Figure 4: Frequency distribution of ozone concentrations in excess of the 180 µg/m3 threshold for hourly values (April-July 1996). For each country the total number of observed exceedances is given in row '#Ex', the number of stations is given in row '#St'. Frequency distributions are presented as Box-Jenkins plots indicating the minimum, the 25-Percentile, the 75-percentile and the maximum value.