The vertical change of coefficient b, used in the relaxed eddy accumulation method for flux measurement above and within a forest canopy

1995 ◽  
Vol 29 (17) ◽  
pp. 2339-2347 ◽  
Author(s):  
W Gao
Keyword(s):  
Forest Canopy ◽  
Flux Measurement ◽  
Relaxed Eddy Accumulation ◽  
Vertical Change ◽  
Accumulation Method

scholarly journals Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

2012 ◽  
Vol 12 (17) ◽  
pp. 8285-8296 ◽  
Author(s):  
N. Zhang ◽  
X. Zhou ◽  
S. Bertman ◽  
D. Tang ◽  
M. Alaghmand ◽  
...  
Keyword(s):  
Measurement Technique ◽  
Forest Canopy ◽  
Sonic Anemometer ◽  
Flux Measurement ◽  
Measurement Systems ◽  
Ambient Concentration ◽  
Solar Noon ◽  
Absorption Photometer ◽  
Upward Flux ◽  
Northern Michigan

Abstract. Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using a long-path absorption photometer (LPAP). A Na2CO3-coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of ±(1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ±(8 × 10−8 + 0.15 FHONO) mol m−2 h−1, with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10−6 moles m−2 h−1. The HONO flux reached a maximal mean of ~0.7 × 10−6 moles m−2 h−1 around solar noon, contributing a major fraction to the HONO source strength required to sustain the observed ambient concentration of ~70 pptv. There were no significant correlations between [NOx] and daytime HONO flux and between JNO2 × [NO2] and HONO flux, suggesting that NOx was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NOx rural environment. Evidence supports the hypothesis that photolysis of HNO3 deposited on the forest canopy surface is a major daytime HONO source.

scholarly journals Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

2012 ◽  
Vol 12 (3) ◽  
pp. 7273-7304 ◽  
Author(s):  
N. Zhang ◽  
X. Zhou ◽  
S. Bertman ◽  
D. Tang ◽  
M. Alaghmand ◽  
...  
Keyword(s):  
Measurement Technique ◽  
Forest Canopy ◽  
Sonic Anemometer ◽  
Flux Measurement ◽  
Rural Environment ◽  
Measurement Systems ◽  
Ambient Concentration ◽  
Solar Noon ◽  
Upward Flux ◽  
Northern Michigan

Abstract. Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using an optical fiber spectrometer with a 1-m long path flow cell. A Na2CO3-coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 2-min averages, with an overall uncertainty of ±(1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ±(8 × 10−8 + 0.15 FHONO) mol m−2 h−1, with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10−6 moles m−2 h−1. The HONO flux reached a maximum mean of ~0.7 × 10−6 moles m−2 h−1 around solar noon, contributing a major fraction (~60%) to the HONO source strength required to sustain the observed ambient concentration of ~70 pptv. There was no significant correlation between NOx and daytime HONO flux, suggesting that NOx was not an important precursor responsible for HONO daytime production on the forest canopy surface in the low-NOx rural environment. Evidence suggests that photolysis of HNO3 deposited on the forest canopy surface is a major daytime HONO source.

Verification of flux measurement using relaxed eddy accumulation

1993 ◽  
Vol 27 (15) ◽  
pp. 2417-2426 ◽  
Author(s):  
Steven P. Oncley ◽  
Anthony C. Delany ◽  
Thomas W. Horst ◽  
Pieter P. Tans
Keyword(s):  
Flux Measurement ◽  
Relaxed Eddy Accumulation

scholarly journals Application of a GC-ECD for measurements of biosphere–atmosphere exchange fluxes of peroxyacetyl nitrate using the relaxed eddy accumulation and gradient method

