POLLUTION
Cold air surges in East Asia are driving up into the tropical skies, increasing quantities of short-lived chemicals previously thought to be of so little harm to the ozone layer that they are not covered by the Montreal Protocol
Newthreat blows in for ozone layer
An international teamof researchers, led by the University of East Anglia’s David Oram, has found an unexpected, growing danger to the ozone layer from substances not regulated by the treaty
the atmosphere decreased in the 1990s and early 2000s, but over the past decade dichloromethane became approximately 60 per centmore abundant. “This was amajor surprise to the scientific community and we were keen to discover the cause of this sudden increase,” says Oram. “We expected that the new emissions could be coming fromthe developing world, where industrialisation has been increasing rapidly.” The teamset out tomeasure air pollution in East
Asia to figure out where the increase in dichloromethane was coming fromand if it could affect the ozone layer. “Our estimates suggest that Chinamay be responsible for around 50-60 per cent of current global emissions [of dichloromethane], with other Asian countries, including India, likely to be significant emitters as well,” says Oram. The scientists collected air samples on the ground
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heMontreal Protocol was agreed 30 years ago to phase-out chemicals destroying the ozone layer, theUV-radiation shield in the Earth’s stratosphere. The treaty has helped the layer begin the slow process of healing,
lessening the impact to human health fromincreased exposure to damaging solar radiation. “Ozone depletion is a well-known phenomenon
and, thanks to the success of theMontreal Protocol, is widely perceived as a problemsolved,” saysDavid Oram, a research fellow of theUK’sNational Centre for Atmospheric Science. But increasing emissions of ozone-destroying substances that are not regulated by theMontreal Protocol are threatening to affect the recovery of the layer, according to new research. The substances in question were not considered
damaging before because, as Oramexplains, they were “generally thought to be too short-lived to reach the stratosphere in large quantities.” The new Atmospheric Chemistry and Physics study raises the alarmover fast-increasing emissions of some of these very short-lived chemicals in East Asia, and shows how they can be carried up into the stratosphere and deplete the ozone layer. Emissions of ozone-depleting chemicals in places
like China are especially damaging because of cold- air surges in East Asia that can quickly carry industrial pollution into the tropics. One of the new threats is dichloromethane, a
substance with uses varying frompaint stripping to agricultural fumigation and the production of pharmaceuticals. The amount of this substance in
inMalaysia and Taiwan, in the region of the South China Sea, between 2012 and 2014, and shipped themback to theUK for analysis. They routinely monitor around 50 ozone-depleting chemicals in the atmosphere, some of which are now in decline as a direct consequence of theMontreal Protocol. Dichloromethane was found in large amounts, and
so was 1,2-dichloroethane, an ozone-depleting substance used tomake PVC. China is the largest producer of PVC, which is used inmany construction materials, and its production in the country has increased rapidly in the past couple of decades. But the rise in dichloroethane emissions was unexpected and surprising, says Oram, because the chemical is both a valuable commodity and highly toxic. “One would expect that care would be taken not to release [dichloroethane] into the atmosphere.” Data collected frompassenger aircraft that flew
over Southeast Asia betweenDecember 2012 and January 2014 showed that the substances weren’t only present at ground level. “We found that elevated concentrations of these same chemicals were present at altitudes of 12 kmover tropical regions,many thousands of kilometres away fromtheir likely source, and in a region where air is known to be transferred into the stratosphere,” says Oram. If the chemicals that were now discovered in
unexpectedly large amounts can reach the ozone layer in significant quantities, they can cause damage. “We are highlighting a gap in theMontreal Protocol thatmay need to be addressed in the future, particularly if atmospheric concentrations continue to rise,” Oramconcludes. EE
December 2017 /// Environmental Engineering /// 19
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