Daytime variations of ozone eddy fluxes to maize

The vertical fluxes of ozone, momentum and heat in the atmospheric surface layer have been measured by eddy correlation above both mature and senescent maize canopies. Aerodynamic formulae are applied to find that the bulk canopy surface resistancer _c to ozone uptake and destruction varies between 4.0 and 0.5 s cm⁻¹ during the daytime. Apparently, surface properties tend to control the removal of ozone at the surface of the earth. For a lush canopy, the stomatal diffusion resistance is the most important property, while changes in surface temperature have little effect. Destruction at the soil and exterior plant surfaces appears to account for 20–50% of the total loss if leaf mesophyll resistances are assumed to be very small. Free water at leaf surfaces may at times inhibit ozone removal by both senescent and healthy plants.