This work consists of the determination of emission factors of CO, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , THC, NOx, and PM2.5 in mass and number, which were measured locally at the metropolitan region of the Aburrá Valley to eight light duty vehicles (less than 3.5 ton), which are representative of the automotive fleet of the region. There were four gasoline and four diesel vehicles. The representative driving cycle of the region made up by ten municipalities was determinated, by means of an estocastic approach based on micro trips. This cycle was translated to a chassis dynamometer, including the road grade. It was found that older vehicles may emit up to 40, 9, 50, 20 times more NOx, CO, THC, and PM2.5, respectively, in regard to a vehicle with newer technology.