The seasonal ozone hole over Antarctica (pictured, blue) was slightly smaller this year than in past years, measuring around 21 million square kilometres in late September, the US National Oceanic and Atmospheric Administration (NOAA) reported last week. "We cannot say that this represents recovery, but it is certainly good news," says NOAA researcher Bryan Johnson. Chlorine levels at the poles, once raised by ozone-depleting foams, sprays and refrigerants, are now on the decline, the agency notes. The use of hydrofluorocarbons (HFCs) as an alternative to these chemicals has raised other concerns, however, because HFCs are powerful greenhouse gases. Last week, negotiations in Bangkok fell short of an agreement to regulate HFCs under the Montreal Protocol on Substances that Deplete the Ozone Layer. See page 593 for more.
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