Atmospheric nitrogen depositions to the Baltic Sea during 1995-2009

Author: Jerzy Bartnicki, EMEP MSC-W

Key message

The total deposition of nitrogen to the Baltic Sea in 2009 was 194 kt N, 19% lower than in 1995. Deposition of oxidised and total nitrogen was lower in 2009 compared to 1995 in all six sub-basins of the Baltic Sea.

Deposition of reduced nitrogen to sub-basins BAP and KAT was higher in 2009 than in 1995 - 3% and 5%, respectively.

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adopted its first Recommendation on Monitoring of Airborne Pollution Load (HELCOM Recommendation 11/1) which was later superseded by the Recommendations 14/1 and 24/1.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 oxidized and reduced nitrogen was computed with the latest version of the unified model developed at MSC-W of EMEP. The latest available emission data for the HELCOM countries and oll other EMEP sources have been used in the model calculations.

Calculated annual oxidized, reduced and total nitrogen depositions to the entire Baltic Sea basin in the period 1995 – 2009 are shown, in per cent of 1995 value, in Figure 1.

Figure 1.  Atmospheric deposition of oxidized, reduced and total nitrogen to the entire Baltic Seabasin for the period 1995-2009 in per cent of 1995 value.

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, but especially in the years 1995 - 2009. Maximum annual deposition of oxidized (137 kt N) and total nitrogen (240 kt N) deposition to the Baltic Sea takes place at the beginning of the considered period, in the year 1995. There are three local maxima of reduced nitrogen deposition in the years 2001-2003 with absolute maximum in 2001 (120 kt N). Minimum of annual oxidised nitrogen deposition can be noticed in the year 2002 (93 kt N), whereas maximum annual deposition of both reduced (86 kt N) and total nitrogen (185 kt N) occur in the year 2005. Annual depositon of oxidized, reduced and total nitrogen in 2007 was respectively 22%, 12% and 20% lower than in 1995.

Average annnual atmospheric nitrogen deposition into the Baltic Sea is 210.7 kt over the period 1995 – 2009 with approximately 16% standard deviation. For most of the years (11 out of 15) the total nitrogen deposition consisted of slightly more (up to 7%) of oxidized than reduced nitrogen. In the years 2001-2004, deposition of reduced nitrogen was up to 4% higher than deposition of oxidised nitrogen.

Calculated annual total nitrogen depositions to the six sub-basins of the Baltic Sea in the period 1995 – 2009 are presented in Figure 2. 

Figure 2. Atmospheric deposition of oxidized, reduced and total nitrogen to six sub-basins of the Baltic Sea for the period 1995 - 2009. 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 – 2009, however annual deposition of oxidised and total nitrogen is lower in 2009 than in 1995 in all sub-basins. Compared to 1995, deposition of oxidised nitrogen decreased between 4% and 31% and deposition of total nitrogen between 0% and 25%.

The most significant reductions of oxidised nitrogen deposition can be noticed in the Belt Sea sub-basin – 31% and for reduced and total nitrogen in the Gulf of Bothnia sub-basin with 26% and 25% decrease, respectively.

The annual load varies across different parts of the Baltic Sea: from 300 mg/m² N in the northern Gulf of Bothnia up to 1,000 mg/m² N in the Belt Sea.

Data

Table 1. Annual depositions of oxidized nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2009. 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)

Table 2. Annual depositions of reduced nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2007. 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)

Table 3. Annual depositions of total nitrogen to the sub-basins and the entire basin of the Baltic Sea in the period 1995-2009. 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)

Metadata

Technical information

1. Source: EMEP/MSC-W.

2. Description of data: The atmospheric depositions of oxidized and reduced nitrogen were calculated with the latest version of EMEP/MSC-W U model developed at EMEP/MSC-W 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 oxidized 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 – 2009.

5. Methodology and frequency of data collection: 

Atmospheric input and source allocation budgets of nitrogen (oxidized, reduced and total) to the Baltic Sea basins and catchments were computed using the latest version of EMEP/MSC-W model. It 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%.

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 Sheets 2011. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/. 

Last updated: 2 April 2012