Current global trends of economical development lead to the expansive urban growth and raise concerns regarding the pollution levels produced in mega cities. The MILAGRO (Megacity Initiative: Local and Global Research Observations) project is a worldwide initiative aiming to understand the sources of urban pollution, its chemical nature and evolution in time. In 2006, the MILAGRO campaign was conducted in Mexico City. During the campaign, ambient concentrations and fluxes of various trace gases and aerosols were measured using eddy covariance methods from 40 meters above the urban landscape in west-central Mexico City. A variety of VOC's were detected using a combination of instruments, while major aerosol species were identified using an aerosol mass spectrometer. Fluxes of CO2, CO and water vapor were also obtained. Preliminary results acquired during the MILAGRO 2006 project will be presented. Their comparison to the data obtained in the similar campaign held in the 2003 and the current Mexico City inventory will also be provided.