2014 ◽  
Vol 7 (2) ◽  
pp. 1917-1974 ◽  
Author(s):  
A. Moravek ◽  
T. Foken ◽  
I. Trebs
Keyword(s):  
Measurement System ◽  
Current Knowledge ◽  
Flux Measurement ◽  
Bowen Ratio ◽  
Terrestrial Ecosystems ◽  
Fast Response ◽  
Electron Capture Detection ◽  
Mixing Ratio ◽  
Peroxyacetyl Nitrate ◽  
Relaxed Eddy Accumulation

Abstract. Peroxyacetyl nitrate (PAN) may constitute a significant fraction of reactive nitrogen in the atmosphere. Current knowledge about the biosphere–atmosphere exchange of PAN is limited and only few studies have investigated the deposition of PAN to terrestrial ecosystems. We developed a flux measurement system for the determination of biosphere–atmosphere exchange fluxes of PAN using both the hyperbolic relaxed eddy accumulation (HREA) method and the modified Bowen ratio (MBR) method. The system consists of a modified, commercially available gas chromatograph with electron capture detection (GC-ECD, Meteorologie Consult GmbH, Germany). Sampling was performed by trapping PAN onto two pre-concentration columns; during HREA operation one was used for updraft and one for downdraft events and during MBR operation the two columns allowed simultaneous sampling at two measurement heights. The performance of the PAN flux measurement system was tested at a natural grassland site, using fast response ozone (O3) measurements as a proxy for both methods. The measured PAN fluxes were comparatively small (daytime PAN deposition was on average −0.07 nmol m−2 s−1 and, thus, prone to significant uncertainties. A major challenge in the design of the system was the resolution of the small PAN mixing ratio differences. Consequently, the study focuses on the performance of the analytical unit and a detailed analysis of errors contributing to the overall uncertainty. The error of the PAN mixing ratio differences ranged from 4 to 15 ppt during the MBR and between 18 and 26 ppt during the HREA operation, while during daytime measured PAN mixing ratios were of similar magnitude. Choosing optimal settings for both the MBR and HREA method, the study shows that the HREA method did not have a significant advantage towards the MBR method under well mixed conditions as it was expected.

A Relaxed Eddy Accumulation System for Measuring Surface Fluxes of Total Gaseous Mercury

2008 ◽  
Vol 25 (2) ◽  
pp. 244-257 ◽  
Author(s):  
Jesse O. Bash ◽  
David R. Miller
Keyword(s):  
Forest Canopy ◽  
Surface Fluxes ◽  
System Response ◽  
Total Gaseous Mercury ◽  
Flux Dynamics ◽  
Relaxed Eddy Accumulation ◽  
Gaseous Mercury ◽  
Measuring Surface ◽  
Turbulent Statistics ◽  
Mercury Analyzer

Abstract A relaxed eddy accumulation (REA) system was designed to continuously measure total gaseous mercury (TGM) fluxes over a forest canopy. TGM concentration measurements were measured at 5-min intervals with a Tekran model 2537A mercury analyzer located above the forest canopy on a walk-up meteorological tower. Ten-minute averages for up- and downdraft mercury concentrations were used to calculate the flux. The multiresolution decomposition technique was used to determine day- and nighttime averaging periods for the turbulent statistics used in the REA technique. This paper documents the REA system for mercury flux measurements and its use over a forest canopy. The REA system response to the averaging times for the turbulent statistics and corrections to up- and downdraft concentrations are major considerations when using the technique with the Tekran mercury analyzer over a forest canopy. TGM flux data collected from 18 August to 12 September 2005 are used here to demonstrate the capabilities of the REA system to measure both short- (1-h time periods) and long-term flux dynamics. During the demonstration period the TGM median flux was 21.9 ± 32.6 ng m−2 h−1 and the median atmospheric TGM concentrations were 1.34 ± 0.13 ng m−2 h−1. Maximum short-term TGM evasive fluxes occurred during the daylight hours with minimums during the nighttime. A consistent bimodal emission pattern was observed during the daytime emissions over the canopy. The first peak occurred immediately following the evaporation of the nighttime dew on the canopy and the second peak occurred in the late afternoon.

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