# Effects of heat and water vapor transport on eddy covariance measurement of CO_{2} fluxes

- Accepted:

DOI: 10.1007/BF00123298

- Cite this article as:
- Leuning, R., Denmead, O.T., Lang, A.R.G. et al. Boundary-Layer Meteorol (1982) 23: 209. doi:10.1007/BF00123298

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## Abstract

Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO_{2} concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO_{2}, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO_{2}. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= *ρ*_{c}w for CO_{2}, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux *ρ′*_{c} w′. Thus, when the net flux of CO_{2} is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., *ρ′*_{c} w′ = −*ρ*_{c} w. Corrections for the mean convective flux are particularly significant for CO_{2} because *ρ*_{c}w and *ρ′*_{c} w′ are often of similar magnitude. The correct measurement of the net CO_{2} flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.