Atmosfærisk deposition, driftsrapport for luft- forurening i 2004

Long term trends of
concentrations
Ammonia
Uncertainties
12
The long-term trends in the concentrations of nitrogen compounds at
the monitoring stations show the same general pattern as previously
reported:
• For NHx (sum of gas phase ammonia and particulate ammonium)
statistically significant reductions of 30-48% have been observed
over the period 1989-2004. The reductions are mainly due to decreases
in concentrations of particulate ammonium, which has
been reduced with 36-53% during the period. For ammonia there
are large variations between the monitoring stations. At Tange
there has been a statistically significant decrease of 41%, while the
trends at the other stations are insignificant.
• For sum-nitrate (sum of nitric acid and particulate nitrate) statistically
significant decreases have been observed at all monitoring
stations. The reductions were between 19 and 29% over the period
1989-2003.
• For nitrogen dioxide no long-term trends can be observed on the
basis of the present time series. The large variations between the
years conceal possible trends.
The long-term trends in particulate ammonia and sum-nitrate are at
the same level for all monitoring stations. It is therefore estimated
that these reductions are representative for Denmark as a whole. The
decreases are mainly due to reductions in the emissions of ammonia
and nitrogen dioxide in Denmark as well as most other European
Countries.
The ammonia concentration has not changed as much as the concentration
of particulate ammonium. This may be due to the pronounced
decrease in atmospheric sulphur content or because local conditions
at the sites of the six monitoring stations do not reflect the general
picture for Denmark as a whole.
The uncertainty in the model calculations of nitrogen deposition to
Danish land and water surfaces is very difficult to quantify. On the
basis of the comparison between model calculations and measurements
it is estimated, that the total uncertainty for the calculations of
annual nitrogen deposition to land surfaces may be as high as 30%.
For the depositions to Kattegat it is estimated that the uncertainty is
about 30%, which is assumed also to be true for the rest of the inner
Danish waters. For the Danish part of the North Sea the uncertainty
may be as high as 50%.
Deposition of phosphorous
It is estimated that the deposition of inorganic phosphorous to the inner
Danish waters (area 31,500 km 2
) is about 130 tonnes P in 2004.
This estimate is based on optimised methods for sampling and analysis.
This figure is regarded as an upper limit. It is estimated that the
phosphorus deposition has not changed significantly during the period
1989-2004. The given estimate is supported by measurements of
the atmospheric content of particulate phosphorous and measurements
carried out by Fyns Amt (2005).