Nitrogen Oxides


Luftverschmutzung durch Autoabgase (© BMU, H.-G. Oed)Luftverschmutzung durch Autoabgase © BMU, H.-G. OedThe use of the collective terms nitrous gases or nitrogen oxides refer to the gaseous oxides of nitrogen – abbreviated to NOx. Nitrogen reacts with oxygen at different levels of oxidation, including N2O (nitrous oxide or laughing gas), NO (nitric oxide), and NO2 (nitrogen dioxide).

The nitrous gases NO and NO2 are created by burning coal, gas and oil. The main emitters are therefore power stations and heating systems, as well as motorised vehicles. The NOx emissions from road traffic are of particular significance for the protection of human health, due to the emission sources being close to the ground.

Under atmospheric conditions, nitric oxide and nitrogen dioxide act as acidifiers and for this reason have the effect of irritants and in high concentrations have a poisonous effect for the human organism. Due to their effect on health, environmental policy took on board the problem of emissions and immissions of nitrous gases at an early stage and introduced limits for vehicles and industrial plants, and for the improvement of air quality. The limits for vehicles are regulated by the Emissions Standards, those for industrial plants by the German Clean Air Act (TA Luft) and air quality by the 22nd Federal Immission Control Act.

After emissions were able to be greatly reduced for industrial plants through waste gas treatment technology, it is now mainly vehicle populations which are the focus of environmental policy. On busy inner city roads around 70 per cent of the NO2 immissions come from motorised vehicles. The remaining 30 per cent come from urban and regional backgrounds, where besides vehicles, domestic fuel is also a source of emissions. Nitrous gases have been regulated since the introduction of the Emissions Standards Euro 1 – initially sum parameters with hydrocarbons - in the emissions regulations for vehicles. With the updating of the Emissions Standards up to Euro 6, a staged reduction among diesel cars is currently taking place from 500 mg/km (Euro 3, since 2000) to 80 mg/km (Euro 6, from 2014) and with trucks and buses from 8 g/kWh (Euro 1, 1992) to 0.4 g/kWh (Euro 6, 2014).

With the EU Directives 1999/30/EC and 2008/50/EC, the Commission has set limits for NO2 which are binding from 2010. The annual limit of 40 µg/m3 is exceeded at many of the measuring points close to roads in Germany – also in Brandenburg – and in other European countries. At many of the measuring points there is no tendency towards a reduction and in individual cases during the past year there was an increase in NO2 concentrations in the air. The high NO2 concentrations near roads can be attributed to vehicle emissions and high buildings close to the roads which makes it harder for the gases to escape. In previous years the proportion of primary NO2 from vehicle exhausts has increased, mainly because diesel cars are in the vehicle population and they release more nitrous gases than petrol engines. It is presumed that the NO2 limit will be permanently and safely complied with only upon the complete introduction into vehicle populations of Euro 6 vehicles. Further measures to reduce NO2 immissions have to be applied to motorised vehicles overall and in addition to technical solutions (such as exhaust treatment systems) and will also involve traffic avoidance and control measures, such as increasing pedestrian and cycle traffic.

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Letzte Aktualisierung: 24.05.2018

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MLUL, Abteilung Umwelt,
Klimaschutz, Nachhaltigkeit
Referat 54
Dr. Frank Beck
Tel.: 0331/ 866 -7210
E-Mail: Dr. Frank Beck