Page 271 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 255

soon as forest damages also were detected on calciferous grounds. A summary of a
long-termed research project of Austrian limestone Alps was published by 1998. 233)
Asimple cause-effect chain could not be deduced from this work either. As early as
at the end of the 1980s, it was concluded that novel damages of forests 234) were a
multi factorial illness caused by various stress factors, the most important of being
air pollutants. 235)
• sulphur dioxide (SO ) → oxidation to sulphuric acid (H SO )
2 2 4
• nitric oxides (NO ) → oxidation to nitric acid (HNO )
x 3
• ammonia (NH ) → oxidation to NO and nitric acid
3 x
• hydrofluoric acid (HF)
• hydrogen chloride/hydrochloric acid (HCl)
• photo oxidants (ozone, peroxyacetyl nitrate, … ) (see Section 4.5.2.4)
• organic compounds which only form in the troposphere by reaction with OH
and NO .
x
These compounds are deposited in and on trees by
• dry deposition
• wet deposition (precipitation)
• occult precipitation: surface of leaves and branches of trees and other plants act
as collectors for condensed water vapour originating from clouds and fog.

The details of the corresponding impacts are so far unknown. A simple conversion
factor for novel forest damage is not possible because of the complexity of the
symptoms and little knowledge of the cause and effect relationship. Damaging
impacts caused by acid gases including the base ammonia are handled by an
acidification potential (AP). 236) Other contributions are covered in the category photo
oxidants (see Section 4.5.2.4).
Acidification (current impact category) and over-fertilisation of low nutrition
soils (see impact category eutrophication, Section 4.5.2.6) must be distinguished
from one another. Further impacts caused by acidification are the washing out of
2+
+
+
nutritive substances (e.g. K ,Na and Mg ) plus the mobilisation of heavy metals.
Both can induce damage to vegetation. Furthermore, heavy metals that are washed
out can pollute ground waters.
For pollutants with regional impact – or more general ‘stressors’ – questions with
regard to the selection of the best impact indicator arise, as already discussed in

233) Special issue of Environmental Science and Pollution Research (ESPR) Vol. 5, No. 1 (1998)
ecomed, Landberg a.Lech.
234) In German: ‘neuartige Waldsch¨ aden’; this rather vague expression was created after the real-
ization that acidification alone could not be the reason; it slowly replaced the older term
‘Waldsterben’ (dying of the forests) used mainly in the popular press.
235) Papke et al. (1987).
236) Heijungs et al. (1992), Udo de Haes (1996), Udo de Haes et al. (1999a,b), Norris (2001, 2002) and
Potting et al. (2002).