Disentangling Turbulent Gas Diffusion from Non‑diffusive Transport in the Boundary Layer Kowalski, Andrew Serrano Ortiz, Penélope Miranda García, Gabriela Fratini, Gerardo Conservation of linear momentum Eddy covariance Reynolds averaging Systematic transport WPL density corrections An analysis based on the law of linear momentum conservation demonstrates unequivocally that the mass fraction is the scalar whose gradient determines gas diffusion, both molecular and turbulent. It illustrates sizeable errors in previous micrometeorological definitions of the turbulent gas flux based on fluctuations in other scalars such as the mixing ratio or density. In deference to conservation law, we put forth a new definition for the turbulent gas flux. Net gas transport is then defined as the sum of this turbulent flux with systematic transport by the mean flow. This latter, non-diffusive flux is due to the net upward boundary-layer momentum, a Stefan flow forced by evaporation, which is the dominant surface gas exchange. A comparison with the traditional methodology shows exact agreement between the two methods regarding the net flux, but with the novelty of partitioning gas transport according to distinct physical mechanisms. The non-diffusive flux is seen to be non-negligible in general, and to dominate turbulent transport under certain conditions, with broad implications for boundary-layer meteorology. 2021-03-15T10:46:49Z 2021-03-15T10:46:49Z 2021-02 info:eu-repo/semantics/article Kowalski, A. S., Serrano-Ortiz, P., Miranda-García, G., & Fratini, G. (2021). Disentangling Turbulent Gas Diffusion from Non-diffusive Transport in the Boundary Layer. Boundary-Layer Meteorology, 1-21. [https://doi.org/10.1007/s10546-021-00605-5] http://hdl.handle.net/10481/67220 10.1007/s10546-021-00605-5 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Springer