In the field of air pollution effects research there is the need to examine the various components of pollutant dose expression (concentration, frequency, and duration) in order to assess each of their contributions to the observed response. The difficulty of selecting an appropriate statistic to characterize plant exposure has been summarized by Heagle and Heck. Pollutant exposure has been characterized by use of mean concentrations with varying averaging times (7-hr, weekly, month, or seasonal), the number of hours above a selected concentration, and the number of hours above selected concentration intervals. However, these values do not reflect the relationships of concentration, frequency and duration of exposures, and the plant response. The use of a mean implies that all concentrations are equally effective in elliciting a plant response and minimizes the contribution of peak concentrations. The mean treats low-level long-term exposures the same as high-concentrations short-term ones. Most exposure statistics are not directly correlated with each other and it is difficult to relate them to ambient air measurements of ozone which are usually reported as 1-hr means.