Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 105

Ozone-Depleting Substances in the Atmosphere Since
January 1989
Warning: For the next few pages, we are going to be faced with some difficult-to-pronounce
chemical names that look as if they were designed for an elocution exam. Their acronyms
are not much better. If you find this difficult, do not despair. You will be able to follow the
storyline by just remembering that CFCs and methyl chloroform were first-generation de-
pleting substances. Most (but not all) of the remainder were second-generation substances
intended to replace them.
January 1989 was the year when the restriction on the first batch of ozone-depleting
substances (the CFCs and methyl chloroform) under the Montreal Protocol entered into
force. The reductions in use of CFCs was originally achieved by replacing them with sub-
stances that still contained chlorine or other halogens but which had shorter lives in the at-
mosphere.Notably,thesewerehydrochlorofluorocarbons(HCFCs),methylbromideandhy-
drobromofluorocarbons (HBFCs). However, these replacements were still a source of chlor-
ine or bromine to the stratosphere. Consequently, they were scheduled for elimination in
subsequent revisions (termed adjustments ) to the protocol.
TheactionsagainstCFCsandmethylchloroformwerenonetoosoon.Aswehaveseen,
a huge reservoir of ozone-depleting substances had built up in the troposphere and strato-
spherebecause mostofthemwereveryresistant toanyformofdegradation. Therefore, CFC
concentrations in the atmosphere continued to increase well into the 1990s despite the fact
that due to the protocol, emissions were falling. It was as if we had turned down the taps
when filling up the bath but had not turned them off. The tub continued to fill. By 2005,
the tide was slowly beginning to turn. Tropospheric chlorine had decreased to roughly 92%
from its peak value reached between 1994 and 1995. Most of the decline came from the re-
latively rapid loss of methyl chloroform because this substance has a comparatively short
atmospheric life of between six months and 25 years. In 2010, the WMO reported that the
total tropospheric abundance of chlorine from ozone-depleting substances had declined by