The dynamic chamber method: trace gas exchange fluxes (NO, NO<sub>2</sub>, O<sub>3</sub>) between plants and the atmosphere in the laboratory and in the field

Abstract

Abstract. We describe a dynamic chamber system to determine reactive trace gas exchange fluxes between plants and the atmosphere under laboratory and, with small modifications, also under field conditions. The system allows measurements of the flux density of the reactive NO-NO 2 -O 3 triad and additionally of the non-reactive trace gases CO 2 and H 2 O. The chambers are made of transparent and chemically inert wall material and do not disturb plant physiology. For NO 2 detection we used a highly NO 2 specific blue light converter coupled to chemiluminescence detection of the photolysis product, NO. Exchange flux densities derived from dynamic chamber measurements are based on very small concentration differences of NO 2 (NO, O 3 ) between inlet and outlet of the chamber. High accuracy and precision measurements are therefore required, and high instrument sensitivity (limit of detection) and the statistical significance of concentration differences are important for the determination of corresponding exchange flux densities, compensation point concentrations, and deposition velocities. The determination of NO 2 concentrations at sub-ppb levels (<1 ppb) requires a highly sensitive NO/NO 2 analyzer with a lower detection limit (3σ -definition) of 0.3 ppb or better. Deposition velocities and compensation point concentrations were determined by bi-variate weighted linear least-squares fitting regression analysis of the trace gas concentrations, measured at the inlet and outlet of the chamber. Performances of the dynamic chamber system and data analysis are demonstrated by studies of Picea abies L. (Norway Spruce) under field and laboratory conditions. Our laboratory data show that the quality selection criterion based on the use of only significant NO 2 concentration differences has a considerable impact on the resulting compensation point concentrations yielding values closer to zero. The results of field experiments demonstrate the need to consider photo-chemical reactions of NO, NO 2 , and O 3 inside the chamber for the correct determination of the exchange flux densities, deposition velocities, as well as compensation point concentrations. Under our field conditions NO 2 deposition velocities would have been overestimated up to 80 %, if NO 2 photolysis has not been considered. We also quantified the photolysis component for some previous NO 2 flux measurements. Neglecting photo-chemical reactions may have changed reported NO 2 compensation point concentration by 10 %. However, the effect on NO 2 deposition velocity was much more intense, ranged between 50 and several hundreds percent. Our findings may have consequences for the results from previous studies and ongoing discussion of NO 2 compensation point concentrations.

Field investigations of nitrogen dioxide (NO&lt;sub&gt;2&lt;/sub&gt;) exchange between plants and the atmosphere

“…The derivation of Eqs. (2)-(4) are described in great detail in Breuninger et al (2012). For the sake of completeness exchange flux densities, deposition velocities, and compensation point concentrations of NO and O 3 are described there as well.…”

“…In Breuninger et al (2012), we have simulated (random number application) the effect of different NO 2 detection limits (1.0, 0.1, and 0.01 ppb) on the minimum possible, but still highly significant NO 2 compensation point concentration considering several ambient and quality parameters (Fig. 2).…”

“…For a detailed listing of all errorprone variables and the derivatives of ∂y/∂x i see Breuninger et al (2012).…”

“…In order to ensure a continuous turbulent mixing of the air inside the chambers and to minimize turbulent and boundary layer resistances, Teflon coated micro-fans mounted inside the chambers were installed (Meixner et al, 1997;Pape et al, 2009;Gut et al, 2002). Details are described in Breuninger et al (2012).…”

“…For the gas exchange measurements a dynamic chamber system was used which consisted of thin transparent Teflon film (FEP) bags (Schäfer et al, 1992;Kesselmeier et al, 1996Kesselmeier et al, , 1997Kuhn et al, 2000), which transmit 90 % of the photosynthetically active radiation and 70 % of the photolysis rate j (NO 2 ) (Schäfer et al, 1992;Breuninger et al, 2012). In order to ensure a continuous turbulent mixing of the air inside the chambers and to minimize turbulent and boundary layer resistances, Teflon coated micro-fans mounted inside the chambers were installed (Meixner et al, 1997;Pape et al, 2009;Gut et al, 2002).…”