The aim of our study was to examine the literature on the phenomenon of the so-called “Weekend Effect” (WE) in Warsaw and its outskirts. An analysis of the temporal and spatial distribution of ozone and nitrogen dioxide concentrations was made using hourly data on ozone and nitrogen dioxide concentrations in the period from May to September 2008 to 2012 from automatic air quality monitoring stations in Warsaw. The analysis uses data for seven stations located in different parts of the conurbation, which represent different types of areas. WE was then calculated using four methods, one of which was based on a calculation of the difference between the maximum daily ozone concentrations on weekends and the concentrations on weekdays. The results showed that most stations see higher concentrations of ozone during the weekend than on weekdays. This confirms the existence of WE, especially in the area of Granica, west of Warsaw in Kampinos National Park. At stations located within the city, average and maximum values of daily ozone concentrations are 13% and 8% higher on weekends than on weekdays, respectively, despite a reduction in NO₂ concentrations of about 20%. Analysis of the diurnal ozone and nitrogen oxide (NO_x) behaviour confirms the hypothesis that the most likely cause of the higher mean ozone levels on weekends is a reduction in ozone suppression due to lower NO_x emissions on weekend mornings. The reduction in emissions in industrial/traffic-heavy sectors on Sunday leads to a greater reduction in NO_x relative to volatile organic compounds (VOC), and thus an increase in VOC/NO_x ratios during weekends.