6.4. Nitrogen deposition

In the atmosphere deposition of nitrogen compounds is the sink process of nitrogen. Nitrogen compounds can get to the surface via both wet and dry deposition pathways determined by the solubility of the compound. Depending on the chemical form, nitrogen can serve as nutrient deposited to land surface or can have detrimental or toxic effects such as acidification. For more information on deposition pathways see Chapter 12.

In wet deposition ammonium (NH4+), nitrate (NO3), etc. is carried to the surface predominantly by rain and snow. Connected to precipitation, spatial distribution of wet deposition is highly variable.

Dry deposition of nitrogen means the removal of gases NH3, NO2, HNO3 (Figure 6.8) and particulate NH4+ and NO3 and organic compounds (e.g. peroxyacetyl nitrate: PAN, Figure 6.9), organic acids, nitrogen containing aerosols, etc.

Chemical structure of nitric acid.

Figure 6.8: Chemical structure of nitric acid.

Chemical structure of peroxyacetyl nitrate.

Figure 6.9: Chemical structure of peroxyacetyl nitrate.

Nitrogen deposited on the vegetation surface can get to the stomata. Nitrogen uptake by leaves (in form of NO, NO2 (Figure 6.10), HNO3, PAN, isoprene nitrates and gaseous amines) are negligible compared to atmospheric abundance but an important pathway of plant N supply. Nitrogen deposition influences carbon sequestration capacity of the terrestrial vegetation, being nitrogen the major constraint of plant development in most geographic locations.

Chemical structure of nitrogen dioxide.

Figure 6.10: Chemical structure of nitrogen dioxide.