The return of the ozone eaters

Atmospheric levels of an ozone-destroying chemical,
trichlorofluoromethane, or CFC-11, are on the rise again despite it being banned under the Montreal Protocol in 2010. CFC-11 was widely used as a foaming agent, but phased out almost a decade ago because of its role in helping to form the ozone hole over Antarctica that begins to form each year in September. The US National Oceanic & Atmospheric Administration based at the University of Boulder Colorado says that emissions of this problematic gas are increasing which points to an unknown and unreported production source. Chlorofluorocarbons CFCs, were once widely used as refrigerants and as foaming agents. Alternatives were found and manufacture of this large class of materials was were phased out because of their damaging effects on the ozone layer. There still exist reservoirs of CFC-11 and other compounds in old refrigeration units and insulating construction materials. The NOAA is yet to identify the cause of this recent rise in atmospheric CFC-11 concentration.