This methodology represents greenhouse gas emissions associated with the combustion of fuel for transport purposes in the geographic contexts of the US, UK and other regions. The data and calculation methodology is based on those provided in the Greenhouse Gas Protocol worksheet GHG emissions from transport or mobile sources (version 2.2), published in June 2011.
The emissions methodology is based upon emissions factors which describe the greenhouse gas emissions associated with the specific quantities of transport fuel. These emissions factors can be contrasted with similar transport-related emissions factors which describe emissions on the basis of distance. This methodology is typically more accurate for calculating transport related greenhouse gas emissions since it involves a more direct measure of fuel consumption without the requirement for assumptions about vehicle fuel efficiencies. Since the CO2 produced during the burning of biofuels in not a net contributor to atmospheric warming (see here), fossil- and biofuel-associated CO2 are explicitly defined.
Emissions - conventionally expressed in terms of mass (e.g. kg) - are calculated by multiplying these rates (mass emitted per volume; e.g. kg CO2 per US gallon) by a volume of fuel (e.g gallons) consumed.
The rate at which fuel combustion produces greenhouse gas emissions varies depending on factors such as the carbon content of the specific type of fuel burned. Therefore, emissions factors for numerous distinct transport fuels are provided, including:
- aviation gasoline
- biofuel blends
- compressed natural gas
- jet fuel
- liquefied petroleum gas
- residual fuel oil
Region-specific emissions factors are provided for each fuel type for the UK, the US and 'other regions'.
Activity data required
According to this methodology, greenhouse gas emissions are directly proportionate to the quantity of fuel consumed. Fuel quantity must be specified on the basis of volume.
Calculation and result
The returned emissions quantities for this methodology represent the CO2 associated with the type and quantity of fuel specified. Two values are returned, as follows:
- CO2: CO2 emissions associated with fossil carbon
- bioCO2: CO2e emissions associated with recently sequestered, biogenic carbon
Other Greenhouse Gas Protocol transport methodologies are available representing fuels consumed in specific transport contexts, freighting of goods, passenger/public transport, and road transportation in the UK (with heavy goods), US and other regions.
Default units for CNG
The emissions factors for compressed natural gas (CNG) are presented in units of kg [emissions] per standard cubic foot (sfc) in the original Greenhouse Gas Protocol documentation.
For consistency with other fuels in this category, these values have been converted to a per US gallon) basis using the US-gallon-to-standard-cubic-feet conversion factor provided in the Reference - EF Fuel Use worksheet of the source documentation, i.e.
emission factorkg per US gallon = emission factorkg per scf / 7.48051948US gallon per scf