HFCs, PFCs and SF₆ Emission Estimates

Hydrofluorocarbons

The UK emissions of HFCs are shown in Table 2.7. It is not currently possible to give emission estimates for individual HFCs.

HFCs had limited usage primarily as refrigerants blended with CFCs. However, CFCs and HCFCs are being phased out under the Montreal protocol, and hence HFCs are now being used increasingly as:

• substitutes for CFCs and HCFCs in domestic, commercial and industrial refrigeration and air conditioning
• substitutes for CFCs in plastic foam blowing
• substitutes for CFCs for some medical aerosols
• substitutes for CFCs for industrial and specialist aerosols
• fire fighting fluids

Salway (1999) reports the emissions estimate methodology and ongoing improvements in some detail. The UK reports both actual and potential emissions of HFCs, although here only the actual emissions are presented.

Fugitive emissions from the manufacture of HCFCs and HFCs accounted for 39% of the total emission in 1998. Refrigeration is the next largest source and contributed 31% of the total. Here emissions arise due to leakage from refrigeration and air conditioning equipment during its life time and from losses during manufacture and the recovery of the refrigerants on decommissioning. In the case of closed foams where the fluid is retained within the foam there will be some leakage from the foam during its lifetime and on disposal but with open foams all losses occur during manufacture. Since 1990, the use of HFCs in aerosols has greatly increased, and this source sector now accounts for 29% of the total emission. The remaining emission sources contributes 0.6% to the total. The total 1998 HFC emission for the UK has increased by a factor of 3.8 compared with the 1990 emission due to the increasing use of HFCs and increased production of halocarbons.

Table 2.7 UK Emissions of HFCs (tonnes)

¹ Includes metered dose inhalers.

Perfluorocarbons

Table 2.8 shows the UK emissions of PFCs. It is not currently possible to give emission estimates for individual PFCs. PFCs had limited usage prior to the phase out of CFCs in the electronics and electrical industry. PFCs are now used in:

• etching processes in the semiconductor industry
• chemical vapour deposition in the electronics industry
• soldering processes
• leak testing of electrical components
• cooling electrical components , for example in supercomputers and radar systems.

Other uses include

• refrigerant blended with HFC
• firefighting in specialist applications
• cushioning in the soles of training shoes

Other minor uses of CFC, which now use PFCs, were in cosmetics and as a tracer gas.

The largest source of PFCs for 1998 is from the electronics sector, where emissions arise from the manufacture of semiconductors- this source sector accounts for around 57% of the total emission. PFCs are also formed as a by-product of aluminium smelting, emission from this sector represent 35% of the UK total in 1998. The emissions are caused by the anode effect which occurs when alumina concentrations become too low in the smelter. This can cause very high electrical current and decomposition of the salt - fluorine bath. The fluorine released reacts with the carbon anode, creating PFC compounds CF₄ and C₂F₆ . Total emissions have declined by 89% since 1990 reflecting steps taken by the industry to reduce emissions.

Table 2.8 UK Emissions of PFCs (tonnes)

Sulphur Hexafluoride

SF₆ is used in the following applications:

• insulation medium in high voltage applications such as switchgear and circuit breakers
• cover gas in magnesium foundries to protect the molten magnesium from re-oxidising when it is cast
• degasser in aluminium casting applications, though its use in the UK is rather limited
• insulating gas in double glazing applications, replacing vacuum as an insulation technique
• plasma etching of polysilicon and nitrite surfaces
• atmospheric tracer for scientific studies
• cushioning in soles of training shoes

Table 2.9 shows the UK emissions of SF₆. The largest source is from magnesium manufacture, where SF₆ is used as a cover gas. It is not possible to recover the SF₆, and hence the total consumption of SF₆ is released to atmosphere- emissions from this sector account for 56% of the UK total in 1998. The other main sources are from the manufacture of trainers, and electrical/electronic equipment. The use of SF₆ as a cushioning in trainers will be phased out in the near future. Emissions from the electrical insulation arise during the manufacture and filling of electrical switchgear and from leakage and maintenance during the equipment’s lifetime. This application has only been in use for the last 20 to 30 years and little of the equipment has been decommissioned. It is expected that users will take great care over future fluid recovery so that emissions will be minimised. SF₆ emissions have increased by 78% since 1990.

Table 2.9 UK Emissions of Sulphur Hexafluoride (tonnes)