Stomatal-scale modelling of the competition between ozone sinks at the air–leaf interface

This paper analyses the existence and relative strength of ozone (O₃) sinks at the leaf level, in particular the implications for the partition of the O₃ flux amongst the several physically, chemically and physiologically differing inner and outer surfaces of a leaf.We used a single-stomatal scale theoretical model to simulate the O₃ transfer into leaves and estimate the flux partition. The theoretical scenarios were compared with experimental values from shoot-scale measurements of O₃ flux onto Scots pine. The conditions where external sinks would prevent the stomatal diffusion involved the existence of very strong sinks at the external surfaces but yielded unrealistically high flux values. Only the possibility of a strong sink localized in the antechamber and/or pore could be of significance. Results also showed that in most instances a significant proportion of the total flux was generated by the external surfaces. For scenarios that consider strong scavenging in the mesophyll and weaker removal in the exterior, the proportion was about 60–80% for small stomatal apertures (∼0.5 μm), and 10–40% for larger apertures (∼1.5 μm). In these cases, however big the proportion of total flux is due to the external surfaces, the existence of sinks at the external surfaces does not prevent the diffusion through open and unoccluded stomata.