Abstract
The Weekend Effect (WE) is a phenomenon that occurs in some urban areas, characterized by increased concentrations of O3 despite of the decreasing in emissions of its precursors (NOx and VOC) during weekend days, in comparison to weekdays. Study of WE is relevant for understanding the behavior of pollutants, and hence, for air quality control. In this study, we analyzed hourly records of the period 2013-2015, from the air quality station in the historic center of the city of Cuenca, Ecuador. For each year, 3 mean-daily profiles were obtained for CO, NO2, PM2.5 and O3, corresponding to weekdays, Saturdays and Sundays. CO, NO2 and PM2.5 profiles declined on Saturdays and Sundays, in comparison to weekdays. However, O3 profiles showed equal or higher concentrations on Saturdays and Sundays. Mean increase of the maximum O3 8-h mean concentrations of Sundays, in comparison to weekdays, ranged between 8.6 and 15.8%. These results suggest the presence of WE around in the historic center of Cuenca, zone where probably there is a VOC-limited regime for photochemical O3 production.
Keywords: Ozone, VOC-limited regime, NOx-limited regime, air quality.
Resumen
El Efecto Fin de Semana (EFS) es un fenómeno que suele presentarse en algunas zonas urbanas, caracterizado por un incremento de las concentraciones de O3 durante los fines de semana, aunque hay una reducción de las emisiones de sus precursores (COV y NOx) en relación con los días laborables. La identificación y estudio del EFS es relevante a fin de entender el comportamiento de los contaminantes del aire y como elemento fundamental para el control de la contaminación atmosférica. En este estudio, se analizaron los registros horarios del periodo 2013-2015 de la estación de calidad de aire localizada en el centro histórico de la ciudad de Cuenca, Ecuador. Para cada año, se generaron 3 perfiles promedio de las concentraciones horarias de CO, NO2, MP2.5 y O3 para los días laborables, sábados y domingos. Los perfiles de CO, NO2 y MP2.5 presentaron concentraciones menores durante los sábados y domingos, con respecto a los días laborables. Sin embargo, los perfiles de O3 presentaron concentraciones iguales o mayores durante los sábados y domingos. El incremento medio de las concentraciones máximas octohorarias de O3 de los domingos, con respecto al promedio de los días laborables, varió entre 8,6 y 15,8%. Estos resultados indican potencialmente la presencia del EFS en el centro histórico de la ciudad de Cuenca, zona en la que probablemente hay un régimen limitado por COV para la generación de O3.
Palabras Clave: Ozono, Régimen limitado por COV, Régimen limitado por NOx, calidad del aire.
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