title: Medusa: a sample preconcentration and GC/MS detector system for in situ measurements of atmospheric trace halocarbons, hydrocarbons, and sulfur compounds.
abstract: Significant changes have occurred in the anthropogenic emissions of many compounds related to the Kyoto and Montreal Protocols within the past 20 years and many of their atmospheric abundances have responded dramatically. Additionally, there are a number of related natural compounds with underdetermined source or sink budgets. A new instrument, Medusa, was developed to make the high frequency in situ measurements required for the determination of the atmospheric lifetimes and emissions of these compounds. This automated system measures a wide range of halocarbons, hydrocarbons, and sulfur compounds involved in ozone depletion and/or climate forcing, from the very volatile perfluorocarbons (PFCs, e.g., CF(4) and CH(3)CF(3)) and hydrofluorocarbons (HFCs, e.g., CH(3)CF(3)) to the higher-boiling point solvents (such as CH(3)Cl(3) and CCl(2)=CCl(2)) and CHBr(3). A network of Medusa systems worldwide provides 12 in situ ambient air measurements per day of more than 38 compounds of part per trillion mole fractions and precisions up to 0.1% RSD at the five remote field stations operated by the Advanced Global Atmospheric Gases Experiment (AGAGE). This custom system couples gas chromatography/mass spectrometry (GC/MSD) with a novel scheme for cryogen-free low-temperature preconcentration (-165 degrees C) of analytes from 2 L samples in a two-trap process using HayeSep D adsorbent.
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA. ben@gaslab.ucsd.edu
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Miller
authors.forename: Ray F
authors.initials: RF
authors.lastname: Weiss
authors.forename: Peter K
authors.initials: PK
authors.lastname: Salameh
authors.forename: Toste
authors.initials: T
authors.lastname: Tanhua
authors.forename: Brian R
authors.initials: BR
authors.lastname: Greally
authors.forename: Jens
authors.initials: J
authors.lastname: Mühle
authors.forename: Peter G
authors.initials: PG
authors.lastname: Simmonds
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D001272:Atmosphere / Q000737:chemistry*; D002140:California; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation* / Q000379:methods*; D006838:Hydrocarbons / Q000032:analysis*; D006846:Hydrocarbons, Halogenated / Q000032:analysis*; D013457:Sulfur Compounds / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D006838:Hydrocarbons; D006846:Hydrocarbons, Halogenated; D013457:Sulfur Compounds