Comparison of air pollutant concentrations between weekdays and weekends in Athens, Greece for various meteorological conditions.

The objective of the present study is to contribute to the understanding of the "ozone weekend effect" as it occurs in the Greater Area of Athens, Greece both in the summer and wintertime. Therefore, weekly cycles of CO, NO and O3 concentrations for the 18-year-period 1983-2000 are studied. Each day of the week is considered separately, while sites with different levels of primary pollutants are examined. The reduction of the meteorological influence in the O3 mechanisms is achieved by applying meteorological classifications. The analysis for the cold period reveals that CO and NO display decreasing concentrations from weekdays to weekends, whereas O3 shows increasing concentrations. During the warm period, although primary pollutants display decreased concentrations compared to the cold period, their weekly cycles remain the same. On the other hand, meteorological changes affect the weekly cycle of ozone peaks. During days with unfavourable meteorology to ozone production, weekend ozone concentrations are higher than weekday O3 concentrations. The reverse is observed during days with favourable meteorology to ozone production.