MEASUREMENTS OF OZONE DEPOSITION TO VEGETATION QUANTIFYING THE FLUX, THE STOMATAL AND NON-STOMATAL COMPONENTS

摘要

Ozone deposition to vegetation represents the major sink for boundary layer ozone and yet the underlying mechanism of reaction and uptake at the surface is poorly understood. While overall rates of O_3 deposition are known, the fractions of the flux absorbed by stomata and deposited to non-stomatal surfaces in the field have been poorly quantified. This paper reports 4 years of continuous fluxes by micromete-orological methods to moorland vegetation in southern Scotland. The flux has been partitioned between stomatal and non-stomatal fluxes and shows over a seasonal scale that the non-stomatal deposition (50 kg O_3 ha~(-1) y~(-1)) dominates the overall flux (77 kg O_3 ha~(-1) y~(-1)) and represents 70% of the total deposition. The surface resistance for non-stomatal O_3 deposition (r_(ns)) decreases with temperature from 400 s m~(-1) at 0°C to 200 s m~(-1) at 15°C in dry conditions and is consistent with thermal decomposition of ozone at the surface with an apparent activation energy of about 36 kJ mole~(-1). The 4 years of continuous flux measurements show that stomatal conductance, when O_3 concentrations are 80 μg m~(-3), is substantially smaller than for smaller O_3 concentrations, although whether this is a response to VPD or O_3 remains unclear.