A team of scientists from the University of Bristol, along with colleagues from the United States, Australia, Switzerland and South Korea, investigated the origin of emissions of carbon tetrachloride (tetrachloromethane), a compound that contributes to the destruction of the Earth's ozone layer. Its production, in which the compound can get into the atmosphere, was banned back in 2010, but studies have shown that emissions have not decreased - about 40 thousand tons are released into the atmosphere annually. Scientists estimated emissions from East Asia using ground and air sources of atmospheric concentration data near the Korean Peninsula, using two models that simulate the transport of gases through the atmosphere.
The study's lead author, Mark Lunt of the University of Bristol, said carbon tetrachloride emissions from the East Asia region account for a large share of global emissions - significantly more than some previous studies have suggested. Despite the phase-out of carbon tetrachloride production in 2010, scientists have found no evidence of subsequent emissions reductions. In fact, emissions from some regions may have even increased slightly since 2010. Moreover, the results of the study show the emergence of a new source of emissions from China's Shandong province after 2012.
Although the results of this and earlier studies in Europe and the United States now explain a large part of the global distribution of carbon tetrachloride emissions, there are still large knowledge gaps among experts. In addition, recent reports have suggested that large quantities may be unintentionally released from the production of other chemicals such as chlorine.
Study co-author Matt Rigby of the University of Bristol said the work shows the location of carbon tetrachloride emissions, but the researchers don't know which processes and industries are responsible for them. This is important to note because, according to Rigby, it is not known whether the emissions are intentional or not. He added that in some areas, such as India, South America and other parts of Asia, emissions of ozone-depleting gases may also continue, but atmospheric measurements are not being taken.
Such studies show the importance of continuous monitoring of ozone-depleting gases, Lunt said, as there is a temptation to mark the problem of ozone depletion as solved. Monitoring is essential to ensure the continued success of the phase-out of such production.
