Statistical Analysis of Ozone Weekend Effect in the Largest Cities in Poland

Abstract

This study examines O₃, NO_x, NO₂ and NO data from five large cities in Poland (Warszawa, Kraków, Łódź, Wrocław and Poznań) over a three-year period (2015-2017) to quantify the phenomenon of ozone weekend effect. The seasonal and diurnal variations of O₃ and NO_x species, showing the interdependence these two gaseous species, were presented. The number of 8-hour running average values above the threshold of 60 ppb and 1-hour above 90 ppb shows that ozone exceeded amounts are more frequent on Saturday and Sunday compared to other days of the week. The analysis of day of the week variations of O₃ indicates distinct, temporal pattern with maximum O₃ concentrations during weekend (especially on Sunday) and minimum noted on Wednesday, Thursday and Friday (depending on the station). The analysis of existence of the ozone weekend effect was performed on the basis of average O₃ concentration at the weekend and on the day of the lowest O₃ concentration during the week. Calculations were performed for the period of the whole year and for individual seasons of the year. The results of performance the non-parametric U-Mann-Whitney test indicate that differences of O₃ concentration between weekend and a specific day of the week were statistically significant for most cases, despite the significantly lower concentration of ozone precursors (NO_x). The analysis of O_x concentrations indicates that limited processes of O₃ titration by NO (ozone quenching hypothesis) are the main cause of the ozone weekend effect in the Polish cities.