3.3. The effects of pollutants on vegetation
ExternE 2 discusses a large number of effects of air pollution on agriculture, forests
and terrestrial ecosystems. However, only three effects are eventually expressed in mone-
tary terms. These include the direct effect of SO* on wheat, barley, rye and oats, the local
effect of 0, on wheat, and the effect of SOZ on timber production.
For the first two categories, we transferred the results for the La&en plant of the
ExternE 2 study, which presents costs per kWh *, to the emissions by road transport in
Belgium. We have used the fact that the Lauffen plant emits 0.83 g SO, and 0.927 g NO,
per kWh. Once again, it should be mentioned that our approach is not perfect.
Emissions from low level transport sources do not behave in the same way as emissions
from high stacks. Moreover, the atmospheric transport of emissions in Germany is not
necessarily the same as that of Belgian emissions. The direct effects of SO* on agricul-
tural crops include the transnational effects whereas those of 0, only cover an area with
a surface comparable to that of Belgium. In the latter case, we have taken into account
that the area under cultivation for wheat around the Lauffen plant is smaller than that in
Belgium (78,525 ha versus 215,750 ha). The results presented in Table 7 are obtained by
using world market prices to value the changes in crop yields.
The effect of SO, on forests is determined on the basis of Nilsson (1991) and IIASA
(referred to in ExternE 9). Nilsson has determined the damage to forests in each country
per ton of SO, deposited. His estimates include both timber and non-timber values. The
IIASA matrix gives the emissions and depositions of sulphur in Europe. On the basis of
the IIASA table, we can determine which percentage of Belgian SO* emissions is
deposited in the different European countries. The conversion from sulphur to SO?
requires that the former is multiplied by 2. The combination of the two data sources
allows us to determine the total damage caused by 1 ktonne of Belgian SO, emissions.
The results are given in Table 7.