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Seasonal variation of the criteria air pollutants concentration in an urban area of a high-altitude city

Abstract:

Analysis of air pollutants (CO, PM2.5, NO2 and O3), during the dry and rainy seasons of 2015, was conducted in a high-traffic area of Quito, Ecuador. Variations in the annual, diurnal, weekdays, weekends, daytime and nighttime concentration of these pollutants were examined using the data obtained from the public records of the monitoring network in Quito. The highest concentrations of CO, PM2.5 and NO2 occurred during the rush hours of the rainy season, while the maximum O3 concentrations occurred during the midday of the dry season due to the improvement in the O3-generating photochemical reactions. The “weekend effect” was also observed in this study and was likely primarily due to the accumulation of O3 in the air. Moreover, the PM2.5 concentration was higher during the nighttime than during daytime, mainly in the dry season due to the poor horizontal diffusion of PM2.5 and the absence of precipitation events, while the O3 concentration was higher during the daytime in both seasons due to the enhancement of the photochemical reactions. A Pearson analysis showed that CO, PM2.5 and NO2 were positively intercorrelated. It was identified, through polar plots and a real-time traffic map that the emission sources of these pollutants were in the proximity to the monitoring station, specifically vehicle exhaust emissions. Atmospheric horizontal mixing was an important dilution mechanism of PM2.5 and NO2 during the dry season, while transportation of O3 contributed to its increasing concentration.