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Ozone is a secondary pollutant with a mobility and distribution higher than its precursors (VOCs, NOx), which causes injuries to vegetation in rural areas. The experiment was carried out over three years (2000-2002) in three localities of the Campania region characterized by different elevations (plain and hill) and atmospheric pollution (sub-urban and rural). The aim of the present research was to study the pattern of ozone concentration and its injuries to plants and to compare the response of two white clover biotypes with different sensitivities to ozone, which were grown according to the experimental protocol defined by the ICP-Vegetation. In this trial, the pollution threshold (40 ppb) was always overcome. The highest ozone concentrations were recorded during the first year and the sub-urban site was the more polluted. The daily trend of ozone shows reduced nighttime degradation at the hilly sites, which tended to have relatively high concentrations also during the night. This involves the importance to consider also nocturnal stomatal conductance for studying ozone uptake through stomata and damage to vegetation in hill or mountain localities. Ozone injuries were estimated using the yield ratio of the sensitive to the resistant biotype [1-(S/R)* 100]. Average yield losses were 20% without differences among the three localities, confirming that ozone pollution can cause injuries to plants also in rural areas located faraway from the emission sources of atmospheric pollutants. [ABSTRACT FROM AUTHOR]