Page 224 - Materials Chemistry, Second Edition

210 R.K. Rosenbaum et al.

Fig. 10.10 Evolution of the hole in the ozone layer over Antarctica in September from 1980 to
2015 (Source NASA Ozone Watch 2016, public domain, http://ozonewatch.gsfc.nasa.gov/
monthly/climatology_09_SH.html)

Data for Europe for example show a decline of 5.4% of stratospheric O 3 con-
centration per decade since the 1980s when measured in winter and spring, with an
improving trend over the period 1995–2000. However, in later years low concen-
tration records were broken on an almost annual basis. To date, the largest ‘ozone
2
hole’ in human history was observed in 2006 with 29.5 million km over
2
Antarctica, but even in 2015 its largest spread still reached 28.2 million km . The
largest Arctic ‘ozone hole’ ever was observed in 2011.
Impacts of stratospheric ozone depletion are essentially linked to reduced
absorption of solar radiation in the stratosphere leading to increased UV radiation
intensities at the planet surface, of which three broad (wavelength) classes are
distinguished: UV-C, UV-B and UV-A. The impact of UV radiation on living
organisms depends on its wavelength, the shorter the more dangerous. UV-C is the
most dangerous wavelength range, but almost completely filtered by the ozone
layer. UV-B (wavelengths 280–315 nm) is of the most concern due to ozone layer
depletion, while UV-A is not absorbed by ozone.
Depending on duration and intensity of exposure to UV-B, impacts on human
health are suspected to include skin cancer, cataracts, sun burn, increased skin cell
ageing, immune system diseases, headaches, burning eyes and irritation to the
respiratory passages. Ecosystem effects are linked to epidermal damage to animals
(observed e.g. in whales), and radiation damage to the photosynthetic organs of
plants causing reduced photosynthesis, leading to lower yields and crop quality in
agricultural produce and loss of phytoplankton, the primary producers of aquatic
food chains, particularly in the polar oceans. Additionally, UV-B accelerates the
generation of photochemical smog, thereby stimulating the production of tropo-
spheric ozone, which is a harmful pollutant (see Sect. 10.10).