Atmospheric nitrogen depositions to the Baltic Sea during 1995-2010

Author: Jerzy Bartnicki, EMEP MSC-W

 

Key message

The total deposition of nitrogen to the Baltic Sea in 2010 was 219 ktonnes, 8% lower than in 1995.

 

Deposition of oxidised, reduced and total nitrogen was higher (for oxidised nitrogen significantly) in 2010 than in 2009 – 20%, 3% and 12%, respectively. The main reason for increased deposition in 2010 was very high level of annual precipitation over the Baltic Sea in 2010 – 25% over annual average.

 

Results and Assessment

Relevance of the indicator for describing the developments in the environment

This indicator shows the levels and trends in oxidized reduced and total atmospheric nitrogen depositions to the Baltic Sea. The deposition of nitrogen compounds represent the pressure of emission sources on the Baltic Sea basin and catchment.

Policy relevance and policy reference

The HELCOM Ministerial Declaration of 1988 called for a 50 % reduction in discharges of nutrients to air and water by 1995 with 1987 as a base year. The 1992 Helsinki Convention and the 1998 Ministerial Declaration reaffirmed the need to further reduce discharges; leading to the adoption of several relevant Recommendations concerning measures to reduce emissions from point sources and diffuse sources. In 1990 HELCOM adopted its first Recommendation on Monitoring of Airborne Pollution Load (HELCOM Recommendation 11/1) which was later superseded by the Recommendations 14/1 and 24/1.

Assessment

Atmospheric deposition of oxidised and reduced nitrogen was computed with the latest version of the EMEP/MSC-W model. The latest available emission data for the HELCOM countries and all other EMEP sources have been used in the model calculations presented here.

Calculated annual oxidised, reduced and total nitrogen depositions to the entire Baltic Sea basin in the period 1995 – 2010 are shown, in per cent of 1995 value, in Figure 1.

 

 

Figure 1. Atmospheric deposition of oxidised, reduced and total nitrogen to the entire Baltic Sea basin for the period 1995-2010 in per cent of 1995 value.

       

To avoid a strong influence of inter-annual meteorological variability on annual nitrogen deposition, the so called “normalised” nitrogen deposition was calculated in the way described in the Appendix D of the EMEP report for HECOM (reference). The calculated normalised annual depositions of total nitrogen  in the period 1995-2010 are shown in Figure 2.

 

 

Fig. 2. Normalised deposition of total nitrogen for the period 1995-2010. Minimium, maximum and actual annual values of the deposition are also shown. The minimum and maximum annual values are determined by the meteorological conditions for each particular year.

 

A quick inspection of Figure 2 indicates slightly decreasing trend in normalised annual total deposition of nitrogen which roughly corresponds to decreasing trend in nitrogen emissions from from the HELCOM area of interest.

No significant trends could be determined for nitrogen loads entering the Baltic Sea in the considered period, however, annual deposition of all nitrogen compounds are approximately 10% lower in 2010 than in 1995.

Mainly because of interannual changes in meteorological conditions, annual nitrogen depostion to the Baltic Sea and its sub-basins varies significantly from one year to another in the entire period 1995 – 2010. Maximum annual deposition of oxidised nitrogen (145 kt N) and reduced nitrogen (112 kt N) to the Baltic Sea takes place in the years 1998 and 2000, respectively. Minimum annual depositons can be noticed in the years 2007 and 2002 for oxidised nitrogen (103 kt N) and reduced nitrogen (85 kt N), respectively. Annual deposition of oxidised, reduced and total nitrogen in 2010 was respectively 9%, 8% and 9% lower than in 1995. However, the levels of  2010 annual depositions of  oxidised, reduced and total nitrogen were respectively 20%, 3% and 12% higher than in 2009.

Average annnual atmospheric nitrogen deposition into the Baltic Sea is 218 kt over the period 1995 – 2010 with approximately 10% standard deviation. The total nitrogen deposition consisted of slightly more (2-8%) of oxidised than reduced nitrogen.

Calculated annual total nitrogen depositions to the six sub-basins of the Baltic Sea in the period 1995 – 2010 are presented in Figure 3.

