# How much perfluorocarbon does the Intergovernmental Panel on Climate Change assume per tonne of aluminium, and why does the cell type matter so much?

Canonical: https://senseible.earth/answers/ipcc-aluminium-pfc-defaults-by-cell-type

The Intergovernmental Panel on Climate Change (IPCC) 2006 Tier 1 defaults for perfluorocarbons (PFCs), in kilograms of tetrafluoromethane (CF4) per tonne of aluminium: 0.4 centre worked prebake, 1.6 side worked prebake, 0.8 vertical stud Søderberg, 0.4 horizontal stud Søderberg. Hexafluoroethane (C2F6) adds 0.03 to 0.4.

## The Tier 1 table, kilograms per tonne of aluminium

- Centre worked prebake (CWPB): CF4 0.4, C2F6 0.04. Uncertainty range -99% to +380%.
- Side worked prebake (SWPB): CF4 1.6, C2F6 0.4. Range -40% to +150%.
- Vertical stud Søderberg (VSS): CF4 0.8, C2F6 0.04. Range -70% to +260%.
- Horizontal stud Søderberg (HSS): CF4 0.4, C2F6 0.03. Range -80% to +180%.
- The guide says these defaults should only be used in the absence of Tier 2 or Tier 3 data.

## Why the default is so loose

The defaults come from median anode effect performance in a 1990 industry survey. The guide says Tier 1 is much more uncertain because a smelter's own anode effect performance, the key driver of PFC emissions, is not taken into account.

## Use your anode effect log instead

Tier 2 and 3 use the slope method: CF4 = slope coefficient x anode effect minutes per cell-day x metal produced. C2F6 is then CF4 times a weight fraction. Tier 2 slope coefficients, in kilograms of CF4 per tonne per anode effect minute per cell-day: CWPB 0.143, SWPB 0.272, VSS 0.092, HSS 0.099. C2F6 to CF4 weight fractions: 0.121, 0.252, 0.053 and 0.085.

Smelters that record overvoltage instead use an overvoltage coefficient. The guide calls a smelter high performing if it runs under 0.2 anode effect minutes per cell-day, or under 1.4 millivolts of overvoltage. For those, the guide says moving from Tier 2 to Tier 3 improves the accuracy of the facility's inventory by less than 5 percent.

## A centre worked prebake line making 50,000 tonnes a year (example)

- Tier 1: 50,000 x 0.4 = 20,000 kilograms of CF4; 50,000 x 0.04 = 2,000 kilograms of C2F6
- Slope method at 1.5 anode effect minutes per cell-day: 0.143 x 1.5 = 0.2145 kilograms of CF4 per tonne
- 0.2145 x 50,000 = 10,725 kilograms of CF4; C2F6 = 10,725 x 0.121 = about 1,298 kilograms

Output and anode effect minutes are example numbers. Convert kilograms to carbon dioxide equivalent with the global warming potentials your report names.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so power and fuel for the smelter are on file month by month. Anode effect minutes come from the potline control system, not from bills.

- [Free calculators](https://senseible.earth/calculators)
- [Aluminium smelter anode CO2 default](https://senseible.earth/answers/ipcc-aluminium-smelter-anode-co2-default-per-tonne)
- [PFC counted in UK CBAM aluminium](https://senseible.earth/answers/uk-cbam-aluminium-pfc-counted)

Sources: [IPCC 2006 Guidelines, Volume 3 chapter 4: Metal Industry Emissions, section 4.4 (Tables 4.15 and 4.16, Equations 4.25 to 4.27)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_4_Ch4_Metal_Industry.pdf)

Last reviewed 2026-11-04. Defaults are from the 2006 IPCC Guidelines and 1990 survey data. A potline anode effect record gives a far tighter figure than the default.