INTRODUCTION General Program Objectives The long-term objective e of this research program is the development of a methodology for predicting the concentrations of motor-vehicle-generated air pollutants throughout and urban area as a function of local meteorology and the distribution of traffic. The results of this work are intended primarily to be used as a tool in planning activities to predict the pollution patterns in any urban region resulting form planned traffic changed or predicted growth. In addition@ the model can be used in an operational mode for short-term predictions. Our first goal has been the development of such a methodology for a quasi-inert pollutant such as carbon monoxide (CO). For the initial development we used available data from five cities having CAMP* air monitoring stations: Chicago@ St. Louis@ Denver@ and Washington@ D.C. The current status of this program is as follows: ? A working model for co has been developed. ? A field program@ designed to fill gaps in the available data@ has been carried out in San Jose@ California. ? On the basis of these data@ the initial refinement and evaluation of the model have been completed. In this and following sections@ the structure and capabilities of the basic model are reviewed@ the results of the field program are reported@ and the progress in the refinement and evaluation of the model is discussed in detail. * Continuous Air Monitoring Program stations@ run by the Federal Air Pollution Control Office@ Environmental Protection Agency.