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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., C[F.sub.4] and C[F.sub.3]C[F.sub.3]) and hydrofluorocarbons (HFCs, e.g., C[H.sub.3]C[F.sub.3]) to the higher-boiling point solvents (such as C[H.sub.3]CC13 and C[Cl.sub.2]=C[Cl.sub.2]) and CH[Br.sub.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.

Experimental and calculated cyclic voltammograms are compared for electrodes modified with thin films of permselective ion exchangers in which the exchange sites are covalently attached redox sites. The voltammograms are considered in the thin-layer limit in which mass transfer does not limit the current response. Additionally, it is assumed that neither the rate of heterogeneous electron transfer at the electrode-film interface nor the rate of homogeneous electron transfer in the bulk of the film limit the current. Under these circumstances, changes in the charge on the polymer backbone change the Donnan potential at the film-solution interface to produce broadened, asymmetrical voltammograms. Shifts in the apparent formal potentials for permselective redox films are also predicted if the activity of the counterion in the bathing electrolyte solution changes. Good agreement between the permselective model and experiment is obtained for the shape of the voltammograms. Once changing liquid junction potentials and changing activity coefficients in solution taken into account, good agreement is also obtained for the shifts in the apparent formal potentials.