Abstract
Day-of-week variations in O_3, NO_x, CO and PM_(10) were analysed in the southwestern region of Europe (specifically Andalusia, Spain) using hourly concentrations collected at 43 stations (representing five typologies) over 6 years (2003-2008). This area has air pollution problems, and the study of the weekend effect is used as a tool to plan future strategies for emissions reductions. Maximum daily 8 h averages for O_3, daily 90^(th) percentiles for NO, NO_2 and PM_(10) and mean daily values for CO were calculated and used to assess the weekend effect by applying three different metrics: weekly evolution, weekend-weekday differences and average daily difference between weekends minus workdays. Based on daily parameters and weekend-weekday differences, all the measured air pollutants exhibited clearly reduced concentrations (oscillating between 25 to 85%) on weekends, mainly at urban and suburban stations, with the exception of O_3 (less than 10 μg/m^3). This decrease on weekend days was mostly observed for NO, NO_2 and PM_(10) at urban stations, while differences at industrial and rural stations were low or null. CO showed a low reduction. Using the daily cycle of differences (weekend minus workdays) as a reference, positive deviations were observed at night and negative differences were observed during the daytime for NO, NO_2 and PM_(10) at urban traffic, urban background and suburban background sites. A reduction in morning rush hour traffic during the weekends was reflected in the data from urban stations, which showed a decrease of up to 50, 15 and 12 μg/m^3 for NO, NO_2 and PM_(10), respectively. An opposite daily behaviour was found for ozone, which showed an increase at urban area sites of up to 15 μg/m^3 in the early morning.
Highlights
The concentrations of primary pollutants show weekly patterns; this temporal variation reflects day-to-day variations in the activities that generate anthropogenic emissions
Using the daily cycle of differences as a reference, positive deviations were observed at night and negative differences were observed during the daytime for NO, NO2 and PM10 at urban traffic, urban background and suburban background sites
Both configurations agree with the definition of the main synoptic configuration over the Iberian Peninsula performed by Martin-Vide (2005)
Summary
The concentrations of primary pollutants show weekly patterns; this temporal variation reflects day-to-day variations in the activities that generate anthropogenic emissions. The decrease in human activity on weekends produces lower emissions, and lower concentrations, of NOx (NO and NO2), CO, PM10 and VOCs than when compared with regular work days. These reductions could cause an opposite effect on ozone concentrations in urban environments, resulting in higher values on weekend days. The level of traffic at midday on weekdays is similar to that on weekends (Fujita et al, 2003) During this time, the different pattern of NOx emissions causes more effective ozone production; 5) Carryover in the lower layers. The increase in traffic on Friday and Saturday nights and the resulting ozone accumulation on the surface
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