Chlorocarbons remain a threat to Earth’s ozone layer

The Montreal Protocol, which went into effect in 1989, led to the phaseout of a suite of chlorofluorocarbons and related halocarbons. Although useful as refrigerants, propellants, and fire-extinguishing agents, these chemicals were found to be destroying Earth’s atmospheric ozone layer, which helps protect the planet from harmful solar UV radiation. The treaty and its revisions have reduced atmospheric concentrations of the problematic chemicals so that the ozone layer, which reached a low point in thickness in the 1990s, has begun to heal—ozone depletion is starting to look like a problem solved. But new measurements from Southeast Asia reported by an international team led by David E. Oram of the University of East Anglia have revealed that increasing emissions of some halocarbons not regulated by the Montreal Protocol are threatening to slow or possibly reverse the recovery (Atmos. Chem. Phys. 2017, DOI: 10.5194/acp-17-11929-2017). In particular, concentrations of 1,2-dichloroethane, used to make poly(vinyl chloride), and dichloromethane, used as a paint stripper and process chemistry solvent, have been rising over the past decade because of growing industrial activity in China and other countries in the region. These chemicals were thought to be too short-lived to reach the stratosphere in significant amounts, so they were not included in the treaty. The rising emissions in Southeast Asia are concerning, Oram explains, because prevailing winds carry the compounds to the tropics, where they more easily rise into the atmosphere and can do damage. “We are highlighting a gap in the Montreal Protocol that may need to be addressed in the future, particularly if atmospheric concentrations continue to rise,” Oram says.