We model the typical behavior of the eight-hour average concentration of Tropospheric Ozone (O 3 ) and Carbon Monoxide (CO) throughout one day. Modeling is conducted using a nonparametric regression technique. Data come from the Cali’s Air Quality Surveillance System (SVCA), and correspond to the years 2003 and 2006. Results show that in the Cali's South side, the O 3 eight hour contamination levels exceed the Colombian standard limit value. Meanwhile, in Cali's downtown the CO eight-hour average contamination levels are very close to the Colombian standard limit. Variability bands associated with the modeling of the typical daily behavior of the eight-hour concentration of CO, show evidence of differences between types of day and also between monitoring zones in all the years considered in the project. The same is observed for the O 3 case, but only for data coming from year 2006.