Emissions are calculated based on the DEFRA methodologies for passenger and freight transport. These methodologies contain emissions factors which describe the rate at which greenhouse gas emissions are produced in relation to distance travelled and - in the case of freight - the quantity of goods freighted.
Emissions - expressed in terms of mass (e.g. kg) - are calculated by multiplying these rates (e.g. mass emitted per distance; e.g. kg CO2 per km) by the great circle distance between two locations (e.g km) travelled (as well as the quantity freighted, in the case of freight).
Great Circle distance calculations
Flight distances are calculated as the 'Great Circle' distance between two locations, which represents the shortest distance between two points on a sphere (an approximation of the Earth) and is derived from departure and destination locations using the haversine formula. Departure and destination locations can be defined on the basis of latitude and longitude or the IATA codes representing the respective departure and destination airports, with distances between airports are calculated by reference to longitude and latitude data for a comprehensive range of global airports.
The DEFRA methodology provides passenger- and freight-based emissions factors representing typical 'domestic', 'short haul' and 'long haul' flights. The selection of the appropriate flight type is determined - following DEFRA methodology - by the relationship between departure and destination locations:
- domestic flights are those which originate and terminate within the UK
- short-haul flights are international flights (originating and terminating in distinct countries) extending no further than 3700 km
- long-haul flights are international flights extending beyond 3700 km
- direct CO2 emissions: carbon dioxide emissions produced during flight, i.e. fuel combustion
- direct CH4 emissions: methane emissions produced during flight, i.e. fuel combustion
- direct N2O emissions: nitrous oxide emissions produced during flight, i.e. fuel combustion
- total direct emissions: all direct emissions, i.e. CO2 + CH4 + N2O
- indirect emissions: emissions associated with stages in the fuel production chain such as raw material extraction and fuel delivery
- total or 'life cycle': the total of direct and indirect emissions
Alternative DEFRA methodologies are available representing passenger and freight transport in which emissions are calculated on the basis of absolute specified distances rather than departure and destination locations.
Using this methodology
Choosing a specific activity type
There are no drill down choices associated with this category.
Activity data required
The activity data which is required varies depending on whether passenger-based or freight-based emissions are required.
In all cases departure and destination locations must be specified using either of the following combinations of profile item values:
- lat1, long1, lat2, long2 (i.e. a pair of latitude and longitude coordinates)
- IATACode1, IATACode2 (i.e. a pair of airport IATA codes)
For freight-based emissions only: If requiring an emissions calculation associated with freight, the quantity (mass) of goods freighted must be specified using the mass profile item value. If multiple instances of the same quantity of freighting are under consideration these can be specified using the journeys profile item value.
For passenger-based emissions: If passenger-based emissions are required a number of options can be specified in order to make the most accurate calculation. Multiple journeys and passengers can be specified by setting the journeys and passengers profile item values respecitively. Return flights can be specified by setting the isReturn profile item value to 'true'. The specific passenger class can also be specified using the passengerClass profile item value with one of the following valid values:
- 'average': use if passenger class is unknown (default)
- 'economy': for economy class
- 'premium economy': for premium economy class or 'economy plus'
- 'business': for business class
- 'first': for first class
In addition the effects of radiative forcing can be incorporated by setting the useRFI profile item value to 'true' (default value is 'false'). The value of the the radiative forcing index can be set using the radiativeForcingIndex profile item value, but defaults to 1.9 otherwise. For an explanation of the radiative forcing index (RFI) see here.
Users can choose to specify their activity data in a comprehensive range of appropriate units.
Calculation and result
Great Circle distances are calcuated using the haversine formula and inflated by 9% to account for indirecting routing and congestion - as specified by DEFRA methodology. Emissions calculations are made based on the calculated Great Circle distance and the appropriate emissions factors for either passenger or freight. Passenger flights are assumed by default; freighting is indicated by the specification of a mass quantity.
The returned emissions quantities for this methodology are inclusive of CO2, CH4 and N2O. The following discrete amounts are returned:
- CO2: CO2 emissions
- methaneCO2e: CH4 (methane) emissions
- nitrousOxideCO2e: N2O (nitrous oxide) emissions
- totalDirectCO2e: total direct emissions
- indirectCO2e: Indirect emissions
- lifeCycleCO2e: Full life cycle emissions