32
Montreal Protocol. Also, it is worth noting that it is inconceivable that the gross
domestic product of any country could be adversely affected by regulation of
HFCs. In other words, the stakes for the world’s economies are low with regard to
regulation of HFCs. On 15 October 2016, at the 28th Meeting of the Parties of the
Montreal Protocol held in Kigali, Rwanda, an agreement was reached to regulate
the future production of HFCs under the Montreal Protocol. This marks the first
time the Montreal Protocol has had direct authority over a class of chemical com-
pounds that pose no threat to the ozone layer.
Perfluorocarbons (PFCs) are a class of compounds containing only carbon and
fluorine that resist heat, oils, and staining. The most abundant PFCs are PFC-14
(CF 4 ), PFC-116 (C 2 F 6 ), and PFC-218 (C 3 F 8 ). Atmospheric levels of these com-
pounds have risen steadily; contemporary levels of CF 4 , C 2 F 6 , and C 3 F 8 are a factor
of 2, 4, and 10 larger, respectively, than observed during the onset of observations
in the early 1970s (Mühle et al. 2010 ). It has been projected that the RF of climate
due to all PFCs could approach 0.04 W m−2 by end of this century (IPCC/TEAP
2005 ; Zhang et al. 2011 ). While this would represent only a small contribution to
global warming, PFCs will continue to be monitored due to their extremely long
atmospheric lifetimes (Table 1.2).
Sulfur hexafluoride (SF 6 ) is an excellent insulator favored in the high voltage,
electric industry because this compound is non-flammable.^31 The atmospheric abun-
dance of SF 6 has risen steadily since the early 1970s and shows no sign of abating
(Rigby et al. 2010 ). It has been estimated that the RF of climate due to SF 6 could
reach 0.037 W m−2 by the end of the century (Zhang et al. 2011 ). As for PFCs, SF 6
bears monitoring due to its atmospheric lifetime of 3200 years (Table 1.2).
The sulfur and fluorine compound sulfuryl fluoride (SO 2 F 2 ) is used as an insecti-
cide and is also monitored, due to a GWP of 800. However, SO 2 F 2 has a lifetime of
only 36 years. As a result, atmospheric abundances would decline relatively soon after
any corrective action were taken, if such action were ever needed.
The sulfur, fluorine, and carbon containing compound SF 5 CF 3 received consider-
able attention in the media following discovery of a surprisingly large atmospheric
abundance (Sturges et al. 2000 ). This gas was termed a “super GHG” because it has
the highest radiative efficiency, 0.57 W m−2 ppb−1, of any GHG ever studied.
However, recent measurements reveal a slowdown in the emissions to the atmo-
sphere (Sturges et al. 2012 ) and the present RF of climate of SF 5 CF 3 is a miniscule
~8.6 × 10−5 W m−2.^32
Finally, nitrogen trifluoride (NF 3 ) is the latest member of the GHG-club. In 2008,
several studies appeared calling attention to the RF of climate due to this previously
unappreciated compound (Prather and Hsu 2008 ; Tsai 2008 ). As noted above, NF 3
was added to the Kyoto Protocol list of GHGs as part of the Doha amendment in
- The lifetime and GWP of NF 3 are given in Table 1.2. The primary atmo-
(^31) At one time SF 6 was used to cushion sports shoes, but this use ceased a decade ago and is not
considered to be atmospherically important.
(^32) Atmospheric abundance of SF 5 CF 3 was 0.00015 ppb in 2012 (Sturges et al. 2012 ); RF of SF 5 CF 3
= 0.00015 ppb × 0.57 W m−2 ppb−1 = 8.6 × 10−5 W m−2.
1 Earth’s Climate System