Nitrogen Oxides - Emissions and Pollution 1995


Effect of Nitrogen Oxides

Nitrogen oxides are acidifiers. They are damaging to human health, cause damage to plants, buildings and monuments and are an essential contributor to the excessive formation of ozone and other health-endangering oxidants during the summer heat periods.

Nitrogen oxides and particularly nitrogen dioxide effect persons and animals. They cause irritations to the mucous membranes in the respiratory tract and can increase the risk of infection (c.f. Kühling 1986). Also cell changes have been observed (c.f. BMUNR 1987). Various epidemiological investigations have shown a connection between deterioration of the lung function, respiratory tract symptoms and increased nitrogen dioxide concentration (c.f. Nowak et al. 1994).


Since the beginning of the 80s, along with discussion around the damaging consequences of motor vehicle traffic for the environment, the pollution of the air with nitrogen oxides has also found increased attention. So the permissible pollution limits for nitrogen dioxide were sunk gradually to around 20 to 30 % in the course of several revisions to the First General Regulation of the Federal Pollution Control Law (Technical Instruction for Clean Air – TA-Luft).

Exceeding the pollution limits of the TA-Luft and/or the 22 BImSchV (Federal Pollution Control Regulations) can lead to measures being imposed on plants which have been identified the polluters. If the violation can not be associated a certain cause, the responsible authorities must set up an Air Purity Plan and place stiffer demands on the licensing of new plants with regard to the permissible emission.

Moreover the European Community, after limiting the concentration of sulfur dioxide, floating dust and lead in the air – with their Guideline from 7 March 1985 on Air Quality Standards, also determined a limit and guide value for nitrogen dioxide. In 1993 this 98 % limit was adopted in national law as Regulation 22 for the Implementation of the Federal Pollution Control Law.

Exceeding the limit of the EC Guideline are to be reported to the Council of the European Community. The national authorities must present plans for reaching the prescribed limits and a time limit for reaching them. Also should become the guide value of the EC Guideline is to be taken into account for all traffic – and building planning. While the EC limits are obligatory, Guide values and standard values serve as an orientation and have solely advisory character.

Moreover, in order to maintain the long-term capacity of the ecosystem, pollution limits must be observed, which take into account its sensitivity. Thus the filter effect through the surface structure of forests causes a high pollutant penetration and accumulation. The damaging nitrogen oxides and their by-products cause manifold effects on forest ecosystems. The forest damage research, since beginning of the 80s pursued intensely on an international plane, has delivered new knowledge in the area of pollution effects, which led to establishment a very critical limit. Limits were set by the UN-ECE 1992. These were values (critical levels, critical loads) at which no changes in structure and function of the ecosystem are to be expected. The Federal Republic of Germany belongs to the initial signatories and co-initiators of the treaty and has ratified the resolutions on new strategies for the European clean air policy.

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Tab. 1: Limits, Standard Values and Recommendations for the Nitrogen Dioxide Pollution in the Air
Image: Umweltatlas Berlin

Causes and Development of Nitrogen Oxide Emissions

Nitrogen oxide emissions are caused primarily by combustion processes in power plants and heavy industry firing plants as well as in motors. Nitrogen oxides develop from the nitrogen and the oxygen of the combustion air and to a lesser extent also through the oxidation of nitrogen-containing elements of the fuel. The formation of nitrogen oxides greatly increases with the combustion temperature. The primary polluters in Berlin are motor vehicle traffic with 19,000 t at approximately 50 % and the power plants as well as other licensed facilities with 16,000 t, or a share of more than 40 % (c.f. Fig. 1).

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Fig. 1: Nitrogen Oxide - Emissions from the Individual Polluter Groups in Berlin (tons per year)
Image: Umweltatlas Berlin

Nitrogen monoxide comprises more than 90 % of nitrogen oxide emissions. Above all it is the reaction with ozone in the atmosphere which forms the nitrogen dioxide so much more damaging to human health. Since these reactions use up ozone, conurbations display, on average, a slighter ozone concentration in the near-ground air than rural regions. Beside ozone, combinations with hydrocarbon molecules also contribute to the transformation of nitrogen monoxide into nitrogen dioxide. Through further oxidation and combination with hydrocarbon molecules acidic aerosols develop from nitrogen dioxide, which deposit on surfaces and/or precipitate from the atmosphere as acid rain.

Under the influence of intense sunlight reactions occur in the Atmosphere simultaneously, by which nitrogen dioxide decays again into Nitrogen monoxide and oxygen atoms. In this process, in which likewise water – and hydrocarbon molecules are involved, more near-ground ozone is produced than consumed. The ozone concentration in the air can rise thereby greatly (c.f. Map 03.06 SenStadtUmTech 1996a).

Verified data on the long-term development the nitrogen oxide emissions and pollution do not exist for Berlin. On the basis of measurements in Frankfurt am Main, an eightfold rise in the nitrogen oxide pollution must be assumed for the period from 1962 to 1976 (c.f. Umweltbundesamt 1989). Nitrogen oxides – like volatile hydrocarbons – have become essential components of air pollution since the end of the Second World War. On the other hand, sulfur dioxide and floating dust have always been a part of the air pollution in central Europe given the prevalent climatic conditions.

Development of Nitrogen Oxide Pollution

Since 1979, nitrogen oxide measurements in Berlin have been carried out by the Federal Health Agency in the west part of the city at the Schloss Strasse in Steglitz and by the District Hygiene Inspectorate Berlin in the east part at the Parochial Strasse in the Borough Mitte. As part of the Berlin Air Quality Monitoring Network (BLUME), nitrogen oxide measurements were also begun at a station in Wedding in 1984.

While the near traffic measurement at the Schloss Strasse is strongly effected by changing traffic conditions and allows no statement as to trends, the measurements at the low traffic Parochial Strasse, which are representative for medium-level inner city pollution, had shown until 1987 an average annual increase in the concentration of about 3.5 % (from 35 to 45 µg/m3 in 8 years). Since 1987 both here as well as at other measuring stations in the city display an reduction (c.f. Fig. 2).

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Fig. 2: The Yearly Average of Nitrogen Dioxide 1979 - 1995
Image: Umweltatlas Berlin

The introduction of denitrifying measures in the large power and heating works (c.f. Tab. 2) as well as the introduction the regulated three-way catalytic converter in passenger cars are reasons for the decrease. The shift to vehicles with catalytic converters in Berlin has advanced especially quickly. In 1995, the share of cars equipped with catalytic converters in Berlin lay at 65 %.

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Tab. 2: Commissioning of Desulfurization and Denitrification Plants in the Berlin Heating Power Plants (HKW) and Power Plants (KW) (as of August 1996)
Image: Umweltatlas Berlin

In comparison to the very positive development with respect to sulfur dioxide (c.f. Map 03.01 SenStadtUmTech 1997a), the pollution development of nitrogen oxides has been unsatisfactory. The reason is the constant growth in traffic volume. About half the near ground nitrogen oxide emissions come from heavy transport vehicles and buses. For these vehicles, substantial improvements to reduce emissions of nitrogen oxides and other pollutants have only taken effect since 1 October 1996. Due to the expected increase in traffic, it must be assumed that the contribution of the polluter group traffic will be decisive in future for the development of nitrogen oxide pollution in the Berlin air.