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 Carbon tetrachloride (CCl 4 ) continues to decrease in the atmosphere  … but its abundance is not consistent with reported emissions and known lifetimes.

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Presentation on theme: " Carbon tetrachloride (CCl 4 ) continues to decrease in the atmosphere  … but its abundance is not consistent with reported emissions and known lifetimes."— Presentation transcript:

1  Carbon tetrachloride (CCl 4 ) 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. CCl 4 lifetime,  = 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 (CCl 4 ) NOAA AGAGE Chapter 1, Figure 1-1, 2010 SAP Report Global Surface Mixing Ratio (ppt) Chapter 1, Figure 1-5, 2010 SAP Report Emission or Production (Gg/yr)

2  Atmospheric lifetime will increase from 35 years (WMO, 2011) to approximately 50 years.    ocean = 94 years,  soil = ∞  Total lifetime increases from 26 years to about 33 years - ~ the lower bound in WMO (2011)  Fraser et al. (2013) estimate that global CCl 4 emissions from landfills could be 8-12 Gg/yr.  Fraser et al. also suggests there may be some small emission from H 2 O 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 (COCl 2 ), which is used on a large scale in production of isocyanates, the precursors of polyurethanes. New information Chapter 1, Figure 1-5, 2010 SAP Report Emission or Production (Gg/yr)

3 CCl 4 summary A revision of the lifetime will reduce the “top- down” emission estimate by approximately 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.

4 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.

5 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: nm Other tropospheric loss processes may contribute a little

6 Lifetimes and ODP 2D model calculations using laboratory data MoleculeLifetime, yrsODP CFC CFC N2ON2O122 R-316c Consistent with simple scaling: 0.54 rel to CFC rel to CFC-12 2 nd model estimated 0.5 for an ODP R-316c is a potent ODS with an ODP of approximately 0.5

7 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 Molecule20-yr GWP 100-y GWP 500-y GWP CFC CFC N2ON2O R-316c


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