Carbon Tetrachloride (CCl4) is an Ozone Depleting Substance with a relatively high ODP value of 1.1 (Montreal Protocol value). In response to continued questions about the discrepancy between CCl4 atmospheric observations and reported production and consumption, a workshop on “The Mystery of Carbon Tetrachloride” was organized in October 2015 by the SPARC (Stratosphere-Troposphere Processes And their Role in Climate) activity on CCl4. The workshop findings have been recently published in the SPARC Report on Carbon Tetrachloride Emissions.
Up to now a large discrepancy was noted between emissions of carbon tetrachloride calculated from atmospheric measurements and those based on reported emissions inventories.
New scientific work discussed during the workshop has effectively narrowed the gap between these estimates and largely solved the “mystery” (which might have been the result of unknown sources of emissions).
The scientific work indicates that the atmospheric lifetime of carbon tetrachloride is significantly longer than previously estimated (hence lower emissions are needed to sustain the measured atmospheric concentrations).
The emissions appear to arise mainly from material produced and used in South East Asia, although there are small continuing emissions from North America and Europe. So-called “fugitive” emissions from use of carbon tetrachloride as a chemical feedstock are small (at less than 1% of global production).