In this study, a two-step statistical approach was used to quantify the phenomenon known as the Weekend Ozone Effect" (WOE) in which higher ozone concentrations in urban areas are evident on weekends than on weekdays. In the first step, Fisher's Least Significant Difference (LSD) procedure was used to discriminate among the means of the calculated ratios. In the second step, weekly cycles were detected using spectral estimation by the Burg method, a powerful non-parametric method for spectral estimation. The method was used to evaluate the data for two stations in Istanbul, Kadikoy and Sarachane, for the period 2000 and 2005. Significant differences were observed between the stations. While the Kadikoy data showed a typical and very clear WOE, the same phenomena was not clearly evident in the Sarachane data. The most probable reasons for this difference is discussed and the main attribute of the different characteristics of the daily traffic activities within the regions.