OZONE UPTAKE BY CORN (ZEA-MAYS-L) - GENERAL-APPROACH

Ozone concentrations at a rural site in Southern Ontario were measured at two levels above a corn field during the 1977 growing season. Fluxes of ozone were calculated using Bowen ratios and the crop energy budget, in conjunction with the ozone gradients. Ozone fluxes were also calculated from the mean ozone concentrations combined with canopy resistances which were computed from measured stomatal resistances of sunlit and shaded leaves. Daytime ozone concentrations were typically 0.08 and 0.10 ppm for southerly winds, with several peaks exceeding 0.12 ppm. For air originating in Northern Ontario, peak concentrations were around 0.04 ppm. The Bowen ratio technique provides estimates of the total flux of ozone to the crop and the soil, whereas the canopy resistance method estimates the flux to the leaves alone. Comparison of results of these two methods shows that about 50 to 65% of the total flux is to the leaves. Typical ozone fluxes to the plants range between 0.3 and 0.8 μg m-2s-1 of land area (LAI = 2.9), when ozone concentration varied between 0.04 and 0.10 ppm. Typical fluxes of ozone at midday for sunlit leaves are between 0.2 and 0.5 μg m-2s-1 of leaf area. The canopy resistance method is very simple and it can be applied to any crop provided stomatal resistances and ozone concentrations are known. © 1979.