Identifying the Ozone Weekend Effect in the air quality of the northern Andean region of Ecuador

Abstract

The Weekend Effect (WE) is a phenomenon that occurs in some urban areas, characterized by increased concentrations of O 3 and decreased emissions of its precursors (NO x and VOC) during weekend days, in comparison to weekdays. The study of the WE is relevant for understanding the behavior of pollutants; and hence, for air quality control. We analyzed the hourly records of the period 2005-2012, from 8 stations of the air quality network from the Distrito Metropolitano de Quito (northern Andean region of Ecuador). Both for each station and year, 3 mean-daily profiles were obtained for CO, NO 2 , PM 2.5 and O 3 , corresponding to weekdays, Saturdays and Sundays. The CO, NO 2 and PM 2.5 profiles from Centro (historic center of Quito) and Belisario (center-north) stations, declined on Sundays. However the O 3 profiles were higher on Saturdays and Sundays. The O 3 8-h mean concentrations of Sundays were higher in Belisario (19.7-31.1%) and Centro (11.7-18.4%), in comparison to weekdays. These results indicate the presence of the WE around these 2 stations, which probably are located in a VOC-limited region for photochemical O 3 production.