In the rural troposphere, the nonmethane hydrocarbon compounds (NMHCs) play a significant role in establishing the absolute, as well as, the relative concentration of the odd-hydrogen radicals. In order to provide data which could be used to estimate OH reactive loss rates with hydrocarbons directly, and to broaden our understanding of the production of biogenic NMHCs in and the transport of anthropogenic NMHCs into the Colorado mountains, in situ hydrocarbon measurements were made during the Tropospheric OH Photochemistry Experiment in the fall of 1993. NMHC measurements were made using an automated gas chromatographic system that was capable of quantifying alkanes C3 (propane) through C10 (decane), alkenes C4 (butene) through C10 (decene), light alcohols from C1 (methanol) through C5 (pentanol), light ketones from C3 (acetone) through C5 (pentanone), aromatics from C6 (benzene) through C9 (trimethylbenzenes), C10 monoterpenes, and acetaldehyde. During periods of influx of urban air masses, the NMHCs appeared to be the dominant sink for OH radicals.¿ 1997 American Geophysical Union