Page 223 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 209

climate conditions. Some endpoint methods have proposed endpoint characterisa-
tion factors (e.g. Ecoindicator99, ReCiPe, LIME, IMPACT World+ and
LC-IMPACT), but due to the state of current climate damage models, they inevi-
tably miss many damage pathways and are accompanied by very large uncertain-
ties, where even the size of these uncertainties is difficult to assess. This is why
other endpoint methods (e.g. IMPACT 2002+) refrain from endpoint modelling for
this impact category and present the midpoint results for climate change together
with the endpoint results for the rest of the impact categories. In any case, endpoint
results for climate change must be taken with the greatest caution in the interpre-
tation of results. For further details see Chap. 40 and Hauschild and Huijbregts
(2015).

10.7 Stratospheric Ozone Depletion

10.7.1 Problem

Ozone (O 3 ) is a highly reactive and unstable molecule consisting of three oxygen
atoms and forms a bluish gas at normal ambient temperature with a distinct
somewhat sharp odour. This molecule is present in lower atmospheric layers
(tropospheric ozone as a consequence of photochemical ozone formation) and in
larger concentrations (about 8 ppmv) also in higher altitudes between 15 and 40 km
above ground (stratospheric ozone). Tropospheric, ground-level ozone is consid-
ered a pollutant due to its many harmful effects there on humans, animals, plants
and materials (see Sect. 10.10). However, as a component of stratospheric atmo-
spheric layers, it is vital to life on planet Earth, due to its capacity to absorb
energy-rich UV radiation, thus preventing destructive amounts of it from reaching
life on the planet’s surface.
Stratospheric ozone depletion refers to the declining concentrations of strato-
spheric ozone observed since the late 1970s, which are observed in various ways:
(1) As the ‘ozone depletion area’ or ‘ozone hole’ (an ambiguous term often used in
public media referring to an area of critically low stratospheric ozone concentra-
tion), a recurring annual cycle of relatively extreme drops in O 3 concentrations over
the poles which start to manifest annually in the late winter/early spring of each
hemisphere (i.e. from around September/October over the South pole and
March/April over the North pole) before concentrations recover again with
increasing stratospheric temperatures towards the summer. ‘Ozone holes’ have been
observed over Antarctic since the early 1980s as shown in Fig. 10.10. (2) A general
decline of several percent per decade in O 3 concentrations in the entire stratosphere.
Ozone concentration is considered as critically low when the value of the integrated
ozone column falls below 220 Dobson units (a normal value being about 300
Dobson units). Dobson Units express the whole of ozone in a column from the
ground passing through the atmosphere.