A Model for Estimating Daily Ozone Dose for Plants from Atmospheric Ozone Concentration and Vapor Pressure Deficit

Abstract

Accurate measurement of the ozone dosages received by plants is difficult because the atmospheric ozone concentration that surrounds a plant is not the concentration that actually impinges upon the plant cells. The plant's cuticle acts as a barrier to direct diffusion of ozone into cells for much of the plant surface. The primary avenue for ozone entry is via the stomata, which are adjustable pores in the epidermis. In this paper, we derive a diffusion model, consistent with Fick's first law, that uses the concurrent ambient ozone concentration and vapor pressure deficit (VPD), together with speciesspecific thresholds of ozone concentration and VPD, to predict the ozone concentration reaching the cells adjacent to the substomatal cavity at a given time. Combining this diffusion model with particular functional forms for the daily curves of atmospheric ozone concentration and VPD allows one to calculate the expected daily ozone dose that the plant's cells receive and the variance of that dose. In addition, this methodology can be modified using hierarchical models to provide realistic regional estimates of the effective daily ozone dose for a species and the variance of that dose, which reflect the regional variation in the diurnal cycles of both atmospheric ozone concentration and VPD. The ozone dose and its variance predicted by this model can be used to assess ozone impact on red spruce in the northeastern United States.