Forward: This project was begun in July 1968 as a continuation of earlier studies on ambient air hydrocarbons supported by a grant from the American Petroleum Institute. Some of the work has been reported in the published literature (see reference list). The data presented in these papers is summarized but not reported in detail in this report. The following were members of the project advisory committee: R. G. Larsen@ H@ E@ Alquist@ P. R. Ryason@ C. S. Tuesday@ A@ P. Altshuller@ J. C. Neerman and J@ M. Heuss.