SPARC Report on the Mystery of Carbon Tetrachloride

Abstract

CCl4 is a major ODS, accounting for about 12% of the globally averaged inorganic chlorine and bromine in the stratosphere, compared to 14% for CFC-12 in 2012. In spite of the MP controls, there are large ongoing emissions of CCl4 into the atmosphere. Estimates of emissions from various techniques ought to yield similar numbers. However, the recent WMO-UNEP Scientific Assessment of Ozone Depletion estimated a 2007-2012 CCl4 bottom-up emission of 1-4 Gg per year (1-4 kilotonnes per year), based on country-by-country reports to UNEP, and a global top-down emissions estimate of 57 Gg per year, based on atmospheric measurements. This 54 Gg per year difference has not been explained.