## APPENDIX C - Emissions Inventory for Greenhouse Gases 

## C.1 Overview 

This appendix discusses the methodolog ies for computing greenhouse gas (GHG) emissions from aircraft engines, auxiliary power units (APU), ground support equipment (GSE), ground access vehicles, stationary sources (such as boilers, generators, and fire training), and other miscellaneous activities such as electrical usage, waste management, and refrigerant usage. See Section 3 ( Sources and Types of Air Emissions ) for a description of GHGs associated with aviation and Section 6.3 ( Preparing an Emissions Inventory – Greenhouse Gases ) for a discussion of available guidance for preparing and reporting a GHG assessment for projects/actions. 

The six primary GHG pollutants which should be considered for a GHG emissions inventory are: carbon dioxide (CO $_{2}$), methane (CH $_{4}$), nitrous oxide (N $_{2}$O), and fluor inated gases such hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF$_{6}$). 

For the most part, GHG emissions should be determined based on the estimated/actual fuel usage (e.g., gallons, cubic feet, etc.) and an appropriate emi ssion factor (e.g., pounds per gallon). The types of sources from which GHG emissions should be calculated using the fuel usage approach include aircraft, APU, GSE, and stationary sources. In the case of motor vehicles, emissions should be based on the estimated/actual activity levels (e.g., vehicle miles travel) or estimated/actual fuel usage (e.g., gallons, cubic feet, etc.) and an approved emission factor (e.g., grams per mile, pounds per gallon). GHG emissions from electrical usage, refrigerant usage, and waste management should also be accounted for within the inventory. 

In all cases, the GHG emission inventory results should be converted to CO$_{2 }$ equivalent (CO$_{2e}$) values using the Global Warming Potential (GWP) 61 values of 1 for CO$_{2}$, 34 for CH$_{4}$, and 298 for N$_{2}$O (based on a 100 year period) as presented in the IPCC’s Fifth Assessment Report. 62 

## C.2 Methodology 

The following sections discuss the methodologies for computing GHG emissions from aircraft, APUs, GSE, ground access vehicles, stationary sources, electrical usage, waste management, and refrigerant usage. 

## C.2.1 Aircraft 

The following section discusses the methodology for computing GHG emissions from aircraft engines within the landing and take -off (LTO) cycle. As noted previously, the LTO cycle includes the take-off, climbout, approach, and taxi/idle operating modes. 

