Aluminium defaults

Summary

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.

The methodology

Emissions model

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:

1. 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.

Model data

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.

Related methodologies

In cases where more detailed activity data are available, the IPCC prebake and Søderberg methodologies may provide more accurate emissions calculations.

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.