Comparison of O3 fluxes measured with the eddy covariance and the gradient methods above a maize field

Loubet, Benjamin; Irvine, Mark; Lamaud, Eric; Larmanou, Eric; Fléchard, Christophe; Zurfluh, Olivier; Cellier, Pierre

Comparison of O3 fluxes measured with the eddy covariance and the gradient methods above a maize field

2005

Between June and September 2002, the fluxes of carbon dioxide (CO2) and ozone (O3), and nitrogen oxides (NO and NO2) were measured above a growing maize crop, together with the components of the energy balance - sensible (H) , ground (G) and latent heat fluxes (H), net radiation (Rn) – , the meteorology, and the canopy structure. All the fluxes, except the NOx, were measured simultaneously with the gradient and the covariance technique. The gradient mast consisted in 9 levels extending from 0.3 to 10 m above ground, where CO2 and H2O was measured with a Licor Li6262, and O3 and NOx was measured with two separate analysers (2 Environnement SA 41M for O3 and 2 ThermoEnvironnement 42C for NOx), each screening the 5 uppermost and the 5 lowermost levels, with a common level allowing for cross calibration. Wind speed and temperature was also measured, and the fluxes were determined using 3 to 4 levels above the canopy. The covariance mast consisted in a Gill R3-50, a Licor Li7500 and a fast O3 chemiluminescent based close-path sensor from ATDD V2.0 with solid-plates “targets” coated with Coumarin. Two identical covariance masts were compared during 15 days, to determine the lifetime of a “target”. In this study, the momentum, energy, CO2, and O3 fluxes estimated with the gradient method and the two eddy-covariance masts are compared, with a special focus on O3.

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