The research reported here is the product of several years’ effort to elucidate one aspect of the air-pollution problem of urban complexes, namely, the direct contribution of combustion to the complement of exotic organic chemicals in the outdoor atmospheric environment. Most attention has been paid to the complex carbonaceous particulates produced by incomplete combustion, although investigations into gaseous byproducts of combustion also have been carried out to a limited extent. Much of the research has been reported in various publications that will be cited. Work by other investigators along converging lines has been copious; however, since this report is not intended as a review of studies in the field of combustion particulates, the many references to the subject are not necessarily included but may be found in the original accounts from this laboratory.