Page 59 - Air Pollution Control Engineering

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Fig. 15. Ozone in the atmosphere. (From US EPA.)

As illustrated in Fig. 15, the stratospheric ozone, which provides protection from the
sun’s radiation, is the “good ozone,” whereas the tropospheric ozone, which is detri-
mental to human health and welfare, is the “bad ozone.” For our health or long-term
survival, we must protect the stratospheric ozone in the ozone layer. CFCs are the major
ozone-depleting substances. Other ozone-depleting substances that also reach the strato-
spheric ozone layer include carbon tetrachloride, methyl chloroform, and halons.
Recent major scientific findings and observations (37,38) include the following: (1)
Record ozone depletion was observed in the mid-latitudes of both hemispheres in
1992–1993, and ozone values were 1–2 % lower than would be expected from an
extrapolation of the trend prior to 1991; (2) the Antarctic ozone “holes” of 1992 and
1993 were the most severe on record, and a substantial Antarctic ozone “hole” is
expected to occur each austral spring for many more decades; (3) ozone losses have
been detected in the Arctic winter stratosphere, and their links to halogen chemistry
have been established; (4) the link between a decrease in stratospheric ozone and an
increase in surface ultraviolet (UV) radiation has been further strengthened; (5) the
ozone depletion potential (ODP) for CFC-11 is designated to be 1, and the ODP for
methyl bromide is calculated to be about 0.6; (6) methyl bromide continues to be