A-1

Annexes to the Inventory of U.S. GHG Emissions and Sinks 

The following seven annexes provide additional information related to the material presented in the main body of 

this report as directed in the UNFCCC Guidelines on Reporting and Review (GE.03-60887). Annex 1 contains an analysis 

of the key categories of emissions discussed in this report and a review of the methodology used to identify those key 

categories. Annex 2 describes the methodologies used to estimate CO2 emissions from fossil fuel combustion, the carbon 

content of fossil fuels, and the amount of carbon stored in products from non-energy uses of fossil fuels. Annex 3 

discusses the methodologies used for a number of individual source categories in greater detail than was presented in the 

main body of the report and includes explicit activity data and emission factor tables. Annex 4 presents the IPCC 

reference approach for estimating CO2 emissions from fossil fuel combustion. Annex 5 addresses the criteria for the 

inclusion of an emission source category and discusses some of the sources that are excluded from U.S. estimates. Annex 

6 provides a range of additional information that is relevant to the contents of this report. Annex 7 provides data on the 

uncertainty of the emission estimates included in this report. Finally, Annex 8 provides information on the QA/QC 

methods and procedures used in the development of the Inventory. 

ANNEX 1 Key Category Analysis ................................................................................................................................................................ 2

ANNEX 2 Methodology and Data for Estimating CO2 Emissions from Fossil Fuel Combustion ............................................................... 27

2.1. Methodology for Estimating Emissions of CO2 from Fossil Fuel Combustion ..................................................................... 27

2.2. Methodology for Estimating the Carbon Content of Fossil Fuels......................................................................................... 59

2.3. Methodology for Estimating Carbon Emitted from Non-Energy Uses of Fossil Fuels ......................................................... 98

ANNEX 3 Methodological Descriptions for Additional Source or Sink Categories................................................................................... 125

3.1. Methodology for Estimating Emissions of CH4, N2O, and Indirect Greenhouse Gases from Stationary Combustion....... 125

3.2. Methodology for Estimating Emissions of CH4, N2O, and Indirect Greenhouse Gases from Mobile Combustion and 

Methodology for and Supplemental Information on Transportation-Related GHG Emissions................................................................. 132

3.3. Methodology for Estimating Emissions from Commercial Aircraft Jet Fuel Consumption................................................. 164

3.4. Methodology for Estimating CH4 Emissions from Coal Mining .......................................................................................... 168

3.5. Methodology for Estimating CH4 and CO2 Emissions from Natural Gas Systems............................................................. 175

3.6. Methodology for Estimating CH4 and CO2 Emissions from Petroleum Systems ............................................................... 202

3.7. Methodology for Estimating CO2, N2O and CH4 Emissions from the Incineration of Waste .............................................. 209

3.8. Methodology for Estimating Emissions from International Bunker Fuels used by the U.S. Military .................................. 214

3.9. Methodology for Estimating HFC and PFC Emissions from Substitution of Ozone Depleting Substances ...................... 219

3.10. Methodology for Estimating CH4 Emissions from Enteric Fermentation............................................................................ 240

3.11. Methodology for Estimating CH4 and N2O Emissions from Manure Management ............................................................ 258

3.12. Methodology for Estimating N2O Emissions and Soil Organic C Stock Changes from Agricultural Soil Management 

(Cropland and Grassland)........................................................................................................................................................................ 287

3.13. Methodology for Estimating Net Carbon Stock Changes in Forest Lands Remaining Forest Lands ................................ 338

3.14. Methodology for Estimating CH4 Emissions from Landfills................................................................................................ 367

ANNEX 4 IPCC Reference Approach for Estimating CO2 Emissions from Fossil Fuel Combustion ....................................................... 385

ANNEX 5 Assessment of the Sources and Sinks of Greenhouse Gas Emissions Not Included............................................................. 395

ANNEX 6 Additional Information.............................................................................................................................................................. 397

6.1. Global Warming Potential Values ...................................................................................................................................... 397

6.2. Ozone Depleting Substance Emissions............................................................................................................................. 406

6.3. Sulfur Dioxide Emissions ................................................................................................................................................... 407

6.4. Complete List of Source Categories .................................................................................................................................. 409

6.5. Constants, Units, and Conversions ................................................................................................................................... 410

6.6. Abbreviations ..................................................................................................................................................................... 412

6.7. Chemical Formulas............................................................................................................................................................ 417

