Automated Gas Chromatograph/Mass Spectrometer for Routine Atmospheric Field Measurements of the CFC Replacement Compounds, the Hydrofluorocarbons and Hydrochlorofluorocarbons

Abstract

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

Robust extraction of baseline signal of atmospheric trace species using local regression

“…The temporal resolution of the measurements was 4 h until December 2004 at Mace Head and until April 2008 at Jungfraujoch. Since then, air samples are analysed every 2 h. The details of the applied experimental methods are given in Simmonds et al (1995) and Miller et al (2008).…”

Cryogen-Free Automated Gas Chromatograph System for Monitoring of Halocarbons in the Atmosphere at Background Concentration Levels

“…Actually, other groups let samples and/or standards flow through a sample loop and calculate the amount injected from the atmospheric pressure 4,9 or the flow rate and sampling duration. [6][7][8] However, these methods are inconvenient or make it impossible to analyze the sample collected in a canister at the ambient or subambient pressure. We have employed a vacuum line and introduced a pressure-measured sample into an evacuated sample loop.…”

“…It is not easy to automate the analytical methods for halocarbons because contamination and/or adsorption of the halocarbons on the analytical system readily occur, due to their extremely low concentrations (in the pptv (pptv=10 -12 v/v) range). In fact, there have been few groups reporting automated analysis of short-lived halocarbons at the background concentration level [4][5][6][7][8][9] , and there still exist at least two difficult problems.…”

“…For a measurement of organic trace constituents, air samples are generally preconcentrated on an adsorbent (for example: porous glass beads 5 , porous polymers 6 , graphitized carbon black 7,8 , carbon molecular sieves 7,8 ) and injected to a gas chromatograph by thermal desorption. However, sufficient adsorption is only achieved at a low temperature that requires a cryogen such as liquid air, liquid nitrogen 5 , liquid argon or carbon dioxide.…”

“…Otherwise, room temperature collection by using active adsorbents requires high temperature desorption that causes thermal decomposition of the trapped trace amount halocarbons on the active adsorbent surface. While Peltier thermoelectric devices were attempted instead of the liquid cryogens 6,8 , they can be applied only to high boiling point compounds due to limited cooling efficiency and another device is needed to prevent the accumulation of ice. Therefore, these previously reported methods are not suitable for non-attended monitoring of trace halocarbon concentrations.…”