The ratio of variance, autocorrelation function and duration of exceedances above selected concentrations have been calculated for ozone measurements at two rural sites in north‐west England. Autocorrelation analysis of hourly ozone concentrations showed a persistent diurnal pattern during the summer months which was largely absent during the winter. Daily maximum hourly ozone concentrations, between 1981 and 1983, exceeded 80 ppb for an average duration of 1.5–2.5 days, each exceedance lasting, on average, between 2.8 and 4.0 hours.