ANNEX 7 Uncertainty............................................................................................................................................................................... 421

7.1. Overview............................................................................................................................................................................ 421

7.2. Methodology and Results .................................................................................................................................................. 421

7.3. Planned Improvements...................................................................................................................................................... 428

7.4. Additional Information on Uncertainty Analyses by Source ............................................................................................... 429

ANNEX 8 QA/QC Procedures.................................................................................................................................................................. 450

8.1. Background........................................................................................................................................................................ 450

8.2. Purpose.............................................................................................................................................................................. 450

8.3. Assessment Factors .......................................................................................................................................................... 451
A-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012

ANNEX 1 Key Category Analysis 

The United States has identified national key categories based on the estimates presented in this report. The 

IPCC’s Good Practice Guidance (IPCC 2000) describes a key category as a “[category] that is prioritized within the 

national inventory system because its estimate has a significant influence on a country’s total inventory of direct 

greenhouse gases in terms of the absolute level of emissions, the trend in emissions, or both.” By definition, key categories

are sources or sinks that have the greatest contribution to the absolute overall level of national emissions in any of the 

years covered by the time series. In addition, when an entire time series of emission estimates is prepared, a determination

of key categories must also account for the influence of the trends of individual categories. Therefore, a trend assessment 

is conducted to identify source and sink categories for which significant uncertainty in the estimate would have 

considerable effects on overall emission trends. Finally, a qualitative evaluation of key categories should be performed, in 

order to capture any key categories that were not identified in either of the quantitative analyses, but can be considered key 

because of the unique country-specific estimation methods.

The methodology for conducting a key category analysis, as defined by IPCC’s Good Practice Guidance (IPCC 

2000), IPCC’s Good Practice Guidance for Land Use, Land-Use Change, and Forestry (IPCC 2003), and IPCC’s 2006 

Guidelines for National Greenhouse Gas Inventories IPCC (2006); includes:

 Tier 1 approach (including both level and trend assessments); 

 Tier 2 approach (including both level and trend assessments, and incorporating uncertainty analysis); and 

 Qualitative approach.

This Annex presents an analysis of key categories, both for sources only and also for sources and sinks (i.e., 

including LULUCF); discusses Tier 1, Tier 2, and qualitative approaches to identifying key categories; provides level and 

trend assessment equations; and provides a brief statistical evaluation of IPCC’s quantitative methodologies for defining 

key categories. Table A- 1 presents the key categories for the United States (including and excluding LULUCF categories) 

using emissions and uncertainty data in this report, and ranked according to their sector and global warming potentialweighted emissions in 2012. The table also indicates the criteria used in identifying these categories (i.e., level, trend, Tier 

1, Tier 2, and/or qualitative assessments). 
A-186 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012

Table A-129: 2012 Data and CH4 Emissions (Mg) for the Natural Gas Transmission Stage

2012 EPA Inventory Values

Activity Activity Data Emission Factor (Potential)aa

Calculated 

Potential 

Emissions 

(Mg)

Fugitives

Pipeline Leaks 303,126 milesa,1 1.55 Scfd/ mileb 3,311.4 

Compressor Stations (Transmission) 

 Station 1,799 stationsc,2 8,778 Scfd/stationb 111,037.1 

 Reciprocating Compressor 7,235 compressors c,2 15,205 Scfd/ compressorb 773,294.3 

 Centrifugal Compressor (wet seals) 659 compressors d,2 50,222 Scfd/ compressord 232,825.7 

 Centrifugal Compressor (dry seals) 66 compressors d,2 32,208 Scfd/ compressord 14,971.9 

Compressor Stations (Storage) 

 Station 344 stations e,2 21,507 Scfd/ stationb 52,013.2 

 Reciprocating Compressor 1,012 compressors e,2 21,116 Scfd/ compressorb 150,224.7 

 Centrifugal Compressor (wet seals) 70 compressors d,2 45,441 Scfd/ compressord 22,346.7 

 Centrifugal Compressor (dry seals) 29 compressors d,2 31,989 Scfd/ compressord 6,531.7 

Wells (Storage) 16,042 wells b,2 115 Scfd/wellb 12,912.2 

M&R (Trans. Co. Interconnect) 2,698 stations c,2 3,984 scfd/stationb 75,573.6 

M& R (Farm Taps + Direct Sales) 80,009 stations c,2 31 scfd/stationb 17,548.7 

Vented and Combusted 

Dehydrator vents (Transmission) 1,146,991 MMscf/year b,2 93.72 scf/MMscfb 2,070.4 

