Page 273 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 257

Sample Calculation

Conversion of 1 kg nitric acid to kilogram SO -equivalents:
2
+
+
A molar ratio of n(HNO )/n(H O ) = 1/1, a molar ratio n(H SO )/n(H O ) = 1/2
3
3
2
3
3
and a molar ratio n(H SO )/n(SO ) = 1/1 implies the following:
3
2
2
m(HNO )× M(SO )
m(SO )= 3 2
2
M(HNO )× 2
3
−1
(M(HNO ) = 63 g mol −1 and M(SO ) = 64 g mol ).
2
3
From (HNO ) = 1 kg thus 0.51 kg SO -equivalents result.
3
2
The conversion for 1 kg ammonia is similar; it produces protons by oxidation into
HNO , in the atmosphere or by nitrification:
3
+
Amolarratioof n(NH )/n(HNO ) = 1/1, amolarratioof n(HNO )/n(H O ) = 1/1,
3
3
3
3
+
amolarration(H SO )/n(H O ) = 1/2andamolarratioof n(H SO )/n(SO ) = 1/1
3
2
2
2
3
3
implies
m(NH )× M(SO )
m(SO )= 3 2
2
M(NH )× 2
3
−
−1
(M(NH ) = 17 g mol −1 and M(SO ) = 64 g mol ).
3
2
For m(NH ) = 1 kg thus result 1.88 kg SO -equivalents.
2
3
As an alternative to mass equivalents mol protons were proposed for charac-
terisation, which is chemically better justified. To ensure consistency with other
impact categories we propose as indicator the ability to segregate protons, and
SO kilogram equivalents as characterisation factor. These can be easily, and above
2
all unambiguously, calculated according to the laws of stoichiometry. The most
important characterisation factors are listed in Table 4.13. Very weak acids as,
for example, carbonic acid (H CO and its anhydride CO , respectively) are not
3
2
2
included in the calculation of the AP in spite of a strong contribution to the
acidification of the seas (see above). In view of decreasing pH-values of the oceans,
characterisation factors for H CO and CO should also be included (separately
3
2
2
calculated if meaningful). 237)
Organic acids, mainly weak acids, are currently also not assigned to the AP.
Strong organic acids (e.g. TCA) should be assigned for the calculation of the AP in
future.
4.5.2.5.2 Characterisation/Quantification The impact category is converted into
an AP according to the values listed in Table 4.13 or to equivalence factors, which
can easily be determined stoichiometrically for every defined (strong) acid, and is
then aggregated:
AP = ∑ (m × AP )(kgSO -equivalents) (4.21)
i
i
2
i
where m = load of the substance contributing to acidification per fU.
i
237) WBGU (2006).