Comparison of methods for the determination of NO-O 3-NO 2 fluxes and chemical interactions over a bare soil

Stella, P.; Loubet, B.; Laville, P.; Lamaud, E.; Cazaunau, M.; Laufs, S.; Bernard, F.; Grosselin, B.; Mascher, N.; Kurtenbach, R.; Mellouki, A.; Kleffmann, J.; Cellier, P.

Tropospheric ozone (O 3) is a known greenhouse gas responsible for impacts on human and animal health and ecosystem functioning. In addition, O 3 plays an important role in tropospheric chemistry, together with nitrogen oxides. The determination of surface-atmosphere exchange fluxes of these trace gases is a prerequisite to establish their atmospheric budget and evaluate their impact onto the biosphere. In this study, O 3, nitric oxide (NO) and nitrogen dioxide (NO 2) fluxes were measured using the aerodynamic gradient method over a bare soil in an agricultural field. Ozone and NO fluxes were also measured using eddy-covariance and automatic chambers, respectively. The aerodynamic gradient measurement system, composed of fast response sensors, was capable to measure significant differences in NO and O 3 mixing ratios between heights. However, due to local advection, NO 2 mixing ratios were highly non-stationary and NO 2 fluxes were, therefore, not significantly different from zero. The chemical reactions between O 3, NO and NO 2 led to little ozone flux divergence between the surface and the measurement height (less than 1% of the flux on average), whereas the NO flux divergence was about 10% on average. The use of fast response sensors allowed reducing the flux uncertainty. The aerodynamic gradient and the eddy-covariance methods gave comparable O 3 fluxes. The chamber NO fluxes were down to 70% lower than the aerodynamic gradient fluxes, probably because of either the spatial heterogeneity of the soil NO emissions or the perturbation due to the chamber itself.



Stella, P. / Loubet, B. / Laville, P. / et al: Comparison of methods for the determination of NO-O3-NO2 fluxes and chemical interactions over a bare soil. 2012. Copernicus Publications.


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