『Abstract
This paper reports an uncertainty analysis of critical loads
for acid deposition for a site in southern England, using the
Steady State Mass Balance Model. The uncertainty bounds, distribution
type and correlation structure for each of the 18 input parameters
was considered explicitly, and overall uncertainty estimated by
Monte Carlo methods. Estimates of deposition uncertainty were
made from measured data and an atmospheric dispersion model, and
hence the uncertainty in exceedance could also be calculated.
The uncertainties of the calculated critical loads were generally
much lower than those of the input parameters due to a “compensation
of errors” mechanism - coefficients of variation ranged from 13％
for CLmaxN to 37％ for CL(A). With 1990 deposition,
the probability that the critical load was exceeded was ＞0.99;
to reduce this probability to 0.50, a 63％ reduction in deposition
is required; to 0.05, an 82％ reduction. With 1997 deposition,
which was lower than that in 1990, exceedance probabilities declined
and uncertainties in exceedance narrowed as deposition uncertainty
had less effect. The parameters contributing most to the uncertainty
in critical loads were weathering rates, base cation uptake rates,
and choice of critical chemical value, indicating possible research
priorities. However, the different critical load parameters were
to some extent sensitive to different input parameters. The application
of such probabilistic results to environmental regulation is discussed.
Keywords: acid deposition; dispersion model; critical load exceedance;
emission control; environmental policy; Liphook; Monte Carlo analysis;
sensitivity analysis; steady state mass balance model; uncertainty
analysis』
1. Introduction
2. Methods
2.1. Background
2.2. Site
2.3. Critical load calculation
2.4. Exceedance
2.5. Monte Carlo analysis
2.5.1. Application
2.5.2. Sulphur deposition
2.5.3. Nitrogen deposition
2.5.4. Total chloride deposition
2.5.5. Non-marine chloride deposition
2.5.6. Base cation deposition
2.5.7. Calcium deposition
2.5.8. Weathering rates
2.5.9. Base cation uptake
2.5.10. Runoff
2.5.11. Limiting base cation concentration
2.5.12. Critical Ca : Al ratio
2.5.13. Gibbsite equilibrium constant
2.5.14. Nitrogen immobilisation
2.5.15. Denitrification
2.5.16. Nitrogen uptake
3. Results
3.1. Uncertainty analysis
3.2. Sensitivity analysis
4. Discussion
Acknowledgments
References