UV radiation induced flux of nitrogen oxides from pine needles

In the latest issue of Nature (March 13, 2003) a group of scientists led by professor Pertti Hari from the University of Helsinki present a novel observation: ultraviolet radiation induced a flux of nitrogen oxides (NOx) from pine needles to the atmosphere. These nitrogen oxides participate in several essential chemical reactions in the atmosphere and plants can also utilize the nitrogen of NOx as their nutrient.

It has been difficult to detect the UV-induced NOx emission in earlier studies, because measuring chambers are usually constructed with UV-opaque materials. The cover of the measuring chamber at the University of Helsinki is made of UV-transparent quartz glass, which enables UV radiation to reach the pine needles. This technical detail might explain why this phenomenon has not been observed earlier.

The origin of the NOx flux is not known yet. It might come from plant metabolism, or UV radiation might release the NOx from needle surfaces.

Magnitude of the flux that the scientists observed was 1 ng s-1 m-2 (needle area). If a flux this large is scaled up to global level we obtain an amount that is comparable to known NOx sources, such as, traffic and industry. The result is important for the atmospheric NOx balance and, besides, it might affect the nitrogen budget of plants.

Reference: Pertti Hari, Maarit Raivonen, Timo Vesala, J. William Munger, Kim Pilegaard, Markku Kulmala, 'Ultraviolet light and leaf emission of Nox', Nature 13.3.2003.

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