INFLUENCE OF THE ATMOSPHERIC CONDUCTIVITY ON THE OZONE EXPOSURE OF PLANTS UNDER AMBIENT CONDITIONS - CONSIDERATIONS FOR ESTABLISHING OZONE STANDARDS TO PROTECT VEGETATION

This paper provides results of ozone flux density measurements above a permanent grassland ecosystem as they relate to an establishment of air quality guidelines or standards. Using a resistance analogue, the product of ozone concentration measured at a standard measurement height and the conductivity of the atmosphere reflect the maximum possible ozone flux density towards the envelope of the plants. In other words, this product can be regarded as the ozone exposure potential of the atmosphere for plants. It could be shown that ozone concentrations between 100 and 180 mug m-3 are likely to have a great phytotoxic potential and are more important than concentrations greater than 180 mug m-3. From the results presented one can deduce that the application of dose-response relationships based on chamber experiments to ambient conditions results in an overestimation of, for example, yield losses. Any guideline or standard has to take into account the influence of the atmospheric conductivity on the absorbed dose of ozone.