The aim of this work is to study the tropospheric ozone concentrations and daily peak cycles in the Lisbon Metropolitan Area (LMA) during the summer season (June, July and August, JJA) covering the 4-yr study period 2002-2005. The results show that all the stations have the same pattern: a minimum in the early morning followed by an increase at 1000 UTC reaching to a peak at 1300-1400 UTC, dropped again to minimum values 1800 UTC but with different concentrations due to regional and local wind circulations and complex dynamic interactions. We identified in Lisbon city the ozone “weekend effect”. Finally, we studied an episode of very high levels of tropospheric ozone and related daily ozone concentrations with some meteorological variables.