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Dichloromethane Delays Ozone Recovery

Established in 1987, the Montreal Protocol aimed to protect the stratospheric ozone layer by eliminating the production and consumption of substances causing ozone depletion. These substances comprise of anthropogenic chlorine-containing chemicals, such as chlorofluorocarbons (CFCs) and halons, and are responsible for phenomena like the Antarctic Ozone Hole.

Thirty years later, the Montreal Protocol successfully reduced the concentration of these gases, decreasing chlorine levels in the lower atmosphere. However, a recent increase in usage of dichloromethane (DCM) may revert ozone recovery to pre-1980 levels. Its popular use in industrial applications, such as being used as a metal cleaner and paint remover may explain this situation. Between 2000 and 2012, atmospheric concentrations of DCM increased at an average rate of approximately eight percent per year.

Unlike other ozone-depleting substances, DCM production and consumption are not monitored by the Montreal Protocol. Scientists previously believed that DCM was too short-lived to reach the atmosphere, containing a shorter half-life of months compared to those of CFCs. Therefore, many industries have adopted the gaseous chemical to produce hydrofluorocarbon HFC-32, a widely used replacement for CFCs.

Researchers from the University of Lancaster gathered measurements from the United States National Ocean and Atmospheric Administration to model the effects of future increases in DCM usage. Using the global Chemical Transport Model (CTM), they predicted that continued dependence on the gaseous substance may offset benefits of the Montreal Protocol and delay recovery of the ozone by thirty years or more. However, if DCM usage does not exceed the current rate, a possible recovery date may be found in the next century.

The Montreal Protocol has been highly successful in preventing ozone loss. Had the Protocol not been established, the Antarctic Ozone Hole would have experienced a significant increase of roughly forty percent by 2014. However, lack of DCM monitoring adds uncertainty to the future of ozone levels. A broad consideration of atmospheric trends and increased regulation on DCM and other non-Montreal Protocol compounds would greatly enhance future ozone predictions.

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Editor: Sydney Korsunsky