110
Chapter 1, Figure 1-1, 2010 SAP Report
NOAA
100
AGAGE
90
1990
1995
2000
2005
Emission or Production (Gg/yr)
Global Surface Mixing Ratio (ppt)
WMO/UNEP (2011) Carbon Tetrachloride (CCl4)
300
Chapter 1, Figure 1-5, 2010 SAP Report
Rate of change

E
200

100
2010
0
1985 1990 1995 2000 2005 2010


Carbon tetrachloride (CCl4) continues to decrease in the atmosphere

… but its abundance is not consistent with reported emissions and known lifetimes.

“Bottom-up” emissions derived from data reported to UNEP are highly
variable and on average appear smaller than ”Top-down” inferred from
observed trends.

Discrepancy (~ 40 Gg per year):

Cannot be explained by the lifetime. CCl4 lifetime, = 28±5 years.

Errors in reporting, or errors in analysis of reported data, possible illegal prod.

Unknown sources or poorly estimated sinks
Emission or Production (Gg/yr)
New information
300
Chapter 1, Figure 1-5, 2010 SAP Report
200
Rate of change

E

100
0
1985 1990 1995 2000 2005 2010

 Atmospheric lifetime will increase from 35 years (WMO, 2011) to approximately 50 years.

 ocean= 94 years, soil=∞
1


1
 atm

1
 ocean

1
 soil
 Total lifetime increases from 26 years to about 33 years - ~ the lower bound in WMO (2011)
 Fraser et al. (2013) estimate that global CCl4 emissions from landfills could be 8-12 Gg/yr.
 Fraser et al. also suggests
 there may be some small emission from H2O chlorination
 Any industrial procedure that uses chlorine in association with organics is likely to produce at
least some CTC. An example is the chlorination of carbon monoxide to produce phosgene
(COCl2), which is used on a large scale in production of isocyanates, the precursors of
polyurethanes.
CCl4 summary
• A revision of the lifetime will reduce the “topdown” emission estimate by approximately 10-20
Gg/yr
• Estimates of global legacy emissions are
approximately 8-12 Gg/yr, revising upward the
“bottom-up” emission estimate
• The 40 Gg/yr emission budget gap between the
“top-down” and “bottom-up” estimates has been
narrowed, but not quite closed.
ODP and GWP of proposed CFC: R-316c
• Two isomers
• Not clear if the use is for only onecould be a mixture
• Atmospheric lifetime and
properties are not very different
for the two isomers
Based on work done at NOAA Boulder:
J. B. Burkholder, V. Papadimitriou, M. McGillen, A. Jubb, S.
Smith, B. Hall, R. Portmann
Work not yet-peer reviewed. To be published.
The photolytic loss of RC-316c
has been evaluated by laboratory studies
• Gas phase reactions in the
troposhere too slow to contribute
o Mainly lost in the stratosphere:
UV photolysis in the stratosphere
is the major loss process
o O(1D) reactions contribute in the
stratosphere
• Similar to CFC-12 and 113
• Slightly higher cross section in
the key “window” region: 190210 nm
• Other tropospheric loss processes
may contribute a little
Lifetimes and ODP
2D model calculations using laboratory data
Molecule Lifetime, yrs
CFC-11
58
CFC-12
102
N2O
122
R-316c
81
Consistent with simple scaling:
0.54 rel to CFC-11
0.41 rel to CFC-12
2nd model estimated 0.5 for an ODP
ODP
1
0.97
0.46
R-316c is a potent ODS with an ODP
of approximately 0.5
IR Cross sections and GWP
Based on laboratory data and calculated atmospheric lifetime,
the GWP has been calculated.
Molecule
20-yr
GWP
100-y
GWP
500-y
GWP
CFC-11
6730
4750
1620
CFC-12
11000
10900
5200
289
298
153
4340
4300
2050
N2O
R-316c
R-316C is a potent greenhouse gas,
roughly half as much as CFC-12 and comparable to CFC-11