An automated gas chromatograph/mass spectrometer is described for the routine field monitoring of the CFC replacement compounds, the hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). Detection limits of 0.5 pptv are achieved by concentration of a 2-L air sample onto a three-stage adsorbent-filled microtrap. The microtrap is cooled to subambient temperatures (-50 °C) using Peltier thermoelectric devices, without a postdesorption cryofocussing step, thereby eliminating the need for liquid cryogens. The enriched air sample is thermally desorbed by direct ohmic heating of the microtrap, and compounds are separated on a 100-m, 5-µthick film high-resolution capillary column. Individual hydrohalocarbons are determined by selected ion masses for quantitation. The instrument is designed to operate automatically at a remote atmospheric research station providing ~2-h replicate air and calibration analyses.The chemical industry is presently replacing the ozonedepleting chlorofluorocarbons (CFCs) with a group of hydrofluorocarbons (HFCs) and hydrochlorofluorcarbons (HCFCs), referred to collectively as hydrohalocarbons. These compounds contain carbon-hydrogen bonds that are subject to destruction in the lower atmosphere through reaction with hydroxyl radicals. This destruction mechanism shortens their atmospheric lifetimes, thereby reducing their potential for ozone depletion.1™3 However, the replacement hydrohalocarbons, like their CFC predecessors, absorb radiation in the 8-12-«m region of the spectrum and therefore contribute to global warming. Model calculations indicate that the potential impact of these compounds as greenhouse gases is ~1 order of magnitude less than the CFCs.4 Since the long-term environmental effects of these hydrohalocarbons