On a worldwide basis, vehicular emissions are prevailing contributors to air pollution in urban areas. The Metropolitan Area of Sao Paulo (MASP), Brazil, is no exception to this rule. Sao Paulo is a megacity of ∼ 18 million inhabitants which bears an unconventional mixture of vehicle types, burning various fuels, e.g., oxygenated gasoline (with ethanol), CNG, hydrated ethanol, and biofuels. Road vehicle emissions are considered the main source of air pollution in MASP. The impact of stationary and mobile sources on tropospheric ozone production in Sao Paulo was studied. The inclusion of the stationary sources resulted in an improvement of the correlation between the simulated and measured data, and a reduction in the mean bias. There is an urgent need to upgrade and update the information regarding other types of sources. The results should be viewed as an incremental enhancement in the knowledge of pollution dynamics in Sao Paulo. This is an abstract of a paper presented at the 101st AWMA Annual Conference and Exhibition (Portland, OR 6/24-27/2008).