A flourishing black market in chlorofluorocarbons is undermining international efforts to restore the ozone layer, an expert has warned.Paul Fraser, a senior principal research scientist with CSIRO Atmospheric Research, warns in the June edition of the international journal Atmospheric Environment that smuggling is a small but direct threat to the ozone layer's recovery.In the same issue, fellow academic Julian Newman identifies China and Russia as the leading suppliers of illegal ozone-depleting substances.