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,τ= 28±5 years.

Errors in reporting, or errors in analysis of reported data, possible illegal prod.

Unknown sources or poorly estimated sinks

WMO/UNEP (2011) Carbon Tetrachloride (CCl4)

NOAAAGAGE

Chapter 1, Figure 1-1, 2010 SAP Report

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Chapter 1, Figure 1-5, 2010 SAP Report

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Atmospheric lifetime will increase from 35 years (WMO, 2011) to approximately 50 years.

τocean= 94 years, τsoil=∞ 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.

New informationChapter 1, Figure 1-5, 2010 SAP Report

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CCl4 summary

• A revision of the lifetime will reduce the “top-down” 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 one-

could 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: 190-210 nm

• Other tropospheric loss processes may contribute a little

Lifetimes and ODP

2D model calculations using laboratory data

Molecule Lifetime, yrs ODP

CFC-11 58 1

CFC-12 102 0.97

N2O 122

R-316c 81 0.46Consistent with simple scaling:0.54 rel to CFC-110.41 rel to CFC-122nd model estimated 0.5 for an ODP

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.

R-316C is a potent greenhouse gas, roughly half as much as CFC-12 and comparable to CFC-

11

Molecule 20-yr GWP

100-y GWP

500-y GWP

CFC-11 6730 4750 1620

CFC-12 11000 10900 5200

N2O 289 298 153

R-316c 4340 4300 2050