Ellermann, T., Andersen, H.V., Christensen, J., Frohn, L.M., Kemp, K. & Monies, C. 2006. Technical report No. 556 from NERI. 85 s.
Summary
This report presents measurements and calculations from the atmospheric part of NOVANA and covers results for 2004. It summarises the main results concerning concentrations and depositions of nitrogen, phosphorus and sulphur compounds related to eutrofication and acidification and selected heavy metals. Depositions of atmospheric compounds to Danish marine waters as well as land surface are presented.
Measurements
In 2004 the monitoring program consisted of nine stations. Wet deposition of ammonium, nitrate, phosphate (semi quantitatively) and sulphate were measured using bulk precipitation samplers at eight of the stations. At six stations additional measurements of atmospheric content of nitrogen, phosphorus, and sulphur compounds in gas and particulate phase were carried out using filter pack samplers. Filters were analysed at the National Environmental Research Institute. Finally, nitrogen dioxide was measured using nitrogen dioxide filter samplers and monitors at two monitoring stations and wet deposition and air concentrations of nine heavy metals were measured.
Model calculations
The measurements in the monitoring programme were supplemented with model calculations of concentrations and depositions of nitrogen and sulphur compounds to Danish land surfaces as well as marine waters, fjords and bays using DEHM (Danish Eulerian Hemispheric Model). The model is a three dimensional Eulerian model and simulates the physical and chemical processes in the atmosphere using meteorological and emission data as input.
The advantage of combining measurements with model calculations is that the strengths of both methods can be utilised. Conclusions concerning:
• actual concentration levels at the monitoring stations,
• deposition at the monitoring stations,
• seasonal variations and
• long term trends in concentrations and depositions
are mainly based on the direct measurements. These are furthermore used to validate the results of the model calculations.
Conclusions concerning
• depositions to land surfaces and to the individual marine waters,
• contributions from different emission sources and
• the contribution from Danish sources
are mainly based on the model calculations.
Acidifying and eutrofying nitrogen compounds
New model
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).
Nitrogen deposition to Danish waters
Measurements at the stations showed, that the nitrogen deposition to Danish waters and land surface in 2004 was comparable to 2003.
2003 compared to 2002
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/km2 with an average of about 1.0 tonnes N/km2 (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.
Nitrogen deposition to land surface
The annual nitrogen deposition to Danish land surfaces was between 1.0 and 2.0 tonnes/N km2 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.
Land + water
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.
Seasonal variation in 2004
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).
Sources of nitrogen deposition
Model calculation shows that the nitrogen deposition to the Danish waters in 2004 originate from farming (about 44%) and combustion processes (about 56%). For areas located close to agricultural areas a somewhat higher contribution from farming is calculated. Some examples are Limfjorden where farming is responsible for about 59% of the deposition and Kattegat where farming is responsible for about 48% of the deposition. Moreover, the model calculations show that about 46% of the nitrogen deposition to land surfaces originates from farming. These results from the model calculations are in good agreement with the results from the monitoring stations, where the measurements show that farming accounts for 45-52% of the deposition to the coastal waters and 39-64% of the deposition to an average land surface (low vegetation).
Danish sources
The model calculations show that Danish sources contribute with 28% and 14% of the total nitrogen deposition to Kattegat and the Danish part of the North Sea, respectively. However, for some fjords and bays this contribution may be as high as 45%. The high Danish contribution to these areas is mainly due to deposition of locally emitted ammonia. On average the Danish contribution is calculated to 19% of the total nitrogen deposition to the Danish waters in 2004. On average the Danish sources contribute with 46% of the nitrogen depositions to land surfaces. The highest contribution from Danish sources is seen in Viborg County (54%) and the lowest is seen on Bornholm (24%). Moreover, there are large geographical variations on a local scale due to emissions of ammonia from individual farms.
Long range transport
The majority of the nitrogen deposited to Danish waters (81%) and land surface (54%) originates from foreign countries; this can be explained by the fact that nitrogen compounds can be transported over large distances in the atmosphere. Considering Denmark it is known from analyses of measurements and model calculations that the main part of the nitrogen compounds comes from the countries south and west of Denmark where there are high emissions of nitrogen compounds from farming as well as combustion processes.
