This work uses a computer model to identify emission sources and chemical reactions that influence ambient formaldehyde (a carcinogenic pollutant) in the San Francisco Bay Area. Results suggest that for some locations, in order to reduce summer-season formaldehyde concentrations, controlling emissions of other pollutants can be as efficient as controlling emissions of formaldehyde. In winter, however, it is more efficient to control emissions of formaldehyde than emissions of other species.