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4. Questions and Answers
Peter Builtjes: You showed that the FRAME model results for wet deposition
compare favourably with observations. Does that mean that your rain intensity
data are correct?
Answer: Yes. The rainfall intensity data can be considered to be reliable. The map
of annual rainfall driving the washout rate in the FRAME model is calculated
from interpolation of measurements from the UK Met Office national rain
gauge network. This simple approach of using measured annual rainfall has
certain advantages, as annual precipitation can be measured accurately but
presents challenges to be well represented by meteorological models. However,
complex Eulerian models do have the advantage of an event based approach to
representing precipitation whereas FRAME assumes constant drizzle.
Christian Reuter: Projections of 2020 acid deposition showed exceedances over
mountainous areas with high precipitation. Are the sources of SO 2 therefore
located outside the UK? If so, how did you account for future SO 2 emissions
outside the UK?
Answer: The boundary conditions for the UK model simulation were generated
from a European scale simulation. Emissions from the UK and Europe are
projected to fall significantly by 2020. Major reductions in SO 2 emissions from
international shipping will also take place by 2020 due to imposition of Annex
VI of the MARPOL convention resulting in large reductions in the sulphur
content of bunker fuel. Trans-continental import and 'background concen-
trations' are considered to make a relatively small contribution, though hemi-
spherical modelling will be required to better quantify their importance. In the
future, nitrogen will become a more significant driver for acidification, through
deposition of both oxidised and reduced nitrogen. The latter can contribute via
in-soil oxidation.