Abstract
Abstract. The nitrogen dioxide (NO2) exchange between the atmosphere and needles of Picea abies 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-NO2-O3 triad and additionally of the non-reactive trace gases CO2 and H2O. For the NO2 detection a highly NO2 specific blue light converter was used, which was coupled to chemiluminescence detection of the photolysis product NO. This NO2 converter excludes known interferences with other nitrogen compounds, which occur by using more unspecific NO2 converters. Photo-chemical reactions of NO, NO2, and O3 inside the dynamic chamber were considered for the determination of NO2 flux densities, NO2 deposition velocities, as well as NO2 compensation point concentrations. The calculations are based on a bi-variate weighted linear regression analysis (y- and x-errors considered). The NO2 deposition velocities for spruce, based on projected needle area, ranged between 0.07 and 0.42 mm s−1. The calculated NO2 compensation point concentrations ranged from 2.4 ± 9.63 to 29.0 ± 16.30 nmol m−3 (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 NO2 compensation point concentration for spruce. Our study resulted in lower values of NO2 gas exchange flux densities, NO2 deposition velocities and NO2 compensation point concentrations in comparison to most previous studies. It is essential to use a more specific NO2 analyzer than used in previous studies and to consider photo-chemical reactions between NO, NO2, and O3 inside the chamber.
Highlights
IntroductionAtmospheric N2 is made available by biological fixation by procaryotic microorganisms delivering amino acids and ammonia, both of which can be taken up by higher plants
Nitrogen is an essential nutrient for all living organisms
Ambient concentrations of nitrogen monoxide (NO), NO2, O3, CO2, and H2O, relative humidity and air temperature were recorded during the entire EGER experiment (Table 1)
Summary
Atmospheric N2 is made available by biological fixation by procaryotic microorganisms delivering amino acids and ammonia, both of which can be taken up by higher plants. Most of the nitrogen taken up by higher vegetation is introduced by nitrification performed by other groups of microorganisms which oxidize ammonia and deliver nitrate (NO−3 ) which is taken up by plant roots. In the course of both nitrification and denitrification, nitrogen monoxide (NO) can be released, oxidized to nitrogen dioxide (NO2) and contribute to the atmospheric pool of these two nitrogen oxides, termed NOx (Williams et al, 1992; Robertson and Groffman, 2007). NO and NO2 are produced by anthropogenic activities such as fossil fuel combustion, and they can be oxidized to nitrate and to nitric acid which is returned to the Earth’s surface by dry and wet deposition. NO, NO2, and O3 are in a photostationary equilibrium, referred to as the NO-NO2-O3 triad (Seinfeld and Pandis, 2006)
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