An international team of researchers has reported a surprising rise in global levels of atmospheric chloroform. The study in Nature Geoscience posits that the ozone-depleting substance is coming from eastern China (2018, DOI: 10.1038/s41561-018-0278-2).
The rate of increase per year in global chloroform emissions from 2010 to 2015
Atmospheric chloroform can come from both natural sources, such as marine algae, and anthropogenic sources, which mainly include chlorodifluoromethane production and water chlorination. The team found that from 2010 to 2015, global chloroform levels rose at a rate of 3.5% each year, despite being relatively stable or declining in previous decades. They calculated that the increase in emissions detected at measurement stations in South Korea and Japan was similar in magnitude to the global emissions increase and, using models of wind patterns, traced the emissions’ origins back to eastern China, which is highly industrialized. Recently, researchers discovered rogue emissions from east Asia of the banned substance trichlorofluoromethane that may delay ozone recovery by a decade. The spike in chloroform emissions could also delay the ozone layer’s recovery by several months or even years if the rate of increase continues.
With an atmospheric lifetime of less than six months, chloroform is considered a very short-lived substance (VSLS) and is not regulated by the 1987 Montreal Protocol, the successful global agreement to reduce the emission of ozone-destroying gases. Susann Tegtmeier of the Helmholtz Center for Ocean Research writes in an accompanying review that the findings are “an important step toward opening the discussion of regulating the anthropogenic VSLS emissions.”