One of the most important questions of the day is exactly how to measure the contribution of identifiable sources to the increasing haze that now covers a good part of the eastern United States in summer. This concern has resulted in a number of large studies of point sources, such as power plants. However, the multitude of small sources in every urban area also combine to form an urban plume that not only contributes to the pollution in the downwind areas immediately under it, but also to the general haze after the plume has lost its identity. Furthermore, the author has only a sketchy idea of what such plumes contribute to the general haze on the days after they have lost their identity. Although it is well known that secondary aerosol mass and O3 are formed in the urban plume, quantitative relationships between primary precursors and secondary products are scarce.