Global emission estimates based on new at- mospheric observations are presented for the acylic high molecular weight perfluorocarbons (PFCs): decafluorobu- tane (C4 F10 ), dodecafluoropentane (C5 F12 ), tetradecafluo- rohexane (C6 F14 ), hexadecafluoroheptane (C7 F16 ) and oc- tadecafluorooctane (C8 F18 ). Emissions are estimated using a 3-dimensional chemical transport model and an inverse method that includes a growth constraint on emissions. The observations used in the inversion are based on newly mea- sured archived air samples that cover a 39-yr period, from 1973 to 2011, and include 36 Northern Hemispheric and 46 Southern Hemispheric samples. The derived emission esti- mates show that global emission rates were largest in the 1980s and 1990s for C4 F10 and C5 F12 , and in the 1990s for C6F14, C7F16 and C8F18. After a subsequent decline, emis- sions have remained relatively stable, within 20 %, for the last 5 yr. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C4F10, C5F12, C6F14 and C7F16, and inventories of C4 F10 , C5 F12 and C6 F14 are reported to the United Nations’ Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol. The atmospheric measurement-based emission es- timates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude larger for C5F12 (with 2008 EDGARv4.2 estimates for C5F12 at 9.6 kg yr−1, as compared to 67±53 t yr−1 as derived in this study). The derived emis- sion estimates for C6F14 largely agree with the bottom-up es- timates from EDGARv4.2. Moreover, the C7F16 emission es- timates are comparable to those of EDGARv4.2 at their peak

in the 1990s, albeit significant underestimation for the other time periods. There are no bottom-up emission estimates for C8 F18 , thus the emission rates reported here are the first for C8 F18 . The reported inventories for C4 F10 , C5 F12 and C6 F14 to UNFCCC are five to ten times lower than those estimated in this study.

In addition, we present measured infrared absorption spec- tra for C7 F16 and C8 F18 , and estimate their radiative effi- ciencies and global warming potentials (GWPs). We find that C8 F18 ’s radiative efficiency is similar to trifluoromethyl sul- fur pentafluoride’s (SF5 F3 ) at 0.57 W m−2 ppb−1 , which is the highest radiative efficiency of any measured atmospheric species. Using the 100-yr time horizon GWPs, the total ra- diative impact of the high molecular weight perfluorocar- bons emissions are also estimated; we find the high molecu- lar weight PFCs peak contribution was in 1997 at 24 000 Gg of carbon dioxide (CO2) equivalents and has decreased by a factor of three to 7300 Gg of CO2 equivalents in 2010. This 2010 cumulative emission rate for the high molecular weight PFCs is comparable to: 0.02 % of the total CO2 emissions, 0.81 % of the total hydrofluorocarbon emissions, or 1.07 % of the total chlorofluorocarbon emissions projected for 2010 (Velders et al., 2009). In terms of the total PFC emission bud- get, including the lower molecular weight PFCs, the high molecular weight PFCs peak contribution was also in 1997 at 15.4 % and was 6 % of the total PFC emissions in CO2 equivalents in 2009.

© 2012 Authors