Effects of recurring exposures to small ozone concentrations on Bel W3 tobacco plants

Exposing Bel W₃ tobacco plants for 12 h to 0.03 ppm ozone did not cause any visible injury. However, subsequent exposure to 0.08 and 0.1 ppm ozone caused the earlier appearance of leaf injury, greater number of injured leaves and a larger proportion of chlorotic leaf surface than in previously untreated plants. A quantitative injury index was defined, enabling statistical testing of the injury differences between the two plant groups, and the differences were found to be significant. These effects should be taken into consideration in assessing crop damage and loss induced by ambient air pollution.