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:
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)
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)
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.
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: nm Other tropospheric loss processes may contribute a little
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
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