Nitrogen oxides are absorbed by vegetation in the same way as CO2 through stomata.

Nitrogen oxides are dissolved in the stomata cavity water and form nitrite and nitrate,

which in turn are reduced to NH3 and eventually incorporated into organic

compounds. (e. g. Wellburn, A.R., Wilson, J., Aldrige, P.H. 1980). If too much NO2 is

absorbed over time, acute damage may occur in form of necrosis. Biological

membranes (e. g. Mudd et al. 1984) and chloroplasts (Wellburn et al. 1972, Lopata &

Ulrich, 1975) are assumed to be damaged. Acute effects occur at very high concentrations,

which are seldom observed in ambient air, except near very large point sources

(Stonybrook Lab., 1994). There is a range of long term exposure effects (Guderian and

Tingey, 1987). Up to a certain level, no effects are observed. Above this, NO2 may

stimulate growth. However, higher doses will decrease growth in relation to controls.

There is at present a dispute over which nitrogen oxides are the most toxic. Further

knowledge is necessary to assess the situation.

 

 

 

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