We have been carrying out a project involving air quality in the Mexico City Metropolitan Area. The main goal is to provide decision-makers in Mexico with objective, balanced assessments of cost-effective solutions to its air pollution problem through scientific, technological, social and economic analysis. The project is multi-disciplinary, and integrates air pollution science, mobility, land-use, health effects, economic and policy considerations. Now in its second year, the Mexico City Project has brought together a diverse group of collaborators in the US and Mexico. Its activities to date include a two-week exploratory field campaign involving real-time measurements of trace gases (O3, NO, NO2, VOC, formaldehyde, CO2, CO, etc.) and aerosol chemical composition (total mass, sulfates, nitrates, organics, water content, etc). Criteria pollutants (O3, NO, NO2, SO2, and PM10) and meteorological variables (wind vectors, temperature, relative humidity and solar radiation) were measured at a number of monitoring stations and boundary sites.