 

Figure 3. Atmospheric deposition of oxidised, reduced and total nitrogen to six sub-basins of the Baltic Sea for the period 1995 - 2010. Units: ktonnes N/year. Note: the scales for the sea regions are different! Click to enlarge.

 

 

No significant trends can be recognized in nitrogen depositions to sub-basins of the Baltic Sea in the Period 1995 – 2010, however annual depositions of oxidised and reduced nitrogen are lower in 2010 than in 1995 in all sub-basins and in the entire Baltic Sea basin.

Compared to 2009 deposition of oxidised nitrogen in 2010 is higher in all sub-basins (2-26%) and deposition of reduced nitrogen is higher in four out of six sub-basins (3-28%). Deposition of reduced and total nitrogen is lower in 2010 compared to 2009 in the sub-basins: BES and KAT, in the south-west of the Baltic Sea.

The annual load in 2010 varies across different parts of the Baltic Sea: from 300 mg/m² N in the northern Gulf of Bothnia up to 1000 mg/m² N in the Belt Sea.

 

Data

Table 1. Annual depositions of oxidised nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2010. Units: kt N per year and basin. (BAP=Baltic Proper; BES=Belt Sea; GUB=Gulf of Bothnia; GUF=Gulf of Finland; GUR=Gulf of Riga; KAT=Kattegat)

 

Year	BAP	BES	GUB	GUF	GUR	KAT	BAS
1995	77.3	10.9	23.0	9.0	6.7	10.2	137.1
1996	78.2	10.8	20.6	9.4	6.2	9.7	135.0
1997	67.9	9.6	17.8	7.5	6.0	9.2	117.8
1998	84.0	12.0	23.4	9.1	6.1	10.6	145.3
1999	75.7	11.5	22.8	8.6	6.1	11.0	135.6
2000	77.5	11.1	25.9	9.7	6.4	11.5	142.0
2001	70.0	10.8	20.3	7.2	5.1	9.4	122.9
2002	63.7	9.7	16.4	6.4	4.9	8.6	109.8
2003	65.1	8.7	21.2	7.9	5.6	9.0	117.4
2004	65.8	9.7	18.3	8.5	5.7	8.6	116.6
2005	64.4	8.7	18.6	8.0	5.4	8.9	114.1
2006	59.7	8.6	16.3	7.0	5.3	7.9	105.0
2007	61.4	8.7	13.5	6.9	4.7	7.5	102.7
2008	66.3	7.7	19.1	9.0	6.2	8.4	116.6
2009	58.6	7.6	17.5	6.8	4.8	8.5	103.8
2010	71.3	8.2	22.0	8.3	5.8	8.6	124.2

 

 

Table 2. Annual depositions of reduced nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2010. Units: kt N per year and basin. (BAP=Baltic Proper; BES=Belt Sea; GUB=Gulf of Bothnia; GUF=Gulf of Finland; GUR=Gulf of Riga; KAT=Kattegat)

 

Year	BAP	BES	GUB	GUF	GUR	KAT	BAS
1995	54.3	13.7	15.1	5.4	4.2	10.3	103.0
1996	54.8	12.5	13.3	6.3	4.2	9.8	101.0
1997	47.3	12.6	9.6	4.0	3.6	9.6	86.7
1998	62.0	15.5	14.6	5.1	3.8	11.5	112.5
1999	53.9	14.7	13.6	4.5	3.7	11.2	101.5
2000	61.3	15.1	18.4	5.7	4.2	12.5	117.3
2001	54.4	14.3	13.7	4.4	3.7	9.9	100.5
2002	46.3	12.7	10.7	3.2	2.9	9.1	84.9
2003	48.4	11.7	14.3	4.4	3.6	9.3	91.7
2004	50.5	13.7	11.0	4.6	3.8	9.7	93.1
2005	48.4	12.6	10.9	4.7	3.7	9.1	89.5
2006	49.2	14.0	10.2	4.3	3.7	9.3	90.6
2007	55.9	14.0	9.6	4.6	3.5	8.2	95.7
2008	52.2	12.2	11.4	5.4	3.6	9.7	94.5
2009	50.8	12.7	11.1	4.0	3.6	9.7	91.8
2010	52.2	10.6	13.9	5.2	4.0	8.5	94.4

