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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, PM<inf>2.5</inf>, NO<inf>2</inf> and O<inf>3</inf>), 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, PM<inf>2.5</inf> and NO<inf>2</inf> occurred during the rush hours of the rainy season, while the maximum O<inf>3</inf> concentrations occurred during the midday of the dry season due to the improvement in the O<inf>3</inf>-generating photochemical reactions. The “weekend effect” was also observed in this study and was likely primarily due to the accumulation of O<inf>3</inf> in the air. Moreover, the PM<inf>2.5</inf> concentration was higher during the nighttime than during daytime, mainly in the dry season due to the poor horizontal diffusion of PM<inf>2.5</inf> and the absence of precipitation events, while the O<inf>3</inf> concentration was higher during the daytime in both seasons due to the enhancement of the photochemical reactions. A Pearson analysis showed that CO, PM<inf>2.5</inf> and NO<inf>2</inf> 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 PM<inf>2.5</inf> and NO<inf>2</inf> during the dry season, while transportation of O<inf>3</inf> contributed to its increasing concentration.