Page 264 - Materials Chemistry, Second Edition

248 4 Life Cycle Impact Assessment

For a quantification of summer smog within an impact assessment (LCIA) it is
not possible to consider continuously changing, climate related weather conditions.
As is well known, LCA bears little relation to space and time, which proves to be a
problem in this impact category. Accordingly there is low consensus among the LCA
method developers: proponents of the causal chain are not amused if emissions
of reactive organic compounds 211) are fully attributed to the summer smog; those
supporting the precautionary principle will accept this attribution of emissions as
the worst case being only a relative one in view of a possible contribution to summer
smog. The fact that it only occurs at times and under unfavourable conditions
is regarded as less important by this approach – according to the principle ‘less is
better’.
A minimum requirement for quantification will therefore be a scale of the relative
effectiveness (reactivity) of hydrocarbons and CO. A respective first scale has been
elaborated as early as 1976. 212) Since the reaction of volatile hydrocarbons and CO
with OH radicals is an important phase, the second order reaction rate constant of
OH with the substance to be weighted is chosen (see also 213) );
3
s
k OH = 10 –10 to 10 –11 cm molecule –1 –1 (very reactive)
This implies a very high reactivity (e.g. propene and terpenes). The reaction rate
constant can be measured over many orders of magnitude. At the other end of
the scale – for persistent compounds – it serves for a determination of a transition
probability into the stratosphere:
3
s
k OH = 10 –15 to 10 –14 cm molecule –1 –1 (inert)
The formation of ozone at ground level serves as a mere parameter of reference for
the noxiousness of the photo smog because O is by no means the only pollutant
3
by which summer smog is incompatible to human health and the environment.
There are a number of other photo oxidants with human- and ecotoxicity such as
peroxyacetyl nitrate and aldehydes like acrolein, a lachrymal gas. Less known are
reaction products of OH and NO with organic compounds such as
x
• trichloroacetic acid (TCA), for example, formed from of trichloro- and tetra-
chloroethane 214)
• nitrophenols (formed from benzene and toluene, BTX hydrocarbons) especially
the extremely phytotoxic dinitrophenols; dinitro-o-cresol (DNOC) is a former in
Germany non-authorised herbicide which is formed besides other nitrophenols
and nitrocresols in the atmosphere). 215)
Both pollutants may play a role in the degradation of forests, which was attributed
to acidification earlier (see Section 4.5.2.5). However, acidification alone cannot be
the cause of these damages as they also occur on calcareous soils.

211) These releases are also designated as non-methane volatile organic compounds (NMVOC).
212) Darnall et al. (1976).
213) Kl¨ opffer and Wagner (2007a).
214) Renner, Schleyer and M¨ uhlhausen (1990).
215) Rippen et al. (1987).