ILCD Handbook: Framework and requirements for LCIA models and ...

ILCD Handbook: Framework and requirements for LCIA models and indicators First edition
4.2 Ozone Depletion
4.2.1 Framework and scope
The ―hole in the ozone layer‖ was detected over Antarctica in 1985. Ozone is continuously
formed and destroyed by sunlight and chemical reactions in the stratosphere. Ozone
depletion occurs if the rate of ozone destruction is increased due to fugitive losses of
anthropogenic substances which persist in the atmosphere. Stratospheric ozone, which is
90% of the total ozone in the atmosphere, is vital for life because it hinders harmful solar
ultraviolet UV-B radiation from penetrating the lower levels of the atmosphere. If not
absorbed, UV-B radiation below 300 nanometres will reach the troposphere and the surface
of the earth, where it can increase the human risk of skin cancer and cataract when
appropriate precautions are not taken. It may also cause premature aging and suppression
of the immune system. In addition to the increased risk to ‗Human Health‘ the UV-B radiation
can also damage terrestrial plant life and aquatic ecosystems.
The characterization factor for ozone depletion accounts for the destruction of the
stratospheric ozone layer by anthropogenic emissions of ozone depleting substances (ODS).
These are persistent chemicals that contain chlorine or bromine atoms. Because of their long
atmospheric lifetime Cl and Br are able to reach the stratosphere. Chlorine atoms in
chlorofluorocarbons (CFC) and bromine atoms in halons are effective in degrading ozone
due to heterogeneous catalysis, which leads to a slow depletion of stratospheric ozone
around the globe. The chlorine and bromine atoms that are released from these reactions
have the ability to destroy a large quantity of ozone molecules in the stratosphere because
they act as free radical catalysts in a sequence of degradation reactions, in which they react
with ozone to split it into molecular and atomic oxygen without being consumed (WMO,
2003) as shown:
Cl + O3 ClO + O2
Br + O3 BrO + O2
ClO + O Cl + O2
ClO + BrO Cl + Br + O2
Ozone depletion potentials
The ozone depletion potential (ODP) of a substance is a relative measure for the potency
to form EESC (Equivalent Effective Stratospheric Chlorine). The ODPs are equivalency
factors that encompass the atmospheric residence time of ozone depleting substances, the
formation of EESC and the resulting stratospheric ozone depletion.
ODP steady state
Steady-state ODPs represent the cumulative effects on ozone over an infinite time scale:
ODP x (
)
O3
x
O3
CFC
11
where δ[O3]x and δ[O3]CFC-11 denote the total changes in the stratospheric ozone in the
equilibrium state due to annual emissions of halocarbon species x and CFC-11, respectively.
The most recent steady-state ODPs were published by the World Meteorological
Organization in 1999 and are the equivalency factors for the impact category of ‗Ozone
Depletion‘. This model is recommended to be used both in midpoint and endpoint methods.
4 Requirements for specific impact categories 33