This European Standard applies to the determination of the impact of ground-level ozone on a bioindicator plant species (tobacco Nicotiana tabacum cultivars Bel-W3, Bel-B and Bel-C) in a given environment. The present document specifies the procedure for the setting-up and use of a system designed to expose these plants to ambient air. It also describes the procedure of leaf injury assessment. Leaf injury caused by ozone appears in the form of necrosis or accelerated leaf aging (senescence) on the leaves of the bioindicator. The macroscopically detectable leaf injury is used as the effect measure (see pictures in Annex A). The measure is the percentage of dead leaf area on the entire leaf surface. The results of the standardised tobacco exposure indicate ozone-caused injury of the exposed bioindicators and thus enable a spatial and temporal distribution of the impact of ozone on plants to be determined. This Standard applies to the outside atmosphere in all environments but does not apply to the assessment of air quality inside buildings. The method described in this European Standard does not replace modelling or physico-chemical methods of direct measurement of air pollutants, it complements them by demonstrating the biological effect.