PFCs are not generated during normal smelting operating conditions. They are only produced during brief upset conditions known as "anode effects". These conditions occur when the level of the dissolved aluminium oxide (the raw material for primary aluminium) in the cell drops too low and the electrolytic bath itself begins to undergo electrolysis. Measures to reduce the frequency and duration of anode effects not only reduce greenhouse gas emissions but also benefit the producer by improving energy and process efficiency. The IAI carries out an annual survey* of anode effects and PFC emissions from the aluminium industry. Results show an overall 76% reduction in the emission rate for PFCs per tonne of aluminium produced over the 1990 to 2005 time period, equating to a 60% reduction in total emissions as CO₂ equivalents, despite a 64% increase in metal production. This is one of the few examples of where the global emissions of a greenhouse gas from an industry sector are actually in decline.

The declining rate of PFC emissions is the result of the industry's efforts to reduce the frequency, and to some extent, the duration of the anode effects in pot line cells. This has been further enhanced through the use of computerised anode effect suppression systems that reduce anode effect duration, as well as point alumina feeding systems and computer feed control programmes that reduce anode effect frequency. The ongoing phasing-out of older technologies and their replacement with more modern technology, wherever economically justified, is also assisting in decreasing relevant emissions.

Another significant reason for this reduction in PFC emissions is the voluntary agreements between government and industry in many countries, such as Australia, Bahrain, Brazil, Canada, France, Germany, New Zealand, Norway and the UK. Together they represent around 50% of world production. For example under the US EPA's voluntary aluminium industrial partnership, the US aluminium industry achieved by 1998 a 46% reduction in PFCs (approximately 2.2 million metric tonnes of CO₂ equivalents).

Full results of the survey can be found by downloading the report (see sidebar). IAI also regularly publishes PFC Emissions and Anode Effect Surveys, see the latest survey data opposite.

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