This methodology represents carbon dioxide (CO2) emissions associated with the production of aluminium. The data and calculation methodology is sourced from the Greenhouse Gas Protocol (GHGP) worksheet tool GHG emissions from the production of aluminum, version 2.0, which is ultimately based on the methodologies described in Volume 3, Chapter 4 - Metal Industry Emissions of their 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
Aluminium is extracted from its ore (aluminium oxide (Al2O3), or 'bauxite') using an electrolysis cell and carbon anodes. During electrolysis, the aluminium (Al) is separated according to the following equation:
- 2Al2O3 + 3C => 4Al + 3CO2
This methodology enables the calculation of aluminium-associated CO2 emissions on the basis of an emissions factor which represents the rate at which CO2 is emitted in relation to the quantity of aluminium produced. Multiplying a quantity of aluminium produced by these emissions factors results in an estimate of the emissions associated with that quantity.
This methodology represents the IPCC Tier 1 approach, and is considered advisable in cases where there is insufficient activity data available to use the more detailed prebake, Søderberg or alternative methodologies.
The rate at which CO2 is emitted in relation to aluminium production depends on the specific type of technology employed. This methodology provides emissions factors representing the typical unit emissions associated with prebake and Søderberg cells. Each technology type is represented by a CO2 emission factor (i.e. kg [emissions] per kg [aluminium]), although these values can be specified on facility-specific basis if data is available.
Activity data required
CO2 emissions are directly proportionate to the quantity of aluminium produced (i.e. mass), which therefore must be provided in order to calculate. In addition, the methodology enables the specification of a facility-specific data CO2 emissions factor where this is available.
Calculation and results
CO2 emissions are calculated by simply multiplying the specified quantity of aluminium produced by the emissions factor. These emissions represent those attributable to the specified quantity of aluminium produced.
IPCC methodologies for aluminium-associated PFC emissions (CF4 and C2F6) are also available, including a simple tier 1 approach and two alternative approaches for tiers 2/3: the slope and overvoltage methods.