Ars Technica: Carbon tetrachloride (CCl4) is one of the ozone-destroying molecules banned by the 1989 Montreal Protocol. On Wednesday, NASA announced that although the atmospheric levels of most of the banned chemicals have fallen as expected, CCl4 levels have not. NASA's comparison of current CCl4 sources with a chemistry-climate model suggests there may be an unknown source. According to Qing Liang of NASA's Goddard Space Flight Center, that source could be unidentified industrial leaks, emissions from contaminated sites, or something else entirely. Finding the source is likely to be difficult: Because CCl4 is highly toxic, the pollution is probably coming from a poorly regulated area.
