Ozone weekend effect in Santiago, Chile

The study examined weekday–weekend differences in ozone, NOx (NO and NO2) and VOC concentrations in Santiago, Chile, from 1999 to 2007. The results provide evidence for the occurrence of an atmospheric phenomenon that produces higher ozone concentrations during weekends despite lower concentrations of ozone precursors. This phenomenon is known as the weekend effect (WE).The overall ozone decrease since the spring of 2004 was a consequence of the implementation of several urban pollution control measures. Although these measures caused a decline in the number of days that exceed the national standard from two-thirds to one-third of summer days, the WE, which became statistically significant beginning in September 2004, could not be eliminated. Furthermore, VOC/NOx ratios decreased during the same period (2004), especially in the most industrialized area of Santiago. Similarly, under these regimes, the VOC/NOx ratios were higher on Sundays than on weekdays and caused higher ozone concentrations on Sundays.

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► Occurrence of an ozone weekend effect in the city of Santiago, Chile.
► Weekday-weekend differences in ozone and nitrogen oxides concentrations in Santiago, Chile, from 1999 to 2007.
► Higher VOC/NOx ratios over the weekend increase the ozone concentration.
► VOC/NOx ratios were higher on Sundays than on weekdays.
► Reduction of VOC thus seems to be the most effective strategy to deal with the high levels of ozone.