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GHG emissions associated with the onsite generation of electricity using coal, oil, natural gas, etc. may be included in an aviation-related GHG emissions inventory. Typically, these values are based on aviation-related electrical usage and emiss ion factors from local utilities or from the EPA eGRID 67 system. 

The GHG emissions associated with refrigeration and heating and air -conditioning systems as well as the GHG emissions from recycling of solid waste associated with an airport are likewise occasionally included. These values are based mostly on product -specific material-balancing methods and emission factors which take into account the use and disposal of these materials. 

Notably, GHG emissions associated with the entire “supply chains” or full “life cycles” (e.g., production, consumption and/or disposal of goods and materials such as paper, plastic and waste products, foodstuffs, building materials, etc.) by either airport facilities or its tenants are typically not included in an aviation-related GHG emissions inventory. 

Moreover, the storage of fuel (e.g., jet fuel, Avgas, gasoline, and diesel) is a potential source of evaporative hydrocarbon emissions, but does not produce the type of HCs that contribute directly to global climate change. 

Due to the fact that CO $_{2}$, CH$_{4}$, and N$_{2}$O are by-products of fuel combustion, they are also the predominant GHGs associated with most airports. Emissions of HFCs, PFCs, and SF 6 linked with refrigeration, air conditioning, and other coolants also occur, but at far lesser amounts. However, in all cases, the estimated GHGs should be converted to CO 2e values using Global Warming Potentials (GWPs). $_{68}$,$_{69 }$ 

Table 6-6 ( GHG Emission Inventory Methods ) provides a summary listing and Appendix C ( Emissions Inventory for Greenhouse Gases ) provides further guidance on the computation of GHG emissions associated with aviation including the emission inventory methods, data sources, and other supporting materials. 

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