Variations of traffic related air pollution on different time scales in Szeged, Hungary and Freiburg, Germany

Economic activities and everyday life may create weekly variations in concentrations of air pollutants in urban settings. The present study contributes to this experience on the example of two typical medium-sized towns in Central Europe, Szeged and Freiburg considering the following air pollutants: NO, NO2, O3, Ox and PM10. Five-year data sets of hourly observations (1997–2001) collected in downtown traffic junctions are analysed. In addition, the effect of the weekly variation on the diurnal course of the air pollutants is also demonstrated, which is especially important when we consider the possible extremes of these traffic related air pollutants. Since the annual variation of the pollutants explains only a minor part of the total variance and, furthermore, the weekly variation behaves rather similarly in the different seasons, the weekly variation of the diurnal peaks is quantified for the whole year. The average annual variations of NO, NO2, O3 and Ox are very similar for both Szeged and Freiburg. Annual levels of NO2 and O3 are moderately higher, while those of PM10 are extremely higher in Szeged, which is reflected in their average weekly and diurnal variations, too. In Freiburg the diurnal variation of PM10 shows a clear daily course with only one wave, compared to that for Szeged with the shape of a double wave. In Szeged, highest percentile values of NO and NO2 occur mostly in the evening, while in Freiburg either in the mourning or in the evening and generally there is very little difference between them. In Szeged, maximum of O3 peak values, while in Freiburg minimum of them are found on weekends.