Airport Greenhouse Gas Emissions Inventory: A Primer (2024)
Chapter: 2. Set Inventory Boundaries
2. Set Inventory Boundaries
One of the first steps when preparing a GHG emissions inventory is to establish the inventory boundaries. Clearly defining inventory boundaries will help you determine which emission sources to include in the inventory and how to organize those emission sources. Well-defined boundaries are foundational to your GHG management strategy—helping you understand and attribute emissions and take steps to reduce them.
2.1 Set Organizational and Operational Boundaries
Inventory boundaries establish 1) organizational boundaries (or the airport operations that should be included in your airport’s inventory) and 2) operational boundaries (or the emission sources to include and how to attribute them to airport operations).
2.1.1 Organizational Boundaries
Airport operators can choose between operational control, financial control, or equity share approaches to consolidate their GHG emission sources. However, most airport operators will likely find that the operational control approach is the most useful for consolidating and accounting for their airport’s emissions.
Under an operational control approach, an airport operator accounts for 100% of emissions from sources that the airport owns or controls—i.e., over which it possesses full authority to introduce and implement operational policies. This includes, for example, facilities and ground support equipment that the airport owns or controls. The remainder of this primer assumes that the airport operator will account for its emissions using the operational control approach.
Quick Tip
The GHG Corporate Standard provides multiple options for setting organizational boundaries. These options include alternatives to the operational control approach, such as establishing boundaries based on its share of equity in operations and based on the financial control it has over operations.
2.1.2 Operational Boundaries
After defining which airport operations to include within the inventory based on your organizational boundaries, the next step is to identify the sources of emissions associated with those operations and determine how to attribute them to your airport.
Emissions are broadly categorized into two types—direct emissions and indirect emissions.
- Direct emissions occur from sources owned or controlled by the airport.
- Indirect emissions result from the activities of the airport but occur at sources owned or controlled by other entities.
Sources of direct and indirect emissions are organized into three scopes.
| Scope 1 | Scope 1 encompasses direct emissions from sources that are owned or controlled by the airport, such as emissions from fuel combustion in owned or controlled boilers, furnaces, vehicles, etc. (e.g., snow removal vehicles owned by the airport operator). |
| Scope 2 | Scope 2 encompasses indirect emissions associated with the generation of electricity and steam purchased by the airport (e.g., electricity used in airport operated facilities). |
| Scope 3 | Scope 3 encompasses all other indirect emissions associated with airport activities. Examples include emissions from tenant facilities, waste treated off site, and aircraft activities. |
Emission sources should be identified and grouped into one of the three scopes based on the scope definitions.
It is best practice to include all Scope 1 and 2 emission sources in a GHG inventory, at a minimum. Airport operators may additionally include Scope 3 emissions for a more complete picture of indirect emissions.
2.2 Scope 3 Emissions
The GHG Scope 3 Standard establishes 15 Scope 3 emission source categories, which are differentiated into upstream and downstream emissions.
- Upstream emission source categories include indirect GHG emissions related to goods and services purchased or acquired by the airport.
- Downstream emission source categories include indirect GHG emissions related to sold or distributed goods and services provided by the airport.
Indirect upstream and downstream emissions are from the perspective of the airport operator. These are direct emissions for the entities within the airport operator’s value chain (e.g., airlines).
The GHG Scope 3 Standard was developed for corporations with a particular focus on manufacturing companies. Not all of the 15 Scope 3 emission source categories (e.g., Category 15: Investments) are relevant to airports. Others may require careful consideration of the activities that occur at your airport to determine relevance. As an example, “Category 11: Use of Sold Products” states that it includes emissions from goods and services sold by the reporting entity. Within the aviation industry, fuel combustion is the largest source of emissions. Airport operators will need to consider whether to account for some aircraft emissions associated with the use of fuel that they sell or handle as a service to aircraft.
Airport Scope 3 emissions will vary in magnitude, the airport’s ability to influence emission reduction, and importance to stakeholders. As discussed more in Section 3. Collect Data and Estimate Emission Sources, these and other criteria should inform decisions on whether or not to include specific Scope 3 emission sources in your inventory. Best practice is to screen Scope 3 emission sources for relevance based on accepted criteria, estimate emissions for the most relevant Scope 3 sources, and then expand the inventory to include additional Scope 3 sources over time and as additional Scope 3 emission sources become relevant.
