Carbon Tetrachloride Emissions from the US during 2008 – 2012 Derived from Atmospheric Data Using Bayesian and Geostatistical Inversions

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Lei Hu1, Stephen A Montzka1, Ben Miller2, Arlyn E Andrews3, John B Miller4, Scott Lehman5, Colm Sweeney4, Scot M Miller6, Kirk W Thoning7, Carolina Siso8, Elliot L Atlas9, Donald Ray Blake10, Joost A De Gouw3, Jessica Gilman11, Geoffrey S Dutton8, James W Elkins1, Brad David Hall7, Huilin Chen12, Marc Laurenz Fischer13, Marikate Ellis Mountain14, Thomas Nehrkorn15, Sebastien Biraud13 and Pieter P Tans16, (1)NOAA Boulder, Boulder, CO, United States, (2)NOAA, Earth System Research Laboratory, Boulder, CO, United States, (3)NOAA Earth System Research Lab, Boulder, CO, United States, (4)NOAA Boulder, ESRL, Boulder, CO, United States, (5)University of Colorado at Boulder, INSTAAR, Boulder, United States, (6)Harvard University, Cambridge, MA, United States, (7)NOAA/ESRL GMD, Boulder, CO, United States, (8)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (9)University of Miami, Miami, FL, United States, (10)University of California Irvine, Irvine, CA, United States, (11)NOAA ESRL, Boulder, CO, United States, (12)Centre for Isotope Research, Groningen, Netherlands, (13)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (14)Atmospheric and Environmental Research, Inc., Lexington, MA, United States, (15)Atmospheric and Environmental Research Lexington, Lexington, MA, United States, (16)NOAA/Earth System Research Lab, Boulder, CO, United States
Global atmospheric observations suggest substantial ongoing emissions of carbon tetrachloride (CCl4) despite a 100% phase-out of production for dispersive uses since 1996 in developed countries and 2010 in other countries. Little progress has been made in understanding the causes of these ongoing emissions or identifying their contributing sources. In this study, we employed multiple inverse modeling techniques (i.e. Bayesian and geostatistical inversions) to assimilate CCl4 mole fractions observed from the National Oceanic and Atmospheric Administration (NOAA) flask-air sampling network over the US, and quantify its national and regional emissions during 2008 – 2012. Average national total emissions of CCl4 between 2008 and 2012 determined from these observations and an ensemble of inversions range between 2.1 and 6.1 Gg yr-1. This emission is substantially larger than the mean of 0.06 Gg/yr reported to the US EPA Toxics Release Inventory over these years, suggesting that under-reported emissions or non-reporting sources make up the bulk of CCl4 emissions from the US. But while the inventory does not account for the magnitude of observationally-derived CCl4 emissions, the regional distribution of derived and inventory emissions is similar. Furthermore, when considered relative to the distribution of uncapped landfills or population, the variability in measured mole fractions was most consistent with the distribution of industrial sources (i.e., those from the Toxics Release Inventory). Our results suggest that emissions from the US only account for a small fraction of the global on-going emissions of CCl4 (30 - 80 Gg yr-1 over this period). Finally, to ascertain the importance of the US emissions relative to the unaccounted global emission rate we considered multiple approaches to extrapolate our results to other countries and the globe.