Eddy covariance measurements of nitric oxide flux within an Amazonian rain forest

Abstract

[1] NO flux measurements by the eddy covariance technique were performed within a tropical rain forest 1 m and 11 m above the forest floor. A fast-response chemiluminescence NO analyzer with a sampling tube of 25 m length was used for the gas measurements. Nighttime similarity between the cospectra of sensible heat and the NO flux offered the possibility to quantify the high-frequency attenuation of the NO eddy covariance by spectral analysis. Integrated flux correction factors of about 21% for the system at 1 m and 5% for the one at 11 m above ground were calculated by transfer functions adopted from the literature and confirmed experimentally. For an independent validation the results of the eddy covariance system were compared with the NO soil emissions obtained by dynamic chambers. For nighttime averages, good agreement within 10% was found. The obtained NO fluxes were 3.5 Ϯ 0.14 and 4.8 Ϯ 0.39 ng N m Ϫ2 s Ϫ1for the two investigated periods at 1 and 11 m heights, respectively. During the day, chemical reaction with ozone entrained from aloft reduced the fraction of the soil-emitted NO that reached the measuring height of the eddy covariance system. The average flux showed a reduction of 48% at 1 m and 92% at 11 m height compared to the corresponding soil emission measured by the chamber system.

Application of thermal-dissociation laser induced fluorescence (TD-LIF) to measurement of HNO<sub>3</sub>, Σalkyl nitrates, Σperoxy nitrates, and NO<sub>2</sub> fluxes using eddy covariance

“…Thus the potential for within-canopy oxidation, measurement height above the canopy, and other factors affecting canopy and atmospheric NO x levels to affect the observed NO, NO 2 and O 3 fluxes. This flux divergence has been observed in an Amazonian rain forest, where NO emissions from the soil were observed near the surface, but were not significant above the canopy (Rummel et al, 2002). NO x fluxes are further complicated by direct leaf exchange that may lead to the presence of a compensation point.…”

“…EC flux measurements of NO y , NO, and NO 2 fluxes have been reported (e.g. Delany et al, 1986, Horii et al, 2004Munger et al, 1996;Rummel et al, 2002). Most other studies of N fluxes have used enclosure or indirect estimation techniques, including gradient measurements or resistance modeling (Hanson and Lindberg, 1991;Wesely and Hicks, 2000).…”

“…Gasche and Papen, 2002;Jaegle et al, 2004;Rummel et al, 2002), both emission and deposition of NO 2 have been observed using eddy covariance over grasslands and fields (Delany et al, 1986;Wesely et al, 1982). At Harvard Forest, Horii observed downward NO fluxes and upward NO 2 fluxes.…”

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

“…As O 3 is completely destroyed in the TRANC (thermal decomposition and reduction by CO), chemical NO loss by gas phase reaction (NO + O 3 → NO 2 + O 2 ) could also be neglected. Even if a small amount of O 3 would pass the TRANC, the influence on concentration changes are expected to be lower than the detection limit of the CLD according to Rummel et al (2002). A schematic overview of the TRANC-CLD system in an ECsetup is given in Fig.…”

“…It generates electronically excited NO * 2 molecules, which rapidly decay to their ground state in a reduced pressure regime by emitting photons. The total light intensity in the reaction chamber, detected by a photomultiplier tube (PMT), is proportional to the NO mixing ratio (Fontijn et al, 1970;Rummel et al, 2002). To minimise electrical noise, the Fig.…”