Atmosfærisk deposition, driftsrapport for luft- forurening i 2004

New model
Nitrogen deposition to
Danish waters
2003 compared to 2002
Nitrogen deposition to land
surface
Land + water
Seasonal variation in 2004
10
Acidifying and eutrofying nitrogen compounds
Model calculations of the nitrogen deposition to the Danish waters
and land surface were carried out with a new and improved air pollution
model, the Danish Eulerian Hemispheric Model (DEHM). This
model has a more advanced description of the physical and chemical
processes in the atmosphere and gives results in better agreement
with the measurements. Model calculations for 2004 with both the
new model (DEHM) and the old model (ACDEP) showed, that the
new model gives nitrogen depositions to the Danish waters and land
surface, which are 13 and 29% lower than the results from the old
model, respectively (Ellermann et al., 2005).
Measurements at the stations showed, that the nitrogen deposition to
Danish waters and land surface in 2004 was comparable to 2003.
The model calculations for 2004 showed, that the total nitrogen deposition
to the Danish waters, fjords and bays varied between 0.9 and
1.7 tonnes N/km 2
with an average of about 1.0 tonnes N/km 2
(Figure
2.13). This gives a total nitrogen deposition to the Danish waters of
107 ktonnes N. The calculated total depositions of nitrogen are given
in Table 2.9 for the Danish main waters. Depositions to fjords and
bays are available on the Internet (www.DMU.DK). The depositions
are highest to the fjords and coastal waters. 60% and 40% of the nitrogen
deposition to the Danish waters are wet and dry deposited, respectively.
The annual nitrogen deposition to Danish land surfaces was between
1.0 and 2.0 tonnes/N km 2 in 2004. The highest deposition is in Jutland
and the lowest in the eastern part of Denmark. For the entire country
the annual nitrogen deposition is calculated to 68 ktonnes. The geographical
variation in the deposition is due to the geographical variation
in the precipitation, differences in the distance to high emission
areas in the countries south of Denmark and intensity of animal husbandry
(and thereby ammonia emissions on a more local scale). The
deposition per area is in general higher to land surfaces compared to
the deposition to water surfaces, mainly due to higher depositions of
ammonia emitted from local farms, higher deposition velocity of nitrogen
dioxide to land surfaces compared to water surfaces and
higher precipitation. In addition the turbulent transport of air pollutants
to the surface is generally higher over land compared with the
conditions over sea.
The total deposition of nitrogen to the Danish land and water surfaces
amounts in 2004 to 175 ktonnes N, which is some-what larger
than the total Danish emissions of nitrogen. In 2003 the total emission
was estimated to 144 ktonnes N (Illerup et al., 2005), and there is therefore
a significant net import of nitrogen to Denmark.
In 2004 there are large monthly variations in the nitrogen deposition
as well as large variations between the different monitoring stations.
In general the deposition is highest during spring and lowest during
winter. The general picture of the seasonal variations averaged over
the monitoring period (1989-2004) has not changed since the previous
annual report (Ellermann et al. 2005).