Abstract |
Defining the appropriate exposure index that 'best' relates plant response to exposure necessitates a consideration of the underlying biological basis for the response and a method for characterizing the temporal variations in pollutant occurrence. Although no single index was deemed 'best' (in all cases) for relating O(3) exposure to plant response, the top-performing exposure indices were those that (1) cumulate the hourly O(3) concentrations over time, (2) emphasize concentrations of 0.06 ppm and higher either by continuous sigmoid weights or by discrete (0 or 1) weights of the threshold indices. The 'best' index gave greater weight to exposures occurring 20 to 40 days before harvest. When assessing the impact of O(3) on plant growth, these findings illustrate the importance of exposure duration, the importance of repeated peaks, and the time of increased plant sensitivity. |