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Abstract:

Perfluorocarbons (PFCs) are extremely long-lived, potent greenhouse gases. PFC-14 (CF4) and PFC-116 (C2F6) have lower limits for atmospheric lifetimes of 50 000 and 10 000 years, respectively, and global warming potentials (100-year time horizon) of 7390 and 12 200, respectively (Montzka et al. 2011). Anthropogenic PFC-14 and PFC-116 were historically emitted as by-products of aluminum production (IAI 2011) and are also emitted from the electronics industry. However, the onset and extent of PFC emissions from the electronics industry is poorly known due to limited reporting (Worton et al. 2007; Mühle et al. 2010). A small natural source of CF₄ from degassing of Earth’s crust has been identified (Harnisch and Eisenhauer 1998; Harnisch et al. 2000), which, because of its extraordinarily long atmospheric lifetime, accounts for its significant preindustrial abundance (Harnisch et al. 1996a,b) of 34.7 ± 0.2 ppt (Mühle et al. 2010), or ~44% of its 2011 abundance. Based on preliminary data, global average surface mixing ratios of PFC-14 and PFC-116 were ~79 ppt and ~4.2 ppt in 2011, respectively (Fig. 2.44). Mixing ratios of PFC-14 rose at ~1.1 ppt yr^-1 from the late 1970s to the early 1990s and by ~0.7 ppt yr^-1 after- wards. Mixing ratios of PFC-116 rose at ~0.09 ppt yr^-1 from the late 1970s to the mid-1990s, at ~0.12 ppt yr^-1 until the mid-2000s, and at ~0.08 ppt yr^-1 in recent years (Mühle et al. 2010 and preliminary data).