Ground level ozone is a major threat to both agricultural crops and forest trees on a global scale. Ozone is absorbed by a plant through the stomata in the leaves, dissolves in the cell wall liquid, and reaches the cell membrane and cytosol, where it oxidizes various cellular components, thus exhibiting a toxicity to plant tissues. The cell wall (or apoplastic) liquid contains ascorbic acid (an aggregate of both neutral ascorbic acid without an electric charge and ionic ascorbate), which, as an antioxidant, serves as the first barrier against the oxidative ozone attack. Plöchl et al. (Planta, 210, 454–467 (2000)) proposed a mathematical model of the ozone detoxification by ascorbate (ASC^-) located in the cell wall. Their model describes (1) diffusive transfer of ozone from the free air to cytosol and concomitant reactions in the apoplast; (2) regeneration of ASC^- from dehydroascorbic acid (a product of ascorbic acid reacted with ozone) in the cytosol and replenishment to the apoplast; and (3) pH-dependent distribution of ASC^- in sub-cellular components. We reviewed the mathematical formula proposed by Plöchl et al. (2000) and corrected some errors in the original paper.