Forms of reactive nitrogen
Reactive nitrogen, unlike nonreactive molecular nitrogen (N2), is in a great many organic and inorganic substance compounds and of vital importance to all life processes. The availability of reactive nitrogen often limits plant growth, which is why sufficient supply of reactive nitrogen is so important in food production. If excessive amounts of reactive nitrogen are deposited to the environment, however, it poses a danger to human health and the viability of ecosystems.
Forms of reactive nitrogen which are especially relevant to the environment are
- the gases ammonia (NH3), nitrogen monoxide (NO), nitrogen dioxide (NO2 ), nitrous oxide (N2O), and
- ammonium (NH4+) and nitrate (NO3), which occur in dissolved form and in atmospheric particulate matter.
The different forms of reactive nitrogen are very mobile and can convert into one another. They circulate in a biogeochemical cycle between air, soil, water and organisms.
Sources of reactive nitrogen
Some 50% of the planet’s nitrogen supply is in gaseous atmospheric nitrogen compounds. The majority of it (more than 99%) is the inert molecular nitrogen, a chemical form that is not usable by most organisms including plants. In the prehuman world molecular nitrogen was converted to reactive nitrogen primarily by a very few bacterial strains. Since the age of the Industrial Revolution, however, human activities have caused far more elemental nitrogen to change into reactive forms, probably at a rate ten times higher than in the pre-industrial era. The major conversion processes are
- combustion of fossil fuels and corresponding emissions of nitrogen oxides (NOx ),
- synthesis of ammonia (NH 3 ) through the Haber-Bosch process (primarily for fertiliser production), and
- cultivation of legumes.
Effects of reactive nitrogen
The excessive release of reactive nitrogen compounds disrupts natural biogeochemical cycles and the delicate balance in ecosystems, which results in considerable negative consequences for man and the environment.
- Atmospheric deposition of reactive nitrogen species contribute to ecosystem eutrophication in German and acidification in German and, as such, to habitat degradation and loss of biodiversity.
- Nitrate leaching in German
- jeopardises drinking water quality.
- Higher emissions of nitrous oxide promote global warming.
- Gaseous nitrogen compounds are precursors of ground-level ozone and secondary particulates and, as such, pose a risk to human health.
- High atmospheric ammonia and ozone concentrations cause widespread damage to sensitive plants in Europe.
- Nitrogen dioxide is harmful to the respiratory tract and human health.
Because of the mutability of nitrogen, reduction measures in one environmental medium might shift an existing problem to another area to become more acute there. Effective reduction of reactive nitrogen compound emissions and corresponding adverse environmental impact requires adoption of integrated concepts. Against this background the German Federal Environment Agency ( Umweltbundesamt ) developed an Integrated Strategy for the Reduction of Nitrogen Emissions for Germany in 2009. Recently, there has been heightened development of supraregional and cross-cutting approaches to solving the problem at both European and international level.
Agriculture holds the greatest reduction potential, as nitrogen efficiency (fertilisation and feeding) must be increased and emissions of reactive nitrogen reduced. Deposition of reactive nitrogen to the environment can also be effectively reduced through energy savings and greater energy efficiency.