Long term trends for the total nitrogen deposition
It is estimated that there has been a small decrease (about 20%) in the general total deposition of nitrogen to water surfaces for the period 1989-2004. This estimate is based on the fact that the average total deposition of nitrogen to the water surface at the coastal monitoring stations has decreased significantly with 20% in the period 1989-2004.
Similarly, it is estimated that the total deposition to average Danish land surfaces (low vegetation) has decreased with about 23% in the period 1989-2004. This estimate is also based on the results from the monitoring stations were there has been a significant decrease on 23% since 1989.
Local changes
On local scale the nitrogen deposition may of course be significantly different from the general trends due to local changes mainly in farming activities.
Long term trends of concentrations
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.
Ammonia
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.
Uncertainties
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 km2) 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).
Deposition of acidifying sulphur
Deposition of sulphur
In 2004 the sulphur deposition to Danish land surfaces is calculated to 0.5-0.8 tonnes S/km2. This leads to a total deposition of 26,000 tonnes S to Danish land surface. This is of the same magnitude as the annual Danish emissions of sulphur; 15,500 tonnes S (Illerup et al., 2005). The model calculations show a fairly even geographical distribution of the sulphur deposition. The lack of significant gradients in the deposition pattern is probably because sulphate originating from sea salt is not included in the model (DEHM).
Sulphur from sea salt
The main part of the deposited sulphur arises from wet deposition (77% in average) of which 17-47% originates from sea salt. The largest contribution from sea salt is measured in the western part of Jutland due to the short distance to the North Sea. In the eastern part of Denmark only a minor part of the wet deposition is due to sea salt.
Sources
The main part of the sulphur deposition originates from long range transport of sulphur from the European countries south and west of Denmark. The DEHM-calculations show that only about 19% of the sulphur deposition is due to emissions from Danish sources.
Long term trends
The long term trends for the sulphur depositions are more pronounced than the trends observed for the nitrogen deposition. For the period 1989-2004 significant and high decreases in the atmospheric content of sulphur dioxide and particulate sulphate as well as in the wet depositions of sulphur were measured at all the monitoring stations. The decrease in the total sulphur depositions is calculated to about 75% during the period 1989-2004. The background for the decrease is the large reductions in the emissions of sulphur dioxide in Denmark and the majority of the European countries which has been carried out during the same period.
Uncertainty
As for the nitrogen deposition a considerable uncertainty is estimated for the model calculations. Based on comparison of model calculations and measurements it is estimated that the uncertainty of the model calculations of the annual sulphur deposition is 30%.
Deposition of heavy metals
In 2004 the annual average deposition of heavy metals to Danish background land areas were Cr = 0.1, Ni = 0.3, Cu = 0.8, Zn = 7.0, As = 0.1, Cd = 0.05 and Pb = 1.0 (all in units of mg/m2). Deposition to Danish waters are 5-20% lower than the deposition to land.
The average concentration of particulate heavy metal (units of ng/m3) were for 2004: Cr = 0.5, Mn = 3.0, Fe = 82, Ni = 1.7, Cu = 1.6, Zn = 15, As = 0.5, Cd = 0.2 and Pb = 5.4. The concentrations are at the same level as in 2003.
During the period 1990 to 20004 there have been clear decreases in the concentrations and depositions of heavy metals. The levels of the heavy metals have decreased by a factor of two to three with the highest decreases for Pb and Cd. The decreases are due to the reductions in the emissions of heavy metals in Denmark and many of the European countries.
For year 2004 the deposition of heavy metals to the inner Danish waters with a total area of 31,500 km2 has been estimated to Cr = 3 tonnes, Ni = 8 tonnes, Cu = 25 tonnes, Zn = 210 tonnes, As = 3 tonnes, Cd = 1 tonnes and Pb = 28 tonnes.
For year 2004 the deposition of heavy metals to Danish land surface (area of 43,000 km2 ) has been estimated to Cr = 5 tonnes, Ni = 13 tonnes, Cu = 36 tonnes, Zn = 300 tonnes, As = 5 tonnes, Cd = 2 tonnes and Pb = 43 tonnes
These estimates are based on measurements performed at all the monitoring stations. The uncertainty of the estimated depositions is about 30%. When the atmospheric depositions are compared with land based runoff of heavy metals it is seen that the contributions from the atmosphere are of the same order of magnitude. For some of the compounds the atmospheric contributions are even larger than the runoff.
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