Comparison of methods for the determination of NO-O3-NO2 fluxes and chemical interactions over a bare soil

[摘要] Tropospheric ozone (O₃) is a known greenhouse gas responsible forimpacts on human and animal health and ecosystem functioning. In addition,O₃ plays an important role in tropospheric chemistry, together withnitrogen oxides. The determination of surface-atmosphere exchange fluxes ofthese trace gases is a prerequisite to establish their atmospheric budgetand evaluate their impact onto the biosphere. In this study, O₃, nitricoxide (NO) and nitrogen dioxide (NO₂) fluxes were measured using theaerodynamic gradient method over a bare soil in an agricultural field. Ozoneand NO fluxes were also measured using eddy-covariance and automaticchambers, respectively. The aerodynamic gradient measurement system, composedof fast response sensors, was capable to measure significant differences inNO and O₃ mixing ratios between heights. However, due to localadvection, NO₂ mixing ratios were highly non-stationary and NO₂fluxes were, therefore, not significantly different from zero. The chemicalreactions between O₃, NO and NO₂ led to little ozone fluxdivergence between the surface and the measurement height (less than 1%of the flux on average), whereas the NO flux divergence was about 10% onaverage. The use of fast response sensors allowed reducing the fluxuncertainty. The aerodynamic gradient and the eddy-covariance methods gavecomparable O₃ fluxes. The chamber NO fluxes were down to 70% lowerthan the aerodynamic gradient fluxes, probably because of either the spatialheterogeneity of the soil NO emissions or the perturbation due to thechamber itself.

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