Specific hydrocarbons emitted from mobile and stationary sources enter into the formation of secondary pollutants, such as ozone and aerosols. The extent to which specific hydrocarbons perform this role is due to their differences in reactivities. Detailed knowledge of the hydrocarbon composition of the atmosphere as a function of time and altitude therefore is desirable. Measurements were carried out at ground level and simultaneously at elvated sites which were frequently above the inversion. Together with continuous information on ozone, two to four ambient air samples were collected per site per day for individual species hydrocarbon analysis by gas chromatography. The resultant data base is examined here in terms of the four major hydrocarbon classes (paraffins, olefins, aromatics, and acetylene) with respect to absolute concentrations, characteristic ratios, decay rates, and ozone/hydocarbon relationships. With occasional notable exceptions all hydrocarbon species were present in lower concentrations at the elevated sites (40--50%); characteristic ratios to acetylene reflected changes in automobile exhaust composition and stationary source contributions. Decreases in hydrocarbon/acetylene ratios were used to estimate ambient hydroxyl radical concentrations. The percent contributions of olefins was lower in 1975/1978 than in 1969. Although hydrocarbon concentrations appear to have declined between 1975 and 1978, ozone concentrations during the study periods were higher in 1978.