Dehydrator vents (Storage) 1,782,492 MMscf/year b,2 117 scf/MMscfb 4,022.9 

Compressor Exhaust 

 Engines (Transmission) 50,908 MMHPhr b,2 0.24 scf/HPhrb 235,315.3 

 Turbines (Transmission) 12,147 MMHPhr b,2 0.01 scf/HPhrb 1,333.5 

 Engines (Storage) 4,387 MMHPhr b,2 0.24 scf/HPhrb 20,277.1 

 Turbines (Storage) 1,541 MMHPhr b,2 0.01 scf/HPhrb 169.2 

 Generators (Engines) 2,491 MMHPhr b,2 0.24 scf/HPhrb 11,515.2 

 Generators (Turbines) 29 MMHPhr b,2 0.01 scf/HPhrb 3.2 

Pneumatic Devices Transmission + 

Storage 

 Pneumatic Devices Transmission 70,827 devices f,2 162,197 Scfy/deviceb 221,256.9 

 Pneumatic Devices Storage 13,542 devices e,2 162,197 Scfy/deviceb 42,304.0 

Routine Maintenance/Upsets 

Pipeline venting 303,126 miles a,1 31.65 Mscfy/mileb 184,779.2 

Station Venting Transmission + Storage 

Station Venting Transmission 1,799 

compressor 

stations c,2 4,359 Mscfy/stationb 151,065.9 

Station Venting Storage 344 

compressor 

stations e,2 4,359 Mscfy/stationb 28,882.0 

LNG Storage - 

LNG Stations 70 stations f,g,3 21,507 scfd/stationb 10,622.8 

LNG Reciprocating Compressors 270 

compressors

f,g,3

 21,116 scfd/compb 40,146.5 

LNG Centrifugal Compressors 64 

compressors

f,g,3

 30,573 scfd/compb 13,766.0 

LNG Compressor Exhaust 

 LNG Engines 579 MMHPhr f,g,3 0.24 scf/HPhrb 2,677.7 

 LNG Turbines 113 MMHPhr f,g,3 0.01 scf/HPhrb 12.4 

LNG Station Venting 70 stations f,g,3 4,359 Mscfy/stationb 5,898.6 

LNG Import Terminals 

LNG Stations 8 stations f,g,3 21,507 scfd/stationb 1,164.2 

LNG Reciprocating Compressors 37 compressors f,g,3 21,116 scfd/compressorb 5,551.8 

LNG Centrifugal Compressors 7 compressors f,g,3 30,573 scfd/compressorb 1,418.5 

LNG Compressor Exhaust 

 LNG Engines 774 MMHPhr f,g,3 0.24 scf/HPhrb 3,576.6 

 LNG Turbines 178 MMHPhr f,g,3 0.01 scf/HPhrb 19.5 

LNG Station Venting 8 stations f,g,3 4,359 Mscfy/stationb 646.4 

Regulatory Reductions (Gg) (0.0) 

Voluntary Reductions (Gg) (390.1)
A-187

Total Reductions (Gg) (390.1)

Total Potential Emissions (Gg) 2,461.1

Total Net Emissions (Gg) 2,071.0

a Pipeline and Hazardous Materials Safety Administration (PHMSA), Office of Pipeline Safety (OPS) (2013)

b EPA/GRI (1996), Methane Emissions from the Natural Gas Industry

c

ICF (2008), Natural Gas Model Activity Factor Basis Change

d

ICF (2010), Emissions from Centrifugal Compressors

e

ICF (1997), Additional Changes to Activity Factors for Portions of the Gas Industry

f

ICF (1996), Estimation of Activity Factors for the Natural Gas Exploration and Production Industry in the U.S.

g EIA (2004), US LNG Markets and Uses

1 Activity data for 2012 available from source.

2 Ratios relating other factors for which activity data are available.

3 2011 activity data are used to determine some or all of the 2012 activity (to be updated).

aa Emission factors listed in this table are for potential emissions (unless otherwise indicated in a footnote). For many of these sources, emission 

reductions are subtracted from potential emissions to calculate net emissions. For this reason, emission factors presented in these tables 

cannot be used to directly estimate net emissions from these sources. See detailed explanation of methodology above.