: Excerpts from the Revised 1996 IPCC Guidelines for National Greenhouse Gas 

Inventories Reference Manual (Volume 3), Chapter 1 – Energy.

Available at: http://www.ipcc-nggip.iges.or.jp/public/gl/invs6a.html
Appendix D

Fortum 2001 - 

Methane and nitrous oxide emissions in the Finnish energy production.

Available at:

http://energia.fi/sites/default/files/non-co2-raportti.pdf
Appendix E

Emission Factor Data from Fortum 2001 Combined with 

NCASI Technical Bulletin 998 Data
Appendix E. Emission Factor Data from Fortum 2001 Combined with NCASI Technical Bulletin 998 Data

(The Fortum 2001 data are shaded.)

CH4, kg/MMBtu N2O, kg/MMBtu

ID

Mill 

type

RF 

type

Spent 

liquor 

feedstock

Other 

fuels Control

No. 

runs

No. 

ND 

runs Min Max Average

No. 

runs

No. 

ND 

runs Min Max Average

BRF5 kraft NDCE softwood DBESP 3 1 0.00039 0.001 0.00093 5 0 0.00062 0.0011 0.00082

DRF1 kraft NDCE softwood DBESP 8 7 0.000034 0.000047 0.000042 7 3 0.00012 0.00018 0.00015

ERF1 kraft NDCE softwood ESP 10 0 0.000065 0.0057 0.0031 10 7 0.000099 0.00065 0.00034

ARF3 kraft DCE softwood

No. 6 

oil DBESP 10 1 0.00008 0.00068 0.0002 9 0 0.00013 0.00043 0.00027

FRF1 kraft DCE unspecified WBESP 6 0 0.002 0.016 0.01 6 0 0.00044 0.00085 0.00065

FRF3 kraft DCE unspecified WBESP 9 0 0.00026 0.0021 0.0011 9 0 0.00034 0.00076 0.00049

GRF1 kraft DCE hardwood DBESP 6 5 0.0001 0.00015 0.00011 6 0 0.00012 0.00031 0.0002

GRF2 kraft DCE hardwood WBESP 5 0 0.0001 0.00016 0.00013 6 0 0.000092 0.00033 0.00019

RB1 unspecified softwood unspecified unspecified

RB1 unspecified hardwood unspecified 0.0011 unspecified 0.0011

RB2 unspecified softwood unspecified 0.0011 unspecified 0.0011

The average was based on 1/2-MDL values for 

ND runs. Average: 0.0018 0.00052

min 0.000042 0.00015

max 0.01 0.00105

median 0.00099 0.00042
Appendix F

Wood Emission Factors from AEA Technology 2001

Available at: http://uk-air.defra.gov.uk/library/reports?report_id=8