Page 221 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 207

• Water vapour: *55%
• Carbon dioxide (CO 2 ): 39%
• Ozone (O 3 ): 2%
• Methane (CH 4 ): 2%
• Nitrous oxide (N 2 O): 2%
Anthropogenic water vapour emissions do not contribute to climate change as
the presence of water vapour is a function of atmospheric temperature and evap-
oration surfaces. For the other constituents however, anthropogenic sources for
CO 2 ,CH 4 and N 2 O do contribute to increasing the greenhouse effect beyond its
natural state. Further relevant GHG emissions also include industrial volatile and
persistent halocarbons (chlorinated fluorocarbons including CFCs (“freons”),
HCFCs and perfluoromethane) and sulphur hexafluoride (SF 6 ). GHG emissions are
attributable to almost any human activity. The most important contributing activ-
ities are: burning of fossil fuels and deforestation (including releasing carbon from
soil and change in albedo). Figure 10.9 shows the global contributions to GWP
from five major economic sectors for the year 2010. Industry, agriculture, housing
and transport are the dominating contributors to GHG emissions.
In addition to the greenhouse gases which all exert their radiative forcing in the
atmosphere over timespans of years to centuries, there are also more short-lived
radiative forcing agents that are important for the atmospheric temperature in a
more short-term perspective. These include:
• Sulphate aerosols (particulate air pollution caused by the emission of sulphur
oxides from combustion processes) that reduce the incoming radiation from the
sun and thus have a negative contribution to climate change
• Nitrogen oxides NO and NO 2 (jointly called NO x ) and VOC from combustion
processes, that contribute to photochemical formation of ozone (see Sect. 10.10)
which is a strong but short-lived radiative forcing gas
The radiative forcing impact of short-lived agents like these is very uncertain to
model on a global scale, and their contribution to climate change is therefore not
currently included in LCIA.

10.6.4 Existing Characterisation Models

All existing LCIA methods use the GWP (Eq. 10.4) for midpoint characterisation.
In terms of time horizon most use 100 years, which has been recommended by
IPCC as the best basis for comparison of GHGs, while some methods use a
500 year time horizon to better incorporate the full contribution from the GHGs. As
mentioned, the longer time perspective puts a higher weight on long-lived GHGs
like nitrous oxide, CFCs and SF 6 and a lower weight on short-lived GHGs like
methane.