ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-13-773-2013 Field investigations of nitrogen dioxide (NO<sub>2</sub>) exchange between plants and the atmosphere Breuninger C. 1 Meixner F. X. 1 Kesselmeier J. 1 Max Planck Institute for Chemistry, Biogeochemistry and Air Chemistry Departments, P.O. Box 3060, 55020 Mainz, Germany 22 01 2013 13 2 773 790 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/13/773/2013/acp-13-773-2013.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/13/773/2013/acp-13-773-2013.pdf

The nitrogen dioxide (NO<sub>2</sub>) exchange between the atmosphere and needles of <i>Picea abies</i> L. (Norway Spruce) was studied under uncontrolled field conditions using a dynamic chamber system. This system allows measurements of the flux density of the reactive NO-NO<sub>2</sub>-O<sub>3</sub> triad and additionally of the non-reactive trace gases CO<sub>2</sub> and H<sub>2</sub>O. For the NO<sub>2</sub> detection a highly NO<sub>2</sub> specific blue light converter was used, which was coupled to chemiluminescence detection of the photolysis product NO. This NO<sub>2</sub> converter excludes known interferences with other nitrogen compounds, which occur by using more unspecific NO<sub>2</sub> converters. Photo-chemical reactions of NO, NO<sub>2</sub>, and O<sub>3</sub> inside the dynamic chamber were considered for the determination of NO<sub>2</sub> flux densities, NO<sub>2</sub> deposition velocities, as well as NO<sub>2</sub> compensation point concentrations. The calculations are based on a bi-variate weighted linear regression analysis (y- and x-errors considered). The NO<sub>2</sub> deposition velocities for spruce, based on projected needle area, ranged between 0.07 and 0.42 mm s<sup>−1</sup>. The calculated NO<sub>2</sub> compensation point concentrations ranged from 2.4 ± 9.63 to 29.0 ± 16.30 nmol m<sup>−3</sup> (0.05–0.65 ppb) but the compensation point concentrations were all not significant in terms of compensation point concentration is unequal to zero. These data challenge the existence of a NO<sub>2</sub> compensation point concentration for spruce. Our study resulted in lower values of NO<sub>2</sub> gas exchange flux densities, NO<sub>2</sub> deposition velocities and NO<sub>2</sub> compensation point concentrations in comparison to most previous studies. It is essential to use a more specific NO<sub>2</sub> analyzer than used in previous studies and to consider photo-chemical reactions between NO, NO<sub>2</sub>, and O<sub>3</sub> inside the chamber.

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