Measuring the biosphere-atmosphere exchange of total reactive nitrogen by eddy covariance

Abstract

Abstract. The (net) exchange of reactive nitrogen (N r ) with the atmosphere is an important driver for ecosystem productivity and greenhouse gas exchange. The exchange of airborne N r includes various trace compounds that usually require different specific measurement techniques, and up to now fast response instruments suitable for eddy covariance measurements are only available for few of these compounds.Here we present eddy covariance flux measurements with a recently introduced converter (TRANC) for the sum of all N r compounds ( N r ). Measurements were performed over a managed grassland field with phases of net emission and net deposition of N r and alternating dominance of oxidized (NO X ) and reduced species (NH 3 ). Spectral analysis of the eddy covariance data exhibited the existence of covariance function peaks at a reasonable time lag related to the sampling tube residence time under stationary conditions. Using ogive analysis, the high-frequency damping was quantified to 19 %-26 % for a low measurement height of 1.2 m and to about 10 % for 4.8 m measurement height.N r concentrations and fluxes were compared to parallel NO and NO 2 measurements by dynamic chambers and NH 3 measurements by the aerodynamic gradient technique. The average concentration results indicate that the main compounds NO 2 and NH 3 were converted by the TRANC system with an efficiency of near 100 %. With an optimised sample inlet also the fluxes of these compounds were recovered reasonably well including net deposition and net emission phases. The study shows that the TRANC system is suitable for fast response measurements of oxidized and reduced nitrogen compounds and can be used for continuous eddy covariance flux measurements of total reactive nitrogen.

Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests

“…Using the H 2 O flux data again an estimate of the correction term can be made. Like the WPL correction, this estimated correction term reaches an absolute maximum during the daytime (0.79 and 0.67 ppt m s −1 on average), about 4-5 times larger than the estimated WPL correction term (consistent with what was found by Ammann et al, 2012). It can therefore become important (> 5 % of the calculated flux); if only the fluxes above the detection limit are considered, about 12 % of the data have correction terms greater than 5 %.…”

“…When the correction term approaches 10 %, the fluxes were almost always below the detection limit (discussed below). As pointed out by Ammann et al (2012), the chemiluminescent reaction on which the detection of reactive nitrogen oxides is based is sensitive to water vapour, which acts as a quencher and could therefore also lead to an artificial component of the flux. Previous lab studies with the instrument used here showed a linear reduction in sensitivity of about 0.6 and 0.7 % per g m −3 of water vapour increase in channel 1 and channel 2 respectively.…”

TRANC – a novel fast-response converter to measure total reactive atmospheric nitrogen

“…Other arising problems when using long tubing such as the correct determination of the lag time (to maximise the covariance), i.e. the time the air sample needs from entering the converter until it reaches the analyser, or possible high-frequency damping will be addressed in Ammann et al (2012).…”

“…The purpose of this paper is the presentation of the converter, its characteristics and results of performance tests. Validation and long-term application of the converter for EC flux measurements is presented in companion papers by Ammann et al (2012) and Brümmer et al (2012b).…”

Eddy covariance for quantifying trace gas fluxes from soils

“…In the future, COS measurements may lead to a better understanding of both ecosystem carbon cycling and ecosystem sulfur cycling (Kesselmeier et al, 1999;Billesbach et al, 2014). In addition to COS studies that aimed at measuring other compounds such as ozone (O 3 ) and reactive components as part of nitrogen cycling (NO x , which is the sum of NO and NO 2 ; NO y , which is the total of NO x plus additional products of atmospheric oxidation of NO x , namely HNO 3 , HONO, NO 3 , N 2 O 5 , HNO 4 , PAN, RONO 2 , and ROONO 2 ; and ammonia, NH 3 ) with micrometeorological approaches have become available in the past decades (Munger et al, 1996;Eugster and Hesterberg, 1996;Hesterberg et al, 1996;Munger et al, 1998;Famulari et al, 2004;Horii et al, 2004;Jones et al, 2011;Ferrara et al, 2012;Ammann et al, 2012;Marr et al, 2013;Geddes and Murphy, 2014). In particular, the ongoing development of easyto-deploy quantum cascade laser spectrometers capable of measuring various scalars in the field opened the door for fast-response concentration measurements (Bruemmer et al, 2013;Famulari et al, 2004;Skiba et al, 2009;Sutton et al, 2007).…”