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Responses
The use of critical
loads/levels in strategic
planning
Discussion
14
agricultural crops and trees and relatively little information is available
on the response of natural vegetation to ozone. The Average
Above Threshold (AOT) is the sum of critical time (hours) multiplied
by the exceedance of the critical level of e.g. 40 ppb (AOT40)which
has been demonstrated to damage agricultural crops and trees. But
plants react to ozone fluxes rather than concentrations and therefore
this criteria is being debated.
DEM can run various scenarios to analyse the relations between
emissions of ozone precursors and critical level exceedances of
ozone. Calculation of consequences of reductions of NO x and VOC
emissions in all European countries and combinations of the two reactants
are carried out. Output scenarios are coupled to the tree
growth model TREGRO to evaluate the effects on tree vegetation and
to separate ozone effects from other stress.
The Danish work on integrated assessment of air pollution is being
built on a number of models in a chain of interactions. At present
only rather preliminary model interaction has been carried out, but
some realistic scenarios will be produced in near future. Internationally,
the RAINS model is used to prepare scenarios for negotiations
for the coming Acidification Strategy for EU and for the Multipollutant/Multi-effect
protocol under the Geneva Convention.
RAINS consist of 5 Alements: 1) Energy and agricultural scenarios, 2)
Emission inventories, 3) Transport matrices, 4) Critical loads and levels
and 5) Abatement costs. The resulting optimisation process calculates
the cost-effective way to achieve the environmental targets.
The critical loads and levels for ecosystems and plants are being used
internationally for strategic planning. These scenarios and negotiations
result in fixed emission ceilings for SO 2, NO x and NH 3 for each
country in the forthcoming Acidification Strategy. The implementation
of necessary abatement measures will be very costly for Denmark
and there is an urgent need to establish an Integrated Assessment
System for the analysis of how to distribute these ceilings
among different sectors in Denmark.
From the base model ADAM satellite models have to be developed to
run scenarios for energy, transport and agricultural sectors. This information
is crucial as starting point for such calculations. The calculation
and mapping of critical loads is another important end of the
chain: what will be the resulting exceedances of critical loads and
levels for Danish and European ecosystems? Cost optimisations will
be needed to analyse which sector can contribute most efficiently to
achieve the emission goals for the year 2010.
The problems, their causes and solutions are indeed complex and
much effort has been spent on enabling the critical loads/levels concept
to be a fundamental criteria for such analysis. A number of uncertainties
are found at each element and at each scale of analysis, but
the endpoint is that consistent calculations over more than a decade
have shown the same general patterns of air pollution. The effects of
implementation of the resulting conventions are now being seen as
well.