The operator shall use the following equations for determining PFC emissions:

CF₄ emissions [t] = AEM × (SEF_CF4/1 000) × Pr_Al

C₂F₆ emissions [t] = CF₄ emissions * F_C2F6

Where:

AEM

Anode effect minutes/cell-day;

SEF_CF4

Slope emission factor [(kg CF₄/t Al produced)/(anode effect minutes/cell-day)]. Where different cell-types are used, different SEF may be applied as appropriate;

Pr_Al

Annual production of primary Aluminium [t];

F_C2F6

Weight fraction of C₂F₆ (t C₂F₆/t CF₄).

The anode effect minutes per cell-day shall express the frequency of anode effects (number anode effects/cell-day) multiplied by the average duration of anode effects (anode effect minutes/occurrence):

AEM = frequency × average duration

Emission factor

The emission factor for CF₄ (slope emission factor, SEF_CF4) expresses the amount [kg] of CF₄ emitted per tonne of aluminium produced per anode effect minute/cell-day. The emission factor (weight fraction F_C2F6) of C₂F₆ expresses the amount [t] of C₂F₆ emitted proportionate to the amount [t] of CF₄ emitted.

Tier 1

The operator shall use technology-specific emission factors from Table 1 of this section of Annex IV.

Tier 2

The operator shall use installation-specific emission factors for CF₄ and C₂F₆ established through continuous or intermittent field measurements. For the determination of those emission factors the operator shall use the most recent version of the guidance mentioned under tier 3 of section 4.4.2.4 of the 2006 IPCC Guidelines16. The operator shall determine each emission factor with a maximum uncertainty of ± 15 %.

The operator shall determine the emission factors at least every three years or earlier where necessary due to relevant changes at the installation. Relevant changes shall include a change in the distribution of anode effect duration, or a change in the control algorithm affecting the mix of the types of anode effects or the nature of the anode effect termination routine.