Coupling of CORINAIR data to cost-effective emission reduction strategies based on critical thresholds

Danish subproject

Impact task

Jesper Bak

The main objective of the Danish impact task is to evaluate and improve the way national critical load calculations are used in assessing ecosystems impacts from air pollution, both for use in developing national abatement policies and in international negotiations. This involves two main tasks:

• Assessment of the influence of spatial variation and uncertainty and the choice of geographical scale in the calculated areas with exceedance of critical loads.

• Assessment of the temporal response of selected Danish ecosystems to different deposition scenarios.

In addition, the sensitivity of Danish impacts and emission ceilings calculated with the RAINS model to changes in Danish data, model and data uncertainty, and to changes in deposition targets for selected EMEP grids is evaluated. This analysis is connected to the Danish subproject on emissions.

The Danish subproject task on impacts is linked to the Danish emission subproject. The two subprojects are performed at two departments of the Danish National Environmental Research Institute, Department of Terrestrial Ecology (impacts) and Department of Atmospheric Environment (emissions).

Effects on Danish ecosystems are assessed on the basis of Danish national critical load maps with a base resolution of 1 km x 1 km. Critical load exceedances are evaluated at four different resolutions (km), · EMEP 150x150, · national 20x20, · national high resolution in selected areas, and · national statistically based high resolution where the deposition in a point is described by a probability distribution.

An assessment of the influence of uncertainty and spatial variation on calculated protected ecosystem area is made by including both uncertainty and spatial variation in the critical loads and deposition values calculated at individual points. The high-resolution (10 m) deposition calculation is partially statistical based. Data from 11 small mixed agricultural and nature areas (size range 425 ha to 3998 ha) has been used to assess the spatial variation in critical loads and ammonia deposition.

As a basis for a national assessment of the temporal response of ecosystems to selected deposition scenarios and assessment of uncertainties regarding temporal dynamics, scenario analyses is performed with the SAFE model at tree intensively monitored sites where model calibration has been performed.

As a first step towards an integrated analysis of economic forecasts, emissions, environmental effects, and abatement costs, an evaluation of the RAINS model and the data used for Denmark in developing the EU acidification strategy is made. Furthermore the sensitivity of calculated Danish emission ceilings for uncertainty in model description and data in the RAINS model is assessed. Special emphasis is put on uncertainty on deposition targets in grids, which are binding in the optimisation calculations.

There are very large differences between the calculated areas with exceedance of critical loads using the traditional method where average deposition values are used for large grids and results obtained when including uncertainty and spatial variation in the calculations. Table 1 illustrates the difference between calculated areas with critical load exceedance using average deposition values and including uncertainty and spatial variation in the calculation. The influence of uncertainty and spatial variation were assessed by estimating probability distributions for both critical loads and deposition values. An expected value and a 90% confidence interval for the protected ecosystem area were then calculated by Monte Carlo simulation. The calculation clearly illustrates that the traditional calculation method underestimates the air pollution problem. Only for eutrophication effects on spruce and pine where the traditional method gives 90 – 97% exceeded area, the modified method shows less exceeded area.

Table 1. Comparison between calculated areas with critical load exceedance in Denmark using average deposition values (traditional method) and including uncertainty and spatial variation in the calculation. The numbers in brackets are 90% confidence intervals.

Figure 1 shows the calculated temporal development in soil water pH for the upper C-horizon at the Danish IM site at Hjerl Hede for four different deposition scenarios. The site is predominantly a heather dominated heathland where present and future management and heather beetle outbreaks are important for the soil geochemistry. The compared scenarios are a REF scenario describing the future deposition according to current legislation and international regulation, and tree different implementations of a reduction scenario. All reduction scenarios gives the deposition level of the B1 scenario in 2020. In the ‘bst’ scenario, depositions are reduced in 2000, in the ‘wst’ scenario in 2020, whereas in the ‘mdm’ scenario, emisisons are linearly reduced between 2000 and 2020.

What is most apparent from this calculation is that the future development in soil geochemistry depends more on the assumptions made on management and beetle attacks than on the development in deposition. All scenarios gives very similar values beyond 2030.

The emission ceilings for Denmark calculated with the RAINS model are very sensitive to uncertainties in deposition targets at a limited number of binding grids. Table 2 shows regression coefficients (+ s.e.) between deposition target and control costs for Denmark for selected grids. The analysis was based on the B1 scenario prepared by IIASA for the EU Commission. The coefficients express the relationship between change in deposition target in meq m^-2 and the corresponding change in abatement costs in million Euro y^-1

• National assessment including fine spatial scale and temporal considerations is important and will in many cases yield different results than European calculations
• For Denmark a national assessment including uncertainties and spatial variability and taking differences in deposition velocity to different ecosystems into account shows much higher area with exceedances of the critical load than the traditional calculation method
• At the investigated Danish sites the situation is expected to be improved by current reduction plans and it will take decades before problems are expected. For the semi-natural ecosystems the situation is also much influenced by management.
• The emission ceilings for Denmark calculated with the RAINS model are very sensitive to uncertainties in deposition targets at a limited number of binding grids.
• Danish emission ceilings are sensitive to changes in the national energy scenario. The sensitivity to changes in cost curves is, however, limited

Main project

Bak, J., Tybirk, K., Gundersen, P., Jensen, J.P., Conley, D., Hertel, O., 1999. Natur- og miljøeffekter af ammoniak, Danish Institute of Agricultural Sciences.

Bak, J., Andersen, J., Asman, W.A.H., Hutchings, N, 1999. Spredning og effekter af ammoniak, Danish Environmental Protection Agency, Technical Report, in press.

Bak, J. and Tybirk, K., 1998. The EU Acidification Strategy: Sensitivity

of calculated emission ceilings for nitrogen and sulphur for Denmark.

Environmental Pollution 102, S1 (1998), pp 625-633.

Bak J. Trends in nitrogen status for Danish forests and heathlands,

National Environmental Research Institute, Denmark, Technical Report, in

preparation.

Holten-Andersen, J., Christensen, N., Kristiansen, L.W., Kristensen, P. & Emborg, L. (ed)., 1998, The State of the Environment in Denmark, 1997, National Environmental Research Institute, Denmark, Technical Report

No. 243, 288 pp.

Danmarks Miljøundersøgelser, 1998. Analyse af RAINS-modellen og beregnede

emissionslofter for Danmark, report in Danish, English title: Analysis of

the RAINS model and calculated emission ceilings for Denmark.