 

Table 3. Annual depositions of total nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2010. Units: kt N per year and basin. (BAP=Baltic Proper; BES=Belt Sea; GUB=Gulf of Bothnia; GUF=Gulf of Finland; GUR=Gulf of Riga; KAT=Kattegat)

 

Year	BAP	BES	GUB	GUF	GUR	KAT	BAS
1995	131.6	24.6	38.1	14.4	10.9	20.5	240.0
1996	132.9	23.4	33.9	15.8	10.4	19.5	235.9
1997	115.2	22.1	27.4	11.5	9.6	18.8	204.6
1998	146.1	27.5	38.0	14.2	9.9	22.2	257.8
1999	129.6	26.2	36.4	13.0	9.8	22.1	237.1
2000	138.7	26.3	44.3	15.4	10.6	24.0	259.3
2001	124.5	25.1	34.0	11.6	8.8	19.3	223.4
2002	110.0	22.4	27.1	9.6	7.8	17.8	194.8
2003	113.5	20.4	35.5	12.3	9.2	18.2	209.2
2004	116.3	23.4	29.2	13.1	9.5	18.3	209.7
2005	112.8	21.3	29.6	12.7	9.1	18.0	203.6
2006	108.9	22.6	26.5	11.3	9.0	17.2	195.6
2007	117.3	22.7	23.1	11.5	8.2	15.7	198.3
2008	118.5	19.9	30.5	14.4	9.7	18.1	211.1
2009	109.4	20.2	28.6	10.8	8.4	18.1	195.6
2010	123.5	18.8	35.9	13.5	9.8	17.1	218.6

 

Metadata

Technical information

1. Source: EMEP/MSC-W.

2. Description of data: The atmospheric depositions of oxidised and reduced nitrogen were calculated with the latest version of EMEP/MSC-W model in Oslo. The latest available official emission data for the HELCOM countries have been used in the model computations. Emissions of two nitrogen compounds for each year of this period were officially reported to the UN ECE Secretariat by several HELCOM Contracting Parties. Missing information was estimated by experts. Both official data and expert estimates were used for modelling atmospheric transport and deposition of nitrogen compounds to the Baltic Sea - http://www.ceip.at/ .

3. Geographical coverage:   Atmospheric depositions of oxidised and reduced nitrogen were computed for the entire EMEP domain, which includes Baltic Sea basin and catchment.

4. Temporal coverage: Timeseries of annual atmospheric depositions are available for the period 1995 – 2010.

5. Methodology and frequency of data collection: 

Atmospheric input and source allocation budgets of nitrogen (oxidised, reduced and total) to the Baltic Sea basins and catchments were computed using the latest version of EMEP/MSC-W model. EMEP/MSC-W model is a multipolutant, three-dimensional Eulerian model which takes into account processes of emission, advection, turbulent diffusion, chemical transformations, wet and dry depositions and inflow of pollutants into the model domain. Complete description of the model and its applications is available on the web http://www.emep.int.

Calculations of atmospheric transport and depositions of nitrogen compounds are performed annually two years in arrears on the basis of emission data officially submitted by Parties to CLRTAP Convention and expert estimates.

Quality information

6. Strength and weakness:

Strength: annually updated information on atmospheric input of oxidised and reduced nitrogen to the Baltic Sea and its sub-basins.

Weakness: gaps and uncertainties in officially submitted by countries time series of nitrogen emissions to air

7. Uncertainty:

The results of the EMEP Unified model are rotinely compared with available measurements at EMEP and HELCOM stations. The comparison of calculated versus measured data indicates that the model predicts the observed air concentrations of lead and cadmium within the accuracy of approximatelly 30%.

 

Figure 4. Comparison of annual wet deposition based on observations (obs) at selected HELCOM stations and calculated by the EMEP model (mod) for the grid squares including these stations, for each year of the period 1995-2006. Units: mg N m^-2. Click graph to enlarge.

8. Further work required:

Further work is required on reducing uncertainties in emission data and better parameterization of physical processes in the EMEP Unified model.

 

For reference purposes, please cite this Baltic Sea Environment Fact Sheets as follows:

[Author’s name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheet(s) 2012. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/. 

Last updated: 22 January 2013