Field studies were conducted during the July-August period of 1981 and 1990 in Atlanta, Georgia. Paraffinic, olefinic, and aromatic volatile hydrocarbon were determined by gas chromatography with flame ionization detection and cryogenic preconcentration. In 1981 samples from three sites were collected in Tedlar bags and stored in canisters, while in 1990 automated gas chromatographs at six sites analyzed air samples directly every hour with no sample storage. Formaldehyde, acetaldehyde, and CO were also measured by other methods in both studies. TNMOC and 30 compounds were available for comparison after method differences and analysis reporting variations were considered. This paper compares TNMOC and individual compound concentrations and concentration ratios from 13 samples in 1981 and 28 samples in 1990 for the 7:00 and 8:00 am period at Georgia Tech, the site common to both studies.