Division Calculation Method B – Overvoltage Method:

Where the anode effect overvoltage is measured, the operator shall use the following equations for the determination of PFC emissions:

• CF₄ emissions [t] = OVC × (AEO/CE) × Pr_Al × 0,001

• C₂F₆ emissions [t] = CF₄ emissions × F_CF2F6

Where:

OVC

Overvoltage coefficient (‘emission factor’) expressed as kg CF₄ per tonne of aluminium produced per mV overvoltage;

AEO

Anode effect overvoltage per cell [mV] determined as the integral of (time × voltage above the target voltage) divided by the time (duration) of data collection;

CE

Average current efficiency of aluminium production [%];

Pr_Al

Annual production of primary Aluminium [t];

F_CF2F6

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

The term AEO/CE (Anode effect overvoltage / current efficiency) expresses the time-integrated average anode effect overvoltage [mV overvoltage] per average current efficiency [%].

Emission factor: The emission factor for CF₄ (‘overvoltage coefficient’ OVC) shall express the amount [kg] of CF₄ emitted per tonne of aluminium produced per millivolt overvoltage [mV]. The emission factor of C₂F₆ (weight fraction F_C2F6) shall express the amount [t] of C₂F₆ emitted proportionate to the amount [t] of CF₄ emitted.

Tier 1:: The operator shall apply technology-specific emission factors from Table 2 of this section of Annex IV.

Tier 2: The operator shall use installation-specific emission factors for CF₄ [(kg CF₄ / t Al ) / (mV)] and C₂F₆ [t C₂F₆/ t CF₄] 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 Guidelines. The operator shall determine the emission factors with a maximum uncertainty of ± 15 % each.

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.