To what extent do molecular collisions arising from water vapour efflux impede stomatal O₃ influx?

Uddling, Johan; Matyssek, Rainer; Pettersson, Jan B.C.; Wieser, Gerhard

To what extent do molecular collisions arising from water vapour efflux impede stomatal O₃ influx?

2012

Uddling, Johan | Matyssek, Rainer | Pettersson, Jan B.C. | Wieser, Gerhard

Pre-requisite for reliable O₃ risk assessment for plants is determination of stomatal O₃ uptake. One unaddressed uncertainty in this context relates to transpiration-induced molecular collisions impeding stomatal O₃ influx. This study quantifies, through physical modelling, the error made when estimating stomatal O₃ flux without accounting for molecular collisions arising from transpiratory mass flow of gas out of the leaf. The analysis demonstrates that the error increases with increasing leaf-to-air water vapour mole fraction difference (Δw), being zero in water vapour saturated air and 4.2% overestimation at Δw of 0.05. Overestimation is approximately twice as large in empirical studies quantifying stomatal O₃ flux from measured leaf or canopy water flux, if neglecting both water vapour-dry air collisions (causing overestimation of leaf conductance) and collisions involving O₃. Correction for transpiration-induced molecular collisions is thus relevant for both empirical research and for large-scale modelling of stomatal O₃ flux across strong spatial Δw gradients.

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