Abstract
Abstract. Air samples collected at Cape Grim, Tasmania between 1978 and 2008 and during a series of more recent aircraft sampling programmes have been analysed to determine the atmospheric abundance and trend of octafluorocyclobutane (c-C4F8 or PFC-318). c-C4F8 has an atmospheric lifetime in excess of 3000 yr and a global warming potential (GWP) of 10 300 (100 yr time horizon), making it one of the most potent greenhouse gases detected in the atmosphere to date. The abundance of c-C4F8 in the Southern Hemisphere has risen from 0.35 ppt in 1978 to 1.2 ppt in 2010, and is currently increasing at a rate of around 0.03 ppt yr−1. It is the third most abundant perfluorocarbon (PFC) in the present day atmosphere, behind CF4 (~75 ppt) and C2F6 (~4 ppt). Although a number of potential sources of c-C4F8 have been reported, including the electronics and semi-conductor industries, there remains a large discrepancy in the atmospheric budget. Using a 2-D global model to derive top-down global emissions based on the Cape Grim measurements yields a recent (2007) emission rate of around 1.1 Gg yr−1 and a cumulative emission up to and including 2007 of 38.1 Gg. Emissions reported on the EDGAR emissions database for the period 1986–2005 represent less than 1% of the top-down emissions for the same period, which suggests there is a large unaccounted for source of this compound. It is also apparent that the magnitude of this source has varied considerably over the past 30 yr, declining sharply in the late 1980s before increasing again in the mid-1990s.
Highlights
Owing to a combination of long atmospheric lifetimes and strong absorption bands in the infrared, fully fluorinated hydrocarbons are among the most potent greenhouse gases known, with global warming potentials three or four orders of magnitude greater than that of CO2 (Forster et al, 2007)
Cumulative global emissions of c-C4F8 up until the end of 2007 are calculated to be 38.1 Gg, which is equivalent to a 100 yr global warming potential (GWP)-weighted emission of 0.39 billion tonnes of CO2 (0.39 Pg)
If our estimated global emissions are correct it would imply that emissions from China and East Asia are only responsible for around 50 %, which is closer to the figure of ∼30 % which was reported by EDGAR v4 (China, Korea, Japan, Taiwan) for the year 2005
Summary
Owing to a combination of long atmospheric lifetimes and strong absorption bands in the infrared, fully fluorinated hydrocarbons (perfluorocarbons or PFCs) are among the most potent greenhouse gases known, with global warming potentials three or four orders of magnitude greater than that of CO2 (Forster et al, 2007). In common with other perfluorinated compounds, c-C4F8 is resistant to the common atmospheric degradation mechanisms, resulting in an estimated lifetime of 3200 yr (Ravishankara et al, 1993) It is a strong greenhouse gas with GWPs of 7310, 10 300 and 14 700 for 20-yr, 100-yr and 500-yr time horizons respectively (Forster et al, 2007), making it one of the most potent greenhouse gases to be identified in the atmosphere to date. We report observations of c-C4F8 between 1978 and 2008 from a long term measurement programme at Cape Grim, Tasmania These data are complemented by more recent measurements in the upper troposphere and lower stratosphere from samples collected by the CARIBIC and Geophysica aircraft. The model-derived emissions are compared with those reported to the EDGAR database
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