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The Carbon Market: A Primer for Airports
Key Takeaways for Airports • The primary opportunity for a methane destruction offset project would be from
an existing landfill on airport grounds. • New landfills are prohibited at airports, limiting the applicability of this offset
project type moving forward.
In its Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008 study, the EPA estimates that methane emissions make up about 9% of all GHG emissions in the United States (EPA 2010). There are a variety of methane emitting sources in the United States; however, the leading sources are enteric fermentation (digestion from livestock), landfills, natural gas systems, coal mining, manure management (from livestock), petroleum systems, and wastewater treatment. Figure 2 presents more information on the relative contribution of these methane sources. Operators of these various sources of methane gas have developed methods for capturing the gas by installing a system of wells, pipes, blowers, caps, and other technologies. After capture, methane is combusted and destroyed, usually by a flare or a boiler which combusts the gas in order to create heat for other processes such as electricity generation. When methane is combusted, the gas is destroyed and the byproduct of combustion emitted is carbon dioxide (CO2) which has a much lower GWP. The result is a lower impact to GHG concentrations in the atmosphere compared to methane seeping into the atmosphere directly from the landfill or other methane source. The following are sources of methane emissions that are recognized by U.S. offset standards bodies to generate offset credits. Landfills—Landfills remain the most common method for disposing of waste in the United States and a potential, albeit unlikely, methane capture and destruction project source for airports. The bacterial decomposition of solid waste in a landfill creates a landfill gas, which is primarily comprised of two GHGs: methane and carbon dioxide. With time—and if not collected, captured, and/or destroyed—landfill gas can be released into the atmosphere, adding to the overall concentration of GHGs. If captured, landfill gas can potentially serve as an energy source. Wastewater Treatment 4% Petroleum Systems 5%
Other 7%
Enteric Fermentation (Livestock Digestion) 25%
Manure Management 8% Coal Mining 12% Natural Gas Systems 17% Source: US EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2008. Washington, D.C., 2010.
Figure 2. U.S. methane emissions by source (average 1990–2008).
Landfills 22%